The Conservative Code for Bit Synchronization

Abstract

A novel coding scheme for bit synchronization, the conservative code, is presented and analyzed in this paper. Each codeword is characterized by having a predefined number of transitions, with a known delimiting transition at the end, i.e., the number of transitions is conserved. As a result, it is possible to decode the incoming serial bit-stream without explicitly recovering the receiving clock with a phase-locked loop. Thus, it is possible to receive messages from asynchronous sources without any training period. This code can be extremely useful in communication over a passive optical star. In the analysis, the efficiency or capacity of the code is computed with two additional constraints 1) limited run-length and 2) balancing. It will be shown that this coding scheme is efficient when both constraints are applied. The objective of this analysis is to show, that the additional constraints imposed on the encoding, do not cause a significant reduction in its efficiency. The design of a serial electronic interface is described. Its goal is to maximize the interface bandwidth (greater than 1 gigabit/s with GaAs technology), which is usually the bottleneck of an optical communication system. It is achieved by reducing the critical timing path to one flipflop and one NOR gate, and by having a hierarchical interface design. © 1990 IEEE