Recent advances in video communications for 4G wireless systems

In recent years, there has been a rapidly increasing demand for the development of advanced interactive multimedia applications such as video telephony, video games, and TV broadcasting. However, these applications are always stringently constrained by current wireless system architectures due to the need for high data rates for video transmission. To better serve this need, 4G broadband mobile systems are in planning and are expected to increase the mobile data transmission rates and bring higher spectral efficiency, lower cost per transmitted bit, and increased flexibility of mobile terminals and networks. The new technology strives to eliminate the distinction between video over wireless and video over wireline networks. In the meantime, great opportunities are provided for proposing novel wireless video protocols and applications, and developing advanced video coding and communications systems, and algorithms for the next-generation video applications that can take maximum advantage of the 4G wireless systems. This special issue was proposed under such background to bridge the gap between the current system constraints and proposed system capabilities. By nature, this special session is not able to cover all the important development or provide a complete overview of the state-of-the-art in this vast area. However, we select eight articles from plenty of high-quality submissions to focus on the most attractive topics in the area such as cross-layer optimized resource allocation, wireless video streaming, video source coding for mobile applications, and wireless video delivery. We hope that these articles serve the purposes of encouraging more researchers to dig deeper into this rich land and to overcome the barriers that constrain today the advanced multimedia applications. In wireless networks, due to the fluctuation of power and bandwidth constraints and random timevarying fading effect, the resource allocation has to be performed dynamically during communications to satisfy the stringent quality of service (QoS) requirements. Therefore, cross-layer design methodologies become natural choices to guarantee reliable and high-quality end-to-end performance. In this issue, two papers are invited on the topic of cross-layer optimized resource allocation. In the first article by Peshala V. Pahalawatta et al. entitled ‘Review of content aware resource allocation schemes for video streaming over wireless networks,’ the wireless video streaming is reviewed from a rate-distortion resource allocation aspect, that is, how to achieve an effective cross-layer design that efficiently manages the limited system resources while taking into account the timevarying wireless channel conditions as well as the varying media content for delivery. The article discusses two well-known scenarios for video streaming one is a downlink case that the video has been pre-encoded and the scheduler adapts to channel conditions and controls the source rate by either packet dropping or scalable coding, and the other is a real-time point-to-point video streaming where the transmitting device has control over the coding and network parameters so that the source coding parameters can be jointly determined along with the transmission power and bandwidth allocation. The second article by Kai Yang et al. entitled ‘Multiuser resource allocation for video transmission over a chipinterleaved multicarrier system’ proposes a system for scalable downlink video transmission over emerging 4G wireless networks where protected bitstreams are sent from the server to potentially thousands of clients over a multicarrier system with two-layer interleaving