20 research outputs found
On the Existence of MDS Codes Over Small Fields With Constrained Generator Matrices
We study the existence over small fields of Maximum Distance Separable (MDS)
codes with generator matrices having specified supports (i.e. having specified
locations of zero entries). This problem unifies and simplifies the problems
posed in recent works of Yan and Sprintson (NetCod'13) on weakly secure
cooperative data exchange, of Halbawi et al. (arxiv'13) on distributed
Reed-Solomon codes for simple multiple access networks, and of Dau et al.
(ISIT'13) on MDS codes with balanced and sparse generator matrices. We
conjecture that there exist such MDS codes as long as , if the specified supports of the generator matrices satisfy the so-called
MDS condition, which can be verified in polynomial time. We propose a
combinatorial approach to tackle the conjecture, and prove that the conjecture
holds for a special case when the sets of zero coordinates of rows of the
generator matrix share with each other (pairwise) at most one common element.
Based on our numerical result, the conjecture is also verified for all . Our approach is based on a novel generalization of the well-known Hall's
marriage theorem, which allows (overlapping) multiple representatives instead
of a single representative for each subset.Comment: 8 page
Weakly Secure MDS Codes for Simple Multiple Access Networks
We consider a simple multiple access network (SMAN), where sources of
unit rates transmit their data to a common sink via relays. Each relay is
connected to the sink and to certain sources. A coding scheme (for the relays)
is weakly secure if a passive adversary who eavesdrops on less than
relay-sink links cannot reconstruct the data from each source. We show that
there exists a weakly secure maximum distance separable (MDS) coding scheme for
the relays if and only if every subset of relays must be collectively
connected to at least sources, for all . Moreover, we
prove that this condition can be verified in polynomial time in and .
Finally, given a SMAN satisfying the aforementioned condition, we provide
another polynomial time algorithm to trim the network until it has a sparsest
set of source-relay links that still supports a weakly secure MDS coding
scheme.Comment: Accepted at ISIT'1
Generalized Reed-Solomon Codes with Sparsest and Balanced Generator Matrices
We prove that for any positive integers and such that , there exists an generalized Reed-Solomon (GRS) code that
has a sparsest and balanced generator matrix (SBGM) over any finite field of
size , where sparsest means that
each row of the generator matrix has the least possible number of nonzeros,
while balanced means that the number of nonzeros in any two columns differ by
at most one. Previous work by Dau et al (ISIT'13) showed that there always
exists an MDS code that has an SBGM over any finite field of size , and Halbawi et al (ISIT'16, ITW'16) showed that there exists
a cyclic Reed-Solomon code (i.e., ) with an SBGM for any prime power
. Hence, this work extends both of the previous results
Balanced Sparsest Generator Matrices for MDS Codes
We show that given and , for sufficiently large, there always
exists an MDS code that has a generator matrix satisfying the
following two conditions: (C1) Sparsest: each row of has Hamming weight ; (C2) Balanced: Hamming weights of the columns of differ from each
other by at most one.Comment: 5 page