HK1208583B - Autonomous adaptation of transmit power - Google Patents

Description

Autonomous adaptation of transmit power

This application is a divisional application of the invention patent application "Autonomous Adaptation of Transmitting Power" with application date of August 8, 2008 and application number 200880102753.6.

Claiming priority under 35 U.S.C. §119

This application claims the benefit of and priority to commonly owned U.S. Provisional Patent Application No. 60/955,301, filed on August 10, 2007, with attorney docket number 072134P1, and U.S. Provisional Patent Application No. 60/957,967, filed on August 24, 2007, with attorney docket number 072134P2, the disclosures of each of which are incorporated herein by reference.

Technical Field

Generally speaking, the present application relates to wireless communications, and more specifically, but not limited to, improving communication performance.

Background Art

Wireless communication systems have been widely deployed to provide various types of communications (e.g., voice services, data services, multimedia services, etc.) to most users. As the demand for high-speed and multimedia data services grows rapidly, challenges are faced in implementing efficient, robust, and performance-enhancing communication systems.

For example, a small-coverage base station can be deployed in a user's home to supplement the base stations of a traditional mobile phone network (e.g., a macrocellular network). Such a small-coverage base station is typically an access point base station, a home node B, or a femto cell, and can be used to provide more robust indoor wireless coverage to mobile station units. Typically, such a small-coverage base station is connected to the Internet and the mobile operator's network via a DSL router or cable modem.

In a typical macrocell deployment environment, RF coverage is planned and managed by the cellular network operator to optimize coverage. On the other hand, users can install femtocells themselves and deploy them in an ad-hoc manner. As a result, femtocells can cause interference on both the uplink (UL) and downlink (DL) of macrocells. For example, a femtocell installed near a window in a residence can cause strong downlink interference to any access terminals outdoors that are not served by the femtocell. In addition, on the uplink, home access terminals served by femtocells can also cause interference at macrocell base stations (e.g., macro Node Bs).

By operating the femtocell network on a different RF carrier frequency than the macrocell network, interference between the macrocell deployment environment and the femtocell deployment environment can be mitigated.

Femtocells can also interfere with each other due to unplanned deployment. For example, in a multi-residential apartment building, a femtocell installed near the wall separating two residences can cause significant interference to adjacent residences. In this case, the strongest femtocell detected by a home access terminal (e.g., in terms of the strongest RF signal strength received by the access terminal) may not necessarily be the serving base station for the access terminal due to the restricted association policy implemented by the femtocell.

In some communication systems, mobile operators do not optimize the radio frequency (RF) coverage of femtocells, and these base stations are deployed in an ad-hoc manner. This can lead to RF interference issues. Therefore, improved interference management in wireless networks is needed.

Summary of the Invention

The following is a summary of exemplary aspects of the invention.It should be understood that when referring to the term aspects herein, this refers to one or more aspects of the invention.

In some aspects, the present invention relates to determining a transmit power (e.g., a maximum power) based on a maximum allowed received signal strength at the receiver and based on a minimum coupling loss from a transmitting node to the receiver. In this manner, receiver desensitization can be avoided in systems where the path loss between these components is relatively small (e.g., the receiver can be arbitrarily close to the receiver).

In some aspects, the present disclosure relates to defining the transmit power of an access node (e.g., a femto node) to limit corresponding outages (e.g., coverage holes) in a cell (e.g., a macrocell) while still providing an acceptable level of coverage to access terminals associated with the access node. In some aspects, these techniques can be employed for coverage holes on adjacent channels (e.g., implemented on adjacent RF carriers) and for coverage holes on co-located channels (e.g., implemented on the same RF carrier).

In some aspects, the present invention relates to autonomously adjusting downlink transmit power at an access node (e.g., a femto node) to mitigate interference. In some aspects, transmit power is adjusted based on channel measurements and defined coverage holes. Here, a mobile operator may specify coverage holes and/or channel characteristics for adjusting transmit power.

In some implementations, the access node measures the received signal strength of signals from the macro access node (or receives an indication of the received signal strength of signals from the macro access node) and calculates the path loss associated with coverage holes in the macro cell (e.g., correcting for penetration loss, etc.). Based on the coverage target (path loss), the access node can select a specific transmit power value. For example, the transmit power at the access node is adjusted based on the measured macro signal strength (e.g., RSCP) and the total signal strength measured at the macro node level (e.g., RSSI).

In some aspects, the present invention relates to defining transmit power based on channel quality. For example, after an access node is installed, the access node initially operates at a default transmit power (e.g., a pilot fraction value) and then dynamically adjusts the transmit power based on DRC/CQI feedback from the access terminal. In some aspects, if the requested DRC is consistently very high for an extended period of time, this indicates that the PF value is too high and the access node may choose to operate at a lower value.

In some aspects, the present disclosure relates to defining transmit power based on a signal-to-noise ratio at an access terminal. For example, a maximum transmit power may be defined for an access node to ensure that the signal-to-noise ratio at the access terminal does not exceed a defined maximum value when the associated access terminal is at or near the edge of the access node's coverage area.

In some aspects, the present invention relates to adaptively adjusting the downlink transmit power of neighboring access nodes. In some aspects, information is shared between access nodes to enhance network performance. For example, if an access terminal is experiencing a high level of interference from a neighboring access node, information related to the interference can be relayed to the neighboring access node via the access terminal's home access node. In one specific example, the access terminal sends a neighbor report to its home access node, wherein the report indicates the received signal strength from the neighboring access node detected by the access terminal. The access node then determines whether the home access terminal is experiencing excessive interference from one of the access nodes in the neighbor report. If so, the access node can send a message to the interfering access node to request that the interfering access node reduce its transmit power. Similar functionality can be achieved by using a centralized power controller.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other exemplary aspects of the present invention will be described in the specification and claims appended hereto, in the accompanying drawings, in which:

FIG1 is a simplified diagram of several example aspects of a communication system including macro coverage and smaller-scale coverage;

FIG2 is a simplified block diagram of several example aspects of an access node;

3 is a flow diagram of several sample aspects of operations performed to determine transmit power based on maximum received signal strength and minimum coupling loss for a receiver;

4 is a flow diagram of several sample aspects of operations performed to determine transmit power based on one or more channel conditions;

5 is a flow diagram of several sample aspects of operations performed to determine transmit power based on total received signal strength;

6 is a flow diagram of several sample aspects of operations performed to determine transmit power based on a signal-to-noise ratio;

FIG7 is a simplified diagram illustrating coverage areas for wireless communications;

FIG8 is a simplified diagram of several sample aspects of a communication system including neighboring femtocells;

9 is a flow diagram of several sample aspects of operations performed to control transmit power of neighboring access nodes;

10 is a flowchart of several sample aspects of operations performed to adjust transmit power in response to a request from another node;

FIG11 is a simplified diagram of several sample aspects of a communication system including centralized power control;

12 is a flow diagram of several sample aspects of operations performed to control transmit power of an access node using centralized power control;

13A and 13B are flow diagrams of several sample aspects of operations performed to control transmit power of an access node using centralized power control;

FIG14 is a simplified diagram of a wireless communication system including a femto node;

FIG15 is a simplified block diagram of several sample aspects of communication components;

16-19 are simplified block diagrams of several example aspects of apparatus for providing power control as taught herein;

As is customary, the various features shown in the drawings are not drawn to scale. Accordingly, the dimensions of the various features may be expanded or reduced for clarity. In addition, some of the drawings have been simplified for clarity. Consequently, the drawings may not depict all components of a given apparatus (e.g., device) or method. Finally, throughout the specification and drawings, like reference numerals are used to indicate like features.

DETAILED DESCRIPTION

Various aspects of the present invention are described below. It will be apparent that the content of this article can be implemented in various forms, and any specific structure, function, or both disclosed herein are merely illustrative. Based on the content of this article, those skilled in the art will recognize that the aspects disclosed herein can be implemented independently of any other aspects, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement a device or implement a method. In addition, other structures, functions, or structures and functions other than one or more aspects set forth herein or structures and functions different from one or more aspects set forth herein can be used to implement such a device or implement such a method. In addition, an aspect includes at least one of the claims.

FIG1 illustrates exemplary aspects of a network system 100 that includes macro-scale coverage (e.g., a large-area cellular network such as a 3G network, often referred to as a macrocellular network) and smaller-scale coverage (e.g., a residential or building-based network environment). As a node (e.g., access terminal 102A) moves through the network, access terminal 102A may be served in certain locations by an access node (e.g., access node 104) providing macro coverage, as represented by area 106, while access terminal 102A may be served in other locations by an access node (e.g., access node 108) providing smaller-scale coverage, as represented by area 110. In some aspects, smaller-scale coverage nodes may be used to provide incremental capacity growth, in-building coverage, and different services (e.g., for a more robust user experience).

As will be described in more detail below, access node 108 may be restricted in that it may not provide certain services to certain nodes (e.g., visitor access terminal 102B). As a result, coverage holes (e.g., corresponding to coverage area 110) may be created in macro coverage area 104.

The size of the coverage hole may depend on whether access node 104 and access node 108 operate on the same frequency carrier. For example, when node 104 and node 108 are co-channel (e.g., using the same frequency carrier), the coverage hole may correspond to coverage area 110. Thus, in this case, when access terminal 102A is within coverage area 110, access terminal 102A may lose macro coverage (e.g., as shown by the dashed line diagram of access terminal 102B).

When the nodes 104 and 108 are on adjacent channels (e.g., using different frequency carriers), a smaller coverage hole 112 is created in the macro coverage area 104 due to adjacent channel interference from the access node 108. Thus, when the access terminal 102A operates on the adjacent channel, the access terminal 102A may receive macro coverage at a location close to the access node 108 (e.g., outside the coverage area 112).

Depending on system design parameters, the co-channel coverage hole may be relatively large. For example, if the interference of access node 108 is at least as low as the thermal noise floor, then, assuming free space propagation losses and no wall separating nodes 108 and 102B, for a CDMA system with a transmit power of 0 dBm at access node 108, the coverage hole may have a radius of approximately 40 meters.

Therefore, there is a trade-off between maintaining adequate coverage in a specific smaller-scale environment (e.g., femtonode coverage in a home) and minimizing disruptions in macro coverage. For example, when a restricted femtonode is located at the edge of macro coverage, there is a high probability that the access terminal will lose macro coverage and drop calls as it approaches the femtonode. In this case, one solution for the macrocellular network is to move the access terminal to another carrier (e.g., on which the adjacent channel interference from the femtonode is less). However, due to the limited spectrum available to each operator, using different carrier frequencies is not always feasible. In any case, another operator can use the carrier used by the femtonode. Therefore, access terminals associated with other operators will experience coverage holes on that carrier caused by the restricted femtonode.

As will be described in detail with reference to Figures 2 through 13B , transmit power values for nodes can be defined to manage such interference and/or address other similar issues. In some implementations, the defined transmit power can be related to at least one of the following: a maximum transmit power, a transmit power of the femto node, or a transmit power used to transmit a pilot signal (e.g., as indicated by a pilot score value).

For convenience, various scenarios for defining transmit power for a femto node deployed in a macro network environment are described below. Here, in some aspects, the term "macro node" refers to a node that provides coverage for a relatively large area. In some aspects, the term "femto node" refers to a node that provides coverage for a relatively small area (e.g., a residence). A node that provides a coverage area that is smaller than a macro area but larger than a femto area is referred to as a pico node (e.g., providing coverage inside a commercial building). It should be understood that various types of nodes and systems can be used to implement the content of this document. For example, a pico node or some other type of node can provide the same or similar functionality as a femto node for a different (e.g., larger) coverage area. Thus, a pico node can be restricted, a pico node can be associated with one or more home access terminals, and so on.

In various applications, other terms may be used to refer to a macro node, a femto node, or a pico node. For example, a macro node may be configured or referred to as an access node, a base station, an access point, an eNodeB, a macrocell, a macro NodeB ("MNB"), etc. Additionally, a femto node may be configured or referred to as a home NodeB ("HNB"), a home eNodeB, an access point base station, a femtocell, etc. Additionally, a cell associated with a macro node, a femto node, or a pico node may be referred to as a macrocell, a femtocell, or a picocell, respectively. In some implementations, each cell may also be associated with (e.g., divided into) one or more sectors.

As described above, in some aspects, femto nodes are restricted. For example, a given femto node may provide service only to a limited set of terminals. Thus, with so-called restricted (or closed) association, a given access terminal may be served by a macrocellular mobile network and a limited set of femto nodes (e.g., a femto node located within a respective user's residence).

The restricted set of provided access terminals associated with a restricted femto node (which may be referred to as a Closed Subscriber Group Home NodeB) may be expanded temporarily or permanently as needed. In some aspects, a Closed Subscriber Group ("CSG") may be defined as a set of access nodes (e.g., femto nodes) that share the same access control list of access terminals. In some implementations, all femto nodes (or all restricted femto nodes) in a region may operate on a designated channel (which may be referred to as a femto channel).

