HK1084789A - Modified power control for hybrid arq on the reverse link - Google Patents

Description

Improved power control for hybrid ARQ on the reverse link

Technical Field

The disclosed embodiments relate generally to the field of communications and, more particularly, to a method and apparatus for improved power control for H-ARQ on the reverse link.

Technical Field

The field of communications encompasses a variety of applications including, for example, paging, Wireless Local Loop (WLL), internet telephony, and satellite communication systems. A typical application is a cellular telephone system for mobile subscribers. Modern communication systems designed to allow multiple users to access a common communication medium have been developed for such cellular systems. These communication systems may be based on Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), or other multiple access techniques known in the art. These multiple access techniques decode and demodulate signals received from multiple users, thereby enabling simultaneous communication among multiple users and providing relatively large communication system capacity.

In a CDMA system, the available spectrum may be efficiently shared among a large number of users, and techniques such as soft handoff are used to maintain sufficient quality to support delay-sensitive services (e.g., voice) without wasting a large amount of power. Recently, systems capable of enhancing the capacity of data services have also become available. These systems provide data services by using higher order modulation, faster power control, faster scheduling, and more efficient scheduling for services with relaxed delay requirements. One example of such a data services communication system IS a high speed data rate (HDR) system that conforms to the telecommunications industry association/electronic industries association (TIA/EIA) cdma2000 high speed data rate air interface specification IS-856(IS-856 standard), published in month 1 2002.

In a CDMA system, data transmission occurs from a source device to a destination device. The target device receives the data transmission, demodulates the signal, and decodes the data. As part of the decoding process, the target device performs a Cyclic Redundancy Code (CRC) check on the data packet to determine whether the packet was received correctly. If the packet is received in error, the target device sends a Negative Acknowledgement (NAK) message on its Acknowledgement (ACK) channel to the source device, where the source device responds to the NAK message by retransmitting the packet that was received in error.

Transmission errors can be particularly severe in certain applications where the bit energy-to-noise power spectral density ratio (Eb/No) is low. In this case, conventional data retransmission schemes, such as automatic repeat request (ARQ), may not meet (or may be designed not to meet) the maximum Bit Error Rate (BER) required for system operation. In this case, the ARQ scheme is generally used in combination with an error correction scheme such as Forward Error Correction (FEC) to enhance performance. This combination of ARQ and FEC is commonly referred to as hybrid ARQ (H-ARQ).

The target device receives the data transmission and retransmission, demodulates the signal, and separates the received data into a new packet and a retransmitted packet after sending the NAK. The new packet and the retransmitted packet do not have to be transmitted simultaneously. The destination device accumulates the energy of the received retransmission packet with the energy of the packet received in error, which has been accumulated by the destination device. The target device then attempts to decode the accumulated data packets. However, if the packet frame (packet frame) is initially transmitted with insufficient energy to allow correct decoding by the target device, as described above, and then retransmitted, the retransmission provides time diversity. Therefore, the total transmit energy (including retransmissions) of the frame is lower on average. On average, the combined symbol energy for the initial transmission and retransmission of the frame is lower than the energy required to initially transmit the frame at full power (e.g., at a power level that is sufficient on its own to allow correct decoding by the target device). In this way, the accumulation of additional energy provided by subsequent retransmissions will increase the probability of correct decoding. Alternatively, the target device may decode the retransmitted packet itself without combining the two packets. In both cases, throughput can be improved because the packet received in error is retransmitted while a new data packet is transmitted. Further, it should be noted that the new packet and the retransmitted packet need not be transmitted simultaneously.

In the reverse link (e.g., the communication link from the remote terminal to the base station), a reverse supplemental channel (R-SCH) is used to convey user information (e.g., packet data) from the remote terminal to the base station and to support retransmissions at the physical layer. The R-SCH may utilize different coding schemes for the retransmission. For example, the retransmission may use the code rate 1/2 for the original (original) transmission. The coded symbols of the same code rate 1/2 are repeated for retransmission. In an alternative case, the underlying code may also be a code rate of 1/4. The original transmission may use 1/2 of the symbol and the retransmission may use the other half of the symbol. An example of a reverse link architecture is described in detail in U.S. patent application No.2002/0154610 entitled "REVERSE LINK channel architecture FOR A WIRELESS communication system" assigned to the assignee of the present invention.

