Title of Invention

A METHOD OF EFFICIENT HYBRID AUTOMATIC REPEAT REQUEST FOR WIRELESS NETWORKS

Abstract

The present invention relates to a method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein for Delay and Jitter sensitive traffic the rate of the channel code depends on the minimum required throughput efficiency where the throughput efficiency is defined as the portion of useful information bits in each packet transmitted considering both the PHY and MAC overheads. The present invention further relates to a method of Efficient Hybrid Automatic Repeat Request for Wireless Networks based on multiple antennas at the transmitter and receiver wherein combining the signal at the received antenna array is done by equal weighted combining, combining packets weighted by the SINR, maximal ratio combining of the packets if the channel information is known where the signal at each element of the antenna array are combined after removing the effect of the channel, combining outputs of the successive antenna elements using an iterative algorithm exchanging soft output information; and/or combining the soft outputs using maximal ratio if the channel state information is known .

Full Text

FIELD OF TECHNOLOGY This invention relates to the field of wireless networks. Particularly this invention relates to efficient Hybrid ARQ strategies taking into account several parameters that influence wireless networks. More particularly the present invention relates to a method of Efficient Hybrid Automatic Repeat Request for Wireless Networks. DESCRIPTION OF THE RELATED ART Forward error correction and automatic repeat request (ARQ) are two basic control techniques for data communication. A hybrid ARQ scheme combines the advantages of pure FEC and pure ARQ offers better performance for wireless communication. Several Hybrid ARQ schemes have been proposed. Hybrid ARQ schemes are chosen based on several parameters which include the nature of data traffic and QoS. The requirements for streaming video will be different from data traffic. In the case of traffic involving streaming video the round trip delay must be small. Different Hybrid ARQ Schemes: 1. Type - II Hybrid ARQ scheme with Chase Combining: In this scheme an arbitrary number of data packets are combined and decoded using the maximum likelihood approach. Whenever there is error the entire data packet is retransmitted in this scheme. The disadvantages of this scheme are delay and retransmission of the entire packet. 2. Type - II Hybrid ARQ Scheme with Incremental Redundancy: This scheme uses the previously received erroneous packets instead of discarding them. Initially the data is transmitted at a high rate. If the received data is erroneous more parity bits are transmitted. Based on this as well as the packet transmitted before an attempt is made to decode. This process is continued till the packet is received correctly or maximum of retries are attempted. Here in successive retransmissions only the parity bits are transmitted. a. In this scheme information bits are encoded by a low rate code b. Information and a selected number of parity bits are transmitted c. If a retransmission is not successful - the transmitter sends selected parity bits and the receiver puts together the new bits and those previously received. d. Note that each retransmission produces a stronger code 3. Type - II Hybrid ARQ Scheme with Selective Combining: This scheme is similar to the Type - II hybrid ARQ scheme with incremental redundancy. Here the notion of selective combing of the data received from successive retransmissions is introduced. A typical wireless channel is a fading channel. Therefore the SINR of the received packets for successively is different. This motivates the possibility of combining packets received selectively instead of combining all the packets received. The packets are selectively combined till the data is decoded correctly or the number of retransmissions has expired. The different packets can be combined after weighting by an appropriate parameter. One possible weighting strategy will be to use SINR. 4. This scheme is similar to IR scheme except that the receiver puts together the new bits and other bits previously transmitted selectively. All possible combinations of the new bits and bits transmitted in each previous transmission is considered 5. Type - III Hybrid ARQ Scheme: This scheme varies from the Type-ll Hybrid ARQ scheme with incremental redundancy. In this case it is assumed that each transmission is self decodable. Since the wireless channel is a fading channel during successive retransmissions the channel state can be different. Therefore if the SINR during a particular retransmission is low we need not use the particular packet for combining. • Here unlike in the case of IR the new bits received alone can be used to construct the transmitted information 6. Asynchronous and Adaptive Incremental Redundancy: This scheme differs from the Chase combining and IR in the sense that a different coding and modulation scheme can be used for each retransmission. If the channel is bad a low rate code and a constellation with smaller number of alphabets can be used for modulation. In the classical IR scheme the modulation scheme remains the same. This classical