# Combined Sweeping and Jumping Method to Enhance Node Insertion Algorithm for Wi-Fi Sensor Networks
## 1 Introduction  
Wi-Fi and Wireless Personal Area Network (WPAN) communication technologies have been employed to create wireless sensor networks [1; 2; 3; 4]. In [1], the applications, the routing and connectivity schemes, the challenges, and the energy supply methods for wireless sensor networks are reviewed. In [2], the Medium Access Control (MAC), routing, and security protocols and energy management methods that are necessary for the medical applications in wireless sensor networks are reviewed. The survey of the technologies for improving the security of wireless sensor networks using machine learning techniques is provided in [3]. In [4], the node insertion algorithm is proposed for the connectivity-based multipolling MAC protocol to be applied to wireless sensor networks based on Wi-Fi networks where a large number of sensors exist. Each sensor has a short transmission range in wireless sensor networks based on WPAN networks like Bluetooth and Zigbee networks; therefore, in some cases, data should traverse through multi-hop links in wireless sensor networks based on WPAN networks. On the other hand, in wireless sensor networks based on Wi-Fi networks, sensors have larger transmission ranges, and can be connected to the Internet via single-hop links with small transmission delay. In [5], the contention-based MAC protocols for Internet of Things (IoT) applications in Wi-Fi-based networks are presented. In [6], a Wi-Fi-based underwater sensor network was demonstrated. In [7], the contention-based MAC protocol was presented to minimize the energy consumption in wireless sensor networks based on non-802.11 networks. In [8], the contention-based cooperative receiver-initiated MAC protocol was proposed to reduceenergy consumption and data collisions in wireless sensor networks based on non-802.11 networks. The hybrid MAC protocol combining Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) and Time Division Multiple Access (TDMA) schemes was presented for satisfying Quality of Service (QoS) requirements in wireless sensor networks based on non-802.11 networks in [9]. The TDMA-based MAC protocol was proposed to optimize the power-saving mechanism in wireless sensor networks based on non-802.11 networks in [10]. The approach for developing the contention-free MAC protocols in Wi-Fi-based wireless sensor networks draws little attention in the literature. However, as stated in [4], an efficient contention-free or polling-based MAC protocol should be developed for Wi-Fi-based wireless sensor networks because the contention-based MAC protocols suffer from severe performance degradation due to the contentions among sensors. Since the initial development of Wi-Fi communication technology, the Distributed Coordination Function (DCF) and Point Coordination Function (PCF) protocols have been the basic MAC protocols to govern the transmissions in Wi-Fi networks [11]. In the DCF protocol, all nodes contend to access a Wireless Medium (WM) to transmit their data, and the DCF protocol functions well in Wi-Fi networks with a small number of nodes. However, in large Wi-Fi networks like wireless sensor networks with a large number of sensors, the DCF protocol has been known to have exponentially degraded MAC performance [12]. In the PCF protocol, each node polled by Access Points (APs) is granted the contention-free access to WM [11]. Therefore, the PCF protocol functions better than the DCF protocol in wireless sensor networks where many sensors attempt to send data. The DCF and PCF protocols are compared in terms of the channel access method and the appropriate network scenario in Table 1.  
For maximizing the performance of the PCF protocol, the connectivity-based multi-polling MAC protocol was presented in [13; 14] where the number of multipolling frame transmissions is minimized by the serially connected multipolling sequences derived based on the connectivity information among nodes.