Alternative to Dynamic Rank Transmission for LTE Mobile Relay Node System

To obtain the appropriate number of layers for spatial multiplexing transmission on a high speed train equipped with moving relay nodes (MRN) cooperating with each other, the rank indicator (RI) is required. The conventional methods for calculating the RI have high levels of computational complexity and to dynamically obtain the RI based on the channel conditions require multiple times the computational complexity of a fixed rank transmission. We derive a method to reduce the computational complexity such that the RI is fixed, but the antenna positioning vary dynamically based on the channel conditions. Our simulation results show that our proposed method can achieve nearly the same throughput as with dynamic rank transmission schemes on the backhaul link with reduced complexity.