Telemetry Signals Research Articles

PCM-formatter: a powerful, low cost system for PCM telemetry decoding and quick look support

An IBM compatible PC board has been developed to simplify acquisition and execution of quick look on telemetry signals. The pulse code modulation (PCM)-FORMATTER can synchronize and decommutate nonreturn to zero level (NRZL) or split phase level (SPL) streams in the range of 5 kb/s to 128 kb/s. Up to eight different functions can enhance the real time data preelaboration. Periodically the host PC can read the reconstructed format frames from two dual port memory buffers. An application software package helps the user in preparing the board and allows a sensible reduction in the data handling code. This code, which is prepared by the user, works like a subroutine making the required elaboration on an entire format subframe at a time. The faster the execution, the lighter the proportion of the analyzed data. The hardware, based on a field programmable gate array (FPGA), can be adapted by software in a different device to operate different tasks.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling of artificial plasma “bubble” in ionosphere

Results of a combination of radio-crossing and in situ measurements of plasma density in an artificial plasma “bubble” in the ionosphere are presented. Shaped — charge barium injection was made at short distance (≤50 m) to plasma diagnostics on the rocket. After injection the rocket passed through expanding plasma shell. Plasma density depletion inside was more than one order and plasma enhancements on the boundary about 3–5 times that of background. When the rocket passed the shell and went away by 2.1 km an abrupt drop of telemetry signal level (≤ 65 dB) was registered though plasma density was not more than 3×10 3sm −3. An estimation of high frequency signal refraction on the plasma shell is in good accordance with refraction data of geostationary satellite signals on equatorial bubbles.

Study of equatorial plasma bubble dynamics using GHz scintillation observations in the Indian sector

To study equatorial plasma bubble dynamics, telemetry signals (4 GHz) were recorded simultaneously from two geostationary satellites. INSAT-1B (74°E) and INSAT-1C (94°E) at Sikandarabad satellite Earth station (dip 42.0°) from January to December 1989 and at the Chenglepet satellite Earth station (dip 10.5°) during September–October 1989 along the same geomagnetic meridian. The characteristics and occurrence pattern of the scintillations suggest that these are equatorial plasma bubble induced events. Observations from the two satellites recorded simultaneously at each of these locations were utilized to estimate the east-west plasma bubble irregularity motion. Plasma bubble rise velocities over the magnetic equator were calculated from the systematic onset time differences observed between an equatorial and a low latitude station. The east-west plasma bubble velocity estimated at Sikandarabad, corresponding to 1200 km altitude in the equatorial plane, shows a night time variation pattern with a peak at around 2100 LT. The mean values over Chenglepet, which correspond to 400 km altitude, start decreasing right from 1900 LT and seem to be influenced by the plasma bubble rise velocities. The differences in magnitude observed between the present results and those reported elsewhere by other techniques are interpreted in terms of vertical shears in the plasma zonal flow over the equator. The near alignment of the two observing stations along a common geomagnetic meridian and the simultaneous use of two satellites located twenty degrees apart in longitude provided an excellent data base to study plasma bubble dynamics.

Retrieval of a wind profile from the Galileo Probe telemetry signal

Ultrastable oscillators onboard the Galileo Probe and Orbiter will permit very accurate determinations of the frequency of the Probe’s telemetry signal as the Probe descends from a pressure level of several hundred mb to a level of about 20 bars. Analysis of the time-varying frequency can provide, in principle, a unique and important definition of the vertical profile of the zonal wind speed in the Jovian atmosphere. In this paper, we develop a protocol for retrieving the zonal wind profile from the Doppler shift of the measured frequency; assess the impact of a wide range of error sources on the accuracy of the retrieved wind profile; and perform a number of simulations to illustrate our technique and to assess the likely accuracy of the retrieval.

