Title :
A maximum likelihood CDMA receiver using the EM algorithm and the discrete wavelet transform
Author :
Sharfer, Ilan ; Hero, Alfred O.
Author_Institution :
Dept. of Electr. Eng. & Comput. Sci., Michigan Univ., Ann Arbor, MI, USA
Abstract :
A maximum likelihood (ML) method for joint estimation of amplitude, phase, time delay, and data demodulation in a single-user direct sequence spread spectrum communication 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 it is not computationally efficient. A variant of the EM algorithm, called space alternating generalized EM (SAGE), has been derived. 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. It is shown that the algorithm has a fast convergence, and essentially achieves optimal performance
Keywords :
amplitude estimation; code division multiple access; convergence of numerical methods; delays; estimation theory; maximum likelihood estimation; phase estimation; pseudonoise codes; radio receivers; recursive estimation; spread spectrum communication; transforms; wavelet transforms; EM algorithm; SAGE algorithm; amplitude estimation; computer simulations; convergence; data demodulation; direct sequence spread spectrum communication; discrete wavelet decomposition; discrete wavelet transform; expectation maximization algorithm; likelihood function; maximum likelihood CDMA receiver; maximum likelihood method; phase estimation; received signal; recursive estimation algorithm; sequence estimation; sequential updates; single-user DS-SS communication system; space alternating generalized EM; sufficient statistic; time delay estimation; Algorithm design and analysis; Amplitude estimation; Delay effects; Delay estimation; Demodulation; Maximum likelihood estimation; Multiaccess communication; Phase estimation; Recursive estimation; Spread spectrum communication;
Conference_Titel :
Acoustics, Speech, and Signal Processing, 1996. ICASSP-96. Conference Proceedings., 1996 IEEE International Conference on
Conference_Location :
Atlanta, GA
Print_ISBN :
0-7803-3192-3
DOI :
10.1109/ICASSP.1996.548010