Comparison of multiple access interference in asynchronous MC-CDMA and DS-CDMA systems

In this paper we make a comparison between the multiple access interference (MAI) incurred in asynchronous multicarrier code division multiple access (MC-CDMA) and direct-sequence code division multiple access (DS-CDMA) systems for uplink satellite communications. Using a symbol by symbol recovery approach, we characterize the MAI produced by both systems in the absence of additive channel noise. For a given set of transmission offsets, the bit-error-rate (BER) is computed, and analyzed for an increasing number of users. This analysis has been performed for codelength´s of N = 8 (using Walsh-Hadamard codes) and N = 7 (using Gold codes). Simulations show that, on average, the MC-CDMA scheme outperforms DS-CDMA in an asynchronous non-selective environment for the spreading codes considered.