1. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 1 Robust Bluetooth Detection using 802.11n Energy Detector Notice: This document has been prepared to assist IEEE 802.19. 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 802.19. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures, 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 TAG 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 Chair 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 802.19 TAG. If you have questions, contact the IEEE Patent Committee Administrator at.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfpatcom@ieee.org Date: 2008-11-11 Authors:

2. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 2 Abstract The presentation illustrates a Robust Bluetooth (IEEE 802.15.1) detector using the 802.11n Energy Detector The goal is to detect strong Bluetooth signals which represent a very close Bluetooth Piconet The goal is to use the standard energy detector circuit so that no hardware modifications are necessary

3. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 3 Background Several tests have been performed which show that under certain conditions that a 40 MHz 802.11n stations can cause perceivable impact on a nearby Bluetooth Piconet [1-4] The worst case condition consists of the following conditions –Bluetooth is not using Adaptive Frequency Hopping (Legacy) –The distance between the 802.11n STA and the Bluetooth Picont is one to two meters –802.11n is operating in 40 MHz mode It has be suggested that under certain circumstances, that 802.11n should switch back to 20 MHz mode There is a suggestion to detect the presence of a very close Bluetooth Piconet and switch to 20 MHz [5]

4. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 4 Goals Focus on the worst case condition –Bluetooth without AHF –Small distance between WLAN STA and Bluetooth Piconet Utilize the standard energy detection circuit Develop a robust detector Demonstrate feasibility of a possible method of robust detection using the standard ED circuit

5. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 5 Bluetooth Detector 1.Make a sequence to energy detection measurements while the current WLAN is quiet 2.Measurements converted to power estimates by scaling by the ED measurement time (P 1, P 2, …P n ) 3.Convert the sequence of ED measurements into a test statistic. The simplest method is to take the maximum T = max(P i ) 4.Compare test statistic to a threshold T > γ then BT is detected

6. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 6 Quiet Times There are several methods of ensuring that the WLAN network is quiet during ED measurements –Quiet the network using protection mechanisms (e.g. RTS/CTS) –Make ED measurements during times when the network is known to be quiet. One example, more than RIFS after the completion of a packet and less than SIFS after the completion of a packet

7. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 7 Simulation Take ED measurements every 100 us ED measurements are 4 us long T = max(P i ) Simulated 40 MHz and 20 MHz 802.11n receivers –Simple FIR band-pass filter 10 dB noise figure on WLAN receiver Bluetooth hop time = 625 us Bluetooth TX time = 366 us Bluetooth duty cycle = 100%, 66% and 33% Bluetooth AFH off

8. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 8 Simulation A single WLAN STA Two nodes in a Bluetooth Piconet Power level from each Bluetooth node when measured at the WLAN station –-35 dBm –-50 dBm Threshold used in detector –Threshold: γ = -40dBm AWGN Channel Recorded P D versus time

9. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 9 Sample ED Histogram

10. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 10 Sample ED Histogram

11. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 11 Probability of Detection versus Time (40 MHz Receiver, AWGN Channel)

12. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 12 Probability of Detection versus Time (20 MHz Receiver, AWGN Channel)

13. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 13 Multipath Channel Added Multipath Channel between Bluetooth Piconet and WLAN receiver Exponential delay spread model Delay spread = 100 us Since Bluetooth is a narrowband signal sometime it will hop into a faded part of the channel frequency response

14. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 14 Probability of Detection versus Time (40 MHz Receiver, Multipath Channel)

15. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 15 Probability of Detection versus Time (20 MHz Receiver, Multipath Channel)

16. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 16 Observations The 40 MHz receiver reaches reliable detection (99%) in approximately half the time of the 20 MHz receiver. This is intuitive since the probability of hopping into the receiver pass band is approximately double The higher the Bluetooth duty cycle the faster we reach reliable detection. Multipath increases the time until we reach reliable detection. This is intuitive since there are time when the channel fades at the Bluetooth frequency With the 40 MHz receiver one reaches reliable detection within 50 ms in a multipath channel with a 33% Bluetooth duty cycle

17. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 17 Next Steps See if 802.11 WG is comfortable with an approach like this. Make sure it can be implemented with only software changes Consider other 802 wireless systems (802.15.4) Determine if this type of method makes it possible to modify the draft so that automatic switching from 40 MHz mode to 20 MHz mode, based on detection of a very strong Bluetooth signal

18. doc.: IEEE 802.19-08/0035r1 Submission November 2008 Steve Shellhammer, QualcommSlide 18 References 1.John R. Barr, Indranil Sen, and Jim VanBosch, 20/40 MHz 11n Interference on Bluetooth, IEEE 802.11-08/992r1, September 2008 2.Mhammad Mansour, York Liu, Eldad Perahia, Measurements of Coexistence between 802.11n 40MHz and Bluetooth SCO, IEEE 802.11-08/1132r0, September 2008 3.Harish Ramamurthy, Raja Banerjea, Ed Reuss, Eldad Perahia, 11n 40 MHz and BT coexistence test results, IEEE 802.11- 08/1140r0, September 2008 4.Ariton Xhafa, Srinath Hosur, Jin-Meng Ho, IEEE 802.11n 40 MHz Impact on BT Performance, IEEE 802.19-27r2, July 2008 5.John R. Barr, Additional 40 MHz Scanning Proposal, IEEE 802.11-08/1101r4, October 2008