Large MISO Beamforming For High Speed Vehicles Using Separate Receive & Training Antennas
Résumé
Traditional Multiple Input Single Ouput (MISO) systems exploit the propagation channel reciprocity in Time Division Duplex (TDD) wireless communication systems and Channel State Information at the Transmitter (CSIT) to transmit data from a Base Station (BS) towards a user efficiently. They achieve a beamforming (BF) gain which increases with the number of transmit antennas. However, if the target user is a high speed vehicle, the BS "misses" its moving target, simply because the vehicle moves during the delay between the channel estimation at the BS and the data reception at the vehicle. As a consequence, a large part of the targeted BF gain is lost. This loss gets obviously worse when the vehicle speed increases, but also, when the number of transmit antenna increases. Hence, the performance of these classical BF systems, which we will latter call Reference Systems (RS), dramatically collapses as soon as the vehicle speed exceeds 50kmph and the number of transmit antennas exceeds 4. In this paper, a new scheme called Separate Receive and Training Antennas (SRTA) is proposed, ensuring that the BS never "misses" its target, even at very high speed, without reducing the TDD frame duration. SRTA performance is assessed over Winner II spatially correlated channel models. SRTA is demonstrated to outperform RS systems since providing a good Block Error Rate (BLER) even for speeds up to 300kmph.