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NTT DoCoMo 4G Network and i-mode Technology, Japan

Key Data

NTT DoCoMo are one of the biggest mobile telecoms operators in Japan and have the distinction of bringing the first Wideband Code-Division Multiple-Access (W-CDMA) 3G network in the world to market in 2001. Following a successful rollout of the network the company has been building its customer base and developing a range of highly successful services and products.

There are over 70 million mobile phone users in Japan (in 2004) and the market is fast approaching saturation point. NTT DoCoMo is already in action with the next step in mobile network technology. In March 2002 the company announced the start of proving trials on the next generation of mobile communication technology, which has been called '4G' (fourth generation).

The new technology, which has been in development since 1998, will increase data transmission rates from 3G data rates, which are currently 384kbps (downlink) to the 4G standard 100Mbps (uplink) and 20Mbps (downlink), allowing more bandwidth for new applications such as video phones, video / audio download and interactive games. One of the two competitor networks to NTT DoCoMo, run by KDDI/AU, has already upgraded to CDMA2000 1xEVDO (an intermediate 3.25G technology that allows a data transmission rate of up to 2.4Mbps).


The economics of the take-up of 3G services has been questioned in several countries where billions have been spent on the required operating licenses and setting up new networks. Companies are worried, and can still only guess at what their new 3G customer base is likely to be. The success of 3G can only be measured in the number of customers it attracts, and indeed how much it can earn for the required company. The successful marketing of 3G will rely on showing consumers how much better it is and what new services and applications they are missing by remaining with 2G.

Already NTT DoCoMo is talking about the introduction of 4G across Japan nationwide by mid 2006. NTT DoCoMo, which has one of the longest running 3G networks worldwide, has only 4.9 million 3G customers (2004) but has 45 million 2G customers (whom it hopes will make the switch in due course).


In May 2003 NTT DoCoMo carried out a field trial of a fourth-generation (4G) mobile communications system in Yokosuka, Kanagawa Prefecture, near the main DoCoMo R&D centre. The Kanto Bureau of Telecommunications granted the company a preliminary / temporary license to conduct the field trial. This followed extensive laboratory research and was the next step towards the development of practical 4G technology. In addition, the trial was conducted to aid in the development of a 4G 'packet wireless transmission system' global standard, which is currently under discussion (2004) by the International Telecommunication Union's Radiocommunication Sector (ITU-R).

The tests used Variable Spreading Factor Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) and Variable Spreading Factor Code Division Multiple Access (VSF-CDMA) technologies. VSF-OFCDM enables downlink connections of extremely high speeds, both indoors and outdoors, while VSF-CDMA realises high-speed, high-efficiency packet transmissions for the uplink. The field trial was conducted to evaluate the following test parameters:

  • Effective packet transmission methods
  • Adaptive modulation and channel coding scheme
  • Adaptive retransmission control
  • Adaptive beam forming based on predicted direction of arrival

One of the main concerns after the field trial is that the speed of the frequency suggests that it would experience severe interference from multi-path secondary signals reflecting off other objects. There have been a number of proposed solutions, including using a variable spreading factor (VSF) and orthogonal frequency code division multiplexing (OFCDM).


It is suggested that 4G technologies will allow 3D virtual reality and interactive video / hologram images. The technology could also increase interaction between compatible technologies, so that the smart card in the handset could automatically pay for goods in passing a linked payment kiosk (i-mode can already boast this capability) or will tell your car to warm up in the morning, because your phone has noted you have left the house or have set the alarm. 4G is expected to provide high resolution images (better quality than TV images) and video-links (all of these will require a band width of about 100MHz).

It is likely that the forecasts of the next 'Killer Apps' for 4G technology will change as customer demand develops over time. The new communications model has already prompted the development of new versions of HTML, Java, GIF, HTTP and many more useful protocols. However, it is expected that new standard protocols will be required for use with 4G.


I-mode is the mobile Internet service introduced by NTT DoCoMo in February 1999, about 18 months before the 3G network was first switched on. Technically, i-mode is an overlay of NTT DoCoMo's ordinary mobile voice system. While the voice system is 'circuit-switched' (need to dial-up), i-mode is 'packet-switched'. This means that i-mode is in principle 'always on', provided the user is in a reception area.

As of summer 2004, there were 42 million i-mode subscribers in Japan, and 4 million i-mode subscribers outside Japan. It is widely thought that the i-mode service is used by 30% of the Japanese population more than ten times each day to check e-mail, book tickets for trains or theatre, check the weather, Internet banking and a variety of other information-rich uses (the competitors to the service in Japan are EZweb from KDDI and Vodaphone live).

I-mode started in Europe (Netherlands, Germany, Belgium, France, Spain, Greece and Italy) in April 2002 and expanded to Taiwan and Australia during 2004.


From 2004 onwards NTT DoCoMo will build smart cards into mobile phones. Prepaid electronic cash applications can be stored in these smart cards. The smart card can be accessed by JAVA i-appli, allowing the user to read the e-cash balance directly with the mobile phone off-line.

The new service is called i-mode FeliCa and was made possible by the synergy of i-mode, the mobile Internet service, and contactless IC chip technology from Sony (FeliCa). The FeliCa fast and secure data transmission technology was combined with i-mode, which enables reliable communication. As a result, a mobile handset becomes a tool for convenient new uses, serving as e-money, credit card, ticket, or even house or office key.

In an i-mode FeliCa handset the IC chip technology is integrated with an internal antenna. This IC chip operates by detecting weak electronic signals emitted by a reader / writer on an external device, and can even function when the handset is turned off or out of range. The device can act as an electronic wallet and even purchase soft drinks from enabled c-mode machines (1000 currently deployed in Tokyo).


I-mode on 2G (MOVA) and on 3G Freedom of MultiMedia Access (FOMA) are very similar but not exactly the same, since the network data rates and handset functionality are different. For example, downloadable movie sketches and video transfer is only possible on 3G (FOMA). However there are some services that have been optimized for 2G and are not available for 3G users (e.g., Citibank's mobile banking currently (2004) is only available for 2G not for 3G).