doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 1 Improved Adjacent Channel Rejection Parameters to solve the Near-Far Interference Problem Steve Brunson & Bob Soranno The Johns Hopkins University – Applied Physics Lab

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 2 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.

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 3 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

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 4 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)

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 5 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.

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 6 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

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 7 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: dBm]

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 8 Keep-Out Range: Type 2, Adj Chnl

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 9 Keep-Out Range: Type 1, Adj Chnl

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 10 Keep-Out Range: Type 1, Alt Adj Chnl

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 11 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).

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 12 Back-up Slides

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 13 Keep-Out Range: Type 2, Alt Adj Chnl

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 14 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

doc.: IEEE /0143r0 Submission January 2004 Steve Brunson & Bob Soranno (JHU/APL)Slide 15 Saturation vs. ACI Max Gain Max Gain – 10 dB