Various relationships may be defined between restricted femto nodes and a given access terminal. For example, from the perspective of an access terminal, an open femto node may refer to a femto node with no restricted association. A restricted femto node may refer to a femto node that is restricted in some manner (e.g., restricted for association and/or registration). A home femto node may refer to a femto node that an access terminal is authorized to access and operate on. A guest femto node may refer to a femto node that an access terminal is temporarily authorized to access and operate on. An alien femto node may refer to a femto node that an access terminal is not authorized to access and operate on except for possible emergency situations (e.g., 911 calls).

From the perspective of a restricted femto node, a home access terminal (or home user equipment, HUE) may refer to an access terminal that is authorized to access a restricted femto node. A guest access terminal may refer to an access terminal that temporarily accesses a restricted femto node. An alien access terminal may refer to an access terminal that is not allowed to access a restricted femto node except for possible emergency situations (such as 911 calls). Thus, in some aspects, an alien access terminal may be defined as an access terminal that is not eligible or allowed to register with a restricted femto node. An access terminal that is currently restricted (e.g., not allowed to access) by a restricted femtocell may be referred to herein as a visitor access terminal. Thus, a visitor access terminal may be equivalent to an alien access terminal, and equivalent to a guest access terminal when service is not allowed.

FIG2 illustrates various components of an access node 200 (hereinafter referred to as a femto node 200) that can be used in one or more implementations as described herein. For example, different configurations of the components depicted in FIG2 can be employed in the various examples of FIG3 through FIG13B. Thus, it should be understood that in some implementations, a node may not include all of the components depicted in FIG2, while in other implementations (e.g., where a node uses multiple algorithms to determine maximum transmit power), a node may employ most or all of the components depicted in FIG2.

Briefly, a femto node 200 includes a transceiver 202 for communicating with other nodes (e.g., access terminals). The transceiver 202 includes a transmitter 204 for transmitting signals and a receiver 206 for receiving signals. The femto node 200 also includes a transmit power controller 208 for determining the transmit power (e.g., the maximum transmit power) of the transmitter 204. The femto node 200 includes a communication controller 210 for managing communications with other nodes and providing other related functionality as described herein. The femto node 200 includes one or more data stores 212 for storing various information. The femto node 200 may also include an authorization controller 214 for managing access to other nodes and providing other related functionality as described herein. Other components shown in FIG. 2 are described below.

Example operations of the system 100 and femto node 200 will be described in conjunction with the flowcharts of Figures 3-6, 9, 10, and 12-13B. For convenience, the operations of Figures 3-6, 9, 10, and 12-13B (or any other operations described or discussed herein) are described as being performed by specific components (e.g., components of the femto node 200). However, it should be understood that these operations can be performed by other types of components, or that a different number of components can be used to perform these operations. It should be understood that one or more of the operations described herein may not be employed in a given implementation.

Referring first to FIG3 , in some aspects, the present invention relates to defining the transmit power of a transmitter based on the maximum received signal strength of the receiver and the minimum coupling loss between the transmitter and the receiver. Here, the access terminal can be designed to operate within a specific dynamic range with a lower limit defined by a minimum performance specification. For example, the maximum received signal strength (RX_MAX) of the receiver can be specified to be -30 dBm.

For certain applications (e.g., employing femto nodes), access nodes and their associated access terminals can be arbitrarily close to each other, potentially creating relatively high signal levels at the receiver. Assuming, in one example, a minimum separation of 20 cm between a femto node and an access terminal, the minimum path loss (also referred to as minimum coupling loss (MCL)) will be close to 28.5 dB. This MCL value is much smaller than the typical MCL values observed in macrocellular deployments (e.g., because macro antennas are often mounted on top of towers or buildings).

If the received power level exceeds the receiver's sensitivity range, the receiver will be subject to internal and external interference and blockers, resulting in degraded intermodulation performance at the access terminal. Furthermore, if the received signal strength is very high (e.g., above 5 dBm), actual hardware damage can occur at the access terminal. For example, in this case, the RF duplexer or SAW filter can be permanently damaged.

Therefore, in some aspects, the maximum transmit power (P _{MAX_HNB} ) can be defined as: P _{MAX_HNB} <P _{HUE_MAX} = (MCL + RX_MAX). As an example, assuming MCL is 28.5 dB and RX MAX is -30 dBm, the maximum power that can be transmitted to the home access terminal (P _{HUE_MAX} ) is: 28.5 - 30 = -1.5 dBm. Therefore, in this example, P _{MAX_HNB} < -1.5 dBm.

FIG3 illustrates several operations performed to determine transmit power based on a receiver's maximum received signal strength and MCL. As shown in block 302, femto node 200 determines a maximum received signal strength (RX_MAX). In some cases, this value may simply be a predetermined design parameter (e.g., when configuring femto node 200). Thus, determining this value may simply include retrieving a corresponding value 216 from data storage 212. In some cases, the maximum received signal strength may be a configurable parameter. For example, determining the maximum received signal strength may include a node (e.g., receiver 206) receiving an indication of the maximum received signal strength from another node (e.g., an access terminal).

As shown in block 304, the femto node 200 determines a minimum coupling loss. In some cases, this value may be a predetermined design parameter (e.g., when the femto node 200 is provided). Thus, determining the minimum coupling loss includes retrieving a corresponding value 218 from the data store 212. In some cases, the minimum coupling loss may be a configurable parameter. For example, determining the minimum coupling loss may include the femto node 200 (e.g., the receiver 206) receiving an indication of the minimum coupling loss from another node (e.g., an access terminal). Additionally, in some cases, determining the minimum coupling loss may include the node (e.g., the coupling/path loss determiner 220) calculating the minimum coupling loss (e.g., based on a received signal strength report received from another node, such as a home access terminal).

The femto node 200 (e.g., transmit power controller 208) determines the transmit power based on the maximum received signal strength and the minimum coupling loss, as shown in block 306. As described above, this step may include defining the maximum transmit power to be less than the sum of these two parameters.

In some cases, the transmit power value determined at block 306 is one of several maximum transmit power values determined by the femto node 200. For example, the femto node 200 may employ other algorithms (e.g., as described below) to determine the maximum transmit power value (e.g., TX_PWR_1 . . . TX_PWR_N) based on other criteria. The femto node 200 may then select the lowest of these determined transmit power values as the actual "maximum" transmit power value. In some cases, the determination of this "maximum" transmit power value may also be subject to a minimum transmit power value, TX_MIN (e.g., to ensure that the femto node 200 provides adequate coverage for its home access terminals) and an absolute maximum transmit power value, TX_MAX. As shown in FIG. 2 , the transmit power parameters 222 described above may be stored in the data memory 212.

Femto node 200 may then communicate with the other node or nodes by transmitting a signal that is constrained according to the determined transmit power, as represented by block 308. For example, a femto node may limit its transmit power to remain below a determined maximum value to avoid desensitizing any visiting access terminals that may be close to the femto node.

4, the present invention in some aspects relates to defining transmit power based on one or more channel conditions. As discussed in more detail below, examples of such channel conditions may include total received signal strength, received pilot strength, and channel quality.

As shown in block 402, in some cases, the determination of the transmit power of the access node may be initiated due to a determination that a node is within the coverage area of the access node, or the transmit power of the access node may be determined based on a determination that a node is within the coverage area of the access node. For example, if the femto node 200 determines that a home access terminal (e.g., a node authorized for data access) has entered the coverage area of the femto, the femto node 200 may choose to readjust the transmit power of the femto (e.g., increase the power). Additionally, if the femto node 200 determines that a visitor access terminal (e.g., not authorized for data access) has entered its coverage area, the femto node 200 may choose to readjust its transmit power (e.g., decrease the power). To this end, the femto node 200 may include a node detector 224 that can determine whether a particular type of node is within a given coverage area.

As shown in block 404, if the femto node 200 elects to re-tune its transmitter (e.g., periodically after being turned on, or in response to a trigger such as block 402), the femto node 200 may determine one or more channel conditions. Such channel conditions may take various forms. For example, in some implementations, the signal strength determiner 226 may determine an overall received signal strength value (e.g., a received signal strength indication, RSSI). In some implementations, the received pilot strength determiner 228 may determine a signal strength value associated with a pilot (e.g., received signal code power, RSCP). Example techniques related to these channel conditions are described in more detail below in conjunction with FIG. 5 and FIG. 6.

In some implementations, the channel quality determiner 230 may determine the channel quality (eg, a channel quality indicator, CQI). For example, such channel quality may relate to the quality of the downlink at the home access terminal.

As described herein, various channel quality indicators may be employed. For example, channel quality may relate to a sustainable data rate (e.g., data rate control, DRC), downlink quality of service, signal-to-noise ratio (e.g., SINR, where noise may include or substantially include interference), or some other quality metric. Channel quality may also be determined for various types of channels (e.g., data channels, common control channels, overhead channels, paging channels, pilot channels, or broadcast channels).

The channel quality determiner 230 can determine the channel quality in various ways. For example, in some implementations, information related to the channel quality can be received from another node (e.g., a home access terminal). For example, this information can take the form of an actual channel quality indication or information that can be used to generate a channel quality indication.

As shown in block 406, the femto node 200 (e.g., transmit power controller 208) determines a transmit power value (e.g., a maximum value) based on the channel conditions. For example, in implementations where the transmit power is based at least in part on an indication of channel quality, the transmit power can be increased in response to a decrease in channel quality, or if the channel quality decreases below a threshold level, the transmit power can be increased. Conversely, the transmit power can be decreased in response to an increase in channel quality, or if the channel quality increases above a threshold level, the transmit power can be decreased. As a specific example, if the requested DRC is consistently very high over an extended period of time, this can be used to indicate that the transmit power value is too high and the femto node 200 can therefore elect to operate at a lower transmit power value.

Femto node 200 may determine one or more other transmit power values (e.g., based on the algorithms described herein or other algorithms or rules), as shown in block 408. As described above in conjunction with FIG. 3 , femto node 200 may thereby select the lowest of the determined transmit power values (e.g., TX_PWR_1 . . . TX_PWR_N stored in data memory 212) as the actual “maximum” transmit power value.

In some implementations, the femto node 200 (e.g., the transmit power controller 208) may determine (e.g., adjust) transmit power based on whether a node is within the coverage area of the femto node 200. For example, as discussed at block 402, the transmit power may be reduced when there are visiting access terminals and may be increased when there are home access terminals.

As shown in block 410, the femto node 200 may communicate with another node or nodes by transmitting a signal that is constrained according to the determined transmit power. For example, if at some point the femto node 200 determines that interference with a visiting access terminal is unlikely, the femto node 200 may increase the transmit power to a minimum of the maximum value determined at block 408.

As shown in block 412, in some implementations, the femto node 200 may repeatedly perform any of the above-described transmit power adjustment operations (e.g., rather than determining the transmit power only once at deployment). For example, when the femto node 200 is first deployed, the femto node 200 may use a default transmit power value and then periodically adjust the transmit power over time. In this case, the femto node 200 may perform one or more of the operations of FIG. 4 at certain times (e.g., acquiring or receiving signal strength or channel quality information). In some cases, the transmit power may be adjusted to maintain a desired channel quality over a period of time (e.g., maintaining a minimum DRC value or a minimum downlink quality of service value at a home access terminal). In some cases, these operations may be performed repeatedly (e.g., daily) to allow the femto node to adapt to changes in the environment (e.g., the installation of a new femto node in a neighboring apartment unit). In some cases, such adjustment operations may be adapted to mitigate large and/or rapid changes in transmit power (e.g., through the use of hysteresis or filtering techniques).

5 , the technique for determining transmit power based on total received signal strength and received pilot strength, as described above, will now be described in greater detail. Access nodes, such as femto nodes (e.g., femto node 200), operating in a macrocell environment need to adjust downlink transmit power based on their location within the macrocell. When a femto node is at the edge of a macrocell, RF leakage outside the femto node environment (e.g., a residence) can significantly reduce the Ec/Io of nearby macro access terminals, as macro signal levels are typically very low at these cell-edge locations. As a result, relatively large coverage holes for macro access terminals may exist near the femto node.

If a macro access terminal not associated with a femto node (e.g., a visitor access terminal) enters the coverage area of the femto node, the macrocellular network can perform an inter-frequency handoff to direct the visitor access terminal to another carrier frequency. While this technique can reduce the likelihood of dropped calls or service interruptions for macro access terminals, it can also result in frequent inter-frequency handoff events for mobile macro access terminals passing through coverage holes, which can cause service interruptions and high signaling loads on macrocellular access nodes. Therefore, in some aspects, it is desirable to minimize the size of coverage holes created by femto nodes on macrocells.

On the other hand, if the transmit power level of a femto node is set too low, adequate femto coverage may not be maintained in the femto environment. Furthermore, the desired transmit power may depend on the location of the femto node. For example, when a femto node is close to a macro access node, a higher transmit power level may be required to provide adequate femto coverage compared to when the femto node is located at the edge of a macro cell. Furthermore, different power levels may be specified in urban environments (e.g., where femto nodes are often deployed in apartments) versus suburban environments with less dense populations.

