Title: A Modified Viterbi Decoder for Joint Data-Recovery and Cycle-Slip Correction
Author(s): James T. Curran,
Published in: Proceedings of the 29th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2016)
September 12 - 16, 2016
Oregon Convention Center
Portland, Oregon
Pages: 257 - 264
Cite this article: Curran, James T., "A Modified Viterbi Decoder for Joint Data-Recovery and Cycle-Slip Correction," Proceedings of the 29th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2016), Portland, Oregon, September 2016, pp. 257-264.
Full Paper: ION Members/Non-Members: 1 Download Credit
Sign In
Abstract: This paper presents a novel modification of the traditional Viterbi decoder which performs a joint recovery of the encoded navigation data and the identification and correction of carrier cycle-slips. Many modern GNSS signals employ a BPSK modulation of a convolutional-encoded navigation message, offering appreciable error-correcting capability in the presence of additive noise. However, in many instances, the sources of error experienced by a GNSS receiver are not additive, and include multiplicative factors such as high phase dynamics and cycle-slips. Under such conditions the performance of the traditional Viterbi is sub-optimal. This paper presents a novel modification which provides improved performance under cycle-slippage by introducing a non-binary decoding trellis. Rather than a binary forking at each node, a quaternary decision is made between 0, 1, inverted-0 and inverted-1. The decoder returns both the most likely un-encoded data and a sequence representing the most likely locations of phase-inversions. The result is that the effective coding rate is reduced, providing slightly lower decoding performance under nominal conditions, but with a significant improvement in the presence of sporadic cycle-slips. Moreover, knowledge of the location of likely cycle slips offers a novel means of slip-correction in the carrier phase observable. A detailed description of the algorithm is provided along with performance results of Monte-Carlo simulation and experiments using live Galileo E1B signals.