14 research outputs found
An RLL code design that maximises channel utilisation
Comprehensive (d,k) sequences study is presented, complemented with the design of a new, efficient, Run-Length Limited (RLL) code. The new code belongs to group of constrained coding schemas with a coding rate of R = 2/5 and with the minimum run length between two successive transitions equal to 4. Presented RLL (4, oo) code uses channel capacity highly efficiently, with 98.7% and consequently it achieves a high-density rate of DR = 2.0. It is implying that two bits can be recorded, or transmitted with one transition. Coding techniques based on the presented constraints and the selected coding rate have better efficiency than many other currently used codes for high density optical recording and transmission
Design of efficient constrained codes and parity-check codes for perpendicular magnetic recording channels
Master'sMASTER OF ENGINEERIN
On row-by-row coding for 2-D constraints
A constant-rate encoder--decoder pair is presented for a fairly large family
of two-dimensional (2-D) constraints. Encoding and decoding is done in a
row-by-row manner, and is sliding-block decodable.
Essentially, the 2-D constraint is turned into a set of independent and
relatively simple one-dimensional (1-D) constraints; this is done by dividing
the array into fixed-width vertical strips. Each row in the strip is seen as a
symbol, and a graph presentation of the respective 1-D constraint is
constructed. The maxentropic stationary Markov chain on this graph is next
considered: a perturbed version of the corresponding probability distribution
on the edges of the graph is used in order to build an encoder which operates
in parallel on the strips. This perturbation is found by means of a network
flow, with upper and lower bounds on the flow through the edges.
A key part of the encoder is an enumerative coder for constant-weight binary
words. A fast realization of this coder is shown, using floating-point
arithmetic
Coding for the Optical Channel: the Ghost-Pulse Constraint
We consider a number of constrained coding techniques that can be used to
mitigate a nonlinear effect in the optical fiber channel that causes the
formation of spurious pulses, called ``ghost pulses.'' Specifically, if is a sequence of bits sent across an optical channel, such that
for some (not necessarily all distinct) but , then the ghost-pulse effect causes to change to 1, thereby
creating an error. We design and analyze several coding schemes using binary
and ternary sequences constrained so as to avoid patterns that give rise to
ghost pulses. We also discuss the design of encoders and decoders for these
coding schemes.Comment: 13 pages, 6 figures; accepted for publication in IEEE Transactions on
Information Theor
Multilevel sequences and line codes
M.Ing. (Electrical Engineering)As the demand for high-speed data communications over conventional channels such as coaxial cables and twisted pairs grows, it becomes neccesary to optimize every aspect of the communication system at reasonable cost to meet this demand effectively. The choice of a line code is one of the most important aspects in the design of a communications system, as the line code determines the complexity, and thus also the cost, of several circuits in the system. It has become known in recent years that a multilevel line code is preferable to a binary code in cases where high-speed communications are desired. Apart from ternary codes, not many multilevel codes are available. Some of the existing line codes also suffer from serious drawbacks regarding a lack of complying to input restrictions, small values of efficiency, and great code complexity. In this study, Markov models and values of channel capacity are presented for several classes of restricted multilevel sequences which are thought to be of practical importance in view of the channel input restrictions that these codes satisfy. Different coding methods are used to construct low-complexity encoders and decoders for generating and decoding these sequences with high values of efficiency, good error behaviour and favourable power spectral densitie