The Design of Data Transmission Terminal in Remote Warning Control System based on CDMA 1X Network [Sensors & Transducers (Canada)]
(Sensors & Transducers (Canada) Via Acquire Media NewsEdge) Abstract: This study proposes a framework of data transmission terminal in remote warning control system based on CDMA 1X network. According to the functional requirements of wireless broadband communication system, the hardware interfaces and software of the CDMA 1X data transmission terminal are designed detailedly and the system is implemented using wireless access and embedded development technologies. It has good applicability and portability so that various wireless data transmissions can be achieved by replacing the data source module. Copyright © 2014 IFSA Publishing, S. L.
Keywords: CDMA IX, Data transmission terminal system, Wireless access.
1. Summary of the Remote Warning Control System
With a wide application range, the CDMA wireless data transmission system can be applied to almost all data transmission businesses of low or medium rate, such as industrial remote telemetry and remote control, automation of city distribution network, tap water and gas pipeline, business POS, INTERNET access, personal information, stock information, finance, transportation, public security [1, 2], etc.. In addition to support traditional Internet application, CDMA also allows the wireless terminal to support B2B, B2C electronic commerce and electronic payment, stock trading, the bank transfer application. The TCP/IP protocol stack is embedded in the CDMA IX data terminal, to simplify the interface design and realize the transparent data transmission between the user terminal and the server. Therefore users can conveniently achieve remote data transmission by using CDMA technology.
In this study, the remote warning control system is designed and implemented by using the CDMA wireless access technology. This system is a typical application of CDMA technology in industrial remote signaling, sensing and telemetry. The remote warning control system has two primary components of the central control center and the remote warning terminal, and the other parts are provided by China Unicom Corporation. The system architecture is shown in Fig. 1. The alarm instructions are issued by the computer in the central control center. Then they are transferred to the remote warning terminal through the Internet and CDMA networks. After receiving the instructions, the remote warning terminal starts the alarm, e.g. electric alarm or acoustic alarm. The alarm ringing is automatically transmitted to the central control center and then displayed on the computer's electronic map.
The remote warning terminal comprises the microcontroller AT89C52 of Atmel company, the CDMA IX data transmission terminal, i.e. the CDMA communication module, the voice circuit, the sound intensity detection module, man-machine interface, and alarm driver, etc., realizing the functions of communication, broadcast, state detection and manual operation, etc.
2. CDMA IX Date Transmission Terminal Architecture
The key of application of the CDMA network in communication fields is to develop the commutation terminals with low cost and easy use according to the practical requirements . There are two modes for the design of the terminals. One is to reform the existing mobile phones, and the other is to design the special terminal satisfying the industry needs by using the CDMA module. The former has the disadvantages of high cost and restriction of reformation, and is difficult to satisfy the needs of some industries. The latter development mode has low cost and great freedom, and the terminal shape and volume are easy to control [4, 5].
The data transmission terminal based on CDMA IX in this study is data transmission equipment, integrating CDMA IX MODEM transmission features and functions of TCP/IP networks . Wide area networks use the CDMA IX connection mode, while internal networks use the serial port connection mode, including RS232 which can be extended to RS485, to realize transformation of serial ports to CDMA IX networks. Fig. 2 illustrates the architecture of data transmission terminal. The data transmission terminal based on CDMA IX is an embedded hardware system, including microprocessors, memory and peripheral devices, I/O interfaces and network controller sections. It has characteristics of strong support capacity for real-time tasks, strong function of memory protection, scalability of the processor structure, and low power consumption of embedded microprocessor, especially for wireless network equipments.
3. CDMA IX Data Transmission Terminal Hardware Design
This CDMA IX based data transmission terminal mainly consists of the high-performance processor W77E58 and the CDMA module Q2358A. W77E58 realizes the core module of the system and the user UART interface. The mobile communication module with functions of CDMA IX network comprises the Q2358A, UIM card, antenna and some other components. The whole system is achieved through mutual cooperation of these modules . Here give details of hardware design. The hardware structure is shown in Fig. 3.
3.1. The Central Control Module W77E58
The processor is the core of embedded system since it provides system with instructions. The data transmission terminal adopts the processor W77E58, a high speed, high integration and high performance single chip of enhanced MCS-51 series launched by Winbond Corporation of Taiwan. The W77E58 with frequency of 40 MHz is equivalent to the single chip 8051 of 100 MHz. With the built-in 32 KB reprogrammable Flash EPROM, 1KB internal SRAM accessed by the MOVX instruction, saving 16 data/address /I/O lines, two enhanced full duplex serial ports and a low price, it is a feature-rich and highly integrated 8-bit microcontroller, which can meet the requirements of the system.
