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Based on GSM and GPRS wireless meter reading system design and comparison

In Electronic Infomation Category: B | on April 20,2011

Wireless meter reading system is the use of embedded systems and LT1575 datasheet and wireless networking technologies such as automatic meter reading and LT1575 price and processing of user data, the user of the water table and LT1575 suppliers and other instruments of the use of electrical transmission of information to the management company for the integrated treatment system. It is wired on the basis of meter reading system developed, but thanks to a wireless communications technology, can solve the cable distance is limited meter reading system, network difficulties, the construction cost and maintenance costs are high, more power is equivalent to problems.

Therefore, the use of GSM / GPRS wireless communications network for remote meter reading, the user water sent to the water company, not only can solve the problem of ordinary user water meter reading, but also on major water users in real-time monitoring, to prevent the stealing of water and pipeline leakage occurred. Currently, the wireless transmission are two kinds: the use of GSM network and the use of GPRS networks. But these 2 methods have advantages and disadvantages, therefore, the use of different occasions, use different transmission system cost will have a huge impact.

Solve this problem, designed based on the GSM / GPRS network for wireless remote meter reading system, from a different perspective on the GSM short message service and GPRS packet data services, pointed out the advantages and disadvantages, given the data for the system transmission scheme for future wireless meter reading system provides a design basis and popularity.

1 wireless meter reading system

Entire wireless meter reading system, including optical direct-reading water meter, Meter-Bus bus interface circuit, GPRS / GSM module, microcontroller and computer monitoring water companies most of the terminal 5, the structure shown in Figure 1 . In order to reduce power consumption, this design does not have all the modules are operating, each module under the command of the microcontroller time work, meter reading system that works all the modules as "a long sleep, a short work." Among them, the sleep cycle (hours, days, weeks, months) controlled by the administrator client computer through the GPRS module is the final release. Micro-controller receives the GPRS / GSM module receives the command, modify the meter reading cycle, while the meter reading cycle, according to the set through the Meter-Bus interface circuit controlled direct reading water meters water meter reads the current value, and then use GSM / GPRS wireless network distributed computer terminals, automatic meter reading time.

Figure 1, remote meter reading system diagram

2 data transmission

1) GSM system, the Global System for Mobile Communications GSM (Global System for Mobile Communication), is the second generation of wireless digital cellular mobile communication system network standards. It defines the construction of the network and provide services of various standards, these standards by the European Telecommunications Standards Institute (ETSI) in charge. Commonly used frequency of 900MHz, 1800MHz, 1900MHz. GSM mobile communication network has to provide voice services, fax, SMS and other communication services capabilities, including messaging due to extensive coverage, low input costs, high reliability, suitable for designing wireless applications and products that meet the requirements of real-time Little data is not very high business needs.

2) GPRS system, GPRS or General Packet Radio Service (General Packet Radio service), is developed based on the GSM system, a new bearer service. It breaks through the circuit-switched GSM networks can only provide ways of thinking, by increasing the corresponding functional entities and some of the existing base station system to achieve the transformation of packet switching. Because GPRS uses the existing GSM wireless network, but based on an increase in its number of hardware and software upgrades, therefore, GPRS coverage is very wide. The hardware and software upgrades to increase the method, a relatively small investment, but the user data rate has been impressive, providing 9.05 ~ 171.2 kbit / s data transfer rate. As a result of packet switching technology, so do not need to take proper channel to improve the utilization of wireless networks, with billing by traffic, long-line, transmission speed, the advantages of fast network, while it supports TCP / IP protocol, to achieve the rapid development of Intemet and seamless, convenient intermittent and occasional bursts of data transmission of large amounts of data.

