Research and improvement of routing protocols in wireless sensor networks

1 Introduction

Wireless sensor network (WSN) is a product of the combination of sensor, communication and computer technologies. It has a wide range of application prospects because it integrates the logical information world with the objective physical world, changing the way humans interact with nature. Wireless sensor networks have many characteristics different from traditional networks, such as severely limited energy and frequently changing topology. Therefore, the design of WSN network protocols is very different from the design of various existing network protocols, and therefore faces various new challenges. Among the many protocols in the protocol stack, the network layer routing protocol algorithm as a key technology has become a hot topic of research.

2 Routing Protocols for Wireless Sensor Networks

Since there are many classification standards for WSN routing protocols, there are also many ways to classify routing protocols. According to the different working principles of routing protocols, routing protocols are divided into two types, and the typical routing protocols of each type are analyzed.

2.1 Planar Routing

Planar routing assumes that each node in the sensor network has the same function and equal role. The node may actively report its event detection results to other nodes, or other nodes may send query information to the node that detects the event. Data transmission is completed through multi-node multi-hop routing collaborative forwarding. Information negotiation sensor SPIN (Sensor Protocols for Information via Negotiation) is the first data-centric algorithm in planar routing. It reduces data redundancy and energy loss through the negotiation mechanism between nodes. SPIN is a data-centric routing algorithm based on the negotiation mechanism. SPIN first abstracts the characteristics of the data received by the node at a high level to form metadata (meta-data) that describes the characteristics of the data received by the node. Before forwarding the received data, node A first negotiates with the adjacent node B using metadata and sends an ADV signal to determine whether node B needs the data (Figure 1a). If node B has a demand for the data represented by the metadata, it sends a feedback signal REO (Figure 1b). Otherwise, the ADV signal is discarded, and then node A forwards the data DATA to node B (Figure 1c). After node B receives the data forwarded from node A, it uses the same processing method as node A. First, the node uses metadata to negotiate with all nodes connected to it whether the data is needed and sends an ADV signal (Figure 1d). If the node has a need, it replies with a REQ signal. If not, it directly discards the ADV signal (Figure 1e). Then, node B sends data DATA to all nodes that reply to the REQ signal (Figure 1f).

The SPIN algorithm does not clearly define the format of metadata. Its specific format is application-dependent. For example, the formats of ADV and REQ can be specified in detail according to specific applications. In addition, when the topology changes, each node only needs to maintain the status of its neighboring nodes in a local range, without broadcasting the entire network, which saves energy and reduces the requirements for node computing power. This type of SPIN is called SPIN-1. However, SPIN-1 cannot guarantee the correct delivery of remote data. For example, if the remote node needs data but the proximal node adjacent to the source node does not, the metadata representing the data will be discarded at the beginning of forwarding, and no REQ reply will be made, resulting in data delivery failure. In order to solve this problem, SPIN-2 adds an energy threshold mechanism based on SPIN-1. Before delivering data, the energy of the neighboring node is detected. If the energy value is lower than a certain threshold value, it is considered that the node does not have sufficient capacity to complete the remote delivery task, and the data is forwarded to other neighboring nodes with sufficient energy. In addition, other extended protocols of SPIN, such as SPIN-BC and SPIN-RL for multicast networks such as sensor networks, and SPIN-PP and SPIN-EC for traditional point-to-point networks, are specially optimized for different application scenarios.

2.2 Hierarchical Routing

Hierarchical routing (also known as cluster-based routing) was first developed and applied to wired networks to meet the needs of efficient communication in large-scale networks. Therefore, the concept of hierarchical routing has also been introduced into WSNs to meet the needs of low energy consumption and high efficiency communication of sensor nodes. In hierarchical routing, high-energy nodes can be used for high-energy applications such as data forwarding, data query, data fusion, remote communication, and global route maintenance; low-energy nodes are used for low-energy applications such as event detection, target positioning, and local route maintenance. In this way, different applications are reasonably allocated according to the different capabilities of the nodes, so that the nodes can give full play to their respective advantages to cope with large-scale network situations and effectively improve the survival time of the entire network. Hierarchical routing mainly includes two levels of routing: one is for selecting cluster head nodes, and the other is for routing selection. LEACH (low-energy adaptive clustering hierarchy) is an early WSN hierarchical routing algorithm based on clustering ideas. Compared with the relatively sufficient energy of fixed gateway nodes in traditional networks, the energy of nodes in WSNs is limited, so the same cluster head node cannot be used as a gateway. LEACH randomly selects a few nodes from WSN as cluster heads. Considering the balance of energy consumption of each node in the network, other nodes that have not been cluster heads take turns to serve as cluster heads, so that the network will not be paralyzed due to a few nodes running out of energy first.

The LEACH algorithm is divided into two stages: cluster head establishment and stable state. The former is the key to the implementation of the LEACH algorithm, and the latter is the guarantee of data transmission. In the cluster head establishment stage, the node randomly selects a value r (O

LEACH's clustering mechanism can reduce the overall energy consumption of the network and extend the network lifetime; TDMA coding is used between nodes within the cluster, and CDMA coding is used between the cluster head and the base station to ensure effective information transmission; data collection and cluster head nodes are periodic, and the network is suitable for monitoring continuously changing events.

3 Conclusion

This paper describes the network layer of wireless sensor networks, takes routing algorithms as the main research line, and deeply analyzes two routing algorithms of WSN. The research on routing algorithms mainly has the following difficulties: (1) Data fusion is performed at the network layer or application layer. The network layer mainly relies on routing algorithm coordination to discard redundant packets, reduce node energy consumption and improve data forwarding efficiency. (2) In order to ensure the reliability of data transmission and minimize the cost of multi-path maintenance, the algorithm should not be too complicated. (3) For WSN, in addition to considering the situation when the node is stationary, the node mobility also needs to be considered. If it is not a mobile tracking node, the radio frequency channel can generally be turned off when the node moves. (4) The routing algorithm should handle the coordination between nodes well, and complete normal data forwarding even when the number of nodes is large, and will not cause failure in a short time. (5) For WSNs with a large number of nodes, due to the randomness of the network topology distribution, some key nodes may consume more energy while other nodes consume less energy, resulting in an unbalanced network load. Therefore, it is necessary to use the Lunan algorithm to enhance the network load balancing. (6) Due to the particularity of WSN, the energy consumption of the node must be considered. Therefore, when studying WSN routing algorithms, it is necessary to reduce node energy consumption as much as possible to extend the network survival time.