1. Anti-Jamming Approaches for 802.11g proposals: OFDM vs. PBCC
MAY 2001
Ephi Zehavi, CTO
Mobilian Corporation
E. Zehavi, Mobilian

2. Outline Summary of previous presentation Jamming Scenarios
May 2001
Outline
Summary of previous presentation
Jamming Scenarios
Analysis of AJ Techniques (no proposal changes)
Analysis of AJ Techniques (proposal changes)
BT throughput vs Jammer
Conclusions
E. Zehavi, Mobilian

3. Summary of the Previous Meeting
May 2001
Summary of the Previous Meeting
Discussed work and timeframe of and applicability to g
Stressed importance of considering coexistence issues (especially relative immunity against BT-type interference) during selection process
If we can make the standard inheritantly more immune… Good for the industry
Better performance when it is done on the PHY layer
The interference model and its parameters
The presentation preliminary quantified data and unified model to compare the two proposal and the feasibility AJ techniques and their initial performance
E. Zehavi, Mobilian

4. May 2001
Main Conclusions
OFDM has built in immunity capability against BT jammer
Localizing the jammer power
Capable to erase symbols/subcarriers
Using interleaver randomize the jammer impact
Very immune AJ scheme against strong interference (J/S>10 dB)
PBCC
Spreading the interfernce power over all the band
Uninterleaved system is susceptible to burst of symbol errors
Lack of capability to use erasure for overcome the jammer
Coding with no interleaver reduces dramatically the immunity against transit effects of jammers
Bluetooth jammers causes major degradation of PBCC performance
E. Zehavi, Mobilian

5. May 2001
Objectives
Previous presentations introduce preliminary quantified data and a model to compare the two proposals with AJ techniques and their initial performance. In the current presentation we shall address
The throughput of system with AJ techniques
The throughput BT system
Applicability of anti jamming technology
E. Zehavi, Mobilian

6. The Bluetooth interference
May 2001
The Bluetooth interference
GFSK modulation, 1 Msps
FH system 1600 hops/sec
For 8 PSK system it behaves like random tone jammer with random phase. The phase changes every 1 micro sec.
For OFDM system it behaves like Partial band jammer
The Power margin is about dB
The change in BT phase is very small during the observation time of 1/11 microsec
No collaborate BT interference
E. Zehavi, Mobilian

7. Operating Scenario for Bluetooth-Non Collocated BT
May 2001
Operating Scenario for Bluetooth-Non Collocated BT
E. Zehavi, Mobilian

8. Throughput vs. location of WLAN AP
May 2001
Throughput vs. location of WLAN AP
E. Zehavi, Mobilian

9. The Effect of 802.11 G TX Power on BT Throughput
May 2001
The Effect of G TX Power on BT Throughput
Assumptions:
BT Independent Pico net at distance 3 m.
BT power is fixed 0 dBm
No add on techniques to increase BT throughput
Distance between BT is 1 m.
802.11G is working with different average power level
E. Zehavi, Mobilian

10. Mac Level Simulation Results
May 2001
Mac Level Simulation Results
E. Zehavi, Mobilian

11. Conclusion of the Impact
May 2001
Conclusion of the Impact
Small fluctuation of 3 dB of power have minor impact on the transition region
The peak to average of OFDM reduces due to the narrow band filtering of the BT receiver (1 micro sec.)
E. Zehavi, Mobilian

12. Analysis of AJ Techniques (no proposal changes)
May 2001
Analysis of AJ Techniques (no proposal changes)
AJ Technique
COFDM
PBCC/CCK
Erasure
Up to 10 sub carriers
Can not use erasure
Adaptive
Filtering
Slow converge time
Small impact of error propagation
Impact of error propagation-no interleaver
Non Linear Jammer Suppression
Built-in mechanism
Not applicable for medium values of J/S
Combine w/ erasures for high values of J/S
Add-on complexity
Residual energy spread uniformly over the band
Outer Code
(optional e)
Allow to overcome transit impact and burst of errors
E. Zehavi, Mobilian

13. Analysis of AJ Techniques (proposal changes)
May 2001
Analysis of AJ Techniques (proposal changes)
AJ Technique
COFDM
PBCC/CCK
Coding scheme
No Change
Use pragmatic trellis code with bit interleaver
Interleaver
Increasing the interleaver size, randomize the effect of the jammer
Add an interleaver
Break the error propagation
Receiver sent NACK based on MAC header
Avoid Backoff when the transmitter knows that packet was failed due to jamming
E. Zehavi, Mobilian

14. COFDM vs. PBCC Crteria COFDM PBCC Peak to Average 4-6 dB more power
May 2001
COFDM vs. PBCC
Crteria
COFDM
PBCC
Peak to Average
4-6 dB more power
Coding technique
Very close to the optimal VD
Can be 2 dB better than COFDM but get almost the same result due to the use of M algorithm
AJ capability
Built-in mechanism
Work with strong jammer
Better throughput
Can not work with strong jammer
Multipath
Built-in Equalization mechanism
Too complex
Complexity
Shall be larger when using a VD instead of M_algorithm type decoder
E. Zehavi, Mobilian

15. OFDM Peak to average fluctuation has minor impact on BT throughput
May 2001
Summary
OFDM provide a more immune system against non collaborated strong jammer
OFDM Peak to average fluctuation has minor impact on BT throughput
Some changes in the G proposal shall improve the immunity of G standard
E. Zehavi, Mobilian