This paper sheds light on the necessity for transmit power control of 802.11 clear-to-send (CTS) frame for better spatial reuse in densely deployed wireless local area networks (WLANs). We first study the effect of the interference caused by CTS frames through both experiments and numerical analysis. Based on the analysis, we raise a limited spatial reuse problem caused by RTS/CTS mechanism and establish a guideline for controlling CTS transmit power to solve the problem. Next, a standard-compliant CTS transmit power control method, namely Quiet CTS (QCTS), is proposed. Through extensive simulations and prototyping using both software-defined radio and commercial devices, we demonstrate that QCTS enhances the average network throughput by up to 50% by enabling more simultaneous data transmissions.

With increasing demand for wireless connectivity, IEEE 802.11 WLANs have become ubiquitous and continue to grow in number. This leads to high density of basic service sets with the significant co-channel interference (CCI) among them. This paper sheds light on the CCI caused by 802.11 MAC ACK frames, which has been less studied than the CCI caused by data frames. Based on stochastic geometry analysis, we propose Quiet ACK (QACK), a dynamic transmit power control algorithm for ACK frames. Fine-grained transmit power adjustment is enabled by CCI detection and CCI power estimation in the middle of a data frame reception. Our prototype using software-defined radio shows the feasibility and performance gain of QACK, i.e., 1.5x higher throughput than the legacy 802.11 WLANs. The performance of QACK is further evaluated in more general WLAN environments via extensive simulations using ns-3.

Antenna selection, a cost-effective way to enhance network performance, has been employed in a limited manner in wireless local area networks (WLANs) due to the lack of channel information at the transmitter. In this paper, a practical antenna selection system without using channel information is proposed. We first describe the practical issues of antenna selection system for infrastructure-based WLANs, and then, analyze its characteristics through an extensive measurement study. Based on that, we propose antenna selection algorithms of access point (AP) for both (1) unicast transmission and (2) multicast transmission and reception. The proposed algorithms are comparatively evaluated using prototype implementation in a commercial AP. It is demonstrated that the proposed algorithms achieve up to 34% throughput gain and 54% frame error rate reduction for unicast and multicast transmissions, respectively.