HK1088144A - Operation of a forward link acknowledgement channel for the reverse link data - Google Patents

Description

Operation of a forward link acknowledgement channel on reverse link data

Technical Field

Embodiments of the present disclosure relate generally to the field of communications, and more particularly, to a method and apparatus for operating a forward link acknowledgement channel.

Background

The field of communications has many applications including, for example, paging, Wireless Local Loops (WLLs), internet telephony, and satellite communication systems. An exemplary application is a cellular telephone system for mobile subscribers. Modern communication systems designed to enable 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 allowing communication systems with relatively large capacity.

In a CDMA system, the available spectrum is efficiently shared among multiple users, and techniques such as soft handoff are applied to maintain sufficient quality so as to support delay-sensitive services (such as voice) without wasting a significant amount of power. Recently, systems for increasing data traffic capacity have been put into use. These systems provide data services for services with relaxed delay requirements by using higher order modulation, faster power control, faster scheduling, and more efficient scheduling. One example of a communication system for such data services IS a High Data Rate (HDR) system that conforms to the Telecommunications industry Association/electronics industry Association (TIA/EIA) cdma2000 high data rate air interface Specification IS-856(IS-856 Standard), month 1 2002.

In a CDMA system, data transmission occurs from a source device to a destination device. The destination device receives the data transmission, demodulates the signal, and decodes the data. As part of the decoding process, the destination device performs a Cyclic Redundancy Code (CRC) check on the data packet to determine whether the packet was received correctly. Error detection methods other than using CRC, such as energy detection, may also be used with or in place of CRC. If the received packet has errors, the destination device sends a Negative Acknowledgement (NAK) message on its Acknowledgement (ACK) channel to the source device, which responds to the NAK message by retransmitting the packet received with errors.

At low signal quality (e.g., low bit energy to noise power spectral density ratio (E)_b/N_o) In a mobile communication system), transmission errors may be particularly acute. In this case, conventional data retransmission schemes, such as automatic repeat request (ARQ), may not meet (or may be designed to not meet) the maximum Bit Error Rate (BER) required for system operation. In this case, a combination of an ARQ scheme and an error correction scheme, such as Forward Error Correction (FEC), is often utilized to improve performance. This combination of ARQ and FEC is commonly referred to as hybrid ARQ (H-ARQ).

After sending the NAK, the destination device receives the data transmission and retransmission, demodulates the signal, and separates the received data into new packets and retransmits the packets. The new packet and the retransmitted packet need not be transmitted at the same time. The destination device accumulates the energy of the received retransmitted packet with the energy that the destination device has accumulated for receiving packets with errors. The destination device then tries to decode the accumulated data packets. However, if the initially transmitted packet frame does not have sufficient energy for the destination device to decode correctly, the packet frame is retransmitted, which provides time diversity, as previously described. As a result, the total transmit energy (including retransmissions) for the frame is lower on average. On average, the combined symbol energy of both the initial transmission and retransmission of the frame is lower than the energy required to transmit the frame initially at full power (i.e., at a power level that is sufficient on its own for correct decoding by the destination device). Thus, accumulating the additional energy provided by subsequent retransmissions increases the probability of correct decoding. Alternatively, the destination device may be able to decode the retransmitted packet by itself without combining the two packets. In both cases, the retransmission of the erroneously received packet is performed simultaneously with the transmission of the new data packet, and therefore the throughput can be improved. Further, it should be noted that the new packet and the retransmitted packet need not be transmitted at the same time.

In the reverse link (i.e., the communication link from the remote terminal to the base station), a reverse supplemental channel (R-SCH) is used to transmit user information (e.g., packet data) from the remote terminal to the base station and to support retransmission at the physical layer. The R-SCH may apply different coding schemes for the retransmission. For example, the retransmission may use the code rate of 1/2 for the initial transmission. The code symbols of the same rate 1/2 may be repeated for the retransmission. In an alternative case, the base code (underlay code) may be an 1/4 rate code. The initial transmission may use 1/2 for the symbol and the retransmission may use the other half of the symbol. One embodiment of a reverse link architecture is described in detail in U.S. patent application No. 2002/154610, entitled "reverse link channel architecture for a wireless communication system," assigned to the assignee of the present invention.

In a CDMA communication system, and more particularly in a system suitable for packetized transmissions, congestion and overload may reduce the throughput of the system. Congestion is a measure of the amount of waiting (pending) and active (active) traffic relative to the rated capacity of the system. System overload occurs when waiting and active traffic exceeds rated capacity. The system can achieve a target congestion level to maintain the traffic state without interruption, i.e., to avoid overloading and underloading of resources.

