Research on Remote Monitoring System Based on ARM11 and MMS

Abstract: This paper introduces the working principle of Multimedia Message Service (MMS) and studies the remote monitoring system based on ARM11 and MMS. The system uses S3C6410 as the core controller and transplants the resource-rich embedded operating system Linux. When the monitored data exceeds the alarm value, the system collects the temperature, humidity, smoke concentration and image data of the scene, encapsulates them into MMS information, and uses the GPRS transmission module SIM300z to send MMS information to the terminal user to achieve the purpose of real-time feedback.
Keywords: ARM11; Multimedia Message Service; Remote Monitoring System; S3C6410; Linux

Introduction
With the rapid development of the national economy and the improvement of people's living standards, various monitoring systems have emerged and are widely used in key areas such as banks, railways, civil aviation, and gradually enter the field of personal home monitoring applications. At present, most monitoring systems send on-site information to remote computers, but computers are inconvenient to carry and cannot meet people's needs to view on-site information anytime and anywhere. Compared with computers, mobile phones have a high penetration rate, low cost, and are easy to carry. In particular, the rapid development of GPRS wireless digital mobile communication network in recent years has provided mobile terminals with wireless access to the Internet, making mobile phones the most common terminal equipment on the Internet. Multimedia Message Service (MMS), as a basic service of GPRS, is used by a large number of mobile phone users. It not only realizes the information transmission between terminals and between terminals and e-mails, but also realizes the diversity of content, including various combinations of pictures, audio, video, images, data and text. It can be seen that the use of GPRS and MMS technology can fully meet the requirements of remote monitoring systems for distance, images, sounds, and high real-time performance, and has important research significance and use value. This paper uses S3C6410 as a microcontroller to design a remote monitoring system based on ARM11 and MMS technology.

1 Overview of MMS
MMS is a mobile messaging service developed by 3PP (Third Generation Partnership Project) and WAP Forum (Wireless Application Protocol Forum). It is a further development of SMS and picture messaging. The MMS system mainly includes Multimedia Messaging Center (MMSC), WAP gateway, database server and value-added service system. There are two ways to implement it: WAP-based and IP-based. At present, the GPRS network uses WAP-based method to send and receive MMS messages. The specific implementation method is shown in Figure 1.

As can be seen from Figure 1, MMS services use WAP as a carrier to transmit information, which shows that WAP technology plays an important role in multimedia messaging services. WAP (Wireless Application Protocol) is a combination of a series of protocols for developing Internet-like applications on mobile networks, which realizes the interconnection between the Internet and mobile communication networks. In the WAP architecture, the WTP protocol and the WSP protocol play a core role. The WSP protocol layer provides a consistent interface in the session service and is optimized for wireless network communication, while the WTP protocol provides services for interactive browsing (request/response). In the GPRS network
, MMS PDU (Protocol Data Unit) is used to send and receive MMS information, and the Multimedia Mail Extension (MIME) protocol is used for packaging. MMS PDU consists of two parts: MMS Header and MMS Body. The Header describes the specific information of the PDU. The Body includes SMIL expressions, which are used to set the location and playback time of the multimedia segment. When the user terminal sends an MMS message, the MMS PDU will be encapsulated as a data unit of the WAP protocol, and will be addressed, stored and forwarded in the mobile network and finally delivered to the receiving user.

2 System overall architecture
In order to fully and in detail grasp the on-site situation, the information collected by this system includes temperature, humidity, smoke concentration, and image data to meet people's needs in production and life. The overall architecture of the system is shown in Figure 2.

