Design and Implementation of Distributed Transmit Beamforming for OFDM system

• Main Authors: Po-Hsun Hu, 胡博勛
• Other Authors: Po-Hsuan Tseng
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/w2f4d6

碩士 === 國立臺北科技大學 === 電子工程系研究所 === 103 === Distributed transmit beamforming enhances the signal quality by a plurality of transmitters transmitting to the same receiver using the spatial diversity. Providing that distributed transmitters are unable to exchange messages with others through the back-haul network, how to use the least amount of feedback signal to reach a distributed transmitting synchronization are the key factors of effectiveness. Note that timing is considered asynchronous and distances from transmitters to the receiver are different. Although the cyclic prefix (CP) tolerant timing synchronization error in an OFDM system, the phase differences between different paths still limit the beamforming gain. We propose the first distributed beamforming N-subcarrier feedback (DB-NSF) scheme where the receiver broadcast feedback signal to the plurality of transmitters and each subcarrier of transmitter individually dynamically adjust phase based on N different subcarriers. The second scheme is the distributed beamforming timing estimation feedback (DB-TEF) scheme where the receiver estimates timing offsets (TOs) by training sequence and feedbacks to the transmitter to adjust phase. Software defined radio (SDR) is utilized for the implementation on the Ettus USRP. The experimental results validate that the proposed DB-NSF and DB-TEF achieve synchronization and feedback mechanism with 41 % amplitude gain over the scheme without DB. The DB-NSF has better scalability that allows a plurality of transmitters to a receiver with a minimum feedback.