A novel multi-user low complexity bit allocation algorithm in cognitive OFDM networks based on AM-GM inequality

Multi-user cognitive orthogonal frequency division multiplexing (C-OFDM) is an extremely promising technique for achieving high transmission capacity in the next generation cellular and wireless local area network (WLAN) systems with limited spectrum resources. Since the greedy bit allocation algorithm is the optimal method for single user, however, in the case of plenty of users and bits to be distributed, the computational complexity will be extraordinarily unacceptable. This paper presents a new bit and power allocation scheme for COFDM systems with the purpose of minimizing the interference power by constraining the fixed data rate and bit error rate. The presented bit allocation algorithm is derived from geometric sequence of the additional one bit transmission power required by the sub-carriers and the AM-GM inequality. Consequently, compared with the algorithm existing now, this algorithm has a simple procedure and low computational complexity. The MATLAB Simulation results show that the proposed algorithm is superior to the traditional algorithm, while reducing the computational complexity from exponential to linear in the number of sub-carriers.