HK1062092B

HK1062092B - Method and apparatus for forward power control in a communication system

Info

Publication number: HK1062092B
Application number: HK04105070.8A
Authority: HK
Inventors: C．E．惠特利三世; R．A．阿塔尔; E．A．S．埃斯特韦斯
Original assignee: 高通股份有限公司
Priority date: 2001-01-05
Filing date: 2001-12-27
Publication date: 2008-05-30

Description

Method and apparatus for forward power control in a communication system

Background

I. Field of the invention

The present invention relates to communication systems. More particularly, the present invention relates to a novel and improved method and apparatus for forward power control in a communication system.

II. background

Modern day communication systems support a variety of applications. One such System IS a Code Division Multiple Access (CDMA) System that conforms to the "TIA/EIA/IS-95 Mobile Station-base compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System," referred to herein as the IS-95 standard. The CDMA system allows voice and data communications between users over a terrestrial link. The use of CDMA techniques IN MULTIPLE ACCESS COMMUNICATION SYSTEMs is disclosed IN U.S. patent No. 4901307 entitled "forward COMMUNICATION SYSTEMs USING SATELLITE COMMUNICATION SYSTEMs," and U.S. patent No. 5103459 entitled "SYSTEM AND mobile COMMUNICATION SYSTEMs IN a CDMA CELLULAR TELEPHONE SYSTEM," both assigned to the assignee of the present invention and incorporated herein by reference.

In a CDMA system, communication between users is performed through either one or more access networks or through a data network for data applications. The access network includes a plurality of access points. In one embodiment, the data network is the internet. In another embodiment, a data network. It will be appreciated by those skilled in the art that the data network may be any known data network in the art. A first access terminal may communicate with a second access terminal by transmitting data on a reverse link to an access network or a data network.

When data is transmitted to an access network, the access network receives the data and then routes it on the forward link to a second access terminal or to another access network. The forward link refers to transmission from the access network to the access terminal and the reverse link refers to transmission from the access terminal to the access network. In an IS-95 system, the forward link and the reverse link are assigned separate frequencies.

The access terminal calculates the signal-to-noise and interference ratio C/I for the received forward link signal. The C/I calculated by the access terminal determines the information rate supporting the forward link from the access point to the user's access terminal. I.e. a certain given performance of the forward link is obtained at the corresponding C/I level. METHODs AND APPARATUS FOR selecting information RATEs are disclosed in U.S. patent application No. 08/963386 entitled "METHOD AND APPARATUS FOR HIGH RATE packet transmission", filed on 3.11.1997, AND now U.S. patent No. 6574211, published on 3.6.2002, assigned to the assignee of the present invention AND incorporated herein by reference.

The power at which the access point transmits data to the access terminal is referred to as the forward link transmit power. The forward link transmit power is at a level required to reliably transmit data over the forward link. It is often larger than required for a given reliable data rate. The value exceeded is called "quantization loss". The quantization loss is the portion of the transmit power on the forward link that exceeds the specified value for the reliable data rate and is therefore lost, i.e., wasted, transmit power. This is a problem since the quantization loss is excessive transmit power that limits forward link throughput efficiency and throughput. The excessive transmit power of an access point causes interference to access terminals served by neighboring access points. This interference causes access terminals served by the access point to follow a low C/I and thus lower data rates. Thus, throughput is limited.

Reducing the quantization loss results in a gain in forward link throughput efficiency and throughput. Therefore, a need exists for systems and methods that reduce the losses caused by excessive transmit power.

The parameters that measure the efficiency and quality of a data communication system are the transmission delay of the transmitted data packets and the average throughput rate of the system. The effect of transmission delay on data communication is different from its effect on voice communication, but an important metric measures the quality of a data communication system. The average throughput rate is a measure of the efficiency of the data transmission capacity of the communication system.

When an access terminal is within a limited interference range, i.e., on a cell boundary, the access terminal may receive pilot signals from multiple access points that interfere with pilots from the access points serving the access terminal. As a result, the C/I that the access terminal conforms to is lower at the cell boundary than when the access terminal is not at the cell boundary. Thus, the access terminal has a lower service rate than if the access terminal was not on a cell boundary. The service rate is the rate at which the access point schedules the access terminal to provide service. The data rate is the rate at which the access point transmits forward link data to the access terminal.

From a service perspective, assuming that access terminals are served by the same access point, the service obtained by access terminals on cell boundaries is slow (higher transmission delay) and lower data rate (i.e., average throughput rate) than access terminals not on cell boundaries. There is a need for a system and method that provides more user services over a period of time and services these users more quickly.

Abstract

The described embodiments are directed to systems and methods for forward power control in a communication system. In one aspect, a system and method of forward power control includes initial power control of an access terminal. In another aspect, a forward power control system and method includes initial power control of an access point.

In one aspect, a system and method for initial power control of an access terminal includes paging the access terminal for upcoming data transmissions, selecting an access point based on a set of parameters, measuring an excess C/I of a forward link signal from the selected access point, transmitting the excess C/I measurement to the selected access point, and transmitting data from the selected access point at a transmit power based on the excess C/I measurement. In another aspect, a system and method for initial forward power control by an access terminal includes sending a data request message including an excess C/I measurement to the access point. In another aspect, a system and method for initial forward power control of an access terminal includes transmitting a data request message to a selected access point on a first channel and transmitting an excess C/I measurement to the selected access point on a second channel.

In one aspect, a system and method for access point initial forward power control includes receiving a data request message from a plurality of access terminals, each of the plurality of access terminals calculating an average service rate, calculating a requested data rate to average service rate ratio for each of the plurality of access terminals, scheduling data transmission from the access terminals having the maximum requested data rate to average service rate ratio, and transmitting data from a selected access point at a randomly varying transmit power in accordance with the data request message. In another aspect, a system and method of initial forward power control for an access point includes implementing a bias for data transmission scheduling instants from the access terminal based on a requested data rate versus an average service rate ratio.

In another aspect, a system and method for access point initiated forward power control includes transmitting data from said selected access point at a randomly variable transmit power in accordance with said data request message. In another aspect, a system and method for initial forward power control by an access point includes transmitting data from a selected access point at a transmit power synchronized with a neighboring access point in accordance with a data request message.

Brief description of the drawings

Fig. 1 is a diagram of a data communication system within an embodiment including a plurality of cells, a plurality of access points, and a plurality of access terminals;

fig. 2 is a subsystem block diagram of a data communication system of an embodiment;

FIGS. 3A-3B are block diagrams of a forward link architecture of an embodiment;

FIG. 4A is a forward link slot structure of an embodiment;

FIG. 4B is a composite waveform of a power control channel;

fig. 5 is a block diagram of a reverse link structure of an embodiment; and

figure 6 is a Cumulative Distribution Function (CDF) of the C/I distribution within a typical hexagonal cellular layout.

Detailed description of the preferred embodiments

I. Access terminal and access point

In this specification, an access point refers to hardware that communicates with an access terminal. In some applications, an access point is also referred to as a base station (also known as a base transceiver station or node B). In some applications, an access terminal is called a mobile station (also known as a mobile, subscriber unit, remote station, or user equipment). A cell refers to either hardware or a geographic coverage area, depending on the situation in which the term is used. A sector is a portion of a cell. Since a sector of a CDMA system has the nature of a cell, the teachings described in terms of a cell can also be applied to a sector.

In communicating, the access terminal communicates with at least one access point. A CDMA access terminal is capable of communicating with several access points simultaneously during soft handoff. Soft handoff is the process of establishing a link with a new access point before disconnecting the link with the previous access point. Soft handoff minimizes the probability of dropped calls. A method and SYSTEM for providing communication with an access terminal through more than one access point during SOFT HANDOFF is disclosed IN U.S. patent No. 5267261, entitled "mobile HANDOFF SOFT HANDOFF IN a CDMA CELLULAR TELEPHONE SYSTEM," assigned to the assignee of the present invention and incorporated herein by reference. Soft handoff is the process by which communication occurs between multiple sectors that are served by the same access point. The process OF soft handoff is described in detail in U.S. patent application No. 08/763498 entitled "METHOD AND APPARATUS FOR PERFORMING HANDOFFBETWEN SECTORS OF A COMMON BASE STATION", filed 12/11.1996, now U.S. patent No. 5933787, published 3/8.1999, assigned to the assignee OF the present invention, AND incorporated herein by reference.

It is known that the signal to noise and interference ratio C/I of any user in a cellular system is a function of the location of the user within the coverage area. To maintain a given level of service, TDMA and access point MA systems employ frequency reuse techniques, i.e., not all frequency channels and/or time slots are used within each access point. In a CDMA system, the same frequency assignment is reused in each cell of the system to improve overall efficiency.

The derived C/I for any given user is a function of path loss, r, for terrestrial cellular systems³To r⁵And increases where r is the distance to the emission source. Also, path loss is affected by random variations of artificial or natural obstacles within the path of the radio wave. These random variations are generally modeled as a log-normal masked random process with 8dB standard deviation. FIG. 6 illustrates a generally hexagonal honeycomb fabric with an omni-directional access point antennaLocally generated C/I distribution, r⁴Propagation law and masking process with 8dB standard deviation.

