Adaptive QoS control for real-time video communication over wireless channels

Robust transmission of real-time video over wireless channels is a challenging problem. This is because the bit error rate (BER) in wireless channels is very high and the bit errors could have devastating effects on the video presentation quality. This paper addresses this problem by introducing adaptive quality-of-service (QoS) control for real-time video communication over wireless channels. The adaptive QoS control consists of optimal mode selection and delay-constrained hybrid automatic repeat request (ARQ). Specifically, optimal mode selection provides QoS support (i.e., error resilience) on the compression layer while delay-constrained hybrid ARQ provides QoS support (i.e., bounded delay and reliability) on the link layer. To provide QoS on the compression layer, we employ a novel approach to rate-distortion (R-D) optimized mode selection for real-time video communication over wireless channels. Different from the classical approach that only takes quantization distortion into account, our optimal mode selection also considers wireless channel characteristics and receiver behavior. To provide QoS on the link layer, we employ delay-constrained hybrid ARQ, which integrates rate-compatible punctured convolutional (RCPC) codes with delay-constrained retransmissions. Our delay-constrained hybrid ARQ has the advantage of providing reliability for the compression layer while guaranteeing delay bound and achieving high throughput. By combining the best features of error-resilient source encoding, forward error correction (FEC) and delay-constrained retransmission, our proposed adaptive QoS control system is capable of achieving bounded delay, high reliability, and efficiency. Simulation results show that the proposed adaptive QoS control achieves better quality for real-time video under varying wireless channel conditions and utilizes network resources efficiently.