Additional Bits Research Articles

Chosen IV cryptanalysis on reduced round ChaCha and Salsa

Recently, ChaCha20 (the stream cipher ChaCha with 20 rounds) is in the process of being a standardized and thus it attracts serious interest in cryptanalysis. The most significant effort to analyse Salsa and ChaCha was explained by Aumasson et al. long back (FSE 2008) and further, only minor improvements could be achieved. In this paper, first we revisit the work of Aumasson et al. to provide a clearer insight of the existing attack (2248 complexity for ChaCha7, i.e., 7 rounds) and show certain improvements (complexity around 2243) by exploiting additional Probabilistic Neutral Bits. More importantly, we describe a novel idea that explores proper choice of IVs corresponding to the keys, for which the complexity can be improved further (2239). The choice of IVs corresponding to the keys is the prime observation of this work. We systematically show how a single difference propagates after one round and how the differences can be reduced with proper choices of IVs. For Salsa too (Salsa20/8, i.e., 8 rounds), we get improvement in complexity, reducing it to 2245.5 from 2247.2 reported by Aumasson et al.

SM/SPPM Aided Multiuser Precoded Visible Light Communication Systems

In this paper, we propose a multiuser precoded visible light communication (VLC) system utilizing optical orthogonal frequency division multiplexing (OFDM), where optical spatial modulation (OSM) and spatial pulse position modulation (SPPM) are invoked for supporting high-rate data transmissions without compromising uniform illumination across multiple light-emitting diodes (LEDs). Both OSM and SPPM exploit the index of data streams for carrying additional information bits, whereas the multiuser interference occurring between different user equipments is mitigated by the MIMO precoder. By evaluating the performances of the proposed VLC systems, we demonstrate that the OSM-aided system is capable of achieving high data rates at sufficiently high signal-to-noise ratios (SNRs). In contrast, the SPPM-aided system has a higher effective bandwidth efficiency at low SNRs, despite the fact that its attainable peak data rate is lower than that of the SM-aided counterpart. Such tradeoffs indicate the potential application scenarios of the proposed schemes for achieving diverse design prerequisites.

Self-stabilization techniques for intermediate power level in stacked-Vdd integrated circuits using DC-balanced coding methods

Two new parallel bus coding methods for generating a DC-balanced code with additional bits are proposed to achieve the self-stabilization of the intermediate power level in Stacked-Vdd integrated circuits. They contribute to producing a uniform switching current in parallel inputs and outputs (I/Os). Type I coding minimizes the difference in the number of switchings between the upper and lower CMOS I/Os by 8B/10B coding followed by toggle conversion. Type II coding, in which the multi-value running disparity control feature is integrated into the bus-invert coding, requires only one redundant bit for any wider bus. Their DC-balanced feature and the stability effect of the intermediate power level in the Stacked-Vdd structure were experimentally confirmed from the measurement results obtained from the developed test chips.

A Method to Design Single Error Correction Codes With Fast Decoding for a Subset of Critical Bits

Single error correction (SEC) codes are widely used to protect data stored in memories and registers. In some applications, such as networking, a few control bits are added to the data to facilitate their processing. For example, flags to mark the start or the end of a packet are widely used. Therefore, it is important to have SEC codes that protect both the data and the associated control bits. It is attractive for these codes to provide fast decoding of the control bits, as these are used to determine the processing of the data and are commonly on the critical timing path. In this brief, a method to extend SEC codes to support a few additional control bits is presented. The derived codes support fast decoding of the additional control bits and are therefore suitable for networking applications.

Overview of the Multiview and 3D Extensions of High Efficiency Video Coding

The High Efficiency Video Coding (HEVC) standard has recently been extended to support efficient representation of multiview video and depth-based 3D video formats. The multiview extension, MV-HEVC, allows efficient coding of multiple camera views and associated auxiliary pictures, and can be implemented by reusing single-layer decoders without changing the block-level processing modules since block-level syntax and decoding processes remain unchanged. Bit rate savings compared with HEVC simulcast are achieved by enabling the use of inter-view references in motion-compensated prediction. The more advanced 3D video extension, 3D-HEVC, targets a coded representation consisting of multiple views and associated depth maps, as required for generating additional intermediate views in advanced 3D displays. Additional bit rate reduction compared with MV-HEVC is achieved by specifying new block-level video coding tools, which explicitly exploit statistical dependencies between video texture and depth and specifically adapt to the properties of depth maps. The technical concepts and features of both extensions are presented in this paper.