The obtained C/I distribution can be achieved at any time and anywhere if the access terminal is served by the best access point that takes the maximum C/I value and regardless of its physical distance to each access point. Due to the random nature of the path loss described above, the signal with the largest C/I value may be a different signal than the smallest physical distance from the other access terminals. In contrast, C/I can be severely degraded if the access terminal only communicates through the minimum distance access point. It is therefore desirable that the access terminal communicates back and forth with the best serving access point at any time to obtain the best C/I value. In the idealized model above and shown in FIG. 6, it can be observed that the range of values obtained for C/I is limited to approximately 1: 56 or 15 dB. It is therefore possible for a CDMA access point to provide services to an access terminal that vary by up to 56 times the information bit rate, since the following relationship holds:

img id="idf0001" file="C0182259300091.GIF" wi="237" he="43" img-content="drawing" img-format="GIF"/

wherein R is_bRepresenting the information rate to a particular access terminal, W is the total bandwidth occupied by the spread spectrum signal, and E_b/I_oIs the energy per bit divided by the interference density to achieve a given level of performance. For example, if the spread spectrum signal occupies a bandwidth W of 1.2288MHZ and reliable communications require an average E_b/I_oIf 3dB, the access terminal obtains the C/I value of 3dB to the optimal access pointAt data rates of up to 1.2288 Mbps. On the other hand, given the parameter values, if an access terminal is affected by significant interference from neighboring access points and can only have a C/I of-7 dB, reliable communication cannot be guaranteed at rates greater than 122.88 Kbps. A communication system designed to optimize average throughput will therefore attempt to support the maximum data rate R reliably supported by the remote user from the best serving access point_bEach remote user is served. There is therefore a need for a data communication system that uses C/I values to improve data throughput from a CDMA access point to an access terminal.

In an embodiment, each access terminal communicates with one or more access points and monitors a control channel during communication with the access points. The control channel may be used by an access point to transmit small amounts of data, radio page messages to particular access terminals, and broadcast messages to all access terminals. The paging message informs the access terminal that the access point has a large amount of data to send to the access terminal.

Upon receiving radio paging messages from one or more access points, an access terminal measures the signal-to-noise-and-interference ratio (C/I) of a forward link signal (e.g., a forward link pilot signal) at each time slot and selects the best access point using a set of parameters, which may include current and previous C/I measurements. A method and APPARATUS FOR selecting the best access point using a set of parameters is disclosed in U.S. patent application No. 08/963386 entitled "method and APPARATUS FOR HIGH RATE PACKET TRANSMISSION mismatch," filed on 3/11/1997, and now U.S. patent No. 6574211, published on 3/6/2002, which is previously incorporated by reference.

At each slot, the access terminal transmits the highest data rate transmission request that the C/I can reliably support, which has been measured, to the selected access point on a dedicated Data Request (DRC) channel. The request may take different forms. In one embodiment, the request indicates a requested data rate. In one embodiment, the request is a number indicating the requested data speed. In another embodiment, the request is an index to a data rate table, thus indicating the requested data rate. In another embodiment, the request indicates the quality of the forward link, which is in turn evaluated by the access point to determine the data rate.

The selected access point transmits data in data packets at a rate that does not exceed the data rate received from the access terminal on the DRC channel. By transmitting from the best access point at each time slot, improved throughput and transmission latency can be achieved.

The access terminal selects the best access point candidate for COMMUNICATION based on the procedure described in U.S. patent No. 6151502, published 21/11/2000, entitled "METHOD AND APPARATUS for communicating SOFT HANDOFF IN A WIRELESS COMMUNICATION SYSTEM," filed 29/1/1997, assigned to the assignee of the present invention, AND incorporated herein by reference. In one embodiment, the access point may join the active set of the access terminal if the received pilot signal is above a predetermined addition threshold and move out of the active set if the pilot signal is below the predetermined addition threshold. In another embodiment, an access point may be added to the active set if the additional energy of the access point (e.g., as measured by the pilot signal) and the energy of access points already in the active set exceed some predetermined threshold. Access points having a transmit energy that includes a non-significant portion of the total energy received at the access terminal are not joined in the active set.

In one embodiment, the access terminal transmits a data rate request on the DRC channel in a manner such that only selected access points within the access points with which the access terminal is communicating can distinguish the DRC message, thereby ensuring that forward link transmissions in any given time slot are from the selected access points. In one embodiment, each access point communicating with an access terminal is assigned a unique Walsh code. The access terminal covers the DRC message with the Walsh code corresponding to the selected access point. Those skilled in the art will recognize that other codes may be used to cover the DRC message. In one embodiment, non-Walsh code orthogonal codes are used to cover the DRC message.

According to one embodiment, forward link data transmission occurs from an access point to an access terminal at or near the maximum data rate that the forward link and system can support (see fig. 1). Reverse link data communication may occur from one access terminal to one or more access points. The calculation of the maximum data rate for the forward link transmission is described in detail below. The data is divided into data packets, each of which is transmitted over one or more time slots. At each time slot, the access point may direct data transmissions to any access terminal in communication with the access point.

Initially, the access terminal establishes communication with the access point using a predetermined access procedure. In the connected state, the access terminal may receive data and control messages from the access point and may transmit data and control messages to the access point. The access terminal monitors a forward link for transmissions from access points in the access terminal's active set. The active set includes a list of access points with which the access terminal is in communication. In particular, the access terminal measures the signal-to-noise-and-interference ratio (C/I) of the forward link pilot from the access point in the active set, which is received at the access terminal. If the received pilot signal is above some predetermined add threshold or below some predetermined drop threshold, the access terminal reports this to the access point. The message from the access point then instructs the access terminal to add or remove the access point from the active set accordingly.

If there is no data to send, the access terminal goes back to sleep and discontinues transmission of data rate information to the access point. When the access terminal is in the dormant state, the access terminal monitors a control channel from one or more access points in the active set for paging messages.

If there is data to be sent to the access terminal, the data is sent by a central controller within the access terminal to all access points in the active set and stored in a queue at each access point. The paging message is then transmitted by one or more access points to the access terminal on a corresponding control channel. The access point may transmit all such paging messages on several access points simultaneously to ensure reception even when the access terminal is handed off between two access points. The access terminal demodulates and decodes the signal on one or more control channels to receive the paging message.

Upon decoding the paging message, and for each slot until the end of the data transmission, the access terminal measures the C/I of the forward link signal according to the access point in the active set received by the access terminal. The C/I of the forward link signal may be obtained by measuring the corresponding pilot signal. The access terminal then selects the best access point based on a set of parameters. The set of parameters may include current and previous C/I measurements and bit error rates or packet error rates. In an embodiment, the best access point is selected based on the largest C/I measurement. The access terminal then identifies the best access point on the data request channel and sends a data request message to the selected access point (referred to herein as a DRC message). In one embodiment, the DRC message includes the requested data rate. In another embodiment, the DRC message includes an indication of the quality of the forward link channel (e.g., the C/I measurement itself, the bit error rate, or the packet error rate).

Description of the System

Referring to the drawings, FIG. 1 represents a communication system of an embodiment that includes a plurality of cells 2a-2 g. Each cell 2a-2g is served by a respective access point 4. Different access terminals 6 are dispersed throughout the data communication system. Each access terminal 6 communicates with at most one access point 4 on the forward link at each time slot, but it may communicate with one or more access points 4 on the reverse link, depending on whether the access terminal 6 is in soft handoff. For example, on the forward link for time slot n, access point 4a transmits data only to access terminal 6a, access point 4b transmits data only to access terminal 6b, and access point 4c transmits data only to access terminal 6 c. In fig. 1, solid lines with arrows indicate data transmission from the access point 4 to the access terminal 6. The broken line with arrows indicates that the access terminal 6 is receiving pilot signals but there is no data transmission from the access point 4. For simplicity, reverse link communications are not shown in fig. 1.

As shown in fig. 1, each access point 4 transmits data to one access terminal 6 at any given moment. The access terminals 6, particularly those located near the cell border, may receive pilot signals from multiple access points 4. If the pilot signal is above some predetermined threshold, access terminal 6 may request that access point 4 be added to the active set of access point 4. Access terminal 6 may receive data transmissions from zero, one, two, or more members of the active set.

FIG. 2 is a basic subsystem block diagram of one embodiment. The access point controller 10 interfaces with the packet network interface 24, the PSTN 30, and all access points 4 within the data communication system (only one access point 4 is shown in fig. 2 for simplicity). The access point controller 10 coordinates communications between the access terminal 6 and other users connected to the packet network interface 24 and the PSTN 30. PSTN 30 interfaces with users through a standard telephone network (not shown in fig. 2).

Only one element is shown in fig. 2 for simplicity, and the access point controller 10 includes a number of selector elements 14. A selector element 14 is assigned to control communications between one or more access points 4 and an access terminal 6. If the selector element 14 has not been assigned to the access terminal 6, the call controller 16 is notified of the need to page the access terminal 6. The call control processor 16 then directs the access point 4 to page the access terminal 6.

Data source 20 includes data to be transmitted to access terminal 6. Data source 20 provides data to packet network interface 24. The packet network interface 24 receives data and routes the data to the selector element 14. The selector element 14 transmits data to each access point 4 in communication with the access terminal 6. Each access point 4 maintains a data queue 40, which includes data to be transmitted to the access terminals 6.

A data packet refers to a predetermined amount of data and is independent of the data rate. In one embodiment, the data packets are formatted and encoded with other control and coding bits on the forward link. If the data transmission occurs over multiple Walsh channels, the encoded packets are demultiplexed into parallel streams, each stream being sent over one Walsh channel.