In CDMA communication systems, particularly in systems adapted for packet transmission, congestion and overload may reduce the throughput of the system. Congestion is a measure of the amount of pending and active traffic relative to the rated capacity of the system. System overload occurs when suspended and active traffic exceeds the rated capacity. The system may implement a target congestion level to maintain traffic state without interruption, e.g., to avoid resource overload and resource underrun.

One problem with overloading is the occurrence of delayed transmission responses. An increase in response time typically results in an application level timeout, where the application requiring the data waits longer than the application is programmed to allow, resulting in a timeout condition. The application will then not need to retransmit the timeout message, which will cause further congestion. If this state continues, the system may reach a state where no service is provided to the user. One solution to this state (for HDR) is congestion control. Another solution (for cdma2000) is proper scheduling.

By monitoring the data rates of both suspended and active users, and monitoring the received signal strength required to achieve a desired quality of service, the level of congestion in the system can be determined. In wireless CDMA systems, reverse link capacity is interference limited. One measure of cell congestion is the total amount of noise at the base station over the entire level of thermal noise (hereinafter referred to as the "rise-over-thermal" (ROT)). The ROT corresponds to the reverse link load. The loaded system attempts to maintain the ROT close to a predetermined value. If the ROT is too high, the cell range (i.e., the range of distances over which the base station of the cell can communicate) will decrease and the stability of the reverse link will decrease. The cell range is reduced due to the increased transmit energy required to provide the target energy level (energy level). A high ROT will also cause small variations in the instantaneous load, which will result in large excursions in the remote terminal output power. A low ROT can indicate that the reverse link is not heavily loaded, thereby indicating that the available capacity may not be fully utilized.

However, operating the R-SCH with H-ARQ requires that the initial transmission of the R-SCH frame not be power controlled as strictly as possible to meet the ROT constraint. Thus, the signal-to-noise ratio (SNR) of the initial transmission of the communicated R-SCH frame may be below a level sufficient to allow correct decoding of the received data packet.

Thus, from the foregoing, it should be apparent that there exists a need in the art for an apparatus and method that enables improved power control for H-ARQ on the reverse link.

Disclosure of Invention

Embodiments disclosed herein address a need for an apparatus and method that enables improved power control for H-ARQ on the reverse link in a wireless communication system.

In one aspect, a method and apparatus for power control of a reverse link in a wireless communication system is described. An initial transmission of a data frame in a reverse link is received and a first energy level of the data frame is measured. If the first energy level is insufficient to correctly decode the data frame, an energy deficit in the first energy level is determined such that the data frame can be correctly decoded with combined energy of the first energy level and the second energy level when the data frame is retransmitted with a second energy level equal to a difference between the first energy level and the energy deficit.

In another aspect, a base station for a wireless communication system is described. The base station includes an RF front end configured to receive and appropriately amplify, filter, and process reverse link traffic channel data frames from the remote terminals, and a Digital Signal Processor (DSP) for demodulating and further processing the received data frames. The base station further comprises a power controller having an energy measuring means and a deficit estimating means. The energy measurement device is configured to measure a first energy level of the data frame. The deficit estimation means is configured to estimate an energy deficit of the first energy level if the first energy level is insufficient to correctly decode the data frame, such that the data frame can be correctly decoded with combined energy of the first energy level and the second energy level when the data frame is retransmitted with a second energy level equal to a difference between the first energy level and the energy deficit.

Other features and advantages of the present invention will become apparent from the following description of exemplary embodiments, which illustrate, by way of example, the principles of the invention.

Brief Description of Drawings

FIG. 1 is a diagram of an exemplary wireless communication system that supports a large number of users and is capable of implementing various aspects of the invention;

FIG. 2 is a simplified block diagram of one embodiment of a base station and a remote terminal of the communication system of FIG. 1;

FIG. 3 illustrates an exemplary forward link ACK channel according to the acknowledgement scheme discussed herein;

FIG. 4 illustrates an exemplary forward link ACK channel that operates under the assumption that the remote terminal can identify which base station is the best base station; and

fig. 5 is a flow chart depicting an exemplary method for implementing the improved power control technique operating in conjunction with an acknowledgement scheme such as that of fig. 3 or fig. 4.