Trimming the threshold dispersion below 10 e-rms in a large area readout IC working in a single photon counting mode

We present a new method of an in-pixel threshold dispersion correction implemented in a prototype readout integrated circuit (IC) operating in a single photon counting mode. The new threshold correction method was implemented in a readout IC of area 9.6× 14.9 mm2 containing 23552 square pixels with the pitch of 75 μm designed and fabricated in CMOS 130 nm technology. Each pixel of the IC consists of a charge sensitive amplifier, a shaper, two discriminators, two 14-bit counters and a low-area trim DACs for threshold correction. The user can either control the range of the trim DAC globally for all the pixels in the integrated circuit or modify the trim DACs characteristics locally in each pixel independently. Using a simulation tool based on the Monte-Carlo methods, we estimated how much we could improve the offset trimming by increasing the number of bits in the trim DACs or implementing additional bits in a pixel to modify the characteristics of the trim DACs. The measurements of our IC prototype show that it is possible to reduce the effective threshold dispersion in large-area single-photon counting chips below 10 electrons rms.

The countermeasures against the blinding attack in quantum key distribution

It has been shown that the single photon detectors (SPDs) based on the avalanche photodiode (APD) can be blinded and controlled by the bright light and short trigger pulses. Eavesdropper can get the full information without causing additional quantum bit error rate. Hence, in order to guarantee the security of the quantum key distribution (QKD) systems, some countermeasures, by changing the characteristic of the SPD or monitoring the parameters of the detector, are presented by some research groups. In this paper, we provide a new and effective countermeasure against the blinding attack based on improving the optical scheme of the decoding unit in the QKD system rather than only considering the characteristic of the SPD. In our proposal we use a coupler with asymmetric splitting ratio to distinguish the detection characteristic of the SPD with blinding attack from that without blinding attack. The detailed analysis shows that the proposed scheme is feasible to defense the blinding attack.

Double space‐time transmit diversity with spatial modulation

A hybrid scheme of the double space-time transmit diversity (DSTTD) and spatial modulation (SM) is proposed. The spectral efficiency of proposed scheme is twice that of DSTTD. Additional bits are transmitted by transmit antenna combinations of SM without widening the bandwidth. An optimised rotated constellation is also proposed according to the antenna combination to reduce inter-channel interference.

Modified phase-conjugate twin wave schemes for fiber nonlinearity mitigation.

The conventional phase-conjugate twin wave (PCTW) scheme can effectively mitigate the fiber nonlinear distortions but reduce the spectral efficiency (SE) by half. In this paper, we show that by modulating one of the conjugated signals with additional bits, the information encoded in the conjugated variants can still suppress the nonlinear distortions in a similar manner as in the conventional PCTW method, while that encoded in the additional bits, representing the improved SE, is the dominant source limiting the system performance. We further introduce redundancy to the additional bits via error correction coding to overcome this performance bottleneck. The overall system performance can thus approach that of the conventional PCTW method while the SE is significantly enhanced. Simulations of a 25-Gbaud polarization-division-multiplexed quadrature phase shift keying system over 15,200 km show that the proposed scheme can increase the normalized SE from 50% to 80% for a similar performance as the conventional PCTW method. We also show that the proposed concept can be applied to higher-level formats.

Low-Complexity ML Detector and Performance Analysis for OFDM With In-Phase/Quadrature Index Modulation

A novel variant of orthogonal frequency division multiplexing (OFDM) techniques, which carries additional information bits through the index domain including in-phase and quadrature dimensions, is recently proposed. For its nature, we refer to this technique as OFDM with in-phase/quadrature index modulation (OFDM-I/Q-IM) . In this letter, we propose a novel low-complexity detector based on the maximum-likelihood (ML) criterion for OFDM-I/Q-IM, which does not need to know the variance of the noise and the possible realizations of the active subcarrier indices. With the proposed ML detector, the asymptotic average bit error probability (ABEP) and the exact coding gain achieved by OFDM-I/Q-IM are also derived.

