Impact of LTE precoding for fixed and adaptive rank transmission in moving relay node system

Improved capacity and reliability of wireless networks can be achieved by users onboard in a high speed train with the use of moving relay nodes (MRN) cooperating with each other. Further improvement in performance is achieved with codebook based precoders adopted by third generation partnership project (3GPP) for spatial multiplexed transmission mode. Open loop and closed loop precoded spatial multiplexing for fixed and adaptive rank transmissions were simulated and analyzed on the backhaul link of a cooperative MRN system in a high speed train. To obtain improved performance, channel information in the form of precoder matrix indicator (PMI) and rank indicator (RI) are required for the closed loop operation while the RI is only needed for the open loop operation. The results show that throughput gain on the backhaul link of the cooperative MRN system can be achieved with the precoded transmission when compared to unprecoded spatial multiplexing transmission. Further improvement in throughput was achieved when the transmission rank changed dynamically according to the channel condition.