IR scheme can be referred to as a no-adaptive IR scheme. • Here we start with a high rate code if the channel conditions are bad retransmit at a lower rate. Also adaptively modify the modulation scheme. If the channel SINR is low use a constellation with a smaller alphabet size. 7. Type III Hybrid ARQ with AMC: Here AMC stands for adaptive modulation and coding. This scheme is similar to scheme (5) except that instead of incremental redundancy we use Type - III HARQ. Performance Evaluation of Different Hybrid ARQ Schemes The performance evaluation of the different ARQ schemes consists of the theoretical analysis as well as simulation studies to obtain the following parameters: (1) The average number of retransmissions (2) The probability of error (3) Over the air throughput (4) Service Throughput (5) Utilization 1. The average number of retransmissions depends on the frame error rate. In hybrid ARQ's the average number of retransmissions is reduced. But the difficulty is that each transmission carries redundant information. Hybrid ARQ scheme base on incremental redundancy reduces retransmission of redundant information. It is important to note that all hybrid ARQ schemes use error correcting codes. Incremental redundancy hybrid ARQ schemes can be constructed using rate-compatible punctured convolutional codes. 2. The probability of error depends on the channel, error correcting code used and Hybrid ARQ scheme. The union bound or the exact expression is obtained based on the nature of the channel and the distance properties of the error correcting code 3. The over the air through put is defined as the ratio of the total number of good bits to the total slots with transmissions multiplied by the slot duration. 4. Service throughput is defined as the ratio of the total number of good bits to total number of slots multiplied by the slot duration. 5. Utilization is the ratio of total slots with transmission to the total number of slots. In wireless networks there is packet loss due to congestion as well as packet loss due to collision. The TCP responds to packet loss by throttling the transmission rate. Therefore MAC has to enable retransmission of packets and collision avoidance strategies. The complex MAC introduces a large overhead. The retransmission is employed in CDMA2000 based on the nACKs by the RLP. In UMTS the ARQ is implemented by the RLC Performance of Hybrid ARQ techniques for WCDMA high data rates has also been studied in certain cases. The performance analysis is based on the performance comparison between Type - I Hybrid ARQ and Type-ll Hybrid ARQ based on incremental redundancy. Here they have shown that using HARQ schemes higher throughput and capacity is achieved when compared to the ARQ schemes currently employed in 3GPP WCDMA standard. The combining schemes can reduce the maximum number of transmissions required. It is important to note that HARQ schemes leads to increased complexity in the UE due to buffering if the round trip delay is large. The hybrid ARQ schemes in literature do not consider varying the parameters associated with retransmission based on the flows. Also the possibility of including multiple hybrid ARQ schemes when there is more than one flow is not considered is the literature presently available. SUMMARY OF THE INVENTION The primary object of the invention is to invent a method for efficient hybrid ARQ for wireless networks taking in to account the requirements of each flow in a wireless network. Some flows can be delay dependent, other flows can be rate dependent. There also exist flows which are rates as well as delay depended. It is another object of invention to define multiple hybrid ARQ strategies for different flows. Here at the same time it is possible that there are multiple flows associated to each user. It is another object of the invention to define the retransmission threshold depending on the nature of flow and the channel conditions. It is another object of the invention to invent the method to adaptively vary the retransmission timers depending on the nature of the flow. It is another object of invention to discuss the block hybrid ARQ parameters depending on the nature of the flow. The present invention relates to efficient hybrid ARQ schemes taking into account the nature of flows. Several methods to improve the efficiency of the hybrid ARQ scheme are included in this document. These include: • Methods adaptive vary the retransmission parameters based on the flow. The parameters are modified based on delay bound, rate jitter, delay jitter, throughput and channel state. Here we propose methods to combine codes. Propose methods to combine concatenated codes when the concatenated codes are decoded using iterative decoding. Method to have an efficient error detecting code without compromising on the effective throughput. • The present invention also discusses methods to pick best packets from successive retransmissions and combine then to obtain the transmitted packets. • For image and voice coded using multiple description codes we propose a scheme for traffic with delay bound. If the maximum number of transmissions is reached and we are able to decode the most critical information we can still reconstruct the image/voice which is recognizable. Therefore