Detailed Description

The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The term "exemplary" used throughout this description means "serving as an example, instance, or illustration," and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the present invention.

In light of the above-described need for an apparatus and method that enables improved power control for hybrid automatic repeat request (H-ARQ) on the reverse link, the present disclosure describes exemplary embodiments for efficiently allocating, utilizing, and controlling reverse link resources. In particular, improved power control provides power control commands that enable a remote terminal to deliver an amount of energy on a retransmission to compensate for an energy deficit on an initial transmission.

While various aspects of the invention will be described in the context of a CDMA communication system, those skilled in the art will appreciate that the techniques described herein for providing efficient operation of the forward link ACK channel are also applicable to a variety of other communication environments, including communication systems based on TDMA, FDMA, SDMA, PDMA, and other multiple access techniques known in the art, and communication systems based on AMPS, GSM, HDR, and various CDMA standards, and other communication standards known in the art. Accordingly, any description relating to a CDMA communications system is intended only to illustrate the inventive aspects of the present invention, with the understanding that these inventive aspects have a wide range of applications.

Fig. 1 is a diagram of an exemplary wireless communication system 100 that supports a large number of users and is capable of implementing various aspects of the invention. Communication system 100 provides communication for a large number of cells, each of which is served by a corresponding Base Station (BS) 104. Various remote terminals 106 are dispersed throughout the system 100. Individual base stations or remote terminals may be identified by alphabetic suffixes, such as 104a or 106 c. Reference numerals 104 or 106 without a letter suffix should be understood to refer to the base station and the remote terminal in the general sense.

At any particular moment, each remote terminal 106 may communicate with one or more base stations 104 on the forward and reverse links depending on whether each remote terminal 106 is activated and whether it is in soft handoff. The forward link refers to transmissions from base stations 104 to remote terminals 106, and the reverse link refers to transmissions from remote terminals 106 to base stations 104. As shown in fig. 1, base station 104a communicates with remote terminals 106a, 106b, 106c, and 106d, and base station 104b communicates with remote terminals 106d, 106e, and 106 f. The remote terminal 106d is in a soft handoff state and is simultaneously communicating with the base stations 104a and 104 b.

In the wireless communication system 100, a Base Station Controller (BSC)102 communicates with base stations 104 and also with the Public Switched Telephone Network (PSTN). Typically, communication with the PSTN is accomplished via a Mobile Switching Center (MSC) (not shown in fig. 1 for simplicity). The BSC may also typically effect communication with the packet network via a Packet Data Serving Node (PDSN), which is also not shown in fig. 1. The BSC 102 provides coordination and control for the base stations 104. BSC 102 also controls the routing of telephone calls between remote terminals 106, between remote terminals 106 and users communicating with the PSTN (i.e., conventional telephones), and to the packet network, via base stations 104.

Fig. 2 is a simplified block diagram of an embodiment of a base station 104 and a remote terminal 106 capable of implementing various aspects of the present invention. For particular communications, voice data, packet data, and/or messages may be exchanged between base station 104 and remote terminal 106. Various types of messages may be communicated, such as messages used to establish a communication session between the base station and the remote terminal, and messages used to control data transmission (e.g., power control, data rate information, acknowledgements, etc.). Some of these message types will be described below. In particular, the use of a forward link ACK channel to implement reverse link data acknowledgement is described in detail.

For the reverse link, at the remote terminal 106, voice and/or packet data (e.g., from a data source 210) and messages (e.g., from a controller 230) are provided to a Transmit (TX) data processor 212, which transmit data processor 212 formats the data and messages and encodes them with one or more coding schemes to generate coded data. Each coding scheme may include any combination of Cyclic Redundancy Check (CRC), convolutional, Turbo, block, and other coding, or no coding at all. Typically, voice data, packet data, and messages are encoded using different schemes, and different types of messages may also be encoded differently.

The encoded data is then provided to a Modulator (MOD)214 and further processed (e.g., covered (cover), spread with short PN sequences, and scrambled with a long PN sequence assigned to the user terminal). The modulated data is then provided to a transmitter unit (TMTR)216 and conditioned (e.g., converted to one or more analog signals, amplified, filtered, and quadrature modulated) to generate a reverse link signal. The reverse link signal is routed through a duplexer (D)218 and transmitted via an antenna 220 to base station 104.

