HK1087575A - Systems and methods for performing outer loop power control in wireless communication systems - Google Patents

Description

Systems and methods for performing outer-loop power control in a wireless communication system require 35 items of priority under 119 in the united states

This application claims a provisional application entitled "reverse link data communication," filed on month 2, 18, 2003, No. 60/448,269; united states provisional application No. 60/452,790 entitled "method and apparatus for reverse link communication in a communication system," filed No. 3/6, 2003; and No. 60/470,770 filed on month 5, 14, 2003, a non-provisional application entitled priority of U.S. provisional application for outer loop power control for rel.d.

Technical Field

The present invention relates generally to the field of telecommunications, and more particularly to mechanisms for providing outer loop power control in a wireless communication channel when data is intermittently transmitted over the channel.

Background

Wireless communication technology is rapidly advancing and wireless communication systems are being used to provide an increasing share of the communication capabilities currently available to users. This is true, although implementation of wireless communication systems faces additional technical hurdles compared to wired systems. For example, wireless communication systems must address issues related to power control between a base station and its mobile stations to optimize system performance, whereas wireline systems do not.

A wireless communication system includes a cellular CDMA (code division multiple access) system configured to support voice and data communications. The system may have a plurality of base stations that communicate with a plurality of mobile stations over wireless channels. (these base stations are also typically connected to a number of other systems, such as the public switched telephone network, via a wired network.) each base station communicates with a group of mobile stations within the sector corresponding to that base station. This base station is responsible for controlling the power of the communications between the base station and the mobile stations in order to minimize interference and maximize throughput, and also to enable the mobile stations to conserve energy and thus extend their lifetime.

Power control between a base station and a mobile station in this type of system is typically based on error rates associated with communications between the base station and the mobile station. The goal of power control is to control the power of the transmitter so that the transmitted data is decoded at a fixed quality level. One measure of quality is the frame error rate, i.e., the proportion of transmitted data frames that are received in error. Ideally, the mobile station transmit power is adjusted to a level that produces the desired predetermined frame error rate. For this reason, power control typically has two loops: an inner loop and an outer loop. The inner loop periodically measures the signal-to-noise ratio (SNR) of the base station and compares it to a target SNR. The measurement may be performed on any channel or combination of channels that can be used as a power reference. For example, in cdma2000 the measurements are typically done on the reverse link pilot channel (R-PICH). The result of this comparison is used to generate power control commands that are communicated to the mobile station. For example, if the SNR measured at the base station is below the target SNR, the inner loop will issue a command instructing the mobile station to increase its transmit power, and if the SNR measured at the base station is above the target SNR, the inner loop will issue a command instructing the mobile station to decrease its transmit power. The outer loop periodically updates the target SNR based on an estimate of the current decoding quality. For example, the outer loop may increase the target SNR by 1dB whenever a frame is decoded incorrectly and decrease the target SNR by 0.01dB whenever a frame is decoded correctly. In this way, the target SNR of the inner loop is adjusted to a level that can maintain a predetermined acceptable error rate.

While such power control algorithms are suitable for channels that continuously transmit data, they are less suitable for channels that are used intermittently. This has a problem that, very simply, there is no data frame that can be a reference for adjusting the target SNR in some time period. E.g., R-PICH, although the inner loop may process continuously transmitted signals, the outer loop does not have any signals available to update the target SNR. In other words, when frames are being transmitted, errors in the frames can be identified and the target SNR can be adjusted to achieve the desired error rate, but when no frames are being transmitted, there is no way to determine whether the target SNR should be adjusted upward or downward. Therefore, after a period in which no data frame is transmitted, the target SNR may not be set at the ideal level, and thus the inner loop may not direct the mobile station to transmit a signal at the optimal power level. If the level is set too low, the originally transmitted frames are almost certainly in error. On the other hand, if the power level is too high, energy is wasted and unnecessary interference may be generated, which may also cause transmission errors for other mobile stations. It is therefore desirable to provide a mechanism by which a preferred target SNR level can be reached without data transmission.

Disclosure of Invention

One or more of the problems outlined above may be solved by the various embodiments of the invention. The present invention generally comprises a system and method for controlling the power level of a mobile station during periods when the mobile station is not transmitting data.

In one embodiment, a wireless communication system includes a base station and one or more mobile stations that communicate via respective wireless communication links. Each link has multiple channels, including both forward link channels for transmitting data from the base station to the mobile stations and reverse link channels for transmitting data from the mobile stations to the base station. A reverse link traffic channel is only used intermittently (i.e., during some periods data is transmitted on the channel and during other periods no data is transmitted). When data is being transmitted on the traffic channel, the transmitted data is used by the base station to perform power control operations (e.g., increase or decrease the base station's target SNR level based on errors in the received data). A "zero-rate indicator" is transmitted on the rate indication channel when there is no data being transmitted on the traffic channel. In this case, the zero-rate indicator is used by the base station to perform outer-loop power control and update the target SNR. It should be noted that when there is data being transmitted on the traffic channel, corresponding rate indicators are transmitted on the rate indicator channel, but these rate indicators are not used for power control.

