Smart home system development technology

For the broad Chinese market, the Internet of Things will be a major opportunity. With the continuous development of information technology and the change of family population structure, people have higher and higher requirements for the safety, comfort and convenience of the living and working environment. The existing smart home has been difficult to meet the public's requirements for information automation and convenience in the living environment. Smart home is a new field of Internet of Things technology applications. Therefore, how to study and design a smart home system that can meet the needs of modern people's life is currently a research hotspot.

Because of the existence of the smart home system, when the user goes out, he can obtain the information of the home environment through terminal devices such as mobile phones and computers, and can control the home devices. For example, the home owner can use the mobile phone to turn on or off the air conditioner in the bedroom and the water heater in the bathroom by SMS on the way to and from work, so that there is a comfortable environment when returning home; Open and close the curtains through the smart home controller, turn on the bedroom lights, or adjust the home environment to sleep mode before going to bed. The most advanced smart home technology should include newer technologies such as computer communications, wireless networks, and embedded systems. It can integrate home lighting system, environmental monitoring system, security monitoring system and home appliance control system together. This is also the significance of the application of Internet of Things technology in the field of smart home.

The smart home control system based on Bluetooth integrates a variety of advanced information technologies. This paper will research and analyze the technology of the smart home control system from the aspects of Internet of Things technology, Bluetooth communication technology and embedded system related technologies.

1. Internet of things technology

The Internet of Things is a concept proposed in recent years. It is a kind of interconnection between objects. It generally refers to the real-time collection and acquisition of light, heat, sound, location and other data information of objects through information sensing equipment such as sensors and radio frequency identification technology. , and connect objects to the Internet in various ways to achieve the purpose of information exchange between objects, so as to realize a network of objects such as perception, monitoring and management. The technologies involved include perception technology, control technology, communication technology, information security technology, etc.

1.1 Sensing technology

(1) sensor

Sensor technology and sensor network technology are the basic technical means for the Internet of Things to obtain information and data, and are the basic units that constitute the Internet of Things system. The sensor can convert a certain form of energy into a required form of energy. Usually, a certain state information of the monitoring target is processed through a series of processes to make it an electrical quantity that can be measured, and then the electrical quantity is extracted. Converted into an electrical signal and sent to the sensor system. Using these information data, the sensor system and the automatic control system are combined into an automatic monitoring and control system, which can realize the automatic control of the controlled target. The system takes the computer as the core, and the user can realize the automatic control of the system through the computer application program. Figure 2-1 shows the composition of the automatic monitoring and control system and the transmission process of data information. Among them, the monitoring object, sensor, data acquisition channel and data display and processing module constitute the sensing system.

According to the different physical properties of the monitored objects, there are many classifications of sensors. The sensors used in the smart home system mainly include temperature sensors, humidity sensors, light intensity sensors, infrared sensors, smoke sensors, door magnetic sensors, etc.

(2) Sensor network

The sensor is one of the elements of the sensor network. The data information collected by the sensor is transmitted to the monitor through the wireless sensor network. Sensor networks can link logical information and physical properties of objects in reality. In this way, we can use information technology to perceive the world, and at the same time, the functions of traditional communication networks have also been enriched and expanded.

A sensor network generally consists of three parts: sensor nodes, management nodes, and collection points. Figure 2-2 shows the architecture of the sensor network. Randomly deploy enough sensor nodes within the monitoring range of the measured object, and these nodes can build a communication network in a self-organizing manner. The information data of the measured object is transmitted along other sensor nodes through the sensor node, and then transmitted to the collection node after a series of multi-hops, and then transmitted to the management node of the sensor network through GPS or the Internet. Finally, we can manually manage and configure the sensor network through the management node, and at the same time collect information data and implement monitoring.

Among them, the sensor node can generally be divided into four parts, which are: power supply module, sensor module, processor module and communication module, and its structure is shown in Figure 2-3. The power supply of the entire sensor node depends on the power supply module; the main function of the sensor module is to realize the collection and exchange of information data of the measured target; the processor module generally includes a processor, storage device and operating system, etc. The storage and processing of information realizes the control of the entire node; the function of the communication module is to realize the transmission of data information and control information between this node and other nodes.

