Hybrid ARQ Method Research Based On Cooperative Communication

As the developing of the 4G wireless communication system, there is a larger demand for the communication development. Compare with the 3G digital communication system, the 4G system need to provide higher data rate, better QoS (Quality of Service), and should be more secure and flexible, while economize the frequency resource at the meantime. The 4G system should support non-symmetrical and many other operations, and make it clear that the wireless access network and the IP network are integrate each other with the development. For these reason, many people make a lot of research and develop some crucial technology, including MIMO (Multiple-Input Multiple-Output), OFDM (Orthogonal Frequency Division Multiplexing), Smart Antenna technology, and Cooperative Communication technology. Cooperative Communication, which provides a real practical use for MIMO, is a pretty hot research direction, and it might bring an evolution in wireless communication. As a new communication conception, Cooperative Communication is being researched and improving all the time.Hybrid ARQ (Automatic Repeat reQuest), which integrate FEC and ARQ technology and take a good advantage of both, is a better error control scheme. The truth that it is being widely used in 3G wireless system, proves its high efficiency and better reliability. Thus we should make a deep research of Hybrid ARQ in Cooperative Communication system, and provide better schemes for the development of the 4G system. This paper, aiming at the practical use and the performance of the Hybrid ARQ scheme in Cooperative Communication system, makes such research as below:Bases on the multi-relay communication system, a Hybrid ARQ system model that single user communicate with the base station while using multi-relay is presented in chapter 3. In this system, the user sends the data to multi-relay, and then the relays transmit data to the base station, and the base station combine the data which transmitted by the relays with MRC (Maximum Ratio Combining). If an error is detected at the decoding, the base station will send a NAK to relays, and then the relays need to retransmit the data. In this chapter, we do a theory research for the system performance, and make some simulation with different relay number. In these researches, it is clear that the Hybrid ARQ performance is greatly improved while increasing the relay number, such as a higher throughput and a lower PER. In chapter 4, aiming at retransmission problem in cooperative communication, proposes a new hybrid ARQ scheme when two users cooperatively communicate with the base station.By sending packets in time-sharing slots, each user stores packets transmitted by its partner last time. After receiving ACK/NAK, each user searches for packets needed to be retransmitted according to indications of the BS. These packets mixed with newly generated ones are then forwarded in the next time slot. This scheme, utilizing space diversity gain introduced by the cooperative communication system, greatly improves the performance of hybrid ARQ. We compared our cooperative system with another system where each user communicates with the BS independently. Moreover, through comparisons of throughput, PER and average delay varying with SNR, we proved that our system could achieve higher throughput and lower PER in the same channel state while increasing the average delay during theoretical analysis and simulation.