The FCC recently announced that it was proposing rule changes in Part 15 with regard to 2.4 GHz spread-spectrum devices. This is big news because the rule changes will allow more flexibility for spread-spectrum systems, while also allowing the development of new devices similar to spread-spectrum systems.

Part 15 regulates the operation of unlicensed devices. These devices must operate with minimal or harmless interference, while they must also accept any interference that they may receive.

Last year, the commission changed its rules to allow for some frequency-hopping, spread-spectrum systems in the 2.4 GHz band that operate with a bandwidth greater than1 MHz, but less than or equal to 5 MHz to use a minimum of 15 hopping frequencies. Previously, the systems were required to use 75 non-overlapping hopping frequencies, as long as the total span of the hopping channels was at least 75 MHz. Those frequency-hopping systems that use as much as 1 MHz of spectrum are required to use at least 75 non-overlapping hopping frequencies.

After the rule change, many companies requested additional clarification. Therefore, the commission has decided to revisit the issue by issuing a Further Notice of Proposed Rule Making and Order requesting comment on some new proposed rule changes.

The FCC has proposed to further amend Rule Section 15.247 to allow a minimum of 15 hopping frequencies regardless of the bandwidth being used in the 2.4 GHz band. The only caveat is that the output power cannot exceed 125 mW and the new device must use adaptive hopping techniques. However, it appears from the NPRM that the FCC is not committed to making the use of adaptive hopping techniques mandatory in this instance. In fact, it invites comment on that particular point. As a result, we could see more change in frequency-hopping, spread-spectrum rules before the final order.

The FCC also proposed last year to change the method for which the processing gain of direct-sequence spread-spectrum is tested. Currently, the rules require that the processing gain be tested by the continuous wave (CW) jamming margin test. The FCC suggested that the CW jamming margin test, “may not measure the true processing gain for certain types of direct-sequence, spread-spectrum systems where a portion of the information signal is embedded in the spreading code.” The solution proposed by the FCC was the use of a Gaussian noise signal in the jamming margin test because it is more like a real-world environment.

Alas, this too met with opposition by commenters, so the FCC now proposes to eliminate the processing gain requirement for direct-sequence, spread-spectrum systems altogether because there is no consensus or standard method for testing the processing gain.

Finally, the FCC noted in the Notice of Proposed Rule Making (NPRM) that its own rules may stand in the way of new technology being developed. To address this important revelation, the FCC is proposing, and inviting comments on, whether digital transmission systems should be allowed to operate at the same power levels as direct-sequence, spread-spectrum systems.

The commission noted that digital transmission systems are similar to spread-spectrum systems and will be required to meet the same rule criteria as spread-spectrum devices, so much so that digital transmission systems will be addressed within Section 15.247 and not in a new rule section. However, digital transmission systems are most similar to direct-sequence, spread-spectrum systems. Accordingly, the FCC proposes that the allowable output power levels for digital transmission systems be the same as for direct-sequence spread spectrum. But the FCC also seeks comment on whether this might cause too much interference to other devices, and therefore should be given a reduced permitted power level.

This is an important NPRM because the FCC is directly addressing and responding to the concerns of manufacturers. The FCC is making it clear that it wants companies to have the flexibility to develop new technology, while protecting existing uses by being fairly conservative in its proposals.

Delaney M. DeStefano is a senior associate with the law firm of Schwaninger & Associates, P.C. DeStefano is a member of the New York State and District of Columbia Bars and a member of the FCC Bar Association. DeStefano's primary practice is in wireless telecommunications. She is a veteran of several FCC auctions.

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