16 research outputs found
Enhanced 3-D OCDMA code family using asymmetric run length constraints
Abstract : This paper suggests an enhanced performance of the 3-D optical code division multiple access (OCDMA) codes, a space/wavelength/time spreading family of codes. The initial codes are in the format wavelength hopping/time sequence (WH/TS), selected according to their performance requirements and the TS sequence is constructed to achieve a linear space- time complexity. The asymmetric run length constraints are introduced in that regard, such that the positive bit positions align with the encoder/decoder frequency spacing pattern, yielding a 3-D WH/WS/TS. The selected 2-D OCDMA codes are one- coincidence frequency hopping codes (OCFHC) and optical orthogonal codes (OOC). As a time sequence code, the OOC code length is extended with a code rate of 0.04. The complexity and the bit error rate (BER) are herein given and compared with previous work. The results of the performance show not only an improvement in the number of simultaneous users due to the code length extension, but better correlation properties and hence a better signal-to-noise ratio
Design of Geometric Molecular Bonds
An example of a nonspecific molecular bond is the affinity of any positive
charge for any negative charge (like-unlike), or of nonpolar material for
itself when in aqueous solution (like-like). This contrasts specific bonds such
as the affinity of the DNA base A for T, but not for C, G, or another A. Recent
experimental breakthroughs in DNA nanotechnology demonstrate that a particular
nonspecific like-like bond ("blunt-end DNA stacking" that occurs between the
ends of any pair of DNA double-helices) can be used to create specific
"macrobonds" by careful geometric arrangement of many nonspecific blunt ends,
motivating the need for sets of macrobonds that are orthogonal: two macrobonds
not intended to bind should have relatively low binding strength, even when
misaligned.
To address this need, we introduce geometric orthogonal codes that abstractly
model the engineered DNA macrobonds as two-dimensional binary codewords. While
motivated by completely different applications, geometric orthogonal codes
share similar features to the optical orthogonal codes studied by Chung,
Salehi, and Wei. The main technical difference is the importance of 2D geometry
in defining codeword orthogonality.Comment: Accepted to appear in IEEE Transactions on Molecular, Biological, and
Multi-Scale Communication
Partitionable sets, almost partitionable sets and their applications
This paper introduces almost partitionable sets to generalize the known
concept of partitionable sets. These notions provide a unified frame to
construct -cyclic patterned starter whist tournaments and cyclic
balanced sampling plans excluding contiguous units. The existences of
partitionable sets and almost partitionable sets are investigated. As an
application, a large number of maximum or maximal optical orthogonal codes are
constructed. These maximal optical orthogonal codes fail to be maximum for just
one codeword