An analytical expression for the probability density function of the signal-to-noise ratio (SNR) at the output of a two-branch maximal ratio and selection diversity system is given. The two branches are assumed to be Rayleigh fading, correlated, as well as of unequal average SNRs. Measurements of the cumulative distribution functions after selection and maximal ratio combining were made in Rayleigh fading channels and compared with the analytical results. Also presented are the exact analytical average probabilities of symbol error for coherent binary phase-shift keying and coherent quaternary phase-shift keying before and after two-branch maximal ratio combining for a slow and flat fading correlated Rayleigh channel.

The next generation CDMA standard, wideband CDMA (W-CDMA), has provision for many performance enhancement options to support high data-rate services. Transmit diversity has been proposed as one mechanism for performance enhancement. This paper presents a real-time implementation of a wideband transmit diversity system. The implementation was carried out to demonstrate transmit diversity in an indoor wireless channel at the handset with a two-element antenna array at 2.05 GHz for a bandwidth of 5 MHz. The diversity algorithm is a closed loop technique and is based on scanning the phase of signal on one antenna relative to the other. Single antenna measurements were also performed to serve as a baseline measure. Measurements were carried out both in line-of-sight (LOS) and in non-LOS (NLOS) environments. The diversity gains when assessed using a cumulative distribution function (CDF), showed gains of 2 dB and 7 dB respectively compared to individual antenna element for the LOS environment (at 1% CDF level). For the NLOS case, the diversity gains were more than 10 dB at the 1% CDF level.

Earth-space communications links operating above 10 GHz may be adversely affected by the earth's atmosphere and hydrometeors, particularly rain. These propagation phenomena are usually evaluated only for fading and depolarization effects. However, dispersion is an important factor in wide-band digitally modulated satellite links. In this paper we examine the mechanisms responsible for dispersion over bandwidths as great as 500 MHz in the 10-30 GHz range. The amplitude and phase effects of dispersion are quantified for a wide range of propagation conditions. The resulting propagation model is then used to generate estimates of performance degradation in wide-band QPSK systems through the use of computer simulation.