Interference suppression schemes by linear combining for wireless multiuser relay communications

This paper proposes interference suppression schemes by linear combining for wireless multiuser relay communications. Interference from base stations and relays in neighboring cells degrades bit error rate (BER) performance of mobile stations (MSs) near cell boundaries. To suppress such interference for half-duplex relay systems, the proposed methods linearly combine received signals of the first and second phases at MS. Without channel state information (CSI) feedback, weight coefficients for the linear combining are first evaluated under the minimum mean-squared error (MMSE) criterion and then estimated by the recursive least-squares (RLS) algorithm. The MMSE combining requires information on preamble symbols of all MSs for channel estimation whereas the RLS-based linear combining requires only information on those of the target MS. In addition to the preamble symbols, the RLS algorithm can use detected symbols, which performs the decision-directed estimation. Computer simulations for orthogonal frequency-division multiplexing (OFDM) transmission under two-cell and frequency selective fading conditions are conducted. It is demonstrated that the RLS-based linear combining with the decision-directed estimation is superior to the RLS-based linear combining using only the preamble and can slightly outperform the MMSE combining with imperfect CSI under low average E_b/N₀ when the number of preamble symbols is as small as four.