  Cognitive radios hold tremendous promise for increasing the spectral
efficiency of wireless communication systems. In this paper, an adaptive bit
allocation algorithm is presented for orthogonal frequency division
multiplexing (OFDM) CR systems operating in a frequency selective fading
environment. The algorithm maximizes the CR system throughput in the presence
of narrowband interference, while guaranteeing a BER below a predefined
threshold. The effect of imperfect channel estimation on the algorithm's
performance is also studied.
