Milestone-Proposal:Mobile Radio Propagation Model “OKUMURA-curve” and First Commercialized Full-Scale Cellular Telephone System, 1968-1979

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Docket #:2021-15

This proposal has been submitted for review.

To the proposer’s knowledge, is this achievement subject to litigation? No

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes

Has an IEEE Organizational Unit agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes

Year or range of years in which the achievement occurred:


Title of the proposed milestone:

Mobile Radio Propagation Model “OKUMURA-curve” and First Commercialized Full-Scale Cellular Telephone System, 1968-1979

Plaque citation summarizing the achievement and its significance:

Nippon Telegraph and Telephone Corporation/NTT DOCOMO, INC. (formerly Nippon Telegraph and Telephone Public Corporation) established mobile radio propagation model “OKUMURA-curve” in 1968 and commercialized the full-scale cellular telephone system based on this model for the first time in the world in 1979. OKUMURA-curve have broadly utilized for the practical design of various radio systems including 1st - 5th generation mobile communications systems.

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.

IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.

In what IEEE section(s) does it reside?

IEEE Tokyo Section, Japan

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: IEEE Tokyo Section Treasurer
Senior Officer Name: Hiromasa Habuchi

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: IEEE Tokyo Section Secretary
Senior Officer Name: Yasuhiro Takishima

IEEE section(s) monitoring the plaque(s):

IEEE Section: IEEE Tokyo Section Chair
IEEE Section Chair name: Hideyuki Tokuda

Milestone proposer(s):

Proposer name: Yukihiko Okumura
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):

<No. 1> Street address: 3-5 Hikarino-oka, Yokosuka-shi, Kanagawa, 239-8536, Japan Latitude: 35.224035 / Longitude: 139.672682
<No. 2> Street address: 3-9-11 Midorimachi, Musashino-shi, Tokyo, 180-8585, Japan Latitude: 35.719216 / Longitude: 139.564523

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need.

<No. 1> Corporate building of R&D center of NTT DOCOMO, INC.: This building is located in the area of Yokosuka City where the World's First Full-Scale Cellular Telephone System was developed.
<No. 2> Corporate building of Historical enter of NIPPON TELEGRAPH AND TELEPHONE CORPORATION: This building is located in the area of Musashino City where the Mobile Radio Propagation Model and the World's First Full-Scale Cellular Telephone System were developed.

Are the original buildings extant?


Details of the plaque mounting:

<No. 1> The plaque will be mounted in the entrance hall on the ground floor of the building.
<No. 2> The plaque will be mounted in the entrance hall on the ground floor of the building.

How is the site protected/secured, and in what ways is it accessible to the public?

If visitors to the plaque site, they will need to go through security.

Who is the present owner of the site(s)?


What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include justification here. (see section 6 of Milestone Guidelines)

In the history of telecommunications services, which was born as an indispensable means for the development of social life and has become widespread, the realization of a full-fledged cellular telephone system from the end of the 1970s to the beginning of the 1980s means that users can receive telephone services at any time in a wide range of usage environments. As a result, telecommunications services began to make a significant contribution to the further development of social life and industry around the world. In Japan, at the end of 1979 the then Nippon Telegraph and Telephone Public Corporation (NTTPC, predecessor of Nippon Telegraph and Telephone Corporation/NTT DOCOMO, INC.) launched commercial car phone service using the Full-Scale Cellular Telephone System ahead of the rest of the world. Thereafter, in the cellular telephone system (the mobile communication system), the radio access method has greatly evolved at a period of approximately 10 years, the generation change has been made, and now the fifth generation system (5G) is commercialized, and the research and development for the sixth generation system (6G) is being promoted all over the world.

On the other hand, although the communication service provided by the cellular telephone system was originally limited to voice communication, it has been gradually expanding to services other than voice, such as data communication and image / video communication, and in addition to human-to-human communications, human - to - machine and machine - to - machine communications are also being carried out by the mobile phone system, which is now indispensable service in social life. Although the cellular telephone system realization method started from the analog method at the beginning, mobile Internet access has spread rapidly due to its affinity with data communication, because it has been digitized to improve speech quality and subscriber capacity. As a result, cellular phones have been transformed from simple communication means to sophisticated user terminals equipped with many applications. However, the basic concept of the cellular system continues to be inherited up to the latest system.