At base station 104, the reverse link signal is received by an antenna 250, routed through a duplexer 252, and provided to a receiver unit (RCVR) 254. Receiver unit 254 conditions (e.g., filters, amplifies, frequency downconverts, and digitizes) the received signal and provides samples. A demodulator (DEMOD)256 receives and processes (e.g., despreads, decovers, and pilot demodulates) the samples to provide recovered symbols. Demodulator 256 may be implemented as a Rake receiver that may process multiple instances (instances) of the received signal and generate a combined signal. A Receive (RX) data processor 258 then decodes the symbols to recover the data and messages transmitted on the reverse link. The recovered voice/packet data is provided to a data sink 260 and the recovered messages are provided to a controller 270. The processing by demodulator 256 and RX data processor 258 are complementary to that performed at remote terminal 106. Demodulator 256 and RX data processor 258 may also be operated to process multiple transmissions received via multiple channels, e.g., a reverse fundamental channel (R-FCH) and a reverse supplemental channel (R-SCH). Further, multiple transmissions may be received simultaneously from multiple remote terminals, each of which may be transmitting on a reverse fundamental channel, a reverse supplemental channel, or both.

On the forward link, at base station 104, voice and/or packet data (e.g., from a data source 262) and messages (e.g., from controller 270) are processed (i.e., formatted and encoded) by a Transmit (TX) data processor 264, further processed (i.e., enveloped and spread) by a Modulator (MOD)266, and conditioned (e.g., converted to analog signals, amplified, filtered, and quadrature modulated) by a transmitter unit (TMTR)268 to generate a forward link signal. The forward link signal is routed through duplexer 252 and transmitted via antenna 250 to remote terminal 106.

If the message from controller 270 in the forward link includes a power control command, controller 270 will act as a power controller that calculates the traffic/pilot ratio (T/P) by measuring the energy level of the reverse traffic channel (i.e., R-SCH) relative to the energy level of the reverse pilot channel. The measured T/P value is compared to a total T/P value sufficient to allow correct decoding of the R-SCH frame by the base station to generate a T/P delta value that is transmitted to the remote terminal to enable the remote terminal to deliver an amount of energy on a retransmission to compensate for the energy deficit of the initial transmission.

At remote terminal 106, the forward link signal is received by antenna 220, routed through duplexer 218, and provided to a receiver unit 222. Receiver unit 222 conditions (i.e., downconverts, filters, amplifies, quadrature demodulates, and digitizes) the received signal and provides samples. The samples are processed (e.g., despreaded, decovered, and pilot demodulated) by a demodulator 224 to provide symbols, and the symbols are processed (e.g., decoded and checked) by a receive data processor 226 to recover the data and messages transmitted on the forward link. The recovered data is provided to a data sink 228 and the recovered messages are provided to a controller 230.

The reverse link has some characteristics that are very different from those of the forward link. In particular, data transmission characteristics, soft handoff behavior, and fading phenomena often vary greatly between the forward link and the reverse link. For example, the base station typically cannot know a priori which remote terminals have packet data to transmit, or how much data to transmit. In this way, the base station allocates resources to the remote terminal and the resources are available whenever requested by the remote terminal. Usage on the reverse link may fluctuate widely due to uncertainty in the user's requirements.

According to exemplary embodiments of the present invention, an apparatus and method capable of efficiently allocating, utilizing, and controlling reverse link resources are provided. The reverse link resources may be allocated via a supplemental channel (e.g., R-SCH) used for packet data transmission. In particular, a reliable acknowledgement scheme and an efficient retransmission scheme are provided. An efficient retransmission scheme also involves improved power control to enable remote terminals to deliver an appropriate amount of energy in retransmissions to compensate for the energy deficit in the initial transmission.

A reliable acknowledgement scheme and an efficient retransmission scheme should take into account several factors that control the communication between the base station and the remote terminal. One of the factors to consider includes the fact that when the path loss from multiple base stations to a remote terminal is about a few dB greater than the minimum path loss from one base station to the remote terminal (e.g., the base station is in close proximity to the remote terminal), which is in the active set of the remote terminal, the base stations have a relatively small chance of correctly receiving the reverse supplemental channel (R-SCH) frame.

