J. Austin

An autoregressive approach to the identification of multipath ray parameters from field measurements

This study is concerned with using modern spectral analysis techniques to derive estimates of multipath ray parameters (delays and amplitudes) from measurements of selective fading over a wide band at microwave frequencies. The applicability of the general category of autoregressive methods is addressed, and the specific method adopted, the Prony algorithm, is described. An illustrative example in which this is applied to a typical field measurement is followed by an investigation into the capabilities and limitations of the algorithm. A statistical analysis of the method has been carried out using a database of laboratory measurements. The Prony algorithms ability to resolve delays to better than half the Fourier limit is shown, and its tendency to yield biased estimates is studied. >

Analysis of the time variant structure of microwave line-of-sight multipath phenomena

The authors report a novel technique, the SVDP (singular value decomposition prony) algorithm, which has demonstrated its superiority in identifying the multipath rays in line-of-sight microwave links. The technique has been applied to field data and it has proved itself to be a very useful tool in analyzing the time-variant structure of the actual physical mechanism, i.e. the evolution of the delay and amplitude of the multipath rays. The authors present the results of analysis of field measurements made at 11 GHz over a wide bandwidth of 400 MHz on the French CNET at Lannion, using a 50 km link. The major applications of this technique are: the modelling of a multipath channel using the least possible number of rays with the objective of minimizing the RMS error; the analysis of the time-variant structure of a channel and hence the design of adaptive equalizers; and the generation of the statistics of the time-domain multipath parameters, particularly the delay and amplitude distributions. >

A novel approach to the simultaneous measurement of phase and amplitude noise of oscillators

An approach for the simultaneous measurement of amplitude and phase noise in oscillators is presented. A description of the measurement system and the associated processing techniques is presented. The measurement system includes a conventional complex (I & Q) demodulator, a high speed sampler and a digital computer. The techniques are named time-domain phase unwrapping and real amplitude de-enveloping. They permit the reconstruction of the demodulated I and Q signals as a vector rotating at a convenient beat frequency randomized, in phase and magnitude, by noise. The problems encountered in conventional AM and PM detection can be overcome using the approaches described. As a result, direct and true amplitude and phase noise can be measured and characterized.<<ETX>>

Analysis of Moderate and Intense Rainfall Rates Continuously Recorded Over Half a Century and Influence on Microwave Communications Planning and Rain-Rate Data Acquisition

This paper is concerned with the statistical investigation of a massive data bank of 49 years of rainfall rate R continuously recorded in Barcelona using a rain-rate gauge with ten seconds response time. With radio communications in mind, the paper addresses and reviews in detail: 1) reliable statistical model for R , 2) number of years required to obtain a database from which to derive a reliable R -distribution, and 3) the CCIR worst-month concept. The research has shown that the generalized Pareto a exp (-\muR)/R^{b} gives nearly perfect fit for all ranges of R followed closely by the gamma distribution, and the simpler square root ( R^{1/2} ) normal distribution gives excellent fit too. The log-normal distribution was unsatisfactory for R \geq 60 mm/h. The spread of the yearly distribution of P(R) is cube root normally distributed ([P(R)]^{1/3}) and between 7 and 10 years are required before a reliable average distribution P(R) can be obtained. The study of the P(R) return time in years is also presented. High resolution of P(R) is presented looking at the evolution of the annual P(R) in terms of the hourly and monthly contributing parts revealing statistical features such as the location in time of rain rates above 50 mm/h. Finally, the study shows that the calendar month contribution to P(R) remains at all times well below the synthetic CCIR worst month and recommendations are then given about its use.

Analysis of joint rainfall rate and duration statistics: microwave system design implications

The joint statistical analysis of duration D and intensity R of rain exceedances relevant to the design of microwave communication systems is considered. The data analyzed are derived from point precipitation-rate observations recorded over a period of 49 years in the city of Barcelona, Spain, using a Jardi gauge. The concept of event and the duration of a single exceedance of a threshold R within that event is introduced. The analysis shows the parametric R dependence of the annual average number of exceedances and of the average duration. >

A spread spectrum communications channel sounder

The design of a microwave channel probing analyzer is presented and discussed. Special attention is paid to the characteristics of the transmission path to be measured; the choice of spread spectrum probing signal; the signal processing methods used; modulation, demodulation, and synchronization at the transmitter and receiver sites; the path model to be fitted to the measured data and finally, the impact of all of these issues upon the necessary hardware and software. Following a formulation of the channel-probing problem, transfer function regression techniques are reviewed to illustrate the advantages of periodic averaging over established correlation methods. The construction of an experimental sounder based on these methods is described. The equipment has been used to measure the time-variant frequency-selective channel dynamics of a short (158 km) troposcatter transhorizon link at a frequency of 11.647 GHz over a 31.25-MHz bandwidth. Off-line, nonlinear spectrum analysis, based on Pronys method and singular value decomposition, is used to estimate parameters of a high-resolution delay model that accurately reflects the underlying ray structure of the transmission path.

A Novel Approach to the Simultaneous Measurement of Phase and Amplitude Noises in Oscillator

This paper presents a signal processing technique called time-domain phase unwrapping applied to the measurement of phase noise in oscillators and which overcomes the dynamic range problem of using phase detectors. The technique can be applied also to the measurement of the amplitude noise of the oscillator. In this paper, the associated theories and the preliminary experimental results are included.

Wideband transhorizon channel characterization

The paper describes a 31.25 MHz bandwidth wideband channel sounder used to characterize a transhorizon path over the English Channel (La Manche) at 11.64 GHz. The measurements were done continuously for a period of 8 months (June 5, 1996, to January 5, 1997), capturing 515 Mb of data each day. A nonlinear regression technique, singular value decomposition prony (SVD-P), was used to estimate the channel impulse response from the measured transfer function. The received signal levels obtained together with their dynamic signatures were used to categorize the mechanisms into three broad groups: ducting, strong enhancements, and troposcatter. The statistical analysis carried out gave strong correlation between signal levels, delay spread, coherence bandwidth, and Doppler spread. The results also help to highlight the limitation of traditional channel characterization parameters such as delay spread. The investigation has also revealed the potential and propagation conditions of an over the sea transhorizon path as a high-data-rate communication channel. The research has qualified and quantified the interference potential in spectrum reuse and the frequency decorrelation probabilities to combat it.

Fading statistics on an over-the-sea transhorizon link

A wideband experimental system designed to analyse an 11.647 GHz transhorizon channel subject to troposcatter and anomalous propagation conditions is described. The evolution of the channel during multipath fading condition is presented with the aid of the estimated channel impulse response. The fading statistics of wideband and narrow band signals for a period of 8 months is presented.

Doppler Correction Of The Telecommunications Payload Oscillators In The UK T-SAT

The article gives values for the doppler shift of an L-band radio path between a UK observer and a 12 h period Molnya orbit satellite. Two doppler correction units for the local oscillators of the UK T-SAT payload are described, one utilising frequency locking and the other phase locking. A critical assessment of the performance of each unit is given.