Electrooptical processing for radio astronomy

A recent report of the first computer-generated radio-derived photographs of the Whirlpool Galaxy will no doubt provide impetus for additional radio photography of astronomical events. Electro-optical techniques, developed in the past decade for obtaining high resolution range, range-rate, and angular target data with array radars, may be highly suitable for generating visible images of astronomical events. The electrooptical processor can furnish continuously and unambiguously, in the form of an optical image, the distribution of radio emission present in the entire effective scan sector of an array without the necessity of electronic steering.     

Estimation of time-varying digital radio channels

In the design of block-oriented digital communication systems that must operate over time-dispersive channels, it is usually assumed that the channel is constant over the duration of a data block, even if the channel fades. The authors study the degradation in receiver performance caused by actual interblock channel variation. For tractability, attention is restricted to the case in which the channel variations are not tracked using decision-directed adaptation. The results suggest that unless the system parameters are carefully chosen, the constant-channel assumption is far from accurate. The quantitative results also offer a measure of the rate of channel time-variations, and give guidelines for deciding when those variations can be considered slow. These guidelines can be used as first-order evaluators of important system design decisions, such as total block size, training overhead, and data rate, for particular channel conditions     

近场光学方法测量大气折射率起伏

精确测量大气的折射率起伏,对于研究大气的光学性质及其在环境监测中的应用有着重要的意义.建立了用近场光学方法测量大气折射率起伏的模型:采用全内反射方法激发金属的表面等离子共振,在金属-空气-金属组成的平面波导中形成振荡的导模,选取衰减全反射曲线中变化最快的一点的角度作为入射光的角度,测量相应的反射光光强的变化,就可以得到相应空气的折射率的变化.初步数值模拟了该模型的测量精度,折射率变化的精度可以达到百万分之五.     

UWB over fiber transmission to multiple radio access units using all-optical signal processing

An ultra-wideband over fiber architecture is proposed where multiple coherent pulsed optical signals are used for transmitting high data rate signals to five different radio access units (RAUs). The RAUs are placed in a star topology to form a broadcast distributive antenna system architecture. The architecture transmits \(5 \times 1.25\) Gbps data from control unit to the RAUs using a wavelength division multiplexed signal. The multiple pulsed optical carriers forming the wavelength division multiplexed signal are generated using a single continuous wave optical source. The data modulated coherent optical pulsed signals are all-optically converted to electrical Gaussian mono-cycle pulses at the RAUs. The proposed architecture is cost-efficient and gives good bit-error rate results.     

Performance analysis of cognitive radio networks using channel-prediction-probabilities and improved frame structure

This paper focuses on potential issues related to the random selection of a sensing channel that occurs after the prediction phase in a Cognitive Radio Network (CRN). A novel approach (Approach-1) for improved selection is proposed, which relies on the probabilities of channels by which they are predicted idle. Further, closed-form expressions are derived for the throughput of Cognitive Users (CUs) in the conventional and proposed approaches. In addition to this, a fundamental approach for computing the prediction probabilities is also proposed. Moreover, a new challenging issue named “sense and stuck” was observed in the conventional approach. The proposed approach is validated by comparing the results achieved with the results of the conventional approach. However, to achieve the prediction probabilities, the pre-channel-state-information is a prerequisite, but it may be unavailable for particular scenarios; therefore, a modified selection method is introduced to avoid the sense and stuck problem. An algorithm to evaluate the throughput using the random, improved, and modified selection methods is presented with its space and time complexities. Furthermore, for additional improvement in the throughput of the CU, a new frame structure is introduced, in which the spectrum prediction and sensing periods are exploited for simultaneous transmission of data via the underlay spectrum access technique (Approach-2). The simulated results of Approach-2 are compared with our pre-obtained results of Approach-1, which confirm significant improvement in the throughput.     

Estimation of Gilbert's and Fritchman's models parameters using thegradient method for digital mobile radio channels

A series of error sequence measurements in a typical mobile radio channel has been conducted to study the time distribution of transmission errors. E.N. Gilbert's (1960) and B.D. Fritchman's (1967) digital communication channel models are shown to describe adequately the observed error bursts occurring in the mobile radio channel. An estimation method based on the gradient algorithm is proposed for computing the parameters values of both models from the experimentally derived error distributions. A digital mobile radio channel simulator based on Gilbert's and Fritchman's models with the parameter values as estimated using the gradient technique is presented     

Estimation of the transfer ratio frequency characteristic of HF radio channel by using the LFM signal

A technique for determining the transfer ratio frequency relationship of a short-wave ionospheric radio channel with high resolution has been considered using the continuous linear-frequency-modulated signal. This technique is based on the filtering of modes of ionospheric propagation at the receiver output following the compression method processing in the frequency domain. The estimates of measurement errors were also presented.     

Functional processing of wideband radio frequency hopping signals

Experimental research results of correlation processing of radio frequency hopping signals (FHSS radio signals) with the help of planar domain-acoustic processor are presented. This processor has linear spectrum of reference frequencies which are used for respective consecutive frequency setting during signal generation.     

