UEP implementation for MPEG-4 video quality improvement on RLC layer of UMTS

Introduction: Any UEP scheme would normally seek to provide greater error protection to the most important parts of a data stream than is afforded the less important bits. Such schemes often utilise enhanced forward error correction (FEC) or automatic repeat request (ARQ) mechanisms for the most important data. In 3G mobile networks various levels of FEC are available for the signal and radio access bearers which can be combined in different ways dependent on the data rates being used (3GPP TS 34.108) [1]. However little flexibility in the schemes is available for the data rates above 32 kbit=s required for video transmission. It is important that any overhead or redundancy be added in a way which does not make the modified video bit-stream incompatible with the standard [2]. Some of the problems arising from FEC implementation can be avoided through the use of the UEP mechanisms provided by the services offered by the RLC (radio link control) layer in the form of the various data transfer modes offered to upper layer protocols. These data transfer services include transparent mode, unacknowledged mode and acknowledged mode [3, 4]. In this Letter, a scheme which utilises the UEP capability provided by the allowed data transfer modes within the RLC layer, coupled with the inter-frame coding structure of MPEG-4, is tested and shown to give improvements in frame loss and PSNR.