Citation
Abstract
Proximity link space communications, such as between a lander and an orbiter, uses the Consultative Committee for Space Data Systems (CCSDS) Proximity-1 space link protocol standard, which specifies a low-density parity-check (LDPC) code of rate 1/2, and a Go-Back-N automatic repeat request (ARQ) protocol in the data link layer. It also includes an optional feedback mechanism by which the receiver can request transmitter changes; this was first used by the Mars Science Laboratory to implement an Adaptive Data Rate (ADR) mechanism based on the received signal quality. If such an ADR mechanism is not used, the Proximity-1 standard can have severely limited throughput due to an inefficient retransmission protocol. In this article, we develop a new adaptive transmissions technology based on Raptor codes for the additive white Gaussian noise channel, with modifications for spacecraft proximity links. In the new design, transfer frames are Raptor encoded, and in place of retransmissions, additional code symbols are generated and transmitted as needed. This new technology matches the coding rate to the instantaneous channel conditions, thereby maximizing the throughput at both high and low signal-to-noise ratio (SNR). By simulation, we show that Raptor codes provide greater throughput than the Proximity-1 (Prox-1) standard operating without ADR over a wide range of SNRs. At high SNR, this scheme improves the throughput by up to 90%, and at low SNR, it provides reliable communication even when the throughput of the Prox-1 standard essentially drops to zero. Our analysis also shows that this Raptor code approach reduces the computational costs for both the encoder and decoder.
Details
- Volume
- 42-224
- Published
- February 15, 2021
- Pages
- 1–24
- File Size
- 935.0 KB