An adaptive MAC-PHY approach for medium access control in VBR MC-CDMA systems

The capability of MC-CDMA to support asynchronous multi-user variable-bit-rate (VBR) transmission over multipath channels is exploited, jointly with an efficient medium access control (MAC) strategy, in order to allow a significant number of VBR users to share the same bandwidth with different quality of service profiles. An application scenario related to WLAN transmission has been considered in order to assess the proposed MAC methodology. Available radio resources (i.e. the orthogonal subchannels) are selectively attributed to transmitting users depending on their achieved performance at the MAC level, measured by an "intelligent" access point (AP). When the quality level is not satisfactory for one or more users, the AP issues a decrease of the data rate for such users while providing them with an increased number of subcarriers, in order to guarantee a lower bitrate fostered against frequency-selective channel distortions. Performance is evaluated through extensive simulation, demonstrating the good performance and high flexibility of the approach.