retransmissions are not necessary. • We propose Hybrid ARQ schemes based on multiple antennas. The output of the antennas is combined is several schemes including maximal ratio combining. • Further this invention proposes methods to modify the TCP time out. Accordingly this invention explains a method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein for Delay and Jitter sensitive traffic the rate of the channel code depends on the minimum required throughput efficiency where the throughput efficiency is defined as the portion of useful information bits in each packet transmitted considering both the PHY and MAC overheads. Accordingly the invention also explains a method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein the packets received from successive transmissions are combined and based on the delay and rate bound modify the combination of the retransmitted packets by combining a subset of the said packets whose SINR is greater than a threshold. Accordingly this invention explains a method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein flows change is dependent on the retransmission timers T_tx and T_rx where T_tx denotes the end of the transmission of a packet and the reception of the status packet. And T_rx denotes the duration of time after which the receiver detects an error in the transmitted packet. The invention also explains a method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein based on combining the transmitted and retransmitted data packet an iterative decoding algorithm is employed where based on a robust channel encoder the number of iterations required is reduced at the decoder for real time traffic. The invention also explains a method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein a block acknowledgement based on channel quality, delay and jitter is used resulting in gain in time where the block size is decided based on the nature of channel predicted for the duration of the transmitted block. Accordingly this invention also explains a method of Efficient Hybrid Automatic Repeat Request for Wireless Networks with a block ARQ scheme wherein few blocks are received correctly and it matches the QoS requirements in terms of the voice/image quality then no retransmission is required where if the QoS requirements are not met in terms of the quality then only those many blocks which are in error to satisfy the required QoS is retransmitted. Accordingly this invention also explains a method of Efficient Hybrid Automatic Repeat Request for Wireless Networks based on multiple antennas at the transmitter and receiver wherein combining the signal at the received antenna array is done by : (1) equal weighted combining ; (2) combining packets weighted by the SINR; (3) maximal ratio combining of the packets if the channel information is known where the signal at each element of the antenna array are combined after removing the effect of the channel; (4) combining outputs of the successive antenna elements using an iterative algorithm exchanging soft output information; and/or (5) combining the soft outputs using maximal ratio if the channel state information is known . These and other objects, features and advantages of the present invention will become more readily apparent from the detailed description taken in conjunction with the drawings and the claims. DETAILED DESCRIPTION OF THE INVENTION The preferred embodiments of the present invention will now be explained with reference to the different methods. The following description is illustrative of the invention and is not to be construed as limiting the innovation. Numerous specific details are described to provide a through understanding of the present invention. However in certain instances well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail. Method -1 As defined in the previous section we look for efficient hybrid ARQ schemes taking into account the channel state, delay bound, rate requirement and jitter requirement. Let /^denote delay bound, r^denotes the minimum required throughput and 7^denotes jitter, .i.e., the delay variance. Taking into account these three parameters the H-ARQ can be suitably defined for three classes of flow as follows: 1. Delay and Jitter sensitive traffic: For traffic which demands a minimum rate the following methods can be adopted for H-ARQ Type-I, H-ARQ Type-ll or Type-Ill H-ARQ. Here the rate of the channel code depends on the minimum required throughput efficiency. Throughput efficiency is defined as the portion of useful information bits in each packet transmitted considering both the PHY and MAC overheads. The following procedures can be adopted: Encode the data to be transmitted using Reed Solomon code. Initially transmit the frame with the useful information, MAC/PHY header and CRC bits alone. In the event of getting a NAK transmit part of parity bits with CRC. This process is continued in the event of getting a NAK. In this scheme the throughput efficiency is high. The initial transmission rate is high. Upon receiving NAK the part of the parity bits are transmitted. Using the transmitted parity bits and the initial information set transmitted the decoder tries to decode the packets. If the decoder is unable to decode further parity bits are send. This process is continued till the maximum number of retransmissions is reached or the packet is received correctly. 