Cooperative Request-answer Schemes for Mobile Receivers in OFDM Systems

Inhalt:
In this paper we propose a practical solution to implement the symbol request sharing (SRS) cooperative scheme in real systems. The SRS scheme is designed for systems with a source and a destination among a group of receivers. The idea of cooperation is that nearby receivers assist the destination in order to enhance its information reception and avoid a retransmission from the source if possible. The SRS scheme follows a request-answer strategy. Specifically, we evaluate SRS when quantization is considered. For an ideal case without quantization, SRS achieves spatial diversity by performing maximum ratio combining (MRC) on selected subcarriers of a coded OFDM-based system. However, it turns out that SRS fails when the shared information is quantized prior to its retransmission to the destination. To overcome this drawback the SRS-EQ scheme is introduced, which is equivalent to SRS. It performs a phase correction at the relays before information is shared. It is shown that SRS-EQ is a viable option for cooperation in real systems.