Multiuser detection for MC-CDMA system with M-QAM using semidefinite programming relaxation

A multiuser detector based on semidefinite programming (SDP) is proposed for multicarrier code-division multiple-access (MC-CDMA) systems with M-ary quadrature amplitude modulation (M-QAM). It is shown that maximum likelihood (ML) detection can be carried out by ´relaxing´ the associated integer programming problem to a SDP problem, which leads to a detector of much reduced complexity. Computer simulations demonstrate that the proposed detector offers a symbol-error rate (SER) performance which outperforms existing suboptimal detectors, and the computational complexity of the proposed detector is considerably reduced compared with that of ML detector.