The present invention, in some aspects, relates to adaptively adjusting femto node transmit power levels using macrocell signal values to limit interference at visitor access terminals. These operations can be employed to adjust visitor terminals operating on adjacent channels of a femto node or on a co-channel of a femto node.

In short, the operations of FIG5 involve determining the maximum allowable interference that a femto node can cause at a visitor access terminal located at the edge of a coverage hole. Here, the maximum allowable interference can be defined as the minimum Ecp/Io (e.g., received pilot signal strength to total received signal strength) required by the visitor access terminal for reliable macro downlink operation on a given channel. The maximum allowable interference can be derived based on the measured received pilot signal strength (Ecp) from the best macrocell on the carrier, the measured total signal strength (Io) on the carrier, and the minimum required Ecp/Io. The maximum transmit power of the femto can then be derived based on the maximum allowable interference and path loss between the femto node and the edge of the coverage hole (and, if applicable, adjacent channel interference suppression).

For a predetermined downlink transmit power _PHNB of a femto node (e.g., Home NodeB, HNB) and a corresponding adjacent carrier to interference ratio (ACIR) of, for example, 33 dB at a distance "d" from the femto node, a visitor access terminal (e.g., User Equipment, UE) may experience interference from the femto node of up to:

Rx _VUE (d) = P _HNB - ACIR - PL _FREE (d) Equation 1

Where PL _FREE (d) is the free path loss between the transmitter device and the receiver device at a distance “d”, and can be calculated using the following _formula :

PL _FREE (d) = 20log ₁₀ (4πdf/c) - _GT - _GR Equation 2

Wherein, f is the carrier frequency (e.g., f = 2 GHz), _GT and _GR are the transmitter antenna gain and the receiver antenna gain, respectively (e.g., _GT = _GR = -2 dB).

As described in further detail below, to limit interference from visitor access terminals, the femto node adjusts downlink transmit power _PHNB by measuring macro signal strength. In some implementations, the femto node measures the following quantities in adjacent channels (e.g., performing the algorithm separately on multiple adjacent carriers) or co-channels:

RSCP _{BEST_MACRO_AC} = received pilot signal strength received from the best macrocell among the adjacent carriers.

RSSI _{MACRO AC} = Total interference signal strength value (Io) in adjacent carriers.

Thus, as shown in block 502 of FIG. 5 , the femto node 200 of FIG. 2 (e.g., signal strength determiner 226) determines the total received signal strength (e.g., RSSI) on the channel of the visitor access terminal. Signal strength determiner 226 can determine signal strength in various ways. For example, in some implementations, femto node 200 measures signal strength (e.g., receiver 206 monitors an appropriate channel). In some implementations, information related to signal strength can be received from another node (e.g., a home access terminal). For example, such information can take the form of actual signal strength measurements (e.g., from a node measuring signal strength) or information that can be used to determine a signal strength value.

Additionally, as shown in block 504, the femto node 200 (e.g., received pilot strength determiner 228) determines the received pilot strength (e.g., RSCP) of the best macro access node on the visitor access terminal's channel. In other words, the signal strength of the pilot signal with the greatest received signal strength is determined at block 504. The received pilot strength determiner 228 can determine the received pilot strength in various ways. For example, in some implementations, the femto node 200 measures the pilot strength (e.g., the receiver 206 monitors the appropriate channel). In some implementations, information related to the pilot strength can be received from another node (e.g., a home access terminal). For example, such information can take the form of an actual pilot strength measurement (e.g., from a node measuring the signal strength) or information that can be used to determine the pilot strength value.

In some implementations, the received pilot strength may be determined based on the total received signal strength obtained at block 502. For example, such a determination may be based on a known or estimated relationship between pilot strength and total strength in the form of information 232 (e.g., a formula, table, or graph) stored in data storage 212. In such an implementation, signal strength determiner 226 may include received pilot strength determiner 228.

As shown in block 506, femto node 200 (e.g., path/coupling loss determiner 220) determines the path loss between the femto node and a given location (e.g., the edge of a coverage hole or the location of a node) on the channel of the visitor access terminal. Path/coupling loss determiner 220 can determine the path loss in various ways. In some cases, path loss may simply be a design parameter predetermined (e.g., when femto node 200 is provided) such that the path loss value corresponds to a coverage hole of a given size. Thus, determining the path loss simply includes retrieving the corresponding value 218 from data storage 212. In some cases, determining the path loss may include the node (e.g., receiver 206) receiving an indication of the path loss from another node (e.g., an access terminal). Additionally, in some cases, determining the path loss may include the femto node 200 (e.g., path/coupling loss determiner 220) calculating the path loss. For example, the path loss may be determined based on the received signal strength received from another node, such as a home access terminal. As a specific example, the path loss to the edge of the coverage boundary of the femto node can be determined based on the last measurement report received from the home access terminal before performing a handover to another access node (e.g., reporting the strength of the signal received from the femto node). Here, it can be assumed that since the access terminal is undergoing a handover, the access terminal may be near the boundary. In some cases, the femto node 200 can determine multiple path loss values over time and generate a final path loss value based on the collected path loss values (e.g., setting the path loss to a maximum value).

As shown in block 508, the femto node 200 (e.g., error determiner 234) may optionally determine one or more error values associated with the determination of the total received signal strength and/or received pilot strength. For example, the error determiner 234 may receive total received signal strength and received pilot strength information from a node (e.g., a home access terminal) that measures these values at various locations within or near the coverage area of the femto node 200. The error determiner 234 may then compare these values with corresponding values measured at the femto node 200. The error value may then be determined based on the difference between the corresponding sets of these values. In some cases, this operation may include collecting error information over time and defining the error value based on the collected information (e.g., based on a range of the collected error information). Error information 236 corresponding to the above may be stored in the data memory 212.

As represented by block 510, the femto node 200 (e.g., interference determiner 238) determines the maximum allowed interference based on the total received signal strength for the visitor access terminal, the received pilot strength, and the minimum required Ecp/Io (e.g., pilot-to-signal ratio).

In WCDMA and 1xRTT systems, pilot and control channels are code-division multiplexed with traffic and are not transmitted at full power (e.g., Ecp/Io < 1.0). Therefore, when a femto node performs measurements, if the neighboring macrocell is unloaded, the total interference signal strength value RSSI _{MACRO_AC} will be lower than the corresponding value when the neighboring macrocell is loaded. In one example, considering the worst-case scenario, the femto node can estimate the system load and adjust the RSSI _{MACRO_AC} value to predict the value under a fully loaded system.

The Ecp/Io (P-CPICH Ec/No in 3GPP terminology) experienced by the visitor access terminal can be calculated as follows:

(Ecp/Io) _LINEAR ＝RSCP _{BEST_MACRO_AC_LINEAR} /(RSSI _{MACRO_AC_LINEAR} +I _{HNB_LINEAR} )

Equation 3

Where all quantities are in linear units (rather than dB), I _{HNB_LINEAR} corresponds to the interference caused by the femto node at the visitor access terminal.

As an example, if the minimum value of (Ecp/Io) _LINEAR required to ensure reliable downlink operation is (Ecp/Io) _{MIN_LINEAR} , the femto node calculates a parameter indicating the maximum allowed interference (which the femto node may sense at a visitor access terminal) as follows, such that the resulting value at the minimum distance is equal to (Ecp/Io) _MIN :

Equation 4

As shown in block 512 of FIG. 5 , femto node 200 (e.g., transmit power controller 208) determines a maximum transmit power based on allowed interference, path loss, and (optionally) an ACIR for femto node 200. As described above, the operations of FIG. 5 can be used to limit coverage holes on adjacent channels or co-channels. In the former case, the ACIR can be a predetermined value (e.g., based on system design parameters). In the latter case, the ACIR is 0 dB. The ACIR value 240 can be stored in data memory 212.

In some aspects, the femto node may thereby convert the calculated maximum allowed interference value at the actual or hypothetical visitor access terminal into a corresponding allowed transmit power value to obtain the predetermined minimum distance I _{HNB — MAX — ALLOWED} . For example, if the allowed coverage hole radius around the femto node is d _{HNB — AC — COVERAGE — HOLE} , then the corresponding path loss value PL may be calculated using the above formula, i.e., PL _{FREE_SPACE} (d _{HNB — AC — COVERAGE — HOLE} ), and:

P _{MAX_HNB} <P _{VUE_AC_MAX} = (I _{HNB_MAX_ALLOWED} +PL _{FREE_SPACE} (d _{HNB_AC_COVERAGE_HOLE} )+ACIR) Equation 5

The transmit power can thus be defined in such a way as to enable operation of a visiting access terminal at a predetermined minimum distance from a femto node (e.g., corresponding to the edge of a coverage hole), without unduly restricting operation of a home access terminal of a femto node. Consequently, both visiting access terminals and home access terminals can operate efficiently near coverage holes.

Based on the above description, consider the following scenario: a macro access terminal (e.g., a visitor access terminal) not associated with a femto node is located within or near the coverage area of the femto node. Here, if passing macro access terminals (e.g., on a street) are unable to handover to the femto node due to restricted association requirements, the femto node (e.g., located near a window) blocks these macro access terminals. The following parameters will be used in this discussion:

Ecp _{MNB_UE} : Received pilot strength (RSCP) received by a macro access terminal (eg, UE) from the best macro access node (eg, MNB) (in linear units).

Ecp _{MNB_HNB} : Received pilot strength (RSCP) received by a femto node (eg, HNB) from the best macro access node (in linear units).

Ec _{HNB_UE} : The total received signal strength (RSSI) (in linear units) received by the macro access terminal from the femto node (also known as RSSI _{MNB_UE} ).

Ec _{HNB_HNB} : The total received signal strength (RSSI) (in linear units) received by the macro access terminal from the femto node (also known as RSSI _{MNB_HNB} ).

As a macro access terminal approaches coverage of a femto node, as described above, the desired action is for the macrocell to move the access terminal to another carrier. In CDMA systems, this trigger is based on the Ecp _{HNB_UE} /Io value exceeding a certain T_ADD threshold. In one example, in 1xEV-DO, the inter-frequency handover trigger would be: Ecp _{HNB_UE} /Io > T_ADD, where an example value is T_ADD = -7 dB (T_ADD _LINEAR = 0.2). On the other hand, in WCDMA systems, the relative signal strength to the best macrocell can generally be used as a trigger. For example, when the Ecp _{HNB_UE} is within a certain range of the Ecp _{MNB_UE} , Ecp _{MNB_UE} - Ecp _{HNB_UE} = Δ _{HO_BOUNDARY} , where Δ _{HO_BOUNDARY} takes a value of approximately (for example) 4 dB, but the 3GPP standard allows for different offsets for each cell.

In some cases, if a macro access terminal with a particular Ecp _{MNB_UE} /Io value approaches a fully loaded (i.e., 100% transmit power) femto node, one question is whether Ecp _{MNB_UE} /Io will drop below a certain minimum threshold (e.g., Ec/Io_min = -16 dB) until the macro access terminal is directed to another carrier. RSSI _MACRO indicates the total received signal strength of the macro access terminal (e.g., 10) excluding interference from the femto node. Then, at the handover boundary:

Equation 6

where α corresponds to the total femtonode transmit power divided by the pilot power value (ie, Ior/Ecp).

For lxEV-DO systems, for example:

Equation 7

For example, the value T_ADD=-7dB, α=1:

Equation 8

In another example, for WCDMA, assuming Δ _{HO — BOUNDARY} = 4 dB, α = 10:

Equation 9

As described above, for mechanisms based on inter-frequency handover, the relative degradation of macro access terminals at the handover boundary is tolerable. Next, the distance from this inter-frequency handover boundary to the edge of the femto node will be considered. In some aspects, if this distance is very large, macro access terminals can use the same carrier frequency very sparingly (particularly if a large number of femto cells are present within a macro cell). In other words, the inter-frequency handover mechanism works well (independent of femto node downlink transmit power), and macro access terminals can operate reliably outside the femto node handover boundary. However, if higher femto node transmit power is used, the handover boundary extends toward the macro cell, and the area in which co-channel macro access terminals can operate efficiently is very limited. In the above example, because the visitor access terminal is assumed to be very close to the femto node at a predetermined distance (e.g., a few meters), it is assumed that the home node can effectively measure the Ecp and RSSI values experienced by the visitor access terminal. However, when the macro access terminal is outside the femto residence, Ecp _{MNB_UE} and Ecp _{MNB_HNB} may take different values. For example, Ecp _{MNB_HNB} experiences penetration loss, while Ecp _{MNB_UE} does not. This would lead to the conclusion that Ecp _{MNB_UE} is always greater than Ecp _{MNB_HNB} . However, sometimes a femto node residence creates a shadowing effect, causing Ecp _{MNB_UE} to be lower than Ecp _{MNB_HNB} (e.g., the femto node is located between a macro access node and a macro access terminal). In one example, the difference between the best macro Ecp measurement of the femto node and the best macro Ecp measurement of the macro access terminal at the handover boundary is:

Δ _{Ecp_MEAS_DIFF_HO_BOUNDARY} =Ecp _{MNB_UE} -Ecp _{MNB_HNB} Equation 10

Similarly, the difference between the macro RSSI measurement of the femto node and the macro RSSI measurement of the macro access terminal at the handover boundary may be calculated as follows:

Δ _{RSSI_MEAS_DIFF_HO_BOUNDARY} = RSSI _{MNB_UE} - RSSI _{MNB_HNB} Equation 11

In some aspects, these values may include the error information described at block 508 above.

