Site: Kokusai Denshin Denwa Co. (KDD)
R&D Laboratories
2-1-15 Ohara Kamifukuoka-shi
Saitama 356, Japan
http://www.kdd.co.jp

Date Visited: June 2, 1997

WTEC: W. Brandon (report author), C. Bostian, A. Mac Rae

Hosts:

BACKGROUND

KDD, Japan's international telecommunications carrier, like COMSAT, participates in INTELSAT and Inmarsat; constructs and operates optical fiber networks, connecting Japan with the rest of the world; and has taken the lead in popularizing the Internet in Japan. KDD R&D Laboratories conducts activities from basic research to development of hardware and software to expand and improve international services. Work centers on transmission technology, network technology, and developing new applications and services. The technical staff includes 130 engineers, of whom 40% have PhDs, and about 15% are either trained in, or have experience in the United States. The locus of junior staff interest is now multimedia communications, rather than satellite communications.

Dr. Marakami introduced the broad accomplishments of KDD through a video. Transmission activities include ATM transmission via satellite, ultrahigh speed transmission using optical soliton pulses; wavelength division multiplexing and optical amplification; Acqua-Explorer 1000, an autonomous robot for maintaining submarine cables (inspection/photography at 1,000 m depth with acoustic link to the surface); and selected items for enabling international mobile communications. Networking developments include technologies for broadband and "intelligent" international networks and systems for planning, operating and managing networks, including restoration. New service-related technology includes speech recognition and language translation, video codecs, multimedia on demand technologies, Internet applications and portable and mobile earth station technologies.

KDD was created by public law somewhat analogous to COMSAT Corp, and its activities are affected by changes in Inmarsat and INTELSAT. KDD is one of ICO Global's largest investors. KDD is developing a dynamic frequency assignment system and electronically steered antennas for non-GEO satellite systems like ICO.

R&D ACTIVITIES

Video Transmission/Compression

Compression products have been a major concern of KDD. The MUCCS2 provides 8 channels on one circuit. HDC 45 and MUCCS2 were used for the Olympic Games. A newer product called ARCH is MPEG2 based and is used in ATM transmission. A VQS product is used on cable networks for video on demand.

KDD has developed a digital satellite news gathering van (SNG) for remote real time transmission of digital video. The Vast-c and VAST-s store and forward video terminals using MPEG 1 and 2 respectively, allow transmission of video via links with 64kbps to T1 data rates.

Satellite Terminals

A new Mini C portable satellite terminal for Inmarsat was shown.

Antennas

KDD has a distinguished history of achievement in antennas going back over 20 years.

Small antennas can experience inter-symbol interference due to multipath. KDD developed a method of changing the polarization presented to the reflected versus the direct ray path. A crossed dipole feed, which radiates a circular polarized wave with an arbitrary axial ratio is rotated relative to the reflector, allowing a "null" of the reflected path.

The team was shown an innovative antenna design, which has already been developed, in which the antenna was mechanically rotated for azimuth coverage, and fed by a rectangular waveguide linear array for elevation.

A low sidelobe USAT antenna of 40-50 cm diameter was used as an illustrative example. ITU standards for large antennas were extrapolated to the small aperture size. An antenna was developed with a slightly elliptical reflector, the larger diameter corresponding to the expected aperture (~45-50 cm). A diamond shaped feed was used. Calculated antenna patterns performed well below the mask based on ITU regulations. A USAT antenna diameter of 46 cm was used in the example.

An ultrasmall Ku-band USAT antenna is targeted for multimedia services, coming to Japan in 1998. PerfecTV has already introduced digital DBS; DirecPC will be introduced shortly, but uses the PSTN for the return path. A bi-directional (all satellite) multimedia service is envisioned with a 46 cm aperture. A 27 MHz transponder will support a 40 mbps QPSK TDM waveform transmitted by a 7 meter hub. The return link (from user to hub) would be 128 kbps, using a chirped BPSK waveform. The chirp is used to spread the energy over a 500 kHz bandwidth, and is sufficient to prevent interference, allowing for a 0.5 pointing error for a home installation, with 3 orbit spacing. A one watt transmitter will be integral to the outdoor unit, designed for continuous transmission in 20 C air. Use of TDM multiple access is anticipated and will produce a low duty cycle.

