Multi-rate access schemes for MC-CDMA

In order to accommodate different types of traffic in future wireless communications, it is necessary to consider a system, which can operate satisfactorily at multiple transmission rates. Due to its capability to cope with the hostile frequency selective fading, that limits transmission rate, and its suitability to handle multi- rate data, multi- carrier CDMA ( MC- CDMA) has recently drawn considerable attention as a suitable candidate for supporting multimedia services in wireless communications. Multi- rate access schemes where users are able to transmit at different data rates on MC- CDMA systems are presented in this paper. Four multi- rate access schemes: uncoded fixed spreading length ( UFSL), coded fixed spreading length ( CFSL), multi- code fixed spreading length ( MFSL) and variable spreading length ( VSL) schemes are proposed. With these schemes, different traffic such as voice, video and high rate data can be transmitted seamlessly through one MC- CDMA infrastructure. A chip- level minimum mean square error combining ( MMSEC) technique is employed for joint energy combining and interference cancellation purpose. The performance of these schemes with MMSEC is compared by both theoretical derivations and simulation results under frequency selective Rayleigh fading channels.