The original model of the sensor network architecture proposed by people in the earlier period referred to the traditional computer network architecture such as the OSI model and the TCP/IP model. Its five-layer model of physical layer, data link layer, network layer, transport layer and application layer corresponds to the traditional computer Internet protocol structure. At the same time, three management platforms have been added: task management platform, mobile management platform and energy management platform. Each sensor node can maintain high work efficiency under the unified control of the management platform, and can realize multi-task and resource sharing. Figure 2-4(a) shows the original model of the sensor network architecture in the earlier period.

Afterwards, improvements were made to the original sensor network protocol stack, and the improved sensor network protocol stack is shown in Figure 2-4(b). The right side shown in the figure incorporates some functions in the protocols of each layer of the original reference model, which can be used to manage and optimize the entire protocol workflow; the remaining parts are relatively independent of the outer layer of the protocol stack, and are implemented through the configuration and management interfaces in it. Manage and configure the corresponding mechanisms, such as security management. Compared with the original model, topology control can optimize routing and the protocol process of the medium access control (MAC) protocol, provide basic information support, and reduce the energy consumption of the entire sensor network. It realizes topology generation through the physical layer or link layer. QoS management mainly provides service management work for each layer, such as designing priority mechanism, realizing queue management or designing bandwidth reservation mechanism, etc. The time synchronization and positioning sublayer plays a very important role in the entire protocol stack: time synchronization coordination and positioning are completed through this sublayer using data transmission channels, and the support of sensor network protocol information at each layer depends on this sublayer. Network management is responsible for coordinating the work of the protocol modules in the entire network. It needs to embed the interfaces of each layer of protocols to ensure the collection of operating status information and flow information of each protocol module.

1.2 Communication Network Technology

The communication network within the home monitoring range and the external communication network constitute the communication network of the Internet of Things, and the communication network is divided into wired and wireless communication methods according to the communication method. Commonly used wired methods include HSE, LonWorks, X-10 and CEBus.

The communication protocol stack of HSE is based on TCP/IP protocol, which has good openness. LonWorks adopts all the seven-layer protocols in the ISO/OSI model, and its design method draws lessons from the object-oriented method, which can simplify the setting of network communication into the setting of parameters. X-10 is a power carrier communication technology with good reliability, stability and compatibility. CEBus adopts spread spectrum technology and is widely used in North America and Europe. The advantage of the wired communication method is that the communication rate is relatively high and the work is stable, but at the same time, there are disadvantages such as high installation cost, need for communication media, and poor compatibility.

In the field of Internet of Things, wireless communication is mainly used in communication networks within the range of perception and monitoring, and the coverage generally does not exceed 200 meters. According to the communication rate, short-distance wireless communication should be divided into two types: low-speed short-distance communication and high-speed short-distance communication. The transmission distance of low-speed wireless communication The transmission rate is generally below 1Mb/s, and the communication distance is not more than 100 meters. ZigBee and Bluetooth are commonly used; the threshold of the communication rate of high-speed wireless communication is generally 100Mb/s, and the communication distance is generally not Beyond 10 meters, UWB technology is a common high-speed wireless communication. The operating frequency of short-distance communication technology is generally in the free frequency band in the fields of science, medical treatment, and industrial applications. Currently commonly used short-distance wireless communication technologies include ZigBee, Bluetooth 2.0 technology, WLAN and ultra-wideband communication technologies.

ZigBee: The technology is based on the IEEE802.15.4 standard. It is a standard wireless communication network protocol designed for low-speed control networks. It can enable a large number of micro-sensors to communicate and work in a coordinated state. ZigBee's network topology supports mesh topology, star topology and cluster-tree network topology. The characteristics of ZigBee are remarkable: low energy consumption, self-organizing network, better self-healing function, high network capacity, fast device access to the network, and low transmission rate.

Bluetooth 2.0: Bluetooth is an open technical standard for low-cost short-distance wireless connections, working in the globally unified free 2.4GHz frequency band. Multiple Bluetooth devices can form a piconet using a master-slave structure, and multiple piconets can form a scatternet. Bluetooth 2.0 technology has strong anti-interference ability, error correction and error detection technology can be realized with simple circuit, which makes the equipment cost low and so on.