Based on the previous measurement results, some values can be used for Δ _{Ecp_MEAS_DIFF_HO_BOUNDARY} . Then, in one example, since in this case the access terminal is not on an adjacent channel but is co-channel with the femto node, the femto node downlink power (P _HNB ) can be determined based on the constraints detailed above (e.g., Equations 4 and 5), where, for example, ACIR = 0 dB, and PL _{FREE_SPACE} (d _{HNB_AC_COVERAGE_HOLE} ) is replaced by the expected path loss value for the co-channel coverage hole.

In some cases, a femto node may be located next to an exterior wall or window of a residence. Such a femto node may cause the greatest amount of interference to the macrocell outside the wall/window. If the attenuation due to the wall/window is PL _WALL , and in one example, for simplicity, Δ _{HNB_MUE_MEAS_DIFF} = 0 dB and Δ _{RSSI_MNB_MUE_MEAS_DIFF} = 0 dB, then Ecp _{HNB UE} (d) = (Ecp / Ior) _PHNB - PL _FREE (d) - PL _WALL , where the total femto node downlink transmit power ( _PHNB ) is determined based on the above constraints.

One way to reduce coverage holes caused by femto nodes is to reduce the Ecp/Ior of the femto nodes. However, it is undesirable to arbitrarily reduce the Ecp/Ior of the femto nodes because this would result in handoff boundaries being close to the femto nodes and because macro access terminal performance could be significantly degraded if the femto nodes are loaded. In addition, a predetermined minimum Ecp level can be defined for successful operation of an access terminal in femto coverage (e.g., channel estimation, etc.) to allow the access terminal to switch from macrocell coverage to femto coverage. Therefore, in some cases, a hybrid approach can be implemented such that the Ecp/Ior can be reduced to a reasonably low value when there are no active users being served by the femto nodes, thereby limiting coverage holes in the macrocell during those time periods. In other words, as discussed above in block 408, the transmit power can be adjusted based on whether the node is in the vicinity of a femto node.

For a home access terminal, Ecp may be calculated as follows: Ecp _HUE = _PHNB - Ecp/Ior- _PLHNB , where _PLHUE corresponds to the path loss from the femto node to the home access terminal.

In some cases, there is no interference from neighboring access terminals and all interference comes from the macrocell and the thermal noise floor. One of the important parameters in the above equation is PL _HUE . A common model for indoor propagation is:

Equation 12

where _Wi is the penetration loss through the interior wall.

6 , in some implementations, the maximum transmit power defined by the femto node 200 can be limited based on the signal-to-noise ratio of home access terminals located near the edge of a coverage hole. For example, if the signal-to-noise ratio is higher than expected at a home access terminal located at a location where the coverage hole is expected to terminate, this means that the coverage hole is actually much larger than expected. As a result, excessive interference may be imposed on visitor access terminals near the intended coverage hole.

In some aspects, the present invention relates to reducing transmit power if the signal-to-noise ratio at a home access terminal is higher than desired. The following parameters are used in the subsequent discussion:

_IoUE : The total received signal strength (Io) received by a home access terminal (e.g., UE) from all access nodes (e.g., Node Bs) in the absence of a femto node (in linear units).

Io _HNB : The total received signal strength (Io) received by the home access terminal from all other access nodes (eg, macro access nodes and femto access nodes) in the system (in linear units).

PL _{HNB_edge} : Path loss (in dB) from a femto node (eg, HNB) to a home access terminal at the coverage edge.

When the femto node is not transmitting, the Ecp/Io received by the macro access terminal is:

Equation 13

When the femto node transmits, the Ecp/Io received by the access terminal is:

Equation 14

The parameter [Ecp/Io] _min is defined as the minimum Ecp/Io required for a macro access terminal to obtain proper service (as discussed with reference to FIG5 ). Assuming that the macro access terminal is at the edge of a femto node coverage hole, and the coverage hole is limited to a certain value (e.g., PL _{HNB_edge} = 80 dB), the following conditions may be imposed on the femto node downlink maximum transmit power _{PHNB_max} (e.g., maintaining [Ecp/Io] _min for the macro access terminal):

Equation 15

Similarly, if a home access terminal (e.g., home UE, HUE) served by a femto node is located at the edge of femto coverage, the SNR (the term SINR will be used in the following discussion, e.g., including interference) of the home access terminal can be described as follows:

Equation 16

In some cases, the transmit power level of the femto node resulting from Equation 16 is large, which can result in an unnecessarily high SINR _HUE . This means, for example, that if a new femto node is installed near an existing femto node, the new femto node may end up receiving high levels of interference from the previously installed femto node. As a result, the newly installed femto node may be restricted to a lower transmit power level and may not be able to provide sufficient SINR for its home access terminals. To prevent this type of effect, an SINR cap may be applied to home access terminals at the edge of their coverage area: [SINR] _{max_at_HNB_edge} . Therefore, a second constraint may be imposed on P _{HNB_max} :

Equation 17

To apply the constraints as described in Equation 15 and Equation 17, Ecp _{MNB — UE} and Io _UE may be measured at the edge of the desired HNB coverage (PL _{HNB — edge} ).

Because professional installation may not be feasible for a femto node (e.g., due to economic constraints), the femto node can estimate these quantities by independently measuring the downlink channel. For example, the femto node can measure Ecp _{MNB_HNB} and Io _HNB to estimate Ecp _{MNB_UE} and Io _UE , respectively. This is discussed in more detail below with reference to Equation 19. Since the femto node location is different from the access terminal location, there will be some error in these measurements.

If the femto node uses its own measurements to adapt its own transmit power, this error will result in transmit power values that are lower or higher than the optimal value. One possible approach to avoid the worst-case error is to set upper and lower limits on _{PHNB_max} , namely: _{PHNB_max_limit} , _{PHNB_min_limit} (e.g., as described above).

In accordance with the above, with reference to block 602 of FIG6 , the transmit power adjustment algorithm may include identifying home access terminals near the coverage edge of a femto node. In the example of FIG2 , this operation may be performed by the node detector 224. In some implementations, the location of the home access terminal may be determined based on path loss measurements between the home access terminal and the femto node (e.g., as discussed herein).

At block 604, the femto node 200 (e.g., SNR determiner 242) may determine an SNR value (e.g., SINR) associated with the home access terminal. In some cases, this may include receiving SNR information from the home access terminal (e.g., in a channel quality report or measurement report). For example, the home access terminal may send measured RSSI information or calculated SNR information to the femto node 200. In some cases, the CQI information provided by the home access terminal may be correlated with the SNR value of the home access terminal (e.g., via a known relationship). Thus, the femto node 200 may derive the SNR from the received channel quality information.

As described above, determining the SNR value may include: the femto node 200 autonomously calculating the SNR value, as described herein. For example, in the case where the femto node 200 performs measurement operations on its own, the femto node 200 first measures:

Ecp _{MNB_HNB} : Total received pilot strength received by the femto node from the best macro access node.

Io _HNB : The total received signal strength (Io) received by the femto node from all other access nodes (e.g., macro nodes, femto nodes) in the system.

The femto node 200 may then determine a power cap:

Equation 18

Equation 19

Here, Equation 18 relates to a maximum transmit power determined in a similar manner as discussed in FIG5 , and Equation 19 relates to another maximum upper limit for transmit power determined based on the SNR. It can be observed that Equation 18 is similar to Equation 17, except that Io is measured at the femto node. Thus, Equation 18 also provides the constraint that the SNR at the node is not greater than or equal to a defined maximum value (e.g., SNR value 244 stored in data memory 212). In these equations, the transmit power is determined based on the signal received at the femto node and based on the path loss to the coverage edge (e.g., based on the distance to the edge).

6 , femto node 200 (e.g., transmit power controller 208) may determine the transmit power based on the maximum value defined by Equation 18 and Equation 19. Additionally, as described above, the final maximum power may be limited by an absolute minimum value and an absolute maximum value:

_{PHNB_total} =max[ _{PHNB_min_limit} ,min( _{PHNB_max1} , _{PHNB_max2} , _{PHNB_max_limit} )] Equation 20

As an example of Equation 20, PL _{HNB_edge} may be specified as 80 dB, _{PHNB_max_limit} may be specified as 20 dBm, _{PHNB_min_limit} may be specified as -10 dBm, and [SINR] _{max_at_HNB_edge} and [Ecp/Io] _min may depend on the specific air interface technology used.

As described above, the teachings described herein can be implemented in wireless networks that include both macro and femto coverage areas. FIG7 illustrates an example of a coverage diagram 700 of a network where several tracking areas 702 (or routing areas or location areas) are defined. Specifically, in FIG7 , the coverage areas associated with tracking areas 702A, 702B, and 702C are outlined with bold lines.

The system provides wireless communications via multiple cells 704 (represented by hexagons) (e.g., macrocells 704A and 704B) to each cell served by a corresponding access node 706 (e.g., access nodes 706A-706C). As shown in FIG7 , at a given point in time, access terminals 708 (e.g., access terminals 708A and 708B) can be dispersed throughout the network. For example, depending on whether the access terminal 708 is in an active state or in soft handoff, each access terminal 708 can communicate with one or more access nodes 706 on a forward link (FL) and/or a reverse link (RL) at a given moment. The network can provide service over a large geographic area. For example, a macrocell 704 can cover several adjacent blocks. To reduce the complexity of FIG7 , only some access nodes, access terminals, and femto nodes are shown.

Tracking areas 702 also include femto coverage areas 710. In this example, each of the femto coverage areas 710 (e.g., femto coverage area 710A) is depicted within a macro coverage area 704 (e.g., macro coverage area 704B). However, it should be understood that not all femto coverage areas 710 may be located within a macro coverage area 704. In practice, many femto coverage areas 710 may be defined as being located within a given tracking area 702 or macro coverage area 704. Additionally, one or more pico coverage areas (not shown) may be defined as being located within a given tracking area 702 or macro coverage area 704. To reduce the complexity of FIG7 , only some of the access nodes 706, access terminals 708, and femto nodes 710 are shown.

8 illustrates a network 800 in which femto nodes 802 are deployed in an apartment building. Specifically, in this example, femto node 802A is deployed in apartment 1, and femto node 802B is deployed in apartment 2. Femto node 802A is the home femto for access terminal 804A. Femto node 802B is the home femto for access terminal 804B.

As shown in FIG8 , in the case where femto nodes 802A and 802B are restricted, each access terminal 804 can be served only by its associated (e.g., home) femto node 802. However, in some cases, restricted association can result in unfavorable geometry and femto node outages. For example, in FIG8 , femto node 802A is closer to access terminal 804B than femto node 802B, thereby providing a stronger signal to access terminal 804B. As a result, femto node 802A can cause excessive interference to reception at access terminal 804B. This situation can affect the coverage radius around femto node 802B, within which associated access terminals 804 initially acquire and maintain a connection to the system.

9 through 13B , the present invention relates in some aspects to adaptively adjusting the transmit power (e.g., maximum downlink transmit power) of neighboring access nodes to mitigate adverse geometry conditions. For example, a maximum transmit power can be defined for overhead channels as described above and then transmitted as a default fraction of the maximum access node transmit power. For purposes of explanation, the following describes a scenario in which the transmit power of a femto node is controlled based on measurement reports generated by access terminals associated with neighboring femto nodes. However, it should be understood that the description herein is applicable to other types of nodes.

The transmit power control described herein may be implemented using a distributed power control scheme implemented at the femto node and/or using a centralized power controller. In the former case, the transmit power may be adjusted using signaling between neighboring femto nodes (e.g., femto nodes associated with the same operator). For example, such signaling may be implemented using upper layer signaling or appropriate wireless components (e.g., via a backhaul). In the latter case described above, the transmit power of a given femto node may be adjusted using signaling between the femto node and a centralized power controller.

The femto node and/or the centralized power controller may use the measurements reported by the access terminal and evaluate one or more coverage criteria to determine whether to send a request to the femto node to reduce transmit power. If the femto node receiving such a request can maintain its coverage radius and its associated access terminals will maintain good geometry, the femto node may respond by reducing its transmit power.

FIG9 illustrates several operations related to an embodiment in which multiple adjacent femto nodes collaborate to control each other's transmit power. Multiple criteria may be employed to determine whether a neighboring node's transmit power should be adjusted. For example, in some aspects, the power control algorithm may attempt to maintain a specific coverage radius around the femto node (e.g., maintaining a specific CPICH Ecp/Io at a specific path loss from the femto node). In some aspects, the power control algorithm may attempt to maintain a specific quality of service (e.g., throughput) at the access terminal. The operations of FIG9 and FIG10 will be described first with respect to the former algorithm. The operations of FIG9 and FIG10 will then be described in more detail with respect to the latter algorithm.

