Identical Bits Research Articles

Enhanced Multi-Level Phase Quantizer for the Optical Processing of M-PSK Signals

This paper presents a novel multi-level phase quantizer with the potential of almost ideal step like transfer function. Its operation relies on the proper combination of phase sensitive amplification in highly nonlinear fibers and amplitude limitation offered by injection locked lasers. Thorough investigation of the quantization properties of the scheme is theoretically and numerically conducted under ideal and non-ideal operating conditions. The properties of the limiter and their impact on the quantization performance are highlighted. The regenerative operation is demonstrated numerically by showing that a regenerated differentially decoded quaternary shifted keyed signal exhibits almost identical bit error rate performance with homodyne detection.

Secure Key Distribution based on Dynamic Chaos Synchronization of Cascaded Semiconductor Laser Systems

A new secure key distribution scheme based on the dynamic chaos synchronization of two cascaded semiconductor laser systems (CSLSs) subject to common chaotic injection and random phase-modulated optical feedback is demonstrated. In this scheme, Alice and Bob adopt two independent random sequences to control the phase modulators of CSLSs, which induces a dynamic perturbation to the chaos synchronization. We thoroughly investigate the chaos synchronization performance under different phase-shift conditions with cross-correlation function, and systematically discuss the feasibility and security of the system. The results show that, with proper injection and feedback strength, the correlation coefficient gap between phase shift match and mismatch is clear and robust to the parameter mismatches in the CSLSs and those between the two CSLSs. Based on this, high-quality key distribution can be performed by picking out the identical random bits from the two independent random sequences according to the computational correlation. Moreover, the investigations on the information theoretic security and rate of the key distribution show that the security of the key distribution scheme can be further enhanced by properly increasing the number of layers in the CSLSs or employing high-order modulation format.

2-D Write/Read Channel Model for Bit-Patterned Media Recording With Large Media Noise

A 2-D write/read channel model, which can accurately capture the media, writer, and reader characteristics, is proposed and investigated for very-high-density bit-patterned media recording (BPMR) system with large media noise. For the write process, a 2-D data-dependent write channel combined with a micromagnetic model of the writer is investigated for BPMR. In order to better understand the proposed channel model, several 2-D patterns are investigated, and the corresponding write failure events are studied. It is observed that the write error rates (WERs) are different for different 2-D patterns due to the 2-D data-dependent nature of the write-in errors, even though the write failure rates are the same for these different 2-D patterns. For the readback process, a read channel, including media noise, is combined with the write channel, and the bit error rates (BERs) are studied for various 2-D patterns as a function of media jitter and write clock phase drift. It is observed that the 2-D pattern corresponding to four identical bits in a square pattern provides the best performance at a target BER of $10^{\mathrm {-2}}$ , because it can provide adequate tolerance to media noise and interference in down-track and cross-track (CT) directions. The difference between the WER and the BER after readback is studied for various 2-D patterns, and the pattern corresponding to 4 bits with transitions in the CT direction is found to exhibit the largest difference among the studied patterns due to the fact that inter-track interference is more severe than the inter-symbol interference. These results motivate possible inclusion of 2-D modulation codes in BPMR channel to avoid certain bit patterns.

Line coding methods for high speed serial links

A line coding for high speed serial transmission is defined by two major characteristics: the maximum guaranteed run length (RL) which is the number of consecutive identical bits, and the running disparity (RD or DC-Balance) which is the difference between the number of 'zeroes' and 'ones' in a frame. Both should be bounded to a certain limit, RL to ensure reliable clock recovery and RD to limit baseline wander. Another important parameter is the overhead predictability. This parameter may be critical for applications that need a regular synchronization but for other applications, especially if the variable transfer rate is handled by the upper layer protocol, a statistical value of this parameter is good enough. In this paper, we propose two programmable line codings which bound RL and RD with fixed or variable overhead. The resulting overhead for the line coding we propose is shown to be the lowest among the existing methods, as much as to 10 times lower than well-known encoding methods. The fixed overhead line coding is based on a generalization of the polarity bit approach and can be dynamically adapted to link quality and the environment. First we propose a line coding which bounds the RL, and then we propose another one which bounds the RD. We end up by combining both methods to build a DC-balanced and Run Length limited line coding.

A Mathematical modeling and Simulation Analysis of Lattice reduction algorithms for large MIMO detections

Abstract – This paper analyses the performance of Multiple Input Multiple Output (MIMO) wireless communication system by combining it with an efficient algorithm Diagonal Reduction (DR). DR is a powerful tool to achieve more efficiently a high performance with less complexity. This paper proposes a DR algorithm in order to reduce its complexity named Greedy Diagonal Reduction (GDR) algorithm which gives reduced complexity with efficient performance at the receiver using the MATLAB communication tool box version 7.0 as a simulation tool. From the simulation results of various reduction algorithms it is observed that, DR can reduce the number of iterations using size reduction operations. Proposed DR algorithm gives identical Bit Error Rate (BER) performance with LLL algorithms when applied to Successive Interference cancellation (SIC) decoding. Greedy DR reduces the computational complexity in Multiple Input Multiple Output systems by improving the efficiency in terms of size reduction operations. Sphere Decoding (SD) technique gives better BER performance on comparing with Successive Interference cancellation decoding technique.

