Time domain constellation shaping technique for peak-to-average power ratio reduction

A new constellation shaping technique has been proposed, which efficiently and effectively reduces the peak-to-average power ratio (PAPR) of orthogonal-frequency-division-multiplexing (OFDM) systems. Its novelty is based upon a simple transformation in the time domain instead of the commonly used frequency domain. This transformation is shown to ensure PAPR reduction regardless of the OFDM system input. As compared with previously known PAPR reduction methods, the proposed technique requires minimal implementation complexity, while it offers considerable performance gains. Closed form analytical expressions for the distribution of the PAPR and the bit error rate are derived. The accuracy of these analytical expressions is verified via equivalent performance evaluation results obtained by means of Monte Carlo computer simulations. Furthermore, performance comparisons made with other competitive techniques show that the proposed technique is an attractive alternative for PAPR reduction.     

水声通信中无边带信息峰均比抑制算法

主要研究了多输入多输出正交频分复用水声通信中的峰均功率比抑制技术。针对传统选择性映射算法(Selective Mapping,SLM)需要将所选加扰相位序列的序号作为边带信息传递给接收端的缺点,提出了一种改进SLM算法,从判决反馈的角度设计图样检测器对所选加扰相位序列的序号进行判断,节约了边带信息传输,克服了传统SLM算法系统的误比特率性能依赖于边带信息准确性的问题,提高了系统的频带利用率。通过仿真验证,改进SLM方法能在不损失峰均功率比抑制性能的前提下,在接收端能够准确地解算出所选择的加扰相位序列序号,实现无边带信息传输的可靠水声通信。     

一种降低OFDM信号峰均功率比的预编码方法

正交频分复用（OFDM）系统的一大缺点就是有较高的峰值平均功率比（PAPR）,大大降低了线性功率放大器的效率。提出了一种用预编码方法,通过引入预编码矩阵将映射后的数据进行功率分配,从而降低OFDM信号的PAPR。该方法不影响频谱效率,不需要进行附加运算以及收发两端的握手信息。计算机仿真表明对传统的64个子载波OFDM系统PAPR有将近9dB的改善。     

Selective post-IFFT amplitude randomising for peak-to-average power ratio reduction in orthogonal frequency-division multiplexing-based systems

The inherent high peak-to-average power ratio (PAPR) of multicarrier transmission, such as orthogonal frequency-division multiplexing (OFDM) or discrete multi-tone (DMT), can lead to a significant degradation in the transmission power efficiency which is unacceptable especially in battery-powered terminals. Among the most popular PAPR reduction techniques proposed in the literature is the selective mapping (SLM) technique which has been shown to offer PAPR reductions of several decibels. However, the SLM technique requires invoking the inverse fast fourier transform (IFFT) process several times per transmitted OFDM block which increases the system's complexity and hence may result in long latencies and high power consumption. The authors propose a new low complexity post-IFFT PAPR reduction technique that can outperform the SLM technique in terms of PAPR reduction while its operational complexity is orders of magnitude less than that of SLM technique.     

Orthogonal frequency-division multiplexing radar signal design with optimised ambiguity function and low peak-to-average power ratio

Considering the important role of the ambiguity function (AF) of a signal regarding the performance of a matched filter bank for the detection of targets and the estimation of their ranges and velocities, the thumbtack shape is assumed to be the desirable shape of the AF and the method of least squares for the synthesis of the AF is introduced. Then, an iterative method for the allocation of a proper phase to the desired AF is proposed to obtain better results. This method is then applied to select the proper codes for the synthesis of pulsed orthogonal frequency-division multiplexing signals. It is also shown how this method can reduce sidelobes, almost uniformly, throughout the entire ambiguity plane. Finally, an efficient algorithm is presented, which modifies the produced codes in order to reach a lower peak-to-average power ratio suitable for transmission.     

Concatenated peak-to-average power ratio reduction scheme with threshold limited selection for coded orthogonal frequency-division multiplexing

The authors propose a concatenated scheme to reduce the peak-to-average power ratio (PAPR) in coded orthogonal frequency-division multiplexing (OFDM) systems. First, they employ a label-bits-inserted encoder of a random-like code to achieve selected mapping (SLM). Then they set a threshold at the selector to limit the number of candidate sequences. Both analytical and numerical results show that the complexity of the SLM implemented by the label-bit-inserted encoder can be significantly reduced by threshold limited selection. With the same complexity, the performance of PAPR reduction is improved. The proposed concatenated PAPR reduction scheme enjoys many advantages including low-complexity, small overhead, no side information transmission and no performance loss or additional complexity at the receiver.     