One problem with overloading is the generation of delayed transmission responses. An increase in response time often results in application level timeouts, where an application requires data to wait longer than the application has programmed to allow, resulting in a timeout condition. Thus, the application will unnecessarily retransmit the message at the time-out, causing further congestion. If this situation continues, the system may reach a state where it cannot serve any user. One solution to this situation (used in HDR) is congestion control. Another solution (used in cdma 2000) is proper scheduling.

The level of congestion in a system can be assessed by monitoring the data rates of waiting and active users, and the received signal strength required to achieve a desired quality of service. In wireless CDMA systems, reverse link capacity is interference limited. One measure of cell congestion is the amount of noise at the base station over the level of thermal noise (hereinafter referred to as the "rise-over-thermal" (ROT)). The ROT corresponds to the load of the reverse link. The load system attempts to maintain the ROT near a predetermined value. If the ROT is too high, the range of the cell (i.e., the distance over which the cell's base station can communicate) may be reduced and the reverse link stability may be degraded. The range of the cell is reduced because the amount of transmission energy required to provide the target energy level is increased. A high ROT also causes small variations in the instantaneous load, which can result in large excursions in the output power of the remote terminal. A low ROT can indicate that the reverse link is not heavily loaded, thus indicating that the available capacity is potentially wasted.

However, operating the R-SCH with H-ARQ may require that the initial transmission of the R-SCH frame need not be power controlled very strictly to meet the ROT constraint. Thus, the delivered signal-to-noise ratio (SNR) of the initial transmission of the R-SCH frame may be below a level sufficient to allow correct decoding of the received data packet. This condition may result in a NAK message being sent on the reverse link ACK channel.

Therefore, from the above discussion, it should be apparent that a need exists in the art for an apparatus and method that can efficiently operate the reverse link ACK channel.

Disclosure of Invention

Embodiments disclosed herein address the need for an apparatus and method that can efficiently operate a reverse link ACK channel in conjunction with a packet data channel in a wireless communication system.

In one aspect, an acknowledgement method and apparatus of a wireless communication system includes receiving a reverse supplemental channel (R-SCH) frame at a base station. The base station then transmits a positive Acknowledgement (ACK) signal if the received R-SCH frame is indicated as good. A Negative Acknowledgement (NAK) signal is sent only if the quality of the received data frame is indicated as bad, but with sufficient energy such that if the received signal frame is combined with the energy of the data frame retransmission, it is sufficient to allow correct decoding of the data frame.

In another aspect, an acknowledgement method and apparatus of wireless communication includes transmitting a reverse supplemental channel (R-SCH) frame from a remote terminal to a base station. The base station then transmits a Negative Acknowledgement (NAK) signal to the remote terminal if the quality of the received R-SCH frame is indicated as bad. The remote terminal also recognizes that the lack of receipt of an acknowledgement indicates a positive Acknowledgement (ACK) signal, and that the quality of the received R-SCH frame is good, indicating a condition where the energy of the R-SCH frame is sufficient to permit correct decoding of the frame. The base station in this aspect is the best base station that provides the least path loss to the remote terminal.

In another aspect, an acknowledgment channel of a wireless communication system includes a block encoder, a mapper, and a mixer. The block encoder receives the ACK/NAK message having at least one bit and encodes the ACK/NAK message using the generator matrix to generate a codeword. The mapper maps the code words to a binary signal. The mixer mixes the binary signal with an orthogonal spreading code, such as a walsh code, to generate an encoded ACK/NAK signal.

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

Drawings

FIG. 1 is a schematic diagram of an exemplary wireless communication system supporting a number of users and capable of implementing various aspects of the present invention;

FIG. 2 is a simplified block diagram of an 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 operating in accordance with the acknowledgement scheme discussed herein;

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

FIGS. 5A through 5C illustrate a flow chart of an exemplary method of implementing an acknowledgement scheme operating on a forward link ACK channel; and

fig. 6 is a block diagram of an exemplary F-CPANCH.

Detailed Description

The detailed description set forth below in connection with the appended drawings is intended as an illustrative embodiment 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 implementations. The detailed description includes specific details for a thorough understanding of the 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.

Recognizing the above-identified need for an apparatus and method that enables efficient operation of the forward link ACK channel, this disclosure describes exemplary embodiments for efficiently allocating and utilizing reverse link resources. In particular, a reliable acknowledgement scheme and an efficient retransmission scheme are described in detail below that can improve the application to the reverse link and allow data frames to be transmitted at a lower transmit power.

Although various aspects of the invention are 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 equally applicable in 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 reference to a CDMA communications system is intended only to illustrate the inventive aspects of the present invention, with the understanding that such inventive aspects have a wide range of applications.

