Combined spectrum pooling and adaptive bit loading for cognitive radio ofdm based system

Abstract

This paper presents the combination of adaptive bit loading and spectrum pooling to be applied in a Cognitive Radio system. Adaptive bit loading is a method to adapt the constellation size of the transmitted signal according to the channel variations by exclusion of heavily faded carriers from transmission and as a compensation higher modulation modes are allocated to subcarriers with good SNR. Windowing of OFDM signal is a spectrum pooling method for shaping the signal spectrumin order to reduce interference to neighbouring system ( legacy users). In this paper different OFDM adaptive bit loading algorithms are combined with serval window funtions, and the bit error rate performance of the system is simulated for a wide sense stationary uncorrelated scattering (WSSUS) mobile mutlipath channel. The new results of this paper show how promising is the combination of bit loading algorithm and window form.