HK1084799B - Method and apparatus for augmenting physical layer arq in a wireless data communication system - Google Patents

Description

Method and apparatus for increasing physical layer ARQ in a wireless data communication system

FIELD

The present invention relates generally to data communications, and more particularly to wireless data communications.

Background

In data communication systems, particularly wireless data communication systems, data packets may be lost for a variety of reasons, including poor channel conditions. Data communicated between two end users may pass through several protocol layers for ensuring proper data flow through the system, where each layer incorporates certain functionality in the delivery of data packets from a source user to a destination user. Proper delivery of data in at least one aspect is ensured by a system that checks for errors in each data packet and automatically requests retransmission of the same data packet if errors are detected in the received data packet (ARQ mechanism). Independent ARQ mechanisms may be used at different protocol layers for data flow between corresponding end users. Data packets are passed sequentially from one protocol layer to another. Sequential delivery of a sequence of data packets is achieved by transmitting a series of data packets at a time from one protocol layer to another. A group of data packets may not be transmitted until the retransmission process of erased data packets within a group of fewer lower protocol layers has been completed. The retransmission request to retransmit the erased data packet may be repeated several times or the retransmission may be performed several times until the erased data packet is correctly received at the destination. Thus, a retransmission process at one protocol layer may reduce data flow between different protocol layers within the system. At the same time, higher layer protocols may request early retransmission of all data packets within a group, including those successfully received at lower layers, which results in very inefficient use of communication resources when data flow from one protocol layer to another is low. Thus, in the case of packet loss, minimizing lower layer packet loss due to erasures on the airlink is as important as minimizing the delay of multiple retransmissions. There is therefore a trade-off between the number of retransmission attempts at the lower layer protocol layer and the delay resulting from such retransmissions that must be taken into account in the ARQ mechanism for end-to-end data packet delivery.

For this and other purposes, there is a need for a method and apparatus for efficiently controlling the flow of data in a communication system.

SUMMARY

Systems and various methods and apparatus for efficient communication of data across various protocol layers are disclosed. The control and transceiver system is configured for determining a Data Rate Control (DRC) value and for determining a maximum number of time slots allowed for transmission of a physical layer packet of data. After detecting a normal abort of the transmission, a decoding threshold is adjusted for decoding a positive acknowledgement message and decoding of the acknowledgement channel is repeated with the adjusted threshold. Retransmitting the packet of physical layer data at least once more is based on whether the repetition of decoding the acknowledgment channel generates a negative acknowledgment message. Retransmissions may be adjusted based on the communication throughput level between the base station and the mobile station.

Brief description of the drawings

The features, nature, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

fig. 1 illustrates a communication system capable of operating in accordance with various embodiments of the invention;

fig. 2 illustrates a forward link channel structure in a wireless data communication system;

fig. 3 illustrates a reverse link channel structure within a wireless data communication system;

FIG. 4 illustrates decoding of acknowledgment channel data bits according to various received energy thresholds;

FIG. 5 illustrates a protocol layer stack for controlling data flow within a communication system;

FIG. 6 illustrates a table that selects a maximum number of transmission slots allowed for communication of data packets at a selected data rate;

FIG. 7 illustrates early and normal termination of sending data packets at the physical layer;

FIG. 8 illustrates an example flow of radio link protocol layer data packets;

fig. 9 illustrates a flow diagram of various steps for determining additional retransmissions of physical layer data packets in accordance with various aspects of the present invention;

fig. 10 illustrates a flow diagram of various steps for ignoring radio link negative acknowledgements in accordance with various aspects of the invention;

fig. 11 illustrates a receiver system for receiving and decoding various channels, and which is capable of operating in accordance with various aspects of the invention;

fig. 12 illustrates a transmitter system for transmitting various channels and capable of operating in accordance with various aspects of the invention;

fig. 13 illustrates a transceiver for receiving and transmitting various channels and capable of operating in accordance with various aspects of the invention.

Detailed description of the preferred embodiments

In general, various aspects of the invention provide for efficient use of communication resources within a communication system by efficiently determining the need for one more transmission of a physical layer data packet on the forward link based on decoding a previously received signal that repeats an acknowledgement channel. Repeating the decoding process may involve using different decoding thresholds. Retransmission of the physical layer packet may then include using time diversity. Time transmit diversity various techniques are known. One or more embodiments described herein are presented in the context of a digital wireless data communication system. Although advantageous for use in this environment, various embodiments of the invention may be included in different environments or configurations. In general, the various systems described herein may be formed using software-controlled processors, integrated circuits, or discrete logic. Data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, circuits, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. Additionally, the modules illustrated within each block diagram may represent hardware or method steps.

