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  7. Fujitsu Develops Millimeter-Band Transmitter Capable of Data Transmission Speeds Exceeding 10 Gbps

Fujitsu Develops Millimeter-Band Transmitter Capable of Data Transmission Speeds Exceeding 10 Gbps

- World's first pulse transmitter operating in 70 - 100 GHz using impulse radio -

Fujitsu Laboratories Ltd.,Fujitsu Limited

Kawasaki and Tokyo, Japan, June 19, 2008

Fujitsu Laboratories Ltd. and Fujitsu Limited announced today, as a world's first, the development of a transmitter operating in the 70-100 GHz band using impulse radio(1) that is capable of transmitting data at speeds of more than 10 gigabits per second. This new development eliminates the need for oscillators and other hardware that had been required for use of earlier millimeter-band transmitters, thus enabling a smaller millimeter-band transmitter. As a substitute for fiber-optic high-speed lines, the new transmitter could be used in wide range of applications geared to help bridge the digital divide(2), including for platform networks and short-range wireless LANs.

This research was carried out as part of the Research and Development Project for Expansion of Radio Spectrum Resources, sponsored by Japan's Ministry of Internal Affairs and Communications. Details of this technology were presented at the 2008 IEEE MTT-S International Microwave Symposium (IMS2008), being held from June 15 - 20 in Atlanta.

Background

With the rapid expansion in mobile phone and Internet users, along with mounting data transmission volumes associated with video and other media, fiber-optic cabling has been used as the medium of choice for trunk-line data networks. But laying such fiber can be difficult when it needs to cross rivers or straits, mountains, roads or train tracks, thereby stalling the buildout of these networks. This has created a demand for an alternative to fiber-optic cabling in these less accessible areas, a wireless one that would offer high transmission speeds (10 Gbps). A high-capacity wireless medium is also becoming increasingly necessary in times of emergency, such as natural disasters or other incidents.

Figure 1: Impulse wireless transmission system

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Technological Challenges

Wireless transmissions with speeds exceeding 10 Gbps are practical using millimeter-band (30-300 GHz) frequencies, which are seldom used commercially and where wide swaths of bandwidth can be readily secured. Within that band, the so-called "radio window" of 70-100 GHz(3) is attractive because signals are relatively unaffected by passage through the atmosphere, allowing them to travel several kilometers or more.

Transmitting in the 70 - 100 GHz band, however, has involved multiple single-purpose electronic components, with little progress on miniaturization. This sparked interest in the development of impulse-radio technology, which needs no oscillator, and the transmitter (millimeter-ban pulse transmitter) can be constructed using only two components: an impulse emitter and an amplifier (see Figure 1). However, 70 - 100 GHz wireless communications required breakthroughs in generating high-energy pulse signals and the development of filters with low energy losses.

Overview of the Newly Developed Technology

To implement millimeter-band transmissions at rates of more than 10 Gbps, Fujitsu and Fujitsu Laboratories developed the following impulse-radio technologies.

  1. World's highest-performance ultra-short pulse(4) generator
    In order to obtain sufficiently high energy pulses in the 70-100 GHz band, especially up to 100 GHz, the pulses need to be very short. The smaller the full-width at half-maximum (FWHM)(5) for a pulse, the higher the energy it carries up to a high frequency; effectively, this requires a FWHM below 10 ps. Fujitsu Laboratories developed and used an indium-phosphide high electron-mobility transistor (InP-HEMT)(6) technology with excellent high-speed performance, resulting in a short-pulse generator based on digital technology. The result is the world's highest-performance short-pulse generator, with a FWHM of 7.6 ps, which has been proven to carry enough energy for frequencies above 100 GHz.
  2. Low-loss filter
    The millimeter-band pulse transmitter carries energy in a short pulse across an extremely wide band, which must be able to extract only that band needed for transmission. Because the millimeter band is highly susceptible to losses caused by the skin effect(7), the researchers created a multi-stage coupled-line filter using a substrate of alumina, which is readily obtainable and offers excellent high-frequency performance. The result is that the filter passes a signal frequency range of 78 - 93 GHz, and losses within that range (insertion losses) were 1.5±0.1 dB, resulting in the levels of performance needed for a millimeter-band impulse radio transmitter.
Figure 2: Newly developed millimeter band pulse transmitter

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Results

These two technologies were combined to create a millimeter-band pulse transmitter (see Figure 2). This resulted in the world's first impulse radio transmitting at over 10 Gbps in the millimeter band (in this case, 78-93 GHz). The new transmitter makes it possible to dispense the oscillator, mixer, and other components that had been needed in previous millimeter-band transmitters, resulting in a compact package that is only approximately 30% as large as its predecessors.

