Cross-Layer Scheduler for Wimax Networks with Outdated Channel State Information to Support Guaranteed QoS

The proposed Cross-Layer scheduling can boost the spectral efficiency of multi-user OFDMA wireless systems with heterogeneous delay requirements. The existing designs usually have two important assumptions that are the users are delay insensitive and Channel State Information at the Transmitter (CSIT) is perfect. In practice, users have heterogeneous delay requirements and CSIT usually becomes outdated in time varying channel which in turn leads to systematic packet errors and hence, results in significant degradation on the throughput. The Adaptive Modulation and Coding (AMC) is a promising tool for increasing the spectral efficiency of time varying channel while maintaining the target Bit Error Rate (BER) and the Packet Error Rate (PER). In this study, a novel design problem is formulated which combines AMC and CSI at the physical layer and scheduling using queuing theory at the Medium Access Control (MAC) layer, in order to maximize the throughput and spectral efficiency under the heterogeneous delay constraints. For the proposed research, transmissions on Rayleigh fading channel including Additive White Gaussian Noise (AWGN) are employed. Simulation results show that the proposed scheduler provides robust system performance enhancement over conventional cross-layer scheduler with perfect CSIT.