A model for calculating the depolarization of microwave signals propagating through rain

A model for calculating the amount of depolarization for linearly polarized electromagnetic waves propagating through rain is described. The presented method provides mathematical expressions for the co-polar and the cross-polar components of the received signal emerging from a rain cell. Calculations are carried out in two ways: with a general distribution of canting angles as measured by Saunders and with an equivalent canting angle together with the associated percentages of the positively and the negatively canted raindrops in a rain cell. The predicted attenuation and the cross polarization as calculated by both methods are found to be in good agreement with the published data measured by various workers.     

Noise behaviour of the m.o.s.f.e.t. at v.h.f. and u.h.f.

The optimum noise figures of an m.o.s.f.e.t. at u.h.f. and at pinch-off are calculated using a simplified equivalent circuit. The noise parameters are also determined experimentally. Theory and experiment are shown to be in good agreement. Noise parameters of the m.o.s.f.e.t. for the frequency range 0.1?0.8 GHz are given.     

Measurement of field strength for mobile services at v.h.f. and u.h.f. for the city of Melbourne

A series of field-strength measurements at both v.h.f. and u.h.f. has been taken in Melbourne to assist in the introduction of mobile-radio-telephone services. These results have been analysed and the results are presented. A comparison is made with curves obtained from Okumura.     

Method of phase-modulating signals in optical fibres: application to optical-telemetry systems

By attaching a piezoelectric transducer that modulates the mechanical tension over a short section of fibre, signals in optical fibres are phase modulated. The technique is applicable to a I-way optical-telemetry system.     

Novel method for amplitude measurement of signals up to microwave frequencies

The method gives very good input/output linearity down to input amplitudes of 100 mV; by using germainum diodes, this could probably be extended down to 10 mV even lower.     

A novel detection criterion for weak m-ary signals and its application to ultrawideband multiple access systems

In this paper, we propose a novel criterion for the detection of weak m-ary signals. In the sense of minimizing the error probability, the proposed criterion is optimal when the signal strength approaches zero. Based on the proposed criterion, a detection scheme for ultrawideband multiple access systems is proposed and analyzed in the presence of impulsive interference. Numerical results show that the proposed detector requires less complexity than, and possesses almost the same performance as, the maximum likelihood detector. In impulsive interference, the proposed detector also offers significant performance improvement over the detector optimized for a Gaussian environment.     

Simple expression for light output of edge-emitting d.h. l.e.d.s

A relatively simple expression for the output power of edge emitters has been obtained by defining a net loss coefficient averaged over all wavelengths, and using the radiation confinement-factor concept. The model is verified with experimental data from (AlGa)As l.e.d.s of varying stripe contact length.     

An application of the diffractor grating to the 11-Gc/s microwave systems

The diffractor grating is a new version of the microwave passive repeater developed to improve the transmission qualities of links utilizing mountain diffraction. It has special advantages in the high-frequency region, as well as in the 11-Gc/s common carrier band, where the construction of a large-aperture flat reflector encounters difficulties and becomes uneconomical. Principles and characteristics of diffractor grating are given with test results. Various factors affecting the diffractor grating behavior are investigated, and comparisons are made with the double-plane reflector system. The diffractor grating is shown to be applicable to short-haul microwave systems and possibly reduce construction costs.     

Reconstruction of chaotic signals with application to channel equalization in chaos‐based communication systems

A number of schemes have been proposed for communication using chaos over the past years. Regardless of the exact modulation method used, the transmitted signal must go through a physical channel which undesirably introduces distortion to the signal and adds noise to it. The problem is particularly serious when coherent‐based demodulation is used because the necessary process of chaos synchronization is difficult to implement in practice. This paper addresses the channel distortion problem and proposes a technique for channel equalization in chaos‐based communication systems. The proposed equalization is realized by a modified recurrent neural network (RNN) incorporating a specific training (equalizing) algorithm. Computer simulations are used to demonstrate the performance of the proposed equalizer in chaos‐based communication systems. The Hénon map and Chua's circuit are used to generate chaotic signals. It is shown that the proposed RNN‐based equalizer outperforms conventional equalizers as well as those based on feedforward neural networks for noisy, distorted linear and non‐linear channels. Copyright © 2004 John Wiley & Sons, Ltd.     

Applications of dual-gate GaAs m.e.s.f.e.t.s for fast pulse shape regeneration systems

The suitability of dual-gate GaAs m.e.s.f.e.t.s for pulse shape reconstruction in the Gbit/s range is presented. The properties of these f.e.t.s and the circuitry for reduction of pulse width and pulse slope are both described. The variation of the input/output pulse-width ratio and the time behaviour for fast pulses are shown.     

A novel defected ground structure for an active device mounting and its application to a microwave oscillator

This letter is to present a new defected ground structure (DGS), which is useful for mounting an active device, and its application to a microwave oscillator. The newly proposed DGS circuit is useful for mounting a transistor such as a BJT or field effect transistor (FET) on ground plane. In order to bias dc to a transistor, it is necessary to implement the dc isolated circuit in a practically applied active device with a DGS. For dc isolation, each branch of DGS should be isolated from ground. However, the proposed DGS structure with dc isolations introduces a degradation of gain performance for a transistor and changes the matching point. In order to overcome these limits, we have investigated a coupling method by using the simple coupling capacitor without degradations in RF performances. This letter displays the comparison of several measurements for the fabricated DGS circuits including the case that compensates the degradations due to the dc isolation. Furthermore, a design example of a microwave oscillator with the proposed DGS is demonstrated to show the validity of this letter.     

