Iterative multiuser detection with spectral efficient relaying protocols for single-carrier transmission

In this paper, we present an iterative multiuser detection scheme using frequency-domain equalization (IMDFDE), which can be incorporated into a single carrier frequency division multiple access (SC-FDMA) framework. The IMD-FDE scheme employs a different interleaver for each user at the transmitter, and removes multiuser interference with an iterative detection method in the frequency domain at the receiver. The extrinsic information transfer (EXIT) charts and bit-error rate (BER) plots are presented to investigate the iterative behavior of the IMD-FDE over additive white Gaussian noise and multipath fading channels. In a conventional time-division multiple-access (TDMA)-based relay protocol, cooperative transmission over two time slots leads to a 50% loss in spectral efficiency. We propose two spectral efficient relay protocols, where multiple sources access a relay, destination, or both simultaneously. We also present a new iterative detection scheme that effectively removes multiuser interferences for the proposed relay protocols.With the proposed protocols and the aid of iterative multiuser detection scheme, the proposed relay-assisted SC-FDMA with IMD-FDE can obtain diversity gain without sacrificing spectral efficiency and approaches the single-user bound over time-varying and frequency-selective fading relay channels.