33,301 research outputs found
Precise Descriptions of VLC Synchronization with CSP Semantic Models
Variable length codes (VLC) have found widespread applications due to their inherent coding efficiency. However, encoder-decoder synchronization becomes critically important for VLC to operate properly. Traditional treebased techniques lack the scalability to analyse the synchronization behaviours of VLC, and simulation techniques are typically used instead for large code sets. Building on an initial paper in which we first described an application of CSP to this domain, we present further advances in this paper. The contributions of this paper are twofold. First, we describe a novel application of the CSP stable failure model to completely describe the VLC synchronization mechanisms. Consequently, we concisely characterize bit patterns that can bring about rapid synchronization. The overall goal is to advance our understanding in this important area of research through an established formal description technique originally developed and used within the computing research community
Synchronization recovery and state model reduction for soft decoding of variable length codes
Variable length codes exhibit de-synchronization problems when transmitted
over noisy channels. Trellis decoding techniques based on Maximum A Posteriori
(MAP) estimators are often used to minimize the error rate on the estimated
sequence. If the number of symbols and/or bits transmitted are known by the
decoder, termination constraints can be incorporated in the decoding process.
All the paths in the trellis which do not lead to a valid sequence length are
suppressed. This paper presents an analytic method to assess the expected error
resilience of a VLC when trellis decoding with a sequence length constraint is
used. The approach is based on the computation, for a given code, of the amount
of information brought by the constraint. It is then shown that this quantity
as well as the probability that the VLC decoder does not re-synchronize in a
strict sense, are not significantly altered by appropriate trellis states
aggregation. This proves that the performance obtained by running a
length-constrained Viterbi decoder on aggregated state models approaches the
one obtained with the bit/symbol trellis, with a significantly reduced
complexity. It is then shown that the complexity can be further decreased by
projecting the state model on two state models of reduced size
Fast antijamming timing acquisition using multilayer synchronization sequence
Pseudonoise (PN) sequences are widely used as preamble sequences to establish timing synchronization in military wireless communication systems. At the receiver, searching and detection techniques, such as the full parallel search (FPS) and the serial search (SS), are usually adopted to acquire correct timing position. However, the synchronization sequence has to be very long to combat jamming that reduces the signal-to-noise ratio (SNR) to an extremely low level. In this adverse scenario, the FPS scheme becomes too complex to implement, whereas the SS method suffers from the drawback of long mean acquisition time (MAT). In this paper, a fast timing acquisition method is proposed, using the multilayer synchronization sequence based on cyclical codes. Specifically, the transmitted preamble is the Kronecker product of Bose–Chaudhuri-Hocquenghem (BCH) codewords and PN sequences. At the receiver, the cyclical nature of BCH codes is exploited to test only a part of the entire sequence, resulting in shorter acquisition time. The algorithm is evaluated using the metrics of MAT and detection probability (DP). Theoretical expressions of MAT and DP are derived from the constant false-alarm rate (CFAR) criterion. Theoretical analysis and simulation results show that our proposed scheme dramatically reduces the acquisition time while achieving similar DP performance and maintaining a reasonably low real-time hardware implementation complexity, in comparison with the SS schem
Secrecy Through Synchronization Errors
In this paper, we propose a transmission scheme that achieves information
theoretic security, without making assumptions on the eavesdropper's channel.
This is achieved by a transmitter that deliberately introduces synchronization
errors (insertions and/or deletions) based on a shared source of randomness.
The intended receiver, having access to the same shared source of randomness as
the transmitter, can resynchronize the received sequence. On the other hand,
the eavesdropper's channel remains a synchronization error channel. We prove a
secrecy capacity theorem, provide a lower bound on the secrecy capacity, and
propose numerical methods to evaluate it.Comment: 5 pages, 6 figures, submitted to ISIT 201
Guess & Check Codes for Deletions and Synchronization
We consider the problem of constructing codes that can correct
deletions occurring in an arbitrary binary string of length bits.
Varshamov-Tenengolts (VT) codes can correct all possible single deletions
with an asymptotically optimal redundancy. Finding similar codes
for deletions is an open problem. We propose a new family of
codes, that we call Guess & Check (GC) codes, that can correct, with high
probability, a constant number of deletions occurring at uniformly
random positions within an arbitrary string. The GC codes are based on MDS
codes and have an asymptotically optimal redundancy that is . We provide deterministic polynomial time encoding and decoding schemes for
these codes. We also describe the applications of GC codes to file
synchronization.Comment: Accepted in ISIT 201
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