An alternative embodiment of the present invention encompasses a method for providing power control in a wireless communication system having a base station and a mobile station connected by a reverse link rate indicator channel and a reverse link traffic channel. The method of this embodiment comprises: transmitting a rate indicator signal on a reverse link rate indicator channel when there is traffic being transmitted on the reverse link traffic channel, the rate indicator signal corresponding to the rate of traffic being transmitted on the reverse link traffic channel and controlling the target SNR for the outer loop of the mobile station based on the traffic being transmitted on the reverse link traffic channel; and periodically transmitting a zero-rate indicator on the reverse rate indicator channel and controlling the target SNR based on the zero-rate indicator when there is no traffic being transmitted on the reverse traffic channel.

Many other embodiments are possible.

Drawings

Various aspects and features of the present invention are disclosed herein by the following detailed description and the introduction to the drawings, in which:

fig. 1 is a block diagram of an exemplary wireless communication system in accordance with one embodiment;

fig. 2 is a functional block diagram of the basic structural components of a wireless transceiver system in accordance with one embodiment;

FIG. 3 is a schematic diagram of a plurality of channels between a mobile station and a base station in accordance with one embodiment;

fig. 4 is a functional block diagram of a structure for a reverse link enhanced supplemental channel (R-ESCH) with an encoder packet size of 768 or 1536 bits, according to one embodiment;

FIG. 5 is a functional block diagram of a general structure of a reverse link rate indication channel (R-RICH) in accordance with one embodiment;

FIG. 6 is a flow chart of operation of a mobile station in accordance with one embodiment; and

fig. 7 is a flow chart of operation of a base station in accordance with one embodiment.

While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood that the drawings and detailed description are not intended to limit the invention to the particular embodiments which are described, in any way.

Detailed Description

One or more embodiments of the present invention are described below. It should be noted that these examples, and any other examples described below, are exemplary and are intended to be illustrative of the invention rather than limiting.

As described herein, embodiments of the present invention include systems and methods for controlling the power level of a mobile station during periods when the mobile station is not transmitting data. As noted above, power control in wireless communication systems is typically based on the signal-to-noise ratio (SNR) and the error rate associated with received frames. The power level of a mobile station is typically controlled by directing the mobile station to increase its power level when the received SNR falls below a target SNR, and to decrease its power level when the received SNR is above the target SNR. The target SNR is similarly increased when the base station receives a frame from the mobile station with an error therein, and the SNR is decreased when the frame received from the mobile station has no error therein.

In one embodiment of a wireless communication system, communication is effectuated between a base station and a mobile station by way of a plurality of wireless communication channels. Some of these channels carry continuous data traffic (e.g., data frames), while others are used only intermittently. One of the intermittently used channels includes a reverse link enhanced supplemental channel (R-ESCH). The R-ESCH is used in conjunction with a reverse link rate indicator channel (R-RICH). When a data frame is transmitted on the R-ESCH, an indicator corresponding to the rate of data transmission on the R-ESCH is transmitted on the R-RICH. Conventionally, when no data is transmitted on the R-ESCH, no rate indication information is transmitted on the R-RICH either. In one embodiment of the invention, a "zero-rate" indicator is transmitted on the R-RICH during some portion of the period when no data is being transmitted on the R-ESCH and rate indication information is being transmitted normally. For example, the "zero-rate" indicator may be transmitted in the first and fifth milliseconds of a20 millisecond frame period. This "zero rate" indicator is used by the base station to determine the power level that the mobile station should use. Thus, when the fading characteristics of a mobile station change, the base station can remain aware of the fading characteristics through the "zero rate" indicator even if the mobile station is not transmitting data, and thus can determine an inappropriate power level for the mobile station.

In one embodiment, the R-ESCH may be used to transmit data from the mobile station to the base station in either a scheduled mode or an autonomous mode. In this embodiment, the transmission in either mode uses a power control algorithm of the type described above. In other words, when no data is being transmitted, a "zero rate" indicator is periodically transmitted to the base station to enable the base station to determine the decoding quality of the received signal and update the target SNR currently suitable for outer-loop power control. Thus, at the start of data transmission, the target SNR of the outer loop is set appropriately. In either mode, once data transmission has begun, control of the power control target SNR level may be conventionally handled (i.e., by increasing or decreasing the target SNR based on whether the received frame has errors).

In an alternative embodiment, the power control method described above may be used in autonomous mode, while transmissions in scheduled mode use a different method. For example, in the scheduling mode, a predetermined target SNR may be used for data transmission that is high enough to ensure with reasonable certainty that the frames at the beginning of the transmission will be received without errors. In this embodiment, the control of the power control target SNR level may be handled conventionally by increasing or decreasing the level based on the frame error rate from the beginning of the data transmission.