The CDMA IX based data transmission terminal is connected to the local terminal equipment through serial port UART1 and is connected to the CDMA module through the serial port UART, realizing the wireless access of serial devices to the Internet. The data terminal's main function is forwarding data packets of networks and local terminals transparently in the application layer . The hardware connection diagram is shown in Fig. 4, where data pins and address pins are marked accordingly.
3.2. CDMA Module Q2358A
WISMO Q2358A module of Wavecom company has completed functions of CDMA2000 IX voice and data transmissions. In summary, it has the following properties.
1. Product properties
On executive standards of FCC/SAR and CDG1, 2&3, it is a CDMA20001xRTT module with single frequency of 800 MHZ.
2. Basic characteristics
It supports voice communications, SMS (Short Messaging Service) of Chinese and English in MT/MO/CB/PDU mode, and dual-tone multifrequency function, DTMF in abbreviation. The input voltage is 5 V - 25 V, the receiving input current is <150 mA, and the free input current is < 3.8 m.
3. Data characteristics.
The range of baud rate is from 300 to 115,200 bits/s and the automatic range is from 2,400 to 19,200 bits/s. The highest rate accessing the Internet is 153 Kbps.
RS-232 and sound connect through the 15-pin interface, and active SIM slots are provided. Communications through interfaces are controlled through AT commands.
5. Additional services.
Additional services involve call transfer, multiparty call, call waiting and maintaining, calling-line authentication, infrared SIM data transmission, SIM locks, etc.
In general, Q2358A provides complete CDMA wireless interfaces, and supports multiple communication means such as data, voice, SMS, fax, etc. using TCP/IP network protocols. The CDMA module and the central controller communicate through the serial port using AT instruction set.
3.3. The Interface between Q2358A and W77E58
Compatible with single chips of MCS-51 core, W77E58 has built-in 1024 B RAM and 32 KB FLASH program memory, as well as two full-duplex UARTs, which are used to realize the simultaneous communications of the single chip with the mobile phone module and the user. Considering implementing communication protocols such as PPP, TCP/IP, etc., the 32 KB external data memory SRAM 62256 is expanded outside the CPU.
The interface circuit between the CPU and Q2358A consists of two signal control lines for ON/OFF and RESET, and asynchronous serial interfaces. After electrifying the module, the ON/OFF signal line controls to turn on and tum off the module. In the applications without special requirements for power consumption, the module remains on after electrified, while the ON/OFF signal line is connected to the VCC through a pull-up resistor. The RESET signal line is effective for low level, and the module restarts when the low level is above 500ps, which is realized by the automatic power-on reset circuit in this system. In addition, the feet P1.0 and Pl.l control the switch and reset of Q2358A through software.
Through the asynchronous serial interface, the controller sends control commands, i.e. AT commands, to the module and reads its state. The Q2358A module has a complete 4-pin asynchronous serial port, and connects with the UART of W77E58 through the level conversion chip MAX3232. Testing results show that two lines of RxD and TxD are enough for controlling the module to realize the usual functions, such as phone calls, SMS, CDMA IX, etc. In the connection circuit of Q2358A and W77E58, the feet 11, 10, 12 and 9 of MAX3232CPE connect with the pin feet P3.1, P3.4, P3.0 and P3.2 of W77E58 respectively, and thus Q2358A and W77E58 are connected.
3.4. R-UIM Interface
The R-UIM (Removable User Identity Module) card, also called UIM card for short, is a kind of smart card adopting the separation technology of machine and card, which stores user information, authentication algorithms and security-related information. As a security mechanism, the role of UIM card in CDMA system is similar to the SIM card in GSM system. The user's subscription data, network parameters, authentication algorithms and encryption keys used in the authentication process are all stored in the UIM card, so that users can use various services offered by the CDMA network conveniently and safely, avoiding economic loss due to identity pilferage. The Q2358A provides an RUIM interface for the CDMA smart card. However, because the R-UIM controller shares some pins with UART-2, the UART-2 can not be used when using the R-UIM interface. The R-UIM interface contains signals of Clock, Data, Pwr En, Pre and Reset. The power supply of R-UIM is controlled by the signal Pwr En, which usually controls the power supply circuit to supply the card with electricity.
3.5. Users UART
The data transmission module implements transparent transmission of data between RS-232 interface and users. The second serial port UART1 of W77E58 provides two-way transmission of user data, which is shown in Fig. 5, and the MAX3232 of MAXIM Corporation is still used to achieve level conversion.