Data is sent from data queue 40 to channel element 42 in data packets. For each data packet, channel element 42 inserts the necessary control fields. The formatted packet includes a data packet, a control field, frame detection sequence bits, and code tail bits. Channel element 42 then encodes the one or more formatted packets and interleaves (rearranges) the symbols within the encoded packets. Next, the interleaved packet is scrambled with a scrambling sequence, covered with a Walsh complex cover, and covered with a long PN code and a short PN code_IAnd PN_QAnd (5) spreading codes. The spread data is quadrature modulated, filtered and amplified by a transmitter within the RF unit 44. The forward link signal is transmitted over the air on a forward link 50 through an antenna 46.

At access terminal 6, the forward link signal is received by antenna 60 and routed to a receiver within a front end 62. The receiver filters, amplifies, quadrature demodulates, and quantizes the signal. The digitized signal is provided to a demodulator (DEMOD)64 for long PN codes and short PN codes_IAnd PN_QCode despreading, decovering with Walsh cover, and descrambling with the same scrambling sequence. The demodulated data is provided to a decoder 66 which performs the inverse of the signal processing functions performed at the access point 4, particularly the de-interleaving, decoding and frame check functions. The decoded data is provided to a data receiver 68. Hardware, as described above, supports data transmission, messaging, voice, video, and communication over the forward link.

There are many implementations of system control and scheduling functions that can be accomplished. The positioning of the channel scheduler 48 depends on whether a central or distributed control/scheduling process is required. For distributed processing, for example, a channel scheduler 48 may be located within each access point 4. Conversely, for centralized processing, the channel scheduler 48 may be located within the access point controller 10 and may be designed to coordinate data transmissions for multiple access points 4. The implementation of the above described functions may be considered within the scope of the present invention.

As shown in fig. 1, access terminals 6 are dispersed throughout the data communication system and may communicate with zero or one access point 4 on the forward link. In one embodiment, channel scheduler 48 coordinates forward link data transmissions for one access point 4. In one embodiment, channel scheduler 48 is coupled to data queue 40 and channel element 42 within access point 4 and receives the queue size, which is indicative of the amount of data transmitted to access terminal 6. In one embodiment, channel scheduler 48 receives DRC messages from access terminal 6.

In one embodiment, a data communication system supports data and message transmission on the reverse link. Within access terminal 6, a controller 76 handles data or message transmission by routing the data or message to encoder 72. The controller 76 may be implemented within a microcontroller, microprocessor, Digital Signal Processing (DSP) chip, or within an ASIC programmed to perform the functions described above.

In one embodiment, encoder 72 encodes the message according to a format consistent with the Blank and Burst signaling data format described in the aforementioned U.S. patent No. 5504773. Encoder 72 generates and adds a set of CRC bits, adds a set of tail bits, encodes the data and the added bits, and rearranges the symbols within the encoded data. The interleaved data is provided to a Modulator (MOD) 74.

The modulator 74 may be implemented in a number of embodiments. In one embodiment (see fig. 5), the interleaved data is covered by Walsh codes, spread by long PN codes, and further spread by short PN codes. The spread data is provided to a transmitter within front end 62. The transmitter modulates, filters, amplifies, and transmits the reverse link signal over the air on a reverse link 52 through an antenna 46.

In one embodiment, the access terminal 6 spreads the reverse link data according to a long PN code. Each reverse link channel is defined in terms of a time offset of a common long PN sequence. The modulation sequences generated at the two different offsets are uncorrelated. The offset of the access terminal 6 IS determined based on the unique digital identification of the access terminal 6, which in the embodiment of the IS-95 access terminal 6 IS an access terminal specific identification number. Thus, each access terminal 6 transmits on an unrelated reverse link channel as determined by its unique electronic serial number.

At access point 4, the reverse link signal is received by antenna 46 and provided to RF unit 44. The RF unit 44 filters, amplifies, demodulates, and quantizes the signal, and supplies the quantized signal to the channel element 42. Channel element 42 despreads the digitized signal with short and long PN codes. Channel element 42 also performs Walsh code decovering and pilot and DRC extraction. Channel element 42 then rearranges the demodulated data, decodes the deinterleaved data, and performs a CRC check function. The decoded data, i.e. data or message, is provided to a selector element 14. The selector element 14 routes the data and messages to the appropriate destination. The channel element 42 may also forward a quality indicator to the selector element 14 to indicate the condition of receiving the data packet.

In one embodiment, an access terminal can direct the transmission of a DRC message to a particular access point by using a Walsh code that uniquely identifies the access point. The DRC message symbol is exclusive-or (XOR) with the unique Walsh code. Since each access point in the access terminal's active set is identified by a unique Walsh code, only the selected access point that implements the same XOR operation as the access terminal, along with the correct Walsh code, can correctly decode the DRC message. The access point uses the DRC message from each access terminal to efficiently transmit forward link data at the highest possible rate.

At each slot, the access point may select any of the paged access terminals to effectuate the data transmission. The access point then determines the data rate at which to transmit data to the selected access terminal based on the most recent value of the DRC message received from the access terminal. In addition, the access point uniquely identifies transmissions to a particular access terminal by using a spreading code that is unique to that access terminal. In one embodiment, the spreading code IS a long Pseudo Noise (PN) code, defined by the IS-95 standard.

An access terminal, which is where a data packet is intended, receives a data transmission and decodes the data packet. Each data packet includes a plurality of data units. In one embodiment, the data unit includes eight information bits, although different data unit sizes may be defined within the scope of the present invention. In an embodiment, each data unit is associated with a sequence number and the access terminal can identify or lose or repeat transmissions. In this case, the access terminal transmits the sequence number of the lost data unit over the reverse link data channel. An access point controller that receives data messages from the access terminals and then indicates to all access points communicating with that particular access terminal which data units were not received by the access terminal. The access point then schedules a retransmission of these data units. Each access terminal within the data communication system is capable of communicating with multiple access points on the reverse link. In an embodiment, the data communication system supports soft handoff and softer handoff on the reverse link for several reasons. First, soft handoff does not consume additional capacity on the reverse link but allows the access terminal to transmit data at a minimum power level so that at least one of the access points can reliably decode the data. Second, the reception of reverse link signals by more access points increases the reliability of the transmission and requires only additional hardware at the access points.

In one embodiment, the forward link capacity of the data transmission system is determined by the rate request of the access terminal. Additional gain in forward link capacity may be achieved by using directional antennas and/or adaptive spatial filters. Exemplary METHODs AND APPARATUS FOR PROVIDING directional transmission are disclosed in U.S. Pat. No. 5857147, filed 5.1.1999 entitled "METHOD AND APPARATUS FOR DETERMINING THETRANSMISSION DATA RATE IN A MULTIPI-USER COMMUNICATION SYSTEM", filed 20.12.1995, AND U.S. application Ser. No. 08/925521 entitled "METHOD AND APPARATUS FOR PROVIDING ORTHOGONAL SPOT BEAMS, SECTORS, AND PICOCELLS", filed 8.9.1997, now U.S. Pat. No. 6285655, published 4.9.2001, both assigned to the assignee of the present invention AND incorporated herein by reference.

In one embodiment, data transmission is scheduled based in part on communication link quality. An exemplary communication system, which selects a transmission rate based on link quality, is disclosed in U.S. patent No. 08/741320 entitled "METHOD AND APPARATUS FOR PROVIDING HIGH SPEED DATA communications in a CELLULAR ENVIRONMENT," filed 11/9/1996, U.S. patent No. 6335922, published 1/2001, assigned to the assignee of the present invention, AND incorporated herein by reference. The scheduling of data communication may be based on additional considerations such as the GOS of the user, the queue size, the type of data, the amount of delay experienced, and the error rate of the data transmission. These are described in detail in U.S. patent No. 08798951 entitled "METHOD AND APPARATUS FOR FORWARD LINK speed circuit RATE scanner", application serial No. 08798951, filed 11/2/1997, AND U.S. patent No. 5923650, filed 13/6/1999, entitled "METHOD AND APPARATUS FOR REVERSE LINK ratescanner", filed 20/8/1997, assigned to the assignee of the present invention, AND incorporated herein by reference.

In an embodiment, data transmission is scheduled based on initial forward power control of the access terminal. In another embodiment, data transmission is scheduled based on initial forward power control of the access point.

Access terminal initial power control

In an embodiment, forward power control is initiated by the access terminal. The use of initial power control by the access terminal reduces forward link rate quantization loss (a result of forward link finite rate).

The access terminal reports the excess C/I estimate for the selected rate to the access point. The access point then reduces its transmit power by an appropriate amount when serving the access terminal.

The excessive C/I is a result of the limited data rate present on the forward link. The excess C/I measurement is the fraction above the C/I required to achieve a given performance at a given data rate. The use of excessive C/I measurements can reduce quantization loss due to forward link transmit power being greater than a given reliable data rate requirement. In an embodiment, the excess C/I measurements are used to reduce the transmit power on the traffic channel commensurate with the excess C/I measurements. In an embodiment, the excess C/I measurements are used to reduce the transmit power on the pilot channel and on the traffic channel commensurate with the excess C/I measurements.

Table 1 illustrates an exemplary definition of supporting data rates and decoding thresholds.