A preferred embodiment of the present invention is implemented in a wireless communication system that generally conforms to a release of the cdma2000 specification. cdma2000 IS a third generation (3G) wireless communication standard based on the IS-95 standard. The cdma2000 standard has evolved and continues to evolve to continue to support new services. The preferred embodiments of the present invention are contemplated for use in systems using release D of the CDMA2000 standard, but other embodiments may be implemented in other releases of CDMA2000 or in systems conforming to other standards (e.g., W-CDMA). The embodiments described herein should therefore be considered in an illustrative rather than in a limiting sense.

Referring to fig. 1, a block diagram of an exemplary wireless communication system is shown. As shown in this figure, system 100 includes a base station 110 configured to communicate with a plurality of mobile stations 120. Mobile station 120 may be, for example, a cellular telephone, a personal information manager (PIM or PDA), or such a device configured for wireless communication. It should be noted that these devices need not actually be "mobile," but may simply be able to communicate with base station 110 via a wireless link. Base station 110 transmits data to mobile stations 120 via corresponding Forward Link (FL) channels, while mobile stations 120 transmit data to base station 110 via corresponding Reverse Link (RL) channels.

It should be noted that for purposes of this disclosure, like items in the figures will be represented by like reference numerals followed by lower case letters, e.g., 120a, 120b, etc. These items may be collectively referred to herein by the reference numeral.

Base station 110 is also connected to switching station 130 by a wired link. The link to switching station 130 allows base station 110 to communicate with a number of other system components, such as a data server 140, a public switched telephone network 150, or the internet 160. It should be noted that the mobile stations and system components in this figure are exemplary and other systems may comprise other types and combinations of devices.

In actual practice, however, the specific designs of base station 110 and mobile station 120 may vary widely, each acting as a wireless transceiver for communications on the forward and reverse links. Therefore, the base station 110 and the mobile station 120 have the same general structure. This configuration is shown in figure 2.

Referring to fig. 2, a functional block diagram of the basic structural components of a wireless transceiver system in accordance with one embodiment is shown. As shown, the system includes a transmit subsystem 222 and a receive subsystem 224, both of which are coupled to an antenna 226. Transmit subsystem 222 and receive subsystem 224 may be collectively referred to as a transceiver subsystem. Transmit subsystem 222 and receive subsystem 224 access the forward and reverse links through antenna 226. Transmit subsystem 222 and receive subsystem 224 are also coupled to processor 228, processor 228 being configured to control transmit and receive subsystems 222 and 224. Memory 230 is coupled to processor 228 to provide workspace and local storage for the processor. A data source 232 is coupled to processor 228 to provide data for transmission by the system. The data source 232 may include, for example, a microphone or an input from a network device. After being processed by processor 228, the data is provided to transmit subsystem 222, which transmits the data via antenna 226. Data received by receive subsystem 224 through antenna 226 is provided to processor 228 for processing and then to a data output 234 for presentation to a user. Data output 234 may include, for example, a speaker, a visual display, or an output to a network device.

It will be apparent to those skilled in the art that the configuration shown in fig. 2 is illustrative and that other embodiments may use alternative configurations. For example, processor 350, which may be a general purpose microprocessor, a Digital Signal Processor (DSP) or a special purpose processor, may perform some or all of the functions of other components of the transceiver or any other processing required by the transceiver. The scope of the claims appended hereto are therefore not limited to the particular configurations mentioned herein.

In view of the implementation of the architecture of fig. 2 in a mobile station, the components of the system can be viewed as a transceiver subsystem coupled to a processing subsystem, where the transceiver subsystem is responsible for receiving and transmitting data over a wireless channel, and the processing subsystem is responsible for preparing and providing data for transmission to the transceiver subsystem, as well as receiving and processing data it obtains from the transceiver subsystem. The transceiver subsystem may be considered to include a transmit subsystem 222, a receive subsystem 224, and an antenna 226. The processing subsystem may be considered to include a processor 228, a memory 230, a data source 232, and a data output 234.

As noted above, the communication link between the base station and the mobile station actually comprises a plurality of channels. Referring to fig. 3, a diagram illustrates a plurality of channels between a mobile station and a base station. As shown in this figure, base station 110 transmits data to mobile station 120 over a set of forward link channels 310. These channels typically include a traffic channel, through which data is transmitted, and a control channel, through which control signals are transmitted. Each traffic channel typically has one or more control channels associated with it. Forward link channels 310 may include, for example, a forward fundamental channel (F-FCH) that may be used to transmit low-speed data, a forward supplemental channel (F-SCH) that may be used for high-speed, point-to-point communication, or a forward high-speed broadcast channel (F-HSBCH) that may be used to broadcast messages to multiple information receivers. The channels may also include a forward paging channel (F-PCH), a forward broadcast control channel (F-BCCH), or a forward dedicated control channel (F-DCCH) for conveying control information regarding traffic channels or other aspects of the operation of the system.