It is expected that more than hundreds of thousands of users will need to be accommodated throughout Japan for the development of the above NTTPC Full-Scale Cellular Telephone System. Therefore, as a frequency band used in a new large-capacity mobile communication system, it is required to develop a new high frequency band exceeding 400 MHz, as opposed to the conventionally used frequency band of 400 MHz or less. The 800 MHz band was selected by a large-scale survey on propagation and a study of the feasibility of equipment that handles high frequencies.

For mobile communication characterized by extremely low mobile station antennas, radio signal propagation is always subject to different terrain irregularities and obstacles (buildings and trees) in its transmission path, which changes its characteristics incessantly. In addition, high antenna gains, frequencies and distances, which were barely known at that time, increase the complexity of mobile radio propagation. Dr. Yoshihisa Okumura, who belonged to the Electrical Communication Laboratories (ECL) of NTTPC at that time, insisted on the necessity of UHF bands radio wave propagation research for the new era of mobile communication, and was responsible for promoting the research. The research aimed to predict a future development path of new mobile communications, elucidate radio propagation characteristics, and create a generalized model for signal strength prediction. To this end, he devised a method to categorize different terrain types and land objects to understand complex propagation characteristics in various areas.

In addition, Dr. Okumura conducted large-scale radio signal propagation experiments in the Kanto region encompassing Tokyo in 1962, 1963 and 1965 to find out the potential of the 4 new frequency bands of 450 MHz, 920 MHz, 1420 MHz, and 1920 MHz capable of meeting the demands of future public land mobile communication services. His team collected a huge amount of field measurement data with parameters such as impacts of terrain and land features (buildings and trees) and heights of transmitting/receiving antennas and summarized distance dependence of radio signals in propagation design diagrams. In addition, he established a pioneering method of predicting field strengths and service areas. His generalized propagation prediction model is highly accurate and practical since it was derived from an accumulation of data obtained through persistent experimental analysis of complex mobile propagation conditions. His research results were published in 1968 as a research paper [1].

Dr. Okumura’s highly acclaimed field strength curves of mobile radio propagation model were further reflected in the Recommendation 370-2 (Report 567) [2] issued by the Comité Consultatif Internationale des Radiocommunications, CCIR (later the International Telecommunication Union Radiocommunication Division, ITU-R) in 1974. His field strength prediction curves, generally called “OKUMURA-curve”, have widely cited in academic papers across the world, and broadly utilized for the practical design of various radio systems including mobile systems in countries around the world. Okumura-curve was empirically formulated by Dr. Masaharu Hata in 1980 [2-1], and this formula was published along with the Okumura-curve in 1982 as an empirical formula for estimating propagation loss (“Okumura-Hata formula (equation)”) in CCIR Recommendation 529 (Report 567-2) [2-2]. In NTT Group, the propagation loss estimation formulas based on Okumura-curve are continuously used in the design of radio access links such as mobile communication systems from the 1st generation system (1G) to 5G, wireless communication systems for disaster countermeasures, and wireless communication systems for IoT. Also, his methods for analyzing data from field experiments are widely used for quality assessment and optimization in the field. Okumura-curve and the propagation loss estimation formula based on Okumura-curve were also introduced in the ITU-R handbook [2-3] in 2002, and is still being used by mobile radio system engineers around the world for the design and construction of actual systems.

Taking advantage of the results of the above-mentioned UHF band radio wave propagation research that led to the establishment of Okumura-curve, Dr. Okumura of ECL envisioned a new cellular system that assumes the use of 800 MHz bands that have never been used in mobile communication systems, and presented the new system concept at the conference of the Technical Committee on Communication Systems of the Institute of Electronics, Information and Communication Engineers (IEICE) of Japan in October 1971 under the title of “Outline of High Capacity Land Mobile Telephone System” [3]. According to his presentation, the design objective of a new system is to accommodate 100,000 subscribers in the area centering on Tokyo within a radius of 50 kilometers and 400,000 subscribers nationwide and to achieve a total automation system. In addition, he listed new frequency band, high-speed channel control, small radio zone, etc. as development items and functions required for achieving large capacity, effective frequency use, and wide-area service, which are the aims of the new system. He also identified the new technologies needed to realize them.

