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An interesting property of the 60 GHz band is that frequencies around 60 GHz experience significant absorption by oxygen. At 58 GHz the attenuation is approximately 12 dB/km. This property is advantageous for interference-limited radio systems, as it simplifies frequency re-use. Additionally, 60 GHz signals undergo severe attenuation when passing through construction materials. 3 to 7 dB of signal strength is typically lost passing through a doule-glazzed window, while 20-30 dB ise lost passing through a concrete wall. These losses can help to confine cell areas for indoor wireless communications. The 5 GHz span between 59 and 64 GHz also represents the largest amount of continuous bandwidth presently available for unlicensed radio communications. This combination of properties make 60 GHz ideal for short range, very high data rate networks.
On December 15, 1995, the FCC made the 59-64 GHz band available for general purpose unlicensed devices in the United States. One expected use of this band is for wide bandwidth computer-to-computer wireless connections at high data speeds (up to 5 Gbps); such wireless connections will potentially benefit both the home and business users. Companies including Hewlett-Packard, Apple, Sun, Motorola, Hughes, and AT&T, formed the Millimeter Wave Communications Working Group (MWCWG) and defined a spectrum etiquette for sharing this band, a necessary condition for the operation of equipment.
FCC rules for use of the 59-64 GHz band follow part 15 regulations. Additionally, the FCC has adopted the recommendations of the MWCWG for radio protocol. Some of the requirements include:
- total radiated power: <500 mW
- power density within 59-64 GHz: < 9 uW/cm2 at a distance of 3 meters.
- power density outside 59-64: spurious only; < 90 pW/cm2 at a distance of 3 meters.
- power measurements will be average measurements based on a 1 MHz bandwidth.
In Europe, the 60 GHz band is also being investigated for possible commercial use. In 1990 the European Radiocommunications Committee (ERC) published the CEPT Recommendation T/R 22-03 E, in which the frequency range 54.25 - 66 GHz is recommended for terrestrial fixed and mobile systems, with 59 to 62 GHz designated for RLANs (referred to as Cordless Local Area Networks). 57.2-58.2 GHz is recommended for for Mobile Broadcast Systems (MBS). 61 - 61.5 GHz is recommended for ISM Cordless Local Area Networks, low and medium capacity fixed links (1.47 GHz forward/return separation based on plan for 54.25 - 57.2 GHz). Alternate frequency ranges for MBS are 62-63 GHz and 65-66 GHz.
ACTS has a project named Median that is developing a 155 mbps 60 GHz system. Details of the Median demo include:
- frequency spectrum: 62-65 GHz
- data rate: 155 Mbps
- modulation: 16OQAM / 4 OQAM
- Access Method: TDMA
- Duplex Method: TDD
- Channels: 34, dynamically allocated
In Japan, the 59-64 GHz spectrum is being set aside for high speed data links. Several fixed link projects with data rates around 155 mbps at 60 GHz have been demonstarted. Work has also been done on 60 GHz broadband high data rate networks in Canada and Australia.
Links to more information:
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