Signal-selective time-difference-of-arrival estimation for passive location of man-made signal sources in highly corruptive environments. I. Theory and method

For the problem of estimating time difference of arrival (TDOA) of radio waves impinging on a pair of antennas for the purpose of passively locating the source of a communications or telemetry signal in the presence of interfering signals and noise, a new class of signal-selective algorithms that are highly tolerant to interference and noise is introduced. Unlike conventional methods, the new methods cross correlate frequency-shifted as well as time-shifted versions of the received data in order to exploit the unique cyclostationarity property of the signal of interest.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Signal-selective time-difference of arrival estimation for passive location of man-made signal sources in highly corruptive environments. II. Algorithms and performance

For pt.I see ibid., vol.40, no.5 p.1168 (1992). For the problem of estimating time difference of arrival (TDOA) of radio waves impinging on a pair of antennas for the purpose of passively locating the source of a communications or telemetry signal in the presence of interfering signals and noise, a new class of signal-selective algorithms that are highly tolerant to interference and noise is introduced. By virtue of the fact that the multiple-signal resolution problem is essentially eliminated by the signal selectivity of the algorithms, performance advantages are gained. The new algorithms exhibit their signal selectivity regardless of the extent of temporal, spectral, or spatial overlap among received signals, yet their computational complexity is no more than that of conventional algorithms. Algorithmic implementations of some of the new methods are given, and theoretical arguments given in pt.I of this work are corroborated by quantitative evaluation of their performance. >

The behavior of a Costas loop in the presence of space telemetry signals

When the Costas loop is operated in the presence of a residual carrier space telemetry signal, the loop reconstructs its carrier reference from an input signal whose carrier component is not completely suppressed. The telemetry signal investigated in this work is generated by phase shift-keying the data onto a subcarrier and then phase modulating onto the sinusoidal carrier. The telemetry modulation index, telemetry bit rate, subcarrier waveform, and subcarrier frequency are shown to be the key system parameters that contribute to the performance degradation of a Costas loop. Furthermore, the effect of Doppler shift on the loop is also investigated in this work. >

Implementation and design of biosignal optical telemetry system based on enforced synchronization

This paper discusses the optical telemetry system for a life science experiment conducted in a space station, the feature of which is the telemetry of multichannel biosignals from a number of objects in the same booth. First, the enforced synchronization telemetry system is proposed. This system is based on two-way communication which forms the key to the simultaneous biosignal telemetry from a number of objects. Based on the proposal, an experimental system is constructed. The external system sends a command signal to the object side and then receives and demodulates the telemetry signal from the object side

The Effect of Exercise on the Atrial Electrogram Voltage in Young Patients

Atrial electrogram sensing is an important function in active individuals with permanently implanted bipolar dual chamber pacing systems. We undertook to determine the effect of vigorous exercise on the atrial electrogram size in 11 children and young adults (average age 12 years). Using a telemetry signal through a handheld programming wand, nine tracings were completely and clearly recorded for analysis. Six patients had tined/passive fixation atrial leads and three patients had screw-in/active fixation lead systems. All leads were bipolar. The atrial electrogram size for each patient was measured at rest and at each minute of exercise. The atrial electrogram size decreased with exercise from a mean of 5.08 mV to 3.44 mV (range 0.9-4.25 mV) (P = 0.002). The 1.64 mV mean decrease represented a 33.8% reduction (range 19%-56%) (P less than 0.001). There was no difference in the change in atrial electrogram size between the two lead types. Treadmill exercise testing with telemetric data of atrial electrograms showed a decrease in atrial electrogram size produced by exercise and may be helpful in determining appropriate atrial sensitivity settings in selected individuals. Because of the documented decrease in atrial electrogram size produced by exercise, we recommend obtaining maximal atrial electrograms at the time of implant and use of pacing systems that allow maximal flexibility in atrial sensing especially in athletically active individuals.

Modeling weak fluctuations of undersea telemetry signals

Numerical calculation of acoustic field perturbation expressions can be used to predict fluctuations after propagation through ocean sound-speed structures, but before the onset of multipath. The general form of the expressions for signal spectra or correlation functions allow numerical evaluation for an unlimited quantity of vector wave-number spectral models of refractive index. In order to help define the bounds of applicability of the theory, log-intensity fluctuation variances have been calculated for three major situations: ocean internal waves, ocean turbulence, and continuous strong large-scale turbulence. Propagation through ocean thermocline internal waves, realistically weak thermocline turbulence, and unrealistically strong turbulence show that scintillations of intensity can be predicted and understood to first order up to ranges of tens of kilometers, given the proper transmission geometry. Internal wave effects dominate over any effects from expected microstructure. Nonhorizontal transmission yields small fluctuations, but eventually refractive effects of the sound channel will contribute some additional spatial variability and multipath, complicating the use of the theory. Multipath due to the sound channel can exist at ranges where the random small-scale structures would contribute only small perturbations (no multipath from small structures). >

