Session
Technical Session XI: Mission Enabling Technologies 2
Abstract
In some cases, a communication session between a satellite and a ground station can be interrupted during the frame reception. Despite the fact that strong FEC (Forward Error Correction) codes such as turbo codes are used to protect frames from errors they are unable to recover the data in the case when the received frame is incomplete. As a result, incomplete frames are lost even if they contain critical mission data. In this paper, we propose a modification to turbo encoding and decoding algorithms which provides an ability to recover incompletely received data frames. The proposed modification causes a negligible rate loss and only a slight increase in encoder and decoder complexity. The proposed algorithm is based on segmentation of the information frame into sub-frames and calculation and insertion of terminations bits after each sub-frame during the encoding process. The inserted termination bits help the ground station decoder to recover the incomplete frames. This modification can be used in any turbo coding/decoding system since it can be realized as a slight adjustment to the maximum a posteriori probability (MAP) decoding algorithm (standard turbo decoder) and hence it does not require any additional hardware. The proposed algorithm has been tested on Consultative Committee for Space Data Systems (CCSDS) turbo codes of rates 1/2 and 1/3 with information frame length of 1784 bits. For incomplete frames which are 1700 bits long the modified decoder provides a 20dB performance gain over the standard turbo encoding/decoding algorithm.
Presentation Slides
Proposed Encoding/Decoding Algorithm to Recover Satellite Uncompleted Received Frames
In some cases, a communication session between a satellite and a ground station can be interrupted during the frame reception. Despite the fact that strong FEC (Forward Error Correction) codes such as turbo codes are used to protect frames from errors they are unable to recover the data in the case when the received frame is incomplete. As a result, incomplete frames are lost even if they contain critical mission data. In this paper, we propose a modification to turbo encoding and decoding algorithms which provides an ability to recover incompletely received data frames. The proposed modification causes a negligible rate loss and only a slight increase in encoder and decoder complexity. The proposed algorithm is based on segmentation of the information frame into sub-frames and calculation and insertion of terminations bits after each sub-frame during the encoding process. The inserted termination bits help the ground station decoder to recover the incomplete frames. This modification can be used in any turbo coding/decoding system since it can be realized as a slight adjustment to the maximum a posteriori probability (MAP) decoding algorithm (standard turbo decoder) and hence it does not require any additional hardware. The proposed algorithm has been tested on Consultative Committee for Space Data Systems (CCSDS) turbo codes of rates 1/2 and 1/3 with information frame length of 1784 bits. For incomplete frames which are 1700 bits long the modified decoder provides a 20dB performance gain over the standard turbo encoding/decoding algorithm.
