Combined Spectrum Pooling and Adaptive Bit Loading for Cognitive Radio OFDM Based System

This paper presents the combination of adaptive bit loading and spectrum pooling to be applied in a cognitive radio orthogonal frequency division multiplexing (OFDM) based 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 spectrum in order to reduce interference to neighbouring system (legacy users). In this paper different OFDM adaptive bit loading algorithms are combined with several window functions, and the bit error rate performance of the system is simulated for a wide sense stationary uncorrelated scattering (WSSUS) mobile multipath channel. The new results of this paper show how promising is the combination of bit loading algorithm and window form