Multimedia broadcasting and communications with WiMAX and implementation for its downlink physical layer

Abstract

Currently, dramatic changes are affecting the way we communicate. New standards for both wired and wireless communications allow increasingly higher data rates at significantly lower costs. As internet access became a commodity, featurerich communication and multimedia services such as Voice over Internet Protocol (VoIP), multiplayer online gaming, Internet Protocol Television (IPTV), and multimode teleconferencing are expanding the traditional voice and messaging services. With technology miniaturization and rapid reductions in integrated circuit size, in addition to wired and wireless communication convergence, we are also witnessing the convergence of fixed and mobile wireless communications. Contrary to multiplatform systems for multiservices, IP based Multimedia Systems (IMS) offer a single platform for a multitude of services resulting in increased revenues at lower operator expense. Mobile communications are playing an increasing role in the IMS services. A high level diagram of an IMS system is illustrated in Fig. 6.1. The latest adoption of WiMAX (Worldwide Interoperability for Microwave Access) as part of the 3G standards by the International Telecommunications Union (ITU) assures compatibility and interoperability of 3GPP with broadband wireless access networks [28]. As a result, WiMAX may be part of the cellular systems as a next generation technology. Together they cover a significant portion of the broadband wireless access. WiMAX is a long-range, fixed, portable, and mobile wireless technology specified in the IEEE 802.16 standard. It provides high-throughput broadband connections similar to IEEE 802.11 wireless LAN systems but with a broader coverage range. Possible applications forWiMAX include: the "last mile" broadband connections, hotspot and cellular backhaul, and high-speed enterprise connectivity for business. The IEEE 802.16 standard defines a Media Access Control (MAC) layer that supports different physical layers and also defines the same Logical Layer Control (LLC) level l for different Local and Wide Area Networks (LAN and WAN), it opens up the possibility of bridging different communication networks together. The IEEE 802.16 standard has been revised to IEEE 802.16-2004 which forms the basis for fixed applications. Further enhancements in 2005 resulted in the finalized IEEE 802.16e-2005 which adds mobility support features to IEEE 802.16-2004 aiming at mobile applications. Fixed WiMAX is based on the IEEE 802.16-2004 OFDM PHY while mobile WiMAX is based on the IEEE 802.16e-2005 OFDMA PHY. In mobile WiMAX, various channel bandwidths ranging from 1.25 to 20MHz are supported with constant OFDM subcarrier spacing. That means the number of OFDM subcarriers varies according to channel bandwidth. This concept is called Scalable OFDM and was introduced to 802.16e OFDMA mode. The Scalable OFDMA (SOFDMA) can reduce system complexity for small channel bandwidths and improves performance for wider channel bandwidths [2, 29]. On the contrary, fixed WiMAX uses a constant number of subcarriers regardless of various channel bandwidths raging from 1.5 to 28 MHz. Thus, for larger channel bandwidths, a larger subcarrier spacing is expected and vice versa for the smaller channel bandwidths. Since a software implementation of both fixed and mobile systems can coexist, throughout the chapter we will focus on two special cases: the 7 and 10 MHz bandwidth systems for fixed and mobile applications, respectively. The system profiles are shown in Table 6.1. This chapter is structured as follows: In Sect. 6.2 we describe the DownLink (DL) physical layer features of both mobile and fixed WiMAX. The receiver algorithms focusing on timing and frequency synchronization are presented in Sect. 6.3. Section 6.4 gives an overview of the Sandbridge DSP architecture and describes the software implementation for both fixed and the mobile WiMAX systems on the Sandblaster processor. A brief summary in Sect. 6.5 ends the chapter. © 2009 Springer Science+Business Media, LLC.