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Performance Evaluation of WiMAX/IEEE 802.16 OFDM Physical Layer - page 16 / 107

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Working Group 802.16 on Broadband Wireless Access (BWA) standard is responsible for development of 802.16 and the included WirelessMan™ air interface, along with associated standards and amendments.

The IEEE 802.16 standard contains the speci ication of Physical (PHY) and Medium Access Control (MAC) layer for BWA. The first version of the standard IEEE802.16­ 2001 [7] was approved on December 2001 and it has gone through many amendments to accommodate new features and functionalities. The current version of the standard IEEE 802.16­2004 [1], approved on September 2004, consolidates all the previous versions of the standards. This standard speci ies the air interface for fixed BWA systems supporting multimedia services in licensee and licensed exempt spectrum [1]. The Working Group approved the amendment IEEE 802.16e­2005 [8] to IEEE802.16­2004 on February 2006. To understand the development of the standard to its current stage, the evolution of the standard is presented here.

2.1.1 IEEE 802.16­2001

This first issue of the standard speci ies a set of MAC and PHY layer standards intended to provide fixed broadband wireless access in a point­to­point (PTP) or point­to multipoint (PMP) topology [7]. The PHY layer uses single carrier modulation in the 10 – 66 GHz frequency range.

Transmission times, durations and modulations are assigned by a Base Station (BS) and shared with all nodes in the network in the form of broadcast Uplink and Downlink maps. Subscribers need only to hear the base station that they are connected and do not need to listen any other node of the network. Subscriber Stations (SS) has the ability to negotiate for bandwidth allocation on a burst to­burst basis, providing scheduling lexibility.

The standard employs QPSK, 16­QAM and 64­QAM as modulation scheme. These can be changed from frame to frame and from SS to SS, depending on the robustness of the connection. The standard supports both Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD) as duplexing technique.

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