Performance Evaluation of SDMA Coordination Schemes for WiMAX Systems

Abstract

Advanced antenna technologies that are technically mature are currently being integrated into modern wireless systems such asWiMAX or LTE. Capacity and service quality provided by wireless links, as well as the spectral efficiency, are expected to be significantly boosted by advanced antenna techniques that are using multiple antennas either at the transmitter, at the receiver or at both sides. Beamforming or Space Division Multiple Access (SDMA) techniques are able to simultaneously transmit different signals to different receivers. Furthermore, concurrent reception of different signals is provided by joint detection techniques. In this manner the Medium Access Control (MAC) layer can also schedule stations separated in space. Thus, the capacity of the system can be increased with the number of concurrent data streams. But an SDMA enabled cell generates more varying interference than a conventional cell, because a changing number of subscriber stations are sending uplink data in parallel or DL streams with changing direction are transmitted by the base station. Thereby the SINR estimation becomes less precise and the link adaptation less effective. This thesis investigates schemes for mitigating inter-cell interference and increasing the precision of SINR estimations in SDMA enhanced system. Three concepts of coordination of BS are developed, implemented and evaluated in this work. System level simulations are conducted in a cellular deployment by means of the open Wireless Network Simulator (openWNS). They show the considerable gain of the developed enhancements compared to an uncoordinated system