As shown in Figure 2, the system mainly includes control module, sensor module, image acquisition module, alarm module, GPRS module and memory module. The main functions of each module are as follows:
① The control module is the core of the whole system. Run the main control program of the system to complete the initialization of the equipment; complete the acquisition, encoding and storage of image information through the control of the image acquisition module; collect the temperature, humidity and smoke concentration of the remote terminal through the sensor module, and convert these information into ASCII code; complete the packaging and sending of MMS information.
② The sensor module mainly completes the acquisition of on-site information, including temperature, humidity and smoke concentration, and realizes the conversion of non-electrical signals to electrical signals.
③ The image acquisition module realizes the acquisition of original image information and the transmission of data.
④ The GPRS module connects to the GPRS wireless network through the PPP protocol, which can realize the sending of MMS information and the reception of SMS (short messages) from terminal users.
⑤ The memory module is mainly used to store the encoded image information.
⑥ When the on-site temperature, humidity or smoke concentration exceeds the preset alarm value, the alarm module generates an alarm signal to prompt the staff to deal with the accident on the scene in time.
Working principle of the monitoring system: When the system is working normally, the microcontroller module will regularly collect the temperature and smoke concentration of the scene and compare them with the preset alarm value. When the temperature or smoke concentration is higher than this value, the microcontroller module will control the image acquisition module to collect the scene image, encode and process the collected data, and store it as the picture data of the MMS message; at the same time, the temperature, humidity and smoke concentration of the scene are collected through the sensor module and stored as the text part of the MMS message. Then these two parts of data are encapsulated and delivered to the terminal user in the form of MMS messages. While completing the sending task, the system will drive the alarm module to generate an alarm signal to achieve the purpose of the alarm.
Users can also send short messages (SMS) to the system to request the monitoring terminal to send the temperature, humidity, image and other information of the scene to realize the user's remote monitoring of the scene.

3 System Hardware Design
3.1 Design of Control Module
In order to make the remote monitoring system work stably, continuously and efficiently, and to respond quickly to emergencies, the control module uses the embedded microprocessor S3C6410. This processor is a low-cost, low-power, high-performance microprocessor based on the 16/32-bit ARM11 version core, which is widely used in mobile phones and other portable applications. In order to provide the best hardware performance for 2.5G and 3G mobile communication services, S3C6410 adopts a 64/32-bit internal bus structure and integrates multiple powerful hardware accelerators such as mobile image processing, display control and image scaling. Its internal integrated JPEG codec supports encoding of images in YCbCr4:2:2/YCbCr4:2:0 format, and the output image file size can meet the image size requirements of MMS information. In addition, S3C6410 also has a camera interface, which supports ITU R BT-656/601 8-bit mode, the maximum input size can be 4096×4096 pixels, supports YCbCr4:2:2 format data as input, and can generate RGB 16/18/24-bit format and YCbCr4:2:2/YCbCr4:2:0 format images. This feature can reduce the system's requirements for image acquisition modules.
3.2 Design of sensor module
The sensor module of the system consists of two parts, namely the temperature and humidity sensor and the smoke concentration sensor. The temperature and humidity sensor uses the high-performance AM2301 capacitive digital temperature and humidity sensor of Guangzhou Aosong Company. The sensor has the advantages of ultra-fast response, strong anti-interference ability, high cost performance, large temperature and humidity measurement range, and high resolution. It can be used in various environments and can work normally even in extremely harsh conditions. AM2301 is a single bus device with a data format of 40 bits of data = 16 bits of humidity data + 16 bits of temperature data + 8 bits of checksum. In this system, the S3C6410 pin GPE1 is used to communicate with the control module with a pull-up resistor, making system integration easier and faster, saving the number of leads and reducing product costs.
The smoke concentration sensor uses MQ-2 as a sensing device. MQ-2 is a resistive sensor that has high sensitivity to natural gas, liquefied petroleum gas, hydrogen and other smoke, can work stably for a long time, and has strong anti-interference. By measuring its output resistance, the smoke concentration on site can be detected.
3.3 Design of image acquisition module
The image acquisition module uses OV7650 produced by Omnivision, USA. It is a highly integrated, high-resolution CMOS image sensor that supports YCbCr4:2:2 data output format and can fully meet the design requirements of the system. Its input and output interfaces have good compatibility with the camera interface of S3C6410, providing great convenience for system development.
3.4 Design of GPRS module
The system uses Simcom's SIM300z as a GPRS module. It uses GPRS technology and GSM mobile communication network as transmission media, which can provide users with fast wireless GPRS connection and high data transmission rate. The module has a wide operating temperature range and can meet the monitoring system's requirements for harsh conditions. SIM300z communicates with S3C6410 through the serial port and can process the AT commands issued by S3C6410 in a timely manner. For the data transmitted by S3C6410, SIM300z can also forward it in time to meet the monitoring system's requirements for data transmission.

