Site: NTT DoCoMo, Wireless Laboratories
Yokosuka, Kanagawa 239-8536
Date Visited: 2 June 1999
WTEC Attendees: R. Pickholtz (report author),T. Ephremides, T. Itoh, L. Katehi, R. Rao, W. Stark, J. Winters, D. Friday, M. Iskander, J. Maurice, N. Moayeri, B. Mooney, H. Morishita, L. Young
Hosts: Toshio Nojima
NTT DoCoMo is the largest provider of wireless services in Japan. The R&D Center was established in 1998 to do R&D in mobile wireless technology projects. It is now housed in an ultra-modern facility in the center of Yokosuka Research Park (YRP), which also hosts many other high technology wireless companies such as Nokia, Motorola, Lucent, and Ericsson. The companies in the park employ about 2,400 staff. The goal is to become a Japanese "Silicon Valley" for wireless.
The DoCoMo R&D facility is the largest among these and employs about 600 technical staff. The complex contains a large anechoic chamber and extensive multimedia facilities. The missions of the R&D center are associated with three laboratories: wireless, multimedia, and networks. DoCoMo covers all aspects of wireless including cellular, pagers, satellite systems and aeronautical radio. Although the R&D center belongs to the central headquarters, the various component companies of DoCoMo share the R&D costs.
The current and continuing projects include, but are not limited to IMT 2000, new W-CDMA systems, etc. NTT DoCoMo researchers have begun to study fourth generation (4G) systems. Among the general goals is to make wireless terminals lighter, smaller, lower in power consumption, and able to provide high quality multimedia information and capable of performing in embedded systems.
A general overview of DoCoMo R&D was provided by Dr. Nobuo Nakajima and Dr. Nojima gave a presentation "R&D Plan for 4th Generation Mobile Communication Systems." The vision is that 4th generation systems will migrate from 3rd generation systems IMT-2000 and the various wideband wireless LANS to provide both high mobility and bit rates exceeding 10 Mbps to meet the next generation Internet capability wirelessly at lower cost.
The typical bit rate objectives for the fourth generation is >10-20 Mbps for indoor and pedestrian use and >2 Mbps for vehicular wireless use. Because of the population density of urban areas and the requirements for nationwide service, a seamless picocell/microcell system is expected to be deployed. It may require dual operation with IMT-2000. To achieve higher data rates, migration to higher RF bands will likely occur. This increases path and circuit loss dramatically. Thus smart, adaptive arrays will be necessary. In addition there may also be wireless and optical fiber entrance links from the micro or picocells to the base station. There are tradeoffs in the access/modulation methods that require study: CDMA, for example, raises such issues as width, multicarrier possibilities, high speed RAKE and Power Control, etc. OFDMA issues are amplifier efficiency and linearity; and with TDMA, very high speed equalizers are an issue. Considerable emphasis is being given to adaptive arrays to provide high gain to cut down the path loss, reduce interference, and minimize multipath. Research requires better tracking algorithms, compact designs, and lower cost. One approach being studied to reduce size and costs of microcells is to use optical RF signals so that all the complex tasks are taken back to the main base station. A principal additional attraction of that method is air-interface independence since the active RF signal is passed to the main base station without digital processing.
The same principle may be applied using a millimeter wave wireless access link for quick, inexpensive deployment. Finally, software radios would allow greater flexibility, but research is needed on high speed, low power DSPs and tunable, inexpensive RF circuits.
A tour of the labs revealed a working hardware demonstration/simulation for transmitting a 2 Mbps video using 20 MHz CDMA through a fading channel at 100 km/hr.
A second demonstration showed a two-way mobile video system with 2 Mbps forward video and 384 kbps reverse link. Since this project is now four years old, H.261 was used, but MPEG 4 is intended. This link also provided 2-way voice. It also was a 20MHZ CDMA, fading channel with dual antenna and RAKE diversity. There were no additional users in the system being demonstrated and the pictures were quite good with no artifacts or apparent "noise".
WTEC panel chair, Dr. Anthony Ephremides, gave the WTEC presentation and vice-chair, Dr. Tatsuo Itoh, described the views presented at the March 1999 workshop by various U.S. companies.
Finally, Dr. Fumiyuki Adachi gave a presentation entitled "W-CDMA: Performance Evaluation and Future Enhancement." He described the phenomenal growth of the cellar market in Japan (>35% and the emerging potential of wireless multimedia that is driving the need for 3G).
For IMT-2000, the research phase ended in 1996, and field tests will be concluded this year. Dr. Adachi described the ongoing field tests, which incorporate advanced receivers including multistage interference cancellation and adaptive antenna arrays forming both beams and nulls. Allusions were made to turbo coding as well, but this was not stressed. Dr. Adachi responded openly to detailed questions about the character and the performance of the interference cancellation scheme being used including a comparison of theory, simulation, and actual measurements.
Dr. Fumiyuki Adachi