Tham khảo tài liệu 'vehicular technologies increasing connectivity part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 4 Resource Allocation for Multi-User OFDMA-Based Wireless Cellular Networks Dimitri Kténas and Emilio Calvanese Strinati CEA LETI MINATEC F-38054 Grenoble France 1. Introduction Modern wideband communication systems present a very challenging multi-user communication problem many users in the same geographic area will require high on-demand data rates in a finite bandwidth with a variety of heterogeneous services such as voice VoIP video gaming web browsing and others. Emerging broadband wireless systems such as WiMAX and 3GPP LTE employ Orthogonal Frequency Division Multiple Access OFDMA as the basic multiple access scheme. Indeed OFDMA is a flexible multiple access technique that can accommodate many users with widely varying applications data rates and Quality of Service QoS requirements. Because the multiple access is performed in the digital domain before the IFFT operation dynamic and efficient bandwidth allocation is possible. Therefore this additional scheduling flexibility helps to best serve the user population. Diversity is a key source of performance gain in OFDMA systems. In particular OFDMA exploits multiuser diversity amongst the different users frequency diversity across the sub-carriers and time diversity by allowing latency. One important observation is that these sources of diversity will generally compete with each other. Therefore efficient and robust allocation of resources among multiple heterogeneous data users sharing the same resources over a wireless channel is a challenging problem to solve. The scientific content of this chapter is based on some innovative results presented recently in two conference papers Calvanese Strinati et al. VTC 2009 Calvanese Strinati et al. WCNC 2009 . The goals of this chapter are for the reader to have a basic understanding of resource allocation problem in OFDMA-based systems and to have an in-depth insight of the state-of-the-art research on that subject. Eventually the chapter will present what we have .
