Bounding Switching Delay in Mobile TV Broadcast Networks Cheng-Hsin Hsu and Mohamed Hefeeda School of Computing Science Simon Fraser University Surrey, BC, Canada ABSTRACT Since mobile devices are battery powered, several mobile TV standards dictate using energy saving schemes to increase the viewing time on mobile devices. The most common scheme for saving energy is to make the base station broadcast the video data of a TV channel in bursts with a bit rate much higher than the encoding rate of the video stream, which enables mobile devices to turn off their radio frequency circuits when not receiving bursts. While broadcasting bursts saves energy, it increases the channel switching delay. The switching delay is an important performance metric, because long and variable switching delays are annoying to users and may turn them away from the mobile TV service. In this paper, we first analyze the burst broadcasting scheme currently used in many deployed mobile TV networks, and we show that it is not efficient in terms of controlling the channel switching delay. We then propose new schemes to guarantee that a given maximum switching delay is not exceeded and that the energy consumption of mobile devices is minimized. We prove the correctness of the proposed schemes and derive closed-form equations for the achieved energy saving. We also implement the proposed schemes in a mobile TV testbed to show their practicability and to validate our theoretical analysis. 1. INTRODUCTION As wireless mobile devices, such as personal digital assistants, smart cellular phones, and mobile media players are getting very popular and computationally powerful, watching TV on the move has become a reality. Mobile TV trials or commer- cial services have been deployed in more than 40 countries, 1 and users are already using it to watch TV shows and sports events while traveling. The mobile TV market is excepted to grow to up to 20 billion Euros with 500 million customers by 2011. 2 Since mobile devices are battery powered, energy consumption in mobile TV networks is an important problem. In fact, common standards for mobile TV networks, such as DVB-H (Digital Video Broadcast-Handheld) 3–5 and MediaFLO (Forward Link Only), 6 dictate using energy saving schemes to increase the viewing time on mobile devices. The typical scheme for saving energy is to make the base station broadcast the video data of a TV channel in bursts with a bit rate much higher than the encoding rate of the video stream. Mobile devices, therefore, can receive a burst of traffic and turn off their radio frequency (RF) circuits until the next burst. This is called time slicing. Mobile devices have stringent battery capacity and heat implementation guidelines, thus they cannot accommodate mobile TV chips that consume too much energy. For instance, the DVB-H standard 7 states that TV signal receiver with power consumption higher than 100 mW cannot be integrated with handheld devices. However, even the state-of-the-art prototype mobile TV chips consume about 200 mW, 8 while commercial chips consume more than 500 mW in continuous mode. Therefore, the energy saving enabled by time slicing is critical to mobile devices. Previous works and measurements show that time slicing can result in a significant energy saving for mobile devices. 7, 9 For example, the DVB-H standard documents 7 mention that the power consumption of the receiving units of mobile devices could be reduced from about 500 mW to 50 mW because of time slicing. Although time slicing enables mobile devices to save energy, it increases the channel switching delay, which is the time a user waits before s/he starts viewing a selected channel when a change of channel is requested by that user. The switching delay is an important performance metric, because many users quickly flip through several TV channels before they decide on watching a specific one. Because long and variable switching delays are annoying to users and may turn them away from the mobile TV service, mobile TV operators have to maintain low and constant switching delays even at a small expense on channel utilization. In this paper, we consider the problem of controlling the switching delay in mobile TV networks that employ time slicing to save energy. 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 particular, the contributions of this paper can be summarized as follows. First, we analyze the time slicing scheme currently used in many deployed mobile TV networks, and we show that it is not efficient in terms of minimizing the energy consumption for mobile devices,