Statistical modelling of a non‐linear high‐power amplifier with memory in multi‐input–multi‐output orthogonal frequency division multiplexing systems

A simple and accurate statistical model (SASM) for a high-power amplifier (HPA) with memory in multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems is proposed. This model is statistically equivalent to the more complex generalised memory polynomial (GMP) model, which is one of the most accurate models. The HPA distortion is modelled using stationary white Gaussian noise sources that pass through finite impulse response (FIR) filters. The filter coefficients and the variance of noise sources are derived analytically from the GMP model parameters by spectral decomposition of the GMP noise power spectrum. The number of FIR filters is equal to the memory length of the GMP model. The HPA effect on the OFDM signal, considered as frequency-dependent attenuation coefficients, is modelled using another FIR filter. These FIR filters with small lengths make the model computationally inexpensive and mathematically tractable. The main characteristics of this model are identical bit error rate (BER) and error vector magnitude of subcarriers with those in the GMP model. The proposed model is the simplest representation of a HPA with memory effects. An excellent agreement between the simulation results of the SASM and GMP model is observed. This verifies the accuracy and efficiency of the proposed method.

Closed-form equation of data dependent jitter in first order low pass system.

This paper presents a closed-form equation of data dependent jitter (DDJ) in first order low pass systems. The DDJ relates to the system bandwidth, the bit rate, the input rise/fall time, and the number of maximum consecutive identical bits of the data pattern. To confirm the derived equation, simulations have been done with a first order RC low pass circuit for various system bandwidths, bit rates, input rise/fall times, and data patterns. The simulation results agree well with the calculated DDJ values by the derived equation.

Experimental demonstration of record high 19125Gb/s real-time end-to-end dual-band optical OFDM transmission over 25km SMF in a simple EML-based IMDD system

Record high 19.125 Gb/s real-time end-to-end dual-band optical OFDM (OOFDM) transmission is experimentally demonstrated, for the first time, in a simple electro-absorption modulated laser (EML)-based 25 km standard SMF system using intensity modulation and direct detection (IMDD). Adaptively modulated baseband (0-2GHz) and passband (6.125 ± 2GHz) OFDM RF sub-bands, supporting line rates of 10 Gb/s and 9.125 Gb/s respectively, are independently generated and detected with FPGA-based DSP clocked at only 100 MHz and DACs/ADCs operating at sampling speeds as low as 4GS/s. The two OFDM sub-bands are electrically frequency-division-multiplexed (FDM) for intensity modulation of a single optical carrier by an EML. To maximize and balance the signal transmission performance of each sub-band, on-line adaptive features and on-line performance monitoring is fully exploited to optimize key OOFDM transceiver and system parameters, which includes subcarrier characteristics within each individual OFDM sub-band, total and relative sub-band power as well as EML operating conditions. The achieved 19.125 Gb/s over 25 km SMF OOFDM transmission system has an optical power budget of 13.5 dB, and shows almost identical bit error rate (BER) performances for both the baseband and passband signals. In addition, experimental investigations also indicate that the maximum achievable transmission capacity of the present system is mainly determined by the EML frequency chirp-enhanced chromatic dispersion effect, and the passband BER performance is not affected by the two sub-band-induced intermixing effect, which, however, gives a 1.2dB optical power penalty to the baseband signal transmission.

Characterization of Measured Indoor Off-Body MIMO Channels with Correlated Fading, Correlated Shadowing and Constant Path Loss

Indoor off-body wireless MIMO links between a mobile user equipped with wearable textile patch antennas and a fixed base station exhibit specific channel behavior due to the near presence and movements of the human body. Therefore, they require a dedicated channel model that captures the effects of correlated small-scale Rayleigh fading and correlated lognormal shadowing. A methodology is presented to construct such a model, allowing to predict the bit error characteristics and channel capacity curves based on the shadowing and fading correlation matrices that are extracted from channel measurements. It is shown that by separating shadowing, including effects caused by movement and reorientation of the human body, from small-scale fading, the main mechanisms of the off-body communication link are accurately captured by the model. A clear dependence of the shadowing correlation values on the physical layout of the antenna system is found. In our measurements, shadowing is not significantly decorrelated by polarization diversity or front-to-back diversity whereas the small-scale fading is clearly decorrelated. From the model, MIMO channel realizations with identical bit error rate and channel capacity characteristics as the measured channel can be quickly generated for link emulation purposes.

