Adaptive Resource Allocation in Multiuser OFDM Systems Malik Meherali Saleh EE 381-14 March 08, 2005

Introduction/Background 4G cellular system proposes hybrid of Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) OFDM eliminates Intersymbol Interference TDMA/FDMA solutions for Multiuser OFDM Fixed allocation of subcarriers Multiuser Environment Creates channel diversity Assign users high gain subcarriers Motivation : Adaptive Multiuser OFDM systems

Key Paper #1 [Wong, Cheng, Letaief and Murch, 1999] Optimal: Minimize total transmit power Perfect Channel knowledge assumed Assumes fixed data rate for users Adaptive assignment of subcarriers, bits and power level to each user. Suboptimal solution Subcarrier allocation Single user bit allocation is applied to the assigned subcarrier for each user

Key Paper #2 [Jang and Lee, 2003] Fixes total transmit power and maximizes sum capacity Applies Subcarrier allocation first Follows it up by transmit power allocation Provides 2 methods for power allocation Water filling policy Equal distribution Results show total data rate increases with increase in users

Key Paper #3 [Shen, Andrews and Evans, (Draft) 2004] Focus on Quality of Service parameter Power constraint with adaptive rate Maintains proportional rates between users Predetermined ratios, variable fairness index Reduce computation complexity by suboptimal algorithm Subcarrier allocation Maximizing sum capacity with Power allocation Both blocks include proportional values Maintain proportional rates among users for EACH channel realization. Explicitly control the capacity ratios among users, each user meets his target data rate Ratios are predetermined and fairness measures the fraction of capacity, 1 meaning all users have same ratios/capacity Like 1 and 2 the system is broken up into two blocks, the only difference is that the subcarrier allocation takes into account the proportional fairness, different from the first two The second block consists of power allocation over the predetermined subcarriers with proportional fairness

What I propose to do I propose to study Paper 2 and 3 in detail and simulate them with controlled parameters and compare them on BER/signal quality, sum capacity, the number of users, average channel power per user. Simulation files I plan to use the simulation files provided for Paper 3 at http://www.ece.utexas.edu/~bevans/projects/ofdm For Paper 1, I hope to get in touch with the authors for the simulation code I will also compare sum capacity of Paper 2 & 3 to TDMA/FDMA approach in Multiuser OFDM