WLAN: WLAN is a wireless local area network standard customized by the IEEE802.11 working group at the end of the 20th century. Typical network architectures of WLAN include distributed peer-to-peer network architecture and basic network architecture. The 802.11a standard of WLAN works in the 5GHz frequency band and supports a maximum transmission rate of 54Mbps; the 802.11b and 802.11g standards work in the 2.4GHz frequency band and supports a maximum transmission rate of 11Mbps and 54Mbps respectively.

Ultra-wideband: Ultra-wideband technology can perform information communication at a relatively high rate (up to 500Mb/s or more) within an extremely low power (about 20mW) and an extremely wide spectrum range (7.5GHz). It has the characteristics of simple system structure, high transmission rate, precise positioning and super penetrability.

1.3 Control technology

The Internet of Things control system is a complex network that integrates a variety of technologies, including embedded controller technology, execution unit design technology, multi-sensor acquisition and multi-source information fusion technology, etc. The IoT control system can be divided into an indirect network control structure and a direct network control structure. The abstract representations of these two structures are shown in Figure 2-5. The IoT network part in the figure is responsible for the transmission of control information, status feedback information and quality information. The main control device, execution device and sensors in the figure share the entire IoT network.

Users can also use the mobile communication network and Web dynamic services to remotely control the controlled equipment and execution units.

2. Wireless bluetooth technology

2.1 Traditional Bluetooth

Bluetooth is a short-distance wireless communication technology based on low cost. It is a unified specification for wireless information data and voice communication services. Its standard is open. Various information terminal devices equipped with Bluetooth modules can achieve the purpose of communicating and operating with each other wirelessly at a relatively low cost. The Bluetooth Group (SIG) is responsible for developing the Bluetooth protocol standard version 802.15.1. Its working frequency band is the 2.4GHz ISM frequency band that is common in the world, providing a transmission distance of 10 meters and a transmission rate of 1Mb/s. In 2005, the Bluetooth group released the Bluetooth communication standard V2.0 version and EDR (higher data communication rate). The new specification increases the transmission rate to a maximum of 10Mb/s, and the transmission distance can reach up to 100 meters. At the same time, because the new specification reduces the communication power consumption of the Bluetooth, the working time of the mobile power supply of the Bluetooth terminal is extended.

There are two working modes of Bluetooth: master working mode and slave working mode. The bluetooth device working in the master device mode is responsible for formulating the frequency modulation sequence and the data transmission rate and time between the master and slave devices, and the slave device must be synchronized with the master device. A master device can work with multiple slave devices at the same time. In terms of networking, traditional Bluetooth supports two modes of piconet and scatternet, and multiple piconets can form a scatternet through node bridging.

The Bluetooth protocol stack is the core part of the Bluetooth specification. According to the implementation of the Bluetooth protocol, the Bluetooth standard includes two parts: hardware and software. General hardware standard radio frequency and radio protocols, baseband and link control protocols, and link management protocols are produced on one chip; the host interface control protocol exists in hardware and software, and is responsible for the communication between the two parts.

2.2 Bluetooth Low Energy

The Bluetooth technical group officially released the Bluetooth specification version 4.0 in 2010, integrating IEEE802.15.1 traditional Bluetooth, 802.11 physical layer and MAC layer and Wibree technology. Due to the addition of Wibree low-power transmission technology, low power consumption has become one of the most prominent features of Bluetooth 4.0. The ultra-low standby and running power consumption ensures that a button battery can keep the device working for 2 to 3 years. In addition, Bluetooth 4.0 supports cross-vendor interoperability, ultra-long communication distance over 100m, AES-128 encryption, 3ms low latency, and low cost. Bluetooth low energy consumption is not only applicable to the WPAN field, but also can be applied to various fields such as heart rate monitors, smart meters, pedometers, sensor Internet of Things, etc., which greatly expands the application range of Bluetooth technology.

