An iterative expectation-maximization algorithm based joint estimation approach for CDMA/OFDM composite radios

In this paper, an innovative frequency domain joint estimation algorithm for synchronization parameter and channel impulse response (CIR) in direct sequence code division multiple access (DS-CDMA) systems is proposed. The algorithm is based on the expectation-maximization (EM) method. It can provide accurate estimation of channel state information and synchronization parameter for a DS-CDMA receiver even with a simple equalization module (e.g., an one-tap multiplier based frequency domain equalizer (FDE)), and a radio receiver with this approach performs better than a costly multi-tap multiplier based equalizer, such as the time domain equalizer (TDE). A generic receiver architecture based on the frequency domain equalization for a composite radio, which works in both CDMA and orthogonal frequency division multiplexing (OFDM) modes, is also proposed. The Cramer-Rao Lower Bound (CRLB) of the proposed estimator and its optimization scheme are derived. This architecture can be implemented with an iterative approach, and the results demonstrate that this adaptive receiver performs very well with a relatively low cost.