Mulitmedia over broadband wireless networks

4 t gives us great pleasure to introduce this special issue, devoted to the very timely topic of multimedia delivery over broadband wireless networks. As most of you can now surely feel, the telecommunications industry is again showing signs of great excitement and very healthy growth, driven by the actual commercial deployment of highspeed “3G” wireless access network technologies, such as UMTS and EV-DO, and emerging HSDPA. In addition, the rapid growth of wireless LAN hotspots across the entire world (according to the hotspot listing service JiWire, the number of hotspots topped the 100,000 mark in January 2006, with an 87 percent growth rate in 2005!) and the increasing penetration of dual-interface (cellular/WLAN) handsets attests to the growing importance of wireless broadband for a variety of enterprise and consumer applications. Equally important, the consumer market is seeing a dramatic shift in usage habits, with cellular and other portable networked devices increasingly being used for a new range of audio and video-based entertainment/media applications, beyond simple voice communication. This can be seen in the slew of newly launched or highly anticipated services, such as VoIP, video and audio downloads and playback, mobile TV and interactive games, specifically targeted to the wireless market. This has, of course, been made possible by significant advances in both networking protocols and signaling technologies, such as 802.11, 802.16 (WiMAX), IP paging, and SIP, as well as newer multimedia standards, such as H.264/MPEG-4 AVC, and specifications, such as Third Generation Partnership Project (3GPP), that provide efficient video compression and delivery over wireless packet networks. Just to underscore the timeliness of this topic and the high level of interest in wireless broadband multimedia, we were pleasantly surprised (and somewhat overwhelmed, we may add) by the very large number of submissions we received. Reflecting the global nature of the emergence of wireless multimedia, the submitted articles came from a truly representative sample of countries in Asia, Europe, and North America, and were equally divided between industry and academia. From this impressive set of submissions, seven articles were carefully selected that provide a concise reference of state-of-the-art efforts in supporting a variety of multimedia applications over emerging packetbased broadband wireless networks. These articles cover a wide range of representative topics, including multimedia signaling and broadcast services, cross-layer approaches for efficient multimedia delivery in wireless environments, multimedia conferencing in wireless environments, and techniques for ensuring quality of service (QoS) in newer broadband wireless access technologies. The first two articles focus on the signaling and architectural aspects needed to provide two important features — smooth handoffs and on-demand reception of broadcast media streams. In the first article, “Seamless SIP-Based Mobility for Multimedia Applications,” Nilanjan Banerjee, Arup Acharya, and Sajal K. Das investigate the use of the Session Initiation Protocol (SIP) to support seamless mobility for multimedia applications in next-generation heterogeneous wireless networks. As the SIP handoff procedure may cause unacceptable QoS degradation for applications like voice over IP or streaming video, the authors present a SIPbased architecture that supports soft handoff, ensuring no packet loss and controlled jitter. In the second article, “Asynchronous and Reliable On-Demand Media Broadcast,” Hrvoje Jenkac, Thomas Stockhammer, and Wen Xu present a scalable wireless broadcasting scheme that supports an arbitrary number of heterogeneous receivers. Receivers subscribe at any time to the ongoing broadcast session, but are still able to display the media stream from the beginning. The media stream is appropriately segmented, and segments are protected by fountain codes. A performance study shows soft decoding gains with respect to erasure decoding. The next two articles focus on cross-layer optimization schemes, where media stream parameters are tuned in conjunction with dynamic variations in network and link layer parameters. The article by Guan-Ming Su, Zhu Han, Min Wu, and K.J. Ray Liu, “Multiuser Cross-Layer Resource Allocation for Video Transmission over Wireless Networks,” investigates how to efficiently transmit multiple video streams over resource-limited wireless networks, such as third-/fourth-generation (3G/4G) systems and future wireless LANs and MANs. Specifically, the article discusses how to dynamically allocate resources, according to the changing environment and requirements, by exploiting a cross-layer design, and multiuser diversity that explores the source and channel heterogeneity for different users. Next, Stark Draper and Mitchell Trott in their article “Costs and Benefits of Fading for Streaming Media over Wireless” present salient aspects of the wireless channel, and the challenges and opportunities they pose for streaming media. Through a set of examples the authors show how, for streaming media over wireless, designGUEST EDITORIAL