Abstract
Advances in wireless technology will soon provide sufficient capacity for the transmission of compressed video to and from mobile terminals. However, high compression ratios and the use of Variable Length Coding in standards such as H.263 and MPEG-4 make the encoded bitstreams particularly sensitive to errors. This thesis investigates methods for the error robust transmission of MPEG-4 coded video over mobile networks. It examines current and future mobile networks, and discusses the quality of service that they are expected to offer with respect to mobile multimedia. Also, the MPEG-4 systems and visual layer standards are briefly described. Real-time MPEG-4 encoder and decoder software has been developed and exploited in the work described here. The MPEG-4 software can send MPEG-4 data over TCP or over RTP. All of the standard MPEG-4 error resilience options are implemented in the software. The effectiveness of these options is demonstrated through the results of simulated transmission over a GPRS channel. MPEG-4 is separated into two different streams via exploitation of the data partitioning option. The two streams may then be transmitted over a mobile network using different bearer channels. The most sensitive data stream is sent using a bearer channel with a low bit error rate compared to the less sensitive data stream. This technique is shown to produce quality improvements. A technique for the insertion of user-defined data is outlined. Insertion of user-defined data is achieved while retaining backwards compatibility with existing standard MPEG-4 decoders. CRC codes are inserted using this scheme, to facilitate more accurate detection of errors. This error detection aids error concealment and results in a gain in decoded video quality after simulated transmission over a GPRS channel. Motion adaptive encoding is employed to increase the error robustness of the encoded bitstream. Video packet size and intra block refresh rates are altered with first partition size, which is used as a guide to the amount of motion within a scene. Transmission of video using RTP is considered. In particular, a mathematical analysis is performed for two different packetisation schemes. One scheme encapsulates one video frame within one RTP packet, while the other scheme encapsulates a single video packet within a single RTP packet.