Design considerations and implementation of a RF front-end for CDMA adaptive array system.

Abstract

Recent studies have shown that considerable system capacity gains in mobile communication systems can be obtained by exploiting the use of antenna arrays at the base station. Unfortunately, these studies make little mention of practical issues concerning implementation. It is thus one of the objectives of the Centre of Excellence (CoE) in Radio Access Technologies at the University of Natal to investigate the development of a widehand CDMA adaptive array transceiver using Alcatel software radios as the transceiver platforms. Such a transceiver system can be subdivided into three major sections: RF front-end, signal digitization and baseband processing stages. Due to the enormity of such an undertaking, the research outlined in this thesis is focused on (but not isolated to) some aspects of the RF front-end implementation for the proposed system. The work in this thesis can be catergorized into two sections. The first section focuses on the theoretical and practical (or implementation) aspects of antenna arrays and beamforming. In particular, it is evident that digital (rather than analogue) beamforming in a multi user environment, is a more viable option from both a cost and implementation standpoint. The second section evaluates the impact of RF component noise and local oscillator generated phase noise in a DS-CDMA system. The implementation of a RP front-end for a BPSK transceiver also forms part of the work in this section. LO phase noise and Error Vector Magnitude (EVM) measurements are performed on this system to support relevant theory. By use of the HP89410A phase noise measurement utility and the phase noise theory developed in this thesis, a quantitative phase noise comparison between two frequency sources used in the system were made. EVM measurement results conclusively verified the importance of an LNA in the system. It has also been shown that the DS-CDMA simulated system exhibits superior performance to the implemented BPSK system. Furthermore, an EVM troubleshooting methodology is introduced to identify possible impairments within the BPSK receiver RF front-end. However, this thesis was written with the intention of bridging the gap between the theoretical and practical implementation aspects of RP wireless communication systems. It is the author's opinion that this has been achieved to a certain extent.