In addition, the developed full-scale system will respond in a timely manner to the increasing demand for potential mobile communication services due to the rapid spread of automobiles in Japan, so that more subscribers will be able to use it. While aiming for accommodation, each process of research and development was devised in order to commercialize the new system in a shorter period of time compared to the conventional system.

Dr. Okumura, who contributed to the establishment of the mobile radio wave propagation model and the concept construction of the High Capacity Land Mobile Telephone System using the 800MHz band described above, received “The 2013 Charles Stark Draper Prize for Engineering [4]” for the pioneering contributions to the world’s first cellular telephone networks, systems, and standards from the United States National Academy of Engineering (NAE) on February 19, 2013, along with other winners. This prize recognizes that Dr. Okumura's achievements will have a great impact on society by improving the quality of life and enabling free and comfortable living and access to information.

What obstacles (technical, political, geographic) needed to be overcome?

The basic concept of the cellular system assumed by the High Capacity Land Mobile Telephone System is as follows.

- The service area is divided into small areas called cells, and the same frequency is repeatedly used in units of a certain number of cell clusters. Therefore, if there is a certain number of frequency groups, frequencies can be assigned to all cells in a service area of an arbitrary size.

- If the cell radius is reduced, the number of channels that can be used per unit area will increase, enabling effective use of frequencies. However, if the cell radius is reduced, a handover process (channel switching process during a call) is indispensable in order to continue communication in the transfer destination cell when the mobile terminal migrates the cell during communication.

NTTPC clarified the system outline [5] with the aim of putting into practical use a full-scale system that can achieve high quality, large capacity, and low cost while incorporating the above basic cellular concept, and promoted the development of technologies and devices required for both radio systems and switching systems [5-1,-2, -3], and finally completed a Full-Scale Cellular Telephone System to which the following features and new technologies were applied.

Technologies for spectrum efficiency:

(1) Small radio zone system We can lower the transmission power over the radio channels between base stations and automobiles by dividing a service area into a number of small radio zones. This allows us to make the parts of areas that suffers from interference relatively small. Consequently, we can reuse the same frequencies simultaneously in multiple radio zones that do not interfere with each other, leading to improvement of spectrum efficiency per radio channel. In determining the size of radio zones, we must consider the following factors: the relationship between the subscriber capacity and required radio channels, the technological and economic balance between the radio propagation characteristics and mobile unit transmission power and the trade-off with radio channel control complexity. In consideration of these parameters, we decided to use radio zones with a radius of about 5 km in an urban area and about 10 km in a suburban area, which we considered to be the most optimal system configuration.

(2) Mobile unit channel switching In order to accommodate as many subscribers as possible in the system, we decided to develop mobile units capable of using and switching multiple radio channels. As a result, we commercialized mobile units with a digital synthesizer capable of switching 600 channels.

(3) Narrow-band radio channels We decided to use 25 kHz, the same channel bandwidth as a 400 MHz band, by improving the frequency stability of oscillator circuits. In technical terms, we developed an oven-controlled crystal oscillator (OCXO) with a stability of 1×10-7/year or less for base stations, and a temperature-compensated oscillator (TCXO) with a stability of 2.5×10-6/year or less for mobile units, both for commercial applications.

Radio channel control technologies:

This system is intended to support a huge number of subscribers and numerous radio channels. To enable efficient use of these channels by such a large number of mobile units, we decided to provide channels dedicated to control as we configured speech channels. In addition, we decided to use digital signaling to enable high-speed processing for the signals that pass through the control channels. High-speed signal transmission, however, is more vulnerable to signaling errors due to fading, urban noise and other radio propagation characteristics unique to mobile communication. Therefore, we have applied several techniques such as repeating signal transmission and adding error correction codes and employed diversity to enhance reliability. Based on the techniques mentioned above, we put the following control technologies into commercial use.

(i) Radio link establishment (disconnection): This is a sequence control technique to detect a radio zone in which the automobile is located upon a call origination or termination (location detection), instruct the automobile to use speech channels available for the call in the radio zone and establish (disconnect) a radio link.

(ii) Channel switching during a call: This is a sequence control technique to detect a new radio zone to which the automobile has just moved from a previous zone during a call, assign new speech channels and ensure the continuity of the call.

