# Sensing and Device Neighborhood-Based Slot Assignment Approach for the Internet of Things
## 2 Literature Review  
In the literature, numerous approaches have been reported to enable simultaneous communication or packet transmissions of multiple (preferably more than two) devices \(C_{i}\) using a common transmission medium [18; 19]. A comprehensive review of those existing mechanisms, which are closely related to the work presented in this article, is presented. Frequency division multiple access (orthogonal-based) approaches were presented to ensure the concurrent packet transmissions of more devices \(C_{i}\) using a common medium [20]. In these schemes, overall bandwidth is divided into smaller frequency bands (also know as sub-channelizations) that are assigned to the competing devices that are eager to initiate a proper communication session. Single carrier FDMA resolves this issue by utilizing the time domain and the frequency domain information. Likewise, a non-orthogonal multiple access (NOMA) mechanism is an ideal solution for the aforementioned problems, preferably with the IoT networks [21]. A NOMA is the most promising random access technique (preferably radio access), which is the current de facto standard for wireless communication as well; it provides numerous benefits that are desirable in wireless communication, such as minimum possible latency with preferably maximum reliability, connectivity, and spectrum efficiency. Generally, a NOMA approach is designed to serve multiple devices competing for the same resources--that is, the receiving device \(S_{j}\) in this case, particularly in terms of time and space. A power-based NOMA is presented where different users are bounded to send data using different power levels while maintaining the same radio band [22; 23]. Although, these methodology are very successful in resolving the issue of the parallel transmission linked with IoT networks, bandwidth wastage is a still an open challenge linked to these schemes. Apart from these approaches, a contention-based multiple access scheme was reported to resolve the scenarios where multiple devices are eager to initiate a proper communication session, preferably with a common receiver. The scenario becomes more complex if these devices are forced to transmit data via a shared channel [24; 25]. It is based on a four-way handshaking scheme to minimize the collision probability of packets transmitted by multiple competing devices. However, registration time overheads and packet collisions are among the common issues with these schemes. Centralized authentication control [26], distributed authentication control [10], and combined authentication/association [11] were designed and developed to resolve various issues associated with the contention-based multiple access scheme. Although, these mechanisms have successfully resolved numerous issues linked to the contention-based schemes, various issues were introduced, such as transmission delay and an average packet collision ratio (APDR). In addition to the contention-based scheme, effective handshaking approaches, i.e., clear-to-send (CTS) and request-to-send (RTS), were reported to address the problem of the hidden terminal scenario in operational resource constraint networks [27]. Although they resolved the hidden terminal scenario,they generated another problem--that is, an exposed terminal scenario where a device is bounded to be in a waiting state until a current transmission session is ended. In [28], a slotted CSMA/CA and TDMA-based approach was developed to ensure collision-free communication sessions, preferably in scenarios where multiple active devices are eager to transmit data to a common receiver over a shared medium in the IoT network. Furthermore, this approach is useful in resolving excessive registration issues as well. Every member device uses the CSMA/CA approach to broadcast authentication requests, whereas the TDMA is utilized for the association request messages. Likewise, [PERSON] et al. [29] proposed a contention-free multiple access scheme to ensure the schedule-based transmission of packets in both the time and frequency domains.