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Reduction of Signal Power Consumption in a Digital Communication using Convolutional Code

Reduction of Signal Power Consumption in a Digital Communication using Convolutional Code

For code rate 1/4; constraint length 4 and frame size 2000 was set. Convolutional encoding performed and random errors were added in the encoded data. Viterbi decoder was used for decoding the message and BER was calculated. In the Matlab code for selecting trellis all octal values from 0 to 17 cannot be taken because some values do not make connections at adder. The values of generator polynomials must be selected so that at least one connection should be between shift register and adder. For this value 17 was set fix and other values of a, b, c were taken from 1 to 17. For each combination of generator polynomial BER was calculated. For these combinations the results were stored in excel sheet and the final optimal results are given in Table 4.
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Blind recovery of k/n rate convolutional encoders in a noisy environment

Blind recovery of k/n rate convolutional encoders in a noisy environment

communication system. To meet the new constraints of data rate or reliability, new coding schemes are currently being developed. Therefore, digital communication systems are in perpetual evolution and it is becoming very difficult to remain compatible with all standards used. A cognitive radio system seems to provide an interesting solution to this problem: the conception of an intelligent receiver able to adapt itself to a specific transmission context. This article presents a new algorithm dedicated to the blind recognition of convolutional encoders in the general k/n rate case. After a brief recall of convolutional code and dual code properties, a new iterative method dedicated to the blind estimation of convolutional encoders in a noisy context is developed. Finally, case studies are presented to illustrate the performances of our blind identification method.
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Hybrid ARQ type I based on convolutional code

Hybrid ARQ type I based on convolutional code

At the receiver, the signal will be demodulated and decoded by Viterbi decoder in order to recover the original message. The bit error rate (BER) is calculated by comparing the decoded data with the original data. Then, CRC detector is used for detecting errors. At the receiving end, the additional bits are used to check if the message needs retransmission. If the receiver detects that there are errors in the received bit stream, the receiver asks the sender to retransmit the data. Negative acknowledgement (NACK) sends to the transmitter to request for retransmission of the previous data. The positive acknowledgment (ACK) sends where there are no errors being detected.
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Performance Improvement of Coded OFDM Communication System in AWGN Channel

Performance Improvement of Coded OFDM Communication System in AWGN Channel

Fig 12 examines the performance of the punctured convolutional code with different rates. It appears that, for the punctured convolutional code with rate 2/3, the rate increases but the performance degrades. For the other curves, as the rate approximately remain constant its error correcting capability still fixed and its performance as the case of the original convolutional code, and its benefit is to save some decoding time and complexity by saving or removing only a small number of bits that out from the encoder. So, the punctured convolutional code adjusted to make a balance between its advantage and disadvantage, to have the same performance with less complexity. Finally, this technique can be adjusted according to the application requirements.
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Design And Implementation Of Coding Techniques For Communication Systems Using Viterbi Algorithm

Design And Implementation Of Coding Techniques For Communication Systems Using Viterbi Algorithm

used to calculate the redundant bits and that for each data bit an additional redundant bit is added. Before the information bits are encoded, four bits are added at the end of the information bits. These bits are all set to zero and are used to reset the convolutional encoder to its initial state. Figure 2.1 shows the complete convolutional coding process for the full rate speech encoder. After the speech data passes through the parity encoder and the convolutional encoder, some of the bits have double protection, some have only a convolutional code protection, and some have no error protection. Good results were still obtained from this peculiar combination of error protection codes because the particular bits which were used for each type of error protection were carefully selected. Researchers discovered that some of the data bits produced by the full rate speech coder were much more important to perceptually good speech quality by testing many different digitally coded speech samples. The different bits have a particular role in the speech coding processing, and have different priority for various reasons. For example, any bit which comes from the most significant bit position of a number is clearly more important to the accuracy of the result than a bit from the least significant bit position.
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Comparison Study between 1/2 Rate And 2/3 Rate Convolutional Encoder with Viterbi Decoder

