User-Centric Energy-Efficient Multimedia Multicast/Broadcast Solutions: A Survey

With the latest advancements in communication technologies, the high-end mobile computing devices, like smartphones, tablets, PDAs, small notebooks, have become increasingly affordable and powerful [1– 3]. Improved CPU, graphics, and display capabilities provide support for a better multimedia experience to the mobile users that have higher expectations and increased demands towards rich services at higher quality levels. Advances in mobile, communications, and multimedia technologies have further led to a drastic increase in the number of heterogeneous consumers that watch multimedia content from several sources, under various formats, and on different types of devices, while on the move (e.g., on foot, in car, on bus) or being stationary (e.g., at home, office, airport, coffee bars), as illustrated in Fig. 1. According to Cisco [4], the global mobile data traffic will further increase thirteen-fold by 2017, when compared to 2012. Estimating more than 11.2 exabytes per month will be transferred, out of that 55% will be exchanged over wireless. Because of the growing popularity of video-sharing websites (e.g., YouTube, Facebook) the mobile video traffic is expected to account for 66% of all mobile data traffic by 2017 with 12% of the global mobile data traffic being generated by tablets. According to [1], video is the largest and fastest growing mobile data traffic segment which would increase 55 percent annually until the end of 2019 and would account for more than 50 percent of global mobile traffic. Additionally, a study reported by Google notes that a person spends on average 4.4 hours per day of his/her leisure time in front of screens (e.g., smartphone, laptop/PC, tablet, television) [5]. Moreover, the report shows that 90% of all media interactions of the users on a daily basis are screen based. Although the fast advances in wide range of technologies – including broadcast (e.g., DVB-T [6], DVB-H [7]), broadband (e.g., IEEE 802.11g, IEEE 802.11n [8]), and cellular (e.g., 3GPP LTE [9], UMTS [10]) – have enabled the network operators to increase their resource capacity, the customer demands for popular multimedia content delivery to their high-end mobile devices are growing even faster. Consequently, the overall quality of user experience (QoE) is still far from optimal. This is because, all these popular rich multimedia content types (e.g., high definition movies, news or sports video clips, live sport/concert event streaming, video games) put pressure on the existing communication resources in terms of their bandwidth requirements and real-time constraints. In this context, unicast transmissions are reliable only when the number of users accessing the multimedia content is low. As the number of users increases, the network becomes overloaded and the users might experience high data loss rates and/or service disconnection, leading to significant degradation in the user’s perceived quality. To this end, broadcast delivery of popular multimedia content is an alternative solution to unicast delivery, as it enables delivery of a single data stream to multiple users simultaneously. Thus, it can provide network access to various services for a practically unlimited number of users [11]. An example of such a network is the terrestrial TV broadcast network. However, a major drawback of the broadcast network is that, it is useful only if all the users are interested in the broadcast data. Another alternative is the multicast transmission which represents the best solution if the content is destined only to a certain group of users. However, the challenges that the network operators are facing include network resources optimization, especially for popular multimedia content delivery while ensuring uninterrupted, continuous, and smooth services over a heterogeneous environment with varying end-user constraints. Another challenge is the quality of service (QoS) provisioning over wireless networks to a high number of customers. This is due to the constraints of wireless links, user mobility, and diversity of multiscreen, high-end mobile devices (different display size, processing capabilities, channel impairments). From the end-user perspective, one of the key consumer interests is the battery lifetime of their high-end mobile devices. It is known that real-time applications, in particular those which are based on