An All-Optical Carrier Recovery Scheme for Access Networks With Simple ASK Modulation

We theoretically investigate and experimentally demonstrate a scheme for all-optical carrier recovery in loopback access networks that avoids orthogonal or complex modulation formats for the downstream or upstream signals. The applied technique is based on a passive resonating circuit that is capable of recovering the optical carrier of the amplitude-shift-keyed downstream signal for remodulation with a reflective modulator as upstream transmitter enabling full-duplex 10 Gb/s operation. The scheme is compared with alternative pattern suppression techniques based on optical gain saturation and electro-optical feed-forward injection for the stringent requirements of next-generation access networks, namely, an extended loss budget and high upstream data rates. Operation at downstream modulation depths of ∼3 dB is reported with the feed-forward approach, while higher modulation depths of up to 9 dB are demonstrated with the all-optical carrier recovery technique, for which the dependence on longer sequences of consecutive identical bits is investigated. Finally, the feasibility of the all-optical downstream cancelation technique for optical access networks is evaluated in a wavelength division multiplexed passive optical network, showing full-duplex transmission with margins of at least 9 dB.

MIMO Transceivers With Decision Feedback and Bit Loading: Theory and Optimization

This paper considers MIMO transceivers with linear precoders and decision feedback equalizers (DFEs), with bit allocation at the transmitter. Zero-forcing (ZF) is assumed. Considered first is the minimization of transmitted power, for a given total bit rate and a specified set of error probabilities for the symbol streams. The precoder and DFE matrices are optimized jointly with bit allocation. It is shown that the generalized triangular decomposition (GTD) introduced by Jiang, Li, and Hager offers an optimal family of solutions. The optimal linear transceiver (which has a linear equalizer rather than a DFE) with optimal bit allocation is a member of this family. This shows formally that, under optimal bit allocation, linear and DFE transceivers achieve the same minimum power. The DFE transceiver using the geometric mean decomposition (GMD) is another member of this optimal family, and is such that optimal bit allocation yields identical bits for all symbol streams-no bit allocation is necessary-when the specified error probabilities are identical for all streams. The QR-based system used in VBLAST is yet another member of the optimal family and is particularly well-suited when limited feedback is allowed from receiver to transmitter. Two other optimization problems are then considered: (a) minimization of power for specified set of bit rates and error probabilities (the QoS problem), and (b) maximization of bit rate for fixed set of error probabilities and power. It is shown in both cases that the GTD yields an optimal family of solutions.

10 Gbit/s burst-mode post-amplifier with automatic reset

A 10 Gbit/s burst-mode post-amplifier with automatic reset generation is presented. The reset signal is created by measuring the time since the last 1. This mechanism is suitable for high bit rate long-reach PONs where the guard time exceeds the maximum time of consecutive identical bits. The post-amplifier consists of four gain stages with automatic offset compensation and an output buffer. It obtains 40 dB gain with 7 GHz bandwidth and consumes 1.1 W from a 2.7 V supply.

Analog Iterative LDPC Decoder Based on Margin Propagation

A margin propagation (MP) algorithm that can be used for implementing analog decoders for low-density parity check (LDPC) codes is presented. Unlike conventional sum-product analog decoders that rely on translinear operation of transistors, MP decoders use addition, subtraction and threshold operations, and therefore can be mapped onto different analog circuit topologies (current-mode, charge-mode, or nonelectronic circuits). This brief describes salient properties of the MP decoding algorithm and compares its performance to the sum-product and the min-sum (MS) decoding algorithms. Simulation results demonstrate that MP based LDPC decoders achieve nearly an identical bit error rate performance as their sum-product counterparts and achieve superior performance as compared to the MS decoding algorithm. Results presented in this brief also demonstrate that, when messages in LDPC decoding are corrupted by additive noise, the MP decoding algorithm delivers superior performance compared to its sum-product and MS counterparts.

Influence of Pinned-Layer Dispersion on Magnetic Tunnel Junction Switching Distributions