Mobile station 120 transmits data to base station 110 via a set of reverse links 320. In addition, these channels typically include both traffic and control channels. Mobile station 120 may transmit data back to the base station on such channels as a reverse access channel (R-ACH), an extended reverse access channel (R-EACH), a reverse request channel (R-REQCH), a reverse enhanced supplemental channel (R-ESCH), a reverse dedicated control channel (R-DCCH), a reverse common control channel (R-CCCH), or a reverse rate indicator channel (R-RICH). Two of these channels, the R-ESCH and the R-RICH (represented by reference numerals 321 and 322 in FIG. 3), are particularly noteworthy because the power control mechanism of the present invention is implemented in both channels in one embodiment.

In one embodiment, the R-ESCH is used to transmit high-speed data from the mobile station to the base station. Data may be transmitted on the R-ESCH at rates ranging from 9.6kbps to 1228.8 kbps. Data is transmitted in a subframe of 5 ms. The general structure of R-ESCH is shown in FIG. 4.

Referring to fig. 4, a schematic block diagram of the structure of the R-ESCH for encoder packets having sizes of 768 or 1536 bits is shown. It should be noted that in this embodiment, the structure will vary when used in conjunction with other sized packets (192, 384, 2304, 3072, 4608 or 6144 bits). This structure may vary in implementation in other embodiments. The structure of fig. 4 is only an example of a possible structure.

As shown in fig. 4, a 16-bit packet CRC is first added to the information bits to be transmitted in block 410. A 6-bit turbo encoder tail trim amount (tailallowance) is added in block 420 so that the current packet size is 768 or 1536 bits (corresponding to a received packet size of 746 or 1514 bits, respectively). Turbo coding (block 430) and block interleaving (block 440) are then performed on the packet. The resulting symbols are modulated (block 450) and covered with walsh codes (block 460). Since these operations are well known to those skilled in the art, they will not be described in detail here.

The R-RICH is used by the mobile station to transmit a rate indicator that indicates the transport format used on the R-ESCH. One rate indicator is sent for each sub-packet transmitted on the R-ESCH. In one embodiment, the rate indicator includes five bits. Three of these five bits represent the size of the corresponding sub-packet on the R-ESCH. The correspondence between these three bits and the packet size is shown in table 1 below.

TABLE 1

Packet size bits of rate indicator	Encoder packet size
		000	192
001	384
		010	763
011	1536
		100	2304
101	3072
		110	4608
111	6144

The other two of the five bits of the rate indicator represent the sub-packet identifier of the corresponding sub-packet on the R-ESCH. For example, in this embodiment, each packet is divided into four sub-packets each of 5 milliseconds, and thus the sub-packet identifier indicates which of the four sub-packets (1, 2, 3, or 4) corresponds to the rate identifier. The correspondence between these bits and the sub-packet identifier is shown in table 2 below.

TABLE 2

Rate indicator sub-packet bits	Sub-packet sequence number (SPID)
		00	1
01	2
		10	3
11	4

Referring to FIG. 5, a block diagram of the general structure of the R-RICH of a preferred embodiment is shown. It should be noted that this structure is exemplary and that variations are possible in other embodiments. As shown in fig. 5, these five bits in the rate indicator are first processed by the quadrature encoder of block 510. Sequence repetition is then performed on the encoded symbols in block 520. The sequence selector 530 next selects either the encoded symbols or the zero-rate indicator, as will be explained in more detail below. Next, in block 550, signal point mapping is performed on each bit of the selected indicator (either the actual rate indicator or the zero rate indicator). The resulting signal is then covered by the appropriate walsh code (block 560). Since these operations are well known to those skilled in the art, they will not be described in further detail herein.

As described above, power control is performed in a conventional manner while data is being transmitted on the R-ESCH. In other words, when the base station receives data from the mobile station, the base station determines whether the SNR of the received signal is higher or lower than the target SNR. If the received SNR is above the target SNR, the base station directs the mobile station to reduce its power level. If the received SNR is below the target SNR, the base station directs the mobile station to increase its power level. The target SNR is adjusted based on whether the received frame contains errors. If the frame contains errors, the target SNR is too low, and thus it is increased. If the frame contains no errors, the target SNR is considered at least somewhat too high and is therefore reduced. Typically, the step size by which both the power level of the mobile station and the target SNR of the base station are increased is much larger than the step size by which they are decreased. For example, the ratio of the size of the increasing step size to the size of the decreasing step size may be 100: 1. Thus, for example, if there are errors in the received data, the power level is increased rapidly, but if there are no errors, the power level is decreased very slowly.