In order for soft handoff to work and reduce the remote terminal transmit power, the remote terminal needs to receive an indication of these lost or bad R-SCH frames. Since the remote terminal is about to receive more negative acknowledgements than positive acknowledgements, a typical acknowledgement scheme (see fig. 3) is configured such that the Base Station (BS) sends an Acknowledgement (ACK) for a good frame to the Remote Terminal (RT), and the base station sends a Negative Acknowledgement (NAK) for a bad frame to the remote terminal only if the received bad R-SCH frame has enough energy, i.e., if the energy of the bad frame is combined with the energy from the retransmission of the R-SCH frame, the combined energy should be sufficient to allow correct decoding of the frame by the base station. The base station will not generate a NAK signal in response to the bad frame having insufficient energy (even when combined with retransmission energy) to allow correct decoding of the frame by the base station. Thus, if the remote terminal does not receive an ACK or NAK signal, the remote terminal assumes that the bad frame received at the base station has insufficient energy to allow correct decoding of the frame, even if combined. In this case, the remote terminal needs to retransmit the frame with a default transmission level sufficient to allow correct decoding. In one embodiment, the default transmission level may be predetermined so that correct decoding may be performed by the base station. In another embodiment, the default transmission level may be dynamically determined according to the transmission state of the wireless CDMA system.

Fig. 3 illustrates the operation of an exemplary forward link ACK channel in accordance with the acknowledgement scheme discussed above with respect to the device of fig. 2. In the illustrated embodiment, the remote terminal transmits an R-SCH frame to one or more base stations. The base station receives the R-SCH frame and transmits an ACK signal if the received R-SCH frame is recognized as a "good" frame.

In one embodiment, the quality of the received R-SCH frame is identified (i.e., identified as "good" or "bad") by observing the reverse link pilot signal, or equivalently, based on power control bits transmitted by the remote terminal. Thus, a frame is considered "good" if the reverse link pilot signal includes sufficient energy to allow correct decoding of the frame by the base station. Otherwise, if the reverse link pilot signal includes insufficient energy to permit correct decoding of the frame by the base station, the frame is considered "bad".

If the received R-SCH frame is identified as a "bad" frame, but has sufficient energy to combine with the retransmission, the base station's typical forward link ACK channel transmits a NAK signal with a traffic-to-pilot ratio (T/P) delta. This occurs when the received bad R-SCH frame has sufficient energy such that if combined with energy from the retransmission of the R-SCH frame, it is sufficient to allow correct decoding of the frame by the base station.

As described above, the traffic/pilot ratio (T/P) may be calculated by measuring the ratio between the energy levels of the reverse traffic channel (e.g., R-SCH) and the reverse pilot channel. Thus, in this embodiment, the ratio is used for power control of the R-SCH and is compared to the total energy level sufficient to allow correct decoding of the R-SCH frame by the base station. The difference between the initially transmitted T/P value and the total energy level sufficient to allow correct decoding provides a parameter called T/P delta. In general, the total energy level is the energy level required to maintain a certain quality of service (QoS), which depends on speed, channel conditions, and other parameters related to QoS.

In one embodiment, the traffic-to-pilot ratio (T/P) varies with the rate of the remote terminal for a given target QoS (e.g., target Frame Error Rate (FER)). The T/P of the pilot energy level required for a given FER may be calculated and averaged for three different possible remote terminal rates (high (e.g., 120km/hr.), low (e.g., 30km/hr.), and static (e.g., Additive White Gaussian Noise (AWGN) at 0 km/hr.). The obtained average value is stored in a gain table such as that shown in "3 GPP2 physical layer standard for cdma2000 spread spectrum system" with document number c.p0002-a published by TIA/EIAIS-2000-2-a on 19/11/1999.

For example, to estimate the T/P ratio for the total energy level required for a remote terminal moving at 120km/hr (i.e., high rate and fast fading), the T/P values in the gain table may be compared to the T/P values for AWGN (i.e., no fading). The difference may be about 2 dB. This value can then be used as an estimate of the total energy level sufficient to allow correct decoding of the R-SCH frame by the base station in the above-described T/P delta calculation. Different QoS parameters may be used to make different estimates of the T/P ratio for the total energy level as long as the estimate meets the ROT requirement for congestion control.