A New Formulation of the Discrete-Time Optimal Linear Regulator. Application to LSS Decentralized Control

On applying the theory of the optimal linear regulator to the decentralized control of a LSS such as a interconnected Power System, due attention has not been paid to some special aspects introduced by the Telecommunication and Computing Systems. Some of these aspects are: 1/ Telemetering delays. 2/ Computational delays. 3/ Loss of synchronism between telemetry and telecommand signals. 4/ Interacction between programs of different levels (samplig period dilation). In this paper a new formulation of the discrete-time optimal linear regulator capable to take these aspects into account is presented. This formulation allows to compensate the loss of optimality due to computational and telemetering delays and also allows the design of a OLR based on a dual control action in each sampling period in order to improve the system stability in front of loss of synchronism and sampling time dilation. Finally, this formulation is applied to the decentralized control of a two-area model (corresponding to the Catalan Power System).

Spacecraft Attitude Real-time Determination System Based on Multiprocessor Distributed Architecture

Abstract A microprocessorization Spacecraft Attitude Real-time Determination System (SARDS) based on multiprocessor distributed architecture has been implemented. A real-time system architecture suitable for multiprocessor concurrent processing were created. A series of mathematical models implemented on microprocessors, including telemetry signal on-line processing, real-time UDU factorization Kalman filter and system I/O controller were built. The microprocessor hardwares and softwares that matched well with real-time attitude determination tasks and models were designed specially. A series of flight tests were conducted in 1, Feb.,1986. The experiences of SARDS system design and flight tests demonstrated that the realization of all microprocessorization satellite ground support system will be possible.

ＶＬＢＩによる静止衛星の高精度軌道決定

Aiming at precise orbit determination of a geosynchronous satellite, a VLBI experiment was conducted to observe the 2GHz band telemetry signal of the DSCS-II satellite stationed at 180deg, East. A differential VLBI method was used, where the satellite and quasars with well-known positions were alternatively observed over 24 hours using stations in Japan, United States and Australia. It was confirmed that a few meter position accuracy of the satellite in an inertial frame referring to the quasars was achieved in orbit determinations and covariance analysis considering observation errors, quasar position errors, and modeling errors in the observation system and satellite dynamics.

Monitoring the tests: Missile flights and test explosions are watched closely to determine whether an adversary's new weapons might upset the strategic balance

US monitoring capabilities related to the surveillance of Soviet strategic forces are reviewed and assessed. Data collected during the testing of military systems and the information derived from it are discussed. The author describes various information gathering systems (satellites, radars, ground sensors, sea sensors) used in the detection of missile telemetry signals, and of land-based military systems. Emphasis is on the detection of Soviet nuclear weapon and missile testing along with their implications for strategic arms limitation treat constraint verification.

A Digital Polarity Correlator with Built-in Self Test and Self Repair

Correlation techniques are widely used in communications, instrumentation, computers, telemetry, and other signal processing systems to detect a desired signal in the presence of noise, to recognize patterns, and to measure time delays. With the development of VLSI, correlation can be performed efficiently with a minimal number of components. The correlator chip presented in this article consists of a linear cascade of identical elements; failure of any one element causes complete chip failure. Therefore, we devised a self-test and self-repair structure to automatically bypass faulty stages. The overhead for self test and self repair was approximately six percent of the chip area. The results of functional testing of the first batch of processed chips demonstrated a nine-to-one yield enhancement and an exhaustive functional test time of less than 150 milliseconds. The self-repair mechanism provides high in-service reliability.

Strong refraction near the Venus surface: Effects observed by descent probes

The high‐pressure atmosphere of Venus causes strong downward refraction of radio rays, with consequences that were evident in the telemetry signals from Pioneer Venus probes. As the probes descended, the strength of the direct signal to the earth gradually diminished because of the combined actions of absorption and refractive defocusing. Both phenomena became increasingly pronounced as penetration proceeded. Like occultation recordings of signal strength, these records too can be analyzed to yield a profile of atmospheric temperature versus altitude. During the final 30 km of descent, there was in addition to the direct signal a second measured component that traveled to the surface of Venus and from there scattered toward the earth. The strong atmospheric refraction played a key role leading to the strengthening (and hence the detectability) of these echoes. Surprisingly, it is found that such surface‐reflected signals provide a good indication of the horizontal winds existing at each altitude during the descent of the probes. Since the refraction is roughly the same in the visible band as it is at radio frequencies, there was some speculation that refractive effects might be visible in the images of the surface returned by the Soviet landers. No such effects were apparent. I demonstrate that the absence is attributable to limited visibility.