As shown in block 902 of FIG. 9 , a given femto node initially sets its transmit power to a defined value. For example, initially, all femto nodes in the system set their respective transmit powers to a maximum transmit power that still mitigates the introduction of coverage holes in macro coverage areas. As a specific example, the transmit power of a femto node may be set such that the CPICH Ecp/Io of a macro access terminal at a specific path loss (e.g., 80 dB) from the femto node is above a specific threshold (e.g., -18 dB). In some implementations, the femto node may employ one or more of the algorithms described above in conjunction with FIG. 2 through FIG. 6 to determine the maximum transmit power value.

Each access terminal in the network (e.g., each access terminal associated with a femto node) may measure the signal strength of signals received in its own operating band, as represented by block 904. Each access terminal may then generate a neighbor report that includes, for example, the CPICH RSCP (pilot strength) of its femto node, the CPICH RSCP of all femto nodes in its neighbor list, and the RSSI for the operating band.

In some aspects, each access terminal may perform this operation in response to a request from its home femto node. For example, a given femto node may maintain a list of neighboring femto nodes that it transmits to its home access terminals. This neighbor list may be provided to the femto node by upper layer processing, or the femto node may populate the list itself by monitoring downlink traffic (assuming the femto node includes appropriate circuitry to do so). The femto node may repeatedly (e.g., periodically) transmit requests for neighbor reports to its home access terminals.

As shown in blocks 906 and 908, the femto node (e.g., transmit power controller 208 of FIG. 2 ) determines whether signal reception at each of its home access terminals is acceptable. For example, for one embodiment attempting to maintain a specific coverage radius, assuming access terminal "i" is at a specific path loss (PL) from femto node "i" (e.g., assuming the measured location of femto node "i" does not change significantly), a given femto node "i" (e.g., Home Node B, "HNB") may estimate the CPICH Ecp/Io_i for a given associated access terminal "i" (e.g., Home User Equipment, "HUE"). Here, Ecp/Io_i for access terminal "i" is

In some implementations, a femto node (e.g., signal strength determiner 226) can determine RSSI on behalf of its home access terminals. For example, a femto node can determine the RSSI of an access terminal based on an RSCP value reported by the access terminal. In this case, the access terminal does not need to send an RSSI value in a neighbor report. In some implementations, a femto node can determine (e.g., estimate) RSSI and/or RSCP on behalf of its home access terminals. For example, signal strength determiner 226 can measure RSSI at the femto node, and received pilot strength determiner 228 can measure RSCP at the femto node.

Femto node "i" may determine whether Ecp/Io_i is less than or equal to a threshold to determine whether coverage for access terminal "i" is acceptable. If coverage is acceptable, operational flow may return to block 904, where femto node "i" waits to receive the next neighbor report. In this manner, a femto node may repeatedly monitor conditions at its home access terminals over time.

If coverage is unacceptable at block 908, femto node "i" may initiate operations to adjust the transmit power of one or more neighboring femto nodes. Initially, as shown in block 910, femto node "i" may set its transmit power to a maximum allowed value (e.g., the maximum value discussed at block 902). Here, for example, if femto node "i" complies with an intervention request from a neighboring femto node to reduce the transmit power of femto node "i," the transmit power of femto node "i" may have been reduced after setting the maximum value for femto node "i" at block 902. In some implementations, after increasing the transmit power, femto node "i" may determine whether coverage for access terminal "i" is now acceptable. If so, operational flow may return to block 904 as described above. If not, operational flow may proceed to block 912, discussed below. In some embodiments, femto node "i" may perform the operations described below without examining the results of block 910.

As shown in block 912, femto node "i" (e.g., transmit power controller 208) may rank the femto nodes in the neighbor report by the strength of their respective RSCPs measured by the access terminal. The ranked list of potentially interfering nodes 246 is then stored in data memory 212. As will be discussed below, operation 912 may exclude any neighboring femto nodes that sent a NACK in response to a request to reduce transmit power and for which a timing associated with the NACK has not expired.

As shown in block 914, femto node "i" (e.g., transmit power controller 208) selects the neighboring femto node with the strongest interference (e.g., femto node "j") and determines by how much the femto node should reduce its transmit power to maintain a given Ecp/Io for access terminal "i" at a specified coverage radius (path loss). In some aspects, the amount of power reduction (e.g., a percentage) may be represented by a parameter alpha_p. In some aspects, as described above, the operations of block 914 may include determining whether Ecp/Io_i is greater than or equal to a threshold.

Next, femto node "i" (e.g., transmitter 204 and communication controller 210) sends a message to femto node "j" requesting that its power be reduced by a specified amount (e.g., alpha_p). Example operations performed by femto node "j" upon receiving such a request will be described below in conjunction with FIG.

As shown in block 916, femto node "i" (e.g., receiver 206 and communication controller 210) will receive a message from femto node "j" in response to the request of block 914. If femto node "j" chooses to reduce its transmit power by the requested amount, femto node "j" will respond to the request with an acknowledgment message (ACK). In this case, operational flow may return to block 904 as described above.

If femto node "j" chooses not to reduce its transmit power by the requested amount, femto node "j" will respond to the request with a negative acknowledgement (NACK). In its response, femto node "j" may indicate that it did not reduce power at all, or it may indicate that it reduced power by a given amount less than the requested amount. In this case, operational flow may return to block 912, where femto node "i" may re-rank the femto nodes in the neighbor report based on the RSCP measured by access terminal "i" (e.g., based on the newly received neighbor report). However, here, femto node "j" does not participate in this re-ranking as long as the timer associated with femto node "j's NACK has not expired. Therefore, the operations of blocks 912 through 918 may be repeated until femto node "i" determines that the Ecp/Io of access terminal "i" is at the target value or has been improved as much as possible.

FIG10 illustrates example operations performed by a femto node that receives a request to reduce transmit power. Block 1002 represents receipt of such a request. In some implementations, node 200 of FIG2 may also be capable of performing these operations, with receiver 206 and communications controller 210 being able to at least partially perform the operations of block 1002, transmit power controller 208 being able to at least partially perform the operations of blocks 1004-1008 and blocks 1012-1014, and transmitter 204 and communications controller 210 being able to at least partially perform the operations of block 1010.

At blocks 1004 and 1006, if the transmit power is adjusted as requested, the femto node determines whether coverage for one or more home access terminals is acceptable. For example, femto node "j" may evaluate a request to reduce its transmit power to alpha_p*HNB_Tx_j by determining whether each of its access terminals passes a test similar to the test described in block 906. Here, femto node "j" may determine whether the Ecp/Io of the associated access terminal at the specified coverage radius is greater than or equal to a threshold.

At block 1006, if coverage is acceptable, femto node "j" reduces its transmit power by the requested amount for a defined period of time (block 1008). At block 1010, femto node "j" responds to the request with an ACK. Operational flow may then return to block 1002, where the femto node processes any additional requests to reduce transmit power as they are received.

At block 1006, if coverage is unacceptable, femto node "j" may determine an amount by which it may reduce its transmit power in order to pass the test of block 1004 (block 1012). Here, it should be understood that in some cases, femto node "j" may choose not to reduce its transmit power at all.

At block 1014, for a defined period of time, if applicable, femto node "j" reduces its transmit power by the amount determined at block 1012. For example, this amount is represented by the value beta_p*HNB_Tx_j.

At block 1016, femto node "j" responds to the request with a negative acknowledgement (NACK). In this response, femto node "j" may indicate that it will not reduce power at all or that it will reduce power by a given amount (e.g., beta_p*HNB_Tx_j). Operational flow may then return to block 1002 as described above.

In some implementations, femtonode "i" and femtonode "j" maintain separate timers for calculating a specified period of time associated with an ACK or NACK. Upon expiration of the timer for femtonode "j," femtonode "j" can reset its transmit power back to its previous level. This prevents femtonode "j" from being disadvantaged if femtonode "i" has moved away.

Additionally, in some cases, each femto node in the network can store measurements received from an access terminal the last time the access terminal was connected to the femto node. In this manner, when no access terminal is currently connected to the femto node, the femto node can calculate the minimum transmit power to ensure Ecp/Io coverage for initial acquisition.

If a femto node has sent requests to all neighboring femto nodes to reduce transmit power and the femto node still cannot maintain the desired coverage at a specific coverage radius, the femto node can calculate how much its common pilot Ec/Ior needs to increase above its default level to achieve the target coverage. The femto node then increases its pilot power accordingly (e.g., within a preset maximum value).

Thus, an implementation utilizing a scheme such as that described above for maintaining coverage radius can be used to efficiently set transmit power values in the network. For example, such a scheme sets a lower bound on the geometry (and throughput) of an access terminal if the access terminal is within a specified coverage radius. Furthermore, such a scheme can make the power profile more static, such that the power profile only changes when femto nodes are added to or removed from the network. In some implementations, to eliminate further CPICH outages, the scheme described above can be modified to adjust the CPICH Ec/Ior based on measurements collected at the femto nodes.

A given femto node may perform the operations of blocks 904-918 for its associated access terminals. If multiple access terminals are associated with the femto node, the femto node may send a request to an interfering femto node when any of its associated access terminals is experiencing interference.

Similarly, when evaluating whether to respond to a request to reduce transmit power, the femto node performs the test for all access terminals associated with it at block 1004. The femto node may then select the minimum power that ensures acceptable performance for all access terminals associated with it.

Additionally, each femto node in the network performs these operations for its respective access terminals. Thus, each node in the network can send a request to reduce transmit power to a neighboring node, or can receive a request to reduce transmit power from a neighboring node. The femto nodes can perform these operations asynchronously with respect to each other.

As described above, in some implementations, a quality of service criterion (e.g., throughput) can be used to determine whether to reduce the transmit power of the femto node. This solution can be used as a supplement to the above solution or as an alternative to the above solution.

In a manner similar to that described above, RSCP_i_j is defined as the CPICH RSCP of femto node "j" (HNB_j) measured by access terminal "i" (HUE_i). RSSI_i is the RSSI measured by access terminal "i". Ecp/Io_i and Ecp/Nt_i are the CPICH Ecp/Io and CPICH SINR (Signal to Interference and Noise Ratio) of access terminal "i", respectively, from femto node "i" (HNB_i) associated with access terminal "i". The femto node calculates as follows:

Equation 21

Equation 22

Wherein, Ecp/Ior is the ratio of CPICH pilot transmission power to total cellular power.

In the case where the femto node is located at the edge of the femto node coverage corresponding to the path loss PL _{HNB_Coverage} , the femto node estimates the Ecp/Io of the home access terminal:

Equation 23

where RSCP_i_i _{HNB_Coverage} is the received pilot strength received from femtonode "i" at access terminal "i" located at the edge of coverage of femtonode "i". The edge of coverage corresponds to a distance from the femtonode that has a path loss (PL) that is equal to PL _{HNB_Coverage} , and

RSCP_i_i _{HNB_Coverage} =HNB_Tx_i*(Ecp/Ior)/PL _{HNB_Coverage} Equation 24

Let (Ecp/Io)_Trgt_A be the CPICH Ecp/Io threshold value pre-set at the femto node. The femto node detects the following relationship:

(Ecp/Io_i) _{HNB_Coverage} >(Ecp/Io)_Trgt_A? Equation 25

If the answer is "yes," the femto node does not send a request to reduce transmit power. If the answer is "no," the femto node sends a request to reduce transmit power as described below. Additionally or alternatively, the femto node may perform similar checks related to throughput (e.g., SINR_i).

The femto node sets its power to the maximum value allowed by the macrocell coverage hole conditions.

Femto node "i" ranks neighbor cells in descending order of RSCP reported by the home access terminal.

Femto node "i" picks the neighbor cellular node "j" with the largest RSCP value (RSCP_i_j).

Serving femto node "i" calculates how much femto node "j" needs to reduce its transmit power to improve performance for access terminal "i." Let (Ecp/Io)_Trgt_A be the target CPICH Ecp/Io preset at the femto node for home access terminals. This target Ecp/Io can be chosen so that home access terminals are not located at an outage. A more aggressive approach is to guarantee minimum geometry for home access terminals to maintain a specific data throughput or performance standard. The expected RSCP_i_j_trgt observed by access terminal "i" from neighbor femto node "j" to maintain (Ecp/Io)_Trgt_A can be calculated as follows:

Equation 26

Additionally, or alternatively, the femto nodes may perform similar checks related to throughput. Femto node "i" calculates the ratio alpha_p_j by which femto node "j" should reduce its power:

alpha_p_j = RSCP_i_j_Trgt/RSCP_i_j Equation 27

Femto node 'i' sends a request to femto node 'j' to reduce its transmit power by a ratio alpha_p_j. As described herein, this request can be sent to a centralized algorithm via upper layer signaling (backhaul) or directly from femto node 'i' to femto node 'j'.

