Several algorithms have been proposed to avoid the error floor region, such as the concatenation codes that requires high computational demands in addition to high complexity. This paper proposes a technique based on using cascaded BCH and convolutional codes that leads to better error correction performance. Moreover, an adaptive method based on sensing the channel's noise to determine the number of the parity bits that will be added to the used BCH that reduces the consumed bandwidth and the transmitted parity bits is presented. A further enhancement is fulfilled by using parallel processing branches, resulting in reducing the consumed time and speed up the performance. The results show that the proposed code presents a better performance. A high reduction in the number of cycles that will be used in the encoding and decoding compared with the classical method and finally a flexible parity bits method based on the signal-to-noise ratio of the channel that reduced the parity bits which leads to reduce the consumed bandwidth. The MATLAB simulation and the field programmable gate array (FPGA) implementation will be provided in this paper to validate the proposed concept.
This paper aims to improve SHA-512 security without increasing complexity; therefore, we focused on hash functions depending on DNA sequences and chaotic maps. After analysis of 45 various chaotic map types, only 5 types are selected in this proposal—namely, improved logistic, cosine logistic map, logistic sine system, tent sine system, and hybrid. Using DNA features and binary coding technology with complementary rules to hide information is a key challenge. This article proposes improving SHA-512 in two aspects: the modification of original hash buffer values, and the modification of additive constants Kt. This proposal is to make hash buffer values (a, b, c, d, e, f, g, and h) and Kt dependent on one-dimensional discrete chaotic maps and DNA sequences instead of constant. This modification complicates the relationship between the original message and hash value, making it unexpected. The performance of the proposed hash function is tested and analyzed the confusion, diffusion, and distributive and compared with the original SHA-512. The performance of security is analyzed by collision analysis, for which the maximum number of hits is only three, showing that the proposed hash function enhances the security and robustness of SHA-512. The statistical data and experimental analysis indicate that the proposed scheme has good properties and satisfies high-performance requirements for secure hash functions.
In this work, a diversity encoder maps vectors of N modulated symbols to vectors of N diversity symbols using an orthogonal matrix. Each modulated symbol appears in N diversity symbols. An Orthogonal-Frequency-Division-Multiplexing (OFDM) modulator converts the diversity vectors to OFDM symbols. The number of subcarriers in the OFDM symbol equals N. Each diversity symbol modulates one subcarrier; therefore, each modulated symbol is transmitted by N orthogonal subcarriers. The diversity bandwidth of the modulated symbols is N times the subchannel bandwidth. The modulated symbols experience independent fading gains on each subchannel since the diversity bandwidth (OFDM bandwidth) is chosen to be multiple of the coherence bandwidth of the transmission channel. In the receiver, an OFDM demodulator converts back the OFDM symbols to vectors of diversity symbols. The diversity detector maps the diversity vectors to vectors of modulated symbols. The noise samples at the output of the diversity detector are uncorrelated. Maximum likelihood and linear decorrelator detectors are used as diversity detectors. The transmitter and the receiver of this work are implemented using Field-Programable-Gate-Array (FPGA) technology. The performance of the implemented system is the same as the performance of the N channels diversity system with the Maximal-Ratio-Combiner (MRC) receiver.
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