Syndrome-based Viterbi decoder node synchronization and out-of-lockdetection

摘要

A method for joint Viterbi decoder node synchronization andout-of-lock detection which applies to trellis codes with a linearencoding rule (such as convolutional codes, Ungerboeck codes, etc.) ispresented. Quadrature phase shift keying (QPSK) transmission combinedwith a transparent rate 1/2 convolutional code is studied; in this casenode synchronization corresponds to 90 carrier phase ambiguityresolution. Usually, node synchronization is derived from the metricgrowth of the most likely path at the Viterbi decoder. Theseconventional methods are not optimal and become unreliable at lowE_b/N_o. Moreover, they are not well suited forout-of-lock detection. The proposed method provides both nodesynchronization and out-of-lock detection by processing, in an optimumway, the receiver's hard decisions: this involves syndrome (paritycheck) sequence computations. Computer simulations show goodperformance, even at low E_b/N_o values (0 dB -2.3dB). This has also been verified experimentally by measurements on a 300Mb/s QPSK modem for satellite communication