CHANNEL ESTIMATION ALGORITHMS FOR OFDM-IDMA: COMPLEXITY AND PERFORMANCE

A number of channel estimation algorithms for iterative receivers are compared for the case of an up-link orthogonal frequency division multiplexing interleave division multiple access (OFDM-IDMA) system. Both pilot based algorithms, used to obtain an initial estimate, as well as semiblind decision-directed algorithms working as a component of the iterative receiver are considered. Algorithms performing either joint minimum mean square error (MMSE) channel estimation,or iterative estimation using space-alternating expectation maximization (SAGE), are evaluated. The considered algorithms differ in terms of complexity, as well as performance. The complexity versus performance tradeoff is at the focal point.There is no single channel estimator providing the best trade-off and the analysis shows how the system load (number of users)and the SNR influence the estimator choice. Keywords—Channel estimation, OFDM-IDMA, algorithm complexity, expectation maximization EM), SAGE, discrete prolate spheroidal (DPS) sequences.