Implementation & Performance Investigation of Dicode PPM over Dispersive Optical Channels

This work is concerned with the development and investigation of a Dicode PPM (DiPPM) system.

A DiPPM coder was developed to code any input PCM signal into DiPPM format. A further investigation took place on the DiPPM spectrum and associated output. Software simulation and mathematical analysis of this PPM code was considered and comparison with previous theoretical results presented. Results show that DiPPM is an advantageous PPM code for optic communication; DiPPM spectrum is not concentrated near to DC and
it is possible to extract the DiPPM framerate
component directly from the pulse stream.

A timing extraction circuit that recovers the clock from a DiPPM sequence and synchronises the slots within the frames, was constructed successfully. This enabled transmission through fibre optics and Free Space Optics (FSO). The technique used for the timing extraction circuit of the DiPPM scheme gives an advantage over many of the PPM formats.

An optical transmitter/receiver system was developed and the DiPPM scheme was investigated through optical channels. Results show that the DiPPM sequence transferred through the optic system was not changed and the clock had been recovered. A DiPPM decoder was constructed and the received DiPPM signal returned to its original PCM form without errors.

Both DiPPM coder and decoder were developed in VHDL and measurements were taken. The timing extraction was programmed in VHDLAMS with the use of digital, analogue and mathematical equations.

DiPPM MLSD was also constructed in VHDL. Simulation results proved the theoretical
expectations.