2. For traffic with a maximum admissible delay bound the data is encoded using a forward error correcting code and transmitted. The error correcting code is assumed to take care of the error introduced by the channel. Turbo coded schemes can be considered. For bandwidth constrained channels turbo trellis coded schemes will give an optimum performance. For delay sensitive applications it is essential to reduce the number of retransmissions. The packets are encoded with Turbo codes and transmitted over the wireless channels. With an optimal channel code the number of retransmissions is reduced and therefore the overall delay. 3. For traffic with maximum admissible delay another approach would be transmit the data packets using an antenna array at the receiver. An antenna array can be employed at the receiver also. The transmitted data packets are coherently combined at the receiver. The antenna gain over and above the coding gain obtained using the channel code increases the reliability of the transmitted data. Therefore the number of retransmissions required is reduced. This scheme is suited for data packets with a delay bound. At the receiver the data packets can be combined using in several ways. If the channel is known at the receiver maximal ratio combining can be employed. 4. Consider the case where the data is encoded by a serially concatenated code. Consider an outer Reed Solomon code and an inner convolutional code. Here we propose the system where the extrinsic information from successive retransmissions are combined using Markovian, maximal ratio and equal gain combining. 5. The CRC bits reduce the through put as extra bits have to be allocated for CRC. Consider the case where the data is transmitted using serial concatenated codes with an inner convolutional code or using turbo code. Here we multiply the data using a polynomial of degree 'n'. This acts as a CRC code of length 'n'. Here no extra bits are allocated for CRC code. Now encode the data using a CRC code. Then in the denominator of the turbo code or the convolutional code use the same polynomial of degree 'n'. Therefore we have an effective CRC code which can detect errors without explicitly allocating extra bits to the same. This scheme is considered when the required throughput is high. 6. Consider the case when the data is encoded by a serially concatenated code. Let the outer code be an outer Reed Solomon code and inner code be a convolutional code. There are two possible decoding schemes. The maximum likelihood decoding and the maximum a posteriori decoder (MAP). The data packets from successive transmissions are combined to recover the transmitted packet. In the case of MAP decoder we propose a scheme where the initial state of the iterative decoder is based on the data packet transmitted in the previous decoding attempt. Here we assume that the entire data packet is transmitted during successive retransmissions. Also the initial state can be obtained by maximal ratio combining the of states obtained from the previous transmissions. Method - II In this method, we propose effective ways to combine the packets received from M successive transmissions. Based on the delay and rate bound modify the combing strategy of the retransmitted packets. We can combine the following approaches (1) Combine a subset of the M packets whose SINR is greater than a threshold (2) Combine a subset of packets weighted by the SINR as well as the adaptive modulation and coding scheme. When SINR is low and a more robust coding and modulation scheme is used the probability of correct decoding is high. (3) The number of packets M depends on the maximum allowable delay. If the maximum allowable delay is small correspondingly M is chosen. (4) The channel model also has a bearing on M. If we consider a channel with finite number of states we can arrive at M based on the number of channel states. (5) Another approach is to measure the SINR. If we receive a NACK the constellation size is reduced and the rate of the channel code is reduced. When the rate of the code is reduced the minimum distance of the code increases. This increases the reliability. This can be done in a set of discrete steps depending on the channel. (6) Another approach is dependent on the complexity of the decoder. When the coding scheme is varied the complexity of the decoder increases and the battery power required at the decoder increases. For battery power constrained applications we propose a decoding scheme based on hard decision decoding. Otherwise one could choose the soft decision decoding based on the maximum likelihood decoding. Further the choice of the encoder also introduces a complexity of the required decoder. Here again the choice is based on the available battery power that the receiver can provide. Method - III In this method we change the retransmission timers based on the flows. Here we consider the following retransmission timers T_tx and T_rx. T_tx denotes the end of the transmission of a packet and the reception of the status packet. T_rx denotes the duration of time after which the receiver detects an error in the transmitted packet. If a set of packets have been