1. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 1 Pros and Cons of RF sensing in TV bands (Comments on the FCC R&O 08-260) IEEE P802.22 Wireless RANs Date: 2009-01-18 Authors: Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chairhttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf Carl R. StevensonCarl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee.org.patcom@iee.org >

2. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 2 DTV Sensing DTV sensing was studied by 802.22 as a means of detecting the presence of DTV incumbents in the TV bands In order to make sensing sufficiently reliable in detecting incumbent DTV operation, the sensing threshold has been set to a very low value (-114 dBm, 19 dB below typical thermal noise level) rendering sensing unreliable for the unlicensed systems because DTV signals will be detected when not necessary: DTV signals will be detected beyond the protected contours where DTV receivers are not protected DTV signals will be detected from very distant DTV transmitters because of the statistical nature of the propagation channel Sensing may no longer be necessary since access to an incumbent database is mandatory for protecting DTV: –TV reception is to be protected inside the DTV contours whether TV signals are detected or not (R&O, para.81) –TV reception is not to be protected outside the DTV protected contours whether DTV signals are detected or not (R&O, para.166)

3. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 3 Co-channel sensing of DTV incumbent DTV TX 118 km DTV protected noise-limited contour 41 dB(uV/m) F(50, 90) Required DTV sensing threshold= -114 dBm to compensate for blockage Sensing CPE Sensing threshold= 22 dB below protected field strength level Sensing threshold: S/N = -19 dB at sensing detector Probability of signal exceeding 19 dB(uV/m) = 99.9953% F(50,1) 437 km F(50,10) 361 km F(10,10) 435 km F(10,1) 520 km F(1,1) 589 km

4. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 4 DTV Sensing (cont’d) Cases when DTV sensing would still be useful even though the database has precedence: 1.when the TVBD operator wants to use the sensing results to correct the database as suggested in the R&O. Such database corrections raise concerns about: –Security: –who would be allowed to modify the incumbent database? –Who would be allowed to remove a ‘pseudo-incumbent’ if it is not detected in the field? –Who would be allowed to add a new 'incumbent' to the database after detection? –Who would establish that this is a valid entry? –Authentication: who can make modifications to the database? –If this is the prime reason for implementing DTV sensing in every license-exempt devices, it is a rather expensive proposition for keeping the database up-to-date. 2.when the TVBD operator decides to yield to DTV reception in areas outside the protected contour of the DTV station where sufficient DTV signal is received. The TVBD could select another channel to operate if available. Implementation of such ‘friendly’ behavior does not need such a low sensing threshold, i.e.,-114 dBm which is equivalent to 22 dB below the protected field strength level. 3.when the TVBD operator wants to identify if a high ambient DTV RF field strength is present. This can be obtained from lower BER performance on the transmission link resulting from apparent higher noise level. Reduction in WRAN coverage distance would result but operation would still be possible.

5. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 5 Potential denial of service from sensing Sensing of DTV –An unlicensed device using an ATSC DTV-like signal would have a de- facto precedence over other unlicensed devices because it would be seen as an incumbent. The database would allow avoiding such potential denial of service for devices that can access it. Sensing results would be discarded. Sensing-only devices would however not have such capability Sensing of wireless microphones –Unlicensed devices using a signal format similar to that of wireless microphones would have a de-facto precedence over other unlicensed devices because they would be seen as incumbents Analog FM microphone Idle FM microphone (producing a Constant Wave) Digitally modulated microphone

6. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 6 Potential denial of services from sensing (cont’d) Sensing of wireless microphones (cont’d) –Any device using a signal format similar to a wireless microphone would have a de-facto precedence on other unlicensed devices because they would be seen as incumbents –The FCC seems to have decided to recognize any wireless microphone operations, be they Part 74 (i.e., operated by broadcasters and for special events), as well as any other wireless microphones on the market. The latter ones will be de-facto unlicensed devices but it will be hard for the sensing to make a difference between one of these microphones in idle mode and a simple oscillator. This will likely open the door to very low cost devices producing denial of service for any other unlicensed devices (e.g., low-cost oscillators available on eBay) It is unclear how the regulators will be able to limit access to such devices since they would work under the same conditions as de-facto unlicensed wireless microphones and could carry or not data without the requirement for sensing and access to the database These devices will only need to emit very low signal levels to upset the operation of other unlicensed devices: -25 dBm EIRP at 1 km line-of-sight

7. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 7 Potential denial of services from sensing (cont’d) Sensing in presence of other unlicensed devices –The level of out-of-band emission allowed by Part 15.209a is 200 uV/m in 120 kHz bandwidth at 3 m –This corresponds to 46 dB(uV/m) in 120 kHz and 63 dB(uV/m) in 6 MHz –The sensing threshold of -114 dBm corresponds to a field strength of 19 dB(uV/m) for the reference 0 dBi antenna gain and 0 dB coupling loss –Sensing will be impacted by the out-of-band emission level allowed from these other unlicensed devices at 10 m in free-space, the RF emission level is 33.5 dB higher that the specified sensing threshold If noise-like, the RF sensor will suffer desensitization by 14.8 dB, and 107 m separation distance will be needed for 1 dB desensitization of the sensor If the out-of-band emission is not noise-like, all bets are out …! –All unlicensed devices on all frequencies will need to use synchronized quiet periods in their transmission to allow reliable sensing of incumbents 1)To avoid that other unlicensed devices hide the presence of incumbents in the channel being sensed (see next slide) 2)To avoid other unlicensed devices operating on other TV channels generating sensing false detections from their out-of-band emission if they are located relatively close to the sensor.

8. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 8 Potential denial of services from sensing (cont’d) Sensing in presence of other unlicensed devices (cont’d) –In the work of 802.22, it has been assumed that all WRAN devices in a channel and its adjacent channels will need to have their quiet periods synchronized in order to avoid that a WRAN operation hides the presence of a broadcast incumbent operation to another WRAN cell –In the work of 802.22, it has also been assumed that the WRAN devices would have to move out of the channel if RF power was detected by the energy detector whether this RF signal can be classified or not (i.e., recognized as a known signal by the detection algorithm or not) This was to cover for the case where an unknown signal would hide the presence of a broadcast incumbent signal In particular, this will cover for the case where an unlicensed device, having a short sensing and interfering range (i.e., close to the ground), is located close to another unlicensed device that has a larger sensing and interference range (higher power or antenna height). The presence of the first device would occult the eventual existence of incumbents to the second device because of the desensitization of its sensing RF path.

9. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 9 Impact of not doing DTV Sensing The sensing RF chain will be simpler –Antenna: The sensing antenna for wireless microphones will be much simpler, e.g., a vertical monopole giving a good omnidirectional pattern with a reasonable gain (0-2 dBi) in the horizontal plane for vertical polarization No need for a complex horizontally polarized sensing antenna: good omnidirectional pattern is more difficult to achieve with horizontal polarization (needs something like crossed-drooping dipoles) Current Functional Requirement Document asks for an omnidirectional antenna with 0 dBi gain in all polarizations: never been verified for feasibility –Low-noise amplifier, frequency converter, filter Bandwidth of the RF chain does not need to be 6 MHz (or wider to capture N and N+/-1 in a single sensing). It could be narrowband if the practice of starting to populate a TV channel with a specific microphone sub-channel was established or even better if a wireless microphone beacon was to be used Using a narrowband filter would reduce the noise level and improve the SNR Simpler narrowband amplifier, converter and filter could be used.

10. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 10 Impact of not doing DTV Sensing (cont’d) The sensing RF chain will be simpler (cont’d) –Sensing detector: Simpler narrowband microphone (or TG1 beacon) detector could be used Complex sensing schemes for DTV would be avoided Detector would be optimized to only detect wireless microphones (or TG1 beacon) The MAC messages to request sensing and report on the detected signals would be simpler –MAC messages in both directions would be limited to wireless microphone (or TG1 beacon) sensing only The CPE spectrum automaton would be simpler The BS spectrum manager would be simpler –Requesting information from the database on existence of DTV stations and registered wireless microphone operation –Managing the sensing reports for wireless microphones (or TG1 beacon)

11. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 11 Conclusions DTV sensing at the proposed low signal threshold (-114 dBm) is unreliable, prone to denial of service and unnecessary since DTV protection will be first ensured through database access Wireless microphone sensing at the low signal threshold (-114 dBm) is unreliable and prone to very easy denial of service. IEEE 802.22.1 has developed a standard for a signal beacon to indicate the presence of wireless microphone operation –This beacon is to emit a digitally encoded signal at 250 mW that will carry all the necessary information for identifying wireless microphone operation including its location and encrypted signature for certification –This beacon can be sensed in a known 200 kHz BW to improve sensitivity –The beacon can be placed at a more prominent place than the wireless microphone receivers to maximize the ‘bubble of protection” –Technical parameters of the beacon were developed to provide protection from unlicensed devices up to 4 W EIRP at any antenna height (sensing range of the unlicensed device is larger than its interference range).

12. doc.: IEEE 802.22-08/0338r2 Submission January 2009 Gerald Chouinard, CRCSlide 12 References IEEE P802.22.1, Draft IEEE Standard for Local and metropolitan area networks, Part 22.1: Methods to Enhance Protection of Low-Power, Licensed Device Operation in the TV Broadcast Bands from Harmful Interference from License-Exempt Devices Operating in those Bands, 05/05/2008