Fig. 1 is a schematic diagram of an exemplary wireless communication system 100 that supports multiple users and is capable of implementing various aspects of the present invention. Communication system 100 provides communication for a plurality of cells, each of which is served by a respective Base Station (BS) 104. Different remote terminals 106 are distributed throughout the system 100. Individual base stations or remote terminals will be identified by an alphabetic suffix such as 104a or 106 c. And reference numerals 104 or 106 without a letter suffix will be understood to refer to the base station and the remote terminal in the usual sense.

Each remote terminal 106 may communicate with one or more base stations 104 on the forward and reverse links at any particular moment, depending on whether the remote terminal is active and in soft handoff. The forward link refers to transmissions from the base station 104 to the remote terminal 106, and the reverse link refers to transmissions from the remote terminal 106 to the base station 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 while communicating with both base stations 104a and 104 b.

In the wireless communication system 100, a Base Station Controller (BSC)102 communicates with base stations 104 and may further communicate with a Public Switched Telephone Network (PSTN). Communication with the PSTN is typically accomplished via a Mobile Switching Center (MSC), which is not shown in fig. 1 for simplicity. The BSC may also communicate with a packet network, which is typically implemented via a Packet Data Serving Node (PDSN), which is also not shown in fig. 1. The BSC 102 is used to coordinate and control the base stations 104. BSC 102 further controls the routing of telephone calls between remote terminals 106, and between remote terminals 106 and users communicating with the PSTN (e.g., conventional telephones) and users 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, which are capable of implementing various aspects of the present invention. For particular communications, voice data, packet data, and/or messages may be exchanged between the base station 104 and the remote terminal 106. Different types of messages may be transmitted, 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 types of these messages are described below. In particular, implementation of reverse link data acknowledgement by utilizing a reverse link ACK channel is detailed.

For the reverse link, at 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 formats and encodes the data and messages 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, as well as different types of messages.

The encoded data is then provided to a Modulator (MOD)214 and further processed (e.g., covered (cover) with short PN sequences, spread, 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 duplexer (D)218 and transmitted via antenna 220 to base station 104.

At base station 104, the reverse link signal is received by an antenna 250, transmitted 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 implement a rake receiver that processes the received signals for multiple instances and generates combined symbols. 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 may be provided to a controller 270. The processing by demodulator 256 and RX data processor 258 are complementary to that performed by remote terminal 106. Demodulator 256 and RX data processor 258 may further 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). Likewise, transmissions may be received simultaneously from multiple remote terminals, each of which may be transmitted 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 (e.g., formatted and encoded) by a Transmit (TX) data processor 264, further processed (e.g., covered 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.

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 (e.g., down converts, 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 further 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 very different characteristics than the forward link. In particular, data transmission characteristics, soft handoff behavior, and fading phenomena are typically very different between the forward and reverse links. For example, the base station typically does not know in advance which remote terminal has packet data to send, or how much data to send. In this way, the base station may allocate resources for the remote terminal whenever requested and when available. Usage on the reverse link may fluctuate widely because of uncertainty in user demand.

In accordance with exemplary embodiments of the present invention, apparatus and methods are provided for efficiently allocating and utilizing reverse link resources. 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.

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 the base station has a path loss that is about a few dB greater than the base station with the smallest path loss to the remote terminal (e.g., the base station closest to the remote terminal), but has relatively little chance of correctly receiving the reverse supplemental channel (R-SCH) frame in the active set of the remote terminal.

In order for soft handoff to occur and the transmit power of all remote terminals to be reduced, the remote terminals need to receive indications of these lost or bad R-SCH frames. Since the remote terminal is going to receive significantly more negative acknowledgements than positive acknowledgements, an exemplary acknowledgement scheme (see fig. 3) is configured such that for good frames, the Base Station (BS) sends an Acknowledgement (ACK) to the Remote Terminal (RT), while for bad frames, the Base Station (BS) sends a Negative Acknowledgement (NAK) to the Remote Terminal (RT) only if the received bad R-SCH frame has enough energy such that, if combined with the energy retransmitted from the R-SCH frame, it would be sufficient for the base station to correctly decode the frame. The NAK signal will not be sent if the bad frame does not have enough energy (even when combined with the energy of the retransmission) to allow the base station to perform correct decoding of the frame. Thus, when the remote terminal does not receive an ACK or NAK signal, the remote terminal will assume that the bad frame received by the base station does not have sufficient energy to allow correct decoding of the frame. In this case, the remote terminal will not need to retransmit frames having a default transmission level sufficient to allow correct decoding. In one embodiment, such default transmission levels may be predetermined to enable correct decoding by the base station. In another embodiment, the default transmit level may be dynamically determined based on transmission conditions of the wireless CDMA system.

