Mattias Wennström

An antenna solution for MIMO channels: the switched parasitic antenna

We investigate the switched parasitic antenna (SPA), which is a novel technique for electronically directing the radiation pattern in a MIMO system. The correlation between the received signal modes is shown to be sufficiently low to yield a diversity gain. The capacity limit using the SPA is investigated for different SPA configurations and it is found that the capacity is comparable with an array antenna configuration in certain situations. Finally, a space time block coding scheme is used to evaluate the bit error rate of a MIMO-SPA system. It is found that the SPA requires a 5 dB higher SNR than an antenna array solution to achieve a BER=10/sup -2/. However, the array antenna requires a radio transceiver for every antenna, as opposed to the SPA which uses only one transceiver.

High-resolution direction finding using a switched parasitic antenna

Direction finding by exploiting the directional radiation patterns of a switched parasitic antenna (SPA) is considered. By employing passive elements (parasites), which can be shorted to ground using pin diodes, directional radiation patterns can be obtained. The direction finding performance of the SPA is examined by calculating a lower bound on the direction finding accuracy, the Cramer-Rao lower bound (CRB). It is found that the SPA offers a compact implementation with high-resolution direction finding performance using only a single radio receiver. Thus, exploiting SPAs for direction finding is an interesting alternative to traditional antenna arrays offering compact and low-cost antenna implementations.

Experimental evaluation of an adaptive antenna for a TDMA mobile telephony system

Measurements (at 1.8 GHz) of an adaptive DCS-1800 base station antenna, used in uplink only, are presented and analysed. Both laboratory measurements and outdoor field trials have been performed. The antenna improves the C/I ratio more than 30 dB. Calculations using measured data, assuming downlink performance equal to that of the uplink, show a spectral efficiency gain of 6 over present base station systems.

Effects of nonlinear distortion on switched multibeam FDMA systems

The effects of using a multicarrier amplifier (MCPA) in the transmit chain of a cellular frequency-division multiple-access system utilizing switched multibeam base-station antennas is investigated. By combining several carriers prior to amplification, the signal envelope will be time varying and the MCPA will introduce nonlinear distortion of the amplified waveforms. It is shown how the main beam direction and frequency of any intermodulation product of any order can be calculated. A frequency allocation scheme is presented that reduces the intermodulation distortion for the mobile users. By Monte Carlo simulations, the probability distribution function of the received intermodulation distortion power is estimated, assuming a GSM system, as a function of the number of antenna elements and the number of active users. Comparisons with a one-element reference antenna are made, and it is shown that the received intermodulation distortion power for the users in the system is substantially reduced when the number of beams is increased or the user activity is reduced.

Antennas for cellular radio systems

The performance and feasibility of switched multibeam array antennas in cellular systems is investigated. We assume that multicarrier power amplifiers (MCPAs) are used in the base-station, to co-amplify the transmitted signals. The MCPA generates intermodulation distortion and it is shown how the multibeam antenna makes the radiated intermodulation distortion dependent on the azimuthal look-direction. Given the carrier to intermodulation distortion ratio of the MCPA, semi-analytical expression for the outage probability for the mobiles is derived assuming a log-normal fading radio channel. Furthermore, the impact of the frequency reuse factor, trunkpool scheme and number of antennas is investigated. The analysis show that when the number of antennas are increased, it is possible to reduce the requirements on the MCPA linearity.

Intermodulation distortion in switched multibeam antennas for cellular radio systems

The performance of switched multibeam antennas for cellular radio systems is investigated when the transmit amplifier is of a multicarrier (MCPA) type. The MCPA nonlinearity generates intermodulation distortion in the transmitted signal that is spatially filtered by the array radiation pattern. Hence, the intermodulation distortion becomes direction-dependent, and the direction of the generated intermodulation products of any order is derived. It is shown by using Monte Carlo simulations how the downlink carrier to interference ratio depends on the frequency reuse distance and on the MCPA linearity measured as its noise power ratio (NPR). For reuse factor one systems, which is made possible by use of multibeam antennas, the linear co-channel interference dominates the interference. On the contrary, for a reuse factor seven system it is shown that a weak nonlinearity directly gives a degradation in carrier to interference ratio (CIR) due to intermodulation distortion. However the reuse factor seven system has a large CIR overhead due to the increase in CIR using a multibeam antenna, and the outage probability is thereby only slightly affected.