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Today spectrum demand for wireless communication is tremendous and even keeps growing. In contrast, there are no blank spots in the spectrum map. Additional spectrum opportunities are available in unlicensed bands and so-called nonexclusively licensed bands which are currently made available. This non-exclusive spectrum can be exploited whenever a license holder is not active.These spectrum opportunities cannot be exclusively accessed so that multiple systems need to coexist. Existing MAC protocols need to be enhanced to allow a system to meet own Quality of Service (QoS) demands while allowing other coexisting systems to meet their QoS requirements.In this work, methods for capacity calculation known from cellular networks are extended and applied to a scenario of coexisting IEEE 802.16 (WiMAX) systems. Developed methods are used to evaluate enhancements for interference mitigation which lead to increased capacity.

Adaptive antennas are currently being integrated into wireless systems. As one of the first standards the wireless metropolitan area network IEEE 802.16 provides means to support smart antenna techniques. By means of adaptive antenna patterns smart antennas allow steering the transmit/receive power into certain directions while suppressing undesired power, i.e. interference. This paper introduces an adaptive space-time sectorization scheme that reduces interference by grouping subscriber stations into space-time sectors. The realization of space-time sectors is achieved only by reorganizing transmit and receive bursts within the MAC frame. The proposed scheme results in the same interference reduction as conventional sectorization, but it avoids major disadvantages. Additionally, the sectorization scheme offers various benefits being combined with SDMA. Finally, a MAC frame structure has been designed to allow for space-time sectorization. The frame design is standard compliant to the promising radio access technology IEEE 802.16.