Abstract: To solve the spectrum resource allocation problem of multiuser in cognitive radio system based on OFDM， a bit and power allocation algorithm was proposed. Firstly， the transmit power of secondary users was constrained to guarantee the communication quality of service (QoS) of secondary user. Secondly， the twostep method and the proportion gene were used to avoid the disequilibrium of spectrum resource allocation. Finally， the algorithm was simulated and the results of the allocation about secondary users showed that the presented method could not only guarantee each user’s QoS but also increase the channel capacity.

Key words: OFDM(orthogonal frequency division multiplexing), cognitive radio, spectrum resource allocation, QoS(quality of service), proportion gene