Submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Telecommunications, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 2009

Multiuser OFDM is considered as a modulation and multiple access method for next generation wireless systems. It is being widely deployed in broadband wireless networks due to its capability to overcome the channel impairments and support high data rates. Adaptive subchannel and power allocation in the downlink of multiuser OFDM systems is presented in this thesis. The problem of maximizing the overall throughput subject to the total transmit power constraint for each user is considered. Compared to existing algorithms, the proposed algorithms is unique in trying to directly incorporate the queue size or buffer state information into the allocation decisions. Our algorithm is divided into two steps, namely subchannel assignment and power allocation. The subchannel assignment is based on not only the channel conditions but also the buffer state information of each user. In this way, the limited transmission resources can be utilized efficiently. The power allocation step is formulated as a convex optimization problem and solved by standard algorithms in Matlab. Matlab is used to simulate the multiuser OFDM system. Simulation results shows that the proposed algorithm achieves better throughput and delay performances than existing algorithms. Finally, the performance improvement obtained from the use of buffer state information is quantified.