Typically, wireless sensor networks (WSNs) use limited-capacity batteries that cannot be recharged or replaced. In general, designing an energy-efficient routing protocol has a significant impact on prolonging the network lifetime. In this article, a novel distributed 2-hop cluster-routing protocol (D2CRP) is introduced to achieve energy efficiency in WSNs. In the cluster formation phase, each node obtains the information of its neighbor nodes within the 2-hop range to form the 2-hop cluster in a fully distributed manner. The transmission distance and residual energy are jointly considered to determine the energy-efficient cluster head (CH) in each 2-hop cluster. After the CH is generated, each member node can transmit packets to its 1-hop neighbor or the CH directly. To reduce the overall transmission distance for intercluster communication, multiple chains can be formed among CHs via their adjacent CHs that are closer to the base station (BS). As a result, energy-efficient intracluster and intercluster routing can be achieved for packet transmission. In addition, the optimal cluster number of 2-hop clustering is formulated and derived to minimize the energy consumption for both intracluster and intercluster communications. Simulation results show that the optimal cluster number of D2CRP can be achieved and D2CRP is effectively improved on the performances of network lifetime, energy consumption, and packet transmission than the other four state-of-the-art competitive routing protocols, including low-energy adaptive clustering hierarchy (LEACH), R-LEACH, power-efficient gathering in sensor information system (PEGASIS), and two-tier distributed fuzzy logic-based protocol (TTDFP).

This research presents a new multi-chain routing strategy named the destination oriented routing algorithm (DORA). The proposed algorithm uses the chain routing feature of Power-Efficient Gathering in Sensor Information Systems (PEGASIS) that considers both the practical transmission power and the direction from any source node to the sink, and then determines the preferred forwarding node. The proposed design generates a new multi-chain routing scheme to transmit packets for energy-balanced WSNs. Based on the multi-chain routing, the optimal transmission distance between any two nodes is derived by the mathematical analysis model. With the optimal distance, the design criterion is to select the furthest forwarding node within the communication range and the direction to the sink, thus forming the multi-chain structures by accurate distance, direction, and multiple paths. With the shorter chain routing, unnecessary energy loss can be reduced to prolong the global network lifespan. Simulation results demonstrate that the proposed DORA doubles the network lifespan, compared with that of conventional PEGASIS and improves 60% lifespan on the RPC protocol.

In this article, a balanced multipath routing and hybrid transmission approach (BMRHTA) is proposed to effectively alleviate the imbalance of the forwarding load in a sink connection area (SCA) and prolong the network lifecycle for wireless sensor networks (WSNs). To achieve the energy efficient and balanced WSNs, three design issues, including the multipath, multihop, and single-hop transmissions, are jointly optimized to maximize the overall network lifecycle. First, the path load aggregation phenomenon in the SCA, which makes the forwarding packet load unevenly distributed among hotspots, is examined. In order to achieve the load balance in SCA, multiple shortest balanced paths are generated in the BMRHTA model. In the first stage, two uncorrelated shortest paths are discovered from each node to the sink and the optimal path selection cycle can be determined to achieve the SCA load balance. Afterward, a network equilibrium policy is offered to resolve the optimal transmission period of energy balance via hybrid transmission. As a result, the balanced shortest paths, the path selection cycle and the transmission period can be determined in the network formation phase to avoid the excessive load concentration in the subsequent maintenance phase. Simulation results show that the joint two uncorrelated balanced routing and the proposed network equilibrium policy can nearly quadruple the network lifecycle extension, as compared to a conventional node power policy. Also, the proposed BMRHTA achieves better performance than the current state-of-the-art competitive approaches in terms of energy efficiency and lifecycle.

This study proposes a multiple mesh-ring (MMR) topology construction with a hybrid routing strategy for Bluetooth low energy (BLE) networks. To achieve the load-balancing network, three design phases, including leader selection, role decision, and scatternet formation, are executed to generate even MMR configurations. First, each master discovers its adjacent slaves to determine a coordinator. Second, the coordinator computes the desired number of piconets with even scatternet link connectivity and distributes the scatternet connection information for each master. Finally, each designated master connects with its associated nodes, including slaves, intrabridges, and interbridges to create the link balanced MMR scatternet. To jointly design an energy-efficient routing protocol for the MMR topology, a hybrid routing strategy is deployed to perform the shortest path routing inside the mesh-ring subnet, and self-routing through different mesh-ring layers. Simulation results demonstrate that the balanced MMR topology leads to a significant gain in terms of network transmission performance and network lifetime when compared to the conventional dual-ring tree (DRT) and cluster-based mesh (CBM) approaches for BLE networks.

In traditional wireless sensor networks (WSNs), packets are mainly transmitted in a multihop routing manner. The multihop transmission, however, leads to a hotspot problem in the sink connectivity area (SCA), and the overall network efficiency is reduced due to the quick battery power exhaustion of nodes in that area. This article proposes a novel balanced routing algorithm with transmission range adjustment (BRATRA) to address the network efficiency problem, including the energy efficiency and utilization issues. First, a balanced routing strategy is designed to deal with the SCA load imbalance problem. With the shortest balanced path, the amounts of forwarding packets for the nodes in the SCA and all the other intralayers become more even. From the perspective of power equilibrium in each routing path, each node then determines its accurate transmission radius according to the derived formula and performs power control to realize the even power utilization between interlayers, thereby prolonging the overall network lifetime. Performance evaluation validates that the proposed BRATRA strategy can achieve efficient power utilization in each intralayer and double the network lifetime as compared to the Dijkstra routing strategy. Additionally, it yields better power utilization fairness among nodes, and on average only 5% of battery power is unused for all network nodes, resulting in a network lifespan ten times larger than that using a conventional strategy.

In this paper, two hybrid multi-hop/single-hop opportunistic transmission strategies with adaptive routing are investigated for prolonging the network lifetime of wireless sensor networks (WSNs). To achieve this goal, a systematic decision model that contains a network distribution block, a routing algorithm block, a traffic pattern block and an optimal policy block is presented to determine the optimal transmission probability of each node. With packet transmission via adaptive shortest paths, two optimization strategies are proposed in the optimal policy block: a power efficiency optimization strategy and a power utilization optimization strategy. The power efficiency strategy aims to minimize the overall power consumption and the power utilization strategy endeavors to minimize the maximum power consumption among nodes. Computer simulations show that the power utilization strategy can achieve almost triple the network lifetime extension compared to the power efficiency strategy. Furthermore, the power utilization strategy is superior to the power efficiency strategy in terms of residual energy utilization for various network sizes.