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.

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.

We consider the problem of detecting known signals contaminated by additive noise with a completely unknown probability density function f. To this end, we propose a new adaptive detection rule. It is defined by plugging a kernel density estimator f/spl circ/ of f into the maximum a posteriori (MAP) detector. The estimate f/spl circ/ can either be computed off-line from a training sequence or on-line simultaneously with the detection. For the off-line detector, we prove that the (asymptotic) error probability for weak signals converges to the minimal error probability of the MAP detector as the number of training data tends to infinity, and we also establish rates of convergence and the optimal choice of bandwidth order for a certain class of noise densities. In a Monte Carlo study, the off-line plug-in MAP detectors are compared with the L/sup 1/- and L/sup 2/-detectors for various noise distributions. When the training sequence is long enough, the plug-in detectors have excellent performance for a wide range of distributions, whereas the L/sup 2/-detector breaks down for heavy-tailed distributions and the L/sup 1/-detector for distributions with little mass around the origin.

This paper deals with the problem of communicating through unspecified noise. Detectors, robust against variations in the probability density function of the noise, are developed and discussed. The paper covers three issues. First, the relation between a distance measuring receiver and a correlating receiver in a general case is shown. Second, a theoretical method for the computation of an upper limit for the probability of symbol error is presented. This computation fits into the ordinary framework for computation of the error probability by changing the inverted noise density 2/N/sub 0/ to efficacy, /spl epsiv/. Efficacy is defined in the paper. Third, detectors based on M-, i.e., maximum likelihood type, and R-, i.e., rank, statistics are tested and compared for GMSK and /spl pi//4-shifted DQPSK. From numerical comparisons of the upper bounds and their simulated estimates for robust detectors, it is concluded that the loss in Gaussian noise is very small compared to the optimum quadratic detector. The gain, compared to a nonrobust receiver optimized to Gaussian noise, is around 0.5 to 2 dB for large SNR and around 2 to 4 dB for low SNR in impulsive noise. This offers new methods of significantly improving communication when the noise is unknown.>

An adaptive antenna for the receiver base station of the NMT 900-system has been designed at the Circuits and Systems Group, Uppsala University. The properties of the antenna have been evaluated by Telia Research AB. The work involved in the antenna design and the field tests is reported.>