Table 1-traffic channel parameters

Parameter(s)	Data rate Kbps
Parameter(s)	Data rate Kbps												38.4	76.8	153.6	307.2	307.2	614.4	614.4	1228.8	1228.8	1843.2	2457.6
2048 bits	1024	1024	1024	1024	1024	1024	1024	2048	2048	3072	4096		38.4	76.8	153.6	307.2	307.2	614.4	614.4	1228.8	1228.8	1843.2	2457.6
2048 bits	1024	1024	1024	1024	1024	1024	1024	2048	2048	3072	4096	Packet length (millisecond)	26.67	13.33	6.67	3.33	3.33	1.67	1.67	1.67	1.67	0.83	0.83
Time slot/packet	16	8	4	1	2	1	2	1	2	1	0.5	Packet length (millisecond)	26.67	13.33	6.67	3.33	3.33	1.67	1.67	1.67	1.67	0.83	0.83
Time slot/packet	16	8	4	1	2	1	2	1	2	1	0.5	Time slot/transmission	16	8	4	2	2	1	1	1	1	1	1
C/I threshold (dB)	-11.5	-9.7	-6.8	-3.9	-3.8	-0.6	-0.8	1.8	3.7	7.5	9.7	Time slot/transmission	16	8	4	2	2	1	1	1	1	1	1
C/I threshold (dB)	-11.5	-9.7	-6.8	-3.9	-3.8	-0.6	-0.8	1.8	3.7	7.5	9.7	Rate indexing	0	1	2	3	4	5	6	7	8	9	10

Those skilled in the art will appreciate that different definitions of supported data rates may be considered within the scope of the present invention. Those skilled in the art will also appreciate that the use of any number of supported data rates and other data rates not listed in table 1 are contemplated within the scope of the present invention.

Table 1 shows the C/I threshold required for decoding at 1% Packet Error Rate (PER) for each data rate. PER # badpockets/# goodpackets. The forward link has a finite set of rates and a threshold required for successful decoding of the packet, e.g., a gap of 3.7dB for 1% of the time of successive rates. In addition, if the estimated C/I is greater than the maximum rate requirement, the access point can reduce its transmit power.

Closer to the cell boundary, the excessive transmit power of the access point causes interference to access terminals served by nearby access points. This interference causes the access terminals served by the neighboring access points to follow a lower C/I and thus the forward link data rate to become lower. Thus, reducing the transmit power of an access point reduces the annoyance to access terminals served by nearby access points, thereby increasing the C/I measurements for the access terminals. The increased C/I measurement by the access terminal causes an increase in the requested forward link data rate at the access terminal. The increased C/I measurement of the access terminal may result in an increase in the effective service data rate.

Once an access terminal reports an excessive C/I, the access point may reduce its transmit power by some suitable amount when transmitting to that access terminal. This ensures that the access terminal decodes the requested packet with a PER of 1%. In addition, forward link interference observed by access terminals in neighboring sectors is reduced.

The DRC channel carries information about the requested rate and the sector from which the request came. In an embodiment, the DRC message further comprises a measure of excess C/I. There are additional bits within the DRC message codeword to indicate the amount of excess C/I. In another embodiment, the excess C/I measurement is included in another message on a separate feedback channel.

Once the access point receives an indication of excessive C/I from an access terminal, if it chooses to serve that access terminal, it reduces its transmit power by an amount equal to the excessive C/I indicated by the access terminal. The transmit power of the digital baseband is modified to reduce the transmit power of the access point.

In one embodiment, the excess C/I ranges from 0.5dB to 3.5 dB. Assuming a step size of 0.5dB and 7 levels, 3 bits represent the message. Those skilled in the art will appreciate that the stride may be any dB increment and may be any number of dB steps and be within the scope of the present invention.

Access point initial power control

In one embodiment, forward power control is automatically implemented at the access point. Scheduling of data transmission is based on access point initial forward power control. The access point initial forward power control method is used to increase the throughput of users that receive a significant amount of interference. The access point changes its transmit power over time or randomly or synchronously with the access points within the communication system.

In an embodiment, all access points vary their transmit power in a time synchronized manner. In another embodiment, all access points vary their transmit power in a random manner. In an embodiment, the random pattern is a periodic pattern, such as a sinusoidal pattern or a triangular pattern. In another embodiment, the random pattern is a non-periodic pattern. One skilled in the art will appreciate that the random pattern may be any pattern.

The access terminal measures a variable C/I as a result of the transmit power variation. The access terminal sends the variable C/I as a rate request to the access point. The access point uses a variable rate request C/I in its scheduling algorithm.

In one embodiment, the forward link scheduler, i.e., the channel scheduler 48 of the access point, uses the variation in the rate request to switch its service to the access terminal when the requested rate for the access terminal is higher than the average service rate for the access terminal.

In one embodiment, the channel scheduler 48 selects the access terminal I with the highest ratio of the instantaneous DRC requested by the access terminal to the average service rate of the access terminal for the next data transmission:

DRC_I(n)/R_I(n) wherein R_I(n)＝(1-1/tc)*R_I(n-1)+(1/tc)。

R_I(n) is the average service rate of the time slot within n-1 to I, and tc is the scheduler time constant. In one embodiment, tc is 1000 slots. Those skilled in the art will appreciate that the time constant can be any integer greater than one and depends on the application.

The C/I of an access terminal is limited interference when the access terminal is located at or near a cell intersection with interference from neighboring cells. If the C/I observed at the access terminal is time-varying, the access terminal may get a higher C/I relative to the average C/I for a portion of the time and a lower C/I relative to the average C/I for the rest of the time. The access point calculates an average C/I of the plurality of C/Is received from the access terminal. Access terminals with higher than average C/I are scheduled by the access point scheduler. Other factors are also considered in scheduling data transmission scheduling and this is within the scope of the invention.

In an embodiment, where all access points vary their transmit power in a synchronous manner, all sectors of one access point are power controlled such that the moment of maximum power generation depends on the access point's center site (boresite) azimuth:

P(t)＝P₀(dBm)+*(dB)*Cos(2*π*t/T-θ)

wherein

P₀Is the access point nominal transmit power;

θ is the azimuth;

t is the time of scanning 360 degrees (1 to 2 seconds); and

delta is peak and Pmax varies 1 to 4 dB.

This results in access terminals having a time-varying C/I at or near the handoff boundary even when the access terminals are stationary, and their maximum C/I is better than their average C/I by approximately dB. As an access point increases power in the direction of the access terminal, another access point around the access terminal decreases their transmit power. The time period of the power change is to be within the time constant of the forward link scheduler. The method of synchronization can be viewed as a process that dynamically moves the handoff boundary as perceived by a fixed user, i.e., the access terminal.

In another embodiment, all access points vary their transmit power in a random pattern. The access point changes power randomly, i.e., in an uncoordinated manner.

In one embodiment, the total power is controlled. In another embodiment, the pilot channel and the traffic channel are controlled. In another embodiment, only the traffic channel is power controlled.

V. no handover situation

Without handoff, the access terminal 6 communicates with one of the access points 4. Referring to fig. 2, data to a particular access terminal 6 is provided to a selector element 14, which is assigned to control communications with the access terminal 6. The selector element 14 forwards the data to a data queue 40 within the access point 4. The access point 4 queues the data and transmits a paging message on the control channel. The access point 4 monitors the reverse link DRC channel for DRC messages from the access terminal 6. If no signal is detected on the DRC channel, the access point 4 retransmits the paging message until the DRC message is detected. After exceeding the predetermined number of retransmission attempts, the access point 4 can abort processing or re-originate calls with the access terminal 6.

In one embodiment, the access terminal 6 sends the requested data rate in the form of a DRC message to the access point 4 on the DRC channel. In another embodiment, access terminal 6 sends an indication of the quality of the forward link channel (e.g., a C/I measurement) to access point 4. In an embodiment, the access terminal 6 transmits the excess C/I measurements to the access point 4.

In one embodiment, the DRC message is 3 bits long and is decoded by the access point 4 with soft decisions. In one embodiment, the DRC message is transmitted in the first half of each slot. If the slot is available for data transmission to access terminal 6, access point 4 then decodes the DRC message with the remaining half of the slot and configures the hardware for data transmission in the next successive slot. If the next successive slot is not available, the access point 4 waits for the next available slot and continues to monitor the new DRC message for the DRC channel.

In one embodiment, access point 4 transmits at the requested data rate. In this embodiment the access terminal 6 makes an important decision to select the data rate. The benefit of always transmitting at the requested data rate is that access terminal 6 knows what data rate is waiting. Thus, access terminal 6 only demodulates and decodes the traffic channel in accordance with the requested data rate. Access point 4 need not transmit a message to access terminal 6 to indicate which data rate access point 4 is using.

In one embodiment, upon receiving the paging message, the access terminal 6 continues to attempt to demodulate the data at the requested data rate. The access terminal 6 demodulates the forward traffic channel and provides soft-decision symbols to the decoder. The decoder decodes the symbols and performs a frame check on the decoded packet to determine whether the packet was received correctly. The frame check may indicate a packet error if a packet error is received or if a packet is directed to another access terminal 6. Alternatively, access terminal 6 demodulates the data on a slot-by-slot basis. In one embodiment, access terminal 6 can determine whether it is a data transmission for it based on a preamble included in each transmitted data packet. Thus, if it is determined that the transmission is for another access terminal 6, then access terminal 6 may abort the decoding process. In both cases, the access terminal 6 transmits a Negative Acknowledgement (NACK) message to the access point 4 to confirm the incorrect receipt of the data unit. Upon receiving the NACK message, the erroneously received data is retransmitted.

The transmission of the NACK message may be implemented in the same manner as the transmission of an Error Indicator Bit (EIB) in a CDMA system. THE implementation AND use OF EIB TRANSMISSION is disclosed in U.S. Pat. No. 5568483 entitled "METHOD AND APPARATUS FOR THE FORMATION OF DATA FOR TRANSMISSION", assigned to THE assignee OF THE present invention AND incorporated herein by reference. Alternatively, a NACK may be sent with the message.

