Cross-Layer 부호기법을 이용한 Hybrid-ARQ 기반의 협력통신 시스템 연구

Abstract

In recent years, the goal of providing high speed wireless data services has generated a great amount of interest among the research community. The main challenge in achieving reliable communications lies in the severe conditions that are encountered when transmitting information over the wireless channel.

Several researchers have shown that the capacity of the system, in the presence of flat Rayleigh fading, improves significantly with the use of multiple transmit and receive antennas. Based on this motivation, STC(space-time codes) have been developed in an attempt to exploit this promised capacity. These codes represent the best known codes for diversity systems with multiple transmit and multiple receive antennas over Rayleigh fading channels to date.

Concatenating LDPC codes to the transmit diversity achieves the coding gain from the concatenated LDPC codes and the diversity gain from the transmit diversity.

However, to feed the soft values to LDPC decoder, the soft values must be calculated from multiple transmitter and receiver antennas in Rayleigh fading channel. It requires high computational complexity to get the soft symbols by increasing number of transmitter and receiver antennas.

Therefore, this thesis proposed on effective algorithm for calculation of soft values from multiple antennas based on LLR. As result, This thesis shows that maximum 61% of computational complexity is reduced with a little loss of performance.

However, MIMO system is required such as diversity gains, multiple antennas, many limitations to design and complexity of calculation. So, these problem of solutions is proposed that a cooperative communication system using cross-layer coding method based on Hybrid-ARQ(H-ARQ). This thesis proposed cooperative H-ARQ system that can improve the above problems and can get the better performance. In proposed cooperative system with H-ARQ method, if the received signal from source node is satisfied by the destination preferentially, the destination transmits ACK message to both relay node and source node, and then recovers the received signal. In addition, if ARQ message indicates NACK message, relay node operates selective retransmission. Based on the simulation results in aspect to BER performance and throughput, the proposed method which combined cooperative system with H-ARQ based on cross-layer coding can improve spectral efficiency reliability of system compared with that of general H-ARQ system.