Design Of Fiber Telephone Based On ADPCM Compression Coding Algorithm

As optical fiber is widely used, optical fiber laying, inspection and maintenance works become more and more important. Construction workers need mutual cooperation to finish these works, so it is necessary for them to communicate. Considering that some optical fiber laying condition is harsh and general wireless communication device may have poor call quality, which cannot meet the communication requirements. In this case, we need a special communication device not affected by the severe environments. Fiber telephone is a kind of communication device designed to solve the problem. Using optical-fiber as a transmission media, fiber telephone makes communication more convenient without setting up a dedicated communication line.Commercial products of fiber telephone are varied. However, there are still some shortages, such as high bit rate, low call quality, high cost and so on. The designed fiber telephone system reduces the transmission bit rate with the compression ratio of 4:1 by adopting the adaptive differential pulse code modulation technology. Speech experimental results show that this coding method has high speech quality. STM32 is adopted in the design as system processor to reduce the hardware cost while satisfying the call quality. Moreover, a fiber optic transceiver combined with light source is used in fiber telephone system and a LCD display module is introduced to display the current communication status.The main research contents in this thesis are as follows:First, the development status, working principle and composition of the fiber telephone is analyzed; then the overall research scheme and targets are put forward aiming at overcoming the shortages of the current fiber telephone.Then, the fiber telephone overall hardware design scheme is proposed based on analyzing the traditional one. And all components of the hardware are designed, mainly including microprocessor control circuit, fiber optic transceiver module circuit, voice codec module circuit, LCD interface circuit, power supply circuit, keyboard control circuit, microphone input and voice output interface circuit.Next, voice compression coding algorithm and its implementation method are researched. The ADPCM algorithm executive program on VS1053 is designed. Moreover, the microcontroller control program, including main program and codec module control program are also designed.At last, the combined fiber telephone system has been debugged, and the speech signal quality is evaluated on coding/decoding speech signals. Experimental results show that the mean opinion score of designed fiber telephone is 3.9 and bit rate is 32 kbps.