Research On Analog Video Secure Transmission System Based On FDM

According to the secure transmission of analog video in closed monitor system, founded on analyzing the shortcoming of character superimposition technology, the idea that video transmit together with data using FDM technology is adopted in this article. The concept of interactive test between terminal cameras and monitoring center is introduced. A new communication system using video tacit encryption technology is designed.The system use the RF cable instead of video lines.This system based on the usable frequency band of the RF cable uses the bidirectional filter acquiring two untroubled signal channels--the uplink channel and the downlink channel. Audio or video signals with characters from the terminal camera are sent to the uplink line by their own frequency-shifting circuit and transmitted by RF. This mixed signal is separated by a filter in monitoring center and taken to relevant demodulation unit restoring base-band signals. Simultaneously, control signals and the secret-key from monitor center are sent into the downlink line by FSK modulation and restore the data signal by a PLL circuit in the terminal. The initiative character in each interactive test process is generated by a microprocessor in monitor center. It will be regarded as a seed and be sent to the microprocessor in terminals for changes. The secondary data is passed backward via the uplink route. Then the center microprocessor will verify it according to the vested algorithm and the data base. The system uses this periodic test to detect the condition of transmission lines and determines whether to trigger the warning circuit.The format of audio and video signals in TV transmission system and the basic theories in digital modulation communication system have been studied. The idea of embedded system design was adopted and each function unit was modularized. The ARM7 processor was selected to support richer resources in data procession and real-time controls to interactive communication. Each hardware circuit has been designed, as of the RF modulation circuit of audio and video signals, the digital FSK modulation circuit of data in the uplink line, the PLL modulation and demodulation circuit of data in the downlink line, etc.The program design contains each interface control among each circuit unit, transmission frequency setting and data encryption algorithm.This system is compatible with CATV network and meets the requirement of monitoring devices communication protocol. The flexible secret key generation algorithm and the bidirectional communication ensure the real-time security of the lines. Its band efficiency is high, as well as its portability. This system has application value on the bank, the Customs, frontier defense and other important departs.