Multiuser OFDM with adaptive subcarrier, bit, and power allocation

Multiuser orthogonal frequency division multiplexing (OFDM) with adaptive m ultiuser subcarrier allocation and adaptive modulation is considered. Assum ing knowledge of the instantaneous channel gains for all users, we propose a multiuser OFDM subcarrier, bit, and power allocation algorithm to minimiz e the total transmit power. This is done by assigning each user a set of su bcarriers and by determining the number of bits and the transmit power leve l for each subcarrier. We obtain the performance of our proposed algorithm in a multiuser frequency selective fading environment for various time dela y spread values and various numbers of users. The results show that our pro posed algorithm outperforms multiuser OFDM systems with static time-divisio n multiple access (TDMA) or frequency-division multiple access (FDMA) techn iques which employ fixed and predetermined time-slot or subcarrier allocati on schemes. We have also quantified the improvement in terms of the overall required transmit power, the bit-error rate (BER), or the area of coverage for a given outage probability.