Communications Research Laboratory Research Articles

STARNET: a multi-gigabit-per-second optical LAN utilizing a passive WDM star

We propose a new broad-band local area network, STARNET, based on a physical passive star topology. Over a single physical network, STARNET offers all users both a moderate-speed packet network and a high-speed WDM circuit interconnect. Based on these two data transport facilities, several topological aDd protocol solutions are available to the users. As a result, STARNET supports traffic of widely different speed and continuity characteristics. Each node of the network requires only two lasers and its structure facilitates the achievement of frequency stabilization for the whole network. An effort toward an experimental demonstration of a 3 Gb/s per node, FDDI-compatible (at the packet network level) STARNET is currently in progress at the Optical Communication Research laboratory of Stanford University

Activity Overview of DYANA Campaign in Japan.

The international DYANA campaign occured between the 15th of January 1990 and the 15th of March, 1990. Japan joined the project and efforts were made so that as many ground observations as possible could be carried out in Japan. These were; ozone density measurements, by both National Institute for Environment Studies and Meteorological Research Institute, sodium layer measurements by Shinshu University, atmospheric turbulence, wind direction and speeds using MU radar by Kyoto University, ionosphere monitoring such as of fmin by Communication Research Laboratory from five ionosondes located in Japan, and finally rocket launchings carried out by two institutions, Japan Meteorological Agency and Institute of Space & Astronautical Science. Activities conducted by these institutions are briefly reviewed below.

The attache case size message communication system via satellite links

The Communications Research Laboratory (CRL) has been carrying out research and development of a very low rate message communication system with an ultra-small earth station called the Attache Case Size Message Communication Terminal (AMCT). In order to minimize the size and power consumption of the AMCT, a transmission rate of 100 b/s is adopted. This is extremely low for satellite communications. As a result, the AMCT is similar in size to an attache case. In the base station, the fast Fourier transform (FFT) technique is used in order to search for a very narrow band signal from the AMCT and compensate for the frequency deviation of the signal. The experiments have been carried out through ETS-V satellite links to estimate the bit error rate (BER) and acquisition performance of this system. Also, the probability of completed message transmission is calculated using these experimental results. Based on these results, it is confirmed that a very low rate transmission system such as this system is applicable to satellite communications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Geodetic VLBI Activities of Communications Research Laboratory

Geodetic VLBI Activities of Communications Research Laboratory

Detection of Philippine Sea Plate Motion by very long baseline interferometry

The Geographical Survey Institute (GSI) deployed a mobile Very Long Baseline Interferometry (VLBI) system at an established site in Chichijima (the biggest island in the Bonin islands), twice in an interval of two years. Two sessions were conducted in the experiments each year by connecting the reference base station at Kashima Space Research Center of Communications Research Laboratory (CRL). The results from the data of four experiments indicate that the Chichijima site moved 7.4±0.8cm in the direction of N67°W in the two years. This is the first successful direct measurement of the motion of Philippine Sea plate (PHS) by any method. Our result is consistent with the predicted rigid motion of PHS from the newest plate velocity model (NUVEL‐1).

Development of a GPS time comparison system and the GPS common-view measurements

An L1 band (1575.42 MHz), C/A (coarse/acquisition) code GPS receiver for precise time comparisons has been developed. GPS measurements in common-view have been carried out between the Korea Standards Research Institute (KSRI) and the Communications Research Laboratory (CRL), Japan. The frequency stability of the KSRI master clock has been measured against the master clock of CRL for 50 d. The frequency stability is about 1 part in 10/sup 13/ for the averaging time of 4 d. >

Hybrid system of communication and positioning determination using two geostationary satellites

The Communications Research Laboratory (CRL) of the Ministry of Posts and Telecommunications in Japan has developed a novel hybrid satellite system which can provide both communications and positioning services in one system using two geostationary satellites. The distinctive feature of this system is that location information can be provided by transmitting and receiving ranging signals over the same channel as communications through two geostationary satellites. Radio determination and communication experiments using the ETS-V and INMARSAT satellites were scheduled to start at the end of 1989. The equipment configuration is examined. and the positioning accuracy is assessed. >

Japanese Activities on Precise Positioning with Space Techniques and Development of the GPS Receiver.

The precise positioning systems with space techniques by use of radio waves, such as the Very Long Baseline Interferometry (VLBI) and Global Positioning System (GPS) have the potential for measuring the three-dimensional position of a point relative to other points on the globe with millimeter to centimeter accuracy. Therefore, the VLBI and GPS would be most attractive and powerful instruments for measurements of crustal movements. In order to predict the earthquake and volcanic eruption, the research on these techniques is very active in both their application and development in Japan.The precise relative positioning receiver by use of GPS satellites, named “PRESTAR”, has been developed in cooperation with Kyushu Tokai. University, Communications Research Laboratory (CRL) and Anritsu Co. Ltd. The baseline vector can be accurately estimated from the phase differences of carriers within an error of several millimeters, without any knowledge of the two positions where the receivers are located.