Comparison Study between 1/2 Rate And 2/3 Rate Convolutional Encoder with Viterbi Decoder

Lin et al [7] employs the combination of both FEC and ARQ systems in order to attain an excellent reliability as exhibited by ARQ system and high throughput as also exhibited by FEC systems. With the HARQ bringing together these two properties of FEC and ARQ, the shortcomings experienced when either of the codes is used independently are overcome. Unlike ARQ system which discards signals that were previously received due to the presence of error, HARQ is rather suggested to improve the performance of the signal by adding all the received signals together so as to decode the message transmitted. The main aim of Convolutional Code (CC) is to make available an efficient and reliable error correcting capability over an impairment channel, in the presence of a physically implementable decoder, to complement the success of J. A. Viterbi as proposed in 1967 [8], when he developed a decoding algorithm for convolutional codes. Though the Viterbi algorithm was relatively simple, it still met the criteria of exhibiting behaviour almost like that of a Maximum Likelihood Decoding (MLD) in practical decoders [9]. This Viterbi algorithm invention opened doors for new developments in convolutional codes as more factual research and advancement followed suit since then, which links convolutional coding with Viterbi decoding. Three types of CC exists which are Automatic Repeat request (ARQ), Forward Error Correction (FEC), and Hybrid Automatic Repeat ReQuest (HARQ).
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Adaptive Power Saving Receiver for DVB H Exploiting Adaptive Modulation and Coding

Adaptive Power Saving Receiver for DVB H Exploiting Adaptive Modulation and Coding

For example, the proposed power saving AM scheme employing two modulation techniques (QPSK and 16-Q- AM) is depicted in Figure 4. This scheme assumes port- able reception (i.e. v=3km/hr, thus channel is quasi- stationary over the period of one super frame). Hence, an adaptation rate of super frame is adopted. Furthermore, 1/2 rate convolutional code is employed in order to main- tain reliable performance in bad SNR conditions. Each transmitted super frame is arranged such that higher mo- dulation symbols (in this example 16-QAM symbols) are transmitted first followed by lower modulation symbols (in this example QPSK symbols). The selected bits are chosen according to the pre-defined selection patterns summarized in Table 6. Assume the receiver decides that the 16-QAM is sufficient to meet the target BER. Then, the receiver will receive 136 instead of 272 OFDM sym- bols. This translates into a power saving of 50% compa- red to the worst case of receiving the whole super frame. 3.2.3. Power Saving Potential
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1.
													Design and analysis of bch-rsc concatenated system with qpsk modulation technique in wireless communication

1. Design and analysis of bch-rsc concatenated system with qpsk modulation technique in wireless communication

According to Shannon’s theorem, bit error rate (BER) performance is typically improved by choosing longer and more complex codes [1]. But with the increase in block length, decoding complexity increases exponentially. Since then efforts have been made for designing good codes that approach the near channel capacity limitation with moderate complexity. Forney in 1966 first introduced the idea of concatenated codes [2]. As per Forney, concatenation is a method of building long codes out of shorter ones in order to resolve the problem of decoding complexity by breaking the required computation into manageable segments according to the divide and conquer strategy. In 1989, concatenation of multiple convolutional codes was introduced [3], and was used with Soft Output Viterbi Algorithm (SOVA). A recent landmark development in channel coding is Turbo codes, in particularly Parallel Concatenated Convolutional Codes (PCCC), by Berrou, et.al. in 1993 with simple iterative decoding technique based on the Maximum A Posteriori (MAP) algorithm with Soft-In Soft-Out [4]. It was shown that the performance of Turbo code, in terms of Bit Error Rate (BER), is very close to Shannon’s limit. The concatenation of convolutional codes was examined further in which turbo code namely Serially Concatenated Convolutional Code (SCCC) was introduced & it was shown that SCCC has better performance than PCCC [5]. An iterative decoding approach to SCCC’s was introduced in [6]. The iterative decoding method provides a significant increase in performance over a single iteration and in some cases approaches the theoretical limit. Through iterative decoding scheme, performance in terms of BER is enhanced, but at the expense of complexity of the system. However, the convolutional codes suffered from the problem of burst errors [7] & Reed Solomon codes suffered from problem of random errors [8]. To compensate this problem, a new concatenated scheme was proposed in which a concatenation of a Reed-Solomon (RS) code and a Recursive systematic convolutional code (RSC) codes was used & it was shown that RS-RSC concatenated codes have good performance than RSC itself [9].
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Channel Encoding Security Via Puncturing and Pruning

