Meteor-burst Systems Research Articles

Operational communication systems and relationships to the ionosphere and space weather

There are a variety of operational communication systems that are dependent upon the ionosphere, and there are others that are influenced by the ionosphere. In the dependent category, we have short-wave (i.e., MF and HF systems) and long-wave systems (i.e., VLF and LF systems). In the influenced category we have some VHF systems such as meteor-burst systems, and higher frequency SATCOM systems in the UHF and SHF bands. The paper will address various resource management issues for specified operational systems, and the relationship with aspects of space-weather will be discussed. Some examples where space-weather information is used in existing systems are presented. We also identify how space-weather information could be used in those situations where it is currently unused. We conclude with challenges facing advocates of a viable space-weather program [Goodman, J.M. Space Weather and Telecommunications. Kluwer international series of Engineering and Computer Science, Springer Science + Buisness Media Inc., New York, 2005].

Measured performance of meteor burst systems using antenna beam steering

This paper describes the use of antenna beam steering to improve performance of meteor burst communications systems. Various techniques used to achieve antenna beam steering are described and compared. Measured comparisons of meteor burst performance with and without antenna beam steering are given. To demonstrate an application of beam steering, a meteor burst system with 10 times the throughput performance of any previous meteor burst system, and with sufficient capacity to provide interactive voice communication, is also described. >

Spaced antenna diversity in temperate latitude meteor burst systems operating near 40 MHz: Variation of signal cross‐correlation coefficients with antenna separation

We have studied 37‐MHz signals received over an 800‐km temperate latitude path using 400‐W continuous wave transmissions. Signals collected during a 9‐day period in February 1990 on two antennas at separations of 5λ, 10λ, and 20λ were analyzed. Three signal categories were identified (overdense, underdense, and not known (NK)) and cross‐correlation coefficients between the signals received by the two antennas were calculated for each signal category. No spatial variation, and in particular no decrease, in average cross‐correlation coefficient was observed for underdense or NK signals as the antenna spacing was increased from 5λ to 20λ. At each antenna separation the cross‐correlation coefficients of these two categories were strongly dependent on time. Overdense signals, however, showed no cross‐correlation time dependency at 5λ and 10λ, but there was a strong time dependency at 20λ. Recommendations are made in regard to the optimum antenna spacing for a meteor burst communication system using spaced antenna diversity. Our measurements support the views of Bartholomé and Vogt [1968], who suggested that a 4λ spaced antenna diversity configuration contributed to the exceptional signal throughput of the COMET meteor burst communication system.

Spaced antenna diversity in temperate latitude meteor burst systems operating near 40 MHz: Variation of signal cross‐correlation coefficient with time

The potential for meteor burst (MB) spaced antenna diversity is studied using cross‐correlation techniques at a temperate latitude, using 37‐MHz signals scattered over an 800‐km path. Approximately 9 hours of data were analyzed from a 2‐day period in February 1990, when the antenna separation was 10λ. The correlation variations with time of signals with durations ≥ 0.75 s, which were categorized as “underdense,” “overdense,” or “not known” (NK), were investigated. The cross‐correlation coefficients of signals from underdense and overdense trails are high when correlated over their total signal envelopes, but this is not true when the signal envelope is segmented in time. NK signals are observed to be more uncorrelated than underdense or overdense signals and are, therefore, likely to be the most advantageous to a diversity system. Analysis of data from all three categories combined shows that 40% of signals with duration ≥ 0.75 s have correlation values of less than 0.6 after the first 0.25 s. The correlation‐time dependency observed for NK and underdense signals is not identified for the overdense signal category. It is proposed that for underdense and NK signals the correlation‐time dependency is due to the vector addition of other weak signal modes. These weak signal modes, however, have little effect on overdense signals which, typically, exhibit higher signal powers in the early stages of the signal envelope.

Efficient communications using the meteor-burst channel

This work presents the results of a theoretical study of the meteor-burst channel which illustrates its time-varying bursty nature. In addition, the authors describe an innovative approach to data transmission over meteor-burst systems, i.e. the use of the feedback adaptive variable rate (FAVR) system which allows the maximum amount of information to be transmitted over each meteor-burst channel. For underdense meteor channels the FAVR performance is compared to an optimum system, i.e. a system capable of changing its bit rate instantaneously to channel conditions so as to maintain a constant SNR in each bit, and to a constant optimum rate/burst system. It is shown that when compared to an optimum rate per burst system, FAVR can result in a throughput increase exceeding a factor of 10. It is also shown that FAVR can approach the optimum system performance, although for practical purposes, it appears that 83-88% of optimum is attainable.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Meteor burst propagation

