6,481 research outputs found
Further Progress on the GM-MDS Conjecture for Reed-Solomon Codes
Designing good error correcting codes whose generator matrix has a support
constraint, i.e., one for which only certain entries of the generator matrix
are allowed to be non-zero, has found many recent applications, including in
distributed coding and storage, multiple access networks, and weakly secure
data exchange. The dual problem, where the parity check matrix has a support
constraint, comes up in the design of locally repairable codes. The central
problem here is to design codes with the largest possible minimum distance,
subject to the given support constraint on the generator matrix. An upper bound
on the minimum distance can be obtained through a set of singleton bounds,
which can be alternatively thought of as a cut-set bound. Furthermore, it is
well known that, if the field size is large enough, any random generator matrix
obeying the support constraint will achieve the maximum minimum distance with
high probability. Since random codes are not easy to decode, structured codes
with efficient decoders, e.g., Reed-Solomon codes, are much more desirable. The
GM-MDS conjecture of Dau et al states that the maximum minimum distance over
all codes satisfying the generator matrix support constraint can be obtained by
a Reed Solomon code. If true, this would have significant consequences. The
conjecture has been proven for several special case: when the dimension of the
code k is less than or equal to five, when the number of distinct support sets
on the rows of the generator matrix m, say, is less than or equal to three, or
when the generator matrix is sparsest and balanced. In this paper, we report on
further progress on the GM-MDS conjecture. In particular, we show that the
conjecture is true for all m less than equal to six. This generalizes all
previous known results (except for the sparsest and balanced case, which is a
very special support constraint).Comment: Submitted to ISIT 201
Improving Distributed Gradient Descent Using Reed-Solomon Codes
Today's massively-sized datasets have made it necessary to often perform
computations on them in a distributed manner. In principle, a computational
task is divided into subtasks which are distributed over a cluster operated by
a taskmaster. One issue faced in practice is the delay incurred due to the
presence of slow machines, known as \emph{stragglers}. Several schemes,
including those based on replication, have been proposed in the literature to
mitigate the effects of stragglers and more recently, those inspired by coding
theory have begun to gain traction. In this work, we consider a distributed
gradient descent setting suitable for a wide class of machine learning
problems. We adapt the framework of Tandon et al. (arXiv:1612.03301) and
present a deterministic scheme that, for a prescribed per-machine computational
effort, recovers the gradient from the least number of machines
theoretically permissible, via an decoding algorithm. We also provide
a theoretical delay model which can be used to minimize the expected waiting
time per computation by optimally choosing the parameters of the scheme.
Finally, we supplement our theoretical findings with numerical results that
demonstrate the efficacy of the method and its advantages over competing
schemes
Reed-Solomon codes over small fields with constrained generator matrices
We give constructions of some special cases of Reed-Solomon codes
over finite fields of size at least and whose generator matrices have
constrained support. Furthermore, we consider a generalisation of the GM-MDS
conjecture proposed by Lovett in 2018. We show that Lovett's conjecture is
false in general and we specify when the conjecture is true.Comment: 21 page
Gabidulin Codes with Support Constrained Generator Matrices
Gabidulin codes are the first general construction of linear codes that are
maximum rank distant (MRD). They have found applications in linear network
coding, for example, when the transmitter and receiver are oblivious to the
inner workings and topology of the network (the so-called incoherent regime).
The reason is that Gabidulin codes can be used to map information to linear
subspaces, which in the absence of errors cannot be altered by linear
operations, and in the presence of errors can be corrected if the subspace is
perturbed by a small rank. Furthermore, in distributed coding and distributed
systems, one is led to the design of error correcting codes whose generator
matrix must satisfy a given support constraint. In this paper, we give
necessary and sufficient conditions on the support of the generator matrix that
guarantees the existence of Gabidulin codes and general MRD codes. When the
rate of the code is not very high, this is achieved with the same field size
necessary for Gabidulin codes with no support constraint. When these conditions
are not satisfied, we characterize the largest possible rank distance under the
support constraints and show that they can be achieved by subcodes of Gabidulin
codes. The necessary and sufficient conditions are identical to those that
appear for MDS codes which were recently proven by Yildiz et al. and Lovett in
the context of settling the GM-MDS conjecture
Coding with Constraints: Minimum Distance Bounds and Systematic Constructions
We examine an error-correcting coding framework in which each coded symbol is
constrained to be a function of a fixed subset of the message symbols. With an
eye toward distributed storage applications, we seek to design systematic codes
with good minimum distance that can be decoded efficiently. On this note, we
provide theoretical bounds on the minimum distance of such a code based on the
coded symbol constraints. We refine these bounds in the case where we demand a
systematic linear code. Finally, we provide conditions under which each of
these bounds can be achieved by choosing our code to be a subcode of a
Reed-Solomon code, allowing for efficient decoding. This problem has been
considered in multisource multicast network error correction. The problem setup
is also reminiscent of locally repairable codes.Comment: Submitted to ISIT 201
RS + LDPC-Staircase Codes for the Erasure Channel: Standards, Usage and Performance
Application-Level Forward Erasure Correction (AL-FEC) codes are a key element of telecommunication systems. They are used to recover from packet losses when retransmission are not feasible and to optimize the large scale distribution of contents. In this paper we introduce Reed-Solomon/LDPCStaircase codes, two complementary AL-FEC codes that have recently been recognized as superior to Raptor codes in the context of the 3GPP-eMBMS call for technology [1]. After a brief introduction to the codes, we explain how to design high performance codecs which is a key aspect when targeting embedded systems with limited CPU/battery capacity. Finally we present the performances of these codes in terms of erasure correction capabilities and encoding/decoding speed, taking advantage of the 3GPP-eMBMS results where they have been ranked first
A new method for constructing small-bias spaces from Hermitian codes
We propose a new method for constructing small-bias spaces through a
combination of Hermitian codes. For a class of parameters our multisets are
much faster to construct than what can be achieved by use of the traditional
algebraic geometric code construction. So, if speed is important, our
construction is competitive with all other known constructions in that region.
And if speed is not a matter of interest the small-bias spaces of the present
paper still perform better than the ones related to norm-trace codes reported
in [12]
- …