Array Antennas for Aircraft

An array antenna for aircraft terminals was shown. A low profile is achieved using two layers of slightly overlayed patch radiators. The 3 x 3 array performs at both 1.5 and 1.6 GHz, as both transmit and receive, and was tested with ETS-V. The antenna uses a conventional beamforming network; for more performance, an active phased array would be used. The second generation model was a single layer with two element sizes on a high dielectric substrate. The axial ratio was not satisfactory, and a third generation model was constructed. Similar to inverted-F, multiple short pins above each patch allowed the sizes to be reduced to almost half; the patches could then be laid out without overlap in groups of four (transmit and receive for each band). There were 18 analog phase shifters (9 elements x 2 frequency bands), digitally controlled, and packaged into a small box. Transmit power is 250 mW per element.

A third array antenna, targeted for ICO and the Japanese Experimental Satellite (ETS VIII), used a quadrifilar helix radiating element. As in Figure C.4 the antenna will have 12 elements arranged in a triangular grid pattern (with corner elements missing from the grid). The antenna had just been delivered and patterns had not been measured.


Fig. C.4. Array antenna with quadrifilar helix radiating element.

The feed electronics were packaged into 4 layers (for ease of further evolutionary changes). Diplexers comprise the first layer, LNAs the second layer, BFN the third layer, analog up and down converters in the fourth layer. A design change is being introduced to substitute a digital beamforming network for the analog BFN. The feed network has 1, 2 or 3 output ports. The antenna has 16 beam positions (switchable). Use of TDM downlinks might allow beams for 2 satellites. While ICO will use 6 kbps links/user, thin route FSS multimedia service is anticipated to operate at 64 kbps, requiring about 10 dB more gain.

Networking and New Services

Much of KDD's development is for multimedia applications and non-GEO satellite systems. A multimedia conferencing system connecting more than three sites for exchange of voice, text, and video has been tested for use in tele-education and telecommuting. For telephone communications with Korea, a speech recognition and automatic interpretation system has been implemented to enable automatic voice connection.

Advanced networking activities include high reliability network technologies, use of "smart cards" for authentication on the Internet, and a network management platform for rapid monitoring and control of transport via overseas carriers. A multi-channel radio LAN with high speed and order wire has been tested. RFI was assessed without on-site measurement using a software product. Base station siting was illustrated for cellular communications, again without on-site measurements. Diversity reception and equalization is being investigated in anticipation that FLMPTS will become a world standard. KDD participated with AT&T in a two year test of ATM transmission via cable and via satellite to the U.S.

Optical soliton transmission has been tested on a repeaterless fiber path of 9,000 km, carrying 2,600 compressed television channels.

Non-Geo System Management

Efficient assignment of particular satellites and gateway stations to mobile users requires position location information of users. Satellite position determination introduces an ambiguity in position. An ambiguity removal technique for passively determining user position at the hub was described.

KDD is also addressing methods of assigning satellites to gateway earth stations so as to minimize the number of hand-offs.

REFERENCES

Ishikawa, H. et. al. 1996. Ambiguity Removal Technique for User Position Determination Method in Non-Geostationary Satellite Systems. 4 page technical paper, IEE Conference Publication No. 424, 1996 and a 17-chart briefing based on the paper.

KDD. Annual Report, for year end 31 March 1996.

KDD R&D Laboratories. n.d. Brochure, 12pp.

____. n.d. Experimental Mobile Satellite Communications System Via Engineering Test Satellite-V (ETS-V). Technical paper. Tokyo.

____. High Performance Aperture Antenna Developments in KDD Labs. n.d. [List of 8 specific antennas developed from 1977 through 1993, and one current investigation].

____. Time-Dependent Service Area Concept for Non-GSO Satellite System. n.d. 16 chart-briefing.

____. Ku-band USAT System. n.d. KDD Laboratories. 15-chart briefing.

____. Nomoto, S. et al. 1989. Multiple Contoured-Beam Synthesis Using a Doubly Curved Reflector and a One-Dimensional Feed Array. Proceedings of ISAP '89: (953-956).


Published: December 1998; WTEC Hyper-Librarian