(iii) Location registration: To respond to dynamic mobility of automobiles, we set up paging areas with a radius ranging from 20 km to 50 km and make a telephone switching center memorize the paging area for each land mobile telephone subscriber (subscriber memory). This is a sequence control technique to enable the switching center to automatically register the current location of each automobile whenever it moves out of the paging area.

Mobile switching technologies:

It is estimated that if the land-mobile telephone service is provided nationwide, it will have 400,000 or more subscribers. In order to respond to such estimations, a new mobile telephone switching system was developed for fully-automated nationwide service provision. As the land mobile telephone system has to deal with moving objects, it requires a unique switching function different from that of the general subscription telephone system. What makes it unique is the need to handle subscribers moving around in a wide area and the installation of a line concentration function in the radio section. The following are some of the major functions that we have added to the conventional D-10 type electronic exchange system.

(i) Subscriber memory: Subscriber information is stored in the memory dedicated to each subscriber and installed at a specific center. The system configuration is designed to allow access to each subscriber’s information in the memory and its retrieval by designating the subscriber number. The subscriber information stored in the memory includes the current location of the subscriber’s automobile, the number of call units and the subscriber class.

(ii) Charging: For a speech call originating from an automobile, the switching center on the call origination side forwards the data on the number of call units, which is determined according to the distance and time of the call.

What features set this work apart from similar achievements?

In October 1971, ECL of NTTPC presented a new cellular system utilizing the results of the mobile radio wave propagation research for 800 MHz, which started in the early 1960s, as the above-mentioned High Capacity Land Mobile Telephone System In parallel with the study of a cellular system at the ECL, the Bell Laboratories of the American Telephone and Telegraph Company (AT&T) in the United States was also conducting studies on a similar system. Almost at the same time as ECL’s presentation stated above, the Bell Laboratories submitted a report showing their concept of a large capacity mobile telephone system titled “High Capacity Mobile Telephone System –Technical Report” to the United States Federal Communications Commission (FCC). The system of the Bell Laboratories was called HCMTS.

On the other hand, following the presentation of the new system, Dr. Okumura and his team started simulation experiments at the ECL, using a prototype line management function, which would become essential in the development of the new system. In early 1972, Dr. Okumura successfully conducted a demonstration of the new system using the experimental environment to the executives of the ECL and reaffirmed his confidence in the system realization. Encouraged by this, Dr. Okumura completed a plan for practical realization of an “800 MHz band automobile telephone system” and was ready to full-scale development toward commercialization. The process from the start of studying the new system to the formulation of the practical application plan was completed in two years, which was unusual for the time.

After that, the development of commercial systems proceeded, and the technologies that form the basis of new systems, such as frequency effective utilization technology, radio channel control technology, and mobile telephone switching technology, were established. The system tests in the fields were also conducted with dividing two phases in 1973-1974 and 1975-1977 for radio access tests and total system tests. In 1979, the final test for commercialization was conducted.

On December 3, 1979, a full-scale mobile telephone service based on the world’s first cellular system using 800 MHz band was then launched in the 23 wards of Tokyo. After that, this commercial cellular service was gradually expanded to other major cities such as Osaka and Nagoya, and in February 1985, approximately five years after the service launched, it covered 500 cities nationwide and reached 39,000 subscribers [5-4].

For reference, it is introduced that “In 1979, the NTT’s network became the world’s first fully integrated commercial cell phone system and had the most advanced electronic switching.” in the explanation of the achievements in the above-mentioned 2013 NAE Charles Stark Draper Prize for Engineering [4].

The HCMTS mentioned above became the first commercial cellular phone system in the United States, which was later called “AMPS (Advance Mobile Phone System) [6-1],” and the commercial service of AMPS started in October 1983 [6].

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.

[1] [NTTPC Journal Paper] Yoshihisa Okumura, Eiji Ohmori, Tomihiko Kawano, and Kaneharu Fukuda, “Field Strength and Its Variability in VHF and UHF Land-Mobile Radio Service,” Review of the Electrical Communication Laboratory, NTT Public Corporation, vol.16, nos.9-10, pp.825-873, Sept.-Oct. 1968.