Femto node "j" evaluates whether it responds to the request of femto node "i" by making its transmit power HNB_Tx_new_j = alpha_p_j * HNB_Tx_j, where HNB_Tx_j is set as described above. In some implementations, femto node "j" checks for two detections.

Detection 1: This detection is based on the scheme previously described with reference to FIG9 . The CPICH Ecp/Io of the associated home access terminal located within the coverage radius of femto node "j" is above a specific threshold (Ecp/Io)_Trgt_B. This detection is to ensure that its own UE has acceptable performance within a specific radius around the femto node and that other registered home access terminals can also obtain the femto node. This can be calculated according to the following equation:

Equation 28

Where RSSI_j and RSCP_j_j are the RSSI and RSCP reported by HUE_j located at the coverage radius to femtonode "j" (or estimated by HNB_j) before the transmission power is modified. The detection is:

(Ecp/Io_j) _{HNB_Coverage} > (Ecp/Io)_Trgt_B? Equation 29

Detection 2: The CPICH SINR of HUE_j is greater than a certain target value to maintain a certain performance criterion (e.g., quality of service such as throughput):

SINR_new_j>SINR_Trgt? Equation 30

in

Equation 31

If one or both tests pass (depending on the particular implementation), femto node 'j' reduces its transmit power to alpha_p_j*HNB_Tx_j and sends an ACK to femto node 'i', assuming the new power is above the minimum allowed value (e.g., -20dBm).

If one or both tests fail, femto node "j" does not reduce its transmit power to the required value. However, femto node "j" calculates how much it can reduce its transmit power without compromising its performance. In other words, in implementations where both tests are used, the femto node can calculate its new transmit power so that both Test 1 and Test 2 pass, and reduce its transmit power to the higher of the two results. However, if both tests pass using the current femto node "j" power setting, femto node "j" does not reduce its power. The femto node can also reduce its power to a minimum standardized limit (e.g., as described herein). In all of these cases, femto node "j" can report a NACK to femto node "i" using the final power setting.

The algorithms discussed above allow femto nodes to adaptively adjust their transmit power in a cooperative manner. These algorithms have many parameters that can be adjusted (by the operator), such as Ecp/Io_Trgt_A, Coverage_radius, Ecp/Io_Trgt_B, SINR_Trgt, and timers. The algorithms can be further improved by making the thresholds adaptive through a learning process.

In some aspects, the timers can be varied (e.g., independently) to optimize system performance. If access terminal "i" is not connected to femto node "i" and femto node "j" is ready to transmit to access terminal "j," access terminal "i" may be unable to acquire femto node "i" due to its low CPICH Ecp/Io. The algorithm described above can then be modified so that each femto node attempts to maintain a minimum CPICH Ecp/Io within a specific radius around the femto node. The disadvantage of this approach is that if femto node "i" has no access terminals associated with it, it can penalize neighboring access terminal "j." To avoid continually penalizing neighboring femto nodes, femto node "i" will send an indication in its request to neighboring femto node "j" that the request is for initial acquisition. If femto node "j" responds by reducing its power, femto node "j" sets a timer and femto node "i" sets a longer timer. After the timer for femto node "j" expires, femto node "j" resets its transmit power to its default value, and before the timer for femto node "i" expires, femto node "i" does not send another request (e.g., for initial acquisition) to femto node "j." However, a problem still exists: femto node "i" needs to estimate RSSI_i because no access terminals are associated with it. Femto node "i" also needs to estimate RSCP_j for neighboring interferers. However, the strongest interferer observed by a femto node is not necessarily the strongest interferer observed by the femto node's access terminal.

To mitigate issues during initial acquisition, an access terminal can be allowed to camp in idle mode on a neighboring femto node with the same PLMN_ID. The access terminal can access a neighbor list for the femto node it is camping on, which includes the scrambling code and timing of the access terminal's own femto node. This can be beneficial when the access terminal is acquiring its femto node under unfavorable geometric conditions.

11 through 13B , an implementation of controlling the transmit power of a femto node using a centralized power controller is described. FIG11 illustrates an example system 1100 including a centralized power controller 1102, a femto node 1104, and an access terminal 1106. Here, femto node 1104A is associated with access terminal 1106A, and femto node 1104B is associated with access terminal 1106B. Centralized power controller 1102 includes a transceiver 1110 (having a transmitter 1112 and a receiver 1114 components) and a transmit power controller 1116. In some aspects, these components may function similarly to the functions of similarly named components in FIG2 .

12 illustrates various operations that may be performed in an implementation in which a femto node (e.g., femto node 1104A) forwards only neighbor list information received from access terminals associated therewith (e.g., access terminal 1106A) to a centralized power controller 1102. The centralized power controller 1102 may then perform operations similar to those described above for requesting femto nodes (e.g., femto node 1104B) located near femto node 1104A to reduce transmit power.

Operations blocks 1202 and 1204 may be similar to the operations described above for blocks 902 and 904. At block 1206, the femto node 1104A forwards the neighbor list 1108A received from the access terminal 1106A to the centralized power controller 1102. The operations of blocks 1202-1206 may be repeated periodically (e.g., periodically) whenever the femto node 1104A receives a neighbor report from the access terminal 1106A.

As shown in block 1208, the centralized power controller 1102 may receive similar information from other femto nodes in the network. At block 1210, the centralized power controller 1102 may then perform operations similar to those described above (e.g., at block 906) to determine whether the femto node should reduce its transmit power. In some aspects, the centralized power controller 1102 may make power control decisions based on information it receives regarding conditions at multiple femto nodes. For example, if a given femto node is interfering with several other femto nodes, the centralized power controller 1102 may attempt to reduce the power of that femto node first.

At block 1212, the centralized power controller 1102 sends a message to each femto node indicating that the centralized controller 1100 has determined that transmit power should be reduced. As described above, this request may indicate the amount by which the power of the designated femto node should be reduced. These operations may be similar to those of blocks 912 and 914.

At block 1214, the centralized power controller 1102 receives a response from the femto node. As shown at block 1216, if no NACK is received after issuing the request at block 1212, the operational flow of the centralized power controller 1102 returns to block 1208, where the centralized controller 1102 continues to receive information from femto nodes in the network and perform the power control operations described above.

On the other hand, if one or more NACKs are received after the request is issued at block 1212, the operation flow of the centralized power controller 1102 returns to block 1210, where the centralized controller 1102 can identify other femto nodes that should reduce their transmit power and then issue new power control messages. These operations can be similar to the operations of blocks 912 and 914.

13A and 13B describe various operations that may be performed in an implementation in which a femto node (e.g., femto node 1104A) identifies neighboring femto nodes (e.g., femto node 1104B) that should reduce power and sends this information to a centralized power controller 1102. The centralized power controller 1102 may then send a request to the femto node 1104B to reduce transmit power.

Operations in blocks 1302-1312 may be similar to the operations in blocks 902-912 described above. At block 1314, the femto node 1104A sends a message to the centralized power controller 1102 identifying the femto node 1104B. For example, the message may identify only a single femto node (e.g., femto node 1104B), or the message may include a ranking of femto nodes (e.g., as described in block 912). This list may also include some or all of the neighbor reports received by the femto node 1104A from the access terminal 1106A. The operations in blocks 1302-1314 may be repeated periodically (e.g., periodically) each time the femto node 1104A receives a neighbor report from the access terminal 1106A.

The centralized power controller 1102 may receive similar information from other femto nodes in the network, as in block 1316. At block 1318, the centralized power controller 1102 may determine whether it should adjust any received requests to reduce transmit power (e.g., based on other requests it received requesting the same femto node to reduce power).

The centralized power controller 1102 may then send a message to each femto node that the centralized controller 1102 has determined that transmit power should be reduced, at block 1320. As described above, this request may indicate the amount by which the power of the designated femto node should be reduced.

At block 1322, the centralized power controller 1102 receives a response from the femto node. As shown at block 1324, if no NACK is received after the request is issued at block 1320, the operational flow of the centralized power controller 1102 returns to block 1316, where the centralized power controller 1102 continues to receive information from femto nodes in the network and perform power control operations as described above.

On the other hand, if one or more NACKs are received after issuing the request at block 1320, operational flow of the centralized power controller 1102 returns to block 1318, where the centralized controller 1102 may identify other femto nodes that should have their transmit power reduced and subsequently issue new power control messages (e.g., based on the ranked list received from femto node 1104A).

Based on the above, it should be appreciated that the description herein can provide an efficient method for managing the transmit power of neighboring access nodes. For example, in a static environment, the downlink transmit power of a femto node can be adjusted to a static value, thereby ensuring that the service requirements of all access terminals are met. Consequently, since all channels can be continuously transmitted at a constant power, this solution is compatible with legacy access terminals. Furthermore, in a dynamic environment, transmit power can be dynamically adjusted to accommodate the changing service requirements of nodes in the system.

Connectivity within a femto node environment can be established in various ways. For example, FIG14 illustrates an example communication system 1400 in which one or more femto nodes are deployed within a network environment. Specifically, system 1400 includes multiple femto nodes 1410 (e.g., femto node 1410A and femto node 1410B) installed within a relatively small-scale network environment (e.g., within one or more user residences 1430). Each femto node 1410 can be connected to a wide area network 1440 (e.g., the Internet) and a mobile operator core network 1450 via a DSL router, cable modem, wireless link, or other connectivity means (not shown). As described herein, each femto node 1410 can be used to serve an associated access terminal 1420 (e.g., access terminal 1420A) and (optionally) other associated access terminals 1420 (e.g., access terminal 1420B). In other words, access to the femto nodes 1410 may be restricted such that a given access terminal 1420 may be served by a designated set of (e.g., home) femto nodes 1410 but not by any undesignated femto nodes 1410 (e.g., neighbor femto nodes 1410).

The owner of a femto node 1410 may subscribe to mobile services, such as 3G mobile services provided by a mobile operator's core network 1450. Furthermore, an access terminal 1420 is capable of operating in both macro environments and smaller network environments, such as residential environments. In other words, depending on the current location of the access terminal 1420, the access terminal 1420 may be served by an access node 1460 of a macrocellular mobile network 1450 or by any one of a group of femto nodes 1410 (e.g., femto node 1410A and femto node 1410B located within a respective user residence 1430). For example, when a user is outside their home, they may be served by a standard macro access node (e.g., node 1460), while when they are at home, they may be served by a femto node (e.g., node 1410A). It should be understood that the femto node 1410 is backward compatible with existing access terminals 1420.

The femto node 1410 may be deployed on a single frequency or, alternatively, on multiple frequencies. Depending on the particular configuration, the single frequency or one or more of the multiple frequencies may overlap with one or more frequencies used by a macro node (e.g., node 1460).

The access terminal 1420 may be configured to communicate with the macro network 1450 and with the femto node 1410, but may not be configured to communicate with both the macro network 1450 and the femto node 1410 simultaneously. In addition, the access terminal 1420 served by the femto node 1410 may not be in soft handoff with the macro network 1450.

In some aspects, an access terminal 1420 may be configured to connect to a preferred femto node (e.g., the home femto node of the access terminal 1420) whenever such connection is possible. For example, whenever the access terminal 1420 is within a user residence 1430, it may be desirable for the access terminal 1420 to communicate only with the home femto node 1410.

In some aspects, if the access terminal 1420 is operating within the macrocellular network 1450 and is not located in its most preferred network (e.g., as defined in the preferred roaming list), the access terminal 1420 may use Better System Reselection (BSR) to continue searching for the most preferred network (e.g., the preferred femto node 1410). This process may include periodically scanning available systems to determine if a better system is currently available and then attempting to associate with the preferred system. Based on the acquisition entry, the access terminal 1420 may limit the search to specific frequency bands and channels. For example, the search for the most preferred system may be repeated periodically. Once the preferred femto node 1410 is found, the access terminal 1420 selects the femto node 1410 to camp within its coverage area.

The content described herein can be used in a wireless multi-access communication system that supports communication with multiple wireless access terminals simultaneously. As described above, each terminal communicates with one or more base stations via transmissions on the forward link and reverse link. The forward link (or downlink) refers to the communication link from the base station to the terminal, and the reverse link (or uplink) refers to the communication link from the terminal to the base station. This communication link can be established via a single-input single-output system, a multiple-input multiple-output (MIMO) system, or other types of systems.

For data transmission, a MIMO system uses multiple ( _NT ) transmit antennas and multiple ( _NR ) receive antennas. The MIMO channel formed by the _NT transmit antennas and the _NR receive antennas can be decomposed into _NS spatial channels (also referred to as spatial channels), where _NS ≤ min{ _NT , _NR }. Each of these _NS independent channels corresponds to a dimension. Using the additional dimensions created by multiple transmit and receive antennas can provide improved performance (higher throughput and better reliability).

MIMO systems can support both time division duplex (TDD) and frequency division duplex (FDD). In a TDD system, forward and reverse link transmissions are on the same frequency region, so the reciprocity principle enables the forward link channel to be estimated based on the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are present at the access point.

