We measure the capacity of multiple-input multiple-output radio systems in microcellular environments. We use a new data evaluation method that allows to evaluate the cumulative distribution function of the capacity from a single measurement. This method is based on an extraction of the parameters of the multipath components and, thereafter, a synthetic variation of their phases. In the analyzed environments, we find capacities to be about 30% smaller than would be anticipated from an idealized model. In addition, the frequency selectivity of the channel makes the CDF of the capacity steeper and, thus, increases the outage capacity, compared with the frequency-flat case, but the influence on the mean capacity is small.

We present a statistical analysis of wideband three-dimensional channel measurements at base station locations in an urban environment. Plots of the received energy over azimuth, elevation, and delay planes suggest that the incident waves group to clusters in most measured transmitter positions. A super-resolution algorithm (Unitary ESPRIT) allows one to resolve individual multipath components in such clusters and hence enables a detailed statistical analysis of the propagation properties. The origins of clusters-sometimes even individual multipath components-such as street apertures, large buildings, roof edges, or building corners can be localized on the city map. Street guided propagation dominates most of the scenarios (78%-97% of the total received power), while quasi-line-of-sight over-the-rooftop components are weak(3%-13% of the total received power). For this measurement campaign, in 90% of the cases, 75% of the total received power is concentrated in the two strongest clusters, but only 55% in the strongest one. Our analysis yields an exponential decay of power with 8.9 dB//spl mu/s, and a standard deviation of the log-normally distributed deviations from the exponential of 9.0 dB. The power of cross-polarized components is 8 dB below copolarized ones on average (vertical transmission).

Intercarrier interference can be a dominant source of errors in OFDM-systems, requiring some sort of equalization. We show that serial and parallel interference cancellation techniques, which were originally developed for CDMA multiuser techniques, can be used for OFDM equalization and are much more efficient than a brute force inversion of the channel matrix. Maximum excess delays of up to 70% of the OFDM block duration can be handled without loss of performance.

We introduce a computationally efficient OFDM transmission technique that does not require a cyclic prefix and thus provides high spectral efficiency. The intersymbol interference (ISI) due to time dispersion of the channel is combated by ISI cancellation. We show that the inversion of the channel matrix for interchannel interference (ICI) cancellation can be done by the "operator perturbation technique" (OPT) much more efficiently than by conventional equation solvers. We supplement the OPT by blind techniques and hence reduce the error floor to zero for frequency-selective channels. The expense for a 2 Mbit/s transmission is about 500 MFlops. The technique can also deal with time-varying channels in a straightforward way.