4 System software design
Completing the hardware design is only the first step to realize the system function. Good software design is the key to the stable operation of the system. The following will introduce the software structure and important software modules of the monitoring system in detail.
4.1 Transplantation of embedded operating system
The embedded operating system is a widely used system software, which is responsible for the allocation and scheduling of all software and hardware resources of the remote monitoring system and is the foundation of the entire system. Linux was selected as the operating system of this system because of its completely open kernel and flexible configuration. The transplantation process is as follows:
① Use a virtual machine on a PC to establish a cross-compilation environment GNU;
② Select TCP/IP and other modules according to system requirements, and compile to generate the Linux kernel;
③ Compile to generate the root file system rootdisk;
④ Download the Bootloader image to the underlying hardware. The main function of the Bootloader is to initialize the hardware and guide the Linux kernel to start;
⑤ Burn the Linux kernel and rootdisk image.
4.2 Design of GPRS networking module
To access the Internet via GPRS in Linux, you must use the PPP protocol for dialing. However, Linux transplanted to ARM does not provide the PPP protocol. It is necessary to configure the network device to support the PPP protocol when compiling the kernel. On this basis, using the pppd source code package, use "ATD*99***1#" to dial up and connect to China Mobile's GPRS network. During the dialing process, the following settings need to be made:
① Set the serial port rate to 115 200 bps, the check bit to NONE, the data bit to 8, the stop bit to 1, and cancel the hardware flow control;
② The user name and password are empty;
③ Use the "AT+CGDCONT=1, "IP", "CMNET"" command to set the access point to CMNET.
4.3 Design of information acquisition module
Information acquisition includes two parts: one is the acquisition of image information, and the other is the acquisition of temperature, humidity and smoke concentration. Since S3C6410 has a camera interface and a powerful JPEG codec as hardware support, Linux functions can be directly called to complete image acquisition and encoding, greatly shortening the development cycle.
The acquisition of temperature and humidity is carried out through the AM2301 module. After it is powered on, it needs to wait for 1s to cross the unstable state. No instructions can be sent during this period. AM2301 and S3C6410 use a single bus data format for communication and synchronization, and the communication time is about 5 ms.
The process of collecting temperature and humidity by microcontroller S3C6410 is as follows: At the beginning of communication, S3C6410 pulls down the bus DATA, releases the bus after 500μs, and starts to detect the response signal of AM2301 after a delay of 20-40μs. The response signal of AM2301 is a low level for about 80μs, and then AM2301 pulls up the bus for about 80μs to indicate that it is about to enter the data transmission state. Then AM2301 transmits 40 bits of valid data. When the last bit of data is transmitted, AM2301 will pull down the bus again for about 50μs, and finally release the bus, which will be pulled up by the pull-up resistor.

Smoke concentration collection process: The sensing device MQ-2 converts the smoke information into an electrical signal, which is then converted into an A/D signal after passing through the amplification circuit and finally transmitted to the S3C6410 for storage.
4.4 Design of MMS sending module
When the system is successfully connected to the GPRS network, it is necessary to send MMS information through the WAP protocol. In this process, the IP of the WAP gateway is set to 10.0.0.172 and the port is 9201. The specific process of sending MMS information is as follows:
① The microprocessor sends a session establishment connection request to the WAP gateway, and the data sent is 0E 00 00 12 01 10 00 00 (8 bytes). The first 4 bytes are WTP invoke PDU, and the last 4 bytes are WSP protocol data unit, representing WSP Connect PDU.
② The server returns a connection confirmation, and its data is 13 80 00 02 92 C7 59 0E… (30 bytes). The first 3 bytes are WTP Result PDU, and the rest are WSP protocol data units, representing WSP ConnectReply PDU.
③ The microprocessor sends WTP Acknowledgement PDU to complete the session connection, and the data sent is 18 00 00.
④ The microprocessor sends WTP, WSP and MMS packets, mainly including WTP Invoke PDU, WSP Post PDU and M-send． req PDU.
⑤ The gateway returns the transaction operation result, and the microprocessor sends WTP Acknowledgement PDU to complete the session. The data sent is: 18 00 01.

5 System test
After multiple tests, most of the MMS information sent by the monitoring terminal can be received by the terminal within 5 s after sending, and can be received even if WTP Acknowledgement is not sent, which can meet the real-time requirements of the monitoring system. The system test is shown in Figure 3.

Conclusion
This article introduces the remote monitoring system based on ARM11 and MMS in detail. The system has good stability and can adapt to different working environments. The MMS technology used can transmit information such as pictures, sounds, texts and videos. Remote monitoring through this technology has become a hot topic today. With the continuous development of embedded technology, the gradual maturity of GPRS network, and the
rapid development of 3G network, remote monitoring through MMS will definitely become a popular trend. I believe that in the near future, people can monitor remote scenes in real time without leaving home and deal with emergencies in a timely manner.