Layered Transmission of Space-Time Coded Signals for Image-Sensor-Based Visible Light Communications

This paper demonstrates the feasibility of layered space-time coding (STC) in an outdoor image-sensor-based (IS-based) visible light communication (VLC) system. We examined that for low-resolution IS-based VLC channel where intensity-modulated signals from two different light emitting diodes (LEDs) are detected by one pixel of an IS, STC allows us to decouple them; thus, succeeding to receive them with no errors. Consequently, STC offers extended transmission distance to pixel-resolution-limited IS-based VLC links. In the layered STC presented in this paper, additional bit streams are laid on the ${2^n\times 2^n}$ LED array for increasing the transmission rate per symbol duration for the case where the pixel resolution is improved. A prototype of a three-layered STC is built with an ${8\times 8}$ LED array, where each of the LEDs is modulated at 1 kb/s and a high-speed camera with IS operating at 1000 fps. Our experimental results validate that the two additional bit streams (layer-2 and -3), aligned in the layer-1 STC matrix pair, are extracted with no errors when the receiver comes within 155 and 55 m, respectively, from the LED array, without decreasing 210 m of the transmission distance of layer-1 bit stream.

Generalization of Orthogonal Frequency Division Multiplexing With Index Modulation

Recently, orthogonal frequency division multiplexing (OFDM) with index modulation (OFDM-IM) was proposed. By selecting a fixed number of subcarriers as active subcarriers to carry constellation symbols, the indices of these active subcarriers may carry additional bits of information. In this paper, we propose two generalization schemes of OFDM-IM, named OFDM with generalized index modulation 1 (OFDM-GIM1) and OFDM-GIM2, respectively. In OFDM-GIM1, the number of active subcarriers in an OFDM subblock is no longer fixed. Dependent on the input binary string, different numbers of active subcarriers are assigned to carry constellation symbols. In OFDM-GIM2, independent index modulation is performed on the in-phase and quadrature component per subcarrier. Through such ways, a higher spectral efficiency than that of OFDM-IM may be achieved. Since both generalization schemes proposed suffer from BER performance loss in low SNR region, an interleaving technique is proposed to tackle this problem. Finally, noting that the two generalization schemes are compatible with each other, the combination of these two schemes, named OFDM-GIM3, has also been investigated. Computer simulation results clearly show our proposed scheme's superiority in both spectral efficiency and BER performance compared to existing works.

Network throughput analysis of IEEE 802.15.4 enabled wireless sensor networks with FEC coding under external interference

IEEE 802.15.4 enabled wireless sensor networks are often impacted by the coexistence of different sources of external interference sharing the ISM band. Such external interference may significantly deteriorate achievable wireless sensor network throughputs due to uncontrollable collisions of interference transmissions with IEEE 802.15.4 packets. Forward error correction may be considered as a mechanism to alleviate the resiliency of IEEE 802.15.4 packets against partial collisions due to interference. In this paper, theoretical analysis of network throughput of IEEE 802.15.4 enabled wireless sensor networks under external interference with deployment of FEC will be presented. The throughput performance of IEEE 802.15.4 network under FEC deployment is governed by the percentage of collided bits within IEEE 802.15.4 coded payloads that the FEC code can withstand. The analysis in this paper considers convolutional codes as FEC candidate codes for IEEE 802.15.4 networks and proceeds to theoretically derive collision percentage thresholds that convolutional codes may tolerate under Viterbi decoding. Numerical results indicate that an optimal FEC coding rate exists for a given IEEE 802.15.4 and external interference configuration. The optimal coding rate introduces enough resiliency for the IEEE 802.15.4 transmissions to withstand external interference. Any additional redundancy bits for more robust codes would render unneeded protection that unnecessarily reduces the goodput of IEEE 802.15.4 networks.