In particular, various embodiments of the invention may be included in a wireless communication system whose operation is based on Code Division Multiple Access (CDMA) technology, as disclosed and described in various standards promulgated by the Telecommunications Industry Association (TIA) and other standards organizations. Such standards include the TIA/EIA-95 standard, TIA/EIA-IS-2000 standard, IMT-2000 standard, UMTS and WCDMA standard, all of which are incorporated herein by reference. The system for Data communication IS further described in detail in "TIA/EIA/IS-856 cdma2000 High Rate Packet Data air interface Specification," which IS hereby incorporated by reference. Copies of the standard may be made by accessing the world Wide Webhttp://www.3gpp2.orgAnd is obtained or written to TIA, standards and technology department, 2500 Wilson Boulevard, Arlington, VA 22201, United States of america. The standard, generally identified as the UMTS standard, is included herein by reference, and is available by contacting the 3GPP support office, 650 Route des Lucioles-Sophia Antipolis, Valbonne-France.

Fig. 1 illustrates a general block diagram capable of operating in accordance with any one of the Code Division Multiple Access (CDMA) communication system standards while incorporating various embodiments of the present invention. The communication system 100 may be used for data communications, or data and voice communications. In general, the communication system 100 includes a base station 101 that provides communication links between a plurality of mobile stations, such as mobile station 102 and 104, and a public switched telephone and data network 105. The mobile stations in fig. 1 may be referred to as data Access Terminals (ATs) and the base stations as data Access Networks (ANs) without departing from the main scope and various advantages of the present invention. Base station 101 may include a number of components such as a base station controller and a base transceiver system. For simplicity, such components are not shown. Base station 101 may communicate with other base stations, such as base station 160. A mobile switching center (not shown) may control various operational aspects of communication system 100 and in relation to communications over a back-haul 199 between network 105 and base stations 101 and 160. Base station 101 communicates with each mobile station that is in its coverage area via a forward link signal transmitted from base station 101. The forward link signals to mobile stations 102 and 104 may be summed to form a forward link signal 106. Each of the mobile stations 102 and 104 that receives the forward link signal 106 decodes the forward link signal 106 to extract the received information. Base station 160 is also in communication with the mobile stations that are in its coverage area via a forward link signal transmitted from base station 160. Mobile station 102 communicates with base stations 101 and 160 via corresponding reverse links. Each reverse link is maintained by a reverse link signal, such as reverse link signals 107-109 corresponding to mobile stations 102-104. The reverse link signal 107-109 may be intended for one base station but may be received at other base stations.

Base stations 101 and 160 may simultaneously communicate with a common mobile station. For example, mobile station 102 may be in close proximity to base stations 101 and 160, which may maintain communication with both base stations 101 and 160. On the forward link, base station 101 transmits on forward link signal 106 and base station 160 transmits on forward link signal 161. On the reverse link, mobile station 102 transmits on reverse link signal 107 to be received by base stations 101 and 160. To transmit data packets to mobile station 102, one of base stations 101 and 160 may be selected to transmit data packets to mobile station 102. On the reverse link, base stations 101 and 160 may attempt to decode traffic data transmissions from mobile station 102. The data rates and power levels of the reverse and forward links may be maintained in accordance with the channel conditions between the base station and the mobile station. The reverse link channel conditions may be different than the forward link channel conditions. The data rate and power level of the reverse link and the forward link may be different. Those of ordinary skill in the art will recognize that the amount of data communicated during a time period varies with the communication data rate. The receiver may receive more data at the high data rate than the low data rate during the same time period. Also, when data packet communication is more than one transmission, the amount of valid data sent over a period of time is reduced. Thus, the throughput of communications between a mobile station and a base station may change over time based on channel conditions. In accordance with one or more aspects of the present invention, after being detected as a lost data packet, based on the communication throughput between the base station and the mobile station, the communication resources of communication system 100 can be efficiently utilized by determining the need for a further retransmission of the physical layer data packet.

In accordance with various aspects of the present invention, in communication system 100, retransmitting a lost data packet at least once after detecting the loss is based on whether the throughput determined for the communication link between the source user and the destination user is above a throughput threshold. The source user may be a base station, such as base stations 101 or 160, and the destination user may be any mobile station 102 or 104. After establishing forward link communication, data packet loss may be detected for the mobile station. The forward link communication throughput may be determined based on the communication data rate, the communication rate, the number of retransmissions used between the source user and the destination user, or a combination thereof. The retransmission may include using transmit diversity. Also, the retransmission reception may include reception diversity. When the throughput is above the threshold, the likelihood of receiving a lost data packet by retransmission is higher because of favorable throughput channel conditions. Thus, when retransmission does not occur because throughput cannot be above a threshold, communication resources are conserved by more efficient use. Moreover, data casting between various protocol layers is minimized by providing timely successful reception of lost data packets during favorable throughput channel conditions when retransmissions occur.

