FCC Opens Spectrum

The Federal Communications Commission Thursday made a major policy shift, allowing hopping channels to span 75 megahertz. Hopping enables data transmission speeds of 10 megabits per second. But some equipment manufacturers, including Cisco, are worried.

by Patricia Fusco
Associate Editor, ISP-Planet
[September 1, 2000]

The Federal Communications Commission Thursday made a major policy shift in the federal rules that govern U.S. wireless communications.

The Commission amended Part 15 of the its rules concerning wireless devices operating in the 2.4-gigahertz band. The FCC's decision permits wideband frequency-hopping products to operate at similar power levels to existing wireless local area network systems, opening the door to innovation and increased competition in the wireless arena.

The new rules call for a minimum of 15 hopping channels, spanning a total of 75 megahertz. Hopping channels are permitted to be up to 5 megahertz wide. With wider bandwidths allowed, providers are free to offer high-speed data rates over wireless devices.

Secure wireless broadband
By utilizing fast frequency-hopping technology, manufacturers will be able to offer low-cost, more power efficient wireless devices that can provide superior interference protection, security, and network scalability.

This FCC action paves the way for development of a new generation of interference-immune, high-speed wireless networking technology designed to extend the reach of broadband multimedia services within homes, schools, and businesses.

The ruling is nothing short of a breakthough for equipment manufacturers.

Spread spectrum devices were only permitted to operate on unlicensed spectrum.

Due to interference in other frequencies, U.S. wireless providers' ability to hop spectrum was limited. The Home RF Working Group lobbied with the FCC to change the rules of the game.

Five
Accepting HomeRF's proposal, the FCC enables frequency hopping spread spectrum devices operating in the 2.4-gigahertz band to increase data transmission speeds five-fold, from 2 megabits per second to 10 megabits per second.

Wide band frequency hopping enables high-speed wireless providers to serve up home access capable of integrating data, voice, and video communications.

The Committee for Unlicensed Broadband Enablement (CUBE) agreed with HomeRF, stating that the proposed rule changes were necessary to preserve the competitive balance between the capabilities of frequency hopping and direct sequence spread spectrum devices operating in this band.

This competition between FHSS and DSSS is a real issue. Proxim notes on its "What is a Wireless LAN?" page,

"Interoperability of Wireless Devices Customers should be aware that wireless LAN systems from different vendors might not be interoperable. For three reasons. First, different technologies will not interoperate. A system based on spread spectrum frequency hopping (FHSS) technology will not communicate with another based on spread spectrum direct sequence (DSSS) technology. Second, systems using different frequency bands will not interoperate even if they both employ the same technology. Third, systems from different vendors may not interoperate even if they both employ the same technology and the same frequency band, due to differences in implementation by each vendor."

Proxim explains the differences between the DHSS and FSSS this way:

There are two types of spread spectrum radio: frequency hopping and direct sequence.

Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise.

Direct-sequence spread-spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer the chip, the greater the probability that the original data can be recovered (and, of course, the more bandwidth required). Even if one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can recover the original data without the need for retransmission. To an unintended receiver, DSSS appears as low-power wideband noise and is rejected (ignored) by most narrowband receivers.

CUBE asserted that allocating the spectrum that frequency hopping technology requires would enable it to be competitive with direct sequence technology and ultimately benefit consumers. In addition to leading to the development of improved wireless devices operating at lower costs, CUBE noted that the proposal to permit up to 5 MHz bandwidths for spectrum hopping would allow backward compatibility with existing devices.

More than 80 additional parties submitted comments and ex parte filings in support of recommendations from CUBE and HomeRF.

Wire-free broadband networking firm and HomeRF member Proxim, Inc. was quick to give federal regulators a corporate "pat on the back" for the rules change.

Page 2: Dissent and the FCC's conclusion