Fig. 3 illustrates an exemplary forward link ACK channel consistent with the acknowledgement scheme described above. In the illustrated embodiment, the remote terminal transmits an R-SCH frame to the base station. The base station receives the R-SCH frame and transmits an ACK signal if the received R-SCH frame is identified as a "good" frame.

In one embodiment, the quality of the received R-SCH frame (i.e., whether it is a "good" or "bad" frame) can be identified 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 the base station to correctly decode the frame. Otherwise, if the reverse link pilot signal includes insufficient energy for the base station to correctly decode the frame, the frame is considered "bad".

The exemplary forward link ACK channel of the base station sends a NAK signal with a traffic-to-pilot ratio (T/P) delta if the received R-SCH frame is identified as a "bad" frame but with sufficient energy to combine with the retransmission. This condition occurs when the received bad R-SCH frame has enough energy that, if combined with energy from the retransmission of the R-SCH frame, is sufficient for the base station to correctly decode the frame.

The traffic-to-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, this ratio is used for power control of the R-SCH and compared to the total energy level sufficient to allow the base station to correctly decode the R-SCH frame. The difference between the initially transmitted T/P value and the total energy level sufficient to allow correct decoding of the R-SCH frame provides a parameter called T/P delta. Generally, 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 QoS related parameters. Thus, the T/P delta provides a differential energy value that must be delivered by the remote terminal upon retransmission to compensate for the lack of energy in the initial transmission and to allow the base station to correctly decode the R-SCH frame on the reverse link. The computed T/P delta may be transmitted to the remote terminal on the forward ACK channel along with an acknowledgement signal. In the event that two or more base stations are in the active set of the remote terminal and both base stations transmit NAK signals with different T/P deltas in response to bad R-SCH frames, the remote terminal should select the signal with the lower T/P delta so that at least one base station can correctly decode the packet.

Furthermore, when the received bad R-SCH frame, combined with the retransmitted energy, does not have enough energy to allow the base station to correctly decode the frame, then the base station will not send a NAK signal (i.e., NULL data). The remote terminal should recognize this "NULL" condition as a signal from the base station to the remote terminal to retransmit the R-SCH frame with a default transmission level sufficient to permit correct decoding.

The acknowledgement scheme illustrated in fig. 3 can be further optimized if the remote terminal can detect or identify which base station has the least path loss to the remote terminal (i.e., the best base station). In one embodiment, a pattern of power control commands from the base station to the remote terminal is used to determine which base station is the best base station. For example, the base station may measure the energy deficit of the actual received frame relative to a power control target (as in closed loop power control) to determine which base station is the best base station. By averaging the energy deficit over some frames, the base station can determine whether it is the best base station. The information may also be transmitted to a remote terminal. For another embodiment, the base station can measure the pattern of power control up/down bits to determine which base station is the best base station.

In an alternative embodiment, the optimal 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 need to know which base station is the best base station. In this way, the remote terminal indicates the channel quality measurement of the optimal base station to the base station using a reverse channel quality indication channel (R-CQICH).

However, with either of the above embodiments, there may still be a period of time when neither end (base station or remote terminal) needs to synchronize with respect to which base station is the best base station. Thus, in one embodiment, during a collision between the two ends, the base station designated and not designated as the best base station is set to send both an ACK signal (when the frame is good) and a NAK signal (when the frame is bad), so that the remote terminal is not confused.

Fig. 4 illustrates an exemplary 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 an R-SCH frame to the best base station and the secondary base station. Since the best base station will receive many more "good" frames than "bad" frames, the acknowledgement scheme of the best base station is biased toward not sending an ACK signal for "good" frames but sending a NAK signal for "bad" frames. While the secondary base station will receive many more "bad" frames than "good" frames, it will be biased towards the reverse. Thus, the acknowledgement scheme of the secondary base station will favor sending an ACK signal for "good" frames but not a NAK signal for "bad" frames.

Thus, in response to receipt of the R-SCH frame by the remote terminal, the exemplary forward link ACK channel of the best base station does not transmit an ACK signal (i.e., NULL data) if the received R-SCH frame is recognized as a "good" frame. The remote terminal should recognize this "NULL" condition as a signal from the best base station that the transmitted R-SCH frame was received with sufficient energy to permit correct decoding and without the 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 sends a NAK signal with a T/P delta. This may occur when the received bad R-SCH frame has enough energy that, if combined with the energy of the retransmission of the R-SCH frame, would be sufficient to allow the best base station to correctly decode the frame. If the received bad R-SCH frame, combined with retransmission energy, does not have enough energy to allow the best base station to decode the frame correctly, the best base station sends 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.