Fig. 2 illustrates a forward channel structure 200 in accordance with an embodiment that may be used for a communication channel structure on the forward link. Forward channel structure 200 may include a pilot channel 201, a Medium Access Control (MAC) channel 202, a traffic channel 203, and a control channel 204. The MAC channels 202 may include a reverse activity channel 206 and a reverse power control channel 207. Reverse activity channel 206 is used to indicate the level of activity on the reverse link. The reverse power control channel 207 is used to control the power at which the mobile station may transmit on the reverse link.

Fig. 3 illustrates a reverse channel structure 300 for a channel structure for communication on a reverse link, according to an embodiment. Reverse channel structure 300 includes an access channel 350 and a traffic channel 301. Access channel 350 includes a pilot channel 351 and a data channel 353. Traffic channel 301 includes pilot channel 304, MAC channel 303, and Acknowledgement (ACK) channel 340 and data channel 302. The MAC channel 303 includes a reverse link data rate indicator channel 306 and a data rate control channel (DRC) 305. Reverse rate indicator channel 306 is used to indicate the rate at which the mobile station is currently transmitting. A Data Rate Control (DRC) channel 305 indicates the rate at which the mobile station can receive on the forward link. For example, a DRC value of 0x3 may indicate a data rate of 153.6 kbps. Moreover, the system may require a predetermined and limited number of retransmissions of physical layer data packets that may occur. For example, at a data rate of 153.6kbps, the system allows 3 retransmissions of the same data packet after the initial transmission, resulting in a total of four transmissions. If the physical layer data packet is not decoded correctly after the initial transmission, as indicated by the reverse link in-ACK channel 340, the transmitter may transmit the same data packet once more. The retransmission may continue up to three times. The transmitter cannot transmit the same data packet more than four times, one initial time and three retransmissions when the data rate is at 153.6 kbps. The ACK channel 340 is used to send whether the received physical layer data packet was successfully decoded at the mobile station. When a data packet is lost within communication system 100, even after a maximum allowed retransmission, retransmitting the data lost packet at least once may be based on determining whether a throughput of a communication link between the mobile station and the serving base station is above a throughput threshold, in accordance with various aspects of the present invention.

The ACK channel 340 is transmitted by the mobile station. The transmission on the ACK channel 340 may indicate a Negative Acknowledgement (NAK) or a positive Acknowledgement (ACK). The mobile station may send a NAK message to the serving base station as indicated by a single NAK bit until the received physical layer data packet is successfully decoded. The physical layer data packet may be successfully decoded before the maximum number of allowable retransmissions. If the received data packet is decoded correctly, the mobile station sends an ACK message indicated by a single ACK bit to the serving base station on an ACK channel 340. The ACK channel 340 may transmit a positive modulation symbol for a positive acknowledgement and a negative modulation symbol for a negative acknowledgement using Binary Phase Shift Keying (BPSK) modulation. In the transmitter described in the IS-856 standard, the ACK/NAK bits are transmitted through a BPSK modulator and repeated. The BPSK modulator modulates the ACK/NAK bits and the resulting signal is Walsh covered according to the assigned Walsh code. In an embodiment, the received signal of the ACK channel 340 may be compared to a positive or negative voltage threshold. If the received signal level meets the positive voltage threshold, the ACK message is deemed to be received on the ACK channel 340. If the signal level meets the negative voltage threshold, the NAK message is considered to be received on the ACK channel 340.

Returning to fig. 4, decoding of the ACK channel 340 may be illustrated. The resulting signal may be compared to a positive threshold 401 and a negative threshold 402. If the signal is above the positive threshold 401, the ACK bit is deemed to have been received on the ACK channel 340. If the signal is below the negative threshold 402, the NAK bit is considered to be received on the ACK channel 340. The positive and negative thresholds 401 and 402 may not be at the same level. In this way, an erased area 403 can be established between the positive and negative thresholds 401 and 402. If the resulting demodulated signal falls within erasure area 403, the receiving base station may not be able to determine whether an ACK or NAK bit was transmitted from the mobile station on ACK channel 340.

The ARQ mechanism may have several problems when the received ACK channel 340 signal is within the erasure area 403. If the erasure is interpreted as an ACK, the base station stops transmitting the remaining number of allowed retransmissions of the physical layer data packet when a NAK is actually transmitted from the mobile station. As a result, the mobile station is unable to receive the physical layer data packet and may rely on a higher layer protocol layer retransmission mechanism. Such as the Radio Link Protocol (RLP) layer to recover lost data packets. However, the delay in receiving the data packets and in using the communication resources is higher at the RLP layer than at the physical protocol layer. One measure of system quality may be certainty associated with proper and timely delivery of data packets to the mobile station. To avoid this problem, in one embodiment, the decoding process for the ACK channel may favor the detection of a NAK by interpreting the erasure as a NAK. If the mobile station actually sent an ACK and the serving base station detected an erasure, the erasure is interpreted as a NAK so that the base station can resume at least one of the remaining number of physical layer packet data transmissions when in fact any retransmission of the data packet is not necessary. Such retransmission, even if it may not be necessary, may actually result in efficient use of communication resources, minimizing delays in the delivery of data packets.