In one embodiment, the data rate is determined by the access point 4 with input from the access terminal 6. The access terminal 6 performs C/I measurements and transmits link quality indications (e.g., C/I measurements) to the access point 4. In another embodiment, the access terminal 6 implements and transmits the excess C/I measurements to the access point 4. Access point 4 may adjust the requested data rate, such as the queue size and available transmit power, based on the resources available to access point 4. METHODs AND APPARATUS FOR achieving RATE determination are described in detail in U.S. Pat. No. 5751725, published 5/12/1998, entitled "METHOD AND APPARATUS FOR DETERMININGTHE RATE OF RECEIVED DATA IN A VARIABLE RATE COMMUNICATION SYSTEM", filed 1996 at 18/10/6175590B 1, also entitled "METHOD AND APPARATUS FOR DETERMINING THE RATE OF RECEIVED DATA IN A VARIABLE RATE COMMUNICATION SYSTEM", filed 1997 at 8/1997, assigned to the assignee OF the present invention, AND incorporated herein by reference. If the frame check is negative, access terminal 6 transmits the NACK message as described above.

Handover situation

In the case of handoff, access terminal 6 communicates with multiple access points 4 on the reverse link. Access terminal initial power control is independent of handoff operations. In handoff, the access terminal transitions from being served by one access point to another access point. At any time, the transmit power of the access point serving the access terminal is reduced in accordance with the excess C/I measured by the access terminal served by the access point.

Access point initial power control is also independent of handoff operations. The access terminal is served by the access point and, together with the access point, the access terminal measures the highest received C/I. The access point schedules forward link data to the access terminal when the requested rate for the access terminal is higher than the service rate for the access terminal.

In one embodiment, data transmission on the forward link to a particular access terminal 6 occurs from one access point 4. However, access terminal 6 may receive pilot signals from multiple access points 4 simultaneously. If the C/I measurement of access point 4 is above a predetermined threshold, access point 4 is added to the active set of access terminal 6. In the soft handoff direction message, the new access point 4 assigns the access terminal 6 to a Reverse Power Control (RPC) Walsh channel, described below. Each access point 4 that performs soft handoff with an access terminal 6 monitors the reverse link transmissions and sends RPC bits on their respective RPC Walsh channels.

Referring to fig. 2, the selector element 14 assigned to control communication with the access terminal 6 forwards data to the access points 4 within the active set of all access terminals 6. All access points 4 receiving data from the selector element 14 transmit paging messages to the access terminal 6 on their respective control channels. When the access terminal 6 is in the connected state, the access terminal 6 performs two functions. First, the access terminal 6 selects the best access point 4 based on a set of parameters, which may be the best C/I measurements. Access terminal 6 then selects a data rate based on the C/I measurement. In one embodiment, the access terminal 6 transmits DRC messages to the selected access point 4. Access terminal 6 can direct the transmission of the DRC message to a particular access point 4 by covering the DRC message with the Walsh cover assigned to that particular access point 4. In another embodiment, the access terminal 6 transmits the excess C/I measurements to the particular access point 4.

Access terminal 6 attempts to demodulate the forward link signal based on the requested data rate for each successive time slot. After transmitting the paging message, all access points 4 in the active set monitor the DRC channel for DRC messages from the access terminal 6. Also, since the DRC message is covered by a Walsh code, the access point 4 that is selected to assign the same Walsh code can decover the DRC message. Upon receiving the DRC message, the selected access point 4 transmits data to the access terminal 6 at the next available slot.

In one embodiment, the access point 4 transmits packet data comprising a plurality of data units to the access terminal 6 at the requested data rate. If the data unit is incorrectly received by access terminal 6, a NACK message is transmitted on the reverse link to all access points 4 in the active set. In an embodiment, the NACK message is demodulated and decoded by the access point 4 and forwarded to the selector element 14 for processing. In processing the NACK message, the data units are retransmitted using the procedure described above. In an embodiment the selector element 14 combines the NACK signals received from all access points 4 into one NACK message and sends the NACK message to all access points 4 in the active set.

In an embodiment, access terminal 6 may detect changes in the best C/I measurements and dynamically request data transmissions from different access points 4 at different time slots to improve efficiency. Since, in one embodiment, data transmission occurs from only one access point 4 at any given time slot, other access points 4 within the active set may not know which data unit, if any, has been transmitted to access terminal 6. In an embodiment, the transmitting access point 4 informs the selector element 14 about the transmission of data. The selector element 14 then sends a message to the access points 4 in all active sets. In one embodiment, the transmitted data is assumed to have been correctly received by access terminal 6. Thus, if the access terminal 6 requests a data transmission from a different access point 4 within the active set, the new access point 4 sends the remaining data units. In one embodiment, the new access point 4 is sent according to the most recent transmission update from the selector element 14. Alternatively, the new access point 4 selects the next data unit to send using a prediction scheme based on previously updated metrics such as average transmission rate and selector element 14. These mechanisms minimize the retransmission of copies of the same data unit by not being transmitted simultaneously by multiple access points 4, as repeated transmissions cause efficiency losses. If the previous transmission was received in error, the access point 4 may retransmit these data units in the sequence because each data unit is identified by a unique sequence number as described below. In an embodiment, if a hole is established (or no data unit is sent), e.g. as a result of a handover from one access point 4 to another access point 4, the missing data unit is considered to be received in error. The NACK message is transmitted for the missing data access terminal 6 and the data units are retransmitted.

In one embodiment, each access point 4 in the active set maintains a separate data queue 40 containing data to be transmitted to the access terminal 6. The selected access point 4 transmits the data in the data queue 40 in sequential order except for the retransmission of the erroneously received data unit and the signaling message. In one embodiment, the retransmitted data units are removed from the queue 40 after transmission.

Forward link traffic channel

Fig. 3A is a block diagram of a forward link architecture of an embodiment. The data is divided into data packets and provided to CRC encoder 112. For each data packet, CRC encoder 112 generates frame check bits (i.e., CRC parity bits) and inserts tail code bits. The formatted packets from CRC encoder 112 include data, frame check and tail bits, and other overhead bits, as described below. The formatted packets are provided to an encoder 114 which, in one embodiment, encodes the packets according to the encoding format disclosed in the aforementioned U.S. patent No. 5933462. Other encoding formats may be used and are within the scope of the invention. The encoded packet from encoder 114 is provided to interleaver 116, which rearranges the symbol symbols within the packet. The interleaved packet is provided to a frame puncturing element 118 which removes a portion of the packet as described below. The punctured packet is provided to multiplier 120 which scrambles the data with a scrambling sequence from scrambler 122. The truncation element 118 and scrambler 122 are described in detail below. The output from multiplier 120 comprises the scrambled packet.

The scrambled packets are provided to a variable rate controller 130 which demultiplexes the packets into K parallel in-phase and quadrature channels, where K depends on the data rate. In one embodiment, the scrambled packets are first demultiplexed into in-phase (I) and quadrature (Q) streams. In one embodiment, the I stream includes even indexed symbols and the Q stream includes odd indexed symbols. Each stream is further demultiplexed into K parallel channels such that the symbol rate of each channel is fixed for all data rates. The K channels for each stream are provided to Walsh cover element 132, which covers each channel with a Walsh function to provide orthogonal channels. The quadrature channel data is provided to gain element 134 which scales the data to maintain a constant total energy per chip (and therefore constant output power) for all data rates. The scaled data from gain element 134 is provided to Multiplexer (MUX)160, which multiplexes the data with a preamble. The preamble sequence is described in detail below. The output from the MUX 160 is provided to a Multiplexer (MUX)162, which multiplexes traffic data, power control bits, and pilot data. The output of MUX 162 includes an I Walsh channel and a Q Walsh channel.

Fig. 3B shows a block diagram of a modulator for modulating data. The I and Q Walsh channels are provided to adders 212a and 212b, respectively, which correspondingly sum the K Walsh channels to provide signal I, respectively_SUMAnd Q_SUM. The first one is_SUMAnd Q_SUMThe signal is provided to a complex multiplier 214. The complex multiplier 214 also receives the PN _ I and PN _ Q signals from multipliers 236a and 236b, respectively, multiplying the two complex inputs according to the following equation:

(I_mult+jQ_mult)＝(I_sum+jQ_sum)·(PN_I+jPN_Q)

(2)

＝(I_sum·PN_I-Q_sum·PN_Q)+j(I_sum·PN_Q+Q_sum·PN_I)

wherein I_multAnd Q_multIs the output from complex multiplier 214 and j represents a complex number. I is_multAnd Q_multThe signals are provided to filters 216a and 216b, respectively, which filter the signals. The filtered signals from filters 216a and 216b are provided to multipliers 218a and 218b, respectively, which apply the signals with in-phase sinusoidal COS (w), respectively_ct) and the orthogonal sine SIN(w_ct) are multiplied. The I and Q modulation signals are provided to a summer 220 which sums the signals to provide a forward modulation waveform s (t).

In one embodiment, the data packet is spread with a long PN code and a short PN code. The long PN code scrambles the packet so that only the access terminal 6 to which the packet is intended can descramble the packet. In one embodiment, the pilot and power control bits and control channel packets are spread with a short PN code rather than a long PN code to allow all access terminals 6 to receive the bits. The long PN code sequence is generated by long code generator 232 and provided to Multiplexer (MUX) 234. The long PN mask determines the offset of the long PN sequence and is uniquely assigned to the destination access terminal 6. The output from MUX 234 is a long PN sequence for the duration of the data portion of the transmission (e.g., for the duration of the pilot and power control portions), and is zero otherwise. Gating of long PN sequences from MUX 234 and short PNI and PN from short code generator 238_QThe sequences are provided to multiplexers 236a and 236b, respectively, which multiply the two sets of sequences to form the PN _ I and PN _ Q signals, respectively. The PN _ I and PN _ Q signals are provided to a complex multiplier 214.

