In recent years, the networks of low-power devices have gained popularity. Typically these devices are wireless and interact to form large networks such as the Machine to Machine (M2M) networks, Internet of Things (IoT), Wearable Computing, and Wireless Sensor Networks. The collaboration among these devices is a key to achieving the full potential of these networks. A major problem in this field is to guarantee robust communication between elements while keeping the whole network energy efficient. In this paper, we introduce an extended and improved emergent broadcast slot (EBS) scheme, which facilitates collaboration for robust communication and is energy efficient. In the EBS, nodes communication unit remains in sleeping mode and are awake just to communicate. The EBS scheme is fully decentralized, that is, nodes coordinate their wake-up window in partially overlapped manner within each duty-cycle to avoid message collisions. We show the theoretical convergence behavior of the scheme, which is confirmed through real test-bed experimentation.
In general, low-power nodes consist of relatively inexpensive hardware components, e.g. clocks that typically drift. Therefore, network-wide synchronization is required, thereby increasing message overheads as well as temporal and spatial instability in the network @cite_18 @cite_17 . Using a single central device to enforcing synchronization by dictating the time is not ideal as it imposes extra messages overload @cite_10 @cite_48 . Moreover, time delay for the synchronization message keeps incrementing with every hop. An additional challenge is the presence of lossy wireless links means that the synchronization packets may be dropped and would have to be sent multiple times.
@cite_48 @cite_18 @cite_10 @cite_17
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A cluster based hierarchical wireless sensor network architecture is proposed to facilitate more than one application sharing the whole or a part of a wireless sensor network, where each application may have its own network, processing requirements and protocols. Such a network is divided into clusters and the clusters are organized hierarchically. For synchronizing the CHWSN there is the requirement for a cluster based hierarchical time synchronization algorithm. None of the already existing time synchronization algorithms satisfy the needs of time synchronization in our CHWSN architecture. Thus the existing time synchronization algorithms TPSN (time synchronization protocol for sensor networks) and FTSP (Flooding Time Synchronization Protocol) are modified to fulfill the needs of time synchronization in CHWSN architecture and developed the cluster based hierarchical, flooding time synchronization algorithm (CBH-FTS). It is a hybrid algorithm, where instead of flooding the synchronization messages to neighbor's node, the root node multicasts the time-sync message to selected cluster-heads using the relevant semantics. Hierarchy of cluster-heads could transmit the synchronization messages down the hierarchy of cluster-heads thus synchronizing only the required part of the network associated with an application. The synchronization could be a result of a decision at root node or could be a result of a request for synchronization from a node to a cluster-head.The CBH-FTS Protocol is semantic driven and covers multiple levels in hierarchy. Recently, a time synchronization algorithm called pairwise broadcast synchronization (PBS) is proposed. With PBS, a sensor can be synchronized by overhearing synchronization packet exchange among its neighbouring sensors without sending out any packet itself. In an one-hop sensor network where every node is a neighbour of each other, a single PBS message exchange between two nodes would facilitate all nodes to synchronize. However, in a multi-hop sensor network, PBS message exchanges in several node pairs are needed in order to achieve network-wide synchronization. To reduce the number of message exchanges, these node pairs should be carefully chosen. In this paper, we investigate how to choose these ldquoappropriaterdquo sensors aiming at reducing the number of PBS message exchanges while allowing every node to synchronize. This selection problem is shown to be NP-complete, for which the greedy heuristic is a good polynomial-time approximation algorithm. Nevertheless, a centralized algorithm is not suitable for wireless sensor networks. Therefore, we develop a distributed heuristic algorithm allowing a sensor to determine how to synchronize itself based on its neighbourhood information only. The protocol is tested through extensive simulations. The simulation results reveal that the proposed protocol gives consistent performance under different conditions with its performance comparable to that of the centralized algorithm. In this paper, we review advanced synchronization techniques for the internet of things. Our study can be directly applied to the single-carrier IEEE 802.15.4 and IEEE 802.15.6 standards. In particular we display the advantages of using a Code-Aided approach and a Bayesian packet-oriented approach. The performances of several phase-locked loop techniques are compared to different Cramer Rao Bounds so that one can see the advantage of respectively the Bayesian approach compared to the on-line approach and of the Code Aided technique compared to the Non Data Aided Data Aided approach.