According to various aspects of the invention, the thresholds 401 and 402 may be changed to reduce the detection of erasures after the physical packet of data is not properly received after the last allowable retransmission. After changing at least one threshold, the previously received signal of the ACK channel 340 may be rechecked to determine whether an ACK message was checked. If a NAK is still detected, retransmission of the physical layer data packet is attempted again above the maximum allowable number of retransmissions. Those of ordinary skill in the art will appreciate that retransmissions may involve multiple time slots depending on the data rate requested by the mobile station, similar to the original transmission. The data rate request message may be re-determined based on the most recently received data before attempting additional retransmissions. The number of slots used in the additional retransmissions may be different based on the most recently received data.

The flow of data between two endpoints may be controlled through several protocol layers. An example stack of protocol layers 500 is shown in fig. 5 for controlling the flow of data between two endpoints. For example, one endpoint may be a source connected to the internet through network 105. The other end point may be a data processing unit such as a computer coupled to or integrated within the mobile station. The protocol layer 50 may have several other layers or each layer may have several sub-layers. The detailed stack of protocol layers is not shown here for simplicity. The stack of protocol layers 500 may be followed for data flow within a data connection from one endpoint to another. At the top layer, TCP layer 501 controls TCP packets 506. TCP packet 506 may be generated from a larger application data message/packet. The application data may be divided into several TCP packets 506. The application data may include text message data, video data, image data, or voice data. The size of the TCP packet 506 may be different at different times. At internet protocol layer (IP)502, a header is added to TCP packet 506 to generate data packet 507. The header may include, among other fields, a destination address for packet routing to an appropriate destination node. At point-to-point protocol (PPP) layer 503, PPP header and trailer data is added to data packet 507 to produce data packet 508. The PPP data may identify a point-to-point connection address for properly routing the data packet from the source connection point to the destination connection point. PPP layer 503 may pass data for one TCP layer protocol connected to different ports.

The Radio Link Protocol (RLP) layer 504 provides a mechanism for retransmission and recovery of data packets erased over the air. While TCP has a transmission scheme for reliable data transmission, the rate of data packets lost over the air may result in overall poor TCP performance. Implementing the RLP mechanism at the lower layer actually reduces the rate at which TCP packets are lost at the TCP layer. At the RLP layer 504, the data packet 508 is divided into several RLP packets within a set of RLP packets 509A-N. Each RLP packet in the set of RLP packets 509A-N is processed independently and assigned a sequence number. Sequence numbers are added to the data within each RLP packet to identify the RLP packet in the RLP packet within the group of RLP packets 509A-N. One or more RLP packets within the RLP packets 509A-N group are placed into a physical layer data packet 510. The physical layer 505 controls the channel structure, frequency, power output, and modulation specification of the data packet 510. The data packet 510 is transmitted over the air. The size of the payload of the data packet 510 may vary depending on the transmission rate. Thus, the size of data packet 510 may vary over time based on the channel conditions and the selected communication data rate.

At the receiving destination, a physical layer data packet 510 is received and processed. The ACK channel 340 may be used to acknowledge success/failure in the reception of a physical layer data packet 510 sent from the base station to the mobile station. If the physical layer data packet 510 is received without error, the received packet 510 is passed to the RLP layer 504. The RLP layer 504 attempts to reassemble the RLP packets within the RLP packet 509A-N group from the received data packets. To reduce the packet error rate seen by TCP 501, RLP layer 504 implements an automatic repeat request (ARQ) mechanism by requesting retransmission of lost RP packets. The RLP protocol reassembles the RP packet 509A-N group to form the complete PPP packet 508. The process may require some time to completely receive all RLP packets within the RLP packet 509A-N group. Several physical layer data packets 510 may be required to completely transmit all RLP packets within the RLP packets 509A-N. When RLP packets of data are received out of order, the RLP layer 504 sends an RLP Negative Acknowledgement (NAK) message on a signaling channel to the transmitting base station. In response, the transmitting base station retransmits the missing RLP packet of data.

Returning to fig. 6, table 600 depicts DRC values for DRC channel 305, corresponding data rates, and corresponding maximum number of allowable transmissions of a physical layer packet of data. For example, for a DRC value of 0x3, the data rate is 153.6kbps and the maximum number corresponding to allowable transmissions is four slots. There may be an early or normal termination of the transmission of the physical layer packet of data. At early termination, the physical layer data packet is decoded properly at the receiver and the transmitting source receives an ACK message on ACK channel 340 corresponding to the receipt of the physical layer data packet. Upon normal termination, all of the allowable transmission slots for the transmitter to use the physical layer data packet have been exhausted without receiving a corresponding ACK message on the ACK channel 340.

