Decoupled maximum likelihood multiuser channel estimation for asynchronous DS-CDMA system

A decoupled maximum likelihood (DEML) channel estimation scheme using recursive matrix computation is proposed for asynchronous code-division multiple access (CDMA) communication systems. The transmission medium is characterized by the presence of multipath components and the parameters of interest are the delays and complex gains of the propagation paths. The DEML estimation is obtained using a training sequence. Followed by DEML estimation, a recursive algorithm is used to find the estimator so as to spread the computational time over each processing window. Lastly, the proposed recursive technique is extended to track a moderate time-varying fading channel using decision feedback. The performance of the derived algorithm is benchmarked against perfect channel knowledge on one hand and DEML estimator without decision feedback on the other hand in terms of bit-error-rate.