Modified Turbo Code Research Articles

An efficient VoLTE covert timing channel for 5 G networks: RDCTC

Covert Channels are necessary to protect the privacy of individuals as well as to obtain confidentiality to governmental and military agencies. A novel covert timing channel is proposed with three main improvements over the existing ones: Reorder Density (RD) metric-based packet reordering that reduces exposure, introducing Modified Turbo Code (MTC) for efficient encoding, and Discrete Haar Wavelet Transform (DHWT) that increases channel reliability. A threat model is proposed and shown to be inefficient to effectively meet covert channel properties against network jitter, noise, and curious attackers that try to identify a channel exists. Run and test is applied to investigate randomness of the proposed covert channel. The proposed covert channel is adoptable to 5 G VoLTE networks. These proposed strategies significantly improve the robustness while also minimizing the detectability of covert channels in VoLTE.

Low-Power VLSI Implementation of Novel Hybrid Adaptive Variable-Rate and Recursive Systematic Convolutional Encoder for Resource Constrained Wireless Communication Systems

In the modern wireless communication system, digital technology has tremendous growth, and all the communication channels are slowly moving towards digital form. Wireless communication has to provide the reliable and efficient transfer of information between transmitter and receiver over a wireless channel. The channel coding technique is the best practical approach to delivering reliable communication for the end-users. Many conventional encoder and decoder units are used as error detection and correction codes in the digital communication system to overcome the multiple transient errors. The proposed convolutional encoder consists of both Recursive Systematic Convolutional (RSC) Encoder and Adaptive Variable-Rate Convolutional (AVRC) encoder. Adaptive Variable-Rate Convolutional encoder improves the bit error rate performance and is more suitable for a power-constrained wireless system to transfer the data. Recursive Systematic Convolutional encoder also reduces the bit error rate and improves the throughput by employing the trellis termination strategy. Here, AVRC encoder ultimately acquires the channel state information and feeds the data into a fixed rate convolutional encoder and rate adaptor followed by a buffer device. A hybrid encoder combines the AVRC encoder and RSC encoder output serially and parallel, producing the solid encoded data for the modulator in the communication system. A modified turbo code is also obtained by placing interleaver between the two encoder units and building the stronger code word for the system. Finally, the conventional encoder system is compared and analyzed with the proposed method regarding the number of LUT’s, gates, clock cycle, slices, area, power, bit error rate, and throughput.

A Novel Architecture of Modified Turbo Codes with an area efficient high speed interleaver

SummaryModified Turbo Codes (MTC) is preferred over conventional Turbo Convolutional Codes (TCC) as they provide nearly the same performance but with the additional benefit of reduced decoding complexity. The Improved Low Complexity Hybrid Turbo Codes (ILCHTC) is a type of MTC, which achieves a Bit Error Rate (BER) performance near to Shannon's limit. This paper presents a high speed novel encoder structure called Enhanced ILCHTC and a high speed low power novel interleaver for the MTC and analyzes its BER performance. From the simulation results, it is observed that BER performance of Enhanced ILCHTC and ILCHTC with proposed interleaver is better and has high degree of error convergence and requires less than 50% of computations than TCC. From the synthesized results, it is observed that the computation time required to shuffle the bits by the proposed interleaver is 7.4% less than the time required by the existing interleaver. In addition, it is observed that the number of logic elements utilized by the proposed interleaver is 95, which is 8% less than the number of logic elements, utilized by the existing interleaver but the tradeoff is power, which is 1.63% more when compared to the existing interleaver. Thus, a high speed area efficient interleaver is proposed along with a novel encoder structure.

Performance enhancement of modified turbo codes with two-stage interleavers

Low complexity modified turbo codes (MTC) offer bit error rate performance close to Shannon's limit with significantly reduced decoding complexity. However, since interleavers used in turbo codes interleave bit positions in one-dimensional (1D) array, they cannot be used for MTC which encode information bits arranged in 2D array. Moreover, MTC use several interleavers which increase the memory requirement to store permutation patterns. Objective of this study is to design two-stage interleaver for MTC with low memory requirement, large values of column spreading factor and dispersion in the interleaved pattern. Expressions have been derived for limits on maximum values of spreading factor and dispersion for 2D information array. Simulation results show superior performance of MTC with two-stage interleavers than that with random interleavers at high bit energy to noise ratio. Moreover, analysis shows that two-stage interleaver requires 50% less memory storage than random interleaver. Proposed interleaver can also be used for turbo codes in which 1D information array is being used.

Improved low complexity hybrid turbo codes and union bound analysis

Turbo convolutional codes (TCC) are excellent error correcting codes for wireless channels. However, TCC decoders require large decoding complexity. Moreover, complexity of TCC decoder does not reduce even if puncturing is used to change the coding rate. Modified turbo codes require lower decoding complexity than TCC as they use multiple concatenations of simple block codes and convolutional codes. Recently, a class of modified turbo codes called low complexity hybrid turbo codes (LCHTC) and improved low complexity hybrid turbo codes (ILCHTC) have been proposed. It has been shown that LCHTC and ILCHTC achieve bit error rate (BER) which is comparable to TCC and have much lower decoding complexity. Simulation results show that BER performance of ILCHTC is better than that of LCHTC. Rate-1/3 ILCHTC achieve BER of 10−5 at bit energy-to-noise ratio (Eb/N0) of 1.9 dB, which is 0.4 dB higher than Eb/N0 for TCC adopted by third generation partnership project (3GPP). Moreover, ILCHTC and LCHTC decoders require half the number of computations as compared to those required for TCC decoder. In this study, union-bound analysis of ILCHTC is presented to investigate BER performance<10−6. For large interleaver lengths, analysis of theoretical union bound requires numerous computations. Therefore approximate analysis of union bound is derived from theoretical union bound. It is shown that the analysis of approximate union bound achieves reasonable accuracy. Moreover, approximate union bound can be evaluated with significantly less computational complexity than the theoretical union bound.

Improving the distance properties of turbo codes using a third component code: 3D turbo codes - [transactions letters

Thanks to the probabilistic message passing performed between its component decoders, a turbo decoder is able to provide strong error correction close to the theoretical limit. However, the minimum Hamming distance (dmin) of a turbo code may not be sufficiently large to ensure large asymptotic gains at very low error rates (the so-called flattening effect). Increasing the dmin of a turbo code may involve using component encoders with a large number of states, devising more sophisticated internal permutations, or increasing the number of component encoders. This paper addresses the latter option and proposes a modified turbo code in which a fraction of the parity bits are encoded by a rate-1, third encoder. The result is a noticeably increased dmin, which improves turbo decoder performance at low error rates. Performance comparisons with turbo codes and serially concatenated convolutional codes are given.