Private:mobileTV
Mobile TV Networks
Mobile TV allows users to watch their favorite TV shows and games on small hand-held devices while traveling. It, therefore, extends the Prime Time viewing of users and provides more business opportunities for content providers. The market for mobile TV is huge: it is expected to grow to up to 20 billion Euros with 500 million customers by 2011 (reference). In fact, mobile TV has already been deployed in parts of Europe and Asia and in pilot-testing in several locations in North and South Americas (official DVB-H site). This rapid adoption is fueled by the desire of users for multimedia content and by the technological advances in wireless mobile devices, such as personal digital assistants (PDAs), smart cellular phones, and mobile media players. Many of these devices have evolved to almost full-fledged mobile computers with high resolution displays, fast network links, large memory and storage space, and fast processors. Therefore, multimedia content can be rendered on most of these mobile devices, which further stimulates the user demands for more content and better quality.
A common issue in all mobile wireless devices is the limited energy supply since they are battery powered. Thus, minimizing the energy consumption in mobile TV networks becomes a critical problem for the success and wide adoption of such systems. Another important issue is reducing the channel switching delay. We address these two important problems. Our goal is to provide a guarantee on the maximum switching delay from a TV channel to any other channel, without scarifying the energy saving for mobile devices. In addition, we are exploring the possibility of using scalable video coding (H.264/SVC) to support heterogeneous receivers, control switching delay, and minimize energy consumption. Furthermore, the interaction between different parameters of mobile TV systems, e.g., FEC, frame refresh delay, time slicing, are being analyzed. All algorithms and schemes are being implemented and evaluated in a real mobile TV testbed that we have developed in our lab.
People
Publications
- M. Hefeeda, C. Hsu, and Y. Liu, Testbed and Experiments for Mobile TV (DVB-H) Networks, ACM Multimedia'08 Technical Demonstration, Vancouver, Canada, October 2008.
- M. Hefeeda and C. Hsu, On Burst Transmission Scheduling in Mobile TV Broadcast Networks, School of Computing Science, Simon Fraser University, August 2008.
- C. Hsu and M. Hefeeda, Bounding Switching Delay in Mobile TV Broadcast Networks, School of Computing Science, Simon Fraser University, July 2008.
Mobile TV (DVB-H) Testbed and Experiments
We have implemented a complete end-to-end testbed for DVB-H (Digital Video Broadcast--Handheld) networks. The testbed provides a realistic platform for analyzing various aspects of these networks, including the energy saving achieved by the time slicing mechanism, average channel switching delay, network capacity in terms of number of TV channels that can be broadcast, visual quality of TV channels transmitting different types of video streams, information exchange and interactivity between base station and receivers, among many others. To the best of our knowledge, there exists no open-source testbed for DVB-H. The details of testbeds and pilot networks created by companies are usually not published, and the source code is not available. Thus academic researchers designing algorithms and protocols for mobile TV networks, including ourselves, had to resort to simulation and/or theoretical analysis. To address this problem, we make the details and source code of our testbed available to the research community.
The main components of our mobile TV testbed are shown in the following figure.
Base Station. The base station is a Linux box (Intel Quad-Core Xeon E5420 (2.5 GHz) PC running Ubuntu Linux) in which we installed the RF signal modulator: Dektec DTA-110T DVB-T/H Modulator and UHF Upconverter for PCI Bus. This modulator implements the physical layer of the protocol stack and transmits DVB-H standard compliant signals via an indoor antenna. The RF output level of the modulator, however, is quite low (-29 dBm) and can only reach up to 1-meter broadcast range with a 6 dB receiver antenna. Using a low-power amplifier, the RF signal can be boosted to about 0 dBm, which gives us approximately 20-meter range in our lab environment.
IP packets of the video streams are encapsulated in MPEs and FEC-coded using the open-source IP Encapsulator; several bug fixes were needed to get it running properly with the RF modulator. The IP Encapsulator also implements a simple time slicing technique. As explained in the following section, we have extended this IP Encapsulator to support more sophisticated and optimal time slicing techniques. We have also re-designed the time slicing module to be well-structured with defined interfaces in order to facilitate implementing and comparing different current/future time slicing algorithms.
Receivers. We use the Nokia N92 device as a receiver. This device is equipped with the receiver-side of the DVB-H protocol and video player. The operating system on this device (Symbian) provides several APIs, including APIs for measuring energy consumption. While the N92 device helps in assessing the visual quality of videos, it does not provide detailed logging functions of the low-level signals, which are needed to evaluate the performance of different protocols. To address this shortcoming, we added the Divi Catch RF-T/H transport stream analyzer to the testbed. This analyzer can be attached to a PC via a USB port. The analyzer records traffic streams as well as provides a very detailed information on the RF signal, the MPEs, jitter, time slicing, and so on. It also comes with a visualization software that can run on the PC for analysis.
We note that the (academic) price of the RF Modulator is about $3,000 and of the Analyzer is about $6,000.
Discussion and Ideas
References and Links
- Wing-TV Project: Docs to test and to verify in detail the DVB-H specification.
- J. Wang, M. Venkatachalam, and Y. Fang, System Architecture and Cross-Layer Optimization of Video Broadcast over WiMAX, IEEE JSAC 25(4), pp. 712--721, MAY 2007. (Check this special issue of JSAC as well.)
- G. Gardikis, G. Xilouris, C. Skianis, Broadband multimedia on the move with DVB-H, Multimedia Tools and Applications, 36(1-2), January 2008. (DVB-H tutorial in inter-active mode.)