delivered and a few more need to be transmitted with in t^ the T__rx can be decreased. This T_rx can be decreased linearly or exponentially between successive transmissions depending on the nature of traffic. If we are considering a real time application the waiting time can be exponentially reduced. For other applications where the longer delay but reliability is important the T_rx is decreased linearly. Method - IV Based on the rate requirement and battery energy requirement model modify the stopping criteria for iterative algorithms decoding in H-ARQ. In H-ARQ based on combining the transmitted and retransmitted data packet an iterative decoding algorithm can be employed. But the computational complexity of the decoding algorithm needs to be taken into account. The number of iterations can be determined based on the requirements of the traffic, e. g., for delay insensitive traffic a larger number of iterations can be set to ensure reliable transmission and for delay sensitive traffic, the number of iterations is set to a lesser value. Here we propose that the stopping criteria of the algorithm should also depend on the available battery power. Method - V Block H-ARQ based on channel quality, delay and jitter. Instead of an acknowledgement from each block consider a block acknowledgement. The advantage of block H-ARQ comes from gain in time. The block size is decided based on the channel prediction. The channel state impacts the SINR. The modulation and coding is decided for all the frames in the block based on channel prediction. Based on block ACK the set of blocks are retransmitted. The Block ACK indicates the frames in the block which are in error. In the Block ACK message the SINR associated with each frame is that is received in error is included. This enables the adaptive modulation and coding for retransmission of the block in error. Further in block H-ARQ we get multiple estimates of the SINR. The multiple estimates of the SINR gives a gives a better estimate of the channel. The above-presented description is of the best mode contemplated for carrying out the present invention. The manner and process of making and using it is in such a full, clear, concise and exact terms as to enable to any person skilled in the art to which it pertains to make and use this invention. New embodiments in particular, which also lie within the scope of the invention can be created, in which different details of the different examples can in a purposeful way be combined with one another. This invention is however, susceptible to modifications and alternate constructions from that disclosed above which are fully equivalent. Consequently, it is not the intention to limit this invention to the particular embodiment disclosed. On the contrary, the intention is to cover all modifications and alternate constructions coming within the spirit and scope of the invention as generally expressed by the following claims which particularly point out and distinctly claim the subject matter of the invention. Method - VI Block H-ARQ based on multiple description coding. Perform quantization of data into different levels. Consider an application involving voice, images or multimedia traffic. In the case of images it is known the edges preserve the important features. Consider encoding the image into several blocks with the important information in first block, the next important one in the second block and so on. Consider a similar encoding for both voice and multimedia. Here we propose a block ARQ scheme. (1) Suppose K1 blocks are received correctly and it matches the QoS requirements in terms of the voice/image quality, decode the data and no further retransmission is required. (2) If the QoS requirements are not met in terms of the quality retransmit only those many blocks which are in error to satisfy the required QoS. (3) If the maximum allowed end to end delay is reached here again decode the received blocks. If the minimum number of blocks which have the critical information are received correctly it is possible to get the data back. Method-VII H-ARQ based on multiple antennas at the transmitter and receiver. Here transmit the same data at each transmit antenna. Combine the data at each receive antenna. The received data at each receive antenna can be combined based on (1) equal weighted combining (2) Combining packets weighted by the SINR (3) If the channel information is known maximal ratio combining of the packets can be performed (4) Consider the case where the outputs of the successive antenna elements are combined using an iterative algorithm exchanging soft output information (5) In the case where the channel state information is known the soft outputs can be combined using maximal ratio combining. The foregoing description of illustrated embodiments of the present invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the present invention, as those skilled in the relevant art will recognize and appreciate. As indicated, these modifications may be made to the present invention in light of the foregoing description of illustrated embodiments of the present invention and are to be included within the spirit and scope of the present invention. Thus, while the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of embodiments