Optimal Combining, Partial Cancellation, and Channel Estimation and Correlation in DS-CDMA Systems Employing the Generalized Detector

The symbol-error rate (SER) of a quadrature subbranch hybrid selection/maximal-ratio combining scheme for 1-D modulations in Rayleigh fading under employment of the generalized detector (GD), which is constructed based on the generalized approach to signal processing in noise, is investigated. At the GD, N diversity branches are split into 2N in-phase and quadrature subbranches. Traditional hybrid selection/maximal-ratio combining is then applied over 2N subbranches. M-ary pulse amplitude modulation, including coherent bi-nary phase-shift keying (BPSK), with quadrature subbranch hybrid selection/maximal-ratio combining is investigated. The SER performance of the GD under quadrature subbranch hybrid selection/maximal-ratio combining and hybrid selection/maximal-ratio combining schemes are investigated and compared with the conventional hybrid selection/maximal-ratio combining receivers. The obtained results show that the GD with quadrature subbranch hybrid selection/maximal-ratio combining and hybrid selection/maximal-ratio combining schemes outperform the traditional hybrid selection/maximal-ratio combining receiver. Procedure of selecting the partial cancellation factor for the first stage of a hard-decision partial parallel interference cancellation of the GD employing in direct-sequence code-division multiple access (DS-CDMA) systems is proposed. A range of the optimal partial cancellation factor, where the lower and upper boundary values can be explicitly calculated from the processing gain and the number of users of the DS-CDMA system, is derived based on the Price’s theorem. Computer simulation results confirmed that, using the average of these two boundary values as the partial cancellation factor for the first stage, we are able to reach the bit error rate (BER) performance that is very close to the potentially achieved BER performance using the GD and surpasses the BER performance of the real partial cancellation factor for DS-CDMA systems discussed in literature. Channel estimation errors have to be taken into account under analysis of receiver in order to the system performance will be not degraded under practical channel estimation. In this paper, we propose the GD, which takes the estimation error of maximum likelihood (ML) multiple-input multiple-output (MIMO) channel estimation and receiver spatially correlation into account in computation of the minimum mean square error (MMSE) GD and log-likelihood ratio (LLR) of each coded bit. Comparative analysis and simulation results show that the proposed MMSE GD can obtain sizable performance gain and outperforms the existing soft-output MMSE vertical Bell Lab Space Time (V-BLAST) detector and its modification versions.