Thus, the T/P delta provides a differential energy value that the remote terminal must deliver in transmission to compensate for the energy deficit in the initial transmission and to enable the base station to correctly decode the R-SCH frame on the reverse link. The calculated T/P delta may be transmitted to the remote terminal along with an acknowledgement signal on the forward ACK channel. In the case where two or more base stations are in the active set of the remote terminal and the two base stations send NAK signals in different T/P increments in response to bad R-SCH frames, the remote terminal selects the one base station with the lower T/P increment so that at least one base station can have sufficient energy to correctly decode the packet.

Errors in the T/P delta bits of the T/P transmitted to the remote terminal for controlling congestion power control will cause the T/P value to differ from the desired value. However, the base station typically monitors the level of the reverse pilot channel for reverse power control or for channel estimation. The base station may also monitor the energy level of the received R-SCH frame. By obtaining the ratio of the R-SCH energy level to the reverse pilot channel energy level, the base station can estimate the T/P used by the remote terminal. If the T/P is not the desired T/P, the base station sets a bit that controls the T/P to correct for the discrepancy. Thus, there is self-correction of bit errors in the T/P delta.

The base station will not send a NAK signal (i.e., NULL data) when the received bad R-SCH frame, when combined with retransmission energy, has insufficient energy to permit correct decoding of the R-SCH frame by the base station. The remote terminal recognizes this "NULL" condition as a signal from the base station to the remote terminal to retransmit the R-SCH frame at a default transmission level sufficient to permit correct decoding.

The acknowledgement scheme as shown in fig. 3 may be further optimized if the remote terminal is able to detect or determine which base station has the smallest path loss to the remote terminal (i.e., the best base station). In one embodiment, the base station can measure the energy deficit of the actual received frame relative to the power control target (as is done in closed power control) to determine which base station has the smallest path loss to the remote terminal. By averaging the energy deficit over a large number of frames, the base station can determine whether it is the best base station. The information may be transmitted to a remote terminal. In an alternative embodiment, the best base station can be easily determined if the remote terminal is operating in the data/voice (DV) mode of a 1xEv-DV system. In this mode, both the base station and the remote terminal must know which base station is the best base station.

Fig. 4 illustrates a typical forward link ACK channel operating under the assumption that the remote terminal recognizes which base station is the best base station. Thus, in the illustrated embodiment, the remote terminal transmits the R-SCH frame to the best base station and one or more secondary base stations(s). Since typically the best base station will receive a large number of "good" frames and there are many more "good" frames than "bad" frames, the acknowledgement scheme from the best base station will tend not to send the ACK signal for "good" frames but rather to send the NAK signal for "bad" frames. Since the second best base station will receive a large number of "bad" frames and there are far more "bad" frames than "good" frames, the second best base station will tend to the opposite situation. Thus, the acknowledgement scheme from the second best base station will tend to send an ACK signal for "good" frames, but not a NAK signal for "bad" frames.

Thus, in response to receiving the R-SCH frame from the remote terminal, if the received R-SCH frame is identified as a "good" frame, the typical forward link ACK channel of the best base station no longer transmits an ACK signal (i.e., NULL data). The remote terminal recognizes the "NULL" condition as a signal from the best base station and indicates that the transmitted R-SCH frame was received with sufficient energy to permit correct decoding and that there is no need to retransmit the frame. If the received R-SCH frame is identified as a "bad" frame, but has sufficient energy to combine with the retransmission, the best base station transmits a NAK signal with a T/P delta. This condition occurs when the received bad R-SCH frame has sufficient energy such that if combined with energy from the retransmission of the R-SCH frame, it is sufficient to allow correct decoding of the frame by the best base station. If the received bad R-SCH frame, combined with retransmission energy, has insufficient energy to allow correct decoding of the frame by the best base station, then the best base station transmits a NAK signal without a T/P delta. In this way, the remote terminal retransmits the R-SCH frame with a default transmission level sufficient to allow correct decoding.