Channel Encoding Security Via Puncturing and Pruning

The security in channel encoder can be improved by puncturing and trellis pruning. The constituent encoders are randomly punctured to produce codes of higher rate and poor performance for specific channel conditions. In addition with secret trellis pruning which increases performance allows legitimate users to experience a low bit error rate. In that the key defines how pruning is applied on the trellis of a mother convolutional code, this results into a secret pruned trellis that legitimate users are using to perform decoding , in contrast to the eaves dropper that employed the full mother trellis diagram. The minimum pruning rate guaranteeing the desired reliability levels. However, security requirements may impose various constraints on , as pruning is performed in a secret fashion. The complexity of cryptanalytic attack depend on , which needs to be large enough to allow for adequate security. The EXIT chart has been presented as an engineering tool for the design of iterative decoding schemes. we have presented the extrinsic information transfer characteristics based on mutual information to describe the flow of extrinsic information through the soft in/soft out constituent decoders.
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Analysis the effect of processing gain on 
		optical coded IDMA at minimum loss using random and tree inter leaver

Analysis the effect of processing gain on optical coded IDMA at minimum loss using random and tree inter leaver

1553nm and optical detector APD having gain 1000, efficiency 0.85, and shape of pulse is Gaussian. The performance of OIDMA system may be upgraded by selecting the proper inter-leaver mechanism. In the system, random inter-leaver and tree inter-leaver are used. Random inter-leaver is simple in generation and it requires a lot of memory. In figure 5 the graph is plotted for bit error rate versus number of users having convolutional code rate (1,3) O-IDMA using random and tree inter- leaver with spreading length 16 and data length 512.In figure 6the graph is plotted for bit error rate versus number of users having convolutional code rate (1,3) O- IDMA using random and tree inter-leaver with spreading length 16 and data length 1024. In Figure-7 the graph is plotted for bit error rate versus number of users having convolutional code rate (1,3) O-IDMA using random and tree inter-leaver with spreading length 32 and data length 512. In Figure-8 the graph is plotted for bit error rate versus number of users having convolutional code rate (1,3) O-IDMA using random and tree inter-leaver with spreading length 32 and data length 1024.
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IMPLEMENTATION OF VITERBI DECODER WITH VARIABLE CODE RATE

IMPLEMENTATION OF VITERBI DECODER WITH VARIABLE CODE RATE

Convolution codes offer an alternative to block codes for transmission over a noisy channel. Convolution coding can be applied to a continuous input stream (which cannot be done with block codes), as well as blocks of data. The overall block diagram of this paper is shown in the fig. 1. The message bits are generated and they are sent to the crypto system and then the decoded output is obtained. The type of crypto system used is Convolution Encoder and Viterbi Decoder. The Convolutional encoder encodes the message and then the encoded bits are generated. The bits which are encoded are again sent to the Viterbi Decoder and then the A Viterbi decoder uses the Viterbi algorithm for decoding a bitstream but here we are using this viterbi decoder for decoding of continuous bit stream that has been encoded using Forward error correction based on a Convolution code. various type of decoders are used for decoding of Convolutional code but viterbi decoder is the best way to decode Convolutional code and it will give the error free original input at the receiver compared to other decoders.
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PERFORMANCE EVALUATION OF WIMAX SYSTEM USING CONVOLUTIONAL PRODUCT CODE (CPC) A. Ebian, M. Shokair, and K. H. Awadalla

