Channel Bonding in Short-Range WLANs B. Bellalta, A. Faridi, J. Barcelo Universitat Pompeu Fabra, Barcelona Email: {name.surname}@upf.edu A. Checco Hamilton Institute, Ireland Email: {alessandro.checco}@nuim.ie P. Chatzimisios Alexander TEI of Thessaloniki, Greece Email: {peris}@it.teithe.gr. Abstract—Channel bonding is one of the strategies considered in the IEEE 802.11ac amendment to improve the performance of Wireless Local Area Networks (WLANs). However, besides the obvious gains attainable from using wider channels in terms of higher achievable transmission rates, there are also several potential drawbacks that may seriously compromise the overall WLAN performance, most notably the higher probability to suffer from external interference. The goal of this paper is to assess the suitability of channel bonding for enhancing the performance of short-range WLANs, which are highly susceptible to external interference. We analytically model and evaluate the performance of the two channel access schemes proposed for the IEEE 802.11ac amendment that enable the use of channel bonding. The results show that for short-range WLANs, the use of channel bonding is able to provide a significant performance boost when the presence of external interference is low to moderate, specially if the dynamic bandwidth channel access scheme is enabled. Index Terms—IEEE 802.11ac, channel bonding, static and dynamic bandwidth channel access, WLANs I. I NTRODUCTION Multimedia communications between nearby multimedia devices, such as smart TVs, high definition video and music players, file storage servers, tablets, and laptops using Short- Range Wireless Local Area Networks (SR-WLANs), is one of the scenarios targeted by next generation IEEE 802.11ac-based WLANs [1], since SR-WLANs are able to offer high transmis- sion rates and low power consumption. Typical scenarios can be desktop, room, and vehicular networks. Moreover, deploy- ing multiple SR-WLANs allows for improving the spectrum utilization by channel reuse. One of the strategies considered in IEEE 802.11ac WLANs that can be used to satisfy the performance requirements of multimedia applications in SR-WLANs is channel bonding [2]. Channel bonding simply consists in grouping several basic channels to obtain a wider one, which allows for higher transmission rates and throughput [3], [4]. In order to support channel bonding, two extensions for the default CSMA-based channel access scheme used in WLANs are being considered: the Static Bandwidth Channel Access Protocol (SBCA), which uses a fixed number of bonded basic channels and requires finding all those basic channels empty before starting a packet transmission; and the Dynamic Bandwidth Channel Access scheme (DBCA), which is able to dynamically adapt the channel width to the instantaneous spec- trum availability [5], [6]. Moreover, to guarantee backward compatibility with devices that are not able to use channel bonding, control and management frames are transmitted only over a single basic channel, which is called the primary channel. The rest of the channels are referred to as secondary channels. For data transmission, one or more basic channels can be used, depending on the channel bonding capabilities of each transmitter and receiver pair. When the receiver is only able to use a single channel, only the primary channel will be used for data transmission. In the case of SR-WLANs, the higher bandwidth provided by channel bonding can be specially advantageous for com- municating multimedia data, without causing any interference on the neighboring WLANs. However, due to their small coverage, SR-WLANs are also prone to external interference coming from neighboring WLANs operating at a higher power in the same channels, since the interfering WLANs may not be able to hear ongoing transmissions from the SR-WLAN and start transmitting before the SR-WLANs transmission is over. This situation worsens when channel bonding is used, as the resulting wider channel exposes the SR-WLANs to a larger number of such interfering WLANs. In this paper, we study exactly this tradeoff by evaluat- ing the performance of SR-WLANs in presence of external interference when channel bonding is enabled. We develop an analytical model that is able to capture the relationship between different system parameters for both SBCA and DBCA channel bonding schemes. The analytical model is then used to investigate the cases and conditions in which each channel access scheme is effective, in terms of the number of channels bonded, the activity from the interfering wireless networks, and the position of the primary channel of the target SR-WLAN within the channel width. The presented analytical model is general enough to be able to highlight the relationships between the different parameters and the effect of tuning them, as well as to assess the negative impact that external interferers have on the network performance. This paper is structured as follows. In Section II, both SBCA and DBCA schemes are described. The analytical model is presented in Section III. In Section IV, we provide graphical presentations of the throughput of each scheme for different values of channel bonding and system parameters to deter- mine the conditions under which each scheme performs best. Finally, conclusions and some future directions are presented in Section V. II. CHANNEL BONDING IN IEEE 802.11 AC WLANS An IEEE 802.11ac WLAN composed of a group of stations is considered. A set of predefined 20 MHz channels, to which