Site: NTT Yokosuka R&D Center
Nippon Telephone and Telegraph Corp. (NTT)
1-2356 Take
Yokosuka, Kanagawa 238-03, Japan

Date Visited: October 22, 1992

Report Author: P. Hager

ATTENDEES

NASA/NSF:

R. DePaula
B. Edelson
P. Hager
R. Kwan
C. Mahle

HOSTS:

Dr. Shuichi Samejima

Executive Manager,
Satellite Communications System Lab

Dr. Takehiro Murase

Executive Manager, Research Planning Dept.

BACKGROUND

NTT is the major domestic telecommunications operator, providing many services to over 57 million subscribers. NTT's network consists mainly of optical fiber and microwave transmission systems. NTT is engaged in development of high speed networks, specifically B-ISDN. For the interim, ATM-based B-ISDN at 156 Mbits/sec, is envisioned for dedicated service local area network (LAN) or wide area network (WAN) applications. NTT has ten times more people working on ISDN than on satellite communications.

NTT operates, in combination with terrestrial systems, a satellite demand-assigned system (DYANET) where satellites CS-3a and CS-3b carry the peak traffic load. NTT Yokosuka predicts that for trunk transmission, 0.4% of telecommunications traffic will be carried via satellite even after the terrestrial fiber network is established. Currently, NTT has about 100,000 narrow-band ISDN subscribers with service having started in 1988. This narrow-band ISDN can also be switched through JCSAT satellites.

NTT has five R&D Centers: Musashino R&D Center, Tokyo; Atsugi R&D Center, Atsugi, Kanagawa; Yokosuka R&D Center, Yokosuka, Kanagawa; Ibaraki R&D Center, Naka, Ibaraki; and Software Laboratories, Tokyo.

The NTT Yokosuka R&D Center is comprised of five laboratories and one development center:

NTT Yokosuka facilities include 95,000 square meters of floor space in the main building, with 2,000 square meters of space in the Experimental Satellite Communications Station. A high ceiling spacecraft integration clean room facility appeared to be well equipped. There were no spacecraft inside it at the time of the NASA/NSF panel's visit. They have a large, high-vacuum chamber. There are anechoic chambers here and at other NTT sites.

NTT has about 3,000 employees in R&D centers in the Tokyo area and 1,500 at Yokosuka, of whom 200 are in the Radio Communications System Laboratories. About 60 people in this laboratory are involved in satellite communications system and hardware work. Thirty employees at other centers also perform satellite communications systems R&D. The Radio Communications System Laboratories have a budget of approximately 6 billion yen per year (about $50 million).

Two missions have been defined for the NTT Yokosuka R&D Center:

  1. Investigation of multibeam satellite (MBS) systems
  2. Expansion of service areas, maritime mobile satellites and land mobile satellites. Start in 1995 using S-band.

More generally, NTT Yokosuka R&D Center's mission is to facilitate communications in the "information age" society of the future. This will require sophisticated basic technology including satellite and optical communications technology for high-speed, long-haul bulk information transport; and intelligent processing technology so that people and networks can interact more naturally.

RESEARCH AND DEVELOPMENT ACTIVITIES

Some key accomplishments of NTT include development of MMICs for satellite OBP (1987), launching of the CS-3 satellite (1988), and development of communications payload equipment for ETS-VI (1989).

As noted above, NTT operates DYANET to carry peak traffic load. This is a 20 Mbits/sec TDMA system with LSI-implemented equipment located at 62 switching centers all over Japan (Kamitsuna 1992). Each center has a dual-feed 20/30 GHz double torus antenna on the roof. NTT has developed a dual-beam antenna with one primary dish. It used two secondary dishes with radiators. This enables simultaneous tracking of two satellites with one dish. The scarcity of antenna mounting areas (on roofs) in Japan justifies this complex design.

CS-3 has ten 20/30 GHz transponders and two C-band transponders, the latter are used for the remote islands. At the end of CS-3's seven year life (1995), N-STAR will take over.

NTT has implemented satellite-based ISDN for limited, remote areas where terrestrial access is not economically viable. Since service was initiated in June, 1992, only six satellite terminals have been deployed, with one ISDN user per terminal. The system uses JCSAT Ku-band transponders. ISDN is transparent to the user.

