Department of Electrical Engineering,Sharif University of Technology
A unified multiple-access performance analysis and comparison of three multicarrier spread-spectrum multiple-access schemes, namely, MC CDMA (Multicarrier Code-Division Multiple-Access), MC-FH (Multicarrier Frequency Hopping) and a hybrid of the above systems, called DS-MC-FH (Direct Sequence MC-FH), in a multirate environment, where each user can have several multirate services, is provided. In MC-CDMA and MC-FH systems, users and their diverse services are differentiated by means of only one kind of signature code. However, in a DS-MC-FH scheme, different users and different services of the same user are distinguished through the first and second signature codes, respectively. The performance of the above systems are evaluated and compared, using a unified structure in synchronous and asynchronous nonfading and synchronous correlated Rayleigh fading channels, with a Maximum Ratio Combining (MRC) receiver. The near-far effect on the systems' performance is also investigated. The (second) signature in the MC-CDMA (DS-MC-FH)scheme is considered to be either a Pseudo-Noise (PN) sequence or a Walsh code. The authors analyses indicate that MC-CDMA systems with Walsh codes outperform the other schemes in different synchronous and asynchronous channels. DS-MC-FH systems with Walsh codes always surpass MC-FH systems. Furthermore, all of the schemes, except synchronous MC-CDMA systems with Walsh codes, are susceptible to a near-far effect with an MRC receiver.