Blind Constant Modulus Multiuser Detection in Multipath Fading Channel via Contracting Regularized BFGS

In this paper, the problem of blind multiuser detection based on constant modulus (CM) criterion is investigated for code division multiple access (CDMA) systems with multipath fading channel. The resultant optimization problem of blind linearly constrained CM multiuser detection is difficult to solve due to the multipath effect and fourth-order cost function. Towards this end, an approach based on contracting regularized BFGS algorithm is proposed. Specifically, the problem is firstly converted into a version of real-valued form. Then, the contracting regularized BFGS algorithm is employed to avoid solving the second derivative and ensure that the approximate Hessian matrix is non-singular. Simulation results show that the proposed method improves the system's robustness by reducing the sensitivity to the number of symbols. Moreover, it can obtain superior performance in terms of output signal-to-interference-plus-noise ratio (SINR) and bit-error rate (BER) at high signal-to-noise ratio (SNR) regime.