Cross-Layer Design for LTE System with Jointly AMC and ARQ on Fading Channel

A cross-layer design is developed for error-sensitive and latency-tolerated traffic over LTE system. Two adaptive techniques, automatic repeat request (ARQ) protocol at radio link control (RLC) sublayer and medium access control (MAC) sub layer and adaptive modulation and coding (AMC) scheme at physical (PHY) layer are combined to improve the average spectral efficiency of the system. The segmentation mechanism and the in-sequence delivery procedure are both considered. Closed-form expressions for performance metrics such as average service data unit (SDU) error rate and average in-sequence delivery SDU delay at RLC sub layer are derived. Using these expressions, an optimization problem is formulated to maximize the average spectral efficiency when the quality of service (QoS) achieves certain requirement. Simulation results reveal that we can further improve the average spectral efficiency by dynamically adjusting the adaptive parameters of the ARQ and AMC module, compared to the previous LTE system.