ETS-VI Multibeam Satellite System

NTT was the ETS-VI payload integrator. NTT both built and integrated for ETS-VI: 20/30 GHz antennas (3.5/2.5 m reflectors, including feeds and dichroic plates, producing four beams); five S-band feeds for 3.5 meter reflector; a C-band feed for a 2.5 m reflector; and, 20/30 GHz, S-band, and C-band transponders. NTT was also responsible for overall antenna system design. Most hardware is a joint effort by NTT with NEC, Toshiba, and MELCO. The 30 GHz receiver uses MMICs for both D/C and LO, utilizing several NTT-developed co-planar waveguide chips. The 20 GHz 10 W TWTAs are made by NEC. The S-band PA is a 100 W matrix amplifier, called a multi-port amplifier (MPA); it has eight SSPAs which support five beams. The 20/30 GHz transponder has a 16 x 12 IF matrix switch, using MMIC switch modules, estimated size 12" x 16" x 3". ETS-VI uses an 8-bit digital CPU for switch control which is slightly smaller than the IF switch matrix.

The 3.5 m S-band reflector generates five 2 degree beams and is a precursor of the N-STAR S-band antenna which will implement similar antenna. Five 2 degree beams at S-band are needed for coverage of Japan including the 200 nautical mile coastal area. These 2 degree beams provide 15 dB more gain than earth coverage beams. This permits the use of a 50 cm rod-type antenna for mobile terminals. MMSS is intended as well as LMSS. A portion of S-band is presently allocated to MSS in Region 3 on a national-boundary-use basis.

Some reflectors developed by the Radio Communications Systems Labs provide HPBWs as narrow as 0.3 degree at Ka-band. Pointing accuracy is 0.015 degree rms using a monopulse beacon receiver at 30 GHz with a beacon station located at Hokkaido. The monopulse receiver drives an XY table on which the subreflector of each 2.5/3.5 m antenna is mounted.

Construction materials for antenna reflectors of truss-honeycomb were used instead of the conventional honeycomb construction to achieve a mass per unit area one-third that of prior approaches. Changing subsystem container boxes (chassis boxes) from aluminum to magnesium to achieved a 3:2 mass reduction.

Electronic Devices

The MMIC work was described in their very well equipped laboratory. NTT has developed co-planar waveguide (CPW) MMICs. A chip set for a 26 GHz communications system was displayed (published at IEEE MTT symposia), as well as a chip for a Ku-band frequency synthesizer.

The main purpose of the MMIC program is size reduction. The program is evolving through 5 stages: single-layer ICs, double-sided ICs, MMICs, uniplanar MMICs, and multilayer MMICs. NTT is now achieving 80 to 90% yield in manufacturing. They hope to have multilayer MMICs by 1999. Switching power levels in MMICs runs about 1 W to several Watts. ETS-VI RF/IF converters are conventional, microstrip-based MMIC technology. Use of MMICs for frequency conversion results in mass reductions of up to 5/6, with average mass reduction of units to 25% of original mass. NTT has built MMICs operating from UHF to 30 GHz.

Uniplanar MMICs will be available later. They will be much thinner and lighter; IF power requirements are much lower. Uniplanar MMICs will contain a higher level of integration and be smaller in size. The smaller chip size is expected to result in a higher manufacturing yield and cost reduction.

NTT makes the LSIC chips. MMIC receivers are manufactured by both MELCO and NTT.

NTT has developed radiation-hardened microprocessors, hardened against dosage of 1 Mrad, manufactured by MELCO. They have developed 64 kbit SRAM. They now have an 8-bit microprocessor hardened against single event upset to 10(superscript-9) manufactured by OKI.

They have a 16-QAM digital microprocessor receiver/transmitter module for operation at 4, 5, or 6 GHz.

NTT was integrator for the NTT subsystems on ETS-VI, all of which were tested extensively at NTT Yokosuka. The subsystems were then turned over to NASDA - Toshiba. Toshiba was system integrator for the rest of the spacecraft. NTT's subsystem was treated as a black box by Toshiba. ETS-VI is scheduled to be launched in August 1994 by the newly developed H-II launch vehicle. ETS-VI is a precursor of N-STAR where many of the developments will be used in operational service. All technology developments are of very high quality and are state-of-the-art.

SUMMARY

NTT is making a massive investment in R&D with its many R&D centers and laboratories. It has significant capability in satellite systems integration and communications subsystems development. NTT developed, built, and integrated the communications system into the ETS-VI spacecraft. They have significant capability in device development in critical areas of advanced communications system payloads, especially MMICs.


Published: July 1993; WTEC Hyper-Librarian