The problem encountered when using this method is caused by the fact that the R-ESCH can be used intermittently. In other words, there may be data transfer on this channel for a period of time, after which the channel may not be used for a while. When no data is transmitted on the R-ESCH, transmission errors cannot be detected, and thus the target SNR cannot be increased and/or decreased based on such errors. The inner loop may continue to update the transmit power based on the channel that is continuously present, but cannot adjust the target SNR. Therefore, if the channel quality of the R-ESCH changes during a period of no data transmission, the target SNR last used when the next data transmission starts may be inappropriate. If this target SNR is too high, the mobile station will unnecessarily consume power and also will cause unnecessary interference with transmissions from other mobile stations. If the target SNR is too low, the originally transmitted frame will contain too many errors to be of any use. Thus, in a preferred embodiment, a zero-rate indicator is periodically transmitted on the R-RICH channel when no data is being transmitted on the R-ESCH, providing a reference only for outer-loop power control. It should be noted that the term "zero rate indicator" as used herein refers to any indicator transmitted when no data is being transmitted on the traffic channel, and is not limited to an indicator that explicitly indicates that the traffic channel data rate is zero.

In the embodiment shown in fig. 5, a zero-rate indicator of "1" is provided to the bit repetition module 540 and the resulting bit stream is provided to the sequence selector 530. If no data is being transmitted on the R-ESCH, a zero-rate signal input to sequence selector 530 is required, resulting in a zero-rate indicator to be selected. This indicator is processed in the same way as the rate indicator when data is transmitted on the R-ESCH.

Although the zero-rate indicator may be transmitted at all times during the time that no data is being transmitted on the R-ESCH, a preferred embodiment transmits the zero-rate indicator only during a portion of the time that no data is being transmitted on the R-ESCH. For example, a20 ms frame may be divided into four 5ms subframes. In a preferred embodiment, the zero-rate indicator is transmitted only during one of the four subframes, e.g., during the first subframe.

When the base station receives the zero-rate indicator, it decodes it, and the base station uses the result of this decoding to determine whether the target SNR for the corresponding mobile station should be adjusted up or down. In one embodiment, the target SNR is increased by 1dB if decoding fails and decreased by 0.1dB if decoding succeeds. The base station's choice of the ratio of decrease to increase is based on the desired zero-rate indicator decoding error rate.

In one embodiment, the mobile station always causes the rate indicator channel to transmit at the same traffic-to-pilot ratio regardless of whether a zero rate indicator or a non-zero rate indicator is being sent. The base station estimates the decoding error rate on the rate indicator channel when there is data to transmit. It then uses this target error rate to set the increment and decrement values used to update the target SNR based on the zero-rate indicator. For example, the base station may count the number k of rate indicators that were misinterpreted during the last 100 subpackets. When the mobile station transmits the zero-rate indicator without transmitting any data on the reverse link, the target SNR is increased by 1dB if the decoding of the zero-rate indicator is erroneous, and the target SNR is decreased by 1/(100/k-1) dB if the decoding of the zero-rate indicator is successful. This ensures that the error rate of the zero-rate indicator will remain around k/100.

The received zero-rate indicator may be processed in a number of different ways. For example, a zero rate indicator may be used to determine the velocity profile of the mobile station. This can be done using a variety of techniques known in the art, such as a plane crossing technique. Once the velocity profile is determined, it can be used to adjust the target SNR. This velocity reduces the performance of the receiver and decoder because the velocity of the mobile station towards or away from the base station causes doppler shifts in the signal transmitted from the mobile station. If the velocity profile of the mobile station is known, the target SNR can be controlled to compensate for the resulting degradation.

The zero rate indicator may also be processed in a variety of other ways, such as by finding the energy density of the zero rate indicator signal and comparing it to the pilot signal. The reliability metric may also be used to determine the reliability of the zero-rate indicator signal. If the signal is determined to be reliable, the SNR is deemed to be sufficiently high, thus reducing the target SNR for the respective mobile station. If the signal is determined to be unreliable, the power level of the received rate indicator is too low, thus increasing the target SNR. These and other techniques may be used in various alternative embodiments of the present invention.

Referring to fig. 6, a flow chart of mobile station operation according to one embodiment of the present invention is shown. In this figure, the mobile station first determines whether there is data to be transmitted (block 610). If there is data to be transmitted, the data may be transmitted by scheduled or autonomous transmissions, as described elsewhere in this disclosure. When the data is transmitted on the reverse link traffic channel, a rate indicator corresponding to each subframe of data on the reverse link traffic channel is transmitted on a reverse link rate indicator channel (block 620). However, if there is no data to transmit, a zero-rate indicator is periodically transmitted on the reverse link rate indicator channel (block 630). In one embodiment, the zero-rate indicator is transmitted in the first 5ms of each 20ms frame.

Referring to fig. 7, a flow chart of a base station operation according to one embodiment of the invention is shown. As shown in fig. 7, based on the received rate indicator, the base station checks the reverse link rate indicator channel (block 710) and determines whether data is being transmitted (block 720). If a non-zero rate indicator is received, the base station knows that the corresponding subframe was transmitted on the reverse link traffic channel. The base station translates the received subframe according to the received rate indicator and adjusts the target SNR based on the error condition in the received data (block 730). If a zero-rate indicator is received on the reverse link rate indicator channel, the base station knows that no data is being transmitted on the reverse link traffic channel, so the base station adjusts the target SNR based on the zero-rate indicator (block 740).

