Mattias Wennström (Frenne)

Licentiate Thesis, Signals and Systems, Uppsala University, October 1999.
 

Abstract:

In this thesis, implementation issues for adaptive array antennas in wireless systems are treated. First, an overview of different implementation options are discussed and their drawbacks and benefits.

We then discuss the performance degradation of the adaptive antenna array when it is implemented in hardware. The degradation is due to quantization of the received signal in the sampling process, the limited accuracy in the weighting units and the accuracy of the calibration. Due to temperature drift of active components in the hardware, the validity of the calibration will degrade over time.

We derive a theoretical model and a simulation model of an adaptive array antenna. The results are compared to measurements on an adaptive antenna testbed, developed at Signals and Systems Group, Uppsala University in cooperation with Ericsson Radio Access AB. From both the theory and the simulations, we concluded that the calibration accuracy limited the ability of the adaptive antenna testbed to suppress interferers.

We also propose two algorithms for on-line calibration of the adaptive antenna array. The direct algorithm is successful in a slowly varying signal environment, which is typical in rural areas. The indirect calibration algorithm estimates the temperature drift and is shown to benefit from a fast varying signal environment, as typical in urban areas. Both algorithms are successful in maintaining the interferer suppression capability despite the temperature drift of the hardware parameters.

 We also investigate, with measurements and simulations, the effect of an non-ideal multicarrier power amplifier in the transmitting downlink of an array antenna. We show how the CDF of the carrier to interference ratio of the mobiles in an cellular system depends on the basestation transmit amplifier back-off. We then define the total degradation function to find a power efficient choice of the amplifier back-off. Furthermore, the derived theory predicts the direction of the radiated intermodulation products. These predictions were verified by measurements on an four element antenna array in an anechoic chamber. Finally, we discuss the impact of weight tapering on the radiated intermodulation power.

Related publications:

Considering Downlink Intermodulation Distortion in Switched Multibeam Antennas for Cellular Radio Systems , VTC 2000, Boston, September, 2000.
Intermodulation Distortion in Switched Multibeam Antennas for Cellular Radio Systems , IEEE PIMRC'2000, London, UK, September, 2000.
An Auto-Calibrating Adaptive Array for Mobile Telecommunications
IEEE Transactions on Aerospace and Electronic Systems, vol.36, no.2, April 2000, pp.729-736 ;
Analysis of Intermodulation Distortion on Log-Normal Shadowed WLAN Channels, IEE Electronic Letters, vol.36, no.9, pp.833-834
Effect of nonlinearities in smart antennas, Wireless99, Munich, 1999
Analysis of quantisation effects in adaptive antenna arrays, RVK99, Karlskrona, 1999
Experimental evaluation of an adaptive antenna...., PIMRC97, Helsinki, 1997
Analysis of quantisation effects in adaptive antenna arrays, Antenn97, Göteborg, 1997

Source:

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