Multimedia Transmission over IEEE 802.11g WLANs: Practical Issues and Considerations

Abstract

Multimedia transmission is widely available over wired networks. With the advent of low-cost WLAN devices, the wireless delivery of multimedia content is highly desirable. However, for media requiring low end-to-end latency, the use of WLAN technology introduces many significant challenges. These challenges are further enhanced if multicast/broadcast transmission is employed to serve a wide range of wireless terminals. This paper provides an understanding of the practical issues associated with WLAN multimedia transmission. A cross-layer measurement programme is performed to identify design issues for low-cost off-the-shelf WLAN multimedia systems. Problems identified include i) broadcast/multicast transmission using the slowest link-speed, ii) common link adaptation mechanisms for all clients, iii) lack of a call admission policy, and iv) irreducible PER even in good channel conditions. (UDP). While UDP offers a time bounded service, it does not guarantee the delivery of the video packets. To use this protocol successfully, the video codec must support strong error resilience and concealment. Furthermore, some video applications require transmission to a large number of remote terminals. Due to a lack of radio bandwidth, in these situations a dedicated point-to-point UDP-IP transmission cannot be accommodated with each remote client. Instead, Broadcast (or Multicast) transmission must be used at the WLAN. For these types of link there is absolutely no retransmission (ARQ) of errored or missing data packets (either at the WLAN MAC or the transport layer). As discussed above, wireless UDP based unicast and multicast/broadcast transmissions pose the problem of packet erasures. The lossy nature of the transmission medium can lead to unacceptable video quality at the client. As a result, it is important to consider the channel behaviour I. INTRODUCTION

Near-Capacity H.264 Multimedia Communications Using Iterative Joint Source-Channel Decoding

“…Furthermore, the decoding trajectories obtained by employing rate-1 3 outer SBCs of type SBC [2,6] and SBC [5,15] , which were generated using Algorithm-II as well as using the rate- Rate-1 SBC Rate-1/3 SBC [2,6] Rate-1/3 SBC [3,9] Rate-1/3 SBC [4,12] . Rate-1/3 SBC [5,15] Rate-2/3 SBC [2,3] Rate-3/4 SBC [3,4] Rate-4/5 SBC [4,5] Rate-5/6 SBC [5,6] Fig. 5.…”

“…EXIT characteristics of the USSPA scheme of Figure 4 using the different SBCs of Table V. the EXIT trajectories of Figures 8, and 9 that as expected, the convergence behaviour of SBCs improves upon increasing d H,min . 3,5,6,9,10,12,15,17,18,20,23,24,27,29,30} 2 Rate-5 6 SBC [5,6] {0, 3,5,6,9,10,12,15,17,18,20,23,24,27,29,30 …”

“…the drive for increased compression efficiency has to be carefully balanced against the increased power consumption of high-complexity signal processing in video coding standards. Furthermore, the integration of the channel coded video system into different types of communication networks, while maintaining an enhanced error-resilience are equally important design aspects of wireless video and multimedia applications [4,5]. In this context the combined efforts of the ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG) resulted in the H.264/AVC video coding standard [6].…”

An architecture for adaptive multimedia streaming to mobile nodes

“…Due to mobility and roaming, the characteristics of the used access link and the terminal device may change dynamically during a session. In multi-access networks, video streams may experience higher bandwidth variation and jitter than in environments supporting limited mobility such as a WLAN network [7]. Furthermore, video streams may suffer from connection outages of different lengths caused by handovers.…”

Mobile and Wireless Access in Video Surveillance System

“…Article [5] discuss the problem of absence of multicast feedback mechanisms and proposes leader-based mechanism to overcome this problem. Article [6] addresses the problems, such as: multicast transmission using the slowest link-speed, common link adaptation mechanisms for clients, lack of a call admission policy, and irreducible PER even in good channel conditions. 802.16 WiMAX standard has been originally designed to support reliable delivery of broadband multimedia data -it has built in scheduled access and Quality of Service (QoS) mechanisms (refer to [7]).…”