Doc.: IEEE 802.11-08/0992r1 Submission September 2008 John R. Barr, Motorola Inc.Slide 1 20/40 MHz 11n Interference on Bluetooth Date: 2008-09-03 Authors:

doc.: IEEE 802.11-08/0992r1

Submission

September 2008

John R. Barr, Motorola Inc.Slide 1

20/40 MHz 11n Interference on BluetoothDate: 2008-09-03

Name Affiliations Address Phone email John R. Barr Motorola 1303 E. Algonquin Road,

Schaumburg, IL 60196 847-962-5407 [email protected]

Indranil Sen Motorola 600 N. US Hwy 45, Libertyville, IL 60048

847-523-1660 [email protected]

Jim VanBosch Motorola 600 N. US Hwy 45, Libertyville, IL 60048

847-523-2530 [email protected]

Authors:

doc.: IEEE 802.11-08/0992r1

Submission

September 2008


Abstract

Over the air measurements of interference experienced by shipping Bluetooth devices in the presence of 40 MHz 802.11n signals in 2.4 GHz spectrum. Measurements document that 40 MHz 802.11n signals from AP/STA seriously degrade performance of Bluetooth applications at distance of 4 ft, and degrades performance even as distance is increased to 12 ft.

40 MHz 802.11n signals (13% duty cycle) increase number of retransmissions sent by a factor of 15 (2% to 30%) and reduce the number of error free packets by a factor of two (94% to 55%) while running the same Bluetooth application.

doc.: IEEE 802.11-08/0992r1

Submission

September 2008


Test setup

• 802.11n 40 MHz signal is generated using Agilent N7617B. Modulation is 64-QAM, 2 spatial streams, 5/6 coding rate, guard interval is 800nsec. Different duty cycles (% - ON) are used to emulate different traffic patterns (25% - low, 50% - medium and 75% - high).

• Tests modified for 13% low at 40 MHz and 25% low for 20 MHz to compare equal traffic.• Motorola S9 is worn on the head by tester. Motorola Z8 was in the front pants pocket (display out and front

side up). Distance between Motorola S9 and Motorola Z8 is ~3ft. Tester is sitting while doing the tests. This orientation is used to emulate a typical link margin between phone and headset.

• Tests were performed for Bluetooth SCO, Bluetooth A2DP and Bluetooth sniff modes.• Frontline Bluetooth sniffer is used to collect the following packet statistics: CRC error in payload, Header

Errors, number of retransmissions and number of packets in no error.• The packet statistics are measured at different times after the 802.11n 40MHz interference has been turned

ON. This is to understand the effect of interference before and after AFH removes the affected channels.

Bluetooth link

Frontline Bluetooth

Sniffer

Laptop running Agilent N7617B Agilent WLAN

signal studio

Motorola S9

Motorola Z8

Agilent signal generator E4438C

d1

doc.: IEEE 802.11-08/0992r1

Submission

September 2008


Transmit Power Variations for Distance

• The transmit power is varied on the signal generator to emulate varying distances between signal generator and Bluetooth devices. The antenna used on the signal generator was a monopole antenna.

• The maximum transmit power from our signal generator is +17dBm. Including the antenna gain (~2.2dB) the output power will be ~19dBm. Our signal generator was ~2 ft from the headset and transmitting at power levels of +19dBm, +13dBm, +7dBm, +3.4dBm, +1dBm to represent separation distances of 2ft, 4ft, 8ft, 12ft and 16ft respectively.

• This correlates with typical free space path loss measurements.• Other power level values can be used for respective distances if required.

doc.: IEEE 802.11-08/0992r1

Submission

September 2008


Bluetooth SCO link 802.11n interference with AFH turned OFF for phone and

headset

• Difficult to quantify SCO performance in terms of packet error statistics (no CRC on payload as in eSCO packets)

• Thus, qualitative audio samples were taken. A call was placed to a 1 KHz test line. Audio samples were then recorded with AFH disabled for varying 802.11n parameters.

