ARM-11-based field WSN base station design and development (1)

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0 Preface

Wireless sensor networks use a large number of inexpensive sensor nodes to detect and return data in the target area, and remote computers process and provide information to decision makers. When monitoring the field environment, it is impossible to supply power or transmit data on a large scale. The sensing scheme is not feasible. The wireless technology can solve this problem well. The field environment is not as good as the indoor environment, and the factors affecting wireless signal transmission are uncontrollable, which may result in more data loss. In the existing solution, the single node is lost. The rate is 80%~90%. After returning to the remote computer with multiple hops, the data is small and the quality is poor, which is not enough as a decision-making basis, thus losing the meaning of monitoring.

Since the data transmitted by a single node is unreliable, a large but more reliable device can be used as a relay base station to receive data of nearby nodes in close proximity and with high quality, and back to the remote computer with mature and reliable technology to make up for the existing The shortcoming of the solution. The ARM11-based development board has the characteristics of large memory, strong computing power, excellent performance and stability, and is suitable for acting as a relay base station here, realizing data classification and transmission, and achieving a positioning function of data. The number of data returned by the sensor network is more. The quality is better, which makes the situation that the decision makers understand more reliable and ensures the monitoring significance.

1 base station

A base station, that is, a public mobile communication base station, is a form of a radio station, and refers to a radio transceiver station that transmits information between a mobile communication switching center and a mobile telephone terminal in a certain radio coverage area.

The base station includes a macro base station, a micro base station, a radio frequency remote station, a repeater station and an indoor distribution system. The macro base station generally has a dedicated rack, which can provide capacity, large capacity, requires a machine room, has good reliability, and is easy to maintain. The micro base station can It is regarded as a miniaturized base station, which condenses all the devices in a relatively small chassis, which can be easily installed. At the same time, the micro base station can provide the same capacity as the macro base station. The radio remote control refers to the radio frequency part of the single sector of the base station. The optical fiber is pulled to a device that is transmitted outside a certain distance, and the baseband portion of the optical fiber is placed at the original base station, and the CE and other resources can be shared with other sectors of the original base station, and the capacity can be provided. The repeater is a signal repeater, The RF signal sent by the base station is amplified according to the need, and the capacity cannot be provided by itself. The application environment mainly includes the area with poor coverage and relatively small capacity requirements and wide area coverage with relatively small capacity requirements.

The most widely used repeaters include wireless repeaters and fiber optic repeaters. The main difference is whether the signal of the donor base station is transmitted to the repeater via wireless or optical fiber. The indoor distribution system passes the macro base station. The RF output signals of base stations and repeaters are introduced into the indoor environment that needs to be covered to improve indoor coverage performance, and cannot provide capacity by itself, including active and passive products.

2 adaptive gateway design

The design block diagram of the adaptive gateway is shown in Figure 1. The ARM-11 development board is used as the core to collect the data collected by the node, and the GPRS module and the 3G module are loaded to implement the transmission. The received data is stored in the form of text and multimedia pictures. The text is transmitted to the terminal mobile phone through the 2G network, and the multimedia picture is transmitted to the terminal PC through the 3G network. The following describes the three aspects of text, multimedia and data type determination.

2.1 The text stored in the text is the local temperature, humidity, illumination and other information collected by the node, transmitted to the ARM-11 development board through the ZigBee network, and the file ends. Txt is the suffix name. The data stored in the text is relatively small, and will be transmitted to the mobile phone terminal through the 2G network by means of the GPRS module. The mobile phone will receive the information in the form of short message. Thus, the quality and speed of the transmission can be achieved. The load is also relatively small.

2.2 Multimedia multimedia data is the geographical information of the local surrounding collected by the node. It is sent to the ARM-11 development board through the WiFi network in the form of pictures, and the file ends. Jpg is the suffix name. The file storage data is relatively large, and will be transmitted to the terminal PC through the 3G network by means of the 3G module. The PC will receive the information in the form of an email attachment. This can ensure the transmission speed and quality of the picture. It can also make full use of the superiority of 3G network transmission for large files and make full use of the network.

2.3 Data type determination To do adaptive transmission of data, that is, the text data and multimedia data mentioned above are transmitted to the terminal by 2G network and 3G network respectively. Here, the file is suffixed to determine the file one by one. If you encounter a suffix named. Txt, which is classified as a text file, is transmitted over a 2G network, again, if the suffix is ​​named. Jpg, classified as a multimedia file, transmitted over a 3G network, thus enabling adaptive transmission.

The specific process is as follows:

(1) Take the addresses one by one.

(2) Determine if .if(filename.endsWith(".txt")) is the file suffix name. Txt. If the decision is yes, it is determined to be text data, and then the short message sending function is sent.

(3) If the judgment in step 2 is negative, if(filename.endsWith(".jpg")) determines whether the file name is. Jpg is the end. If the decision is yes, the file is multimedia data, and then sent by the mail sending function.

(4) If the decision in step (3) is negative, the file is incorrect, skipped, and continues to take the next file address.

3 test

The focus of the test is adaptive transmission. The testing environment was selected in the woods outside the School of Information Science and Technology of Northwestern University. The main processes are as follows:

(1) Arrange 10 nodes, 5 of which collect temperature, humidity, illumination, and 5 collect multimedia data;

(2) Set up the base station initialization system and send the collected files;

(3) The terminal checks the file.

The base station initialization interface is shown in Figure 2. The main information of the system is the name of the base station, the mobile phone number receiving the information, the email address of the received mail, and the local coordinate values ​​collected. In addition, there are related control buttons.