The content described herein can be incorporated into a node (e.g., a device) that uses multiple components to communicate with at least one other node. FIG. 15 illustrates several example components that can be used to facilitate communication between nodes. Specifically, FIG. 15 illustrates a wireless device 1510 (e.g., an access point) and a wireless device 1550 (e.g., an access terminal) of a MIMO system 1500. At device 1510, traffic data for multiple data streams is provided from a data source 1512 to a transmit (TX) data processor 1514.

In some aspects, each data stream is transmitted through a separate transmit antenna. TX data processor 1514 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.

Using OFDM technology, the coded data of each data stream is multiplexed with pilot data. The pilot data is typically a known data pattern processed using known techniques and is used to estimate the channel response at the receiver system. The multiplexed pilot data and coded data of the data stream are then modulated (i.e., symbol mapped) according to the specific modulation scheme selected for each data stream (e.g., BPSK, QPSK, M-PSK, M-QAM, etc.) to provide modulation symbols. The data rate, coding, and modulation scheme for each data stream are determined by instructions executed by processor 1530. Data memory 1532 stores program code, data, and other information used by processor 1530 or other components of device 1510.

The modulation symbols for all data streams are then provided to a TX MIMO processor 1520, which further processes the modulation symbols (e.g., for OFDM). The TX MIMO processor 1520 then provides _NT modulation symbol streams to _NT transceivers (XCVR) 1522A through 1522T. In some aspects, the TX MIMO processor 1520 applies beamforming weights to the symbols of the data streams and the antenna from which the symbol is being transmitted.

Each transceiver 1522 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. _NT modulated signals from transceivers 1522A through 1522T are then transmitted from _NT antennas 1524A through 1524T, respectively.

At device 1550, the transmitted modulated signals are received by _NR antennas 1552A through 1552R and the received signal from each antenna 1552 is provided to a respective transceiver (XCVR) 1554A through 1554R. Each transceiver 1554 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding "received" symbol stream.

A receive (RX) data processor 1560 then receives and processes the _NR received symbol streams from _NR transceivers 1554 based on a particular receiver processing technique to provide _NT "detected" symbol streams. The _RX data processor 1560 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by the RX data processor 1560 is complementary to that performed by the TX MIMO processor 1520 and the TX data processor 1514 of the device 1510.

Processor 1570 periodically determines which precoding matrix to use (described below). Processor 1570 generates a reverse link message comprising a matrix index portion and a rank value portion. Data memory 1572 may store program code, data, and other information used by processor 1570 or other components of device 1550.

The reverse link message may include various information regarding the communication link and/or the received data stream. The reverse link message is then processed by the TX data processor 1538, which also receives traffic data for multiple data streams from the data source 1536. The reverse link message is modulated by the modulator 1580, conditioned by the transceivers 1554A through 1554R, and transmitted back to the device 1510.

At device 1510, the modulated signal from device 1550 is received by antenna 1524, conditioned by transceiver 1522, demodulated by demodulator (DEMOD) 1540, and processed by RX data processor 1542 to extract the reverse link message sent by device 1550. Processor 1530 then determines which precoding matrix to use to determine the beamforming weights and then processes the extracted message.

Figure 15 also shows that the communication component can include one or more components that perform power control operations as described herein. For example, in the description herein, the power control component 1590 can cooperate with the processor 1530 or other components of the device 1510 to transmit information to another device (e.g., device 1550) or receive a signal from another device (e.g., device 1550). Similarly, the power control component 1592 can cooperate with the processor 1570 or other components of the device 1550 to transmit a signal to another device (e.g., device 1510) or receive a signal from another device (e.g., device 1510). It should be understood that for each device 1510 and device 1550, the functions of the two or more components described can be provided by a single component. For example, a single processing component can provide the functions of the power control component 1590 and the processor 1530, and a single processing component can provide the functions of the power control component 1592 and the processor 1570.

The present disclosure may be used in various types of communication systems and/or system components. In some aspects, the present disclosure may be used in multiple-access systems that support communication with multiple users by sharing available system resources (e.g., by specifying one or more of bandwidth, transmit power, coding, interleaving, etc.). For example, the present disclosure may be used in any one of the following technologies, or a combination of the following technologies: code division multiple access ("CDMA") systems, multi-carrier CDMA ("MCCDMA"), wideband CDMA ("W-CDMA"), high-speed packet access ("HSPA," "HSPA+") systems, high-speed downlink packet access ("HSDPA") systems, time division multiple access ("TDMA") systems, frequency division multiple access ("FDMA") systems, single-carrier FDMA ("SC-FDMA"), orthogonal frequency division multiple access ("OFDMA") systems, or other multiple access technologies. Wireless communication systems utilizing the present disclosure may implement one or more standards such as IS-95, cdma2000, IS-856, W-CDMA, TDSCDMA, and others. A CDMA network can implement a radio technology such as Universal Terrestrial Radio Access ("UTRA"), cdma2000, or some other technology. UTRA includes W-CDMA and Low Chip Rate ("LCR"). cdma2000 technology covers the IS-2000, IS-95, and IS-856 standards. A TDMA network can implement a radio technology such as Global System for Mobile Communications ("GSM"). An OFDMA system can implement a radio technology such as Evolved UTRA ("E-UTRA"), IEEE 802.11, IEEE 802.16, IEEE 802.20, etc. UTRA, E-UTRA, and GSM are part of the Universal Mobile Telecommunications System ("UMTS"). The present invention can be implemented in 3GPP Long Term Evolution ("LTE") systems, Ultra Mobile Broadband ("UMB") systems, and other types of systems. LTE is a release of UMTS that uses E-UTRA. Although 3GPP terminology is used when describing certain aspects of the present invention, it should be understood that the contents of the present invention are applicable to 3GPP (Re199, Re15, Re16, Re17) technologies, 3GPP2 (IxRTT, IxEV-DO RelO, RevA, RevB) technologies, and other technologies.

The present invention may be incorporated into (e.g., implemented in or performed by) a variety of devices (e.g., nodes). For example, the access node described herein refers to an access point ("AP"), a base station ("BS"), a node B, a radio network controller ("RNC"), an eNodeB, a base station controller ("BSC"), a base transceiver station ("BTS"), a transceiver function ("TF"), a wireless router, a wireless transceiver, a basic service set ("BSS"), an extended service set ("ESS"), a radio base station ("RBS"), a femto node, a pico node, or some other terminology.

In addition, the access terminals described herein may be referred to as mobile stations, user devices, subscriber units, user stations, remote stations, remote terminals, user terminals, user agents, or user equipment. In some embodiments, such nodes may consist of, be implemented in, or include a cellular telephone, a cordless telephone, a Session Initiation Protocol ("SIP") phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device with wireless connectivity, or other suitable processing equipment connected to a wireless modem.

Accordingly, one or more aspects of the present invention may be comprised of, implemented in, or include various types of apparatuses, including telephones (e.g., cellular phones or smartphones), computers (e.g., laptop computers), portable communication devices, portable computing devices (e.g., personal digital assistants), entertainment devices (e.g., music or video devices or satellite radios), global positioning system devices, or any other suitable device operable to communicate via a wireless medium.

As described above, in some aspects, a wireless node comprises an access node (e.g., an access point) in a communication system. For example, such an access node can provide connectivity to a network (e.g., a wide area network such as the Internet or a cellular network) via a wired communication link or a wireless communication link, or provide connectivity to a network. Accordingly, an access node can enable another node (e.g., an access terminal) to access the network or perform some other function. In addition, it should be appreciated that unilateral or bilateral nodes can be portable, or in some cases, relatively speaking, they are not portable. Similarly, it should be appreciated that a wireless node (or wireless device) can also transmit and/or receive information in a non-wireless manner via an appropriate communication interface (e.g., via a wired connection).

A wireless node communicates via one or more wireless communication links based on or supporting any suitable wireless communication technology. For example, in some aspects, a wireless node is associated with a network. In some aspects, the network includes a local area network or a wide area network. A wireless device may support or use one or more of a variety of wireless communication technologies, protocols, or standards (such as those described herein, for example, CDMA, TDMA, OFDM, OFDMA, WiMAX, Wi-Fi, etc.). Similarly, a wireless node may support or use one or more of a variety of corresponding modulation schemes or multiplexing schemes. Thus, a wireless node includes appropriate components (e.g., air interfaces) for establishing one or more wireless communication links using the above-mentioned wireless communication technologies or other wireless communication technologies and communicating via the one or more wireless communication links. For example, a wireless node includes a wireless transceiver, which includes associated transmitter components and receiver components, wherein the transmitter components and receiver components include various components (e.g., signal generators and signal processors) that facilitate communication via a wireless medium.

The components described herein can be implemented in various ways. Referring to Figures 16-19, devices 1600-1900 can be represented as a series of related functional blocks. In some aspects, the functions of these blocks can be implemented as a processing system including one or more processor components. In some aspects, at least a portion of one or more integrated circuits (e.g., ASICs) can be used to implement the functions of these blocks. As described herein, an integrated circuit can include a processor, software, other related components, or a combination thereof. The functions of these blocks can also be implemented in some other ways as described herein. In some aspects, one or more dotted boxes in Figures 16-19 are optional.

Apparatuses 1600-1900 may include one or more modules for performing one or more of the functions described above with respect to the various figures. For example, maximum received signal strength determination module 1602 may correspond to a signal strength determiner as described herein. For example, minimum coupling loss determination module 1604 may correspond to a coupling loss determiner as described herein. For example, transmit power determination module 1606, 1704, or 1804 may correspond to a transmit power controller as described herein. For example, total received signal strength determination module 1702 may correspond to a signal strength determiner as described herein. For example, received pilot signal strength determination module 1706 may correspond to a received pilot strength determiner as described herein. For example, error determination module 1708 may correspond to an error determiner as described herein. For example, node in coverage area determination module 1710 may correspond to a node detector as described herein. For example, node identification module 1712 or 1806 may correspond to a node detector as described herein. For example, signal-to-noise ratio determination module 1706 or 1808 may correspond to a signal-to-noise ratio determiner as described herein. For example, the channel quality determination module 1802 may correspond to a channel quality determiner as described herein. For example, the receiving module 1902 may correspond to a receiver as described herein. For example, the identifying module 1904 may correspond to a transmit power controller as described herein. For example, the transmitting module 1906 may correspond to a transmitter as described herein.

It should be understood that the use of any element reference symbols, such as "first," "second," etc., herein is generally not intended to limit the number or order of the elements. Rather, these reference symbols are used herein as a convenient way to distinguish between two or more elements or to distinguish between multiple instances of an element. Thus, a reference symbol for a first element, a reference symbol for a second element does not mean that only two elements can be used, nor does it mean that the first element must precede the second element in some manner. Similarly, unless otherwise stated, a group of elements may include one or more elements.

Those skilled in the art will appreciate that information and signals can be represented using a variety of different technologies and methods. For example, data, instructions, commands, information, signals, bits, symbols, and chips mentioned throughout the above description can be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those skilled in the art will also understand that the various exemplary logic blocks, modules, processors, devices, circuits, and algorithm steps described in conjunction with the aspects disclosed herein may be implemented as electronic hardware (e.g., digital implementations, analog implementations, or a combination thereof designed using source code or other techniques), various forms of programs, or design codes in combination with instructions (e.g., for convenience, referred to herein as "software" or "software modules"), or a combination thereof. In order to clearly represent the interchangeability between hardware and software, the various exemplary components, blocks, modules, circuits, and steps are generally described above around their functions. Whether such functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the entire system. A skilled person may implement the described functionality in a flexible manner for each specific application, but such implementation decisions should not be interpreted as departing from the scope of protection of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the various aspects disclosed herein may be implemented in or performed by an integrated circuit ("IC"), an access terminal, or an access point. The IC may include a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic devices, discrete hardware components, electronic components, optical components, mechanical components, or any combination thereof to perform the functions described herein, and may execute code or instructions residing within the IC, external to the IC, or both. A general-purpose processor may be a microprocessor, or the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in combination with a DSP core, or any other such configuration.

It should be understood that the specific order or sequence of process steps disclosed is merely an example of an exemplary method. Based on design preferences, it should be understood that the specific order or sequence of process steps may be rearranged without departing from the scope of the present invention. The accompanying method claims provide elements of the various steps in an exemplary order, but are not intended to limit the order of the elements of the various steps to the specific order or sequence provided.

The functions of the present invention can be implemented in hardware, software, firmware or any combination thereof. If software is used for implementation, these functions can be stored in a computer-readable medium or transmitted as one or more instructions or codes on a computer-readable medium. Computer-readable media include computer storage media and communication media, wherein communication media include any medium that is convenient for transmitting a computer program from one place to another. The storage medium can be any available medium that a computer can access. By way of example and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage media or other magnetic storage devices, or any other medium that can be used to carry or store program codes in the form of desired instructions or data structures and can be accessed by a computer. In addition, any connection can be referred to as a computer-readable medium. For example, if the software is transmitted from a website, server or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) or wireless technologies such as infrared, wireless and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL or wireless technologies such as infrared, wireless and microwave are included in the definition of the medium. As used herein, disk and disc include compact disc (CD), laser video disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks typically reproduce data magnetically, while discs use lasers to reproduce data optically. The above combinations should also be included in the scope of protection of computer-readable media. In summary, it should be understood that computer-readable media can be implemented in any suitable computer program product.

