Milestone-Proposal:Mobile Radio Propagation Model “OKUMURA-curve” and First Commercialized Full-Scale Cellular Telephone System, 1968-1979
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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 Public Corporation (Predecessor of Nippon Telegraph and Telephone Corporation/NTT DOCOMO, INC.) 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.
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
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 of the intended milestone plaque site(s):
<No. 1> Street address: 3-5 Hikarino-oka, Yokosuka-shi, Kanagawa, 239-0847, Japan GPS coordinates: 35.13'31.0"N / 139.40'21.8"E <No. 2> Street address: 3-9-11 Midorimachi, Musashino-shi, Tokyo, 180-8585, Japan GPS coordinates: 35.43'09.5"N / 139.33'52.8"E
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. <No. 2> Corporate building of Histrical enter of NTT Corporation
Are the original buildings extant?
Details of the plaque mounting:
<No. 1> The building in the ground floor entrance hall <No. 2> The building in the ground floor entrance hall
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)?
<No. 1> NTT DOCOMO, INC. <No. 2> NTT Corporation
What is the historical significance of the work (its technological, scientific, or social importance)?
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) launched the Full-Scale Cellular Telephone System ahead of the rest of the world. Thereafter, in the cellular telephone 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 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 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 450MHz, 920MHz, 1420MHz, and 1920MHz capable of meeting the demands of future public land mobile communication services. His team collected a huge amount of 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 .
His highly acclaimed field strength curves of mobile radio propagation model were further reflected in the recommendation document  issued by the Comité Consultatif Internationale des Radiocommunications, CCIR (later the International Telecommunication Union Radiocommunication Division, ITU-R). 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. For example, in NTT Group, estimation formulas are continuously used in the design of wireless links such as mobile phone systems from the 1st generation to the 5th generation, 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.
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 described above and the concept construction of the high-capacity mobile telephone system using the 800MHz band  described later, received “The 2013 Charles Stark Draper Prize for Engineering ” 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 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. The following new elemental technologies  were developed for each problem that needs to be overcome when realizing the cellular system based on the above basic concept.
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.
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 exchange 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, Dr. Okumura of ECL presented the concept of a new system under the title of “OUTLINE OF HIGH CAPACITY LAND MOBILE TELEHPONE SYSTEM”  at a Technical Committee on Communication Systems of IEICE, Japan. According to his papers, 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, the new system is aimed at achieving large capacity, spectrum efficiency and wide-area service. For each of these targets, he clarifies the required conditions and functions, which includes new spectrum development, high-speed channel control and small radio zones. Hereinafter, this system is called HCMTS.
In parallel with the study of a cellular system at the ECL, the Bell Laboratories of AT&T in the United States was also conducting studies on a similar system. Almost at the same time as Dr. Okumura’s presentation stated above, the Bell Laboratories presented a report showing their concept of a large capacity mobile telephone system titled “High Capacity Mobile Telephone System –Technical Report” to the United Staties Federal Communications Commission (FCC).
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 exchange 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.
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 became a nationwide service.
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 .
The HSCMTS mentioned above became the first commercial cellular phone system in the United States, which was later called “AMPS (Advance Mobile Phone System) ,” and the commercial service of AMPS started in October 1983.
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.
 [ECL Journal Article] Y. Okumura, E. Ohmori, T. Kawano, and K. 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, no.9-10, pp.825-873, Sept.-Oct. 1968.
 [CCIR recommendation] CCIR Recommendation 370-2: “VHF and UHF propagation curves for the frequency range from 30 MHz to 1000 MHz,” ITU, 1974.
 [IEICE Technical Report] Y. Okumura, Y. Matsuzaka, and M. Watanabe, “OUTLINE OF HIGH CAPACITY LAND MOBILE TELEHPONE SYSTEM,” Technical Report, Institute of Electronics and Communication Engineers of Japan, CS71-76, Oct. 1971 (since the original text is in Japanese, an English translation is attached).
 [NAE Information] Explanatory material regarding 2013 NAE Charles Stark Draper Prize for Engineering
 [IEEE Journal Article] 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.
 [IEEE Magazine] 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.
A following document can also be referred to for the main contents of this proposal.
 [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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