Meteor burst communication systems are introduced with emphasis placed on the unusual propagation mode which they employ. The origin of meteors and their trails is reviewed and the trail characteristics relevant to communication systems described. The restriction on scattering geometries for viable transmission paths is exlained and the related footprint and hot-spot properties of meteor burst systems outlined. Meteor burst transmission loss is formulated in the conventional way as a modified bistatic radar equation and the origins of the modifying factor qualitatively explained. Meteor burst equipment, operating principles and applications are also briefly discussed. Finally, important quantities for assessing the performance of meteor burst systems are defined and typical values quoted.

High Data Rate Meteor-Burst Communications

The meteor burst communications channel offers a largely untapped means of communications that can alleviate congestion in many existing communications systems. It also provides some interesting advantages over other beyond-line-of-sight systems, including lower susceptibility to atmospheric perturbations, a limited footprint, and relatively low cost. Past system applications have been quite limited, however, due to the random nature of the meteor burst phenomenon which has resulted in relatively low throughput and lengthy wait-times.This paper presents the results of an experimental study of the meteor burst channel which illustrates its time-varying bursty nature. In addition, the authors describe an innovative approach to data transmission over meteor burst systems, ie, the use of the Feedback Adaptive Variable Rate (FAVR) system which allows the maximum amount of information to be transmitted over each meteor burst channel.For underdense meteor channels the FAVR performance is compared to an optimum system, ie, a system capable of changing its bit rate instantaneously to channel conditions so as to maintain a constant SNR in each bit, and to a constant optimum rate/burst system. It is shown that for such a system FAVR can result in a throughput increase exceeding a factor of 10.

Spatial Properties of Meteor-Burst Propagation

The experiments described in this paper were carried out to determine the probability of simultaneous reception of meteor-burst signals at different geographic locations (interception) so that the possibility of interference and frequency sharing as well as the suitability of this type propagation to broadcasting may be assessed. Interception tests were conducted at five different sites using transmissions on a 1000-km circuit between Terminal A, near The Hague, The Netherlands, and Terminal B, near Toulon, France. The five monitoring stations were located at Harrogate (Station C) in England, Station D near Paris, Station E near Frieburg in Germany, Station F near Rome, Italy, and Station G, some 35 km from Terminal A. It was found that at Station G the same signal bursts were received as at Terminal A and interception was practically total. At the other four stations, interception was mainly due to the simultaneous occurrence of two meteor trails reflecting waves in different directions. The amount of information intercepted was on the average between 3 and 16 percent, but could occasionally be 100 percent due to sporadic-E reflections. However, the experiments used a frequency of 36 MHz; by operating at 70 MHz or higher interception due to abnormal ionospheric propagation conditions could be virtually eliminated. It is estimated that interference to meteor-burst link from beyond the horizon would be very inefficient since the power ratio at 40 MHz is about 25 to 1 in favor of the link. At higher frequencies the advantage for the link would be much greater. The results of the interception tests show that meteor-burst systems can be used for broadcasting provided that three separate antenna systems are employed to cover ranges up to 2000 km and to repeat the message continuously from one to several minutes to achieve a high probability of reception. Frequency sharing between several meteor-burst links operating in the same area also appears to be feasible with frequencies high enough to eliminate ionospheric scatter and sporadic-E layer reflections.

Directional Characteristics of Meteor Propagation Derived from Radar Measurements

The directivity of radio reflections from meteor trails and the distribution of trail orientations (radiants) control the directional properties of meteor propagation. Because of the geometrical correspondence between radar and oblique path detection of meteors, the directional properties of meteor propagation can be determined from the range and azimuth distributions of the echoes detected by a radar system. The gross features of these directional properties for an east-west path in northern temperate latitudes are such that-for maximum circuit duty cycle (product of number of echoes and their average duration)-the antenna beams at the transmitter and receiver should be pointed north of the great circle bearing during the morning hours and south of this bearing during the evening. The optimum off-path angle may vary from a few degrees to greater than 20°. For a north-south path, the beams should be pointed west of the path at night and east of the path during the day, for maximum duty cycle. These gross features appear to repeat each day. In addition, short-term fluctuations in the radiant distribution have been noted, some of these fluctuations presumably being due to heretofore undetected meteor showers of very short duration. It appears that the information capacity of meteor burst and ionospheric scatter communication systems could be markedly increased by varying the bearings of the antenna beams according to the known diurnal variations in meteor radiants.