Code Excited Linear Prediction(CELP) can provide high voice quality at low bit rates,but it has high computational complexity.Adaptive code-book search plays an important role in most CELP by replacing long-term prediction.In this paper a new adaptive code-book search algorithm is applied for the conventional algorithm of 4.8 kbp FS1016 and the new algorithm can significantly simplify the computation of code-book search.

To reduce error codes between the receiver and the transmitter and to achieve credible transmission performance of underwater digital speech communication system, low density parity check code (LDPC) is introduced to underwater digital speech communication system. Based on the characteristics of the system, (864,432) LDPC code with code rate 1/2, row weight 6, column weight 3 is selected. We also compare the LDPC code with Turbo code with 1/2 code rate. The experiment results show that digital speech signal transmission is reliable if signal to noise is more than 1.5dB in the underwater digital speech communication system.

methods

Fast search algorithm of adaptive code-book for speech coding

Performance analysis of underwater digital speech communication system based on LDPC codes

This paper presents an 8Kbit/s speech coding algorithm whose delay is 2.5ms on the base of G.728 algorithm to reduce coding rate. Adaptive codebook structure is introduced in the proposed algorithm, which is composed of the recent excitation. The algorithm uses double codebook structure which contains adaptive codebook and normalized fixed codebook. In codebook searching, the algorithm detects backward pitch, and then searches the adaptive codebook subtly round the pitch period T. After searching 64 adaptive code words, 8 gains, 256 fixed code words and 8 gains, the best excitation is obtained. Testing with the average segment SNR and Perceptual Evaluation of Speech Quality (PESQ), the improved algorithm is close to G.728 in speech coding quality. And it achieves desirable balance in coding rate, delay time and coding quality.

8Kbit/s LD-aCELP Speech Coding with Backward Pitch Detection

Due to the limitations of weather effects in the terrestrial environment, underwater communication has been chosen as a method of high efficiency and security. It has been emerged as a promising technique due to low power consumption, compact size and better data rate. Despite of the benefits it offers, this technique has various lagging effects like it has high bit error rate, battery power and bandwidth limitation and many more which are discussed in this paper and the means to combat those limitations have also been discussed.

background

/pdf/under-water-environment-a-brief-of-explored-work-and-future-2f68tqkeom.pdf

Under Water Environment: a Brief of Explored Work and Future Scope

LD-aCELP algorithm has 2.5ms delay and speech coding rate is 8Kbit/s. The adaptive codebook and backward pitch detection is used. LDaCELP depends on the Levinson-Durbin(L-D)algorithm to update gain filter coefficients. Because quantizer has not existed at optimizing gain filter, the quantization SNR can not be used to evaluate its performance. We use a new scheme to estimate SNR so that the gain predictor can be separately optimized with the quantizer. In this paper, using this scheme L-D method is replaced by three different methods which are the weighted L-S recursive filter, the finite memory recursive filter and the BP neural network, respectively. Experiments showing, they are all very effective to improve gain filter performance. The weighted L-S algorithm has the best effect, which is accordant with real speech coding. Its average segment SNR is higher than LD-aCELP about 0.720dB.

Fast search algorithm of adaptive code-book for speech coding

Citations

Performance analysis of underwater digital speech communication system based on LDPC codes

8Kbit/s LD-aCELP Speech Coding with Backward Pitch Detection

Under Water Environment: a Brief of Explored Work and Future Scope

Improving LD-aCELP's gain filter

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