4. System Software Design
As a network embedded equipment, the data transmission terminal based on CDMA IX uses the design mode of no-operating system, which reduces the overhead of the system and saves hardware resources, but increases the difficulty of system development.
IP OVER PPP is adopted as the wireless access way to Internet in the CDMA mobile communication module. Due to the limited resources of embedded system, protocol reduction is critical for the design and implementation of software. The significant reduction of TCP/IP protocols can improve the executing speed of the program and reduce memory consuming. Not all the protocols must be implemented in the wireless data module, and it should select necessary ones according to the requirements of projects. The PPP protocols are needed for wireless access to CDMA IX network and further access to the Internet. Among PPP protocols, the LCP protocol, the IPCP protocol and the PAP authentication protocol are implemented in this system. On the network layer the IP protocol, together with the ICMP protocol which reports data transmission errors, are implemented due to the reason that the data module should be able to communicate on the Internet. On the transport layer the TCP or UDP protocol should be implemented . Considering the needs of the application, the TCP protocol which orients to reliable transmission of data stream is adopted and simplified.
The development of embedded system needs complete tools and an integrated development environment. The environment Keil C51 v8.0 is used for developing and debugging the system. All programs are written in C language and the software is hierarchical structured . From bottom to top of the software architecture, six layers giving access to the CDMA IX network involves the serial driver layer, the CDMA module driver layer, the PPP protocol layer, the IP protocol layer, the TCP protocol layer and the application layer. The upper layer functions call the underlying layer functions which provide services for upper layer, and thus the application layer tasks of data transmission are ultimately accomplished.
The data transmission in this system is transparent. The terminal device doesn't process the information which is sent through the serial ports and sends them in the form of TCP/IP data packets to the wireless CDMA network, while the data received from the wireless CDMA network is unpackaged and sent to the terminal device. All processing work of the application layers is completed by the terminal. It increases the independence of the terminal software and the compatibility of the controller and the terminal equipment, and simplifies the design of the data terminal software. Due to the space limitation for this article, it focuses on the realization of the CDMA module. The work of Q2358A is controlled by software. A reasonable software structure is needed to control the module appropriately, including real-time control of the module state and accurate control of its working. The module control commands are AT commands. Beginning with "AT" or "at", these commands control the communication between MODEM, communication modules, etc. and hosts. Main functions in the Q2358A module are implemented to realize various aspects of the wireless transmission.
1. CDMA module initialization.
After the system starts, the function CDMA_init 0 is called for initialization, including the serial port initialization, Q2358A state setting, etc.
2. Receiving and sending of AT commands
Through UART1 the CDMA module communicates with W77E58, which sends AT commands through the serial port to the CDMA module and read its input. By calling the function of int send_cdma_cmd (int fd, char *send_buf), W77E58 sends AT commands to the CDMA module, and through the function of int read cdma datas (int fd, char * rcv_buf), W77E58 reads data of the CDMA module. If the communication is successful, the function returns CDMA OK, and otherwise it returns CDMA_ERR.
3. Short message dispatching.
The CDMA module sends short messages to mobile phones. When module initialization, message contents, service centers and target phone numbers are all preset. Short messages can be dispatched by calling the AT commands if needed. The command AT+CMGS=n indicates sending short messages of length n. After sending the command, CDMA module sends ">". Receiving the prompt, the processor sends message contents to the CDMA module. If messages are sent successfully it returns OK, otherwise it returns ERR. The receiving of short messages is realized by the instruction AT+CMCR=<Index><CR>.
This study proposes the framework of a dedicated data transmission terminal based on CDMA IX network. According to the functional requirements of the wireless broadband communication system, the terminal is implemented by applying wireless access and embedded application development technologies. The system development mainly involves the design and implementation of hardware interfaces and software. Various wireless data transmissions can be achieved by replacing the data source module. Through this way different wireless data transmission systems are constituted, such as remote meter reading system, water conservancy and data acquisition system , parking and traffic monitoring system , etc.. Therefore, the system developed in this study has good applicability and portability, and it is a direction of the future wireless data transmission.
This work was supported by University Natural Science Research Project of Jiangsu Province (12KJD520003) and applied Basic Research Program of Jiangsu University of Technology (No. KYY10059) (No. KYY11080). Furthermore, we are indebted to the support and encouragements received from the staff and colleagues of the school of computer engineering.
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Dan CHEN, Hongfen JIANQ Yijun LIU
School of Computer Engineering, Jiangsu University of Technology,
Changzhou, Jiangsu, China, 213001
Received: 28 November 2013 Accepted: 28 February 2014 Published: 31 March 2014
(c) 2014 International Frequency Sensor Association
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