Sensitivity of Multi-Carrier Two Dimensional Spreading Schemes to Synchronization Errors

International audienceThis paper presents the impact of synchronization errors on the performance of a downlink multi carrier two dimensional spreading OFDM-CDMA system. This impact is measured by the degradation of the Signal to Interference and Noise Ratio obtained after despreading and equalization. The contribution of this paper is twofold. First, we use some properties of random matrix and free probability theories to derive a new expression of the SINR. The latter is then independent of the actual value of the spreading codes while still accounting for the orthogonality between codes. This model is validated by means of Monte-Carlo simulations. Secondly, the model is exploited to derive the SINR degradation of OFDM-CDMA systems due to a synchronization error which includes a timing error, a carrier and a clock frequency offsets. It is also exploited to compare the sensitivities of MC-CDMA and MC-DS-CDMA systems to these errors in a frequency selective channel. This work is carried out for zero-forcing and minimum mean square error equalizers