Interference Mitigation in WiFi Networks using Multi-sector Antennas Henrik Lundgren † , Anand Prabhu Subramanian ‡ , Theodoros Salonidis † , Marianna Carrera † , Pascal Le Guyadec † † Thomson, Paris, France ‡ Stony Brook University, New York, USA ABSTRACT Sectorized antennas provide an attractive solution to in- crease wireless network capacity through interference mit- igation. Despite their increasing popularity, the real-world performance characteristics of such antennas in dense wire- less mesh networks are not well understood. We demon- strate our multi-sector antenna prototypes and their per- formance through video streaming over an indoor wireless network in the presence of interfering nodes. We use our graphical tool to vary the sender, receiver, and interferer antenna configurations and the resulting performance is di- rectly visible in the video quality displayed at the receiver. Categories and Subject Descriptors C.2.1 [Network Architecture and Design]: Wireless Com- munication; C.4 [Performance of Systems]: Measure- ment Techniques General Terms Experimentation, Measurement, Performance Keywords Interference Mitigation, Sectorized Antenna, Sector Selec- tion 1. INTRODUCTION Interference is a major issue in wireless networks. In WiFi- based networks, all wireless devices that operate on the same frequency and are located within each others sensing range share the wireless medium. Sectorized antennas can miti- gate interference in dense wireless networks by limiting both the transmission and reception to certain directions. These antennas thus promise increased wireless network capacity through higher spatial reuse. Despite their increasing popu- larity and extensive studies in theory and using simulations, their performance characteristics when deployed in real net- works are still not well understood. While the concept of sectorization works well for outdoor line-of-sight commu- nication, indoor and dense wireless networks pose unique challenges due to its node density and reflection rich envi- ronment [3, 1]. Copyright is held by the author/owner(s). MobiCom’09, September 20-25, 2009, Beijing, China. ACM X-XXXXX-XX-X/XX/XX. We have developed a demonstrator that complements our previous measurement campaigns [3, 4] and its primary goal is to demonstrate the operation, the challenges, and the resulting performance of sectorized antennas in real-world dense 802.11 wireless mesh networks. We have designed a four-sector antenna [2] for operation in the 5GHz band with off-the-shelf 802.11 wireless cards. We equip a number of wireless nodes with these antennas and place them in vicin- ity of each other. We stream video content from a sender to a receiver in the presence of an interfering node while vary- ing antenna configuration (i.e., sector activation) at these nodes. The perceived video quality is affected by changes of the antenna configurations. We thus demonstrate the impact of sector selection on network performance through the perceived video quality at the receiver. In addition, we complement the qualitative video performance evaluation by collecting and graphically displaying quantitative link char- acteristics. 2. EXPERIMENTAL SETUP AND OPERA- TION We detail our demo architecture and its operation and specific requirements. Sectorized Antennas. We use Thomson multi-sector antennas as the one shown in Figure 1. This antenna con- sists of four Vivaldi sectors, each covering one quarter of the azimuth plane. These sectors can be simultaneously ac- tivated in any combination, and when all four sectors are active, it represents omni-mode. Sector activation is con- trolled by a switch integrated on the antenna system, which we control from the parallel port of the host computer (for more details on the antenna system, see [2]). Figure 1: A prototype of the Thomson multi-sector antennas used in our demo.