Issue 2
Fielding questions for wireless manufacturers is one of the many activities that we perform at ACB. PACKETS provides an overview of just a small portion of the communiqués that run in and out of our office. This PACKETS focuses on unlicensed transmitters, particularly digitally modulated devices…by far one of the more active areas in wireless product launches.
Question:
Band edge correction factor: Is it possible to use a correction factor for compliance with the Band Edges testing?
Response:
When a signal is pulse-modulated, a correction factor could be used per FCC rule part 15.35. We must consider the worst-case duty factor in any 100 ms period in any mode of operation. This correction factor could be used for example for a DSSS transmitter, if one can prove that when the unit is set to a maximum duty factor, it would not be exceeded due to the unit inherent function.
Question:
Co-located transmitters: What condition produces co-located transmitters and what tests are required?
Response:
Co-located transmitters exist when two or more transmitters are installed less than 20 cm apart and all transmitters transmit simultaneously. An MPE estimate for mobile configurations is performed using the RF Exposure limits from OET Bulletin 65: “Evaluating compliance with FCC-Specified Guidelines for Human Exposure to Radio Frequency Radiation”, and Subpart I of Part 1 of the 47 CFR: Radio frequency radiation exposure limits” and 47 CFR paragraph 2.1091: Radio frequency radiation exposure evaluation: mobile and unlicensed devices. If either of the transmitters require SAR evaluation due to a portable configuration, there will be additional considerations that must be taken into account during this testing. For example, the area of highest SAR must be evaluated twice. Once with the second transmitter turned on and again with it turned off.
Question:
SAR evaluation: We have a 2.4 GHz PCMCIA transmitter card that is used in a portable configuration. Do we need SAR evaluation and can this device be approved by a TCB?
Response:
Whether SAR evaluation is required depends on the peak output power (both conducted and EIRP) and spacing between antenna and user under all expected applications.
(a) If the PCMCIA card is considered for use in a variety of host devices, then < 2.5 cm operation must be assumed since devices such as a notebook computers may be used while located in the user’s lap. To avoid SAR testing, the peak conducted and EIRP levels must be less than 24 mW. If the conducted or EIRP is greater than 24 mW the device will require SAR evaluation. SAR should be evaluated with the transmitter installed in the slot(s) producing the maximum SAR values. The minimum number of positions that must be evaluated for notebook computers and body-worn PDAs are bottom-face of the host device in parallel and in contact (0 cm) with flat phantom, and device perpendicular to phantom with recommended spacing of 1.5 cm. If the peak conducted or EIRP output power exceeds 100 mW, SAR testing will be required using a minimum of three hosts within each platform type (i.e. three PDAs, three notebooks, etc.). TCB’s may approve these devices unless the peak output power (conducted or EIRP) exceeds 368 mW. Portable 2.4 GHz devices exceeding 368 mW may only be approved by the FCC.
(b) When the distance from the transmitting antenna is é 2.5 cm, the device will require SAR when the peak conducted and EIRP level is é 49 mW. TCB’s may approve these devices unless the peak output power exceeds 368 mW (in which case may only be approved by the FCC). Note that portable configurations may only be classified as é 2.5 cm where it can be shown that the device can maintain the 2.5 cm distance in all expected applications.
Question:
RF exposure evaluation: How does the FCC evaluate the RF exposure distance for a steering beam antenna?
Response:
Classical equations are not appropriate for a steering beam antenna, due to the beam, which is fully focused at the location of the intended receiver. The surface power of the beam using phased array antennas is very low at the vicinity of the antenna. However, the FCC is still considering an approach to calculate the exposure distance for this type of antenna. Previously the FCC has accepted the use of equation 11 given in OET Bulletin 65 for applications using such antennas. Nonetheless, if you are developing a steering beam antenna, please inform us about it. We could, on your behalf, contact the FCC and consider their position depending on the antenna gain and the maximum power output of the unit. The usual far field MPE estimation formula is probably not appropriate here.
Question:
OFDM: Is an OFDM (Orthogonal Frequency Division Multiplexing) device considered a spread spectrum device?