Returning to fig. 7, the early and normal termination of the transmission of the physical layer packet of data is illustrated for the case of DRC value 0x3 corresponding to a data rate of 153.6 kbps. For an early termination of physical layer packet data transmission for the DRCOx3 case corresponding to a data rate of 153.6kbps, the DRC value is received on DRC channel 305 at slot 702 prior to the first transmission of the physical layer packet of data. The DRC value is used to determine the communication data rate and the maximum number of allowed retransmissions of the physical layer packet of data. At slot "n" of slot 701, a first transmission of a physical layer packet of data may occur. In the next three time slots "n +1, n +2, n +3," the transmitter expects an ACK or NAK to be received on ACK channel 340. Time slot 703 shows that a NAK was received before time slot "n + 4". The first retransmission of the physical layer packet of data occurs during slot "n + 4". The transmitter waits three more slots to receive an ACK or NAK on ACK channel 340. Time slot 703 shows that a NAK is received at time slot "n + 8". A second retransmission of the physical layer packet of data occurs during slot "n + 8". For a data rate of 153.6kbps, the transmitter is allowed to transmit the same physical layer packet of data once more. The transmitter waits three more slots to receive an ACK or NAK message on the ACK channel 340. The ACK message is received on ACK channel 340 before slot "n + 12". Thus, the transmitter prematurely terminates the transmission of the physical layer packet of data before exhausting all allowed transmission slots. Time slot "n + 12" may be used for transmission of another physical layer packet of data.

For the case of DRC value 0x3 corresponding to a data rate of 153.6kbps, the normal termination of transmission of the physical layer packet of data, the DRC value is received on DRC channel 305 at slot 802 prior to the first transmission of the physical layer packet of data. The DRC value is used to determine the communication data rate and the maximum number of allowed retransmissions of the physical layer packet of data. At slot "n" of slot 801, a first transmission of a physical layer packet of data may occur. In the next three time slots "n +1, n +2, n +3," the transmitter expects an ACK or NAK to be received on ACK channel 340. Time slot 803 shows that a NAK was received before time slot "n + 4". The first retransmission of the physical layer packet of data occurs during slot "n + 4". The transmitter waits three more slots to receive an ACK or NAK on ACK channel 340. Time slot 803 shows that a NAK was received before time slot "n + 8". A second retransmission of the physical layer packet of data occurs during slot "n + 8". For a data rate of 153.6kbps, the transmitter is allowed to transmit the same physical layer packet of data once more. The transmitter waits three more slots to receive an ACK or NAK message on the ACK channel 340. A NAK message is received on ACK channel 340 before slot "n + 12". Thus, the transmitter performs the last allowed transmission of the physical layer packet of data on time slot "n + 12" and performs a normal termination of the data physical layer transmission after exhausting all of the allowed transmissions of the physical layer packet of data.

In general, the transmitter need not monitor the ACK channel 340 to detect whether the last transmission was received successfully or unsuccessfully. The physical layer packet may not be successfully received at the mobile station after a normal abort. In this case, the RLP packet reassembly of data at the RLP layer 504 may not be complete. As a result, the RLP layer 504 requests retransmission of the RLP packet of data by sending an RLP NAK signaling message. In accordance with various aspects of the invention, after a normal termination of transmission of a physical layer packet of data, the base station may monitor the ACK channel 340 and, if a NAK is received, may repeat decoding of the previously received signal of the ACK channel 340 with the adjusted ACK/NAK thresholds 401 and 402. The ACK/NAK thresholds 401 and 402 are adjusted so that the decoding bias is towards the detection of the ACK message. Such a bias may be achieved by treating erasures as ACKs without changing the level of NAK threshold 402 from the previously used level or by selecting different thresholds together.

