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Node localisation for wireless sensor networks (WSNs) is applied in various fields, and is an indispensable core to promote the development of WSNs. Since the previous localisation algorithms did not fully utilise the anisotropy of nodes, according to the actual radiation model of the node's communication, a novel range-free localisation algorithm called range-free localisation based on the anisotropy of nodes (RLAN) is proposed. RLAN not only uses the information of multi-hop neighbours, but also considers fully the anisotropy of nodes in real networks, which influences the hop relationship and average hop distance, so as to improve the accuracy of node localisation. The simulation results demonstrate that RLAN has better localisation accuracy than other range-free node localisation algorithms. When the nodes are relatively uniformly deployed in the localisation area, the normalised localisation average error using RLAN can be

For real-time applications in mobile low-duty-cycle (DC) wireless sensor networks (WSNs), discovering neighbours needs to be achieved in both short average latency and high fraction of discoveries (FDs) with low energy consumption. A novel asynchronous probabilistic method is proposed, in which a node randomly chooses a prime, e.g. p, from a pre-configured prime set and wakes up only at the first slot during every p continuous slot which is for a hyper-cycle length, i.e. a fixed number continuous slots, determined by the prime sets, and then selects another prime for the next hyper cycle. For low-DCs, especially

A novel probabilistic algorithm for low duty-cycle dynamic (mobile sensors) wireless sensor networks (WSNs) is proposed. The rapid development of smart phones and mobile sensors had fostered a demand for opportunistic encounter-based networking to support mobile social networking and proximity-based gaming. However, the performance of such applications was restricted by a lack of specialised neighbour discovery algorithms. For existing algorithms, even though the probabilistic algorithms have good performance in average discovery latency, when working with a low duty-cycle, the performance is not so encouraging. Deterministic algorithms can provide bound time for the worst discovery latency, but they sacrificed the average discovery latency. In response, a novel prime-set-based neighbour discovery algorithm (PSBA) is proposed. The PSBA is a probabilistic algorithm tailored to low duty-cycle dynamic WSNs. Leveraging on the certainty of the deterministic algorithm and the randomness of the probabilistic algorithm, the inherent long tail of the probabilistic algorithm can be improved. Also, the average discovery latency of the PSBA can be drastically reduced compared to existing algorithms, which precisely meets the requirements in low duty-cycle dynamic WSNs.

For range-free localisation in a wireless sensor network (WSN), the importance of indirect anchor neighbours of an unknown node has been underestimated in the past. In this reported work, for the unknown node, we show that its (n + 1)th-hop anchor neighbours are more useful than its nth-hop ones. By employing a theoretical model to analyse the possible localisation area (PLA) of the unknown node, it is found that the PLA and the hop count are negatively correlated, which indicates that (n + 1)th-hop anchor neighbours can provide more information to more accurately localise the unknown node. Meanwhile, the property of convergence of the theoretical model means that localisation accuracy cannot be unlimitedly improved with increasing hop counts. In the simulations, the presented theory is verified.

A novel distributed range-free localisation algorithm to accurately locate regular nodes in wireless sensor networks is presented. Existing methods reduce the possible area where a regular node would be located by using anchors (i.e. nodes with known locations) only. These methods are effective only when anchor density is high. In contrast, the work presented here reduces the possible area of a regular node iteratively, using both anchor node locations and the possible areas of its neighbouring and non-neighbouring ‘regular’ nodes from early iteration. This allows a significant improvement in the localisation accuracy. Simulations verify the advantage of the proposed algorithm and show that the localisation error can be controlled within 15% with off-the-shelf devices.

A novel distributed range-free localisation algorithm, named polygonal overlapped possible area (POPA), is proposed to accurately localise an unknown node. First, for an unknown node, to theoretically define its possible localisation area (PLA), virtual radiation regions of its n th-hop anchor neighbours are introduced. Then an effective area-splitting algorithm is employed to simplify and speed up the computation of the possible localisation area. Simulation shows localisation error can be controlled within 20% with off-the-shelf devices.

An effective coupling coefficient is introduced for gain-coupled distributed feedback lasers with absorptive grating. When radiation and other partial wave coupling effects are considered, the effective coupling coefficient will change significantly. In some cases, it will become real, although both loss and index coupling are presented.