A MAXIMUM LIKELIHOOD CDMA RECEIVER USING THE EM ALGORITHM AND THE DISCRETE WAVELET TRANSFORM - Acoustics, Speech, and Signal Processing, 1996. ICASSP-96. Conference Proceedings., 1996 IEEE Inte

A Maximum Likelihoocl (ML) method for joint estimation of amplitude, phase, time delay, antl da ta demodulation in a single-user direct sequence spread spectrum comniunication system is developed. The likelihood function is analytically intractable, so a recursive estimation algorithm is considered. The Expectation Maximization (EM) algorithm has been used in similar problems, however, in this case i t is not computationally efficient. Recently, a variant of the EM algorithm, called Space Alternating Generalized EM (SAGE), has been derived. In this work we apply the SAGE algorithm to the sequence estimation problem in a way which results in simple sequential updates of all the estimated parameters. An important feature of the proposed algorithm is the use of a discrete wavelet decomposition of the received signal as a sufficient statistic. The consequence is that all the information is still available to the receiver, while the complicated estimation problem is considerably simplified. Computer simulations of a single user system were performed. I t is shown that the algorithm has fast convergence, and essentially achieves optimal performance.