Optimal encoding capacity of a linear optical quantum channel

Here, we study the capacity of a quantum channel, assuming linear optical encoding, as a function of available photons and optical modes. First, we observe that substantial improvement is made possible by not restricting ourselves to a rail-encoded qubit basis. Then, we derive an analytic formula for general channel capacity and show that this capacity is achieved without requiring the use of entangling operations typically required for scalable universal quantum computation, e.g. KLM measurement-assisted transformations. As an example, we provide an explicit encoding scheme using the resources required of standard dense coding using two dual-rail qubits (2 photons in 4 modes). In this case, our protocol encodes one additional bit of information. Greater gains are expected for larger systems.

Energy-Efficient All-Spin Cache Hierarchy Using Shift-Based Writes and Multilevel Storage

Spintronic memories are considered to be promising candidates for future on-chip memories due to their high density, nonvolatility, and near-zero leakage. However, they also face challenges such as high write energy and latency and limited read speed due to single-ended sensing. Further, the conflicting requirements of read and write operations lead to stringent design constraints that severely compromises their benefits. Recently, domain wall memory was proposed as a spintronic memory that has a potential for very high density by storing multiple bits in the domains of a ferromagnetic nanowire. While reliable operation of DWM memory with multiple domains faces many challenges, single-bit cells that utilize domain wall motion for writes have been experimentally demonstrated [Fukami et al. 2009]. This bit-cell, which we refer to as Domain Wall Memory with Shift-based Write (DWM-SW), achieves improved write efficiency and features decoupled read-write paths, enabling independent optimizations of read and write operations. However, these benefits are achieved at the cost of sacrificing the original goal of improved density. In this work, we explore multilevel storage as a new direction to enhance the density benefits of DWM-SW. At the device level, we propose a new device--multilevel DWM with shift-based write (ML-DWM-SW)--that is capable of storing 2 bits in a single device. At the circuit level, we propose a ML-DWM-SW based bit-cell design and layout. The ML-DWM-SW bit-cell incurs no additional area overhead compared to the DWM-SW bit-cell despite storing an additional bit, thereby achieving roughly twice the density. However, it requires a two-step write operation and has data-dependent read and write energies, which pose unique challenges. To address these issues, we propose suitable architectural optimizations: (i) intra-word interleaving and (ii) bit encoding. We design “all-spin” cache architectures using the proposed ML-DWM-SW bit-cell for both general purpose processors as well as general purpose graphics processing units (GPGPUs). We perform an iso-capacity replacement of SRAM with spintronic memories and study the energy and area benefits at iso-performance conditions. For general purpose processors, the ML-DWM-SW cache achieves 10X reduction in energy and 4.4X reduction in cache area compared to an SRAM cache and 2X and 1.7X reduction in energy and area, respectively, compared to an STT-MRAM cache. For GPGPUs, the ML-DWM-SW cache achieves 5.3X reduction in energy and 3.6X area reduction compared to SRAM and 3.5X energy reduction and 1.9X area reduction compared to STT-MRAM.

Innovative bit channel in downstream passive optical network frames based on reusing of bit sequences

ABSTRACTIn this article, a novel idea of a hidden bit channel established in the downstream passive optical network (PON) frames is proposed. As the downstream frames in time‐division multiplexed, PONs are broadcasted and delivered to all active end‐point optical network units (ONUs), and this bitstream could be potentially used for creating an additional hidden bit channel containing bits for all ONUs. Therefore, the downstream frames could simply transmit standard information fields and ONU contributions according to the standard PON principles; however, these bits could be also reused multiple times to carry additional data for each ONU in a form of segmented bit sequences spread within the entire bitstream. To establish effective bit channel with positive bit gain, an effective algorithm for addressing its bits is necessary. The most promising bit addressing algorithm is proposed within this article together with the results obtained by its simulations and performance evaluations. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2346–2351, 2015

Block cipher based separable reversible data hiding in encrypted images

While most reversible data hiding in encrypted images (RDH-EI) are based on stream cipher, this paper aims to present an alternative method feasible for block-enciphered images. Before uploading data to a remote server, the content owner encrypts the original image with a block cipher algorithm using an encryption key. Then, the server embeds additional bits into the encrypted image with an embedding key to generate the marked encrypted image. On the recipient side, the additional bits can be extracted if the receiver has the embedding key. In case the receiver has only the encryption key, the marked encrypted image can be directly deciphered to a plaintext image with good quality. When both the embedding and encryption keys are available for the receiver, he can recover the original image without any errors. Compared with the existing block cipher based RDH-EI method, drawbacks of the encryption and the recovery are avoided, and good embedding payloads are achieved.

