OFDMA WiMAX Physical Layer
IEEE 802.16 physical (PHY) layer is characterized by Orthogonal Frequency Division Multiplexing (OFDM), Time Division Duplexing, Frequency division Duplexing, Quadrature Amplitude Modulation and Adaptive Antenna Systems. After discussing the basics of OFD
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OFDMA WiMAX Physical Layer Ramjee Prasad and Fernando J. Velez
Abstract IEEE 802.16 physical (PHY) layer is characterized by Orthogonal Frequency Division Multiplexing (OFDM), Time Division Duplexing, Frequency division Duplexing, Quadrature Amplitude Modulation and Adaptive Antenna Systems. After discussing the basics of OFDM and Orthogonal Frequency division Multiple Access (OFDMA), scalable OFDMA is presented and supported frequency bands, channel bandwidth and the different IEEE 802.16 PHY are discussed. The similarities and differences between wireless MAN-SC, wireless MAN-OFDM and wireless MAN-OFDMA PHY are finally highlighted.
2.1
Introduction
The IEEE 802.16 standard belongs to the IEEE 802 family, which applies to Ethernet. WiMAX is a form of wireless Ethernet and therefore the whole standard is based on the Open Systems Interconnections (OSI) reference model. In the context of the OSI model, the lowest layer is the physical layer. It specifies the frequency band, the modulation scheme, error-correction techniques, synchronization between transmitter and receiver, data rate and the multiplexing techniques. For IEEE 802.16, Physical layer was defined for a wide range of frequencies from 2–66 GHz. In sub frequency range of 10–66 GHz there essentially is LoS propagation. Therefore, single carrier modulation was chosen, because of low
R. Prasad (*) Center for TeleInFrastruktur (CTIF), Aalborg University, Niels Jernes Vej 12, DK–9220 Aalborg Øst, Denmark e-mail: [email protected]
R. Prasad and F.J. Velez, WiMAX Networks, DOI 10.1007/978-90-481-8752-2_2, # Springer ScienceþBusiness Media B.V. 2010
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system complexity. Downlink channel is shared among users with TDM signals. Subscriber unit are being allocated individual time slots. Access in uplink is being realized with TDMA. In the 2–11 GHz bands, communications can be achieved for licensed and non-licensed bands. The communication is also available in NLoS conditions. To ensure the most efficient delivery in terms of bandwidth and available frequency spectrum, the IEEE 802.16 physical layer uses a number of legacy technologies. These technologies include Orthogonal Frequency Division Multiplexing (OFDM), Time Division Duplexing (TDD), Frequency Division Duplexing (FDD), Quadrature Amplitude Modulation (QAM), and Adaptive Antenna System (AAS). The WiMAX physical layer is based on OFDM. OFDM is the transmission scheme of choice to enable high speed data, video, and multimedia communications and presently, besides WiMAX, it is used by a variety of commercial broadband systems, including DSL, Wi-Fi, Digital Video Broadcast-Handheld (DVB-H). Above the physical layer are the functions associated with providing service to subscribers. These functions include transmitting data in frames and controlling access to the shared wireless medium, and are grouped into a media access control (MAC) layer. This Chapter is organized as follows. Section 2.2 addresses the history, evolution and applications of OFDM. Section 2.3 presents the O
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