Repetition Coding Research Articles

Multipoint-to-Multipoint Cooperative Multiuser SIM Free-Space Optical Communication: A Signal-Space Diversity Approach

In this paper, a novel signal-space diversity (SSD) technique based multipoint-to-multipoint cooperative scheme for a multiuser free-space optical communication system is proposed. In SSD technique, constellation points of the transmitted signal are rotated by a certain angle and in-phase and quadrature components of two different symbols are interleaved to obtain diversity from the signal space. In the proposed scheme, the diversity of each cooperative user gets improved through joint encoding/decoding of the rotated symbols using subcarrier intensity modulation (SIM). The joint encoding/decoding can be done by connecting all the users' transceivers by wires that ensure the availability of the information of a user to all other users. The average symbol error rate for the proposed scheme under log-normal and gamma-gamma channel models is evaluated analytically and corroborated through Monte Carlo simulations. It is reported through intensive analyses and comparisons that the proposed cooperative scheme not only achieves full diversity order but also outperforms non-cooperative and repetition coding schemes.

GCBlock: A Grouping and Coding Based Storage Scheme for Blockchain System

To achieve the tamper-proof, reliability and traceability of transactions in a trustless environment, the blockchain requires each peer node to store the whole global ledger. However, as transactions keep increasing over time, the storage cost of each node increases. In addition, many schemes have been proposed to boost rapid transactions which will even lead transactions to grow explosively. The problem of storage is becoming one challenge of blockchain since the storage overhead of each node increase rapidly. Reducing the storage overhead of each participant is very urgent and worthy. In this paper, we present GCBlock: a grouping overlay network storage scheme for the blockchain which can reduce the storage overhead of nodes and cut the whole storage cost of the blockchain greatly while keeping the underlying protocols. In our scheme, we try to group the nodes according to their physical fuzzy distance to reduce the overall delay when tracing. We set rules of autonomous check to deal with evil behavior within the group. To further enhance the stability of our scheme, we propose the transcript fractional repetition code which is newly constructed based on the fractional repetition code to encode data. Finally, we make a comprehensive evaluation of GCBlock and the results show that it is workable and reasonable.

Repetition Cat Qubits for Fault-Tolerant Quantum Computation

We present a 1D repetition code based on the so-called cat qubits as a viable approach toward hardware-efficient universal and fault-tolerant quantum computation. The cat qubits that are stabilized by a two-photon driven-dissipative process, exhibit a tunable noise bias where the effective bit-flip errors are exponentially suppressed with the average number of photons. We propose a realization of a set of gates on the cat qubits that preserve such a noise bias. Combining these base qubit operations, we build, at the level of the repetition cat qubit, a universal set of fully protected logical gates. This set includes single-qubit preparations and measurements, NOT, controlled-NOT, and controlled-controlled-NOT (Toffoli) gates. Remarkably, this construction avoids the costly magic state preparation, distillation, and injection. Finally, all required operations on the cat qubits could be performed with slight modifications of existing experimental setups.

Joint Artificial Noise and Repetition Coding for Secure Wireless Communications in TDD Systems

In this letter, we study the secure transmission in the wireless single-antenna time division duplexing (TDD) system when there is a passive eavesdropper. A joint artificial noise and repetition coding scheme is designed, in which the artificial noise can be removed only by the legitimate receiver instead of the eavesdropper. We prove that by using the proposed scheme, the capacity of the wiretap channel is limited by an upper bound, and the achievable secrecy rate can be maximized by power allocation. Finally, simulation results are supplied to corroborate the theoretical analysis.

Near-Capacity Detection and Decoding: Code Design for Dynamic User Loads in Gaussian Multiple Access Channels

This paper considers the forward error correction (FEC) code design for approaching the capacity of a dynamic multiple access channel (MAC) where both the number of users and their respective signal powers keep constantly changing, resembling the scenario of an actual wireless cellular system. To obtain a low-complexity non-orthogonal multiple access (NOMA) scheme, we propose a serial concatenation of a low-density parity-check (LDPC) code and a repetition code (REP), this way achieving near Gaussian MAC (GMAC) capacity performance while coping with the dynamics of the MAC system. The joint optimization of the LDPC and REP codes is addressed by matching the analytical extrinsic information transfer (EXIT) functions of the sub-optimal multi-user detector (MUD) and the channel code for a specific and static MAC system, achieving near-GMAC capacity. We show that the near-capacity performance can be flexibly maintained with the same LDPC code regardless of the variations in the number of users and power levels. This flexibility (or elasticity) is provided by the REP code, acting as “user-load and power equalizer”, dramatically simplifying the practical implementation of NOMA schemes, as only a single LDPC code is needed to cope with the dynamics of the MAC system.