Figure 3: Results of actual measurements of 10Gbps-level pulse signals

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These results established the basic technologies for millimeter-band wireless communications equipment, which could be used as an alternative for fiber-optic cable in a way that could help bridge the digital divide and bring broadband to locations otherwise inaccessible due to rivers, roads, geography, or a natural disaster. This technology could also be used for a wide range of applications, such as indoor high-speed wireless LANs and high-resolution radar.

Future Developments

Fujitsu Laboratories plans to combine the transmitter with a receiver, to conduct transmission testing with a fixed target. Field testing will be conducted, targeting development of practical-use systems by around 2012.



  • [1] Impulse radio

    The general principles behind impulse-radio technology are the same as those commercialized by Marconi roughly a century ago in his spark-gap emitter radio. It emits a pulsed signal that varies over an extremely short period and uses a filter to extract only the portion of the band needed for transmission.

  • [2] Digital divide

    Unequal access to information. Related to economic inequalities between people or regions with good access to electronic communications (especially the Internet), and those without.

  • [3] Radio window

    Typically with radio, as frequencies increase so does atmospheric absorption, thereby attenuating the signal so that it can carry less. But absorption decreases in the region around certain frequencies (40 GHz, 90 GHz, 220 GHz, etc), permitting carriage over relatively long distances. These bands behave somewhat like a "window" through the air, hence the origin for this name.

  • [4] Short pulse

    A pulse is a signal that rises and falls, describing a fixed shape over a fixed period of time. A short pulse is one where the signal varies over a short period of time.

  • [5] Full-width at half-maximum (FWHM)

    Taking the full extent of a pulse's variation as 1, this is the amount of time the pulse spends above one-half (1/2) value. A pulse with a low FWHM carries high-frequency energy.

  • [6] Indium phosphide high electron-mobility transistor (InP-HEMT)

    Invented in 1979 by Fujitsu Laboratories' Takashi Mimura (currently a Fellow at Fujitsu Laboratories), this is a transistor made of compound semiconductors with excellent speed and noise characteristics. Using an indium-phosphide (InP) substrate results in higher speed and lower noise than with conventional gallium-arsenide. This is considered useful in high-speed communications and millimeter-band image sensors.

  • [7] Skin effect

    A phenomenon observed when high-frequency current is flowing through a conductor, where the higher the frequency, the more current tends to concentrate near the surface of the conductor. In effect, resistance increases the higher the frequency.

About Fujitsu Laboratories

Founded in 1968 as a wholly owned subsidiary of Fujitsu Limited, Fujitsu Laboratories Limited is one of the premier research centers in the world. With a global network of laboratories in Japan, China, the United States and Europe, the organization conducts a wide range of basic and applied research in the areas of Multimedia, Personal Systems, Networks, Peripherals, Advanced Materials and Electronic Devices. For more information, please see:http://jp.fujitsu.com/group/labs/en/

About Fujitsu

Fujitsu is a leading provider of IT-based business solutions for the global marketplace. With approximately 160,000 employees supporting customers in 70 countries, Fujitsu combines a worldwide corps of systems and services experts with highly reliable computing and communications products and advanced microelectronics to deliver added value to customers. Headquartered in Tokyo, Fujitsu Limited (TSE:6702) reported consolidated revenues of 5.3 trillion yen (US$53 billion) for the fiscal year ended March 31, 2008. For more information, please see: www.fujitsu.com.

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Company and product names referenced herein are trademarks or registered trademarks of their respective owners. Information provided in this press release is accurate at time of publication and is subject to change without advance notice.

Date: 19 June, 2008
City: Kawasaki and Tokyo, Japan
Company: Fujitsu Laboratories Ltd., Fujitsu Limited, , , ,

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