A generalized Karhunen-Loeve basis for efficient estimation of tropospheric refractivity using radar clutter

In this paper, we consider the problem of obtaining a reduced-dimension parameterization of a propagation medium for the purpose of estimating the medium from transmission data. The application addressed is microwave remote sensing of tropospheric index-of-refraction profiles over the sea surface, using radar clutter returns. The proposed parameterization balances the desire to represent features prominent in the a priori statistics of the profiles versus the need to capture elements of the profile that significantly affect the observed clutter data. In linear estimation problems, basis vectors for the unknown parameter vector that optimizes this tradeoff have been derived as the reduced-rank Wiener filter or, equivalently, the generalized Karhunen-Loeve transform (GKLT). In this paper, we reinterpret the linear result, producing an extension to the nonlinear refractivity estimation problem. The resulting procedure produces basis vectors for tropospheric refractivity that are less dependent on features that have little effect on the clutter measurements. This results in a more efficient parameterization and reduces mean-square estimation error relative to an approach driven purely by the statistical prior. Application of the generalized KL technique to finding efficient basis vectors for refractivity profiles taken off the southern California coast is presented.     

Enhancing the noise immunity of multichannel radio reception system using a game-theory algorithm for signal processing

This paper deals with a possible enhancement of noise immunity of a multichannel radio reception system that can be achieved by significant reduction of the number of complex units and a fundamental change of the algorithm for game-theory processing of signals and interferences. The efficiency of the proposed system has been estimated in comparison with those of the known systems.     

A statistical technique for processing radio interferometer data

The output of a radio interferometer is the Fourier transform of the object under investigation. Due to the limited coverage of the Fourier plane the reconstruction of the image of the source is blurred by the beam of the synthesized array. In this paper a maximum-likelihood processing technique is described that uses the statistical properties of the received noise-like signals. This technique has been used extensively in the processing of large aperture seismic arrays. This inversion method results in a synthesized beam that is more uniform, has lower sidelobes, and higher resolution than the normal Fourier transform methods. The maximum-likelihood method (MLM) algorithm was applied successfully to very long baseline (VLB) and short baseline interferometric data.     

Estimation of the radio pulse duration with unknown phase

Quasi-likelihood and maximum likelihood algorithms for estimating the duration of a radio signal having arbitrary waveform and unknown phase were synthesized. Asymptotically exact characteristics of the estimates were also found.     

Signal processing hardware in a radio LAN demonstrator

In order to demonstrate the practicality of high speed radio LANs, such as HIPERLAN, a hardware demonstrator has been built. To overcome the inter-symbol interference caused by the dispersive nature of the indoor radio channel, a decision feedback equaliser has been included in the system. No central synchronisation is provided in a network and a node must be able to derive all synchronisation from a received packet. This paper describes all of the signal processing hardware built for the demonstrator. The demonstrator is not standards compliant but the physical layer parameters are very similar and the signal processing required in HIPERLAN equipment will be very similar to that in the demonstrator.     

Wire transfer of charge packets using a CCD-BBD structure forcharge-domain signal processing

A structure for the virtual transfer of charge packets across metal wires is described theoretically and is experimentally verified. The structure is a hybrid of charge-coupled device (CCD) and bucket-brigade device (BBD) elements and permits the topological crossing of charge-domain signals in low power signal processing circuits. A test vehicle consisting of 8-, 32-, and 96-stage delay lines of various geometries implemented in a double-poly, double-metal foundry process is used to characterize the wire-transfer operation. Transfer efficiency ranging between 0.998 and 0.999 is obtained for surface n-channel devices with clock cycle times in the range from 40 ns to 0.3 ms. Transfer efficiency as high as 0.9999 is obtained for buried n-channel devices. Good agreement is found between experiment and simulation     

电波环境及微波超视距传播

为衡量海上蒸发波导环境下的超视距通信系统性能,提出了一种超视距信道建模方法及容量估计方案. 基于蒸发波导折射率模型和抛物方程（parabolic equation, PE）模型研究电波沿海面蒸发波导信道传播的大尺度衰落特性,结合统计性模型研究其小尺度衰落特性,形成基于电磁仿真和统计规律的混合蒸发波导信道模型,并由此推导出系统信道容量的估算方案. 对实际海面传播环境进行电磁建模,计算了蒸发波导环境中的路径损耗分布和多天线系统的信道容量,量化了使用多输入多输出（multiple-input multiple-output, MIMO）技术带来的超视距传播性能提升. 仿真结果表明,在蒸发波导环境中采用MIMO技术能够有效地提升信道容量,实现较好的超视距传播效果. 本文结果对海上超视距通信系统的应用及性能评估具有重要意义.     

HF-band radio receiver design based on digital signal processing

The authors address the design of an HF band receiver using commercially available technology, with the aim of producing a receiver whose performance is better than that available with the current purely analogue designs and which incorporates a significant element of digital signal processing. To give the reader an appreciation of some of the system, component and architectural constraints, they first review component limitations and candidate architectures. This is followed by a detailed analysis of a prototype HF band (0.1 to 30 MHz) receiver designed by the authors as part of a recent research programme     

基于软件无线电的机载射频信号综合处理技术

当前飞机中通信、导航和监视这些关键功能,例如VHF通信、VOR、ADF、DME、ILS、MKR、应答机和ADS-B等,通常由独立的机载设备实现,其体积、重量和功耗很大,成本也非常高,影响了这些功能在通用飞机上的应用.解决这个问题的有效方法就是将这些功能综合到统一平台上,本文提出了一种基于软件无线电的射频信号综合处理技术,并建立仿真验证平台进行了验证,证明了该方法的技术可行性.     

软件无线电中的数字信号处理技术研究

软件无线电是近几年来颇受关注的一种无线通信体系结构,由于软件无线电技术的灵活性,其被广泛应用于无线电领域。文章主要介绍了软件无线电中的数字信号处理技术。     

Efficient receiver structure for GSM mobile radio

The paper describes a receiver structure for the digital GSM mobile radio which is suitable for implementation using a DSP processor. The simulation results show that proposed simplifications have minor influence on the receiver performance and drastically reduce its computational complexity.