In the Matter of                         )

                                         )

Amendment of Parts 2 and 15 of the       )      ET Docket No. 96-8

Commission’s Rules Regarding Spread )       RM-8435, RM-8608, RM-8609 

Spectrum Transmitters                    )       

COMMENTS

1. The Wireless Consumer Communications Section ("the Section") of the Telecommunications Industry Association ("TIA") User Premises Equipment Division hereby offers its Reply Comments on the above-captioned matter. While most commenting parties are generally supportive of the Commission’s proposals as put forth in the Notice of Proposed Rule Making, ("NPRM"), several parties suggested modifications which are based on erroneous or incomplete reasoning. The Section addresses those suggested modifications herein.

I. TELETRAC

2. Teletrac License, Inc. ("Teletrac") proposes that frequency hopping ("FH") devices with less than 50 hopping frequencies be allowed "to operate with no more than 50% of their total utilized bandwidth" within the location and monitoring services ("LMS") multilateration bands, and that the non-interference presumption ("safe harbor") established in the Report and Order in PR Docket 93-61 ("the LMS Order") not apply to reduced-hop devices that use any part of the LMS multilateration bands¹. This proposal is based on Teletrac’s concern that reduced-hop FH devices will be able to concentrate their transmissions in the LMS bands, thereby causing more interference to LMS operations than they would, were they operating under the current rules².

3. The Commission has already anticipated this concern, noting that "We recognize that the chance of collisions with other transmissions, and resulting interference, will be increased since there are a fewer number of hopping channels³," and proposed a remedy which is more straightforward than that suggested by Teletrac. The NPRM proposes that FH systems in the 902-928 MHz band using less than 50 hopping frequencies be limited to a maximum output power of 500 mW "to reduce the potential for interference due to the smaller number of hopping channels⁴." However, the NPRM also requests comments "as to whether or not a greater reduction in output power should be applied⁵." In its Comments in this proceeding, the Section responded to that request, and demonstrated that if the power output limit is proportional to the square of the number of hopping frequencies, then the probability of interference (i.e., the probability of a collision) from a reduced-hop system is at worst no greater than the probability of interference from a comparable system operating under the existing rules in �15.247. This power reduction therefore would address Teletrac’s concerns that allowing reduced-hop FH devices could increase the risk of interference to multilateration LMS systems.

4. Teletrac also states that the "risk" of interference "would exist even at power levels that were far below both the current and proposed maximums for frequency hopping systems⁶." Although there is undeniably an "interference risk" associated with operation in the 902-928 MHz band, the fact is irrelevant. The power limit reduction for reduced-hop FH devices is intended not to eliminate the interference risk, but rather to maintain it at the same level as under the existing rules, and interference probability would seem to be the most reasonable measure of "risk". Since the probability of interference from reduced-hop devices would be no greater than from FH devices operating under the existing rules, there is no need to impose additional restrictions on operating frequencies or to make any exceptions to the safe harbor provisions⁷. Therefore, Teletrac’s proposals are unnecessary and should not be adopted.

II. GEC PLESSEY SEMICONDUCTORS

5. GEC Plessey Semiconductors ("GPS"), alone among the commenting parties, requests that the Commission "reconsider" its decision to deny the Petition for Rule Making of Symbol Technologies, Inc. ("Symbol")⁸, which requested that the minimum number of hopping frequencies be reduced for frequency hoppers operating in the 2400-2483.5 MHz band, so hoppers could use emission bandwidths larger than the current maximum (1 MHz). GPS maintains that a wideband frequency hopper will pose no more of an interference threat than a hopper with a 1 MHz emission bandwidth. As support for this contention, GPS gives an example of a direct sequence ("DS") receiver with a 20 MHz bandwidth sustaining interference from the frequency hopper, asserting that the probability of interference depends on the bandwidth of the DS receiver, regardless of whether the hopper has a bandwidth of 1 MHz, 2 MHz, or 4 MHz⁹. The power output of the hopper is assumed to be independent of its bandwidth.

