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Electronic Engineering

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Browsing Electronic Engineering by Subject "Antenna arrays."

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    Design considerations and implementation of a RF front-end for CDMA adaptive array system.
    (2000) Roopram, Kelesh D.; McDonald, Stephen A.
    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.
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    Implementation of a WCDMA AAA receiver on an FPGA based software radio platform.
    (2001) Kora, Saju P.; McDonald, Stephen A.
    WCDMA promises to achieve high-speed internet, high quality image transmission and high-speed data services with larger system capacity. However, Multiple Access Interference is one of the major causes of transmission impairment, which reduces the link capacity in WCDMA systems. The Adaptive Antenna Array (AAA) technique reduces multiple access interference by directing antenna beam nulls towards the interfering signals by weighting the received signals from all antennas before combining the signals. With the very rapid advancement of wireless personal communications services, a new challenge to the cellular industry is the integration of multiple systems and applications on a single device. A software radio technique offers a possible solution to achieve this goal including international roaming and multiple standard operations within the same geographical area. The main attraction of a software radio is it's flexibility, in that it can be programmed for emerging cellular standards allowing it to be updated with new software without any changes in the hardware infrastructure. A software radio incorporating adaptive array beamforming at the receiver can increase the total carried traffic in a system and transmit power while the probability of call blocking and forced termination can also be decreased. This dissertation examines WCDMA, AAA, power control and software radio techniques in the world of wireless communication systems. Once the theoretical background of CDMA and AAA has been substantiated, the thesis establishes the need for power control in mobile systems by examining simulation results. An AAA receiver with six antenna elements is proposed and evaluated in different environments as a precursor to implementation. It can be inferred that when the link is interference limited, the link capacity can be increased and it has been shown that the AAA receiver with six antenna elements increases the link capacity to about 2.9 times that of the single antenna RAKE receiver. This thesis also examines the basic concepts of VHDL and considers this as the principle means to program reconfigurable core FPGA's in the software radio. A three-layered (PC/DSP/FPGA) software radio test bed is used to implement an AAA receiver. The architecture of the test bed is designed in such a way that it can be used to evaluate the performance of various FPGA based transceivers and coding schemes etc. Many of the desirable features and flexibilities inherent in the software radio concept are available on this test bed and the system has proved to be capable of high speed digital processing and is ideally suited to the development of time critical system components. The bit error rate achieved using the implemented receiver is assessed and compared to simulation results in an environment incorporating Rayleigh fading and AWGN.