Multiuser diversity and adaptive bit loading for OFDM-based spectrum agile radios

In this paper we discuss exploiting multiuser diversity and adaptive modulation in conjunction with spectral load smoothing (SLS) as a medium access control protocol for spectrum agile radios (SAR) in a multiuser OFDM/OFDMA based wireless communication system operating in frequency selective fading channel. The ability of the spectrum agile radios to identify unused spectrum can be used effectively to assign sub- carriers and bits adaptively depending on the user´s channel state information in a distributed fashion. We illustrate by simulation the performance improvement in terms of the bit error rate obtained for a multiuser OFDM system when multiuser diversity and adaptive bit loading is used in combination with SLS.