6. GPS has ignored the case in which the bandwidth of the victim receiver is less than the bandwidth of the hopper, which becomes increasingly likely as the bandwidth of the hopper increases. While DS high-speed data systems, such as wireless local area networks, may have bandwidths on the order of 10 or 20 MHz, many other devices, such as cordless telephones, do not. When the bandwidth of the frequency hopper exceeds that of the victim device, the interference probability increases as the bandwidth of the hopper increases, assuming the total bandwidth from which the hopper selects its frequencies is fixed¹⁰. This is true for both DS and frequency hopping victim devices, as well as non-spread spectrum devices. GPS therefore has neglected an important case in its assessment of the interference impact of wideband frequency hoppers.

7. Even with a reduction in the maximum power output, the Section believes that allowing wideband frequency hopping systems would contribute to increased interference, because it would encourage the use of frequency hopping by applications requiring a high data rate. Currently, high-rate applications use DS modulation. A stationary wideband DS signal can easily be avoided by adaptive narrowband DS or frequency hopping devices, such as cordless telephones. In contrast, it would be virtually impossible to avoid interference from a nearby wideband frequency hopping transmitter (as envisioned by GPS) hopping over the entire band. The Section therefore opposes GPS’ proposal, and supports the Commission’s decision to deny Symbol’s petition.

III. ERICSSON

8. The Ericsson Corporation ("Ericsson") expresses concerns about the impact of reduced-hop FH systems on low-power unlicensed devices operating under the general limits �15.249. Ericsson proposes that reduced-hop FH systems be limited to a power output of 100 mW and be required to operate in non-LMS spectrum. As discussed supra, these measures are unnecessary if the quadratic power output reduction proposed by the Section in its comments is adopted. Ericsson also proposes a modification to �15.249, which would allow a power output that varies linearly with the number of carriers used by a system. Such a change in the Commission’s Rules is beyond the scope of this proceeding. For these reasons, Ericsson’s proposals should not be considered.

IV. WESTERN MULTIPLEX

9. Western Multiplex Corporation ("Western Multiplex") supports the use of high-gain antennas in the 2400-2483.5 MHz band, and claims that "when there may be potential interference from long distance systems with directional antennas into non-directional systems, the long distance system will not operate due to much more severe interference from the non-directional system¹¹." Western Multiplex supports this claim with an example calculation of the mutual interference between a point-to-point ("PTP") system using high-gain (27 dBi) antennas, and an indoor wireless local area network ("LAN") which is 1000 feet away from one of the high-gain antennas and aligned with its direction of maximum radiation. In that example, the interference from the wireless LAN to the PTP system causes the carrier-to-interference ratio of the PTP system to drop below its critical value, whereas the LAN can continue to operate in the presence of the interference from the PTP system. Western Multiplex concludes from this example that systems using high-gain antennas are more vulnerable to interference from other devices in the band, than those devices are to interference from the high-gain systems.

10. Western Multiplex seems to have incorrectly drawn a general conclusion from a single specific example¹². In fact, as demonstrated in the Attachment to these Comments, no general statement can be made regarding the ability of a system with a high-gain antenna to degrade the performance of another system, compared to the degradation in the performance of the high-gain system due to interference from the other system. The system that will suffer the most from the mutual interference will be the one with the least interference margin. That margin depends on the carrier-to-interference ratio required for acceptable performance, as well as the desired signal power received by each of the receivers from its companion transmitter, which in turn depends on transmitter-receiver separation and other factors affecting propagation. In short, whether a high-gain PTP system or another system in its path will suffer the greatest performance degradation will depend on the specific situation.

11. The Section continues to believe that if high-gain antennas are allowed in the 2400-2483.5 MHz band, without the dB-for-dB backoff of transmitter output power as required under the existing rules, the result will be an increase in interference to other systems operating in the band. This is not because a single isolated system is necessarily more of an interference threat with a high-gain antenna¹³, but rather because allowing high-gain antennas without the power backoff would invite a new set of applications in the band, causing an increase in the general level of interference. The Section therefore continues to support the proposal in the NPRM to allow high-gain antennas without the dB-for-dB power backoff only in the 5725-5850 MHz band.

Respectfully submitted,

TELECOMMUNICATIONS INDUSTRY ASSOCIATION
WIRELESS CONSUMER COMMUNICATIONS SECTION

Jay E. Padgett
Chairman, Wireless Consumer Communications Section
User Premises Equipment Division