of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. Therefore, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the present invention. It is intended that the invention not be limited to the particular terms used in following claims and/or to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include any and all embodiments and equivalents falling within the scope of the aooended claims. Glossary of Terms: AP: Access Point AR: Access Router ARQ: Automatic Repeat Request ACK: Acknowledgement Block H - ARQ: Block Hybrid ARQ CN: Correspondent Node DL: Down Link H ARQ: Hybrid ARQ UE: User Equipment We Claim 1. A method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein for Delay and Jitter sensitive traffic the rate of the channel code depends on the minimum required throughput efficiency where the throughput efficiency is defined as the portion of useful information bits in each packet transmitted considering both the PHY and MAC overheads. 2. A method as claimed in claim 1 wherein the data to be transmitted is encoded using Reed Solomon code where initially the frame is transmitted with useful information, MAC/PHY header and CRC bits alone. 3. A method as claimed in claim 1 wherein the said method is continued in the event of getting a NAK transmit part of parity bits with CRC. 4. A method as claimed in claim 1 wherein the decoder tries to decode the packets using the transmitted parity bits and the initial information set transmitted and parity bits are send if the decoder is unable to decode further where the said method is continued till the maximum number of retransmissions is reached or the packet is received correctly. 5. A method as claimed in claim 1 wherein for traffic with a maximum admissible delay bound the data is encoded using a forward error correcting code and transmitted where the error correcting code take care of the error introduced by the channel. 6. A method as claimed in claim 1 wherein traffic with a maximum delay bound is used to increase the probability of decoding in a minimum number of retransmissions where it is achieved using an error correcting channel code which corrects the error introduced by the wireless channel. 7. A method as claimed in claim 1 wherein the packet is encoded using turbo code and transmitted over the wireless channel where the decoding complexity of the turbo code is high. 8. A method as claimed in claim 1 wherein for traffic with maximum admissible delay the data packets are transmitted using an antenna array at the receiver where the transmitted data packets are coherently combined at the receiver. 9. A method as claimed in claim 1 wherein the antenna gain over and above the coding gain obtained using the channel code increases the reliability of the transmitted data and the number of retransmissions required is reduced. 10. A method as claimed in claim 1 wherein for data packets with a delay bound the data packets is combined at the receiver and if the channel is known at the receiver maximal ratio combining is employed. 11. A method as claimed in claim 1 wherein in a bandwidth constrained channel where the delay bound on the packets is specified a turbo trellis coded scheme is performed. 12. A method as claimed in claim 1 wherein when the data is transmitted using serial concatenated codes with an inner convolutional code or using turbo code the data is multiplied using a polynomial of degree 'n' which acts as a CRC code of length 'n'. 13. A method as claimed in claim 1 wherein when the required throughput is high the data is encoded using a CRC code where the denominator of the turbo code or the convolutional code use the same polynomial of degree 'n' thus detecting errors without explicitly allocating extra bits. 14. A method as claimed in claim 1 wherein when data is encoded by a serially concatenated code the data packets from successive transmissions are combined to recover the transmitted packet or the entire data packet is transmitted during successive retransmissions where the initial state is obtained by maximal ratio combining the states obtained from the previous transmissions. 15. A method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein the packets received from successive transmissions are combined and based on the delay and rate bound modify the combination of the retransmitted packets by combining a subset of the said packets whose SINR is greater than a threshold. 16. A method as claimed in claim 15 wherein the set packets are weighted by the SINR and the adaptive modulation and coding scheme where when SINR is low and when a robust coding and modulation scheme is used the probability of correct decoding is high. 17. A method as claimed in claim 15 wherein the number of packets depends on the maximum allowable delay and is chosen if the maximum allowable delay is small. 18. A method as claimed in claim 15 wherein the channel model depends on the number of packets. 19. A method as claimed in claim 15 wherein if a NACK is received the constellation size is reduced and the rate of the channel code is reduced where the rate of the code is reduced and the minimum distance of the code increases resulting in increased reliability. 