3 GSM and GPRS Comparison and Selection

3.1 Comparison of technical complexity

Wireless meter reading using GSM networks is relatively simple, consisting of optical direct-reading meter, data acquisition, GSM module and control centers. Data acquisition and control center through the GSM module can be connected to the GSM network to the data in the form of text messages through the GSM network to a monitoring center, the system structure shown in Figure 2. GPRS for meter reading system based on direct reading from the header, data acquisition, GPRS module, Intemet network and monitoring centers, the system structure shown in Figure 3. Data acquisition and GPBS serial communication module, the collected data sent over the network through GPBS, and then access Intemet network, and finally transmitted to the monitoring center, remote meter reading. Among them, beginning in the communications, GPRS module first initiates a connection control center, monitoring center received packets from the access to necessary information, communication can be established between the two. Monitoring center through the GPRS network Internet access, you need to use dynamic domain name, address mapping and other technologies to achieve seamless connectivity. To sum up, GPRS installation, configuration and technical requirements is much more complex than GSM, the general need to refer to relevant manuals to set up.

Figure 2, GSM-based remote meter reading chart

Figure 3 GPRS-based remote meter reading chart

3. 2 between the two Implementation

GSMs SMS (Shortage Message Service) SMS is a GSM Phasel point standard definition of the business, it is through the proprietary control signaling channel to send short messages via short message service center (SMSC) to store and can pass When forward (power, in the service area, etc.), and transmission using proprietary channel, high reliability, but the transmission rate be limited. Block Mo Shi can use its control, Text mode and PDU mode, Either way, send it the length of the data was limited, so SMS for a small amount of data transmission.

GPRS uses packet switching technology, breakthrough proprietary GSM circuit switched data channel transmission mode, the data package (Packet) transparently, so multiple users can simultaneously use the same radio channel for transmission and improve the network resource utilization, but the network is vulnerable to congestion, the data easy to lose. GPRS carrying TCP / IP protocol, you can access high-speed nte-met, can transmit large amounts of data.

3.3 Comparison of cost and time delay

GSMs SMS program costs include meter reading: 2 GSM module 600 million, two SIM cards a total of 80, during transmission, GSM module to a text message every time the frequency of the amount of data packets to send the user , each message is 0.1 yuan, the monthly fee is 3 yuan, if hour meter reading cycle, the cost is even higher. GPRS solution includes: a GPRS module 400, SIM card, a 40 yuan, 5 yuan minimum monthly tariff packages, flow 30M, with 100 bytes per SMS, SMS 300 000 off contract, if using SMS Frequent meter reading program costs will be very high.

The short message forwarding to be stored in the SMSC, so weak when in fact. Test data show that the use of GSM mobile network in China, SMS module within the same area and between brands of mobile phones, non-peak SMS, cell phone signal good case, a text message of the time delay for at least 10 s, up to a maximum number of minutes. 60 B using GPRS to send data packets, the average delay time of 5 s. To sum up, GPRS plan costs are lower, real-time high.

3.4 the scope of both

GSMs SMS and GPRS working principle and characteristics of their own decisions for their own situation and scope. Using GSM-SMS data transfer, system integration, and technical configuration is more simple and easy to implement. However, using SMS, text messages sent each of numbers or letters up to 160, suitable for small amounts of data and send and receive infrequent occasions. But the delay time is longer, in real time and send and receive on the Arts for high frequency, where a large amount of data, the cost will be significantly discounted, no longer apply.

GPRS works to ensure that it can not only support the intermittent bursts of data transmission, but also support the occasional transmission of large amounts of data. Data transmission speed, according to traffic accounting, network "always on" communication both ways, you can ensure more rapid exchange of data in real time. Therefore, a system based on GPRS communications frequently for such a large amount of data, real-time requirements of high complexity systems.

4 this design, the program

4.1 system data transmission in the design

Sum up, on in a "long sleep, a short work" mode, real-time requirements are not very high, the smaller amount of data the wireless meter reading system, GSM-SMS program can be taken to meet the requirements . But in order to reduce costs and improve reliability of data transmission, the design uses a combination of both methods: high frequency in the transceiver, the network is not congested, the use of GPRS data transmission program; low frequency of the transceiver, network congestion, the use of GSM The SMS program to text message for remote meter reading. This may delay the network congestion is more serious when the text message, but the program can be avoided using GPRS data loss caused by the trouble. In this real-time requirements are not very strict meter reading system, a little delay is acceptable, but the reliability of the data transceiver is very important.