Fig. 3A and 3B illustrate a block diagram of a traffic channel that is one of many structures that support data encoding and demodulation on the forward link. Other architectures, such as those compliant with the IS-95 standard for forward link traffic channels in CDMA systems, may also be used and are within the scope of the present invention.

In one implementation, the data rates supported by the access point 4 are predetermined and each supported data rate is assigned a unique rate index. Access terminal 6 selects one of the supported data rates based on the C/I measurements. Since the requested data rate needs to be sent to the access point 4 to enable the access point 4 to send data at the requested data rate, there is a tradeoff between the number of data rates supported and the number of bits needed to identify the requested data rate. In an embodiment, the number of supported data rates is seven and a 3-bit rate index is used to identify the requested data rate. Those skilled in the art will appreciate that data supporting data rates and n-bit rate indices are contemplated and are within the scope of the present invention.

In one embodiment, the minimum data rate is 38.4Kbps and the maximum data rate is 2.4576 Mbps. The minimum data rate is selected based on the worst-case C/I measurement within the system, the processing gain of the system, the design of the positive-error code, and the desired level of performance. In one embodiment, the supported data rates are selected such that the difference between successive supported data rates is 3 dB. This 3dB increase is a coordination among several factors, including the accuracy of the C/I measurements available to the access terminal 6, the loss due to quantizing the data rate based on the C/I measurements (invalidity), and the need to send the bit data (or bit rate) of the requested data rate from the access terminal 6 to the access point 4. More supported data rates require more bits to identify the requested data rate but allow more efficient use of the forward link due to less quantization error between the calculated maximum data rate and the supported data rate.

In one embodiment, the traffic channel transmission is divided into frames. The frame in one embodiment is defined as the length of a short PN sequence or 26.67 milliseconds. Each frame can carry control channel information to all access terminals 6 (control channel frames), traffic data to all particular access terminals 6 (traffic frames), or can be a null frame (idle frame). The content of each frame is determined by the scheduling implemented by the transmitting access point 4. In one embodiment, each frame includes 16 slots, each slot lasting 1.667 milliseconds. A 1.667 millisecond time slot may be sufficient for access terminal 6 to perform C/I measurements of the forward link signal. A 1.667 millisecond time slot ensures sufficient time for efficient packet data transmission. In one embodiment, each slot is further divided into four quarter slots.

In one embodiment, each data packet is transmitted on one or more time slots as shown in table 1. In one embodiment, each forward link data packet includes 1024 or 2048 bits. Thus, the number of slots in which each data packet is transmitted is dependent on the data rate and range, from 16 slots for 38.4Kbps to 1 slot or more for 1.2288 Mbps.

Fig. 4A is a forward link slot structure of an embodiment. In one embodiment, each time slot includes three of four time multiplexed channels, a traffic channel, a control channel, a pilot channel, and a power control channel. In one embodiment, the pilot and power control channels are transmitted in two pilot and power control bursts, which are located in the same location in each slot. A description of pilot AND power control bursts is described in U.S. patent application No. 08/963386, entitled "METHOD AND APPARATUS FOR HIGH RATEPACKET TRANSMISSION mismatch," filed on 3/11/1997, now patent No. 6574211, published on 3/6/2002, the preceding references being incorporated herein by reference.

Forward link pilot channel

In one embodiment, the forward link pilot channel provides a pilot signal that is used by access terminal 6 for initial acquisition, phase recovery, timing recovery, and scaling. These uses are similar to those of CDMA communication systems conforming to the IS-95 standard. In an embodiment, the pilot signal is also used by the access terminal 6 to perform C/I measurements.

Fig. 3A shows a block diagram of a forward pilot channel in one embodiment. The pilot data comprises a sequence of all zeros (or all 1 s) provided to multiplier 156. Multiplier 156 uses Walsh code W₀The pilot data is covered. Due to Walsh code W₀Is an all-zero sequence and the output of multiplier 156 is pilot data. The pilot data is time multiplexed by MUX 162 and provided to the short PN in complex multiplier 214 (see FIG. 3B)_ICode spread I Walsh channels. In one embodiment, pilot data is not spread with a long PN code, and is turned off by MUX 234 during pilot bursts to allow all access terminals 6 to receive. The pilot signal is thus an unmodulated BPSK signal.

Fig. 4A shows a graph of a pilot signal. In one embodiment, each slot includes two pilot bursts 306a and 306b that occur at the first and third quarter ends of the slot. In one embodiment, each pilot burst 306a and 306b lasts for 64 chips (Tp-64 chips). In the absence of each traffic data or control channel, access point 4 transmits only pilot and power control bursts, causing discontinuous waveform bursts at a periodic rate of 1200 Hz.

IX. reverse link power control bit gain

In one embodiment, the forward link power control channel is used to send power control commands for controlling the transmit power of reverse link transmissions from remote station 6. On the reverse link, each transmitting access terminal 6 acts as a source of interference to all other access terminals 6 in the network. To minimize interference on the reverse link and maximize capacity, the transmit power of each access terminal 6 is controlled by two power control loops. IN one embodiment, the POWER control loop is similar to that found IN a CDMA SYSTEM, which is disclosed IN U.S. Pat. No. 5056109 entitled "METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMACELLULAR MOBILE TELEPHONE SYSTEM", assigned to the assignee of the present invention AND incorporated herein by reference. Other power control mechanisms are also contemplated as being within the scope of the present invention.

The first power control loop adjusts the transmit power of the access terminal 6 so that the reverse link signal quality is maintained at a set level. Signal quality is determined by the energy per bit to noise plus interference ratio E of the reverse link signal received at access point 4_b/I_oAnd (6) measuring. The set level is called E_b/I_oA set point. The second power control loop adjusts the setpoint to maintain a desired level of performance for Frame Error Rate (FER) measurements. Power control is particularly critical on the reverse link because the transmit power of each access terminal 6 is interference to other access terminals 6 in the communication system. Minimizing reverse link transmit power can reduce interference and increase reverse link capacity.

E of reverse link signal in first power control loop_b/I_oMeasured at the access point 4. The access point 4 will then measure E_b/I_oCompared to a set point. Such asMeasured of fruit meridian E_b/I_oAbove the set point, the access point 4 sends a power control message to the access terminal 6 to reduce the transmit power. Or, if measured E_b/I_oBelow the set point, the access point 4 sends a power control message to the access terminal 6 to increase the transmit power. In one embodiment, the power control message is implemented by one power control bit. In one embodiment, a high value of the power control bit commands the access terminal 6 to increase its transmit power and a low value commands the access terminal 6 to decrease the transmit power.

In one embodiment, the power control bits for all access terminals 6 communicating with each access point 4 are transmitted on a power control channel. In one embodiment, the power control channel comprises up to 32 orthogonal channels, spread by a 16-bit Walsh cover. Each Walsh channel transmits one Reverse Power Control (RPC) bit or one FAC bit at periodic intervals. Each active access terminal 6 is assigned an RPC index that defines the Walsh cover and QPSK modulation phase (e.g., in-phase or quadrature) for transmission of the RPC bit stream to the access terminal 6. In one embodiment, 0 in the RPC index is reserved for the FAC bit.

Fig. 3A shows a block diagram of a power control channel. The RPC bits are provided to a symbol repeater 150, which repeats each RPC bit a predetermined number of times. The repeated RPC bits are provided to Walsh cover element 152, which covers the bits with a Walsh cover corresponding to the RPC index. The covered bits are provided to gain element 154. In one embodiment, gain element 154 scales the bits prior to modulation to maintain a constant total transmit power. In an embodiment, the gain of the RPC Walsh channel is normalized such that the total RPC channel power is equal to the total available transmit power. The gain of the Walsh channel may be a function of the time of efficient utilization of the total access point transmit power while maintaining reliable RPC transmission to all active access terminals 6. In an embodiment, the Walsh channel gain of inactive access terminal 6 is set to zero. Automatic power control of the RPC Walsh channel is possible when using an estimate of forward link quality measurements from the corresponding DRC channel from the access terminal 6. The scaled RPC bits from the gain element 154 are provided to the MUX 162.

In one embodiment, the RPC indices are assigned to Walsh covers W from 0 to 15, respectively₀To W₁₅And is sent approximately at the second pilot burst in the slot (RPC bursts 304a and 304B of fig. 4B). RPC indices 16 through 31 are correspondingly assigned to Walsh code W₀To W₁₅And is sent approximately at the second pilot burst in the slot (RPC bursts 308a and 308B of fig. 4B). In one embodiment, the RPC bits are covered with even Walsh (e.g., W)₀、W₂、W₄Etc.) BPSK modulation on the in-phase signal, and odd Walsh covering (e.g., W)₁、W₃、W₅Etc.) are modulated on the quadrature signal. To reduce the peak-to-average envelope, it is desirable to balance the in-phase and quadrature power. In addition, to reduce cross-talk due to demodulator phase estimation errors, it is desirable to assign quadrature covers to the in-phase and quadrature signals.

In an embodiment, up to 31 RPC bits may be transmitted on 31 RPC channels in each slot. In one embodiment, 15 RPC bits are transmitted on the first half slot and 16 RPC bits are transmitted on the second half slot. The RPC bits are combined by adders 212a and 212B (see fig. 3B), and fig. 4B shows a composite waveform of the power control channel.

