Channel decoding makes use of redundancy in the coded bits. However, any redundancy in the information bitstream can also improve the decoding process. This paper shows that a careful examination of communication stan...
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Channel decoding makes use of redundancy in the coded bits. However, any redundancy in the information bitstream can also improve the decoding process. This paper shows that a careful examination of communication standards (including the headers added by the network layers) exhibits some fields which can be considered as redundant, either based on already received packets, or on the standard. The efficient use of this knowledge in the channel decoding process is denoted as protocol-assisted channel decoding. Assuming perfect synchronization and available channel state information, the proposed method applied on 802.11a PHY and MAC layers provides a substantial link budget improvement without modifying the standard, while the introduction of an additional interleaver provides additional bit error rate improvements.
In this study, we propose a list single-wrong turn (SWT) convolutional decoding algorithm that is computationally less complex than the serial list Viterbi Algorithm (SLVA). We present the simulation results for the p...
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ISBN:
(纸本)0780385233
In this study, we propose a list single-wrong turn (SWT) convolutional decoding algorithm that is computationally less complex than the serial list Viterbi Algorithm (SLVA). We present the simulation results for the performance of the proposed algorithm for Gaussian and Rayleigh fading channels using one of the channel encoding schemes adopted in GSM narrowband adaptive multi-rate (AMR) speech application. It has been observed that the performance of the proposed algorithm is very close to that of the list Viterbi algorithm, when the number of search is limited to best 3 sequences. Moreover, the complexity of the proposed algorithm is considerably less than list VA. Therefore, we believe that the proposed scheme is an attractive alternative to the list VA algorithm.
This paper addresses the problem of estimating a rapidly fading convolutionally coded signal such as might be found in a wireless telephony or data network. We model both the channel gain and the convolutionally coded...
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This paper addresses the problem of estimating a rapidly fading convolutionally coded signal such as might be found in a wireless telephony or data network. We model both the channel gain and the convolutionally coded signal as Markov processes and, thus, the noisy received signal as a hidden Markov process (HMP). Two now-classical methods for estimating finite-state hidden Markov processes are the Viterbi algorithm and the a posteriori probability (APP) filter. A hybrid recursive estimation procedure is derived whereby one hidden process (the encoder state in our application) is estimated using a Viterbi-type (i.e., sequence based) cost and the other (the fading process) using an APP-based cost such as maximum a posteriori probability. The paper presents the new algorithm as applied specifically to this problem but also formulates the problem in a more general setting. The algorithm is derived in this general setting using reference probability methods. Using simulations, performance of the optimal scheme is compared with a number of suboptimal techniques-decision-directed Kalman and HMP predictors and Kalman filter and HMP filter per-survivor processing techniques.
Beginning with an observed document image and a model of how the image has been degraded, Document Image decoding recognizes printed text by attempting to find a most probable path through a hypothesized Markov source...
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ISBN:
(纸本)0819439851
Beginning with an observed document image and a model of how the image has been degraded, Document Image decoding recognizes printed text by attempting to find a most probable path through a hypothesized Markov source. The incorporation of linguistic constraints, which are expressed by a sequential predictive probabilistic language model, can improve recognition accuracy significantly in the case of moderately to severely corrupted documents. Two methods of incorporating linguistic constraints in the best-path search are described analyzed and compared. The first, called the iterated complete path algorithm, involves iteratively rescoring complete paths using conditional language model probability distributions of increasing order, expanding state only as necessary with each iteration. A property of this approach is that it results in a solution that is exactly optimal with respect to the specified source, degradation, and language models;no approximation is necessary. The second approach considered is the Stack algorithm, which is often used in speech recognition and in the decoding of convolutional codes. Experimental results are presented in which text line images that have been corrupted in a known way are recognized using both the ICP and Stack algorithms. This controlled experimental setting preserves many of the essential features and challenges of real text line decoding, while highlighting the important algorithmic issues.
The operating speed of a sequential decoder with stack algorithm is usually limited by the time to search the best node for further extension. This problem can be completely alleviated by using the systolic priority q...
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The operating speed of a sequential decoder with stack algorithm is usually limited by the time to search the best node for further extension. This problem can be completely alleviated by using the systolic priority queue to replace the stack memory. However, the systolic priority queues developed previously are accessible only in the cases when the number of inputs processed is small. This is because the complexity of a queue grows up quickly as the volume of data flowing through it increases. Since the largest amount of data flowing through a systolic priority queue is equal to the number of inputs to this queue, the systolic priority queue is not suitable for a system with many inputs. A modified version of previously developed circuits is proposed. The number of transmission gates required in this circuit is proportional to 3N instead of N-2, where N is the number of inputs. And the total number of control signals is proportional to 3N(2) instead of N-3. But the number of comparators required is proportional to C-2(N+1), as before. This modified circuit can be used in cases where the number of inputs is small (N less than or equal to 8). A new algorithm for the multiple-inputs systolic priority queue (MISPQ) is proposed. By using this algorithm, a MISPQ may be implemented with several smaller queues, each is used to process a part of data in the MISPQ. Since the volume of data flowing through each queue is small, these queues will be simpler. However, some additional circuits should be used for the interactions between queues. A circuit for implementing this algorithm is presented and its complexity is analysed. The number of transmission gates for the MISPQ is proportional to 3N, the number of control signals is proportional to (3N(2)/2), and the number of comparators is proportional to 4C(2)(N/2+1). Thus this new architecture is feasible for large N (e.g. N greater than or equal to 8).
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