A Survey on Incremental Relaying Protocols in Cooperative Communication

Cooperative communication is one of the latest techniques in wireless communication to form virtual antenna arrays. Cooperative communication is an alternative method for MIMO (Multiple input multiple output) system. This scheme assumes TDMA (Time division multiple access) channel accessing and divides the communication into two phases which includes direct transmission and retransmission by the relay terminal. A few cooperative diversity protocols ,for example fixed relaying, selection relaying and incremental relaying are used in order to perform different sorts of processing by the relay terminals, and combining at the destination terminals. Each diversity protocol exhibits its own unique performance. Fixed relaying can be further classified into amplify and forward (AF) relaying and decode and forward (DF) relaying. In AF , relay users amplifies the signal and retransmits it, and in the case of DF, the relay users decodes and retransmits the signal. The Selection relaying is performed by taking the fading coefficient into account. In this report, the recent works on incremental relaying protocol has been summarized. Incremental relaying is based on the feedback mechanism. In this scheme, relay users perform retransmission only if needed, based on the received SNR (Signal to noise ratio) or decoding error that occurs during direct transmission. It is used in cooperative communication in order to attain efficient use of degrees of freedom and to overcome bandwidth inefficiency. The authors have presented a number of protocols such as Incremental selection amplify and forward (ISAF), Joint incremental selection relaying (JISR), Fractional Incremental relaying (FIR), Selective Fractional Incremental relaying (SFIR) and Efficient Incremental relaying (EIR).