The low-energy protocol of Bluetooth 4.0 is basically the same as the bottom layer of the previous Bluetooth protocol, except that the General Attribute Profile (GATT) and Attribute Protocol (ATT) are introduced for sensor network applications.

The physical layer (PHY) adopts GFSK modulation, provides three fixed broadcast channels, and compresses the time of discovering devices and establishing devices to about 3ms.

The role of the link layer (LL) is to implement the underlying data packet management protocol of the baseband protocol. The link layer device has five working states: standby, initiate, connect, broadcast, and scan.

The host control interface (HCI) provides an application program interface for the upper-layer software part, and provides a hardware control interface for the lower-layer hardware circuit to realize data communication between the host and the control layer.

The logical link and adaptation protocol layer (L2CAP) provides data encapsulation for the upper layer, and provides P2P logical data communication.

The security management layer (SM) formulates pairing and secret key distribution methods to ensure the security of links and data exchange.

The attribute protocol layer (ATT) is responsible for data information verification.

The general management layer (GAP) provides a common application program interface and manages the underlying protocols, such as the five working state transitions of link layer devices.

The general attribute profile (GATT) function is to realize data exchange between two devices, so that one device can provide its data information to other devices in the form of "attributes". Wherein, one end providing data information is a server end, and the other end is a client end. Data information verification is in charge of the attribute protocol layer.

3. Embedded system related technologies

Embedded systems can be understood as microcomputer systems that have special requirements for volume, function, cost, and stability and reliability. operating system and associated applications. Embedded systems are widely used in our daily life, such as smart phones, tablet computers, information appliances, health care, etc.; they are also widely used in industrial control and military applications.

3.1 ARM processor technology

Embedded processors commonly used by embedded system design engineers include PowerPC, MIPS processors, Intel Atom processors, ARM processors, and Xilinx FPGAs. Among them, the ARM processor adopts the reduced instruction set (RISC) architecture, and is favored by the majority of embedded system designs for its advantages of high efficiency, low power consumption, wide application range, and low cost.

3.2 Android operating system

The embedded operating system is an important component of the embedded software system. The management and allocation of software and hardware resources, system task scheduling, and concurrent activities of the control management system of the entire embedded system all depend on the embedded operating system. Therefore, the performance of the embedded operating system determines the performance and user experience of the embedded product to a large extent. At present, the mainstream embedded operating systems in various application fields include: Microsoft's WinCE, Wind River System's VxWorks, Embedded Linux, Google's Android, and open source μCOS-II.

Google's Android is currently widely used in smart phone products, but Android is not only suitable for smart phones, it can be extended to various mobile devices and PCs. Android is developed based on the open source Linux system, using C language at the bottom layer to ensure hardware access speed; the application layer uses Java language which is powerful and convenient for developers, which makes Android win many developers and enthusiasts. Android's design strategy utilizes the idea of platform integration, and its platform includes the underlying Linux system, middleware, and upper-level Java applications.

Applications: Applications are Java-language development, including SMS applications for smartphones, contact management, web browsers, and more.

Application framework: simplifies the reuse of component software, the function blocks released by an application can be reused by any other application, and these components can be replaced by users. The main components and services include: Views (Views), Activity Manager (Activity Manager), Content Providers (ContentProviders), Resource Manager (Resource Manager), Notification Manager (Notification Manager).

Android library: provides services for developers through the Android application framework, including core libraries: system C library, media library, SQLite, etc.

Android runtime library: Provides most of the functions of the Java core library, including the Dalvik virtual machine.

Linux kernel: The core parts of Android system services are derived from the Linux operating system kernel, such as process management, memory management, and driver models.

Summarize

This paper mainly studies and analyzes the key technologies in wireless smart home. Firstly, the Internet of Things technology used in the smart home architecture is studied, including sensor technology and sensor network technology, and the sensor network protocol stack is mainly analyzed. Then the bluetooth technology is analyzed, including the traditional bluetooth technology and the latest low power bluetooth technology of the bluetooth low energy protocol stack, and the technology and performance of the two are compared. Finally, the embedded technology used in the design of smart home controller is analyzed, including ARM embedded processor technology, Android operating system introduction and platform architecture.

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