However, if the received R-SCH frame is recognized as a "good" frame, then the exemplary forward link ACK channel of the secondary base station will transmit an ACK signal in response to receiving the R-SCH frame from the remote terminal. If the received R-SCH frame is identified as a "bad" frame but has enough energy to combine with the retransmission, the secondary base station will send a NAK signal with a T/P delta. This may occur when the received bad R-SCH frame has enough energy such that if combined with the energy of the retransmission of the R-SCH frame, it would be sufficient to enable correct decoding of the frame by the secondary 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, does not have enough energy to allow the base station to correctly decode the frame. The remote terminal should recognize this "NULL" condition as a secondary base station to remote terminal signal to retransmit the R-SCH frame with a default transmission level sufficient to allow correct decoding.

An exemplary method for implementing the above-described acknowledgement scheme operating on the forward link ACK channel is illustrated in the flow diagrams shown in fig. 5A through 5C. At block 500, a determination is made as to whether the remote terminal is in a state where the terminal has knowledge of which base station has the smallest path loss to the remote terminal (i.e., the best base station). As described above, this may be determined by measuring the energy deficit of the actually received frame relative to the power control target. By averaging the energy deficit over a sufficient number of frames, the base station can determine whether it is the best base station. Such information may be transmitted to the remote terminal. If the remote terminal is operating in the data/voice (DV) mode of a 1xEv-DV system, both the base station and the remote terminal must know which base station is the best base station. Thus, in the DV mode, it will not be necessary to determine which base station is the best base station.

If at block 500 the remote terminal is unable to determine which base station is the best base station, a "no" will result, and then if the received R-SCH frame is identified as a "good" frame, the base station that received the R-SCH frame will send an ACK signal (at block 504). The quality of the received R-SCH frame may be identified (i.e., either "good" or "bad" identified) according to the process described above.

At block 506, a determination is made whether the received bad R-SCH frame has sufficient energy such that, if combined with the energy of the retransmission of the R-SCH frame, it would be sufficient to allow the base station to correctly decode the frame. If this is the case, the exemplary forward link ACK channel of the base station transmits a NAK signal with a T/P delta at block 508. Otherwise, the base station will not send a NAK signal (i.e., NULL data) for the bad R-SCH frame, at block 510. The remote terminal should recognize this "NULL" condition as a signal from the base station to the remote terminal to retransmit the R-SCH frame with a default transmission level sufficient to permit correct decoding.

If the remote terminal is able to determine which base station is the best base station at block 500, block 500 outputs "yes," and then at block 502 it will be determined whether the source of the ACK/NAK signal is the "best" base station or the "secondary" base station. If the source is the "best" base station, then at block 512, the exemplary forward link ACK channel of the best base station will not send an ACK signal (i.e., NULL data) in response to the "good" frame. The remote terminal recognizes this "NULL" condition as a signal from the best base station that the transmitted R-SCH frame is received with sufficient energy to be correctly decoded and that no retransmission of the frame is required.

At block 514, a determination is made whether the received bad R-SCH frame has sufficient energy that, if combined with energy from retransmission of the R-SCH frame, the frame will be correctly decoded by the base station. If this is the case, the exemplary forward link ACK channel of the best base station sends a NAK signal with a T/P delta at block 516. Otherwise, at block 518, 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.

If the source of the ACK/NAK signal is determined (at block 502) to be a secondary base station, then at block 520 the exemplary forward link ACK channel of the secondary base station sends an ACK signal in response to the "good" frame. At block 522, a determination is again made whether the received bad R-SCH frame has sufficient energy that, if combined with energy from retransmission of the R-SCH frame, the frame will be correctly decoded by the base station. If this is the case, the exemplary forward link ACK channel of the secondary base station transmits a NAK signal with a T/P delta at block 524. Otherwise, if the received bad R-SCH frame, combined with retransmission energy, does not have sufficient energy to allow the base station to correctly decode the frame, then the secondary base station does not send a NAK signal (i.e., NULL data) at block 526. The remote terminal should recognize this "NULL" condition as a secondary base station to remote terminal signal in order to retransmit the R-SCH frame with a default transmission level sufficient to allow correct decoding.

As described above, the base station sends Acknowledgements (ACKs) and Negative Acknowledgements (NAKs) for data transmission on the R-SCH. Further, the ACK/NAK may be transmitted by using a forward common packet acknowledgement channel (F-CPANCH). Fig. 6 is a block diagram of an exemplary F-CPANCH.

