The constantly increasing demand for capacity in modern communication systems such as wireless backhaul has led to the employment of frequencies above 10 GHz where the dominant fading mechanism is rain attenuation which is usually modelled as a lognormal random variable (when expressed in dB - log-lognormal in linear scale). In addition, in the context of green communications the use of cooperative diversity techniques can be considered as an important tool which improves the performance, reliability and efficiency of such systems. In this paper, the outage performance analysis of a cooperative system operating at frequencies above 10 GHz is presented, where the propagation medium consists of spatially correlated fading channels. In addition, the energy and spectral efficiency of various multiple-access protocols as well as different relay retransmission and receiver combining techniques are investigated. Moreover, it is proposed that the high correlation coefficient between various rain fading channels can be exploited by the relay to estimate the rain fading of the next hop. Extended numerical results present the impact of various system parameters on the end-to-end performance. Finally, comparison with an energy- and bandwidth- equivalent direct link highlights the system parameter regions where cooperative diversity offers gains over non-cooperation.

The ever increasing demand for multimedia services has led to the extensive use of fixed wireless outdoor networks, where the transmitted information signals arrive to the final destination through a relay node, creating a dual-hop transmission. Due to the increased demand for bandwidth and the spectral congestion at low frequencies, operation at frequencies above 10GHz satisfying the Line-Of-Sight condition is required. At this frequency range, the dominant fading mechanism exposing spatial and temporal stochastic properties is rain attenuation, typically modeled as a lognormal flat fading channel when expressed in dB (log-lognormal in linear scale). In this paper, the outage performance of a dual hop system using several radio relay types is presented and physical prediction models with analytical formulas are proposed, employing spatially correlated lognormal fading channels. Extended numerical results investigate the impact of various operational, geometrical and geographical radio relay parameters, as well as the impact of the employment of a relay channel estimator, on the end-to-end performance.