Guided Scrambling techniques for QPSK signalling alphabets
Soumalya Ghosh · 2013
Guided scrambling coding was first introduced for fiber optic communication systems because of its ease of implementation and good performance when appropriately configured. This technique is simple in concept, being based on source stream scrambling following augmentation, and at the receiver, the source stream is recovered by descrambling followed by removal of the augmenting bits. These procedures can easily be implemented with sequential logic circuits thus enabling fast operation which supports high bit rates in fiber optic systems. Guided scrambling was introduced as a line coding technique for communication systems which transmit two-level signals. This research proposes a new development in guided scrambling by extending the procedures for generating balanced binary sequences with guided scrambling to generate balanced sequences with symbols from QPSK signalling constellations using polynomial arithmetic based on the GF (4) finite field. The report begins with a formal introduction to guided scrambling codes and builds on this background to provide detailed results on the extension to the GF (4) field. Simulation results and calculated power spectra are provided which confirm that this approach can be used to create spectral nulls.