Adaptive combining in MB-OFDM UWB systems

In this paper, an adaptive combining scheme based on a constrained least-mean-square (LMS) algorithm is proposed for multi-band orthogonal frequency-division multiplexing (MB-OFDM) ultra-wideband (UWB) systems. The minimum mean-square-error (MMSE) combining is achieved adaptively at the cost of using a small amount of training symbols. Moreover, the channel state information (CSI), which is usually employed in conventional schemes, can be obtained from the set of converged weights in our scheme. The superiority of the proposed algorithm is that, in all cases, the convergence behavior is only governed by the step size normalized by the input power to the adaptive filter, not influenced by input signal correlation matrix. Analytical expressions are derived for the constraints and some parameters of the algorithm. Simulation results confirm the effectiveness and correctness of the derived expressions.