Narrowband heterodyne reception using unstabilized sources

Source power for laboratory-type experiments is often limited at millimeter and submillimeter wavelengths. This requires the use of sensitive receiving equipment. Cooled square-law detectors and narrowband heterodyne detectors are examples. We have developed a coherent mechanical frequency shifter, which makes possible narrowband heterodyne detection without the need for highly frequency stable sources. Identical frequency and phase fluctuations of the transmit and local oscillator signals derived from one source are eliminated at the intermediate frequency. The widely tunable frequency shifter, designed for a 637GHz scale-model radar, was tested in a 140GHz non-radar configuration. We investigated the receiver's minimum coherently resolvable bandwidth and its sensitivity. Several types of sources were compared for the effect of local oscillator amplitude noise on receiver sensitivity at low intermediate frequency.     

Generation and reception of wideband ultrasound

A previous article on ultrasonic spectroscopy described the applications of wideband ultrasonic techniques to materials testing. Here it is shown how wideband (0.5–20 MHz) transducers for pulse-echo systems can be produced. Excitation is achieved by specially-shaped electrical pulses while, for the reception mode, high-gain wideband amplifiers and gates are available. Frequency analysis of the ultrasonic pulses is carried out by a novel, inexpensive spectrum analyser. New ideas for data processing, both analogue and digital, are reviewed.     

Correlation reception of thermal acoustic radiation

Correlated signals of thermal acoustic radiation from heated sources extending in the transverse direction (a pair of narrow plasticine plates and a wide plasticine strip) are measured. The measurements are performed by multiplying together the signals that are shifted in time with respect to each other and detected by two piezoelectric transducers. The values of the correlated signals of thermal acoustic radiation are determined by the spatial variation of temperature in the medium under study.     

Porous piezoelectric composites with extremely high reception parameters

The reception parameters Q ₃₃ ^* and Q _h ^* of modified fiber composites based on high-e ₃₃ ^FC /c ₃₃ ^{FC, E} ferroelectric piezoceramics (e ₃₃ ^FC is the piezoelectric constant, c ₃₃ ^{FC, E} is the elastic modulus) are considered as functions of the electromechanical properties and the porosity of the components. Pore configurations at which the values (Q ₃₃ ^* )²≈(Q _h ^* )²≈7×10⁻⁹ Pa⁻¹ for the polymer matrices of 1-0-3 composites are much higher than for conventional ternary composites are analyzed.     

Spatially polarized adaptive array and reception of wideband signals

The effect of spatial and polarization characteristics of the wideband signal and noise on the efficiency of the spatially polarized adaptive array without frequency compensation is investigated. It is shown that the major factors reducing the efficiency of the adaptive system are the frequency spectrum and partial depolarization of the noise.     

Age of Information Minimization for Radio Frequency Energy-Harvesting Cognitive Radio Networks

The Age of Information (AoI) measures the freshness of information and is a critic performance metric for time-sensitive applications. In this paper, we consider a radio frequency energy-harvesting cognitive radio network, where the secondary user harvests energy from the primary users’ transmissions and opportunistically accesses the primary users’ licensed spectrum to deliver the status-update data pack. We aim to minimize the AoI subject to the energy causality and spectrum constraints by optimizing the sensing and update decisions. We formulate the AoI minimization problem as a partially observable Markov decision process and solve it via dynamic programming. Simulation results verify that our proposed policy is significantly superior to the myopic policy under different parameter settings.     

Accuracy of body-rotation-parameter measurement with monochromatic illumination and two-element reception

Analysis of the components of optimum processing of a backscattered field is used to derive analytic formulas for the accuracy of estimation of the proper-rotation velocity-vector components of an illuminated body in the general case of progressive—rotational motion. It is shown that two-element measurement is considerably more accurate than single-element.Moscow Aviation Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 5, pp. 433–439, May, 1992.     

Diversity reception and equalization techniques for laser communication in space

The principle of band-limited space optical communication system using the techniques of space diversity methods and time domain Rake receiver is analyzed. The joint channel equalizer method combining diversity reception and equalization technique is presented in space laser communication. By computer simulation, the bit error rates of noncoherent pace optical on-off keying signal using different space diversity methods, Rake reception with different inter-symbol interferences, joint diversity equalizations with different signal noise rates and different channel numbers are analysed. The results identify that joint diversity equalization method can enhance space optical communication erformance evidently.     

Effect of spectral envelope smearing on speech reception. I.

The effect of reduced spectral contrast on the speech-reception threshold (SRT) for sentences in noise and on phoneme identification, was investigated with 16 normal-hearing subjects. Signal processing was performed by smoothing the envelope of the squared short-time fast Fourier transform (FFT) by convolving it with a Gaussian-shaped filter, and overlapping additions to reconstruct a continuous signal. Spectral energy in the frequency region from 100 to 8000 Hz was smeared over bandwidths of 1/8, 1/4, 1/3, 1/2, 1, 2, and 4 oct for the SRT experiment. Vowel and consonant identification was studied for smearing bandwidths of 1/8, 1/2, and 2 oct. Results showed the SRT in noise to increase as the spectral energy was smeared over bandwidths exceeding the ear's critical bandwidth. Vowel identification suffered more from this type of processing than consonant identification. Vowels were primarily confused with the back vowels /c,u/, and consonants were confused where place of articulation is concerned.     

Correlation reception of a diffraction sound field in an oceanic waveguide

Intensity matched processing is considered for a diffracted signal when the object is detected by the main lobe of the shadow scattered sound field. The consideration is based on the few-parameter model that adequately describes the characteristics of the desired signal. It is shown that, in the absence of noise and fluctuations in the parameters of the medium, the proposed algorithm provides the determination of the exact parameters of the signal and the moving object.     

水声正交频分复用异步多用户接入方法

水声信道传播时延大导致水声通信网中上行用户同步困难,因此需要接收端具备异步多用户检测能力。针对水声正交频分复用(OFDM)异步多用户系统提出一种基于滑动迭代的异步多用户接入方法,包括重叠截断、干扰消除、频域过采样、多用户信道估计与解码、以及干扰重构5个处理模块,并通过滑动迭代结构同时消除前向干扰和后向干扰影响。仿真结果表明,所提方法在不同异步到达时延,以及有、无信道估计误差下的误比特率均明显低于逐块解调异步接收算法。水池实验结果表明,滑动迭代异步接收算法在多径扩展18 ms、异步到达时延大于或等于循环前缀1.5倍时实现了两用户异步接入的可靠通信。     

射频网络频率特性分析仪

利用对数运算放大器、高速直接数字合成器、微控制器和CPLD等技术设计成结构新颖的数字化频率特性分析仪,频率扫描范围100kHz~400MHz,测量结果可在液晶屏上显示并通过RS232接口送到外部计算机.     

邮票上的物理学史(72)--射频和微波波谱学

射频和微波波谱学是物理学的一个分支学科,它通过射频或微波电磁场与物质的共振相互作用研究物质的性态和结构,简称波谱学．射频和微波电磁波的频率范围约为10^4～10^12Hz,随着实验技术的发展,其范围还在向更高频段延伸．波谱学的测量以频率厂为主,其准确度比可见光(原子光谱)和红外