40 research outputs found
New Codes on Graphs Constructed by Connecting Spatially Coupled Chains
A novel code construction based on spatially coupled low-density parity-check
(SC-LDPC) codes is presented. The proposed code ensembles are described by
protographs, comprised of several protograph-based chains characterizing
individual SC-LDPC codes. We demonstrate that code ensembles obtained by
connecting appropriately chosen SC-LDPC code chains at specific points have
improved iterative decoding thresholds compared to those of single SC-LDPC
coupled chains. In addition, it is shown that the improved decoding properties
of the connected ensembles result in reduced decoding complexity required to
achieve a specific bit error probability. The constructed ensembles are also
asymptotically good, in the sense that the minimum distance grows linearly with
the block length. Finally, we show that the improved asymptotic properties of
the connected chain ensembles also translate into improved finite length
performance.Comment: Submitted to IEEE Transactions on Information Theor
Continuous Transmission of Spatially Coupled LDPC Code Chains
We propose a novel encoding/transmission scheme called continuous chain (CC) transmission that is able to improve the finite-length performance of a system using spatially coupled low-density parity-check (SC-LDPC) codes. In CC transmission, instead of transmitting a sequence of independent code words from a terminated SC-LDPC code chain, we connect multiple chains in a layered format, where encoding, transmission, and decoding are performed in a continuous fashion. The connections between chains are created at specific points, chosen to improve the finite-length performance of the code structure under iterative decoding. We describe the design of CC schemes for different SC-LDPC code ensembles constructed from protographs: a (J,K) -regular SC-LDPC code chain, a spatially coupled repeat-accumulate (SC-RA) code, and a spatially coupled accumulate-repeat-jagged-accumulate (SC-ARJA) code. In all cases, significant performance improvements are reported and it is shown that using CC transmission only requires a small increase in decoding complexity and decoding delay with respect to a system employing a single SC-LDPC code chain for transmission.This material is based upon work supported in part by the National Science Foundation under Grant Nos. CCF-1161754 and CCSS-1710920, in part by NSERC Canada, and in part by the Spanish Ministry of Economy and Competitiveness and the Spanish National Research Agency under grants TEC2016-78434-C3-3-R (AEI/FEDER, EU) and Juan de la Cierva Fellowship IJCI-2014-19150
Unsourced Random Access with ThresholdBased Feedback
In this paper we focus on a feedback mechanism for unsourced random access
(URA) communications. We propose an algorithm to construct feedback packets
broadcasted to the users by the base station (BS) as well as the feedback
packet format that allows the users to estimate their channels and infer
positive or negative feedback based on the presented thresholding algorithm. We
demonstrate that the proposed feedback imposes a much smaller complexity burden
on the users compared to the feedback that positively acknowledges all
successful or negatively acknowledges all undecoded users. We also show that
the proposed feedback technique can lead to a substantial reduction in the
packet error rates and signal-to-noise ratios (SNR)s required to support
various numbers of active users in the system
Ordered Reliability Direct Error Pattern Testing Decoding Algorithm
We introduce a novel universal soft-decision decoding algorithm for binary
block codes called ordered reliability direct error pattern testing (ORDEPT).
Our results, obtained for a variety of popular short high-rate codes,
demonstrate that ORDEPT outperforms state-of-the-art decoding algorithms of
comparable complexity such as ordered reliability bits guessing random additive
noise decoding (ORBGRAND) in terms of the decoding error probability and
latency. The improvements carry on to the iterative decoding of product codes
and convolutional product-like codes, where we present a new adaptive decoding
algorithm and demonstrate the ability of ORDEPT to efficiently find multiple
candidate codewords to produce soft output