Repeater-enhanced millimeter-wave systems in multi-path environments

The millimeter Wave (mmWave) is considered as a promising technology of the future fifth-generation wireless systems due to the currently underutilized multi-GHz spectrum surrounding the 60GHz carrier frequency, particularly with the recent advances in low cost sub-terahertz semiconductor circuitry. Since the mmWave suffers high attenuation during transmission, the repeater is a key technique to enable mmWave systems with seamless coverage. This paper considers the following practical design issues of Amplified-and-Forward Repeater (AFR) enhanced mmWave systems. First, the distribution of excess delay through multiple AFR hops is derived, which helps the design of cyclic-prefix length to avoid inter-symbol interference in orthogonal frequency division multiplexing systems. In addition, we show that the AFR decreases the channel coherence bandwidth and then propose a novel AFR design with a finite impulse response filter based channel equalizer to address this problem. Simulation results show that the proposed method is able to significantly increase channel coherence bandwidth and effectively reduce bit error rate.