The transmission of digital signals through random, time-variant, dispersive channels with application to chaff scatter

This paper is a report on the characterization and modeling of a specific dispersive communication channel, a chaff scatter channel. Theoretical and experimental results are given. The basic modeling of the chaff scatter channel as a linear, time-variant, random-parameter filter is given and its salient properties developed. Based on this model, a theoretical analysis of a continuous-phase binary FSK communications system operating over the chaff scatter channel is given. Experimental results obtained in the use of this system on an actual chaff scatter channel are then presented and compared with the theoretical results.     

综合电子信息系统体系工程方法研究与应用

为了实现综合电子信息系统的有效集成,提出了多视角的体系工 程顶层设计方法、标准规范研究先行的体系工程工作模式设计方法、现代项目管理和共性技 术管理以及使用管理相结合的体系工程管理方法、全过程验证的体系工程评估方法等。这些 方法和具体措施在工程实践中取得了很好的应用效果,对同类综合电子信息系统的工程研制 具有参考意义。     

Use of trimethylantimony and trimethylarsenic for organometallic v.p.e. growth of GAAs1-ySby and Ga1-xInxAs

The use of trimethylarsenic and trimethylantimony as group V sources for the organometallic v.p.e. growth of GaAs1-ySby (0 ? y ? 0.11) and Ga1-xInxAs(x ? 0.29) is reported. No room-temperature reaction is observed between triethylindium and trimethylarsenic and the growths are made at ambient pressure with no special reactor modifications.     

Overview and comparison of equalization schemes for space-time-coded signals with application to EDGE

This paper describes and compares several practical equalization schemes for space-time-coded transmissions over broadband wireless channels. For space-time trellis codes (STTCs), we describe and compare two reduced-complexity trellis-based joint equalization and decoding schemes whose performance is further optimized by a front-end finite-impulse response (FIR) channel-shortening prefilter. For space-time block codes, we describe and compare three joint equalization and decoding schemes based on a block-level implementation of the well-known Alamouti scheme either in the time or frequency domains. We consider the third-generation time division multiple access (TDMA) cellular system known as Enhanced Data rates for Global Evolution (EDGE) and recommend a promising equalization scheme for space-time trellis-coded and for Alamouti-type space-time block-coded dual-antenna transmissions based on simulation results for typical urban channel conditions where the delay spread is few symbol periods.     

Integration of signals/systems and electromagnetics courses through the design of a communication system for a cardiac pacemaker

The integration of multiple concepts and courses through laboratory design projects are part of a new experimental program at the University of Utah, supported by the National Science Foundation, the College of Engineering, and the University of Utah. One such project is the design of an FSK communication system for a cardiac pacemaker, which combines labs from the junior-level "signals and systems" courses and the junior-level electromagnetics course, which are both taught in the same semester. The electromagnetic and the signal and system labs are briefly described in this paper.     

Toward an improvement of H.264 video transmission over IEEE 802.11e through a cross-layer architecture

The recently developed H.264 video standard achieves efficient encoding over a bandwidth ranging from a few kilobits per second to several megabits per second. Hence, transporting H.264 video is expected to be an important component of many wireless multimedia services, such as video conferencing, real-time network gaming, and TV broadcasting. However, due to wireless channel characteristics and lack of QoS support, the basic 802.11-based channel access procedure is merely sufficient to deliver non-real-time traffic. The delivery should be augmented by appropriate mechanisms to better consider different QoS requirements and ultimately adjust the medium access parameters to the video data content characteristics. In this article we address H.264 wireless video transmission over IEEE 802.11 WLAN by proposing a robust cross-layer architecture that leverages the inherent H.264 error resilience tools (i.e., data partitioning); and the existing QoS-based IEEE 802.11e MAC protocol possibilities. The performances of the proposed architecture are extensively investigated by simulations. Results obtained indicate that compared to 802.11 and 802.11e, our cross-layer architecture allows graceful video degradation while minimizing the mean packet loss and end-to-end delays.     

A maintenance planning and business case development model for the application of prognostics and health management (PHM) to electronic systems

This paper presents a model that enables the optimal interpretation of prognostics and health management (PHM) results for electronic systems. In this context, optimal interpretation of PHM results means translating PHM information into maintenance policies and decisions that minimize life cycle costs, or maximize availability or some other utility function. The electronics PHM problem is characterized by imperfect and partial monitoring, and a random/overstress failure component must be considered in the decision process. Given that the forecasting ability of PHM is subject to uncertainties in the sensor data collected, the failure and damage accumulation models applied, the material dimensions and properties used in the models, the decision model in this paper addresses how PHM results can best be interpreted to provide value to the system maintainer. The result of this model is a methodology for determining an optimal safety margin and prognostic distance for various PHM approaches in single and multiple socket systems where the LRU’s in the various sockets that make up a system can incorporate different PHM approaches (or have no PHM structures at all).The discrete event simulation model described in this paper provides the information needed to construct a business case showing the application-specific usefulness for various PHM approaches including health monitoring (HM) and life consumption monitoring (LCM) for electronic systems. An example business case analysis for a single socket system is provided.     

Method of correction for linear distortion of signals and application to DNA fingerprint data

An algorithm has been derived that will identify the situation where a one-dimensional signal is a linearly stretched version of another and then correct for such distortion by expanding the 'compressed' trace. The application of the algorithm to the analysis of DNA fingerprint data is discussed.<>