Performance of High-Mobility MIMO Communications With Doppler Diversity

A rapid change of channels in high-speed mobile communications will lead to difficulties in channel estimation and tracking but can also provide Doppler diversity. In this paper, the performance of a multiple-input multiple-output system with pilot-assisted repetition coding and spatial multiplexing is studied. With minimum mean square error (MMSE) channel estimation, an equivalent channel model and the corresponding system model are presented. Based on random matrix theory, asymptotic expressions of the normalized achievable sum rate of the linear receivers, such as the maximal ratio combining (MRC) receiver, MMSE receiver and MRC-like receiver, are derived. In addition, according to the symbol error rate of the MRC-like receiver, the maximum normalized Doppler diversity order and the minimum coding gain loss can be achieved when the repetition number and signal-to-noise ratio tend to infinity, and the corresponding conditions are derived. Based on the theoretical results, the impacts of different system configurations and channel parameters on the system performance are demonstrated.

Design and performance evaluation of bitwise retransmission schemes in wireless sensor networks

The previously proposed bitwise retransmission schemes which retransmit only selected bits to accumulate their reliability are designed and evaluated. Unlike conventional automatic repeat request (ARQ) schemes, the bitwise retransmission schemes do not require a checksum for error detection. The bitwise retransmission decisions and combining can be performed either after demodulation of the received symbols or after channel decoding. The design and analysis assume error-free feedback, however, the impact of feedback errors is also considered. The bit-error rate (BER) expressions are derived and verified by computer simulations in order to optimize the parameters of the retransmission schemes. The BER performance of coded and uncoded bitwise retransmissions is compared with a hybrid ARQ (HARQ) scheme over additive white Gaussian noise (AWGN), slow fading, and fast fading channels. It is shown that bitwise retransmissions outperform block repetition coding (BRC) over AWGN channels. In addition, the selection diversity created by the bitwise retransmissions can outperform the HARQ at large signal-to-noise ratio (SNR) over fast fading channels. Finally, the practical design of a bitwise retransmission protocol for data fusion in wireless sensor networks is presented assuming Zigbee, WiFi and Bluetooth system parameters.

Bit error rate and outage analysis of MIMO-FSO communications over K-distributed atmospheric channels with imperfect feedback

In this paper, we propose a weighting scheme (WS) for an imperfect feedback-based multiple-input multiple-output free-space optical (MIMO-FSO) system over K-distributed fading channels which employs equal gain combining (EGC) at the receiver. More precisely, the optimal beamforming vector is obtained so as to minimize the upper bound of the average bit error rate (BER) of the proposed scheme. For performance comparison, we consider three competitive schemes referred to as error-free feedback (EF), erroneous feedback (FWE) and repetition coding (RC). Moreover, the performance of the proposed method is analyzed in terms of outage probability. To this aim, we first derive the expression of the outage probability for the WS (proposed), FWE, RC and EF schemes and then, the performance of these methods is compared through different numerical simulations. We show that the proposed beamforming scheme outperforms the FWE and RC schemes in terms of BER and outage probability, even under an imperfect feedback link. Moreover, we show that the performance of the proposed scheme approaches that with ideal feedback by decreasing the error probability of the feedback link.

Fractional Repetition Codes With Optimal Reconstruction Degree

Fractional repetition (FR) codes form a special class of minimum bandwidth regenerating codes by providing uncoded repairs via a table-based repair model. For a given file size, it is desirable to design FR codes that minimize the reconstruction degree, which is defined as the number of storage nodes required for data retrieval. In this paper, we first consider a lower bound on the reconstruction degree of FR codes obtained by Silberstein and Etzion. We present several families of FR codes that attain this lower bound, which are derived from combinatorial designs and regular graphs. We further provide a new lower bound on the reconstruction degree of FR codes, which is tighter than the existing one. Moreover, we show that for an FR code with reconstruction degree achieving the lower bounds, the corresponding dual code attains upper bounds on the supported file size.

Recurrent neural network (RNN) for delay-tolerant repetition-coded (RC) indoor optical wireless communication systems.

Indoor optical wireless communications have been widely studied to provide high-speed connections to users, where the use of repetition-coded (RC) multiple transmitters has been proposed to improve both the system robustness and capacity. To exploit the benefits of the RC system, the multiple signals received after transmission need to be precisely synchronized, which is challenging in high-speed wireless communications. To overcome this limit, we propose and demonstrate a recurrent neural network (RNN)-based symbol decision scheme to enable a delay-tolerant RC indoor optical wireless communication system. The experiments show that the proposed RNN can improve the bit-error-rate by about one order of magnitude, and the improvement is larger for longer delays. The results also show that the RNN outperforms previously studied fully connected neural network schemes.

