FCC TO VOTE ON ORDER THAT WOULD ADD FLEXIBILITY TO PART 15 RULES

Further notice approved by FCC last year would allow spread spectrum devices at 2.4 GHz user fewer hops than 75 that have been required under existing Part 15 rules. Adaptive hopping would permit FHSS systems at 2.4 GHz to use as few as 15 hops regardless of bandwidth utilized as long as output power was limited to 125 mW, rather than 1 W limited that typically applies to FHSS and direct spread spectrum systems such as 802.11b. Proposed reduction in maximum allowable transmitter power was designed to reduce possibility of interference between FHSS systems that used fewer hops and wideband, frequency static systems such as 802.11b. Proposal responded to petition for partial reconsideration or clarification filed by 3Com and others over Aug. 2000 order. That order had changed FCC’s Part 15 rules to allow spread spectrum devices in 2.4 GHz band to use wider frequency-hopping channels for first time. Further notice adopted last year addressed new digital technologies that let signal hop in given swathe of spectrum more intelligently to avoid interference. FHSS systems spread energy by changing center of frequency of modulated signal. Under direct sequence spread spectrum systems, data stream and high-speed digital spreading code produce signal with relatively wide bandwidth. That spreading technology reduces power density of signal at any frequency over transmitted bandwidth to reduce potential for interference.

Bluetooth Special Interest Group urged FCC in filing last week to: (1) Adopt proposal allowing reduced hopsets for FHSS devices in 2.4 GHz band. (2) Require that devices that used those reduced hopsets to use adaptive hopping. Point of requiring adaptive hopping in concert with reduced hopset is that it would ameliorate interference in band, said Washington attorney Scott Harris, who is representing Bluetooth SIG in proceeding. Otherwise, it “leaves open the possibility that somebody could roll out technology that took advantage of reduced hop sets without doing adaptive hopping -- that wouldn’t help the interference environment,” he said. Bluetooth SIG told FCC in filing that “simply reducing permitted power levels for devices using reduced hopsets would not be sufficient to allow industry and consumers to benefit fully from a reduced interference environment.”

Lucent spinoff Agere, which makes 802.11b devices that operate at transmission speeds of up to 11 Mbps and FHSS products that use Bluetooth technology, also stressed in its filing that adaptive hopping should be required in exchange for use of reduced hopsets. “It is Agere’s understanding that a draft report and order has been circulated to the Commissioners’ offices by OET [Office of Engineering & Technology] for review and possible action at the Commission’s May 16, 2002, meeting,” Agere said May 8. “We are very concerned that the rules proposed in the draft R&O may not require the use of adaptive hopping techniques in exchange for the ability to employ a reduced hopset.” Current requirements that systems with bandwidths of about 1 MHz, such as Bluetooth, hop over at least 75 hopping frequencies, makes it “fundamentally impossible for such systems to avoid collisions with wider bandwidth, frequency static systems such as IEEE 802.11b wireless local area networks (WLAN),” Agere told FCC. “The span of the hopping frequencies covers so much of the band that it is impossible to avoid hopping, at least on some of the hops, within the channel used by a WLAN device, resulting in collisions and a loss of performance for both systems.” Using smaller hopset together with intelligent, adaptive method for selecting hopping frequencies based on interference environment would let FHSS systems avert collisions with wireless LAN devices operating in band in same areas and to avoid collisions with other FHSS systems. Agere stressed that “simply reducing the hopset without incorporating the intelligence to adapt to the changing interference environment in the band does virtually nothing to improve coexistence and eliminate unnecessary interference.”

“We want the adaptive hopping to be mandatory for small hopsets because each frequency will be occupied more of the time,” said Fletcher, Heald & Hildreth attorney Mitchell Lazarus, who represents several spread spectrum manufacturers in this proceeding. Wireless LANs are now limited to maximum speeds of 11 Mbps in this spectrum. Proposed rule changes under consideration at FCC “would take off that speed limit and you will see anything from 24 to 50 to 60 Mbps over the next few years,” he said. Besides faster Part 15 devices, changes also would give more flexibility to engineers who wouldn’t have to work in confines of 2 spread spectrum modulations that are now permitted, Lazarus said.