PERFORMANCE EVALUATION OF WIMAX SYSTEM USING CONVOLUTIONAL PRODUCT CODE (CPC) A. Ebian, M. Shokair, and K. H. Awadalla

CPC is a new coding method in which the information bits are placed into two dimensions (2D) matrix. The rows and the columns are encoded separately by using recursive systematic convolutional encoders. Each row of the matrix is encoded using a convolutional code, the same recursive systematic convolutional code is used to encode each row. Once all rows have been encoded, the matrix is sent, if desired, to an interleaver. Our original data matrix dimensions are (n × k), and the encoded data matrix dimensions will be (2n × k). The coded rows matrix is then recoded by column using the same or different recursive systematic convolutional encoder. CPC uses a recursive systematic convolutional code with rate 1/2 and generator polynomials (1, 5/7) octal to encode each row and column. Hence, the overall code rate is 1/4.
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Power Aware Wireless Communication System Design for Body Area Networks

Power Aware Wireless Communication System Design for Body Area Networks

Figure 5 is a performance comparison between the convolutional codes and BCH codes for the implant- to-body surface channel with random errors. It is clear that the higher the SNR, the lower the BER. From Fig- ure 5, we can see that, while SNR > 10dB, convolutional code shows lower BER than BCH code, as convolutional code has higher ability to correct random errors while BCH code is super for burst errors correction. Figure 5 also indicates that conv.(2,1,7) shows the best BER per- formance among the list. It must be noted, that if the data rate is sensitive, BCH (63,51) code must be chosen. Oth- erwise, convolutional code is preferred.
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Interleaved Convolutional Code and Its Viterbi Decoder Architecture

Interleaved Convolutional Code and Its Viterbi Decoder Architecture

By substituting I delays for each delay (or storage) ele- ment in SMM and path memory cell (PMC) of PM, an area- e ffi cient high-speed interleaved Viterbi decoder architecture for interleaved convolutional code is obtained. In this archi- tecture, we can get the throughput rate of the Viterbi decoder as high as the operating clock speed. Since the decoding la- tency of the state-parallel Viterbi decoder with register ex- change path memory structure is the same as the decoding depth, the decoding latency of the interleaved Viterbi de- coder is increased by I × DD. Therefore, the decoding la- tency of proposed architecture is the decoding depth mul- tiplied by the interleaving degree, that is, decoding latency = DD × I. Since interleaved convolutional coding scheme uses extra delay (A), its overall decoding latency becomes DD × I + A.
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High-rate systematic recursive convolutional encoders: minimal trellis and code search

High-rate systematic recursive convolutional encoders: minimal trellis and code search

3.2 Minimal trellis for systematic recursive encoders Originally, minimal trellises have been constructed for codes, not for matrices (or encoders). However, the con- vention that the upper branches refer to the information bit 0 and the lower branches refer to the information bit 1 yields a particular encoding which, in general, is not systematic. We note that the association of solid/dashed branches with codeword bits can not be changed, as any change in this regard would result in a trellis which would no longer represent the convolutional code. However, by enforcing a different convention on the association of the branches to the information bits, only a different encoding for the same code is obtained.
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Novel PAPR Reduction Technique Based On Conventional Partial Transmit Sequence (PTS)

Novel PAPR Reduction Technique Based On Conventional Partial Transmit Sequence (PTS)

The major simu lation para meters of OFDM system have been assumed as follow. FFT point is 64 (i.e . 64- subcarriers), modulation technique is QPSK, , 16-symbols cyclic pre fix, and convolutional code with code rate 1/3. Two channel models have been assumed. AWGN channel and multipath fading channel model (3 paths, frequency selective, Doppler shift=20Hz, Rayle igh). In case of fading channel, ma ximal ratio channel equalizer is assumed. In addition, other para meters inc luding o versampling factor (IF=1 &2), number of iterations (n = 4), c lipping rat io (CR= 6dB), and number of PTS groups (V = 4) have been considered in our simulation. The overall perfo rmance of OFDM system has been evaluated and investigated with and without the proposed PAPR approach (CRCF_ PTS). The simulation results are shown in Fig.5 through Fig.8.
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Implementation Of High Throughput And Area Efficient Hard Decision Viterbi Decoder Using Verilog Hdl