McMaster University: Research openings at the Communications Research Laboratory

McMaster University: Research openings at the Communications Research Laboratory

Routeing and filtering in the ETS‐V transponder for mobile communication experiments

AbstractThe Japanese spacecraft ETS‐V implemented an experimental mobile satellite communication system via a transponder called AMEX (aeronautical maritime experimental transponder). L‐band was used for the mobile link and C‐band for the feeder link. For the L‐band two‐beam system routeing and filtering were performed through 12 SAW filters and four switches in the IF part. The effective frequency allocation plan was obtained considering the features of the links used and the characteristics of SAW filters. The filtering to prevent EMC problems was also studied for AMEX, which handles high‐ and low‐level signals simultaneously. AMEX shows good performance in orbit and is being used for a variety of mobile communication experiments by many organizations including the Communications Research Laboratory.

The Space Weather Forecast Program

This paper describes the Space Weather Forecast Program managed by the Communications Research Laboratory of Japan. It is a long-range program consisting of three phases of five years each. This program emerged after an effort to investigate future needs for space environment prediction. We conclude that solar flares and magnetic storms are two main critical phenomena which will affect human's space activities in the 21st century. The core of the program is to set up a Space Weather Forecast Center which has core facilities: (1) a computer network system; (2) ground facilities for continuous observation of the Sun; and (3) a satellite-based space environment monitoring system. Emphasis is placed upon the necessity of internal cooperation for efficient operation of the Forecast Center.

Calibration of the delay time in the GMS/GPS time transfer receivers using portable reference receivers

The Communications Research Laboratory (CRL) of Japan and the National Measurement Laboratory (NML) of Australia have performed international time transfer using the Geostationary Meteorological Satellite (GMS) and the Global Positioning System (GPS) since 1986. The precision of the time transfer using GPS is 10 ns, while that using GMS is 20 ns. However, there has been a bias of 200 ns between the time transfer results of the two time links, which is mainly due to the estimation error of the delay time in the time transfer receivers. To improve this bias error, CRL developed a portable reference receiver (PRX) for the GMS time transfer to calibrate the delay time in the time transfer receivers. In November and December 1987, a calibration experiment was carried out by the PRX method for GMS and GPS between CRL and NML. As the result of the experiment, the bias was reduced from 200 to 75 ns and the accuracy of the time transfer between CRL and NML was significantly improved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Time comparisons between KSRI and CRL via the geostationary meteorological satellite of Japan

A time comparison system using the ranging signal of the geostationary meteorological satellite (GMS) of Japan has been developed, and GMS measurements have been carried out between Korea Standards Research Institute (KSRI), Korea and Communications Research Laboratory (CRL), Japan. The result of the time comparison has shown that the precision of the GMS time comparison system at KSRI is about 10 ns. The GMS time-comparison system can be used for T/F transfer in the Asian and surrounding oceanic area with a precision of several tens of nanoseconds. >

Whistler‐triggered emissions observed by ISIS satellites

VLF emissions triggered by whistlers are often observed at middle and high latitudes in the topside ionosphere by ISIS satellites. Most of them are so‐called LHR emissions lasting for a few seconds. Latitudinal distributions of the occurrence rate for the whistler‐triggered emissions in the topside ionosphere have been obtained by using VLF electric field data (50 Hz to 30 kHz) received from the ISIS 1 and 2 satellites at Kashima station, Communications Research Laboratory, Japan. These VLF emissions are classified into two groups according to the type of whistlers, i.e., ducted whistlers with a continuous trace over the full frequency range of the spectrum and nonducted whistlers without a complete trace below fLHR. The latitudinal distribution of the occurrence rate for emissions triggered by ducted whistlers is considerably different from that for emissions triggered by nonducted whistlers, especially at high latitudes. The occurrence rate for the emissions by nonducted whistlers is distributed rather randomly in latitude between L = 2.0 and L = 4.2. The occurrence rate for emissions by ducted whistlers increases with latitudes between L = 1.5 and L = 2.9, and it attains a maximum of 0.33 at L = 2.7. It then abruptly drops to 0.1 at L = 3.0, and it remains below 0.1 between L = 3.0 and L = 4.0. The decrease of the occurrence rate for emissions by ducted whistlers at L = 3.0 seems to be caused by the decrease of the radiation belt electron flux near the slot region. These results suggest that the VLF emissions triggered by ducted whistlers in the topside ionosphere are generated by the cyclotron resonant interaction of ducted whistlers with the magnetospheric electrons near the geomagnetic equatorial plane. Most VLF emissions triggered by nonducted whistlers seem to be observed as the LHR hiss produced by nonducted whistlers in the vicinity of the satellite in the topside ionosphere.

