An efficient optimization approach for packet-wise DF and incremental DF relaying for uplink CDMA communications

In this paper, we define a multi-access interference (MAI) cost that can assess the extra interference, inherent to relaying use and perceived by the whole cellular network. This MAI cost shadows an implicit and smart power control for CDMA uplink communications. In fact, this cost takes into account not only the reception quality required at the serving base station but also the global interference generated to all others base stations in the cellular system. Here, the optimization goal aims to enhance the system performance, in terms of Packet-Error-Rate (PER), for a required quality of service (QoS). The optimization approach is achieved for both Decode-and-Forward (DF) and Incremental DF relaying schemes, carried out on packet-by-packet basis. A variety of simulation results are obtained using the analytical expressions of Packet-Error-Probability (PEP) that we derive for both DF and IDF schemes. By way of an example, for a target PER of 10^-2, our optimized IDF scheme could afford more than 13 dB gain, in terms of MAI cost reduction, over the direct transmission scheme. Furthermore, simulation results underline that the optimized IDF relaying is more powerful than the optimized DF scheme and provides as much as 3 dB gain for some relay positions.