184 research outputs found
Sphere-constrained ML detection for frequency-selective channels
The maximum-likelihood (ML) sequence detection problem for channels with memory is investigated. The Viterbi algorithm (VA) provides an exact solution. Its computational complexity is linear in the length of the transmitted sequence, but exponential in the channel memory length. On the other hand, the sphere decoding (SD) algorithm also solves the ML detection problem exactly, and has expected complexity which is a low-degree polynomial (often cubic) in the length of the transmitted sequence over a wide range of signal-to-noise ratios. We combine the sphere-constrained search strategy of SD with the dynamic programming principles of the VA. The resulting algorithm has the worst-case complexity determined by the VA, but often significantly lower expected complexity
Improved Sequential MAP estimation of CABAC encoded data with objective adjustment of the complexity/efficiency tradeoff
International audienceThis paper presents an efficient MAP estimator for the joint source-channel decoding of data encoded with a context adaptive binary arithmetic coder (CABAC). The decoding process is compatible with realistic implementations of CABAC in standards like H.264, i.e., handling adaptive probabilities, context modeling and integer arithmetic coding. Soft decoding is obtained using an improved sequential decoding technique, which allows to obtain various tradeoffs between complexity and efficiency. The algorithms are simulated in a context reminiscent of H264. Error detection is realized by exploiting on one side the properties of the binarization scheme and on the other side the redundancy left in the code string. As a result, the CABAC compression efficiency is preserved and no additional redundancy is introduced in the bit stream. Simulation results outline the efficiency of the proposed techniques for encoded data sent over AWGN and UMTS-OFDM channels
Decoding Strategies at the Relay with Physical-Layer Network Coding
Cataloged from PDF version of article.A two-way relay channel is considered where two
users exchange information via a common relay in two transmission
phases using physical-layer network coding (PNC). We consider
an optimal decoding strategy at the relay to decode the network
coded sequence during the first transmission phase, which is
approximately implemented using a list decoding (LD) algorithm.
The algorithm jointly decodes the codewords transmitted by
the two users and sorts the L most likely pair of sequences
in the order of decreasing a-posteriori probabilities, based on
which, estimates of the most likely network coded sequences and
the decoding results are obtained. Using several examples, it is
observed that a lower complexity alternative, that jointly decodes
the two transmitted codewords, has a performance similar to the
LD based decoding and offers a near-optimal performance in
terms of the error rates corresponding to the XOR of the two
decoded sequences. To analyze the error rate at the relay, an
analytical approximation of the word-error rate using the joint
decoding (JD) scheme is evaluated over an AWGN channel using
an approach that remains valid for the general case of two users
adopting different codebooks and using different power levels.
We further extend our study to frequency selective channels
where two decoding approaches at the relay are investigated,
namely; a trellis based joint channel detector/physical-layer
network coded sequence decoder (JCD/PNCD) which is shown
to offer a near-optimal performance, and a reduced complexity
channel detection based on a linear receiver with minimum mean
squared error (MMSE) criterion which is particularly useful
where the number of channel taps is large
Sequential decoding of trellis codes through ISI channels
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (leaves 56-57).by Patrick M. Maurer.M.S
DESIGN OF HIGH SPEED &LOW POWER VITERBI DECODER FOR TREELIS CODED MODULATION(TCM)
High-speed, low-power design of Viterbi decoders for trellis coded modulation (TCM) systems is presented in this paper. It is well known that the Viterbi decoder (VD) is the dominant module determining the overall power consumption of trellis coded modulation decoders. We propose a pre-computation architecture incorporated with T-algorithm for Viterbi decoder, which can effectively reduce the power consumption without degrading the decoding speed much. A general solution to derive the optimal pre-computation steps is also given in the paper. Implementation result of a VD for a rate-3/4 convolutional code used in a TCM system shows that compared with the full trellis VD, the pre-computation architecture reduces the power consumption by as much as 70% without performance loss, while the degradation in clock speed is negligible
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