一种新的OFDM峰均功率比抑制算法

峰均功率比(PAPR)过高是OFDM系统的一个主要缺点,由于OFDM发射端功率放大器的非线性,高的峰均功率比会导致信号的频谱扩展,同时降低了放大器的工作效率。传统的削波算法虽然能够简单有效地降低信号的峰均功率比,但是会带来较大的额外频谱增益。为了克服传统削波算法的缺点,文中提出一种新的削波算法,该算法在降低PAPR的同时做到零频谱增益。并基于传统削波产生误差信号,通过对误差信号的滤波,以牺牲信号的EVM实现了零频谱增益。但又会带来较大的带内干扰,仿真表明配合相应的噪声消除算法,其误码性能接近未削波的原始信号水平。     

Redundancy-free and BER-maintained selective mapping with partial phase-randomising sequences for peak-to-average power ratio reduction in OFDM systems

Selective mapping (SLM) is one of the most effective peak-to-average power ratio (PAPR) reduction techniques proposed for orthogonal frequency-division multiplexing systems. However, the fact that this technique requires the transmission of side information (SI), to enable the receiver to reverse the randomisation process before performing signal demodulation, can make it undesirable for certain applications as it degrades the system's bandwidth efficiency and, more significantly, the bit error rate (BER) performance. A modified SLM technique (MSLM) that can operate without the need for any dedicated SI for both channel-coded and uncoded scenarios while providing similar PAPR reduction performance as the ordinary SLM technique is proposed. It will be demonstrated that the proposed MSLM technique not only improves the system's bandwidth efficiency, but also achieves significantly better BER performance than the ordinary SLM technique.     

3 x 3 matrix for unitary optical systems

We introduce a 3 x 3 matrix for the study of unitary optical systems. This 3 x 3 matrix is a submatrix of the 4 x 4 Mueller matrix. The elements of this 3 x 3 matrix are real, and thus complex-number calculations can be avoided. The 3 x 3 matrix is useful for illustrating the polarization state of an optical system. One can also use it to derive the conditions for linear and circular polarization output for a general optical system. New characterization methods for unitary optical systems are introduced. It is shown that the trajectory of the Stokes vector on a Poincaré sphere is either a circle or an ellipse as the optical system or input polarizer is rotated. One can use this characteristic circle or ellipse to measure the equivalent optical retardation and rotation of any lossless optical system.     

Peak-to-average power ratio reduction in OFDM using cyclically shifted phase sequences

Two approaches for reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) are proposed that are relied on a set of cyclically shifted phase sequences (CSPS) and implemented using the time domain circular convolution. After multiplying CSPS with the frequency domain data, the signal candidates can be expressed as weighted sum of the circularly shifted OFDM time domain data in the first method, which is called CSPS method. In the second method, weighted coefficients for generating the signal candidates in CSPS method are optimally selected to improve its performance; thus, the second method is referred to as optimised CSPS (OCSPS) method. The performances of the CSPS and OCSPS methods are evaluated using simulated data and compared with those of selective mapping (SLM) and partial transmit sequences (PTS). The simulation results show that both the CSPS and OCSPS methods can reduce the PAPR effectively, and that the OCSPS performs even better than the CSPS. The OCSPS can achieve the same performance as compared to the PTS. A distinct feature of the proposed methods is that only one inverse discrete Fourier transform is needed, and thus, the candidates can be calculated in time domain directly.     

Comparison of unitary transforms using Franson interferometry

Unknown unitary transforms may be compared to each other in a way which makes it possible to obtain an unambiguous answer, indicating that the transforms are different, already after a single application of each transform. Quantum comparison strategies may be useful for example if we want to test the performance of individual gates in a quantum information or quantum computing network. It is then possible to check for errors by comparing the elements to a master copy of the gate, instead of performing a complete tomography of the gate. In this paper we propose a versatile linear optical implementation based on the Franson interferometer with short and long arms. A click in the wrong output port unambiguously determines that the tested gate is faulty. This set-up can also be used for a variety of other tasks, such as confirming that the two transforms do not commute or do not anticommute.     

A matrix formulation for the dynamic analysis of spatial mechanisms using point coordinates and velocity transformation

Summary. This paper presents a matrix formulation for the dynamic analysis of spatial mechanisms with common types of kinematic joints. The formulation is derived in two steps. Initially an equivalent constrained system of particles that replaces the rigid bodies is constructed and used to define the configuration of the mechanical system. This results in a simple and straightforward procedure for generating the equations of motion in terms of the rectangular Cartesian coordinates of the particles without introducing any rotational coordinates. The equations of motion are then derived in terms of relative joint coordinates through the use of a velocity transformation matrix. The velocity transformation matrix relates the relative joint velocities to the Cartesian velocities. For the open loop case, this process automatically eliminates all of the non-working constraint forces and leads to an efficient integration of the equations of motion. For the closed loop case, suitable joints should be cut and few cut-joints constraint equations should be included for each closed loop. An example is used to demonstrate the generality and efficiency of the proposed method.     