Implementation Of High Throughput And Area Efficient Hard Decision Viterbi Decoder Using Verilog Hdl

Abstract- We propose a pre-computation architecture incorporated with T-algorithm for VD, 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. The Add Compare Select (ACS) unit in path metric unit is designed to reduce the latency of ACS loop delay by using Modified Carry Look Ahead Adder and Digital Comparator. We also consider the design of Survivor Memory Unit (SMU) which combines the advantages of both Register Exchange method and Trace Back method, to reduce the decoding latency and total area of the Viterbi decoder. The proposed Viterbi decoder design is described using Verilog HDL 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 precomputation architecture reduces the power consumption without performance loss, while the degradation in clock speed is negligible.
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Effect of code rate variation on 
		performance of optical convolutionally coded IDMA using random and tree 
		interleavers

Effect of code rate variation on performance of optical convolutionally coded IDMA using random and tree interleavers

Optical interleave division multiple access technology (IDMA) is used in recent communication system to cope up with higher code rate, longer traffic intensity as well as superior interference rejection capability. In present article the qualitative performance of OIDMA is analyzed using random and tree interleavers and optimum selection of interleavers are decided by comparing BER performance of random and tree interleavers. Convolutional coding technique is used here for error correction purpose. Code rate has been changed by varying number of Ex-OR gates in encoder design. The memory elements which decide the constraint length is kept fixed. Code rate variation of fixed constraint length convolutional code has been incorporated in encoder design and effect of qualitative performance of OIDMA has been observed and BER is calculated for different users.
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Cryptanalysis  of  a  code-based  one-time  signature

Cryptanalysis of a code-based one-time signature

Abstract. In 2012, Lyubashevsky introduced a new framework for building lattice-based signature schemes without resorting to any trapdoor (such as GPV [6] or NTRU [7]). The idea is to sample a set of short lattice elements and construct the public key as a Short Integer Solution (SIS for short) instance. Signatures are obtained using a small subset sum of the secret key, hidden by a (large) Gaussian mask. (Information leakage is dealt with using rejection sampling.) Recently, Persichetti proposed an efficient adaptation of this framework to coding theory [12]. In this paper, we show that this adaptation cannot be secure, even for one-time signatures (OTS), due to an inherent difference between bounds in Hamming and Euclidean metrics. The attack consists in rewriting a signature as a noisy syndrome decoding problem, which can be handled efficiently using the extended bit flipping decoding algorithm. We illustrate our results by breaking Persichetti’s OTS scheme built upon this approach [12]: using a single signature, we recover the secret (signing) key in about the same amount of time as required for a couple of signature verifications.
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Performance Improvement by using a Concatenated Levels of Encoding in Wavelet based OFDM Systems

Performance Improvement by using a Concatenated Levels of Encoding in Wavelet based OFDM Systems

Channel encoder used in the communication system to detect and correct the bit errors due to the channel impairments at the receiver. Choosing the encoder/decoder types that detect and correct large numbers of bits enhance the performance of the communication system. The coding algorithm used in this paper is series concatenated hamming /convolutional encoder/decoder levels. This algorithm enhances the system performance by reducing BER at a suitable SNR and low simulation time. The simulation time for the hamming/convolutional algorithm is less than the simulation time for two convolutional cascaded encoders. Increasing the encoder/decoder stages increase the complexity and consume much time in simulation without any effective decreasing in BER. The future scope for this work is applying the proposed channel codding algorithm on the image, voice and video as an input signal.
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