Performance Evaluation of the IEEE 802.16 MAC Protocol for Broadband Wireless Access

The IEEE 802.16 is establishing itself as one of the leader technologies in the context of Broadband Wireless Access (BWA), as corroborated by the huge number companies that have joined the WiMAX Forum since it was formed in June of 2001 to promote the adoption of IEEE 802.16 compliant equipment by operators of BWA systems. Since its first release in 2001, the IEEE 802.16 standard included native support for Quality of Service (QoS) at the Medium Access Control (MAC) layer, with several mechanisms to support different types of applications, classifi ed by the standard into four scheduling services. However, the standard does not specify the algorithms to actually provide QoS support by means of these mechanisms. This allows any manufacturer to implement its own optimized proprietary algorithms, thus gaining a competitive advantage over rivals. The IEEE 802.16 standard provides four diff erent scheduling services: Unsolicited Grant Service (UGS), real-time Polling Service (rtPS), non-real-time Polling Service (nrtPS), and Best Effort (BE). This work is aimed at verifying, via simulation, the effectiveness of rtPS, nrtPS and BE in managing traffic generated by data and multimedia sources. Performance is assessed for an IEEE 802.16 wireless system working in Point-to-Multipoint (PMP) mode, with Frequency Division Duplex (FDD), and with full-duplex Subscriber Stations (SSs). Our results show that the performance of the system, in terms of (e.g.) throughput and delay, depends on several factors: the frame duration, the mechanisms for requesting bandwidth (uplink only), the multimedia traffic type, and the offered load partitioning, i.e. the way traffic is distributed among SSs, connections within each SS and traffic sources within each connection. Finally, we propose an algorithm, namely Half-Duplex Allocation algorithm (HDA), that can be employed by the BS to serve SSs with half-duplex capabilities (HD-SSs) in Frequency Division Duplexing (FDD) mode. Based on the extensive simulations, we show that the performance degradation of HD-SSs, with respect to SSs with full-duplex capabilities (FD-SSs), is negligible, provided that HDA is employed by the BS.