By providing a zero-rate indicator on the R-RICH, the system is able to perform power control operations without transmitting control information on the R-FCH or R-DCCH. This will greatly reduce the overhead. It should also be noted that the R-RICH can be used to provide additional channel estimates for R-ESCH demodulation by using it as an additional pilot. This function may be performed at a lower power level than the power level used to transmit the rate indicator corresponding to the R-ESCH data transmission.

In a preferred embodiment, data transfer on the R-ESCH may be performed in either of two modes: a scheduled transmission mode or an autonomous transmission mode. As the names of these modes indicate, the mobile station may interact with the base station to acquire the specified time of day for transmitting data on the R-ESCH, or under certain conditions, the mobile station may autonomously initiate a data transmission on the R-ESCH without first acquiring the specified transmission time of day.

In one embodiment, the reverse link is designed to maintain a rise-over-thermal (rise-over-thermal) of the base station at a relatively fixed level as long as there is reverse link data to be transmitted, while still allowing each mobile station to transmit at the highest data rate that each mobile station can achieve. This design attempts to provide the time division multiplexing gain required on the reverse link, yet allows mobile stations with small amounts of data to autonomously transmit their data in order to minimize the delay in transmitting the data. As mentioned above, the reverse link is designed to provide these features by allowing the mobile station to transmit data on the R-ESCH in two different ways: by autonomous transport; and transmitted by scheduling.

Autonomous transmission is used to transmit traffic that cannot tolerate much delay. Autonomous transmissions are used to reduce delay and controlled overhead for delay sensitive data and are particularly useful for transmissions from mobile stations at the cell edge where overhead costs are high. At any time the mobile station has data to transmit, the mobile station can autonomously transmit the data up to a certain transmission rate determined by the base station. The maximum data transfer rate is set based on the ratio (T/P) of the maximum traffic signal to the pilot signal specified by the base station during call setup. This T/P can be modified by subsequent signaling between the base station and the mobile station. The maximum T/P is different for different mobile stations and is related, among other things, to the quality of service (QoS) requirements of different mobile stations.

Autonomous transmission is particularly useful when small amounts of data need to be transmitted. Autonomous transmissions are characterized by small latency, which is the time elapsed before a data transmission (i.e., the amount of time the data must wait before it is transmitted). Autonomous transmissions use the same hybrid automatic repeat request (H-ARQ) mechanism as scheduled transmissions. In some cases, however, the mobile station may not be able to transmit at a rate higher than the lowest rate, and as such, it may be too costly for the base station to send an acknowledgement to the mobile station, and therefore scheduled transmissions cannot be used. In these cases, the autonomous transmission may be established by layer 3 signaling, thereby eliminating the need for the mobile station to monitor the forward link control channel for this purpose. In alternative embodiments, this information may be communicated by other means, such as a Handoff Direction Message (HDM) on the traffic channel.

Scheduling transmission is used when the T/P that can be supported by the mobile station is at least one level higher than the maximum T/P for autonomous transmission, and the data in the mobile station buffer is sufficient to fill at least one complete packet larger than the packet supported by the maximum T/P for autonomous. In determining whether these conditions are met, the mobile station uses autonomous transmissions that will occur during the delay between the request for a scheduled transmission and the grant of the scheduled transmission.

If the request for scheduled transmission is granted, the mobile station sends the request through a 5ms message on a request channel (e.g., R-REQCH). Alternatively, the request may be transmitted over a control channel (e.g., R-DDCH). The request includes four bits indicating the T/P supported by the R-ESCH, four bits indicating the queue size of the mobile station, and four bits indicating the QoS level required for the transmission. In response to receiving the request, the base station transmits a grant message to the mobile station. This message may convey either individual licenses or common licenses. Thus, the grant may be transmitted over a forward grant channel (e.g., T-GCH) or a forward common grant channel (e.g., F-CGCH). The individual grants specifically grant a scheduled transmission time period for the mobile station, while the common grant allows any mobile station that wishes to transmit to do so.

After transmitting a request to the base station, the mobile station needs to wait a predetermined amount of time (minimum re-request delay, or T _ MRRD) before sending another scheduled transmission request. The T _ MRRD is transmitted to the mobile station by layer 3 signaling. To allow recovery from lost request messages while preventing premature requests, the mobile station needs to wait this amount of time before re-requesting a scheduled transmit grant.

The base station can schedule transmissions from any requesting mobile station. The scheduling decisions of the base stations may be based on factors such as the Soft Handoff (SHO) status of the mobile station. The scheduling decision may be made by the receiving base station alone or by all base stations in the active set simultaneously. The inclusion of all active set members may result in longer scheduling delays, but may also save the energy required for grants due to diversity.

Various aspects and features of the present invention have been described with respect to specific embodiments. As used herein, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion of the elements or limitations which follow the terms. Thus, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment.

