Investigation Of Hybrid Automatic Repeat Request Techniques In Wireless Relay Networks

In wireless communication systems, the spectrum efficiency and the transmission reliability should be guaranteed simultaneously. For the special scenario with the high speed mobility and wide frequency bandwidth, the higher requirements for both spectrum efficiency and transmission reliability are presented. The Forward Error Correction (FEC) can correct the transmission error via the channel coding technique, which can guarantee the spectrum efficiency. However, it degrades the transmission reliability when the channel error can't be fully corrected. In the other way, the automatic repeat request (ARQ) may check whether the errors exist in the received packet. If the packet has errors, it will be transmitted repeatedly, which will lead to a high reliability in the cost of a low transmission reliability. In order to support the high spectrum efficiency and transmission quality, the hybrid automatic repeat request (HARQ) is proposed, which combines the FEC and ARQ together.This paper introduces the definitions, research background, the state-of-art development, and challenges for HARQ techniques firstly. The theoretical performance metrics for these three typical HARQ schemes are derived, which includes the outage probability, average delay and average throughput. According to the derived expressions for these three performance metrics, the performances of these three HARQ schemes are compared, and the simulation results are discussed.With the evolution of wireless communication systems, to improve the communication performances, the wireless relay technique is utilized to extend the network coverage and increase the system capacity. Especially, the users in the cell edge can also get good performances. The HARQ schemes applied in the wireless relay system can improve the spectrum efficiency and transmission reliability further, however, how to utilize the HARQ in wireless relay systems is still a challenging work. Based on the survey of wireless relay researching and impacts on the network structure, we investigate the mechanisms and theoretical performances of the HARQ schemes in wireless relay systems. According to the different relaying configurations, the corresponding transmission mechanisms are designed, and the theoretical performances are analyzed, the simulation performances are discussed as well.The novelty of this paper includes:(1) Three HARQ schemes in the single relay node model are designed, and the outage probability expressions are derived. The simulation results show the performance comparisons. (2) One new HARQ scheme in two relays nodes model is presented, where the outage probability expressions are derived. Simulation performance is compared between the two-relay-node and single-relay-node models.