%0 Journal Article
%T ARQ-Aware Scheduling and Link Adaptation for Video Transmission over Mobile Broadband Networks
%A Victoria Sgardoni
%A David R. Bull
%A Andrew R. Nix
%J Journal of Computer Networks and Communications
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/369803
%X This paper studies the effect of ARQ retransmissions on packet error rate, delay, and jitter at the application layer for a real-time video transmission at 1.03£¿Mbps over a mobile broadband network. The effect of time-correlated channel errors for various Mobile Station (MS) velocities is evaluated. In the context of mobile WiMAX, the role of the ARQ Retry Timeout parameter and the maximum number of ARQ retransmissions is taken into account. ARQ-aware and channel-aware scheduling is assumed in order to allocate adequate resources according to the level of packet error rate and the number of ARQ retransmissions required. A novel metric, namely, goodput per frame, is proposed as a measure of transmission efficiency. Results show that to attain quasi error free transmission and low jitter (for real-time video QoS), only QPSK 1/2 can be used at mean channel SNR values between 12£¿dB and 16£¿dB, while 16QAM 1/2 can be used below 20£¿dB at walking speeds. However, these modes are shown to result in low transmission efficiency, attaining, for example, a total goodput of 3£¿Mbps at an SNR of 14£¿dB, for a block lifetime of 90£¿ms. It is shown that ARQ retransmissions are more effective at higher MS speeds. 1. Introduction Mobile WiMAX (IEEE 802.16e) [1] and 3GPP LTE (Long-Term Evolution) [2] represent mobile broadband standards that offer high user data rates and support for bandwidth hungry video applications. Both standards use very similar PHY and MAC layer techniques, especially for downlink (DL) transmission. In order to provide strong QoS, cross-layer adaptive strategies must be implemented in the wireless network [3, 4]. Video applications demand a low Packet Error Rate (PER), which may be achieved via the use of MAC layer Automatic Repeat ReQuest (ARQ) and the choice of suitable Modulation and Coding Schemes (MCS). However, ARQ consumes additional bandwidth and causes increased end-to-end latency and jitter. ARQ is controlled in the MAC layer by the block lifetime and ARQ Retry Timer parameters, which define how many and how frequently retransmissions may occur. Link adaptation is used in mobile broadband networks to improve the PER by matching the QAM constellation and forward error correction coding rate to the time varying channel quality. The impact of specific ARQ parameters and mechanisms has been extensively studied in the literature, for example, [5¨C9]. In [8], the authors analyze delay and throughput using probabilistic PHY layer error modelling. In [9], packet errors were modelled as an uncorrelated process in time. Often packet errors are modelled
%U http://www.hindawi.com/journals/jcnc/2012/369803/