Simultaneous ground‐satellite observations of quasi‐periodic (QP) ELF‐VLF emissions near L=6

Simultaneous ground‐satellite observations of ELF‐VLF emissions have been carried out at Syowa station (L∼6) in Antarctica during the IMS period by receiving the telemetry signals from the ISIS 1 and 2 satellites. The quasi‐periodic intensity modulation of ELF‐VLF emissions at the satellite level, which had one‐to‐one correspondence with the intensity modulation of QP emissions at Syowa, was observed in the wide latitude range from −54° to −78° MLAT, and also in the region ∼2 hours apart from Syowa in magnetic local time. The spectral form of QP emissions observed on the ISIS satellite showed a clear dependence on latitude, i.e., emissions in the higher frequency range were observed at lower latitudes, while emissions in the lower frequency range were observed at higher latitudes. Although quasi‐periodic intensity modulation of polar chorus had generally one‐to‐one correspondence between the ground and satellite data, burst‐like discrete emissions did not show always one‐to‐one correspondence between both data. These results give a basis to confirm a phenomenological model proposed by Sato and Fukunishi [1981] for the generation mechanism of QP emissions.

Chatanika/Triad observations of unstable ionization enhancements in the auroral F‐region

Preliminary results are presented from a campaign of coordinated measurements between the Chatanika radar and the TRIAD satellite to investigate production mechanisms responsible for localized high‐latitude scintillations. The radar measured the latitudinal variations of plasma density and electric field while the satellite measured the field‐aligned current distribution with latitude. This information was used to calculate the linear growth rate of the current convective instability. We find that field‐aligned ionization enhancements, which are a common feature of the auroral F‐region, are unstable, with instability growth times of ≤ 6 minutes. The observed plasma configuration, which was already gradient drift unstable on its poleward edge, was further destabilized by a field‐aligned current of ∼ 0.8 µA/m². The presence of electron density irregularities produced in the unstable region was verified by observing VHF scintillations on the TRIAD telemetry signal.

ETS-II Experiments Part V: Effect of Ionosphere

Propagation characteristics of gigahertz and very high frequency waves through the mid-latitude ionosphere have been studied applying the coherent beacon signals of 1.7, 11.5, and 34.5 GHz and the 136-MHz telemetry signal, which are emitted from the geostationary Engineering Test Satellite Type II (ETS-II). Total electron content (TEC) was obtained by measuring the differential phase shift between 1.7 and 11.5 GHz waves and also by the Faraday rotation of the 136-MHz carrier, the former method being more sensitive than the latter one for detecting fluctuating TEC. During the observations, amplitude scintillations at 136 MHz and 1.7 GHz, usually accompanied with an irregular variation of TEC, were recorded frequently in the nighttime and sometimes in the daytime. Specially noted is the 11.5-GHz scintillations less than 0.8 dBp-p that were observed during the severe magnetic storm on February 15, 1978, simultaneously with 136-MHz and 1.7-GHz scintillations. This was the first observation showing that the disturbed ionosphere affects waves above 10 GHz. Presented first are the techniques for the ETS-II ionospheric wave propagation experiment, including a description of the coherent receiver system in the gigahertz frequency range at Kashima and a description of the 136-MHz Faraday rotation receiver at Kokubunji. The capabilities of the facilities for monitoring the mid-latitude ionosphere by giving some observational results are then presented.

Data compression techniques and applications

Several data compression methods are reviewed for signal and image digital processing and transmission, including both established and more recent techniques. Methods of prediction-interpolation, differential pulse code modulation, delta modulation and transformations are examined in some detail. The processing of two-dimensional data is also considered.Results of the application of these techniques to space telemetry and biomedical digital signal processing and telemetry systems are presented.Some of the considerations and comparison criteria presented, even though not completely general because extracted from experimental results, can be useful in selecting and defining the more pertinent data compression system for the different practical applications.