Doc.: IEEE 802.11-04/0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 1...

January 2004

Steve Brunson & Bob Soranno (JHU/APL)Slide 1

doc.: IEEE 802.11-04/0143r0

Submission

Improved Adjacent Channel Rejection Parameters to solve the

Near-Far Interference Problem

Steve Brunson & Bob SorannoThe Johns Hopkins University –

Applied Physics Lab

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Scenario of Interest

• Victim – A vehicle is parked in a gas station located on the corner of a major street. A large transaction is being performed on a short range link to an antenna under the canopy (~6m). (“Minimum” link power assumed)

• Interference – The roadway is 15 meters from the parked vehicle. Vehicles on the road may be conducting Traffic Probe transactions at 20 dBm and Vehicle-Vehicle transactions at 33 dBm in other channels.

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

The Near/Far Problem• Near – Loud transmitter on a different channel

(interference)• “Far” – Distant or weak transmitter in tuned channel

(desired signal)

• Interferer “Keep Out” Range Desired– 15 m• Interference Power

– Most transmitters will be 33 dBm or less

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Mitigation Approaches

• Antenna Patterns –some help, but unfavorable geometries cannot be avoided

• Added IF filtering (SAW) – can be effective (40 dB beyond adjacent channel), but will increase cost (~$10?). Could be required for interference outside the DSRC band.

• Increased baseband filtering – effective, basis for Type 2 receiver

• Increased desired signal level – effective for short, low power links (-21 to -4 dBm required for 6 meter link with 0/0 dBi antennas)

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Measure of Effectiveness• Interferer “Keep-Out” Range – How close can you let an

out-of-channel interferer get before you start losing packets?

• Inputs:

– Level of Desired Signal (relative to MDS)

– Level of Interference Rejection

– Interference Power Transmitted

– Antenna Patterns (0 dBi omni’s assumed)

– Propagation (free space assumed)

• Interference independent of own xmt pwr.

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Limiting Conditions

• Adjacent or Alternate Adjacent Channel Interference – leakage from strong signals in nearby channels

• Front End Saturation – nonlinear effects caused by strong signals in any other channel or out-of-band signals

• In general, Adjacent Channel problems seem more severe than Front End Saturation

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Keep-Out Range Plots• Keep-Out Range vs Received Power• Received Power from MDS to MDS + 20 dB

– One line for each data rate with applicable MDS and ACI-rejection (per Atheros)

– Blue Lines: Interference Power = 20 dBm– Green Lines: Interference Power = 33 dBm– Both antennas 0 dBi– 15 meter line in RED

• Faster Modes Lower because of poorer MDS– [mds: -85 -84 -82 -80 -77 -70 -69 -67 dBm]

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Keep-Out Range: Type 2, Adj Chnl

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Keep-Out Range: Type 1, Adj Chnl

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Keep-Out Range: Type 1, Alt Adj Chnl

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Conclusions• Type 1 receivers will experience losses with 20 & 33 dBm

adjacent channel interferers, BUT early deployment densities will be low.

• Type 2 receivers will be OK except for high power interferers (40 & 44.8 dBm), but these should be low density and/or transitory.

• Antenna Patterns will help the situation in most cases, especially high EIRP transmitters (these have narrow regions of max EIRP).

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Back-up Slides

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Keep-Out Range: Type 2, Alt Adj Chnl

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Front End Saturation

• Saturation analysis based on information provided by Atheros

• Saturation can be caused by signals outside the DSRC band

• If out of band signals are a problem, a SAW filter in the IF may be required

January 2004


doc.: IEEE 802.11-04/0143r0

Submission

Saturation vs. ACI

Max Gain

Max Gain – 10 dB

Doc.: IEEE 802.11-04/0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 1...

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