The Research Of Image Transferring System Based On PSTN

With the development of technology and the improvement of human beings'standard of living, traditional ways of exchanging information no longer satisfy the need of society in the 21st century. Images, carrier of information, are widely used in many fields. As a result, the demand for image transferring system is growing stringent.The methods of image transferring that are often being used now require wider frequency band, and the equipment are complicated and very expensive. But with the development of image compressing technique, which reduces band width for transferring condensed image data quite a lot, transmitting static images in Public Switched Telephone Network (PSTN) becomes possible.Actually, the transfer of video is not always necessary in many occasions, sometimes transmission of static images can meet the needs. The PSTN has some advantages, for instance, wide distribution, no restriction from time and site, no extra investment, easy prevalence, etc. The image transferring system based on PSTN adequately uses existing resources with good expectation in the market. The system under researched in this thesis shows several characteristics, such as small volume, low cost and stability, etc. It will find its application in home surveillance and other situations that with no human guarding, for example, uptown security surveillance, remote education, oil field observation, traffic control and flood prevention, etc.The system can be divided by function into three parts: image collection, DSP image compressing and image transmitting in PSTN. Image collecting section: TMS320VC5402 initializes the register of the SAA7111A through I2C bus. Then the collected images are put into the SRAM under the control of CPLD. DSP image compressing section: mainly fulfills the task of transplanting JPEG arithmetic and optimizing. Image transmitting in PSTN section: C5402 sends the data that have been compressed to the remote host computer by extended asynchronous communication serial port's controlling outside Modem. Also, the functions of terminal server program, achieving the control of Modem by serial ports and receiving compressed image data, are explained.