Fig. 4A depicts a timing diagram of a power control channel. In one embodiment, the RPC bit rate is 600bps, or one RPC bit per slot. Each RPC bit is time multiplexed and sent over two RPC bursts (e.g., RPC bursts 304A and 304B), as shown in FIGS. 4A and 4B. In one embodiment, each RPC burst is 32 PN chips (or 2 Walsh symbols) in width, and the total width of each RPC bit is 64 PN chips (or 4 Walsh symbols). Other RPC bit rates can be obtained by varying the number of symbol repetitions. For example, an RPC bit rate of 1200b0ps (to support up to 63 access terminals 6 simultaneously or to increase the power control rate) may be obtained by sending a first set of 31 RPC bits over RPC bursts 304a and 304b, and a second set of 32 RPC bits over RPC bursts 308a and 308 b. In this case, all Walsh covers are used for the in-phase and quadrature signals.

The power control channel is bursty in that the number of access terminals 6 communicating with each access point 4 may be less than the data of the available PRC Walsh channel. In this case, some of the RPC Walsh channels are set to zero by appropriate adjustment of the gain of gain element 154.

In an embodiment, the RPC bits are sent to the access terminal 6 without encoding or interleaving to minimize processing latency. In addition, erroneous reception of power control bits is not detrimental to the data communication system, since errors can be corrected by the power control loop in the next time slot.

In an embodiment, access terminal 6 may be in soft handoff with multiple access points 4 on the reverse link. Methods and apparatus for reverse link power control of access terminal 6 during soft handoff are disclosed in U.S. patent No. 5056109. The access terminal 6 in soft handoff monitors the RPC clean channel for each access point 4 in the active set and combines the RPC bits according to the method described in the aforementioned U.S. patent No. 5056109. In one embodiment, access terminal 6 implements a logical OR of the down power command. If any received RPC bits command access terminal 6 to decrease transmit power, access terminal 6 decreases transmit power. In one embodiment, access terminal 6 in soft handoff may combine the soft decisions of the RPC bits before making a hard decision. Other embodiments of processing the received RPC bits are also contemplated within the scope of the present invention.

In one embodiment, the FAC bit indicates whether the traffic channel of the pilot channel associated with access terminal 6 is transmitted on the next half frame. Using the FAC bits improves the C/I estimation of the access terminal 6 and the data rate request by broadcasting knowledge about the interference activity. In one embodiment, the FAC bits are changed only at the boundaries of a field and repeated in the next eight consecutive slots, resulting in a bit rate of 75 bps.

Using the FAC bits, access terminal 6 may compute the C/I measurement as follows:

img id="idf0002" file="C0182259300281.GIF" wi="340" he="61" img-content="drawing" img-format="GIF"/

wherein (C/I)_iIs a C/I measurement of the ith forward link signal, C_iIs the total received power, C, of the ith forward link signal_jIs the received power of the jth forward link signal, if all access points 4 are transmitting, then I is the total interference, a_jIs the FAC bit of the jth forward link signal and may be either 0 or 1 depending on the FAC bit.

X. reverse link structure

In the data communication system of an embodiment, the reverse link transmission differs from the forward link transmission in several ways. On the forward link, data transmission typically occurs from one access point 4 to one access terminal 6. On the reverse link, however, each access point 4 may concurrently receive data transmissions from several access terminals 6. In one embodiment, each access terminal 6 may transmit at one of several data rates, depending on the amount of data to be sent to the access point 4. The design of the system reflects the asymmetry of data communication.

In one embodiment, the time base units on the reverse link are equal to the time base units on the forward link. In one embodiment, forward link and reverse link data transmissions occur over time slots having a duration of 1.667 milliseconds. However, since data transmission on the reverse link typically occurs at lower data rates, longer time base units may be used to improve efficiency.

In one embodiment, the reverse link supports variable rate data transmission. Variable rate provides flexibility and allows access terminal 6 to transmit at one of several data rates, depending on the amount of data to be transmitted to access point 4. In an embodiment, access terminal 6 may transmit data at the lowest data rate at any time. In an embodiment, the transmission of data at a higher data rate requires obtaining permission from the access point 4. This implementation minimizes reverse link transmission latency while providing efficient utilization of reverse link resources.

In one embodiment, the reverse link supports two channels: pilot/DRC channels and data channels. The function and implementation of each of these channels is as follows. The pilot/DRC channel is used to transmit pilot signals and DRC messages, and the data channel is used to transmit traffic data.

In one embodiment, whenever access terminal 6 receives a high speed data transmission, access terminal 6 transmits a DRC message on the pilot/DRC channel in each slot. Alternatively, when access terminal 6 is not receiving high speed data transmissions, the entire slot on the pilot/DRC channel includes the pilot signal. The pilot signal is used to perform a number of functions by receiving the access point 4: to facilitate initial acquisition, as a phase reference for pilot/DRC and data channels, as a source of closed loop reverse link power control.

In one embodiment, the bandwidth of the reverse link is selected to be 1.2288 MHZ. This bandwidth selection allows the use of existing hardware designs for CDMA systems that conform to the IS-95 standard. However, other bandwidths may be used to increase capacity and/or meet system requirements. In one embodiment, the same long PN code and short PN specified by the IS-95 standard_IAnd PN_QThe code is used to spread the reverse link signal. In one embodiment, the reverse link channel is transmitted using QPSK modulation. Alternatively, OQPSK modulation may be used to minimize peak-to-average amplitude variation of the modulated signal, which may improveAnd (4) performance. The use of different system bandwidths, PN codes, and modulation schemes may be considered within the scope of the invention.

In one embodiment, the transmit power and data channel of the reverse link transmission on the pilot/DRC channel are controlled such that the E of the reverse link signal measured at the access point 4_b/I_oIs maintained at a predetermined E_b/I_oSet point, as discussed in U.S. patent No. 5506109, discussed above. In communicating with access terminal 6, power control is maintained by access point 4, with instructions being sent via RPC bits as described above.

XI reverse link data channel

Fig. 5 is a block diagram of a reverse link architecture of an embodiment. The data is divided into data packets and provided to an encoder 612. For each data packet, encoder 612 generates CRC parity bits, inserts tail bits, and encodes the data. In one embodiment, encoder 612 encodes packets according to the aforementioned U.S. patent application serial No. 08/743688, now published as U.S. patent No. 5933462. Other encoding formats are also available within the scope of the invention. The encoded packet from encoder 612 is provided to a module interleaver 614, which reorders the symbol symbols within the packet. The interleaved packets are provided to multiplier 616, which performs data covering with Walsh covering and provides the covered data to gain element 618, which performs scaling of the data by gain element 618 to maintain a constant energy-per-bit E at any data rate_b. The scaled data from gain element 618 is provided to multipliers 650b and 650d, which spread the data with corresponding PN _ Q and PN _ I sequences. The spread data from multipliers 652b and 650d are provided to respective filters 652b and 652d, which filter the data. The filtered signals from filters 652a and 652b are provided to adder 654a, and the filtered signals from filters 652c and 652d are provided to adder 654 b. Adders 654a and 654b sum the signal from the data channel and the signal from the pilot/DRC channel. The outputs of adders 654a and 654b include IOUT and QOUT, respectively, and use in-phase sinusoidal COS (w), respectively_ct) and quadrature positiveString SIN (w)_ct) are modulated (as in the forward link) and summed (not shown in fig. 5). In one embodiment, traffic data is transmitted in the in-phase and quadrature phases of the sinusoid.

In one embodiment, the data is spread with a long PN code and a short PN code. The long PN code scrambles the data so that the receiving access point 4 can identify the transmitting access terminal 6. The short PN code spreads the signal over the system bandwidth. The long PN sequence is generated by long code generator 642 and provided to multipliers 646a and 646 b. Short PN_IAnd PN_QThe sequences are generated by a short code generator 644 and provided to multipliers 646a and 646b, respectively, which multiply the two sets of sequences to form the PN _ I and PN _ Q signals, respectively. The timing/control circuit 640 provides a timing reference.

One block diagram of the data channel structure shown in fig. 5 is one of many structures that support data coding and modulation on the reverse link. For high rate data transmission, a structure similar to the several orthogonal channels used by the forward link may be used. Other architectures, such as the architecture of the reverse link traffic channel in CDMA conforming to the IS-95 standard, are contemplated within the scope of the present invention. The scheduling mechanism for high speed data transmission is described in detail in the aforementioned U.S. patent application serial No. 08/798951, now published as U.S. patent No. 6335922.

Reverse link pilot/DRC channel xii

Fig. 5 shows a block diagram of a pilot/DRC channel. The DRC message is provided to a DRC encoder 626, which encodes the message according to a predetermined encoding format. The encoding of the DRC message is important because it must be guaranteed that the error probability of the DRC message is sufficiently small because incorrect forward link data rate determinations affect system throughput performance. In one embodiment, DRC encoder 626 is a rate (8, 4) CRC block encoder that encodes a 3-bit DRC message into an 8-bit codeword. The encoded DRC message is provided to a multiplier 628 that covers the message with a Walsh code that uniquely identifies the target access point 4 to which the DRC message is directed. The Walsh codes are provided by Walsh generator 624. The covered DRC message is provided to a Multiplexer (MUX)630 that multiplexes the message with pilot data. The DRC message and pilot data are provided to multipliers 650a and 650c, which spread the data with PN _ I and PN _ Q signals, respectively. Thus, the pilot and DRC messages are transmitted simultaneously on the in-phase and quadrature phases of the sinusoid.

