Using the MPEG-4 advanced audio coder (AAC) music as an example of streaming applications, we investigate the improvement of error performance for the streaming service by link-adaptation and power-control techniques in an enhanced general packet radio services (EGPRS) cellular network. A low packet error rate and variability are essential in providing a short error-burst length so that error concealment techniques can be effectively applied to music packets. In this paper, we study the effects of a combined link adaptation and power control scheme (referred to as the error-based scheme) for achieving a target error rate and reducing error variability. By simulation, we compare the error performance of the error-based scheme at both the EGPRS block and AAC frame level with another adaptation algorithm (referred to as the throughput-based scheme) with a goal of maximizing overall network throughput. It is found that when offered with a similar traffic load, the former scheme can provide noticeable improvement of music quality over the throughput-based scheme. To achieve a similar AAC frame error rate, our results also show that the error-based scheme can increase the link throughput over the throughput-based scheme by 66.7% in one of our examples. These results reveal that by aiming at required error targets and thus reducing error variability, the error-based scheme for link adaptation and power control are helpful in improving quality and capacity for streaming applications. Index Terms-Adaptive Kalman filtering, adaptive modulation, error analysis, information rates, land mobile radio cellular systems, music, power control, radio communication. I. INTRODUCTION W ITH the promise of the third-generation (3G) wireless networks [1], wireless data services will become very popular soon. It is expected that the networks will initially provide best-effort data services such as wireless Internet access. As the systems continue to evolve, a variety of streaming data applications such as encoded music and compressed video and audio programming will be supported in the future. So, it is important to investigate techniques for supporting such streaming services. In particular, we shall examine in this paper how link adaptation and power control can improve the error performance for delivering MPEG-4 advanced audio coder (AAC) [2] coded music in the enhanced general packet radio services (EGPRS) network [3].
We investigate the ability of multiple descriptions (MD) and layered coding to improve the quality of video transmitted over EGPRS networks. One-layer video sent over a single channel on such a network has a fairly sharp quality transition, depending on a user's location. Either the video can be transmitted reliably (if the video rate is less than or equal to what the channel can sustain), or it is subjected to many lost packets. In this system, MD and layered video may offer two ways to improve video quality beyond that of the one-layer video. First, each sub-stream can be sent on a separate channel, essentially doubling the assigned bandwidth and increasing video quality. Second, MD and layered video are more error resilient than one-layer video, potentially improving the video quality seen by users in poor locations. We find that for the system scenarios considered, one-and two-layer coding outperform MD coding, depending upon the number of wireless channels used for the video transport.
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