Preliminary Coexistence Tests
• The same 802.11 wireless signal was used as the victim:– Power Level = 0 dBm– BW = 20 MHz– Center Frequency = 2.412 GHz– Orthogonal frequency-division multiplexing
(OFDM) Data Rate = 6 Mbps– BPSK
OFDM concept• Transmit data is spread over a number of
orthogonal subcarriers in the frequency domain
Comparing Impacts of Different Interference Modulation/Technologies
• Setup– Currently conductive – Eventually move to radiated
• Target protocol – WLAN• Interfering Modulation/Technologies – CW AM Signal– Bluetooth (BT)– LTE– WLAN
Peak Spectrum of 802.11 WLAN Test Signal
2.401 2.4034679492.4059358972.4084038462.4108717952.4133397442.4158076922.418275641 2.42074359-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Peak Power Spectrum of 802.11 WLAN Signal (0 dBm Power, 20 MHz BW)
WLAN
Frequency (GHz)
Mea
sure
d Po
wer
(dBm
)
Interfering signal spectrums (with 20 MHz WLAN at center frequency = 2.417 GHz)
2.404 2.40525 2.4065 2.40775 2.409 2.41025 2.4115 2.41275 2.414 2.41525-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
Peak Power Spectrums of CW AM, Bluetooth, LTE, WLAN (all at -10 dBm Power setting)
LTE (10 MHz)BluetoothAMWLAN (20M, 2.417G)
Frequency (GHz)
Mea
sure
d Po
wer
(dBm
)
Interfering Signal 1: CW AM Signal
• Parameters:– Center Frequency = 2.41 GHz (within, but off
center, of WLAN band)– AM Modulation: 1 kHz and 80% (as in IEC 61000-
4-3, Annex A) – Power level = -10 dBm
• WLAN does not fail• RMS EVM of approx. -23 dBm (by inspection)
as an instant average over all subcarriers
Interfering Signal 2: Bluetooth
• Parameters– Power Level = -10 dBm– Center Frequency = 2.41 GHz (same as Signal 1)– Max Payload length, Carrier Burst
• WLAN intermittently fails as a result of the BT signal• RMS EVM of WLAN is regularly about -50 dBm (by
inspection), with short periods of Higher EVM (at failure)– Consistently much lower EVM from signal 1
Interfering Signal 3: LTE
• Parameters– Power Level = -10 dBm– Center Frequency = 2.41 GHz– BW = 10 MHz
• With these Parameters the WLAN Receiver was never able to establish a link
Interfering Signal 3: LTE Cont.
• Highest 10 MHz LTE power that allowed the WLAN system to make a connection was -27 dBm– Consistent EVM of about -25 dBm (by inspection)– Large number of subcarriers are affected (see
following EVM plot) by this signal– This is due to the wider bandwidth of LTE
compared to Bluetooth or the CW AM signal
Interfering Signal 4: 802.11 WLAN
• The interfering WLAN is on the 802.11 band nearest the victim:– Power = -30 dBm– Center Frequency = 2.417 GHz– BW = 20 MHz
• -30 dBm interference power setting was the highest that allowed consistent victim connection
• Consistent average RMS EVM of about –29 dBm (from inspection)
Peak Spectrum Comparison of CW AM, Bluetooth , and LTE from Tests
2.404 2.40525 2.4065 2.40775 2.409 2.41025 2.4115 2.41275 2.414 2.41525-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
Peak Power Spectrums of CW AM, Bluetooth, LTE (all at -10 dBm Power setting)
LTE (10 MHz)BluetoothAM
Frequency (GHz)
Mea
sure
d Po
wer
(dBm
)