It is expected that up to 26 billion Internet of Things (IoT) equipped with sensors and wireless communication capabilities will be connected to the Internet by 2020 for various purposes. With a large scale IoT network, having each node connected to the Internet with an individual connection may face serious scalability issues. The scalability problem of the IoT network may be alleviated by grouping the nodes of the IoT network into clusters and having a representative node in each cluster connect to the Internet on behalf of the other nodes in the cluster instead of having a per-node Internet connection and communication. In this paper, we propose a multi-hop clustering mechanism for IoT networks to minimize the number of required Internet connections. Specifically, the objective of proposed mechanism is to select the minimum number of coordinators, which take the role of a representative node for the cluster, i.e., having the Internet connection on behalf of the rest of the nodes in the cluster and to map a partition of the IoT nodes onto the selected set of coordinators to minimize the total distance between the nodes and their respective coordinator under a certain constraint in terms of maximum hop count between the IoT nodes and their respective coordinator. Since this problem can be mapped into a set cover problem which is known as NP-hard, we pursue a heuristic approach to solve the problem and analyze the complexity of the proposed solution. Through a set of experiments with varying parameters, the proposed scheme shows 63–87.3% reduction of the Internet connections depending on the number of the IoT nodes while that of the optimal solution is 65.6–89.9% in a small scale network. Moreover, it is shown that the performance characteristics of the proposed mechanism coincide with expected performance characteristics of the optimal solution in a large-scale network.

IEEE 802.16J multi-hop relay (MR) task group has been chartered in order to adapt the promising advantages of multi-hop wireless access in terms of capacity, throughput, and coverage to WiMAX systems. In the MR networks, due to introduction of the RSs (relay stations), MS (mobile station) mobility management for the provision of seamless handover becomes more challenging compared to the traditional one defined in IEEE 802.16e-2005. In this paper, a systematic approach to classify the handover scenarios for de-centralized MR networks when using high capability RSs will be presented. Then, we define the MAC handover procedure and corresponding MAC management messages over multi-hop relay links. The simulation results show that the proposed handover protocol not only reduces the MAC management message overhead transferred on the wireless links compared to IEEE 802.16J/D1, which is the current standard for MR networks, but also performs the rapider and more secure MS handover than IEEE 802.16e and IEEE 802.16J/D1.

Mobile WiMAX provides mobile wireless broadband services for data communication by using IP protocol. In order to provide various IP-based applications, managing the efficiency of wireless resources is necessary at the radio links. Pay load Header Suppression (PHS) is defined as an optional header compression mechanism for mobile WiMAX in order to enhance the efficiency of the radio link utilization. It has, however, a very limited compression capability. We, therefore, propose to deploy ROHC, which is proposed for higher compression efficiency in wireless environments, instead of PHS. We study the performance of ROHC over mobile WiMAX. We also examine the compression parameters that are recommended for the implementation in the ROHC specification in order to propose appropriate values for mobile WiMAX environments.