Generalized Space-and-Frequency Index Modulation

Unlike in conventional modulation where information bits are conveyed only through symbols from modulation alphabets defined in the complex plane (e.g., quadrature amplitude modulation (QAM), phase shift keying (PSK)), in index modulation (IM), additional information bits are conveyed through indices of certain transmit entities that get involved in the transmission. Transmit antennas in multi-antenna systems and subcarriers in multi-carrier systems are examples of such transmit entities that can be used to convey additional information bits through indexing. In this paper, we introduce {\em generalized space and frequency index modulation}, where the indices of active transmit antennas and subcarriers convey information bits. We first introduce index modulation in the spatial domain, referred to as generalized spatial index modulation (GSIM). For GSIM, where bits are indexed only in the spatial domain, we derive the expression for achievable rate as well as easy-to-compute upper and lower bounds on this rate. We show that the achievable rate in GSIM can be more than that in spatial multiplexing, and analytically establish the condition under which this can happen. It is noted that GSIM achieves this higher rate using fewer transmit radio frequency (RF) chains compared to spatial multiplexing. We also propose a Gibbs sampling based detection algorithm for GSIM and show that GSIM can achieve better bit error rate (BER) performance than spatial multiplexing. For generalized space-frequency index modulation (GSFIM), where bits are encoded through indexing in both active antennas as well as subcarriers, we derive the achievable rate expression. Numerical results show that GSFIM can achieve higher rates compared to conventional MIMO-OFDM. Also, BER results show the potential for GSFIM performing better than MIMO-OFDM.

Extending lifetime of flash memory using strong error correction coding

Demand for flash memory based storage systems is on the rise because flash memory has many advantages when compared with hard disk drives, such as lower latency and resistance to physical shock. However, flash memory permits only a limited number of program/erase (P/E) cycles, and after the guaranteed number of P/E cycles, data cannot be reliably retrieved due to uncorrectable errors. Given a target bit error rate, the guaranteed number of P/E cycles decreases as more bits are stored in one cell and as the cell size is scaled down. In this paper, a novel lifetime extension mechanism for flash memory, referred to as a gradual error correction code (GECC), is proposed. A G-ECC provides a stronger level of error correction than a standard ECC by sacrificing a small portion of storage capacity in order to store additional parity bits. The proposed method can extend the lifetime of flash memory by 124% at the cost of a 12% loss in capacity. The use of additional parity bits necessarily leads to performance loss due to increased accesses for those additional parity bits and garbage collection operations involving those bits. Thus, methods to alleviate such performance loss are proposed; these methods reduce the performance overhead from 17% (without the proposed methods) to 3% even in the worst case.

Protograph-Based Raptor-Like LDPC Codes

This paper proposes protograph-based Raptor-like (PBRL) codes as a class of rate-compatible low-density parity-check codes for binary-input AWGN channels. As with the Raptor codes, exclusive-OR operations on precoded bits produce additional parity bits providing extensive rate compatibility. Unlike Raptor codes, each additional parity bit in the protograph is explicitly designed to optimize the density evolution threshold. During the lifting process, approximate cycle extrinsic message degree (ACE) and circulant progressive edge growth (CPEG) constraints are used to avoid undesirable graphical structures. Some density-evolution performance is sacrificed to obtain lower error floors, particularly at short block-lengths. Simulation results are shown for information block sizes of k = 1032 and 16 384. For a target frame error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> , at each rate, the k = 1032 and 16 384 code families perform within 1 dB and 0.4 dB of both the Gallager bound and the normal approximation, respectively. The 16 384 code family outperforms the best known standardized code family, namely, the AR4JA codes. The PBRL codes also outperform DVB-S2 codes that have the advantages of longer blocklengths and outer BCH codes. Performance is similar to RC code families designed by Nguyen et al. that do not constrain codes to have the PBRL structure and involve simulation in the optimization process at each rate.