Performance Evaluation and ParameterOptimization of MC-CDMA

The performance of multicarrier systems depends on the propagation channel behavior. The latter is subject to time and/or frequency selectivity. The designer has to select properly the guard interval and the number of carriers for a given system bandwidth to combat the channel dispersiveness. In this paper, we investigate the sensitivity of downlink multicarrier code-division multiple-access (MC-CDMA) performance to these parameters in different environments. We derive closed-form expressions of the useful and the different interference powers after maximum ratio combining and despreading. The optimum parameters correspond to the minimum of the signal-to-noise-ratio degradation. It turns out that the derivations in the paper of Steendam and Moeneclaey ( IEEE Trans. Commun., 1999) that are restricted to the orthogonal frequency-division multiplexing (OFDM) system are a particular case of our results. Numerical evaluation of the analytical expressions reveals that the optimum parameters of the MC-CDMA and its corresponding OFDM system are similar and depend in the same way on the channel characteristics. We show in this paper that the load of the MC-CDMA system only has small influence on the optimization of the parameters. Therefore, from the point of view of parameter optimization, single-user transmission is sufficient to find the optimum parameters. Furthermore, as the optimum parameters mainly depend on the channel characteristics, similar conclusions can be drawn for the uplink transmission