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The Scientific World Journal
Volume 2014, Article ID 920937, 11 pages
http://dx.doi.org/10.1155/2014/920937
Research Article

Beamforming Transmission in IEEE 802.11ac under Time-Varying Channels

1Department of Information and Communication Engineering, Yeungnam University, Gyeongsan 712-749, Republic of Korea
2School of Information and Communication Engineering, Chungbuk National University, Cheongju 361-763, Republic of Korea

Received 21 May 2014; Accepted 13 July 2014; Published 24 July 2014

Academic Editor: Changyong Pan

Copyright © 2014 Heejung Yu and Taejoon Kim. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The IEEE 802.11ac wireless local area network (WLAN) standard has adopted beamforming (BF) schemes to improve spectral efficiency and throughput with multiple antennas. To design the transmit beam, a channel sounding process to feedback channel state information (CSI) is required. Due to sounding overhead, throughput increases with the amount of transmit data under static channels. Under practical channel conditions with mobility, however, the mismatch between the transmit beam and the channel at transmission time causes performance loss when transmission duration after channel sounding is too long. When the fading rate, payload size, and operating signal-to-noise ratio are given, the optimal transmission duration (i.e., packet length) can be determined to maximize throughput. The relationship between packet length and throughput is also investigated for single-user and multiuser BF modes.