While the invention will be described with reference to specific embodiments, it will be understood that these embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is intended that all such variations, modifications, additions and improvements fall within the scope of the invention as detailed within the following claims

Within the scope of the invention.

Claims (45)

1. A system for wireless communication comprising:

a base station; and

a mobile station;

wherein the base station and mobile station are configured to communicate over a plurality of wireless communication channels including a reverse link traffic channel and a reverse link rate indicator channel;

wherein when the mobile station is transmitting traffic on the reverse link traffic channel, the mobile station transmits a corresponding rate indicator on the reverse link rate indicator channel, and when the mobile station is not transmitting traffic on the reverse link traffic channel, the mobile station periodically transmits a zero rate indicator on the reverse link rate indicator channel; and

wherein when the base station receives data on the reverse link traffic channel, the base station performs power control based on the received data, and when the base station does not receive data on the reverse link traffic channel, the base station performs power control based on the zero-rate indicator.

2. The system of claim 1, wherein the system conforms to a release of the cdma2000 specification.

3. The system of claim 2, wherein the reverse link traffic channel comprises a reverse link enhanced supplemental channel (R-ESCH).

4. The system of claim 2, wherein the reverse link indication channel comprises a reverse link rate indication channel (R-RICH).

5. The system of claim 1, wherein the zero-rate indicator is transmitted during a partial period in each frame period, wherein the partial period comprises less than an entire frame period.

6. The system of claim 5, wherein each frame comprises a plurality of subframes, wherein the zero-rate indicator is transmitted in one or more of the subframes.

7. The system of claim 6, wherein the rate indicator is transmitted in one subframe of each frame.

8. The system of claim 7, wherein each frame comprises a period of 20ms, the frame being divided into four sub-frames each of 5 ms.

9. A mobile station operable to communicate with a base station over a wireless communication channel, wherein the mobile station comprises:

a processing subsystem; and

a transceiver subsystem coupled to the processing subsystem and configured to transmit data on a reverse link traffic channel and a reverse link rate indicator channel;

wherein the processing subsystem is configured to cause the transceiver subsystem to perform the following functions:

transmitting a rate indicator signal on the reverse link rate indicator channel when traffic is being transmitted on the reverse link traffic channel, wherein the rate indicator signal corresponds to the rate of the traffic being transmitted on the reverse link traffic channel, an

Periodically transmitting a zero-rate indicator on the reverse link rate indicator channel when there is no traffic being transmitted on the reverse link traffic channel.

10. The mobile station of claim 9, wherein the mobile station conforms to a version of the cmda2000 specification.

11. The mobile station of claim 10, wherein the reverse link traffic channel comprises a reverse link enhanced supplemental channel (R-ESCH).

12. The mobile station of claim 10, wherein the reverse link indication channel comprises a reverse link rate indication channel (R-RICH).

13. The mobile station of claim 9, wherein the zero-rate indicator is transmitted during a partial period of each frame period, wherein the partial period comprises a period less than an entire frame period.

14. The mobile station of claim 13, wherein each frame comprises a plurality of subframes, wherein the zero-rate indicator is transmitted in one or more of the subframes.

15. The mobile station of claim 14, wherein the rate indicator is transmitted in one subframe of each frame.

16. The mobile station of claim 15, wherein each frame comprises a period of 20ms, the frame being divided into four sub-frames each of 5 ms.

17. A base station operable to communicate with a mobile station over a wireless communication channel, wherein the base station comprises:

a processing subsystem; and

a transceiver subsystem coupled to the processing subsystem and configured to transmit data on a reverse link traffic channel and a reverse link rate indicator channel;

wherein when the base station receives data on the reverse link traffic channel, the base station performs power control based on the received data, and when the base station does not receive data on the reverse link traffic channel, the base station performs power control based on the zero-rate indicator.

18. The base station of claim 17, wherein the base station conforms to a release of the cdma2000 specification.

19. The base station of claim 18, wherein the reverse link traffic channel comprises a reverse link enhanced supplemental channel (R-ESCH).

20. The base station of claim 18 wherein the reverse link indicator channel comprises a reverse link rate indicator channel (R-RICH).

21. The base station of claim 17, wherein when the base station receives data on the reverse link traffic channel, the base station is configured to perform power control by directing a mobile station from which the data is received to increase a power level associated with the mobile station when a signal-to-noise ratio (SNR) of the received data is below a target SNR and to decrease the power level associated with the mobile station when the SNR of the received data is above the target SNR.

22. The base station of claim 17, wherein when the base station does not receive data on the reverse link traffic channel, the base station is configured to perform power control by calculating a reliability metric for the zero-rate indicator, increasing a power level of a mobile station from which the zero-rate indicator is received when the reliability metric indicates that the zero-rate indicator is unreliable, and decreasing the power level when the reliability metric indicates that the zero-rate indicator is reliable.

