Start of Transmission from Tokyo Skytree —Part 1: History of the Relocation Project— Executive Chiharu Research Kamise Engineer ShinjiSenior Sasade Director Technology Research and Development Department Transmission Engineering Division, Technical Department Fuji Television Network, Inc. Fuji Television Network, Inc. Efforts to switch over to digital in regions with large numbers of residential broadcasting began to gather momentum households, such as the service areas of the from around 1997, when NHK (Japan Tama and Utsunomiya relay stations, it Broadcasting Corporation) and five was decided that low-power transmissions commercial broadcasters based in Tokyo would be made from the Tokyo Tower entered into discussions regarding a suitable during the initial stage of digital transmission site. broadcasting. Therefore, a plan was drawn Although the idea of attaching up whereby the existing Tokyo Tower transmitters to the Tokyo Tower was would initially be used only for low-power investigated, its operator (Nippon transmissions for a few years, and then a Television City Corporation) was initially single-frequency network (SFN) would be of the opinion that the tower had neither also the number of relay stations required, configured using high-power transmissions enough space for the attachment of digital and summarized these results in an interim from a new transmitter tower, together with broadcast antennas, nor enough strength to report. low-power transmissions from the Tokyo support their weight. As a result, we found that a tower Tower, before completing the transition to There was also insufficient space to at least 500 m tall could also reduce the new transmitter tower. house the transmitter equipment, so the number of relay stations required. An issue to be resolved in this case if the Tokyo Tower were to be used for (However, since there was not enough time was the degree to which SFN interference broadcasting, a new building would have for relocation to take place before the end would result in households being to have been built nearby to house the of analog transmissions, it was ultimately unable to receive a signal. It was found transmitter equipment. not possible to reduce the number of relay that the number of affected households Besides, there are many more high-rise stations.) was very large, so a stepped transition buildings in central Tokyo today compared After that, a new tower study project would be difficult to achieve in an SFN with when the Tokyo Tower was built, so and a current tower project were set up in configuration. This meant that a single the interference of radio waves from the conjunction with a further six companies overnight switchover was the only viable Tokyo Tower has increased significantly. based in Tokyo. These projects published option. The construction of tall buildings is likely two reports in June 1999. Thereafter, from 2000, Nippon to continue into the future. Due to the time taken to conduct these Television City Corporation proposed the Therefore, in 1998, a transmission- studies, it was by this stage starting to construction of a new tower situated 130 related project was set up by NHK and seem unlikely that a new tower could be m away from the existing Tokyo Tower. five commercial broadcasters, who began constructed in time for the start of digital This proposal was also considered by the discussing the idea of building a new broadcasting. transmission-related project. broadcasting tower. Therefore, to make the September Although technically sound, this 1999 plan more realistic, scenarios were proposal was severely hampered because 1. Initial studies of the new tower prepared for the introduction of terrestrial the vicinity of the existing tower is digital broadcasting. designated as an existing non-compliant At this stage, the investigations initially structure according to Japanese aviation focused on three candidate sites — the 2. Proposal of a stepped law, which would mean having to obtain Tokyo Tower, Saitama Tower and Tama transition to transmissions a special dispensation from the Ministry Tower. Plans had been made to use UHF from a new tower of Transport to build a new tower in this signals for digital broadcasting, but these location. were said to have a shorter propagation This proposed scenario corresponds to distance than VHF signals. It was also the case where high-power broadcasting is 3. Expanding the One-Seg necessary to consider the cliff effect (cut- performed from another transmission point area, and increasing the field off characteristic) that is inherent to digital after broadcasting at low power from the strength broadcasting. It was therefore concluded existing tower. that a taller tower was needed to allow Before starting digital broadcasting, There were some broadcasting signals to propagate further, and that the it was necessary to change the frequencies companies that questioned the need tower should be roughly 500 m tall. We used for analog broadcasting. for this, and in 2002 a private research investigated the total cost of each approach, Since full-power transmissions were to establishment was commissioned to including not only the master station but start after changing the analog frequencies examine the feasibility of a new tower. The 14 New Breeze Winter 2014 report on this study was submitted in 2003. was decided that the new tower would be protection ratio for channel 27 (used This resulted in a significant called the Tokyo Skytree. by the Skytree) and channel 28 (which expansion of the area in which One-Seg After resolving many issues relating continues to broadcast from the Tokyo can be viewed, and also increased the to the tower's design and construction Tower) field strength. This makes it possible to (bearing in mind the prevalence of • Reception countermeasures for ensure that critical infrastructure remains earthquakes in Tokyo), the construction communal reception facilities in available in the event of a natural disaster, was completed in May 2011. The Tokyo outlying areas and for communal and from a business perspective it also had Skytree is 634 m tall, making it the highest reception facilities with interference advantages such as support for advertising free-standing broadcasting tower in the countermeasures: Countermeasures for in the mobile communication era. world and a center of tourism in Tokyo. reduced/increased electric field strength Initially, it was decided that digital or interference occurring due to changes transmissions would start at the Tokyo 5. Advance investigation of in the reception environment at the Tower, and would then be transferred to reception hindrances caused point of reception the new tower. The structure of the Tokyo by relocating the transmitter • Interference countermeasures for Tower was partially reinforced, and a new station to the Tokyo Skytree reception at relay stations: Counter- transmitter room was installed below the measures for reduced/increased electric tower's observation deck. A multi-faceted NHK and the five commercial field strength or interference occurring antenna for digital transmissions was broadcasting companies formed an due to changes in the reception installed in the lower part of the gain tower investigative working group, and convened environment at the point of reception for the existing analog antenna. 83 times on a once-per-week basis. The • Reception surveys and countermeasures From December 2003, terrestrial working group conducted wide-ranging for relay stations receiving signals from digital television was first started in field studies as described below. The the tower, methods for the utilization of Japan’s major cities — Tokyo, Osaka and procedure for the simulation of reception test signals Nagoya. In Tokyo, the signals were initially difficulties was more or less the same as the transmitted at low power from the Tokyo procedure used by the joint council for the 6. Basic concepts of simulation Tower promotion of terrestrial digital broadcasting (an organization formed by the Ministry of The area being studied was subdivided 4. Establishment of a new Internal Affairs and Communication) when by a fine grid drawn onto a map, and at Tokyo Tower expert studying the change of analog frequencies a representative point in each grid cell, committee in 2004 and the start of terrestrial digital television a table (called an electric field list) was broadcasting (master stations and relay produced from data including the electric Considering the growing rivalry stations). Studies were conducted on the field strengths of the Tokyo Skytree signal, between potential locations for the new following topics: the Tokyo Tower signal, and other signals tower, the six companies established an • Interference countermeasures in the that use the same frequency and arrive expert committee on candidate sites for the Kanto region: Interference between from relay stations necessary for studies and new tower. The members of this committee relay stations constituting the single the like. This data was then subjected to were chosen from among university frequency network (SFN) probabilistic analysis according to statistical professors and other specialists in fields • Interference countermeasures for methods by using the macro function of such as urban landscaping, seismology, neighboring prefectures: Interference of a spreadsheet application. As a result of city planning, electromagnetic wave broadcasting in neighboring prefectures this analysis, decisions were made such as propagation,