In general, the ARQ mechanism by the RLP layer requires some time, which includes the round trip delay between the mobile station and the base station and the processing delay. Returning to fig. 8, message flow 800 illustrates an example flow of providing RLP packets of data. For example, RLP packets with sequence numbers "01" to "07" are sent from a source to a destination. The source and destination may be a base station and a mobile station or a mobile station and a base station, respectively. At the RLP layer 504, the RLP packets 509A-N are accumulated to complete the packet 508. Once all RLP packets are received, the RLP packets 509A-N are passed to higher layers. At the physical layer 505, communication of the physical layer data packet 510 also includes an ARQ method through use of the ACK channel 340. One or more RLP packets may be combined into a common payload and transmitted on one physical layer data packet 510. Within the example message flow 800, the RLP packet identified as RLP packet "03," for example, does not reach the destination. The failure may be due to a number of factors, including erasures on the radio link between the source and destination. In this case, a normal abort of the transmission of the physical layer packet of data of the RLP packet including the data "03" may occur. After the destination receives the RLP packet "04," the RLP layer 504 detects that the RLP packets are received out of order. The RLP layer 504 sends an RLP NAK message identifying the RLP packet "03" as lost in the communication. The process of detecting a missing RLP packet of data, the propagation of an RLP NAK message, and a subsequent RLP retransmission may take time. The duration may be long enough to allow a fast retransmission of the physical layer of the data packet beyond the maximum allowable number of retransmissions for early recovery. The RLP NAK message may not be transmitted if the additional retransmission is successful before the RLP NAK message is transmitted in accordance with various aspects of the invention.

If an RLP NAK message is sent, the RLP layer 504 starts a timer at the same time. The timer sends the amount of time elapsed after sending the RLPNAK message. If the timer expires, e.g., after 500 milliseconds, and before the missing RLP packet "03" is received, the destination RLP 504 assumes that the retransmission of the missing RLP packet failed. Upon receipt of the missing RLP packet "03", the timer is aborted. Correctly received data packets may be collected in a storage unit to form a set of data packets. Thus, the detection and retransmission process for a missing RLP packet of data may take some time. The duration may be long enough to allow retransmission of the physical layer packet of data more than the maximum allowable number of retransmissions. If the additional retransmission is successful before the timer expires according to various aspects of the present invention, the timer may be aborted because the retransmission of the physical layer data packet was successfully received. Possibly an RLP NAK is sent before successful reception of additional physical layer retransmissions. In this case, either the base station chooses to ignore the received RLP NAK message, or it implements RLP retransmission of the missing packet, which is discarded as a duplicate at the mobile station. It is possible that the additional physical layer retransmissions will end up with a failed normal abort. In this case, the usual RLP retransmission mechanism can provide recovery of lost packets.

Various aspects of the invention may be more readily apparent by referring to flow diagram 900 in fig. 9. At step 901, the transmitter may determine a DRC value for a physical layer packet of data transmission. The DRC value may be determined by decoding the DRC channel 305. At step 902, the maximum number of slots allowed for transmission of a physical layer packet of data may be determined by reference to table 600 of fig. 6. At step 903, the transmitter may detect a normal termination of transmission of a physical layer data packet over the maximum number of allowable slots when no consecutive ACK on the ACK channel 340 is received. At step 905, the ACK and NAK thresholds 401 and 402 may be adjusted to bias towards detection of ACK messages. At step 906, the previously received ACK channel 340 signal is re-decoded using the adjusted threshold to determine the bits on the ACK channel 340. If the re-decoding generates NAK bits, the physical layer data packet is transmitted in one more round in step 907. This additional round of transmission comprises a plurality of transmissions up to the maximum allowable slot according to table 600 of fig. 6, depending on the DRC requested at the retransmission start time. At this point, the transmitter may determine a new DRC value by decoding the DRC channel 305 to determine the maximum number of slots allowed for transmission of the physical layer packet of data. The channel conditions may change during the process. A new round of transmission may start after some delay. A delay may be necessary to allow decorrelation within the channel conditions. When channel condition decorrelation occurs, the probability of success of transmission of a physical layer packet of data is higher. A new round of transmission may be based on the newly received DRC value; therefore, the number of allowable retransmissions may be different in the round of transmission. At step 910, the next physical layer packet of data is sent. The last retransmission in step 907 may arrive and be decoded correctly at the destination and may remove the need to retransmit the RLP packet of data. Thus, delayed arq (darq) at the physical layer is helpful for efficient communication of data. Channel correlation simply means that if a packet is erased in a slot, it is likely that it will be erased again if it is retransmitted immediately. This is particularly considered within slow fading channel conditions. Therefore, the retransmission must be time-domain decorrelated from the lost transmission. This means that the retransmission should occur at an earlier time such that there is sufficient channel decorrelation following the lost transmission. Thus using "delayed arq (darq)". Simulation studies indicate that 10 or 20mSec is sufficient, but other time-delayed periods are possible, as desired.

DARQ in accordance with various aspects of the present invention may result in significant performance gains for high throughput users under some traffic conditions. TCP and lower inter-layer interactions within the system can result in significant throughput loss for some users under some typical (1% Packet Error Rate (PER)) operating conditions. This loss can be attributed to several factors. The forward link loss resulting in RLP retransmission causes delay in the receipt of the TCP segment affected by the loss and delay in the subsequent TCP segment received but cannot be immediately transmitted due to the requirement for RLP in-order transmission. This delays the generation of TCP ACKs at the receiver. When lost packets are recovered due to RLP retransmission, bursts of packets may be delivered to the TCP layer, which may then generate a TCP ACK burst, which may temporarily overload the reverse link. The result is that the TCP sender may time out and thus cause a retransmission of the packet, which has been successfully received at the first location. Also, the congestion window of the TCP sender is reduced to its slow start value (typically one TCP segment) and it takes some time to recover before a stable flow of packets can be obtained, which can lead to "starvation" of the forward link.