Performance Analysis of Repetition-Coding and Space-Time-Block-Coding as Transmitter Diversity Schemes for Indoor Optical Wireless Communications

The benefits of 2 × 1 multiple-inputs-single-output scheme for transmitter diversity in the infrared indoor optical wireless communication link are theoretically investigated. The performance of repetition-coding (RC) and Alamouti-type real-valued space-time-block-coding (STBC) as effective transmitter diversity schemes is systematically compared under conditions of channel gain variation caused by the degradation in the received optical power due to the blocking of one optical beam of the optical wireless channel. It is shown that the linear addition of channel gains in the RC scheme outperforms the root-sum-square of channel gains in the STBC scheme with regards to the bit-error-rate (BER) performance. Proof-of-concept experiments are carried out with both schemes under emulated scenarios of channel blockage. The RC scheme exhibits better BER performance when observed experimentally, validating the proposed theoretical model for the two spatial diversity schemes. To understand the performance of RC and STBC schemes against the optical delay caused by the two optical channel path difference within one-bit interval, both schemes are experimentally investigated using on-off-keying modulation, and results show that RC still outperforms STBC. Both theoretical and experimental results indicate that RC has better robustness to channel blockage and differential channel paths induced optical delay.

Comparison of OFDM and OOK modulations for vehicle-to-vehicle visible light communication in real-world driving scenarios

Visible light communication (VLC) is seen as an interesting technology to complement the IEEE 802.11p-based systems commonly used for vehicle-to-vehicle (V2V) communication. However, the reliability of such a V2V-VLC link in real-world driving scenario had not been demonstrated up to very recently. The results obtained, at that time with orthogonal frequency division multiplexing (OFDM) at 2 kbps, are complemented in this paper with additional results using on-off keying (OOK) at 100 kbps. The overall performances of this second modulation are rather close to those of OFDM. The packet reception rate (PRR) remains more than 90% over a service area of 30 m length-wise and the link is not affected by multipath propagation. Error-free transmission is even demonstrated over 60 m using repetition coding, at the cost of a reduced data rate of 10 kbps. However, it is shown that OFDM is able to cope with the narrow-band interferences generated by outdoor lighting such as LED signs whereas the OOK link is completely jammed. Despite its simplicity and good overall performances, OOK is thus not as robust as OFDM to the variety of situations experienced in real-world driving scenario.

Tackling Biased PUFs Through Biased Masking: A Debiasing Method for Efficient Fuzzy Extractor

This paper presents an efficient fuzzy extractor (FE) design for biased physically unclonable functions (PUFs). To remove entropy leak from helper data in an efficient manner, we propose a new debiasing method, namely biased masking (BM). The proposed scheme removes the entropy leak by applying artificial noise (i.e., biased mask) such that the resulting response is uniform, and the added noise is removed by ECC decoding at the reconstruction as well as PUF noise. In addition, BM-based debiasing can be easily implemented with only additional random number generator and bit-parallel AND or OR operation in an enrollment server. Client devices with PUF, which are sometimes resource-constrained, require no additional operation. Furthermore, we show that the BM-based FE is reusable as well as the conventional code-offset FE. We evaluate the efficiency and effectiveness of the BM-based FE compared with the conventional debiasing-based FEs. Consequently, we confirm that the BM-based FE can achieve approximately 20 percent lower PUF size for nonnegligible biases (e.g., 60 percent) by just increasing the length of repetition code, which indicates that the BM-based FE is suitable for resource-constrained devices in terms of hardware cost for implementing PUF and computational cost at the reconstruction.

A Scaled Cyclic Delay Diversity Based Precoding for Coded MIMO-OFDM System

In this paper, we propose a scaled cyclic delay diversity (SCDD) based precoding for coded multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. In order to improve the bit error rate (BER) performance, the proposed precoding reduces the maximum correlation of the precoded channel in frequency domain. In addition, a decision criterion for the scaling factor is suggested by analyzing the bit error probability of repetition codes, convolutional codes, and turbo codes. We present the simulation results for the BER performance to verify the effect of proposed SCDD-based precoding.

Invisible watermarking framework that authenticates and prevents thevisualization of anaglyph images for copyright protection

In this work, a watermarking framework to authenticate and protect the copyright that prevents the visualization of nonauthorized anaglyph images is proposed. Designed scheme embeds a binary watermark and the Blue channel of the anaglyph image into the discrete cosine transform domain of the original image. The proposed method applies the quantization index modulation-dither modulation algorithm and a combination of Bose-Chaudhuri-Hocquenghem with repetition codes, which permit to increase the capability in recovering the watermark. Additionally, Hash algorithm is used to scramble the component where the watermark should be embedding, guaranteeing a higher security performance of the scheme. This new technique prevents the visualization of 3D content to unauthorized users. Additionally, its high robustness against the most common image processing attacks, such as JPEG compression, impulsive and Gaussian noises, etc. has been demonstrated in this study.