In one embodiment, the ACK and NAK are sent as n-bit ACK/NAK messages, each of which is associated with a corresponding data frame transmitted on the reverse link. As such, each ACK/NAK message may include 1, 2, 3, or 4 bits (or possibly more bits), where the number of bits in the message depends on the number of reverse link channels in the service configuration. The n-bit ACK/NAK message may be block coded to enhance reliability or transmitted in the clear. To improve reliability, the ACK/NAK message for a particular data frame may be retransmitted in a subsequent frame (e.g., 20 milliseconds later) to provide time diversity for the message. This time diversity provides additional reliability or can allow the power used to send the ACK/NAK messages to be reduced while maintaining the same reliability. The ACK/NAK message may use error correction coding as is known in the art. For retransmission, the ACK/NAK message may repeat exactly the same codeword, or increased redundancy may be used. The encoding method will be described in further detail below.

In the embodiment illustrated in fig. 6, the MAC ID j, and the F-CPANCH input with k 1, 2, 3, or 4 every 20 msec k bits are referred toIs fed to a (6, k) block encoder 602. Typically, the (n, k) block code is specified according to its generator matrix. The encoder outputs a codeword, y ═ y₀y_1ky_n-1]Is equal to y ═ uG, where u = [ u ]₀u_1ku_k-1]Is an input sequence, u₀Is the first input bit, y₀Is the first output bit and G is the k × n generator matrix.

For the generator matrix of (6, 1), the F-CPANCH code is G ═ 111111.

For the generator matrix of (6, 2), the F-CPACH code is

For the generator matrix of (6, 3), the F-CPACH code is

For the generator matrix of (6, 4), the F-CPACH code is

The output of the encoder 602 is then the signal point mapped in the mapper 604 such that a0 is a +1 and a1 is a-1. The resulting signal is mixed by mixer 606 with a Walsh code, such as a 128-ary Walsh code (W)¹²⁸) And (4) mixing. The use of walsh codes provides channelization and prevents phase errors in the receiver. It should be noted that for other CDMA systems, other orthogonal or quasi-orthogonal functions may be used in place of walsh code functions (e.g., OVSF for WCDMA).

To improve reliability, the ACK/NAK message for a particular data frame may be retransmitted in a subsequent frame (e.g., 20 milliseconds later) to provide time diversity for the message. Retransmission is achieved by inserting a block 612 that provides a sequence delay for a20 ms frame, a mapper 614 (substantially similar to mapper 604) and a mixer 616 (substantially similar to mixer 606). However, mixer 616 is mixed with the walsh code starting at 65 and ending at 128.

The outputs of mixers 606 and 616 are combined by summing element 618. The output of summing element 618 is then demultiplexed by demultiplexer 620 to generate ACK/NAK signals with 384 symbols every 20 milliseconds (19.2ksps) suitable for forward link transmission.

Table 1 gives the characteristics of the F-CPANCH code.

Code (n, k)	Possibly optimal dmin	D of implementationmin	Code word
					Weighting	Number of
			(6，1)	6			6	06	11
(6，2)	4	4			0	1

			4	3
					(6，3)	3	3	034	143
(6，4)	2	2	02346	13831

TABLE 1F-CPACNH code characteristics

An efficient and reliable acknowledgement scheme can improve utilization of the reverse link and can also transmit data frames at a lower transmit power. For example, without retransmission, a higher power level (P) is required to achieve a percentage frame error rate (1% FER)₁) To transmit the data frame. If retransmission is utilized and is reliable, it may be possible to achieve the required lower power level (P) of 10% FER₂) To transmit the data frame. 10% of the erased frames may be retransmitted to achieve an overall 1% FER for the transmission (i.e., 10% × 10% ═ 1%). In addition, retransmissions provide time diversity, which may improve performance. The retransmitted frame may also be combined with the initial transmission of the frame at the base station, and the combined power of the two transmissions may also improve performance. The recombination may allow retransmission of an erased frame at a lower power level.

Those skilled in the art will appreciate that the steps of the method may be interchanged without departing from the scope of the invention. Those of skill in the art would 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 of a technique 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 a conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or other such configuration.

The steps of a method or algorithm 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. A typical storage medium may be coupled to the processor such that 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.

Moreover, 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 spirit or scope 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 (45)

1. A method of acknowledgement in a wireless communication system, comprising:

receiving a reverse link traffic channel data frame;

transmitting an Acknowledgement (ACK) signal if the quality of the received data frame is indicated as good;

a Negative Acknowledgement (NAK) signal is sent only if the quality of the received data frame is indicated as bad, but has enough energy such that it, in combination with the energy from the retransmission of the data frame, would be sufficient to allow correct decoding of the data frame.

2. The method of claim 1, wherein the reverse link traffic channel is a reverse supplemental channel (R-SCH).

3. The method of claim 1, further comprising:

determining a quality of the received data frame.

