Dynamic Sub-Channel Allocation in Multiuser OFDM Systems to Achieve Variable Data Rate

This paper investigates the problem of dynamic multiuser subchannel allocation in the downlink OFDM systems. In traditional TDMA or FDMA systems, resource allocation for each user is non-adaptively fixed. Since the subchannel allocations among the users are not optimized, a group of users is likely to suffer from poor channel gains resulting from large path loss and random fading. To resolve this problem a low-complexity adaptive subchannel allocation algorithm is proposed in this paper. By adaptively assigning frequency subchannels, n take advantage of channel diversity among users in different locations, which is called Multiuser diversity. The capacity of MU-OFDM is maximized when each subchannel is assigned to the user with the best channel-tonoise ratio for that subchannel. However, fairness among the users cannot generally be achieved with such a scheme. In this paper, a set of proportional fairness constraints is imposed to assure that each user achieve a required data rate, that ensures quality of service. In the proposed algorithm, subchannel allocation is performed by assuming an equal power distribution. Index Terms OFDM, Sub-Channel, Multiuser, Variable Data Rate.