23. The base station of claim 17, wherein when the base station does not receive data on the reverse link traffic channel, the base station is configured to perform power control by calculating a velocity profile of a mobile station from which the zero-rate indicator is received based on the power of the zero-rate indicator and adjusting the power level of the mobile station based on the calculated velocity profile.

24. The base station of claim 17, wherein when the base station does not receive data on the reverse link traffic channel, the base station is configured to perform power control by calculating a power density of the zero-rate indicator and adjusting a power level of a mobile station from which the zero-rate indicator is received based on the calculated power density.

25. A method performed in a system having a reverse link traffic channel and a reverse link rate indicator channel, wherein the method comprises:

when traffic is being transmitted on the reverse link traffic channel,

transmitting a rate indicator signal on said reverse link rate indicator channel, wherein said rate indicator signal corresponds to the rate of said traffic being transmitted on said reverse link traffic channel, an

Controlling a power level based on the traffic being transmitted on the reverse link traffic channel; and

when no traffic is being transmitted on the reverse link traffic channel,

periodically transmitting a zero-rate indicator on the reverse link rate indicator channel, an

Controlling the power level based on the zero-rate indicator.

26. The method of claim 25, wherein the reverse link traffic channel comprises a cdma2000 reverse link enhanced supplemental channel (R-ESCH).

27. The method of claim 25, wherein the reverse link indicator channel comprises a cmda2000 reverse link rate indicator channel (R-RICH).

28. The method of claim 25, wherein the zero-rate indicator is transmitted during a partial period of each frame period, wherein the partial period comprises a period of less than an entire frame period.

29. The method of claim 28, wherein each frame comprises a plurality of subframes, wherein the zero-rate indicator is transmitted in one or more of the subframes.

30. The method of claim 29, wherein the zero-rate indicator is transmitted in one subframe of each frame.

31. The method of claim 30, wherein each frame comprises a period of 20ms, the frame being divided into four sub-frames each of 5 ms.

32. A method performed in a mobile station operable to communicate with a base station via a wireless communication link, wherein the method comprises:

transmitting a rate indicator signal on a reverse link rate indicator channel if the mobile station has data to transmit, wherein the rate indicator signal corresponds to a rate of traffic being transmitted on a reverse link traffic channel; and

transmitting a zero-rate indicator on the reverse link rate indicator channel if the mobile station has no data to transmit.

33. The method of claim 32, wherein the reverse link traffic channel comprises a cdma2000 reverse link enhanced supplemental channel (R-ESCH).

34. The method of claim 32, wherein the reverse link indicator channel comprises a cmda2000 reverse link rate indicator channel (R-RICH).

35. The method of claim 32, wherein the zero-rate indicator is transmitted during a partial period of each frame period, wherein the partial period comprises a period of less than an entire frame period.

36. The method of claim 35, wherein each frame comprises a plurality of subframes, wherein the zero-rate indicator is transmitted in one or more of the subframes.

37. The method of claim 36, wherein the zero-rate indicator is transmitted in one subframe of each frame.

38. The method of claim 37, wherein each frame comprises a period of 20ms, the frame being divided into four sub-frames each of 5 ms.

39. A method performed in a base station operable to communicate with a mobile station over a wireless communication link, wherein the method comprises:

when traffic is being received on the reverse link traffic channel,

controlling a power level based on the traffic being transmitted on the reverse link traffic channel; and

when no traffic is received on the reverse link traffic channel,

receiving a null rate indicator transmitted periodically on a reverse link rate indicator channel, an

Controlling the power level based on the zero-rate indicator.

40. The method of claim 39, wherein the reverse link traffic channel comprises a cdma2000 reverse link enhanced supplemental channel (R-ESCH).

41. The method of claim 39, wherein the reverse link indicator channel comprises a cmda2000 reverse link rate indicator channel (R-RICH).

42. The method of claim 39, wherein controlling the power level based on the traffic being transmitted on the reverse link traffic channel comprises directing a mobile station from which the data is received to increase a power level associated with the mobile station when a signal-to-noise ratio (SNR) of the received data is below a target SNR and to decrease the power level associated with the mobile station when the SNR of the received data is above the target SNR.

43. The method of claim 39, wherein controlling the power level based on the zero-rate indicator comprises calculating a reliability metric for the zero-rate indicator, increasing the power level of the mobile station from which the zero-rate indicator is received when the reliability metric indicates that the zero-rate indicator is unreliable, and decreasing the power level when the reliability metric indicates that the zero-rate indicator is reliable.

44. The method of claim 39, wherein controlling the power level based on the zero-rate indicator comprises calculating a velocity profile of a mobile station from which the zero-rate indicator was received based on the power of the zero-rate indicator, and adjusting the power level of the mobile station based on the calculated velocity profile.

45. The method of claim 39, wherein controlling the power level based on the zero-rate indicator comprises calculating a power density of the zero-rate indicator and adjusting the power level of a mobile station from which the zero-rate indicator is received based on the calculated power density.