# WLAN Aware Cognitive Medium Access Control Protocol for IoT Applications
## 1 Introduction  
Wi-Fi is one of the major contributors to today's global connectivity and economy [1]. With a significant increase in wireless data transfer demands in recent years, the wireless spectrum has become a scarce and expensive resource. As the number of Internet of Things (IoT) devices utilizing the open spectrum bands (like the 2.4 GHz band) is increased, this calls for a reevaluation of spectrum access protocols. Since the medium access control protocols are designed for a particular technology, they fail to achieve fair and efficient wireless resource sharing in the presence of interference from other miscellaneous technologies [2; 3; 4; 5; 6; 7; 8; 9]. Wi-Fi is the major source of interference in the Industrial, Scientific, and Medical (ISM) radio band due to its high power and data rate as compared to the other technologies sharing the same 2.4 GHz ISM band [10]. Other technologies, such as IoT devices operating in the ISM band, can greatly benefit from the knowledge of current spectrum occupancy and design protocols for wireless coexistence, thus improving their transmission efficiency. IoT devices consist of battery-powered wireless sensor nodes, and depletion of the battery will strip IoT devices from network communication. A common scenario in the future will be the co-existence of various IoT devices (consisting of IEEE 802.15.4 based wireless sensor nodes) with the already installed IEEE 802.11-based Wireless Local Area Network (WLAN). Both these wirelesstechnologies operate in the unlicensed ISM band of 2.4 GHz and cause interference to each others' transmissions. For this particular scenario, IoT devices will be subjected to more interference caused by the high-powered WLAN system. On the other hand, interference from the low-powered IEEE 802.15.4 transmissions will not impact the performance of the IEEE 802.11 devices [11]. A key issue in IoT is that WLAN nodes are unaware or blind to the existence of IEEE 802.15.4-based IoT devices due to the difference in the magnitude of transmission power. Therefore, WLAN nodes do not defer channel access when there is an ongoing packet transmission of packet IoT nodes. This overlapping of transmission results in frequent packet drop and energy loss for the IoT nodes when they are communicating with the IoT edge devices or sink nodes. An efficient medium access control protocol for IoT nodes is required to reduce packet loss due to transmission overlap so that the energy efficiency of IoT devices can be improved. Performance evaluation of WLAN shows that its traffic is bursty, i.e., data frames are transmitted together in clusters and have short intervals between them, while the idle inactive periods between the cluster of frames are notably longer and can be exploited by IoT nodes for their transmission [12]. Cognitive medium access is a dynamic spectrum access method that allows secondary users to access the primary user's radio spectrum (which is not currently used by the primary user) [13; 14; 15; 16]. In this paper, we propose a WLAN Aware Cognitive Medium Access Control (WAC-MAC) protocol that is adopted by the IEEE 802.15.4-compliant IoT nodes to reduce the interference of co-existing WLAN nodes. IoT nodes employ a sensing mechanism based on energy detection to find WLAN user activity and identify inactive periods of WLAN transmission. This is done by introducing a sensing phase in the superframe structure. WAC-MAC also uses an adaptive wake-up scheduling technique that reduces the current beacon interval in case the medium is busy after the sensing phase. This results in quicker sensing of the medium, again, instead of sleeping for the long beacon interval. Lastly, the WAC-MAC protocol uses an adaptive backoff scheme based on the node's battery lifetime. This mechanism allows nodes with less remaining energy to transmit quickly, hence conserving their energy. Results show that the proposed WAC-MAC protocol reduces the packet loss, as well as improves network energy life time and end-to-end delay.