20. A method as claimed in claim 15 wherein when the coding scheme is varied the complexity of the decoder increases and the battery power required at the decoder increases where for battery power constrained applications a decoding scheme based on hard decision decoding is used or a soft decision decoding based on the maximum likelihood decoding is chosen. 21. A method as claimed in claim 15 wherein the choice of the encoder introduces a complexity of the required decoder and the choice is based on the available battery power that the receiver provides. 22. A method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein flows change is dependent on the retransmission timers T_tx and T_rx where T_tx denotes the end of the transmission of a packet and the reception of the status packet. And T_rx denotes the duration of time after which the receiver detects an error in the transmitted packet. 23. A method as claimed in claim 22 wherein if a set of packets have been delivered and a few more need to be transmitted with in delay bound t^ the T_rx is decreased where the T_rx is decreased linearly or exponentially between successive transmissions depending on the nature of traffic. 24. A method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein based on combining the transmitted and retransmitted data packet an iterative decoding algorithm is employed where based on a robust channel encoder the number of iterations required is reduced at the decoder for real time traffic. 25. A method as claimed in claim 24 wherein for delay insensitive traffic which needs a high reliability a large number of iterations is set and for delay sensitive traffic, the number of iterations is set to a lesser value. 26. A method as claimed in claim 24 wherein the stopping criteria of the iterative algorithm depend on the available battery power. 27. A method of Efficient Hybrid Automatic Repeat Request for Wireless Networks wherein a block acknowledgement based on channel quality, delay and jitter is used resulting in gain in time where the block size is decided based on the nature of channel predicted for the duration of the transmitted block. 28. A method as claimed in claim 27 wherein the modulation and coding is decided for all the frames in the block based on channel prediction and based on block ACK the set of blocks are retransmitted where the Block ACK indicates the frames in the block which are in error. 29. A method as claimed in claim 27 wherein in the Block ACK message the SINR associated with each frame received in error is included where the Block ACK reduces the time required. 30. A method as claimed in claim 27 wherein for traffic which is sensitive to delay, based on the Block ACK the frames that are error are transmitted again where the transmitted packets have the same size and all the frames in the block are not be retransmitted which enables the adaptive modulation and coding for retransmission of the block in error. 31. A method as claimed in claim 27 wherein the adaptive modulation and coding is decided based on the measured SINR and required throughput where increasing the coding rate reduces the reliability of the decoder and increases the throughput. 32. A method as claimed in claim 27 wherein in block H-ARQ a multiple estimates of the SINR is got based on each frame in the block where the multiple estimates of the SINR are used to obtain an estimate of the channel state. 33. A method of Efficient Hybrid Automatic Repeat Request for Wireless Networks with a block ARQ scheme wherein few blocks are received correctly and it matches the QoS requirements in terms of the voice/image quality then no retransmission is required where if the QoS requirements are not met in terms of the quality then only those many blocks which are in error to satisfy the required QoS is retransmitted. 34. A method as claimed in claim 33 wherein if the maximum allowed end to end delay is reached the received blocks are decoded and if the minimum number of blocks which have the critical information are received correctly then the data is retrieved back accordingly. 35. A method of Efficient Hybrid Automatic Repeat Request for Wireless Networks based on multiple antennas at the transmitter and receiver wherein combining the signal at the received antenna array is done by : a. equal weighted combining ; b. combining packets weighted by the SINR; c. maximal ratio combining of the packets if the channel information is known where the signal at each element of the antenna array are combined after removing the effect of the channel; d. combining outputs of the successive antenna elements using an iterative algorithm exchanging soft output information; and/or e. combining the soft outputs using maximal ratio if the channel state information is known . 36. A method of Efficient Hybrid Automatic Repeat Request for Wireless Networks substantially as herein described particularly with reference to the descriptions. Dated this 25^^ day of May 2005

Documents:

0484-che-2004 abstract duplicate.pdf

0484-che-2004 claims duplicate.pdf

0484-che-2004 description(complete) duplicate.pdf

484-che-2004-abstract.pdf

484-che-2004-claims.pdf

484-che-2004-correspondnece-others.pdf

484-che-2004-correspondnece-po.pdf

484-che-2004-description(complete).pdf

484-che-2004-description(provisional).pdf

484-che-2004-form 1.pdf

484-che-2004-form 9.pdf