The influence of pinning field dispersion (PFD) on the coercivity (Hc) and offset field (Ho) of IrMn/NiFeCo/AlOx/NiFeCo magnetic tunnel junctions (MTJ) has been studied by repeated in situ measurement of the resistance as a function of magnetic field, R(H), hysteresis loops of the MTJs after resetting the IrMn/NiFeCo pinned layer. Magneto-thermal magnetic random access memory, MT-MRAM, cells were used to perform this task. Here, the pinned layer is reset by pulsing a current through the tunnel barrier of the MT-MRAM MTJ in the presence of an external magnetic field. This permits rapid field cooling of the pinned layer through the blocking temperature of the IrMn. Repeated measurements of an R(H) loop after a pinned layer reset cycle show only minor variation. R(H) loops measured for different pinned layer reset cycles however, can show large changes in Hc , Ho, and R(H) loop shape. The effect is believed to be due to the random magnetostatic field distribution resulting from the frozen-in PFD of the IrMn/NiFeCo pinning layer. In order to test this conclusion, the evolution of the R(H) loop is studied as a function of reset pulse amplitude. Because of the intrinsic distribution of blocking temperatures of the IrMn layer, PFD should decrease as reset pulse amplitude increases. Results show that Hc increases, while the R(H) loops become more square as the reset pulse amplitude is increased. Ho shows a more complex dependence, which is a competition between ferromagnetic magnetic-roughness-induced Neel coupling and anti-ferromagnetic stray field coupling. A micromagnetic model for studying the dependence of the R(H) loops on the alignment of the IrMn crystallites was developed, and simulated results are in good agreement with the measurements. This work provides a simple explanation for large switching field distributions that can result in arrays of seemingly identical MRAM bits

Smooth upgrade of existing passive optical networks with spectral-shaping line-coding service overlay

A simple and cost-effective upgrade of existing passive optical networks (PONs) is proposed, which realizes service overlay by novel spectral-shaping line codes. A hierarchical coding procedure allows processing simplicity and achieves desired long-term spectral properties. Different code rates are supported, and the spectral shape can be properly tailored to adapt to different systems. The computation can be simplified by quantization of trigonometric functions. DC balance is achieved by passing the dc residual between processing windows. The proposed line codes tend to introduce bit transitions to avoid long consecutive identical bits and facilitate receiver clock recovery. Experiments demonstrate and compare several different optimized line codes. For a specific tolerable interference level, the optimal line code can easily be determined, which maximizes the data throughput. The service overlay using the line-coding technique leaves existing services and field-deployed fibers untouched but fully functional, providing a very flexible and economic way to upgrade existing PONs.

Universal lossless source controlled channel decoding for I.I.D. sequences

Messages coded and transmitted over a channel usually contain some redundancy which is not utilized by channel decoding techniques, especially if its governing statistical parameters are unknown. We propose to integrate universal lossless source coding techniques into channel decoding of redundant sequences with unknown statistics to improve performance of Viterbi and turbo decoding. Simulation results demonstrate that we achieve identical bit error rate (BER) performance to nonuniversal techniques that utilize prior knowledge of the message statistics and that if redundancy exists even in an a-priori unknown form, we can improve the code performance over standard techniques.

Dynamic Functional Unit Assignment for Low Power

A hardware method for functional unit assignment is presented, based on the principle that a functional unit's power consumption is approximated by the switching activity of its inputs. Since computing the Hamming distance of the inputs in hardware is expensive, only a portion of the inputs are examined. Integers often have many identical top bits, due to sign extension, and floating points often have many zeros in the least significant digits, due to the casting of integer values into floating point, and other reasons. The accuracy of these approximations is studied and the results are used to develop a simple, but effective, hardware scheme.

A novel fingerprint image compression technique using wavelets packets and pyramid lattice vector quantization

A novel compression algorithm for fingerprint images is introduced. Using wavelet packets and lattice vector quantization , a new vector quantization scheme based on an accurate model for the distribution of the wavelet coefficients is presented. The model is based on the generalized Gaussian distribution. We also discuss a new method for determining the largest radius of the lattice used and its scaling factor , for both uniform and piecewise-uniform pyramidal lattices. The proposed algorithms aim at achieving the best rate-distortion function by adapting to the characteristics of the subimages. In the proposed optimization algorithm, no assumptions about the lattice parameters are made, and no training and multi-quantizing are required. We also show that the wedge region problem encountered with sharply distributed random sources is resolved in the proposed algorithm. The proposed algorithms adapt to variability in input images and to specified bit rates. Compared to other available image compression algorithms, the proposed algorithms result in higher quality reconstructed images for identical bit rates.

An efficient quantization technique for wavelet coefficients of fingerprint images

In this paper, a novel quantization scheme for the wavelet coefficients is introduced. Using the wavelet packet transform (WPT) and lattice vector quantization (LVQ), we present here a new lattice optimization scheme based on an accurate model for the distribution of the wavelet coefficients. The model is based on the generalized gaussian distribution (GGD). A least squares algorithm on a non-linear function of the shape parameter is formulated to estimate the model parameters. The proposed algorithm adapts to non-stationarity in input images and to given bit rates. Compared to other wavelet-based algorithms, the technique proposed here results in higher reconstructed image qualities for identical bit rates.

Impact of long periods of identical bits on the choice of a scrambler for SDH

AbstractThe statistical properties of sequences of consecutive identical bits at the output of various scrambler types are analyzed and discussed in order to provide designers of Synchronous Digital Hierarchy systems with a wide range of choices for scrambling implementation.