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Performance Evaluation of WiMAX/IEEE 802.16 OFDM Physical Layer - page 17 / 107





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An important feature of 802.16­2001 is its ability to provide differential Quality of Service (QoS) in the MAC Layer. A Service Flow ID does QoS check. Service flows are characterized by their QoS parameters, which can then be used to specify parameters like maximum latency and tolerated jitter [10]. Service flows can be originated either from BS or SS. 802.16­2001 works only in (Near) Line of Sight (LOS) conditions with outdoor Customer Premises Equipment (CPE).

2.1.2 IEEE 8020.16a­2003

This version of the standard amends IEEE 802.16­2001 by enhancing the medium access control layer to support multiple physical layer speci ications and providing additional physical layer specifications. This was ratified by IEEE 802.16 working group in January 2003[9]. This amendment added physical layer support for 2­11 GHz. Both licensed and license­exempt bands are included. Non Line of Sight (NLOS) operation becomes possible due to inclusion of below 11 GHz range, extending the geographical reach of the network. Due to NLOS operation multipath propagation becomes an issue. To deal with multipath propagation and interference mitigation features like advanced power management technique and adaptive antenna arrays were included in the specification [9]. The option of employing Orthogonal Frequency Division Multiplexing (OFDM) was included as an alternative to single carrier modulation.

Security was improved in this version; many of privacy layer features became mandatory while in 802.16­2001 they were optional. IEEE 802.16a also adds optional support for mesh topology in addition to PMP.

2.1.3 IEEE 802.16c­2002

In December 2002, IEEE Standards Board approved amendment IEEE 802.16c [6]. In this amendment detailed system pro iles for 10­66 GHz were added and some errors and inconsistencies of the first version of the standard were corrected.


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