Reading Notes-Iot-oriented Sensor Networks

Overview of Iot-oriented sensor networks: Qian Zhihong, Wang Yijun, Journal of electronics and information, 2011,1 vol.35 No.1

1. What is the relationship between wireless sensor networks (WSN) and Iot?

A wireless sensor network is a multi-hop self-organizing network formed by a large number of sensor nodes deployed in the monitoring area through wireless communication.

The Iot system architecture consists of four parts: underlying network distribution, convergence Gateway Access, interconnection network convergence, and end users.

Relationship: wireless sensor networks are an important technical form of Iot underlying networks.

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2. What are the key technologies that need to be broken through in WSN?

The key technologies of WSN are embodied in three aspects: information collection system design, network service support, and network communication protocol design.

3. What are the key technologies in the design of the information collection system?

• WSNs Network Model Design

• System Platform and Operating System

• Data Storage Methods

• Test Bed Design

Network Model of the sensor network: the network application-oriented characteristics are fully grasped, and the network structure is coordinated to adapt to different application environments.

Major dilemma: the WSN network model supports a wide range of sensor nodes. However, the sensor node products of each vendor vary in the wireless communication module, microprocessor, and storage space, it is a huge challenge to integrate multiple sensor nodes into a unified system platform.

The operating system must support multiple types of sensor nodes, while ensuring the efficiency of data Sensing and Processing.

Research on the storage data of WSN is concentrated in three aspects: external network storage, local storage, and data-centric Storage.

Test Bed design: it is very important for researchers to conduct WSNs experiments in real physical environments.

It provides researchers with an effective platform to verify related protocols, algorithms, and various network applications. Idriya and motelab are the test beds.

However, there is no uniform standard specification for the design of the test bed.

4. What are the key technologies in network service support?

• Sensor node configuration, processing, and control

• Data Management and Control Service

• Network Security Mechanism

Node configuration has two main applications: network coverage and positioning.

Coverage: it is very important for WSN. It affects the number of sensor nodes to be configured, node location, connectivity, and energy.

Location: location information is an indispensable parameter for sensor nodes to perceive data. sensor data without location information is usually meaningless.

Time Synchronization Technology: Used in sensor data fusion, node data processing, measurement distance, and positioning.

Due to energy restrictions, traditional network synchronization algorithms are not applicable to WSN.

The time synchronization algorithm of WSN must be comprehensively considered in terms of scalability, stability, energy efficiency, and robustness. Guarantees the compromise between the maximum precision and the minimum energy consumption.

At present, most of the applications of WSNs have assumed that the system clock has been synchronized. However, in actual application systems, there will always be some deviations in the clock, and the application structure will inevitably be affected.

Positioning of WSN: ranging and non-ranging locating Algorithms

The former has high positioning precision, but high hardware requirements and high overhead. There are four main methods: Arrival angle (AoA), arrival time (TOA), arrival time difference (TDOA), and signal receiving intensity (SNR ).

The latter has poor positioning accuracy, but has low hardware requirements and low overhead. Mainly include the centroid algorithm and DV-hop algorithm.

At present, the former technology is relatively mature, and the latter is still in the theoretical research stage.

The latter is more concerned because of its advantages in cost and power consumption.

Network Topology coverage: When network connectivity and coverage are met, you can select a policy for the nodes in the network to avoid redundant communication links between nodes and form a network structure optimized for data forwarding.

Currently, there are two main methods: hierarchical topology control and power control.

Hierarchical topology control: uses the clustering mechanism and selects some nodes in the network as the cluster head. The cluster head nodes form a data processing and forwarding transmission system.

Power Control: by adjusting the transmit power of nodes in the network, the number of neighboring nodes and network energy consumption of nodes are balanced while the network is connected.

The existing algorithms are usually optimized and designed for one aspect of the network topology, and the relevant research lacks systematic knowledge.

Therefore, the topology Research of WSN is still in the theoretical research phase. The combination of multiple topology structures may achieve good results. heuristic or computational Geometric algorithms can be used.

Data Fusion and Compression

There are three data collection modes in WSN: Query-based data collection mode, periodic report-based data collection mode, and event report-based data collection mode.

Network Security Mechanism:

The security policies of WSN include security routing, access control, intrusion detection, authentication, and key management.

In traditional computer networks, hosts are connected through a fixed network and adopt a layered network architecture.

Due to the scattered connection of the WSN, each node can be moved freely. nodes are connected through wireless channels, and the nodes act as routers themselves. As a result, the security mechanism in the traditional network is no longer suitable for the WSN.

5. What are the key technologies used in network communication protocol design?

The research focus of the communication protocol stack of WSN is on the data link layer, network layer, transmission layer, and cross-layer interaction.

Data link layer: uses media access control to build the underlying infrastructure and control the node working mode.

Network Layer: the routing protocol determines the transmission path of the perceived information.

Transport Layer: ensures data reliability and efficiency at the source and target nodes.

① 802.15.4/ZigBee protocol

The IEEE 802.15.4 standard is dedicated to low-speed networks, and ZigBee is built on the IEEE 802.15.4 standard.

The IEEE 802.15.4 protocol specifies the physical layer and MAC layer of the network;

The ZigBee protocol specifies the network layer and application layer;

The 802.15.4 + Zigbee protocol has the characteristics of flexible networking, low cost, and low energy consumption. Therefore, the Protocol is usually used as the standard for wireless communication.

The objective of the IEEE 802.15.4/ZigBee protocol is to achieve minimum power consumption on the basis of ensuring data transmission quality.

The goal of researchers is to minimize network energy consumption.

For the IEEE 802.15.4 standard physical layer, the design of low-power radio transceiver that only stays in the physical layer or the software simulation of the physical layer has almost no research on protocol improvement.

The Research on the standard MAC layer of 802.15.4 focuses on solving problems such as hidden nodes, precise synchronization, competitive management, and asynchronous wake-up. The core is how to save energy.

There are few researches on the ZigBee network layer, and there is no mature theoretical system. The existing research bureaus are limited to the analysis and improvement of the existing protocols. Almost all research efforts focus on energy conservation.

The current and future research of ZigBee will focus on routing algorithms such as further reducing network energy consumption and extending network life.

② 6lowpan Protocol

Iot has two meanings:

• The Internet is the core and foundation of the Internet of Things. The Internet of Things must be extended and expanded on the basis of the Internet;

• End users can exchange and communicate information between all items;

At present, one of the key issues to be solved by the IOT is the convergence of the underlying heterogeneous network language internet.

The IEEE 802.15.4 protocol is a standard for short-distance wireless communication,

IPv6 is the dominant technology at the next generation Internet network layer,

Therefore, the convergence of underlying Iot heterogeneous networks and the Internet based on the IP protocol will be the main development direction of wireless sensor networks in the future.

At the network layer, future research focuses on the seamless connection between the wireless sensor network (WSN) and the Internet, routing security, and routing service quality assurance.

Appendix: Key Technologies and challenges faced by WSN

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Reading Notes-Iot-oriented Sensor Networks