Factorization of the polarization transformation matrix in integrated photoelasticity

In integrated photoelasticity, assessment of stresses in a three-dimensional specimen is based on the measurement of the change of polarization on many light rays that pass the specimen. Since the medium is optically anisotropic and inhomogeneous, the optical phenomena are nonlinear and solution of the inverse problem is complicated. Several methods of solving the inverse problem demand an efficient algorithm for solving the direct problem, i.e., for the calculation of the polarization transformation matrix on the basis of the stress field in the medium. We propose for this use factorization of the transformation matrix. We show that if the transformation of polarization is described by characteristic parameters, the three characteristic parameters can be determined by solving a single third-order differential equation. Since characteristic parameters can be measured experimentally, this approach can be used in practical three-dimensional stress analysis with integrated photoelasticity.     

RMS matrix strains in transformation toughened alumina

The Warren Averbach technique was used to determine the RMS strain profile in the Al₂O₃ matrix surrounding ZrO₂ particles in zirconia toughened alumina. The X-ray domain size was found to be 100nm in all but the most severely microcracked sample. The RMS strain, averaged over all domains, decreased nearly linearly from the edge of the domain (presumably from the ZrO₂ particle), except when microcracking was detected and then the RMS strain level was reduced near the surface of the domain. The maximum RMS strain level increased with increasing ZrO₂ particle size up to the point where microcracking occurred then decreased. The results were explained by noting that the maximum RMS strain was directly related to the monoclinic content of the sample.     

Discrete-time method for signal-to-noise power ratio measurement

The measurement of signal-to-noise power ratio (SNR) is of fundamental importance in many areas of electrical engineering, such as communications, signal processing, tests and measurements, circuits and systems, etc. In this paper, we propose two algorithms for estimating the signal-to-noise ratio of a noisy sinewave from discrete-time data obtained by sampling the input signal. One algorithm is based on the estimation of the four parameters of the input sinewave. The second algorithm is based on estimating the average noise power by averaging the squared magnitude of the FFT bins attributed to the noise. Both methods show excellent performance. Simulation results indicate that the four-parameter method requires the input SNR to be at least 10 dB and the input signal frequency not exceeding one-third of the sampling frequency. On the other hand, the second approach, the spectrum averaging method, shows a remarkable robustness over a very wide range of normalized frequencies (with respect to the Nyquist frequency) and SNRs (well over 100 dB). This spectrum averaging method should prove to be very useful in a wide range of applications     

Nonlinearity of the transformation functions of thermoelectric microwave power transducers

Translated from Izmeritel'naya Tekhnika, No. 5, pp. 53–55, May, 1988.     

Reducing the measurement error and power input in resonance moisture control transducers

A two-parameter method of resonance moisture control is proposed as a means of decreasing the error that arises when dielectric measurements are carried out under conditions of elevated conductance of the controlled substance. The design of a transducer that realizes this method is developed and experimentally investigated, and the precision is substantially increased and the power consumption of the control transducer reduced.     

Reducing power loss in magnetic bearings by optimizing current allocation

Conventional magnetic bearings control current or flux by operating symmetrically about a bias current or bias flux. This approach is known to be much easier to control than operating without a bias but has the disadvantage of introducing additional power loss. Although one obvious way to minimize the power loss is to alternate activation of the two opposing electromagnetic actuators, this single actuator allocation strategy has not been successful in practical applications because it results in severe performance degradation. In this paper, we investigate the fundamental reasons behind the performance degradation under the single actuator allocation strategy. One major reason is voltage saturation in the circuit systems. On the basis of this result, we formulate the problem of minimizing the energy consumption by allocating the currents under the constraint of bounded voltages. We establish necessary conditions and properties for the optimal solution, which we use to determine the optimal allocation strategy for some common force signals. Since the optimal solution is very sensitive to the variation of the force signal, we propose a simple static allocation strategy to approximate the optimal solution.     

Aspect ratio requirements for nanotube-reinforced, polymer–matrix composites

A fiber’s efficiency in a short-fiber composite can be accurately solved by shear-lag methods, which can account for fiber geometry, an imperfect interface (or interphase), and extend to low volume fractions. Such an analysis was used to evaluate the aspect ratio requirements for single-walled nanotubes (SWNT) in a polymeric composite and contrast it to conventional fibers. The aspect ratio requirements are indistinguishable among all stiff fibers, except at low volume fractions where stiffer fibers require higher aspect ratios. The required aspect ratio decreases significantly at higher volume fractions. A scaling effect in the interphase term implies the interphase is more important for nano-fibers than for larger fibers. If the interface between nano-fibers and the matrix is not excellent, those fibers will not provide effective reinforcement. The most promising SWNT composites should use higher volume fractions and focus on systems where the fiber can stiffen the matrix in the interphase region.