The above-described problems may be greatly alleviated if additional physical layer retransmissions are implemented on the forward link relatively quickly in accordance with various aspects of the invention. The extra retransmissions provide additional robustness. The rapidity of retransmission helps to reduce latency and thus to eliminate TCP sender timeouts. Also, fast retransmissions reduce the delay variability seen by the TCP sender, which results in improved performance. There are other by-products of this scheme, such as the case where the last byte in the forward link transmission is lost. Since this will not generate a NAK from the mobile station, the base station maintains a refresh timer to cause a forced retransmission. DARQ in this case would result in automatic retransmission and a refresh timer may not be necessary.

Various aspects of the present invention may be useful in many different system conditions, including high throughput conditions. High throughput conditions occur when channel conditions are very favorable for low error rate communications and there may be fewer users within the system. The additional retransmissions may provide more gain for high throughput users than for low throughput users. For low throughput users, overhead may result without any benefit. Thus, to add an additional control layer for various aspects of the invention, after step 903 and before step 905, the transmitter may determine the user throughput of the received communication at block 904. If the throughput is above the throughput threshold, the process moves to step 905 to prepare for a decision whether an additional retransmission of the physical layer packet of data occurs.

The RLP layer 504 may begin and send an RLP NAK message after a normal termination of the transmission of the physical layer data packet and before additional transmission of the physical layer data packet is completed. If an RLP NAK message arrives along with an ACK indication on the ACK channel 340 for proper reception of additional transmissions after a normal abort, the RLP NAK may be ignored in accordance with various aspects of the invention. Various aspects of the invention may be made apparent by referring to flow diagram 1010 shown in fig. 9. At step 1011, an ACK is received on ACK channel 340. The ACK refers to the physical layer data packet sent after the normal termination of the first transmission failure. An RLP NAK message may also be received at step 1012. The RLP NAK message may be associated with an RLP packet of data that is included in a physical layer packet of data. This detection may be performed at step 1013. At step 1014, the received RLP NAK message may be ignored and the controller may consider that the RLP data packet at the destination was properly received based on the ACK bits received on the ACK channel 340. The mobile station may delay sending the RLP NAK message after detecting that the last transmission of the physical layer packet of data should occur while the last transmission is not received.

Fig. 11 illustrates a block diagram of a receiver 1200 for processing and demodulating a received CDMA signal. Receiver 1200 may be used for decoding information on the reverse and forward links signals. The Received (RX) samples may be stored in RAM 1204. The received samples may be generated by a radio frequency/intermediate frequency (RF/IF) system 1290 and an antenna system 1292. The RF/IF system 1290 and antenna system 1292 may include components for receiving multiple signals and RF/IF processing of the received signals to take advantage of receive diversity gain. Multiple received signals propagate through different propagation paths, which may be from a common source. Antenna system 1292 receives RF signals and delivers RF signals to RF/IF system 1290. The RF/IF system 1290 can be any conventional RF/IF receiver. The received RF signal is filtered, down-converted and digitized to form RX samples at baseband frequencies. The samples are provided to a multiplexer (mux) 1202. The output of Mux1202 is provided to searcher unit 1206 and finger elements 1208. To which a control unit 1210 is coupled. A combiner 1212 couples a decoder 1214 to finger elements 1208. Control system 1210 may be a software controlled microprocessor and may be located on the same integrated circuit or on a separate integrated circuit. The decoding function within decoder 1214 may be in accordance with a turbo decoder or any other suitable decoding algorithm.

In operation, received samples are provided to mux 1202. Mux1202 provides samples to searcher unit 1206 and to finger elements 408. Control system 1210 configures finger elements 1208 to demodulate and despread received signals at different time offsets based on search results from searcher unit 1206. The demodulation results are combined and sent to decoder 1214. The decoder 1214 decodes the data and outputs the decoded data. Despreading of the channels is accomplished by multiplying the received samples by the complex conjugate of the PN sequence and assigned Walsh function at a single timing hypothesis and digitally filtering the resulting samples, often using an integrate and dump accumulator circuit (not shown). Such techniques are generally known in the art. Receiver 1200 may be used in the receiver portion of base stations 101 and 160 for processing the received reverse link signals from the mobile stations, or in the receiver portion of any mobile station for processing the received forward link signals.