• Numerous crackles can be heard in the 1 KHz tone in the presence of 802.11n interference

1 KHz recording played with

802.11n 20 MHz (25% duty cycle)





doc.: IEEE 802.11-08/0992r1

Submission

September 2008


Bluetooth eSCO link 802.11n 40 MHz low duty cycle (13%): 4ft from headset

Packet statistics after interference

is present for 120s

Packet statistics with no

interference

Packet statistics after interference is present for 10s


• Minimal impact to eSCO due to 802.11n 40MHz (mid and high duty cycle) interference.

• Minimal clicks and pops heard in audio in presence of 802.11n 40MHz low duty cycle interference with these specific Bluetooth devices since AFH keeps releasing the “affected” channels due to low duty cycle of interference.

doc.: IEEE 802.11-08/0992r1

Submission

September 2008


Bluetooth eSCO link 802.11n 20 MHz low duty cycle (25%): 4ft from headset


is present for 120s


interference



• Minimal impact to eSCO due to 802.11n 20MHz (mid and high duty cycle) interference.

• Minimal clicks and pops heard in audio in presence of 802.11n 40MHz low duty cycle interference with these specific Bluetooth devices since AFH keeps releasing the “affected” channels due to low duty cycle of interference.

doc.: IEEE 802.11-08/0992r1

Submission

September 2008


Bluetooth A2DP link 802.11n 40 MHz low duty cycle (13%): 4ft from headset

• When the distance between 802.11n and Bluetooth devices is less than 12ft, irrespective of the duty cycle of the interference, there are numerous silence periods until the time AFH detects the bad channels. Even after AFH detects the interference, due to the high interference level in the remaining channels, we still have audible silence periods in the music.

• A significant amount of retransmissions, CRC errors in payload and header errors are observed.


is present for 120s


interference



doc.: IEEE 802.11-08/0992r1

Submission

September 2008



•As the duty cycle of the interference increases, there are more retransmissions.•Music quality is very poor due to audible pauses till the time interference is not detected. Interference detection time will vary depending on the AFH implementation.

•After 120s, this is the worst case scenario for A2DP with maximum retransmissions.


is present for 120s


interference



doc.: IEEE 802.11-08/0992r1

Submission

September 2008



• Minimal impact to Bluetooth A2DP performance since AFH detects the bad channels and removes them from the channel map


is present for 120s


interference



doc.: IEEE 802.11-08/0992r1

Submission

September 2008


Bluetooth link in sniff mode

• For tests conducted when the Bluetooth devices are in idle mode (in sniff), it was observed that at 2ft with high and medium 802.11n 40 MHz traffic, it is possible to drop the Bluetooth connection

doc.: IEEE 802.11-08/0992r1

Submission

September 2008


• Backup Slides

doc.: IEEE 802.11-08/0992r1

Submission

September 2008


Bluetooth SCO link with 802.11n 40 MHz signal

Interfering Source

Distance between

headset and interference

Test 1 Test 2 Test 1 Test 2 Test 1 Test 2No

interferenceNA - - - - [1, 0, 2, 97] [1, 0, 1, 98]

802.11n signal at low

traffic2ft [7, 0, 0, 93] [8, 3, 0, 89] [9, 1, 0, 90] [4, 1, 0, 95] [5, 0, 5, 90] [10, 4, 4, 82]


traffic4ft [5, 0, 0, 95] [2, 0, 0, 98] [6, 3, 0, 91] [2, 0, 0, 98] [13, 5, 3, 79] [19, 3, 1, 78]


traffic8ft [4, 0, 0, 96] [2, 0, 0, 98] [3, 0, 0, 97] 6, 0, 0, 94] [5, 13, 0, 82] [10, 0, 14, 76]

802.11n signal at medium traffic

2ft [6, 2, 0, 92] [7, 1, 0, 92] [3, 1, 0, 96] [8, 1, 0, 91] [6, 1, 7, 86] [8, 1, 1, 90]