Outage Capacity of Rate-Adaptive Relaying for FSO Links With Nonzero Boresight Pointing Errors

An outage capacity analysis of a three-way free-space optical (FSO) setup based on the optical path selection, either source-destination (S-D) or source-relay-destination (S-R-D), with a greater value of channel gain along with the use of repetition coding (RC) is analyzed over atmospheric turbulence channels with nonzero boresight pointing errors. The developed expression, which is validated through Monte Carlo simulation, is used to carefully analyze the performance and design of rate-adaptive relaying FSO systems from an information theory point of view. It is highlighted that a greater outage diversity is achieved by the obtained results without investing in extra hardware at the expense of an information rate reduction.

Interleave-Division Multiple Access in High Rate Applications

Interleave-division multiple access (IDMA) is a multiple access scheme that has been considered in several recent proposals for the 5th generation cellular system. In this letter, basing on evolution analysis, we show that the performance of IDMA can be enhanced using the transfer function matching principle. Such matching can be realized by superposition coded modulation, power control, repetition coding, and zero padding. Zero padding together with cyclic shifting also leads to reduced implementation complexity. Our analysis is based on additive white Gaussian noise channels and we show by simulations that the matching techniques can also provide impressive performance in fading channels.

Error detection algorithm for Lempel-Ziv-77 compressed data

In this study, we develop a novel error detection algorithm for Lempel-Ziv-77 (LZ77) compressed data. In the proposed algorithm, additional bits are not used to detect bit errors, unlike in conventional methods such as checksum, cyclic redundancy check, Hamming code, and repetition code. We also introduce eight special features of LZ77-compressed data for detecting the presence of errors. We demonstrate the feasibility of the algorithm based on simulations and evaluate it using two publicly available databases comprising the Calgary and Canterbury corpora. The error detection rate using the proposed algorithm is below those of conventional methods, but the compression ratio is better. The application of a parity bit in the algorithm improves the error detection performance. The number of redundant bits increases owing to the insertion of the parity bit, but the code rate is still greater than or equal to 0.9, whereas conventional methods obtain code rates less than 0.9. Simulations demonstrate that the algorithm obtains significant performance improvements when a parity bit is periodically inserted. In particular, we achieve an error detection rate of 100% using the parity bit when the number of bit errors is greater than seven.

Reliable and Modeling Attack Resistant Authentication of Arbiter PUF in FPGA Implementation With Trinary Quadruple Response

Field programmable gate array (FPGA) is a potential hotbed for malicious and counterfeit hardware infiltration. Arbiter-based physical unclonable function (A-PUF) has been widely regarded as a suitable lightweight security primitive for FPGA bitstream encryption and device authentication. Unfortunately, the metastability of flip-flop gives rise to poor A-PUF reliability in FPGA implementation. Its linear additive path delays are also vulnerable to modeling attacks. Most reliability enhancement techniques tend to increase the response predictability and ease machine learning attacks. This paper presents a robust device authentication method based on the FPGA implementation of a reliability enhanced A-PUF with trinary digit (trit) quadruple responses. A two flip-flop arbiter is used to produce a trit for metastability detection. By considering the ordered responses to all four combinations of first and last challenge bits, each quadruple response can be compressed into a quadbit that represents one of the five classes of trit quadruple response with greater reproducibility. This challenge-response quadruple classification not only greatly reduces the burden of error correction at the device but also enables a precise A-PUF model to be built at the server without having to store the complete challenge-response pair (CRP) set for authentication. Besides, the real challenge to the A-PUF is generated internally by a lossy, nonlinear, and irreversible maximum length signature generator at both the server and device sides to prevent the naked CRP from being machine learned by the attacker. The A-PUF with short repetition code of length five has been tested to achieve a reliability of 1.0 over the full operating temperature range of the target FPGA board with lower hardware resource utilization than other modeling attack resilient strong PUFs. The proposed authentication protocol has also been experimentally evaluated to be practically secure against various machine learning attacks including evolutionary strategy covariance matrix adaptation.

On codes over the finite non chain ring A = F4+vF4; v2 = v and its covering radius of codes with Bachoc weight

In this paper, some lower and upper bounds on the covering radius of codes over the nite non chain ring A = F4 + vF4; v2 = v with respect to Bachoc weight is given. Also, the covering radius of various Block Repetition Codes of same and different length over the nite non chain ring A = F4 + vF4; v2 = v is obtained.In this paper, some lower and upper bounds on the covering radius of codes over the nite non chain ring A = F4 + vF4; v2 = v with respect to Bachoc weight is given. Also, the covering radius of various Block Repetition Codes of same and different length over the nite non chain ring A = F4 + vF4; v2 = v is obtained.