The disclosed aspects have been described above to enable those skilled in the art to implement or use the present invention. Various modifications of these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may also be applied to other aspects without departing from the scope of the present invention. Therefore, the present invention is not intended to be limited to the aspects set forth herein, but is intended to be consistent with the broadest scope of the principles and novel features disclosed herein.

Claims (51)

1. A method for wireless communication, comprising: Determine the total received signal strength on the channel of the visitor's access terminal at a base station with limited coverage; The transmit power value of the transmitter of the base station with smaller coverage is determined based on the determined total received signal strength. The transmit power value includes a maximum transmit power level, wherein the base station with smaller coverage is allowed to use the transmitter to transmit at the maximum transmit power level, and the visitor access terminal is an access terminal restricted by the base station with smaller coverage. 2. The method of claim 1, further comprising: determining a received pilot signal strength associated with a pilot signal from a macro base station, wherein the determination of the transmit power value is further based on the determined received pilot signal strength. 3. The method according to claim 2, wherein: Determining the strength of the received pilot signal includes: Pilot signals are received from multiple macro base stations. Determine which pilot signal has the highest received signal strength; The determined received pilot signal strength corresponds to the highest received signal strength. 4. The method according to claim 2, wherein determining the strength of the received pilot signal comprises: estimating the strength of the received pilot signal based on the determined total received signal strength. 5. The method according to claim 2, wherein: Determining the total received signal strength includes receiving an indication of the total received signal strength from the home access terminal; Determining the strength of the received pilot signal includes receiving an indication of the strength of the received pilot signal from the home access terminal. The home access terminal is an access terminal authorized by the base station with smaller coverage area. 6. The method according to claim 2, wherein determining the transmit power value further includes: Determine the maximum amount of interference that a transmission from the base station with smaller coverage might cause at the visitor access terminal without reducing the pilot signal ratio of the visitor access terminal below the minimum pilot signal ratio, wherein the determination of the maximum amount of interference is based on the determined total received signal strength and the determined received pilot signal strength. The transmit power value is determined such that the transmission does not cause an interference level exceeding the maximum interference level at the visitor access terminal, wherein the determination of the transmit power value is also based on path loss associated with the coverage area of the base station with smaller coverage. 7. The method of claim 6, wherein the coverage area is related to a co-channel coverage blind zone. 8. The method of claim 6, wherein the determination of the transmit power value is further based on an adjacent channel interference suppression value between a first channel for which the transmit power value is determined and a second channel for which the total received signal strength is determined. 9. The method of claim 8, wherein the coverage area is associated with adjacent channel coverage blind spots. 10. The method according to claim 2, wherein: The transmit power value is determined for the first channel; The determined total received signal strength was measured on the first channel. 11. The method according to claim 2, wherein: The transmit power value is determined for the first channel; The determined total received signal strength was measured on the second channel. 12. The method of claim 2, further comprising: determining at least one error associated with at least one of the determined total received signal strength and the determined received pilot signal strength, wherein the determination of the transmit power value is also based on the at least one error. 13. The method of claim 12, further comprising: receiving information from a home access terminal authorized to access data at the less covered base station for which the transmit power value is determined, wherein the determination of the at least one error is based on the received information. 14. The method according to claim 1, further comprising: Determine whether the visitor's access terminal is within the coverage area of the base station with the smaller coverage, for which the transmit power value is determined; The determined transmit power value is adjusted based on whether the visitor's access terminal is within the coverage area. 15. The method according to claim 1, further comprising: Determine whether the visitor's access terminal is within the coverage area of the base station with the smaller coverage, for which the transmit power value is determined; Determine the path loss between the visitor's access terminal and the base station with limited coverage; The determination of the transmit power value is also based on the path loss. 16. The method of claim 15, wherein: The visitor's access terminal was not authorized to access data at the base station with limited coverage. Determining the path loss includes estimating the path loss based on information received from the home access terminal. The home access terminal is an access terminal authorized by the base station with smaller coverage area. 17. The method of claim 1, wherein the transmit power value is determined such that the signal-to-noise ratio at adjacent nodes remains less than or equal to a defined value. 18. The method according to claim 1, wherein: The transmit power value is determined for the base station with the smaller coverage area; The method further includes: identifying home access terminals located near the edge of the coverage area of the base station with smaller coverage; The method further includes: determining the signal-to-noise ratio associated with the home access terminal based on the determined total received signal strength; The transmit power value is determined based on the established signal-to-noise ratio and the defined maximum signal-to-noise ratio. The home access terminal is an access terminal authorized by the base station with smaller coverage area. 19. The method according to claim 18, wherein determining the signal-to-noise ratio includes: receiving signal-to-noise ratio information from the home access terminal. 20. The method of claim 18, wherein identifying the home access terminal includes: determining that the home access terminal is near the edge based on the path loss between the base station with smaller coverage and the home access terminal. 21. The method of claim 20, wherein the visitor access terminal is not authorized to access data at the base station with less coverage. 22. The method of claim 1, wherein the transmit power value is determined to initiate operation of the visitor access terminal located at a predetermined minimum distance from the access node for which the transmit power value was determined. 23. The method according to claim 1, wherein the transmit power value includes the transmit power value of the common control channel. 24. The method of claim 1, wherein the transmit power value includes the downlink transmit power value of the base station with smaller coverage. 25. The method of claim 1, wherein the transmit power value includes a first initial maximum transmit power value, and the method further includes: Determine at least one other initial maximum transmit power value; The maximum transmit power value is determined based on the minimum of the first initial maximum transmit power value and the at least one other initial maximum transmit power value. 26. The method of claim 1, wherein the transmit power value is determined for the base station with limited coverage, the base station with limited coverage being restricted in at least one of the following: signaling, data access, registration, paging and services for at least one access terminal. 27. The method of claim 1, wherein the transmit power value is determined for a femtonode or a piconode. 28. A base station with limited coverage, comprising: A signal strength determiner is used to determine the total received signal strength on the channel of the visitor's access terminal; A transmit power controller is used to determine the transmit power value of the transmitter of the base station with smaller coverage area based on the determined total received signal strength. The transmit power value includes a maximum transmit power level, wherein the base station with smaller coverage is allowed to use the transmitter to transmit at the maximum transmit power level, and the visitor access terminal is an access terminal restricted by the base station with smaller coverage. 29. The base station with smaller coverage according to claim 28, further comprising: a receive pilot strength determiner for determining the receive pilot signal strength associated with a pilot signal from a macro base station, wherein the determination of the transmit power value is also based on the determined receive pilot signal strength. 30. The base station with limited coverage according to claim 29, wherein: Determining the strength of the received pilot signal includes: Pilot signals are received from multiple macro base stations. Determine which pilot signal has the highest received signal strength; The determined received pilot signal strength corresponds to the highest received signal strength. 31. The base station with limited coverage according to claim 29, wherein determining the transmit power value further includes: Determine the maximum amount of interference that a transmission from the base station with smaller coverage might cause at the visitor access terminal without reducing the pilot signal ratio of the visitor access terminal below the minimum pilot signal ratio, wherein the determination of the maximum amount of interference is based on the determined total received signal strength and the determined received pilot signal strength. The transmit power value is determined such that the transmission does not cause an interference level exceeding the maximum interference level at the visitor access terminal, wherein the determination of the transmit power value is also based on path loss associated with the coverage area of the base station with smaller coverage. 32. The base station with limited coverage according to claim 31, wherein the determination of the transmit power value is further based on an adjacent channel interference suppression value between a first channel for which the transmit power value is determined and a second channel for which the total received signal strength is determined. 33. The base station with limited coverage according to claim 29, further comprising: an error determiner for determining at least one error associated with at least one of the determined total received signal strength and the determined received pilot signal strength, wherein the determination of the transmit power value is also based on the at least one error. 34. The base station with limited coverage according to claim 28, further comprising: A node detector is used to determine whether the visitor access terminal or home access terminal is within the coverage area of a base station with a smaller coverage area for which the transmit power value is determined; The transmit power controller is further configured to adjust the determined transmit power value based on whether the visitor access terminal or the home access terminal is within the coverage area, wherein the home access terminal is an access terminal authorized by the base station with smaller coverage. 35. The base station with limited coverage according to claim 28, wherein the transmit power value is determined such that the signal-to-noise ratio at adjacent nodes remains less than or equal to a defined value. 36. The base station with limited coverage according to claim 28, wherein: The transmit power value is determined for base stations with limited coverage; The base station with smaller coverage also includes: a node detector, used to identify home access terminals located near the edge of the coverage area of the base station with smaller coverage; The base station with smaller coverage also includes: a signal-to-noise ratio determiner, used to determine the signal-to-noise ratio associated with the home access terminal based on the determined total received signal strength; The transmit power value is determined based on the established signal-to-noise ratio and the defined maximum signal-to-noise ratio. The home access terminal is an access terminal authorized by the base station with smaller coverage area. 37. The base station with limited coverage according to claim 28, wherein the transmit power value includes the transmit power value of the common control channel. 38. The base station with limited coverage according to claim 28, wherein the transmit power value is determined for the base station with limited coverage, the base station with limited coverage being restricted in at least one of the following: signaling, data access, registration, paging and services for at least one access terminal. 39. The base station with smaller coverage according to claim 28, wherein the transmit power value is determined for a femtonode or a piconode. 40. A base station with limited coverage, comprising: A module used to determine the total received signal strength on the channel of a visitor's access terminal; A module for determining the transmit power value of the transmitter of the base station with smaller coverage based on the determined total received signal strength. The transmit power value includes a maximum transmit power level, wherein the base station with smaller coverage is allowed to use the transmitter to transmit at the maximum transmit power level, and the visitor access terminal is an access terminal restricted by the base station with smaller coverage. 41. The base station with smaller coverage according to claim 40, further comprising: a module for determining the strength of a received pilot signal associated with a pilot signal from a macro base station, wherein the determination of the transmit power value is also based on the determined strength of the received pilot signal. 42. The base station with limited coverage according to claim 41, wherein: Determining the strength of the received pilot signal includes: Pilot signals are received from multiple macro base stations. Determine which pilot signal has the highest received signal strength; The determined received pilot signal strength corresponds to the highest received signal strength. 43. The base station with limited coverage according to claim 41, wherein determining the transmit power value further includes: Determine the maximum amount of interference that a transmission from the base station with smaller coverage might cause at the visitor access terminal without reducing the pilot signal ratio of the visitor access terminal below the minimum pilot signal ratio, wherein the determination of the maximum amount of interference is based on the determined total received signal strength and the determined received pilot signal strength. The transmit power value is determined such that the transmission does not cause an interference level exceeding the maximum interference level at the visitor access terminal, wherein the determination of the transmit power value is also based on path loss associated with the coverage area of the base station with smaller coverage. 44. The base station with limited coverage according to claim 43, wherein the determination of the transmit power value is further based on an adjacent channel interference suppression value between a first channel for which the transmit power value is determined and a second channel for which the total received signal strength is determined. 45. The base station with limited coverage according to claim 41, further comprising: a module for determining at least one error associated with at least one of the determined total received signal strength and the determined received pilot signal strength, wherein the determination of the transmit power value is also based on the at least one error. 46. The base station with limited coverage according to claim 40, further comprising: A module for determining whether the visitor access terminal or home access terminal is within the coverage area of the base station with smaller coverage for which the transmit power value is determined; The module for determining the transmission power is used to adjust the determined transmission power value based on whether the visitor access terminal or the home access terminal is within the coverage area, and the home access terminal is an access terminal authorized by the base station with smaller coverage. 47. The base station with limited coverage according to claim 40, wherein the transmit power value is determined such that the signal-to-noise ratio at adjacent nodes remains less than or equal to a defined value. 48. The base station with limited coverage according to claim 40, wherein: The transmit power value is determined for the base station with the smaller coverage area; The base station with smaller coverage also includes a module for identifying home access terminals located near the edge of the coverage area of the base station with smaller coverage; The base station with smaller coverage also includes a module for determining the signal-to-noise ratio associated with the home access terminal based on the determined total received signal strength; The transmit power value is determined based on the established signal-to-noise ratio and the defined maximum signal-to-noise ratio. The home access terminal is an access terminal authorized by the base station with smaller coverage area. 49. The base station with limited coverage according to claim 40, wherein the transmit power value includes the transmit power value of the common control channel. 50. The base station with limited coverage according to claim 40, wherein the transmit power value is determined for the base station with limited coverage, and the base station with limited coverage is restricted in at least one of the following: signaling, data access, registration, paging and services for at least one access terminal. 51. The base station with smaller coverage according to claim 40, wherein the transmit power value is determined for a femtonode or a piconode.