System Of Wireless Date Transmission Based On GSM/GPRS

1. IntroductionAlong with the rapid development of automaticality level of industry fieldin China, there is increasing numbers of equipments which have to be supervised,operated and maintenanced in the open air. Confronted with this situation, it is outof date for traditional operation such as maintenancing respectively and supervisingby manpower, which wastes manpower and material resource. Themulti-microcomputer composing of SCM and PC by serial has been widely appliedin industry controlling and environment supervising field, in which RS232, RS485or wiry modem are adopted. Although economical, wiry data transmission limits itsapplication field at a large extent. The application of GSM/GPRS module has itsown advantages, such as being on line all the time, no demand to dial, low priceand wide scope covering, which is especially suitable in the field in which amountof data transmitted by frequency is low, for instance, attempering vehicles,supervising and navigating. In virtue of SMS and GPRS wireless network,collecting data and supervising equipment terminal remotely by embeded systemhas been a hotspot of people's study.2. Composing of system based on GSM/GPRSUsing its dual-transmission characteristic, long-distance wireless supervisingsystem based on GSM/GPRS network can control, test and communicate with thesystem equipment and running environment remotely, which makes supervising,operating, and maintenancing equipment in the open air easier. Kinds of applicationfield which have nice prospect can be exploited by using GSM/GPRS network asmedia to transmitting data, such as bidirectional transmission of wireless data,long-distance inspection and controlling.Data transmission system introduced in this paper is a essential part ofsupervising system, including controlling module and GSM/GPRS module ofsupervising terminal, which can collecting data, controlling and transmittingwireless data. Supervising terminal transmits information bidirectional, whichsends the collected data information to supervising centre and receives the orderfrom supervising centre at the same time, thus do some relative operations tocontrolled equipment.Controlling module adopts RABBIT2000 micro-processor as communicationterminal controller, which can directly be applied in small-sized and middle-sizedcontroller. Furthermore, Rabbit2000 is easy to use because its hardware andsoftware interface are both convenient and intelligent. The data transmissionsystem introduced in this paper is a embeded system, which can collect andtransmit data, supervise and control the working state of supervising point andrunning environment.3. SMS system based on GSM networkIt is a good idea to actualize the remote supervision of supervising point byutilizing relative subjects of GSM network (including SMS, data and voicefield),which has been highly regarded because of its nice performance, namelyconvenient and prompt. The long-distance supervising system, based on GSMnetwork, has several function concentrating in itself, such as long-distance measure,data collecting, switching operating remotely and supervising malfunction ofterminal equipment.The advantages of SMS is apparent, which can be mainly described asfollows:1. low in price;2. available everywhere;3. adapted to multiple kinds of data;4. safe in transmission;Based on the advantages of SMS mentioned above, the supervising systemdevised in this paper actualizes its data transmission in the way of SMS, whichperformance of supervision in real-time and veracity can both meet the demand.Compared with common wireless communication method, this one doesn't needantenna and special frequency, which also has a low disturbance and rate of error.SMS is a supervision means worth popularizing, which also have some advantagessuch as being convenient to install and available to supervise respectively andremotely. Every coin has its own two sides, the SMS based on GSM has itsdisadvantages either, for instance, delay.4. protocols using in data transmission based on GPRSGPRS technology is the combination of mobile telecommunication and IPtechnology. Data obey TCP/IP protocol, that is to say, data must have its source anddestination IP address. The supervising centre is directly connected with Internetand assigned a fixed IP address. But the supervising terminal existing in GPRSnetwork cannot be assigned a fix IP address, which has a variational IP addressassigned dynamic. MC35 only embed PPP protocol, in order to connect GPRSwirelessly to the Internet, the PPP must be actualized in SCM and protocols beapplied in IP and its upper layer protocol。PPP protocol is utilized as an interface toGPRS network and to apply IP address.5. Software actualization of data transmission based on GPRS networkGPRS stands for General Packet Radio Service , which is 2.5G mobiletelecommunication system regarded as the transition for GSM to develop into 3G.GPRS is a wireless data transmission system based on GSM system by introducingnew components.Compared with the telecommunication network being used, GPRS has somenew characteristics, of which the most famous one is "being on line for ever".GPRS uses packet-switching , which has no need to dial and connect like modemand occupy resources only when it send and receive data. GPRS is charged bytransmission flux that is more reasonable for consumers.GPRS has the following technique advantages:1. high ratio of resource utilizing;2. high rate of transmission;3. less time of interfacing;4. supporting IP and X.25 protocol;According the telecommunication regulations of GPRS dial-up, the process oflogging in GPRS is:1. TE sends AT to set the initial parameters in order to enter PPP mode, MEsends the returned value to TE;2. TE sends ATD*99***1#,prpare to establish PPP connection with ME;3. PPP protocol contained in ME sends LCP Configure-Request packet sothat TE and ME can establish PPP connection;4. TE sends back LCP Configure-Ack packet to ME to prepare to establishPPP connection;5. PPP protocol contained in TE sends LCP Configure-Request packet toconsult Authentication protocol, such as CHAP and PAP.6. ME sends back Configure-Ack packet to TE to testify the Authenticationprotocol used. PPP protocol contained in TE sends ME NCP Configure-Requestpacket to activate IP protocol;7. If ME still has not attach to GPRS, TE sends AT+CGATT in order to makeME perform attach to GPRS;8. TE sends AT+CGDCONT, ME performs PDP context activation;9. ME sends NCP Configure-Ack to TE to activates IP protocol contained inTE.Since SCM is the counterpart of TE and MC 35 of ME in this paper, afterfinishing the process mentioned above, a Socket can be established in SCM wheredata information is reformed into UDP packet and then IP packet sent to MC35.MC35 divides PPP packet to GPRS packet and sends them by air interfaces . Theprinciple is almost same in the reverse situation.Since TCP format is to complex that needs establish handshake connectionwith receiving end during transmitting data, UDP format is adopted to transmit datain this paper for its easiness. UDP protocol occupies less network resources anddeals with data more rapidly, therefore, which is necessary in some circumstancesneeding high real-time demand. It provides connectionless service, althoughtrustless transmission, which satisfies the demands of data transmission, thus UDPis adopted to transmit data.