Therefore, the design chosen to support both GSM and GPRS data transmission kernel MC52i (SIEMENS) of the GPRS MODEM. It supports MT / MO / CB / PDU Mode 4 SMS mode, support CSI-CS4 data coding, to carry TCP / IP protocol stack, you can access directly through the AT commands can be Internet, eliminating the common TCP / IP processing module and programming of various API function is called when the trouble.

4. 2 SMS and GPRS auto switch basis and to achieve

Based on the above analysis shows, for not very demanding requirements of real-time wireless meter reading system, consider the data transfer program is the cost of 2 main factors and the level of data reliability, and decided that two factors are is the high and low frequency data transceiver and the network is congested busy. If the high frequency transceiver, SMS program costs will increase, this time select the GPRS data transfer can greatly reduce the cost more reasonable; if heavy network congestion, GPRS solution will be the possibility of data loss, select the SMS to transmit data reliably at this time higher. So according to these 2 cases, the design according to different conditions, the program will automatically switch the data transfer is necessary, both to reduce costs, but also improve reliability.

1) Select the entire meter reading system based on GPRS real-time clock (RTC) timer wake-up data collection in the MCU to achieve regular meter reading. Required, time period is set to hour, day, week and month 4 modes, respectively, by the monitoring center via GPRS module released a computer administrator, and then modify the MCU automatically. If the peak in the water or water deficiency, it is necessary for real-time monitoring of water users, this time sending and receiving high frequency. Assuming hour meter reading cycle mode, copy a table every 4 hours, the cost per day is 6 times the daily cycle mode, this time with higher cost of SMS mode. Therefore, in order to reduce costs, system applications for the GPRS transmission mode the default mode, so no matter what mode, can be done to reduce costs.

2) select the SMS based on system defaults to GPRS data transmission mode, but once the heavy network congestion, GPRS mode data loss phenomenon, would not achieve the role of monitoring data. At this point it is necessary to allow the system to automatically switch to GSM, SMS program, because of its short message service center through the (SMSC) store and forward, high reliability, to ensure reliable data transmission. Determine whether the network is busy mainly confirmed information by detecting the delay time to return is greater than the default value. If greater than the preset value, then that network busy at this time, switch to the SMS mode to re-send, until the return confirmation message, the system that sent successfully, then go to sleep, waiting for the next wake-up. Instead, follow the system default GPRS transmission of data.

3) system software design most of the time the network is normal, so the system is in GPRS mode most of the time, only a fraction of time in SMS mode, this design will not only greatly reduce the cost and increase the data transfer rate, and improve system reliability and stability. Whether it is used by GPRS mode or SMS mode through software control to automatic switching, which saves hardware costs, lower system cost, the software control flow chart shown in Figure 4.

software control flow chart in Figure 4

5 experimental results

Both by the comparison of data transfer program costs can be seen, the use of GPRS mode, every 4 hours if the meter reading in accordance cycle meter reading, will save 13 per month, the shorter the cycle, save more . After the test, even in heavy network congestion, the use of SMS text messages sent in data mode, control centers received accurate data is almost 100% probability, but a little less real time, but for the meter reading system is acceptable. Thus, the use of GSM, GPRS SMS program and the method of combining the use of software for automatic switch remote meter reading, the cost will be lower, reliability will be higher.

6 Conclusion

As the GSM network to third-generation network over the GPRS technology, its use is very wide. Use it for remote wireless meter reading system will be more and more popular, but the peak in the network, multiple users use the same channel at the same time when data loss occurs the phenomenon of system reliability. However, if this article mentioned a combination of both methods, according to the network, automatically select the data transmission and improves the systems intelligence and reliability, and low cost, suitable for promotion.

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