802.11n signal at medium traffic

4ft [2, 0, 0, 98] [9, 0, 1, 90] [1, 0, 1, 98] [9,1, 0, 90] [5, 6, 0, 89] [11, 1, 1, 87]

802.11n signal at

high traffic2ft [6, 1, 0, 93] [6, 0, 1, 93] [4, 0, 0, 96] [3, 0, 0, 97] [2, 0, 5, 93] [4, 0, 5, 91]

% after 10s [CRC Error in Payload, Header,

Retransmission, No error]





doc.: IEEE 802.11-08/0992r1

Submission

September 2008


Bluetooth A2DP link with 802.11n 40 MHz signalInterfering

Source

Distance between

headset and interference

Test 1 Test 2 Test 1 Test 2 Test 1 Test 2No

interferenceNA - - - - [1,0,2, 97] [1,0,1,98]

802.11n signal at low traffic 2ft [18, 19, 61,

2][28, 16, 54, 3] [12, 10, 76, 2] [14, 9, 75, 2] [8, 5, 82, 4] [11, 7, 78, 3]

802.11n signal at low traffic 4ft

[10, 24, 46, 20]

[10, 24, 31, 35] [6, 16, 62, 16] [5, 10, 76, 10] [1,4,65,30] [4,6,81,9]


[19, 19, 20, 41]

[17, 17, 16, 50]

[13, 11, 44, 32] [11, 8, 25, 55] [6,2,48,43] [11,2,24,63]


[22, 13, 29, 36] [22,9,21,48]

[16, 12, 41, 31] [13, 5, 22, 60] [4, 9, 28, 59] [6,2,22, 70]

802.11n signal at medium

traffic2ft [9, 3, 73, 15] [14, 6, 70, 9] [8, 1,81, 10] [6, 1, 80, 13] [12, 1, 78,9] [9, 2, 80, 9]


traffic4ft

[23, 4, 27, 46] [9,2, 64, 25] [30, 5, 24, 42] [4, 1, 64, 31] [11,2, 24, 63] [2, 0, 55, 43]


traffic8ft

[17, 2, 16, 64] [27, 3, 30, 40] [19, 2, 26, 53] [12, 2, 44,42] [10, 1, 43, 46] [3, 0, 62, 34]


traffic12ft

[23, 4, 16, 57] [11,6,33,49] [15, 2, 29, 55] [19, 4, 25, 53] [10, 1, 18, 71]

[19, 2, 20, 59]


traffic16ft [14,2,16,68] [23, 4, 25, 47] [13,2,15,70] [14, 2, 33, 50] [8, 1, 14, 77] [6, 1, 30, 63]

802.11n signal at high traffic 2ft

[52, 4, 30, 14] [95, 5, 0, 0] [60, 4, 17,19] [96,4, 0] [46, 3, 17,34] [80, 3, 2, 15]


[14, 1, 61, 24] [9, 1, 54, 36] [14, 0, 66, 20] [8, 1, 56, 35] [6, 0, 62, 33] [6, 0, 47, 46]


[13, 3, 37, 47] [16, 2, 37, 45] [7, 2, 57, 35] [8, 1, 54, 36] [6, 1, 26, 68] [2, 0, 67, 31]


[15, 3, 24, 58] [19, 4, 20, 57] [8, 2, 24, 66] [16, 3, 29, 52] [5, 1, 21, 73] [6, 1, 27, 65]

802.11n signal at high traffic 16ft [7, 3, 9, 80] [20, 2, 14, 65] [6, 1, 9, 84] [16, 2, 18, 65] [3, 1, 10, 86] [6, 1, 10, 84]

% after 10s [Payload/CRC Error, Header,






doc.: IEEE 802.11-08/0992r1

Submission

September 2008


References

• https://mentor.ieee.org/802.11/file/08/11-08-0984-00-000n-bluetooth-test-cases-for-802-11n-40-mhz.ppt

Documents

Doc.: IEEE 802.11-08/0992r1 Submission September 2008 John R. Barr, Motorola Inc.Slide 1 20/40 MHz 11n Interference on Bluetooth Date: 2008-09-03 Authors: