Voice Quality Evaluation for Wireless Transmission with ROHC (extended version and software code)

Robust Header Compression (ROHC) has recently been proposed to reduce the large protocol header overhead when transmitting voice and other continuous media over RTP/UDP/IP in wireless networks. In this paper we evaluate the real-time transmission of GSM encoded voice with ROHC over a wireless link. We first present a tutorial on voice quality evaluation. We introduce an evaluation methodology that combines elementary objective voice quality metrics with a frame synchronization mechanism. The methodology allows networking researchers to conduct effective and accurate quality evaluation of packet voice. Besides the impact of ROHC on the voice quality we consider the impact of ROHC on the consumed bandwidth and the delay jitter in the voice signal. We find that for a wide range of error probabilities on the wireless link, ROHC roughly cuts the bandwidth required for the transmission of GSM encoded voice in half. In addition, ROHC improves the voice quality compared to transmissions without ROHC, especially for large bit error probabilities on the wireless link. The improvement reaches 0.26 on the 5-point Mean Opinion Score for a bit error probability of 10−3.