In response to receiving the R-SCH frame from the remote terminal, the exemplary forward link ACK channel of the secondary base station sends an ACK signal if the received R-SCH frame is recognized as a "good" frame. If the received R-SCH frame is identified as a "bad" frame, but has sufficient energy to combine with the retransmission, the secondary base station sends a NAK signal with a T/P delta. This condition occurs when the received bad R-SCH frame has sufficient energy such that if combined with energy from the retransmission of the R-SCH frame, it is sufficient to allow correct decoding of the frame by the secondary base station. In contrast to the best base station, the secondary base station does not send a NAK signal (i.e., NULL data) when the received bad R-SCH frame, combined with retransmission energy, has insufficient energy to permit correct decoding of the frame by the base station. The remote terminal recognizes this "NULL" condition as a signal from the secondary base station to the remote terminal to retransmit the R-SCH frame with a default transmission level sufficient to allow correct decoding.

A flowchart illustrating an exemplary method of implementing the improved power control operation described above in conjunction with the acknowledgement schemes of fig. 3 or 4 is shown in fig. 5. In a first operation, at box 500, a first energy level of a reverse traffic channel is measured. In a first embodiment, the energy level is the energy level measured on the R-SCH. At box 502, a second energy level is measured on the reverse pilot channel. Then, at box 504, a ratio (T/P) between the first energy level and the second energy level is calculated. At box 506, the total energy level sufficient for correct decoding of the R-SCH frame is estimated. At box 508, a T/P delta is calculated by taking the difference between the total energy level and T/P. Finally, at box 510, the T/P delta is appropriately transmitted on the forward ACK channel, causing the remote terminal to deliver the appropriate amount of energy in the retransmission to compensate for the energy deficit in the initial transmission. The conditions under which the T/P delta may be transmitted on the forward ACK channel are specified according to the procedures described for the acknowledgement schemes of fig. 3 or fig. 4.

As described above, improved power control can improve the use of the reverse link and can also allow data frames to be transmitted at lower transmit power. For example, without retransmission, the data frame needs to be transmitted at the higher power level (P1) required to achieve one percent frame error rate (1% FER). If retransmission is used and is reliable, the data frame will be transmitted at a lower power level (P2) required to achieve a frame error rate of ten percent (10% FER). These 10% erased frames may be retransmitted to achieve an overall 1% FER for the transmission (i.e., 10% to 1%). In addition, the retransmission provides time diversity, which will improve performance. The retransmitted frame may also be combined at the base station with the initial transmission of the frame, and this recombination may enable the erasure frame to be retransmitted at a lower energy level.

Those skilled in the art will appreciate that method steps may be interchanged without departing from the scope of the invention. Those of skill in the art would further understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The methods or algorithms described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a subscriber station. In the alternative, the processor and the storage medium may reside as discrete components in a subscriber station.

The previous description of the disclosed 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 defined herein may be applied to other embodiments without departing from the scope or spirit of the invention. 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 (29)

1. A method for power control in a wireless communication system, comprising:

receiving an initial transmission of a data frame in a reverse link of the communication system;

measuring a first energy level of the data frame; and

estimating an energy deficit in the first energy level if the first energy level is insufficient to correctly decode the data frame, such that when the data frame is retransmitted with a second energy level equal to a difference between the first energy level and the energy deficit, the data frame can be correctly decoded with combined energy of the first energy level and the second energy level.

2. The method of claim 1, wherein measuring the first energy level of the data frame comprises measuring an energy level of a traffic channel in the reverse link.

3. The method of claim 2, wherein the traffic channel is a reverse supplemental channel (R-SCH) of the communication system.

4. The method of claim 2, wherein measuring the first energy level of the data frame further comprises measuring an energy level of a pilot channel in the reverse link.

5. The method of claim 4, wherein measuring a first energy level of the data frame further comprises calculating a ratio between the energy level of the traffic channel and the energy level of the pilot channel.

6. The method of claim 1, further comprising:

estimating a total energy level sufficient to correctly decode the data frame.

7. The method of claim 1, further comprising:

transmitting the energy deficit and an appropriate negative acknowledgement for receipt of the data frame on a forward acknowledgement channel.

8. A method for controlling power on a reverse link in a wireless communication system, comprising:

calculating a ratio between an energy level of a data frame and an energy of a pilot channel transmitted on the reverse link;

estimating an energy deficit ratio if the data frame is received in error, such that the energy deficit ratio enables a remote terminal to adjust the energy level of the data frame so that the data frame can be correctly decoded in a retransmission when the energy level of the data frame is combined with the energy level of the retransmission.