Response:
Indoor and typical short-range RF communications in the unlicensed bands must allow for multi-path fading and the presence of other unlicensed radios (and interferers). The three main techniques for this requirement are: frequency hopping, direct sequence (spreading techniques), and orthogonal frequency-division multiplexing (OFDM). Although OFDM is similar to frequency hopping and direct sequence, it is not technically a spreading technique. Transmitters operating under FCC Part 15.247 have specific spreading requirements and the FCC recently allowed OFDM to operate in the 2.4 GHz band as a DTS modulation type.
Question: OFDM Devices Continued
FCC Subpart C, Part 15.247 only covers 5725-5850 MHz bands. Where does 5150-5350 MHz spread spectrum/OFDM devices fit?
Response:
OFDM signal is considered as a type of spread spectrum signal. However, for a unit that falls under the frequency band 5150-5350 MHz and 5725-5825 MHz, this unit would have to meet 15.407 subpart E.
Question: UNII Devices
The freq band 5150-5350 MHz and 5725-5825 MHz bands are also covered under the U-NII Subpart E, Part 15.401. Does this part cover spread spectrum devices?
Response:
OFDM modulation is considered as a part of 15.401 subpart E. This unit could be tested and approved in the Spread spectrum band, but there is some restriction for each band 5150-5250 MHz, 5250-5350 MHz, and 5725-5825 MHz, with respect to the authorized power output, and antenna radio connectivity. If both UNII and DTS approval are required, a composite application is necessary.
Question:
Integral Antennas
One of the requirements in this section is 15.401(d), wherein the transmitting antenna shall be an integral part of the device. Consider the following two cases:
• Case 1: (Separate LAN Module + Separate Antenna Module) both integrated inside a Laptop. Need to remove screws of laptop to see and get to the LAN & AE modules. Fixed in laptop by manufacturer, and not portable by user.
• Case 2: (Integrated LAN and AE module) inside a Laptop. Need to remove screws of laptop to see and get to the integrated LAN & AE module.
Are both these cases acceptable under this section 15.401(d)? Are there any special labeling requirements?
Response:
FCC Part 15.407(d) states precisely that the antenna should be an integral part of the unit to avoid the changing or modification of the antenna to avoid any interference. This area of the frequency spectrum is very sensitive as part of the band is used by satellite communication. However the FCC has stated that an antenna that attaches with a connector inside of the case is acceptable, provided that there is no need for the users (or OEM integrators in the case of modular approvals) to ever open the case. The antenna connector portion of the product may only be accessible to the original manufacturer.
Regarding the label aspect, it would depend on whether the unit would be integrated directly on the laptop and could be sold as a stand-alone. In the first configuration, there should be a clear statement that a radio is installed in the laptop. In the second configuration, the FCC ID should be listed on the unit itself.
New rules have been published affecting the measurements and compliance of Cellular equipment (WT Docket No. 01-108).
§22.917 Emission limitations for cellular equipment.
The rules in this section govern the spectral characteristics of emissions in the Cellular Radiotelephone Service.
(a) Out of band emissions. The power of any emission outside of the authorized operating frequency ranges must be attenuated below the transmitting power (P) by a factor of at least 43 + 10 log(P) dB.
(b) Measurement procedure. Compliance with these rules is based on the use of measurement instrumentation employing a resolution bandwidth of 100 kHz or greater. In the 1 MHz bands immediately outside and adjacent to the frequency block a resolution bandwidth of at least one percent of the emission bandwidth of the fundamental emission of the transmitter may be employed. A narrower resolution bandwidth is permitted in all cases to improve measurement accuracy provided the measured power is integrated over the fully required measurement bandwidth (i.e., 100 kHz or 1 percent of emission bandwidth, as specified). The emission bandwidth is defined as the width of the signal between two points, one below the carrier center frequency and one above the carrier center frequency, outside of which all emissions are attenuated at least 26 dB below the transmitter power.
(c) Alternative out of band emission limit. Licensees in this service may establish an alternative out of band emission limit to be used at specified band edge(s) in specified geographical areas, in lieu of that set forth in this section, pursuant to a private contractual arrangement of all affected licensees and applicants. In this event, each party to such contract shall maintain a copy of the contract in their station files and disclose it to prospective assignees or transferees and, upon request, to the FCC.
(d) Interference caused by out of band emissions. If any emission from a transmitter operating in this service results in interference to users of another radio service, the FCC may require a greater attenuation of that emission than specified in this section.
Amendment(s) published December 17, 2002, in 67 FR 77191
Effective date(s) February 18, 2003