Scheduling for throughput optimization in WiMAX networks

WiMAX emerged as one of the important Broadband Wireless Access (BWA) networks based on OFDMA technology and is anticipated to be an alternative to wired broadband networks. WiMAX supports different emerging applications with different Quality of Service (QoS) requirements like voice over IP (VoIP), video conference, voice conference and online gaming. Those emerging wireless applications have high throughput demand and impose a challenge to the underlying Radio Access Network (RAN) scheduling algorithms. Efficient allocation of WiMAX shared resources like subchannels is critical to meeting the high throughput demand.;The WiMAX resource allocation algorithms determine which users to schedule, how to allocate subcarriers to them, and how to determine the appropriate power levels for each user on each subcarrier. In WiMAX, the DL TDD OFDMA subframe structure is a rectangular area of N subchannels by K time slots. Users are assigned rectangular bursts in the downlink subframe. The burst size varies based on the user's channel quality and data to be transmitted for the assigned user.;In this dissertation we study the problem of assigning users to DL bursts in WiMAX TDD OFDMA system with the objective of maximizing downlink system throughput for the PUSC subchannelization permutation mode. We show that finding the optimal burst assignment that maximizes throughput is NP-hard. In this dissertation, we study this problem following two distinct approaches: (1) Integer Programming Approach: we formulate the problem as an IP problem and then relax it to LP, we propose different methods to resolve conflicts resulting from the LP relaxation and through extensive simulations we compare the performance of the proposed conflict resolution methods to the optimal solution. (2) Best Channel Approach: we propose several efficient and effective methods to assign bursts to users based on channel quality, we prove that our Best Channel burst assignment method achieves a throughput within a constant factor of the optimal and through extensive simulations with real system parameters, we study the performance of the Best Channel burst assignment method. To the best of our knowledge, we are the first to study the problem of DL Burst Assignment in the DL OFDMA subframe for PUSC subchannelization permutation mode taking user's channel quality into consideration in the assignment process.