Link-Layer Coding for GNSS Navigation Messages

Abstract

In this paper, we face the problem of ensuring reliability of Global Navigation Satellite Systems (GNSSs) in harsh channel conditions, where obstacles and scatter cause long outage events that cannot be counteracted with channel coding only. Our novel approach, stemming from information‐theoretic considerations, is based on link‐layer coding (LLC). LLC allows us to significantly improve the efficiency in terms of time‐to‐first‐fix with respect to current operational GNSSs, which adopt carousel transmission. First, we investigate the maximum theoretical LLC gain under different Land Mobile Satellite channel conditions. Then, some practical LLC coding schemes, namely, fountain codes and a novel low‐density parity‐check plus low‐rate repetition coding, are proposed and tested in realistic single‐satellite and multi‐satellite Land Mobile Satellite scenarios, considering the Galileo I/NAV message as study case. Simulation results show that our designed schemes largely improve on carousel transmission and achieve near‐optimal performance with limited increase in complexity. Also, back‐compatibility of LLC is assessed with respect to present‐time GNSS specifications. © 2018 Institute of Navigation.

Multi-Round Message Scheduling for Fast GNSS Packet Broadcasting

“…, K} from the ground segment; the choice of π s,n is the true subject of the scheduling discussed in the next Section; 2) satellite s transmits packet π s,n ; 3) each receiver in a position x such that v s,n (x) = 1 decodes the packet; 4) if the receiver has already obtained packet π s,n during previous rounds or from another satellite, it discards the packet, otherwise it stores the packet in its buffer; 5) once the receiver has collected all the K packets, it reconstructs message p and waits for a new message. Note that the proposed protocol is compatible with any channel code mechanism, e.g., the Fountain codes used, for instance, in [1], [9], [14]. Moreover, our solution can also be applied without channel coding.…”

“…Algorithm 2 is the proposed strategy for the Maximization of the Average Number of Different Received Packets (MRP), where marp_max solves (1) and round_eval is a function that takes as input the set of received packets at the end of the previous round, u k,n−1 (P n−1 , x), and outputs the coverage and the set of received packets at the end of round n, u k,n ({P n−1 , S n }, x), by using ( 2)- (9).…”

“…In this context, the typical solution is the carousel scheduling strategy [9], where each different packet is scheduled sequentially in time. This solution is currently used for disseminating the almanacs, used to aid the receiver's signal acquisition phase.…”

“…No further link-level solution has been proposed for OS-NMA yet. A fountain code-based solution was also proposed in [9] and compared to the carousel strategy used for dissemination of the I/NAV messages in Galileo [6].…”

A comparison analysis on forward error correction technology: a future perspective for GNSS

“…They introduced several coding methods used in present-day GNSS signals, and then their performance against noise and interference was evaluated based on block error rate. Tarable et al (2018) explored the appropriateness of link layer coding techniques for Galileo I/ NAV messages (Tarable et al, 2018). They found that the use of simple link-layer codes offers a substantial reduction in signal processing time.…”