4. The method of claim 3, wherein determining the quality of the received data frame comprises indicating that the quality of the frame is good when a reverse link pilot signal has sufficient energy to allow correct decoding of the frame.

5. The method of claim 1, further comprising:

transmitting a traffic-to-pilot ratio (T/P) delta with the NAK signal.

6. The method of claim 5, further comprising:

adjusting an energy level of the data frame using the T/P delta.

7. The method of claim 6, further comprising:

retransmitting the adjusted data frame if the NAK signal is indicated.

8. The method of claim 1, wherein the receiving and transmitting are performed by a secondary base station.

9. A method in a wireless communication system, comprising:

transmitting a reverse link traffic channel data frame;

receiving an Acknowledgement (ACK) signal if the quality of the transmitted data frame is indicated as good;

a Negative Acknowledgement (NAK) signal is received only if the quality of the transmitted data frame is indicated as bad, but has sufficient energy such that if combined with energy from a retransmission of the data frame would be sufficient to allow correct decoding of the data frame.

10. The method of claim 9, wherein transmitting and receiving are performed by a remote terminal.

11. A method of acknowledgement in a wireless communication system, comprising:

receiving a reverse supplemental channel (R-SCH) data frame;

transmitting a Negative Acknowledgement (NAK) signal if the quality of the received R-SCH data frame is indicated as bad;

causing the remote terminal to recognize the absence of an acknowledgement as an Acknowledgement (ACK) signal to indicate that the quality of the received R-SCH frame is good.

12. The method of claim 11, wherein the confirmation method is performed by an optimal base station.

13. The method of claim 12, further comprising:

transmitting an Acknowledgement (ACK) signal to the remote terminal when there is a collision between the remote terminal and the best base station as to which base station is the best base station.

14. The method of claim 11, further comprising:

determining a quality of the received R-SCH frame.

15. The method of claim 14, wherein determining the quality of the received R-SCH frame comprises indicating that the quality of the frame is bad when the energy of the R-SCH frame combined with retransmission energy is insufficient to allow correct decoding of the frame.

16. The method of claim 11, wherein transmitting a NAK signal comprises transmitting a traffic-to-pilot ratio (T/P) delta if the received R-SCH frame has sufficient energy such that, if combined with energy from retransmission of the R-SCH frame, it would be sufficient to allow correct decoding of the frame.

17. The method of claim 16, further comprising:

adjusting an energy level of the R-SCH frame using the T/P delta.

18. The method of claim 17, further comprising:

retransmitting the adjusted R-SCH frame if the NAK signal is received.

19. A wireless communication system that operates an acknowledgement channel, comprising:

a base station device configured to receive a reverse supplemental channel (R-SCH) frame, the base station device transmitting an Acknowledgement (ACK) signal if a quality of the received R-SCH frame is indicated as good; and

a remote device configured to transmit the R-SCH frame to the base station device, the remote device receiving the ACK signal and identifying an absence of acknowledgement as a Negative Acknowledgement (NAK) signal to indicate that the quality of the received R-SCH frame is bad.

20. The apparatus of claim 19, wherein the base station device comprises a quality determination element configured to determine a quality of the received R-SCH frame.

21. The apparatus of claim 19, wherein the base station device comprises a power controller configured to compute and transmit a NAK signal with a T/P delta if the received R-SCH frame has sufficient energy such that, if combined with energy from retransmission of the R-SCH frame, it would be sufficient to permit correct decoding of the frame.

22. The apparatus of claim 21, wherein the remote device comprises an energy level adjuster configured to use the received T/P delta to adjust an energy level of the R-SCH frame and to retransmit the R-SCH frame to the base device.

23. The apparatus of claim 19, wherein the base station device is a secondary base station device.

24. A wireless communication system having a forward link acknowledgement channel, comprising:

a base station device configured to receive a reverse supplemental channel (R-SCH) frame, the base station device to transmit a Negative Acknowledgement (NAK) signal if a quality of the received R-SCH frame is indicated as bad; and

a remote device configured to transmit the R-SCH frame to the base station device, the remote device configured to receive the NAK signal and identify an acknowledgement lack as an Acknowledgement (ACK) signal to indicate that the quality of the received R-SCH frame is good.

25. The apparatus of claim 24, wherein the base station device comprises a quality determination element configured to determine a quality of the received R-SCH frame.

26. The apparatus of claim 24, wherein the base station device comprises a power controller configured to compute and transmit a NAK signal with a T/P delta if the received R-SCH frame is bad but has sufficient energy such that, if combined with energy from retransmission of the R-SCH frame, it would be sufficient to allow correct decoding of the frame.

