Performance evaluation of 32 kbits/s real-time and dual-directionvideo communication system for wireless channels

摘要

This paper describes the construction and performance evaluation of a mobile video communication system composed of an H.263 video encoder, decoder, and RF transceiver equipment. It can establish a video connection using a 32 kbits/s wireless channel because it uses automatic repeat request (ARQ) as the error control scheme. Retransmission control can produce excessive transmission delay, but the improved ARQ protocol and coding-rate control scheme adopted by this system minimizes the delay. This ARQ protocol uses short ARQ frame length and an acknowledgementegative acknowledgement (ACK/NAK) indicator. The coding-rate control scheme uses backward NAK signals to reduce the coding rate of the video encoder as necessary. We measure the transmission delay characteristics of this video system and confirm that the proposed scheme can reduce the delay over a noisy channel. Subjective assessment tests involving videophone usage are also conducted. Test results show that in a noisy channel (BER=3×10-3), this system can achieve the same mean opinion store as in a noiseless channel