In one embodiment, the DRC message is sent to the selected access point 4. This is accomplished by covering the DRC message with a Walsh code that identifies the selected access point 4. In one embodiment, the Walsh code is 128 chips long. 128 chip Walsh code derivation is known in the art. A unique Walsh code is assigned to each access point 4 that communicates with access terminal 6. Each access point 4 decovers the signal on the DRC channel with its assigned Walsh code. The selected access point 4 can decover the DRC message and transmit the data to the requesting access terminal 6 on the forward link accordingly. The other access points 4 can determine that the requested data rate is not addressed to them because the access points 4 are assigned different Walsh codes.

In one embodiment, the reverse link short PN codes are the same for all access points 4 in the data communication system and there is no offset in the short PN sequence to distinguish between different access points 4. The data communication system of one embodiment supports soft handoff on the reverse link. The use of the same short PN code without offset allows several access points 4 to receive the same reverse link transmission from an access terminal 6 in soft handoff. The short PN code provides spectrum spreading but does not allow for identification of the access point 4.

In one embodiment, the DRC message carries the data rate requested by access terminal 6. In another embodiment, the DRC message carries an indication of the forward link quality (e.g., a C/I message measured by access terminal 6). Access terminal 6 can simultaneously receive forward link pilot signals from one or more access points 4 and perform C/I measurements on each received pilot signal. The access terminal 6 then selects the best access point 4 based on a set of parameters, which may include current and previous C/I measurements. The rate control information is formatted as a DRC message that may be sent to the access point 4 in one of several embodiments.

In one embodiment, access terminal 6 transmits the DRC message based on the requested data rate. The requested data rate is the highest supportable data rate that has satisfactory performance at the C/I measured by access terminal 6. From the C/I measurements, access terminal 6 calculates a maximum data rate, which yields satisfactory performance. Once the maximum data rate has been calculated, the maximum data rate is then quantized to one of the supported data rates, and referred to as the requested data rate. A data rate index corresponding to the requested data rate is transmitted to the selected access point 4. An exemplary set of supported data rates and corresponding data rate indices is shown in table 1.

Access terminal 6 also calculates excess C/I measurements. The excess C/I measurement is the C/I that exceeds the satisfactory performance requirement. In an embodiment, access terminal 6 sends DRC messages based on C/I measurements. In this embodiment, the access point 4 calculates the maximum data rate that yields satisfactory performance. In other embodiments, access terminal 6 transmits DRC messages based on the C/I measurements and the excess C/I measurements. In another embodiment, access terminal 6 transmits the excess C/I measurements on another channel. In embodiments where the excess C/I measurements are calculated, the access point 4 calculates the maximum data rate that yields satisfactory performance and reduces the traffic channel transmit power based on the excess C/I measurements. Access terminal 6 demodulator 64 then scales the traffic channel transmit power based on the reduction.

In an embodiment in which the access terminal 6 transmits a forward link quality indication to the selected access point 4, the access terminal 6 transmits a C/I index, which represents a quantized value of the C/I measurement. The C/I measurements may be mapped to a table and associated with a C/I index. More bits are used to represent the C/I index to achieve finer quantization of the C/I measurement. Also, the mapping may be linear or pre-distorted. For a linear mapping, each increment in the C/I index represents a corresponding increment in the corresponding C/I measurement. For example, each level within the C/I index represents a 2.0dB increase within the C/I measurement. For the pre-distortion map, each increase in the C/I index may represent a different increase in the C/I measurement. For example, the predistortion map may be used to quantify the C/I measurements to match the Cumulative Distribution Function (CDF) curve of the C/I distribution as shown in FIG. 6.

It is also contemplated within the scope of the invention that other embodiments may enable the transmission of rate control information from the access terminal 6 to the access point 4. In addition, it is within the scope of the present invention that a different number of bits be used to represent rate control information.

In one embodiment, the C/I measurements and excess C/I measurements may be performed on the forward link pilot signal in a similar manner as used by CDMA systems. METHODs AND APPARATUS FOR achieving C/I measurements are disclosed in U.S. Pat. No. 5903554 entitled "METHOD AND APPARATUS FOR MEASURING LINE QUALITY IN ASPREAD SPECTRUM COMMUNICATION SYSTEM", filed on 9/27 of 1996, assigned to the assignee of the present invention, AND incorporated herein by reference. In summary, the C/I measurement on the pilot signal can be obtained by despreading the received signal with the short PN code. The C/I measurement of the pilot signal may have inaccuracy if the channel conditions change between the time of the C/I measurement and the actual data transmission time. In one embodiment, the use of the FAC bit allows access terminal 6 to take forward link activity into account when determining the requested data rate.

In another embodiment, the C/I measurements and the excess C/I measurements may be performed on a forward link traffic channel. The traffic channel signal is first despread with the long PN code and the short PN code and decovered with the Walsh code. The C/I measurement of the signal on the data channel may be more accurate since a greater portion of the transmitted power is allocated for data transmission. Other methods of measuring the C/I of the received forward link signal of access terminal 6 are also contemplated within the scope of the present invention.

In an embodiment, the requested data rate is sent to the access point 4 using an absolute reference and a relative reference. In this embodiment, the absolute reference comprising the requested data rate is transmitted periodically. The absolute reference allows the access point 4 to determine the exact data rate requested by the access terminal 6. For each time slot between the transmission of the absolute reference, the access terminal 6 transmits a relative reference to the access point 4 indicating that the requested data rate for the upcoming time slot is higher, lower, or the same as the requested data rate for the previous time slot. Periodically, the access terminal 6 sends an absolute reference. The periodic transmission of the data rate index allows the requested data rate to be set to a known state and ensures that erroneous receptions to the reference do not accumulate. The use of the absolute reference and the relative reference can reduce the transmission rate of DRC messages to the access point 6. Other protocols for transmitting the requested data rate are also contemplated within the scope of the present invention.

The access terminal 6 uses the reverse link access channel to transmit messages to the access point 4 during the registration phase. Access terminal 6 transmits a NACK message on the reverse link NACK channel.

Although the present invention is described in the context of a NACK protocol, the use of an ACK protocol is contemplated within the scope of the present invention.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method of packet data transmission from at least one access point to another access terminal, comprising:

paging an access terminal for an upcoming data transmission;

selecting an access point based on a set of parameters;

measuring an excess C/I of a forward link signal from the selected access point;

sending the excess C/I measurement to the selected access point; and

transmitting data from the selected access point at a transmit power based on the excess C/I measurement.

2. The method of claim 1, wherein the transmitting step is scheduled by a scheduler based on a priority of the access terminal.

3. The method of claim 1, wherein the measuring, selecting, and sending steps are performed on each time slot until the data transmission is complete.

4. The method of claim 1, wherein the transmitting step is performed using directional beams.

5. The method of claim 1, wherein the data is sent to the access terminal in data packets.

6. The method of claim 5, further comprising:

sending a Negative Acknowledgement (NACK) message for data packets not received by the access terminal.

7. The method of claim 5, further comprising:

retransmitting the data packet not received by the access terminal according to the NACK message.

8. The method of claim 5, wherein the data packets are of a fixed size for all data rates.

9. The method of claim 5, wherein the data packet is transmitted on one or more time slots.

10. The method of claim 5, wherein each data packet includes a preamble.

11. The method of claim 10, wherein a length of the preamble is based on the data rate.

12. A method of packet data transmission from at least one access point to an access terminal, comprising:

a paging-free access terminal regarding an upcoming data transmission;

selecting an access point according to a set of parameters;

sending the excess C/I measurement to the selected access point; and

13. The method of claim 12, wherein the data request message indicates a requested data rate.

14. The method of claim 12, wherein the requested data rate is one of a plurality of data rates.

15. A method of packet data transmission from at least one access point to an access terminal, comprising:

paging an access terminal for an upcoming data transmission;

selecting an access point according to a set of parameters;

transmitting a data request message to the selected access point on a first channel;

transmitting excess C/I measurements to the selected access point on a second channel; and

transmitting data from said access point at a data rate in accordance with said data request message and at a transmit power in accordance with said measured excess C/I measurement.

16. The method of claim 15, wherein the data request message indicates a requested data rate.

17. The method of claim 15, wherein the requested data rate is one of a plurality of data rates.

18. An access terminal, comprising:

a receiver for receiving a radio paging message on a forward link signal and performing C/I measurements and excess C/I measurements of the forward link signal;

a controller coupled to said receiver to receive said paging message, C/I measurements and excess C/I measurements from the receiver, said controller selecting an access point; and

a transmitter coupled to the controller to transmit a data request message including a C/I measurement and an excess C/I measurement.

19. An access point, comprising:

a receiver for receiving the C/I measurements and the excess C/I measurements;

a channel scheduler coupled to said receiver to receive said C/I measurements and excess C/I measurements therefrom, said channel scheduler selecting access terminals for data transmission; and

the transmitter is coupled to the channel scheduler to transmit data based on the C/I measurements and the excess C/I measured transmit power.

20. A communication system for high rate packet data transmission from at least one access point to an access terminal, comprising:

a transmitter in each of said at least one access point to transmit paging messages in a forward link signal to said access terminal;

a receiver in said one access terminal for receiving said paging message and performing C/I measurements of said forward link signal and excess C/I measurements from said transmitter in said at least one access point.

A controller within each of said at least one access terminal, said controller coupled to said receiver to receive said C/I measurements and excess C/I measurements, said controller identifying a selected access point; and

a transmitter within the access terminal is coupled to the controller to transmit a data request message.