27. The apparatus of claim 24, wherein the base station device having the smallest path loss to the remote device is an optimal base station device.

28. A base station for a wireless communication system, the base station comprising:

an RF front end configured to receive and appropriately amplify, filter and process a reverse supplemental channel (R-SCH) frame from a remote terminal or terminals; and

a Digital Signal Processor (DSP) adapted to demodulate and further process the received R-SCH frame, the DSP configured to instruct the RF front end to send an Acknowledgement (ACK) signal if the quality of the received R-SCH frame is indicated as good, the DSP configured to instruct the RF front end to send a Negative Acknowledgement (NAK) signal only if the quality of the received data frame is indicated as bad but has sufficient energy such that, if combined with energy from a retransmission of the data frame, it would be sufficient to allow correct decoding of the data frame.

29. The base station of claim 28 wherein the DSP includes a quality determination element configured to determine a quality of a received R-SCH frame.

30. The base station of claim 28 wherein the DSP includes a power controller configured to compute and instruct an RF front end to transmit a NAK signal with a T/P delta to the remote terminal if the received R-SCH frame has sufficient energy such that, if combined with energy from retransmission of the R-SCH frame, it would be sufficient to allow correct decoding of the frame.

31. The base station of claim 28, wherein the base station is a secondary base station.

32. A base station for a wireless communication system, the base station comprising:

an RF front end configured to receive and appropriately amplify, filter and process reverse supplemental channel (R-SCH) frames from a remote terminal or terminals; and

a Digital Signal Processor (DSP) adapted to demodulate and further process the received R-SCH frame, the DSP configured to instruct the RF front end to send a Negative Acknowledgement (NAK) signal if the quality of the received R-SCH frame is indicated as bad, the DSP configured to enable the remote terminal to recognize the absence of an Acknowledgement (ACK) signal as indicating an acknowledgement of receipt of the R-SCH frame at the base station.

33. The base station of claim 32, wherein the base station with the smallest path loss to the remote terminal is an optimal base station.

34. A wireless remote terminal for a communication system, the remote terminal comprising:

an RF front end configured to transmit a reverse supplemental channel (R-SCH) frame to a base station, the RF front end configured to receive and appropriately amplify, filter, and process an Acknowledgement (ACK) signal from the base station to indicate that the quality of the R-SCH frame received at the base station is good and to identify an absence of acknowledgement as a Negative Acknowledgement (NAK) signal to indicate that the quality of the R-SCH frame received at the base station is bad; and

a Digital Signal Processor (DSP) adapted to demodulate and further process the received ACK signal.

35. A wireless remote terminal for a communication system, the remote terminal comprising:

an RF front end configured to transmit a reverse supplemental channel (R-SCH) frame to a best base station, the RF front end configured to receive and appropriately amplify, filter and process a Negative Acknowledgement (NAK) signal from the base station to indicate that the quality of the R-SCH frame received at the base station is bad, and to identify the absence of acknowledgement as an Acknowledgement (ACK) signal to indicate that the quality of the R-SCH frame received at the base station is good; and

a Digital Signal Processor (DSP) adapted to demodulate and further process the received NAK signal.

36. A forward link acknowledgement channel driver for wireless communication, the driver comprising:

a block encoder configured to receive an ACK/NAK message with at least one bit, the block encoder encoding the ACK/NAK message with a generator matrix to produce a codeword;

a first mapper configured to map the codeword into a first binary signal; and

a first mixer configured to mix the first binary signal with a first orthogonal spreading code.

37. The driver of claim 36, further comprising:

a delay element configured to provide a sequential delay of one frame period, the delay element configured to delay the codeword by one frame period;

a second mapper configured to map the delayed codeword into a second binary signal; and

a second mixer configured to mix the second binary signal with a second orthogonal spreading code.

38. The driver of claim 37, further comprising:

a summing element configured to sum outputs of the first and second mixers.

39. The driver of claim 38, further comprising:

a demultiplexer for demultiplexing the output of the summing element to generate an ACK/NAK signal suitable for forward link transmission.

40. The driver of claim 36, wherein the acknowledgement channel is a forward common packet acknowledgement channel (F-CPANCH).

41. The driver of claim 36, wherein the generator matrix of the one-bit ACK/NAK is [111111 ].

42. The driver as claimed in claim 36, wherein the generator matrix of the two-bit ACK/NAK is

43. The driver as claimed in claim 36, wherein the generator matrix of the three-bit ACK/NAK is

44. The driver of claim 36, wherein the generator matrix of the four-bit ACK/NAK is

45. The driver of claim 36, wherein the orthogonal spreading codes are walsh codes.