SpaceWeather Forecast

We are looking ahead to the first part of the next century when regular space weather forecasts will be needed to warn people living in orbit of imminent radiation danger. X-rays and gamma rays, infrared and ultraviolet rays, and radioactivity from the Van Allen belts and the solar flares could all be potential sources of hazard. And in addition to affecting people and living beings they can also damage space equipment. Communications Research Laboratory (CRL) plans to undertake space weather forecast by measuring dangerous and non-stationary changes in the space environment to ensure the protection of human health and the safe operation of space equipment.

Coarticulation and the identification of initial and final plosives

Natural CVt and tVC utterances (V = |i,u,α|; C = |p,t,k,b,d,g|) of one American English male speaker were used to evaluate which information in CV and VC syllables is perceptually relevant for the identification of initial and final plosives. Different initial or final parts of the utterances were deleted and replaced by silence or by a 300-ms burst of noise. Subjects were asked to identify the (deleted) plosives. The noise paradigm was introduced to make the incomplete (C)Vt or tV(C) syllables sound more natural: it improved the correct score for initial plosives. Identification results are interpreted in articulatory and spectral terms. For initial unvoiced plosives most coarticulation takes place in the aspiration part and hardly any information about the preceding plosive is preserved in the vowel (transition) part. For the heavily truncated (C)ut stimuli, subjects give mainly |b| responses, while |p| is the favorable response for all heavily truncated tV(C) stimuli. [Research carried out at Speech Communications Research Laboratory, Inc., Santa Barbara and supported by the Netherlands Organization for the Advancement of Pure Research (ZWO).]

Interactive laboratory system on an IBM 370/158

A broad, flexible, and powerful set of interactive programs for the acoustic analysis of speech have been developed at the Speech Communications Research Laboratory of Santa Barbara. This interactive laboratory system (ILS) was originally developed for use on minicomputers. The present paper will describe an adaptation of ILS for use within a major time-sharing configuration. Operating on an IBM 370/158 under OS, ILS remains an extremely powerful tool for acoustic phonetic research. An added benefit of operating in this environment is the availability of other resources which are available at our installation, e.g., SPEAKEZ, SPSS, SAS, MINITAB, etc., which are extremely valuable for rapid data reduction.

A high speed digital modem for experimental work on the Communications Technology Satellite

The Communications Technology Satellite (CTS), launched on 17 January, 1976 from Cape Canaveral, provides a very powerful and versatile vehicle for the experimental testing of new communications technology. The Communications Research Laboratory (CRL) of McMaster University has since 1972 been conducting a comparative study of digital modulation techniques for experimental work using the CTS system. This study which has been conducted in three phases, under contract to the Communications Research Centre, Ottawa is the subject of the present paper. The first phase consisted of the comparative evaluation by means of computer simulation of a variety of digital modulation techniques using a satellite type of channel. The results of this show that the best performance in terms of digital error-rate as a function of signal to noise ratio is obtained using the so-called fast-frequency shift keying (FFSK) modulation type. The second phase of the study consisted of the design and construction of a fast frequency-shift keying modem (modulator/demodulator) at a nominal data rate of 60 Mbits/sec. The details of this design and the results of preliminary testing of the modem are presented in the paper, and show that when the modulator and demodulator are operating back-to-back there is a performance degradation from theoretical of 1 dB in signal to noise ratio at a bit error-rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> . The third phase of the study consisted of the detailed laboratory testing of the modem under a variety of channel conditions preparatory to actual satellite testing. Some of the results of this testing are presented in the paper, and indicate that the FFSK is a very viable modulation type for use in high rate data communications via satellite.

The Future of Educational Telecommunication

Twelve years have gone by since federal funding of educational television began in the United States; seven years since the goal of a national service that is also responsible to local needs was set by the Public Broadcasting Act of 1967. Today there is a working national system which encompasses both educational and cultural purposes. But many of the original ambitious objectives have not yet been attained and much of the system has grown in response to day to day problems. In an effort to clarify the policy issues and identify future needs for educational telecommunications, the Communication Research Laboratory of Battelle Memorial Institute conducted a planning study for the U.S. Office of Education in 1973. This study was based on evaluations of published information, tempered by in-depth interviews of policy makers, site visits, and lengthy discussions with more than sixty educational broadcast licensees. This paper is based on highlights of the Battelle study.

Measurement of Time Spent Communicating

The relative amount of time people spend in workday activities was estimated by both an observational and questionnaire method. Results from professional, technical, administrative and clerical people in a communications research and development laboratory show that 50%–80% of the workday is spent in communicating, two-thirds of that in talking. People tend to underestimate time spent talking and overestimate time spent reading and writing. Telephone and equipment use is estimated correctly on the average. People in one-man offices and laboratories spend more time talking than people in multi-man offices, but this result is confounded with supervisory level.