Cooperative Diversity Performance in Millimeter Wave Radio Systems

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.

I. Introduction

Modern wireless networks are in increasing demand for large bandwidth in order to support increasing data rates for multimedia services. Broadband operation at frequencies above 10GHz is therefore considered as a mandatory requirement in Fixed Wireless Broadband Networks for the success of future high bandwidth multimedia services. These networks can be used in two main application scenarios. Firstly, they can be used in wireless backhaul networks to support the next generation 4G mobile networks, such as the Long Term Evolution (LTE) standard, that pose significant capacity requirements [1]–[4]. Secondly, they can be used as an alternative to Digital Subscriber Line (DSL) last-mile technology with a constantly growing market potential. These networks are well known as IEEE 802.16 (10–66GHz part) or LMDS technology and are described in detail in [5]–[7]. They have been proposed to connect users with the existing core networks, i.e. subscriber terminals (clients) become server nodes and offer the interconnection in a mesh arrangement, since the IEEE 802.16 WirelessMAN (WiMAX) standard covers the case of multi-hop wireless networks operating at frequencies above 10GHz. In addition, another requirement has recently been raised in the context of “green communications”, the efficient design of communication systems which satisfy both data rates and reliability constraints [8].