[2] [ITU Publication Document] CCIR Recommendation 370-2: “VHF and UHF propagation curves for the frequency range from 30 MHz to 1000 MHz” and CCIR Report 567: “Propagation Curves and Statistics Required for Land Mobile Services using the Frequency Range 30 MHz to 1 GHz,” Recommendations and reports from CCIR XIIIth Plenary Assembly (Geneva), Volume V, 1974.

[2-1] [IEEE Journal Paper] Masaharu Hata, “Empirical Formula for Propagation Loss in Land Mobile Radio Services,” IEEE Transactions on Vehicular Technology, vol.VT-29, no.3, pp.317-325, Aug. 1980.

[2-2] [ITU Publication Document] CCIR Recommendation 529: “VHF and UHF Propagation Curves for Land Mobile Services” and CCIR Report 567-2: “Methods and Statistics for Estimating Field-strength Values in the Land Mobile Services using the Frequency Range 30 MHz to 1 GHz,” Recommendations and reports from CCIR XVth Plenary Assembly (Geneva), Volume V, 1982.

(Note) CCIR Recommendation 529 was derived from CCIR Recommendation 370 and was intended for land mobile communications. Okumura-curve and the estimation equation appears in Section 2.2 of Annex I in the later version, Recommendation ITU-R P.529-3: “Prediction methods for the terrestrial land mobile service in the VHF and UHF bands”!!PDF-E.pdf

[2-3] [ITU Publication Document] The Radio Communication Sector of ITU, “Terrestrial land mobile radiowave propagation in the VHF/UHF bands,” ITU-R Handbook, 2002.

[3] [IEICE Technical Report] Yoshihisa Okumura, Yasushi Matsuzaka, and Matsuhiko Watanabe, “OUTLINE OF HIGH CAPACITY LAND MOBILE TELEHPONE SYSTEM,” Technical Report, Institute of Electronics and Communication Engineers of Japan, CS71-76, pp.1-11, Oct. 1971 (since the original text is in Japanese, an English translation is attached).

[4] [NAE Information] Explanatory material regarding 2013 NAE Charles Stark Draper Prize for Engineering

[5] [IEEE Journal Paper] Sadao Ito and Yasushi Matsuzaka, “800-MHz band land mobile telephone system—Overall view,” IEEE Transaction on Vehicular Technology, vol.VT-27, no.4, pp.205-211, Nov. 1978.

[5-1] [NTTPC Journal Paper] Terumochi KAMATA, Masayuki SAKAMOTO, and Kazuo FUKUZUMI, “800 MHz Band Land Mobile Telephone Radio System,” Review of The Electrical Communication Laboratories, vol.25, nos.11-12, pp.1157-1171, Nov.-Dec. 1977.

[5-2] [NTTPC Journal Paper] Noriaki YOSHIKAWA, Sadaatsu OKASAKA, and Hiroshi KOMAGATA, “800 MHz Band Land Mobile Telephone Control System,” Review of The Electrical Communication Laboratories, vol.25, nos.11-12, pp.1172-1190, Nov.-Dec. 1977.

[5-3] [NTTPC Journal Paper] Yoshikazu HONMA, and Hideo OGATA, “Land Mobile Telephone Switching System,” Review of The Electrical Communication Laboratories, vol.25, nos.11-12, pp.1191-1202, Nov.-Dec. 1977.

[5-4] [IEEE Conference Paper] Takaaki Kikuchi, K. Tsujimura, and K. Kato, “Progress in the 800MHz land mobile telephone system in Japan,” 35th IEEE Vehicular Technology Conference, pp.304-309, May 1985.

[6] [IEEE Magazine Article] Richard H. Frenkiel, “Creating Cellular: A History of the AMPS Project (1971-1983),” IEEE Communications Magazine, vol.48, no.9, pp.14-24, Sept. 2010.

[6-1] [AT&T Journal Paper] W. R. Young, “Advanced mobile phone service: Introduction, background, and objectives,” The Bell System Technical Journal, vol.58, no.1, pp.1-14, Jan. 1979.

A following document can also be referred to for the main contents of this proposal.

[7] [IEEE Conference Paper] Yukihiko OKUMURA, “The Mobile Radio Propagation Model “OKUMURA-curve” and the World’s First Full-Scale Cellular Telephone System,” 2017 IEEE HISTory of ELectrotechnolgy CONference (HISTELCON), pp.107-112, Aug. 2017.

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