9. A reverse link power controller in a wireless communication system, comprising:

means for receiving an initial transmission of a data frame in the reverse link;

measuring means for measuring a first energy level of the data frame; and

estimating means for estimating an energy deficit in the first energy level if the first energy level is insufficient to correctly decode the data frame, such that the data frame can be correctly decoded with combined energy of the first energy level and the second energy level when the data frame is retransmitted with a second energy level equal to a difference between the first energy level and the energy deficit.

10. The power controller of claim 9 wherein the measuring means comprises means for measuring an energy level of a traffic channel in the reverse link.

11. The power controller of claim 10, wherein the traffic channel is a reverse supplemental channel (R-SCH) of the communication system.

12. The power controller of claim 10 wherein the measuring means comprises means for measuring an energy level of a pilot channel in the reverse link.

13. The power controller of claim 12 wherein the measuring means comprises means for calculating a ratio between the energy level of the traffic channel and the energy level of the pilot channel.

14. The power controller of claim 9, further comprising:

means for estimating a total energy level sufficient to correctly decode the data frame.

15. The power controller of claim 9, further comprising:

for transmitting the energy deficit and an appropriate negative acknowledgement for receipt of the data frame on a forward acknowledgement channel of the communication system.

16. A reverse link power controller in a wireless communication system, comprising:

a receiver configured to receive an initial transmission of a data frame in a reverse link of the communication system;

a measuring device configured to measure a first energy level of the data frame; and

an estimating device configured to estimate an energy deficit in the first energy level if the first energy level is insufficient to correctly decode the data frame, such that the data frame can be correctly decoded with combined energy of the first energy level and the second energy level when the data frame is retransmitted with a second energy level equal to a difference between the first energy level and the energy deficit.

17. The power controller of claim 16, wherein the measuring means comprises a first measuring device configured to measure an energy level of a traffic channel in the reverse link.

18. The power controller of claim 17, wherein the traffic channel is a reverse supplemental channel (R-SCH) of the communication system.

19. The power controller of claim 17, wherein the measuring means further comprises a second measuring device configured to measure an energy level of a pilot channel in the reverse link.

20. The power controller of claim 19, wherein the measuring means comprises a computing device configured to compute a ratio between the energy level of the traffic channel and the energy level of the pilot channel.

21. The power controller of claim 16, further comprising:

an estimator configured to estimate a total energy level sufficient to correctly decode the data frame.

22. The power controller of claim 16, further comprising:

a transmitter configured to transmit the energy deficit and an appropriate negative acknowledgement for receipt of the data frame on a forward acknowledgement channel.

23. A base station of a wireless communication system, the base station comprising:

an RF front end configured to receive, appropriately amplify, filter and process a reverse link traffic channel data frame from a remote terminal;

a Digital Signal Processor (DSP) for demodulating and further processing the received data frame; and

a power controller, comprising:

a measuring device configured to measure a first energy level of the data frame; and

an estimating device configured to estimate an energy deficit in the first energy level if the first energy level is insufficient to correctly decode the data frame, such that the data frame can be correctly decoded with combined energy of the first energy level and the second energy level when the data frame is retransmitted with a second energy level equal to a difference between the first energy level and the energy deficit.

24. The base station of claim 23, wherein the measuring means comprises a first measuring device configured to measure an energy level of a traffic channel in the reverse link.

25. The base station of claim 24, wherein the traffic channel is a reverse supplemental channel (R-SCH) of the communication system.

26. The base station of claim 24, wherein the measuring means further comprises a second measuring device configured to measure an energy level of a pilot channel in the reverse link.

27. The base station of claim 26, wherein the measurement device further comprises a computing apparatus configured to compute a ratio between the energy level of the traffic channel and the energy level of the pilot channel.

28. The base station of claim 23, further comprising:

an estimator configured to estimate a total energy level sufficient to correctly decode the data frame.

29. The base station of claim 23, further comprising:

a transmitter configured to transmit the energy deficit and an appropriate negative acknowledgement for receipt of the data frame on a forward acknowledgement channel.