Fig. 12 illustrates a block diagram of a transmitter 1300 for transmitting the reverse and forward link signals. The channel data for transmission is input to a modulator 1301 for modulation. The modulation may be according to any commonly known modulation technique such as QAM, PSK or BPSK. Data is encoded at a data rate in modulator 1301. The data rate may be selected by a data rate and power level selector 1303. The data rate selection may be based on feedback information received from the receiving destination. The reception destination may be a mobile station or a base station. The feedback information may include a maximum allowable data rate. The maximum allowable data rate may be determined according to various commonly known algorithms. The maximum allowable data rate is often based on channel conditions, among other considerations. The data rate and power level selector 1303 selects the data rate in modulator 1301 accordingly. The output of modulator 1301 is passed through a signal spreading operation and amplified in block 1302 for transmission from antenna 1304. The data rate and power level selector 1303 is also used to select a power level for the amplification level of the transmitted signal based on the feedback information. The selected data rate and power level combination allows for proper decoding of the transmitted data at the receiving destination. Pilot signals are also generated in block 1307. The pilot signal is amplified to an appropriate level at block 1307. The pilot signal power level may be based on the channel conditions at the receiving destination. The pilot signal is combined with the channel signal in combiner 1308. The combined signal may be amplified in an amplifier 1309 and transmitted from the antenna 1304. The antenna 1304 may be any number of combinations including antenna arrays and multiple-input multiple-output configurations.

Fig. 13 depicts a general block diagram of a transceiver system 1400 for including a receiver 1200 and a transmitter 1300 for maintaining a communication link with a destination. The transceiver 1400 may be included in a mobile station and a base station. Processor 1400 can be included in a mobile station or a base station. A processor 1401 may be coupled to receiver 1200 and transmitter 1300 to process the received and transmitted data. Various aspects of receiver 1200 and transmitter 1300 may be common, although receiver 1200 and transmitter 1300 are shown separately. In an aspect, receiver 1200 and transmitter 1300 may share a common local oscillator and a common antenna system for RF/IF reception and transmission. Transmitter 1300 receives data for transmission on input 1405. Transmit data processing block 1403 prepares the data for transmission on a transmit channel. Received data, after being decoded in decoder 1214, is received at an input 1404 of processor 1401. Received data is processed in a received data processor module 1402 in processor 1401. The processing of the received data typically includes checking for errors in the received data packets. For example, if the received data packet has an unacceptable error level, the receive data processing module 1402 sends an instruction to the transmit data processing module 1403 for making a request for retransmission of the data packet. The request is sent on a transmit channel. Various channels, such as the ACK channel 340, may be used for the retransmission process. As such, control system 1210 and processor 1401 may be used to implement various aspects of the invention, including the various steps described in connection with flow diagram 900. A receive data storage unit 1480 may be used to store the received data packets. The various operations of processor 1401 may be integrated within a single or multiple processing units. The transceiver 1400 may be connected to another device. Transceiver 1400 may be an integral part of a device. The device may be a computer or operate similar to a computer. The device may be connected to a data network, such as the internet. In the case of incorporating the transceiver 1400 into a base station, the base station may be connected to a network, such as the internet, through several connections.

Those of skill would further appreciate that the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. Various illustrative components, blocks, modules, circuits, 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 logical blocks, modules, and circuits disclosed in the illustrative embodiments herein may be implemented or performed in the manner of: a general purpose processor, a Digital Signal Processor (DSP) or other processor, 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, to implement 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 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 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. An exemplary processor is preferably 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 application specific integrated circuit, ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. 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 (5)

1. A method for a communication system, comprising:

establishing a communication link between a source user and a destination user;

detecting a loss of data packets communicated between the source and destination users;

determining a throughput of the communication link;

retransmitting the lost data packet at least one more time if the determined throughput is above a throughput threshold, wherein the retransmission is after exhausting a maximum allowable retransmission, and wherein the maximum allowable retransmission is based on a communication data rate between the source user and the destination user.

2. The method of claim 1, wherein the retransmitting comprises using transmit diversity.

3. An apparatus for use in a communication system, comprising:

a controller and a transceiver system for establishing a communication link between a source user and a destination user, wherein said controller is further configured for detecting a loss of a data packet of a communication between said source and destination users and determining a throughput of said communication link, and said transceiver system is further configured for retransmitting said lost data packet at least once more if said determined throughput is above a throughput threshold, wherein said retransmitting is after exhausting a maximum allowable retransmission, and wherein said maximum allowable retransmission is based on a communication data rate between said source user and said destination user.

4. The apparatus of claim 3, wherein said communication link is a forward link from said source user to said destination user, and wherein said destination user is a mobile station within said communication system.

5. The apparatus of claim 3 wherein said transceiver system is further configured for transmit diversity for said retransmission of said lost data packet.