1. Comparison of IEEE 802.11g Proposals: PBCC, OFDM & MBCK
Sean Coffey, Ph.D., Anuj Batra, Ph.D., Srikanth Gummadi, Matthew Shoemake, Ph.D., Ron Provencio and Chris Heegard, Ph.D.
Home and Wireless Networking
Texas Instruments
141 Stony Circle, Suite 130
Santa Rosa California
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Sean Coffey, Texas Instruments

2. Outline Overview of comparison with CCK-OFDM Comparison with MBCK
Details of PBCC vs. CCK-OFDM
Conclusion
Sean Coffey, Texas Instruments

3. Comparison with CCK-OFDM
Sean Coffey, Texas Instruments

4. The fundamental PBCC performance edge
The PBCC solution uses a more sophisticated code
Advantage of PBCC solution of 3.75 dB over CCK-OFDM solution in received power (22Mbps versus 26.4Mbps)
The CCK-OFDM solution requires approximately 130% more received power in the same environment.
3.35 dB, 22Mbps vs 24Mbps (115% more )
2.95 dB over CCK-OFDM solution in received pwr per bit
100% more received power for the same performance after normalizing for rate differences.
This doubles area coverage, battery-life, cell density or combination.
Sean Coffey, Texas Instruments

5. PBCC solution in multipath
The PBCC performance advantage carries over to all channel conditions
slightly greater in multipath
PBCC uses an optimized "cover code" that makes the code effectively time-varying and inherently more resistant to multipath
This is the "P" in "PBCC"
Sean Coffey, Texas Instruments

6. Achievable rates/throughput
Top mandatory rates:
22 Mbps for PBCC
26.4 Mbps for CCK-OFDM
Top optional rates:
33 Mbps for PBCC
59.4 Mbps for CCK-OFDM
10% higher than for a
Sean Coffey, Texas Instruments

7. Achievable throughput (cont)
Substantial extra overhead in CCK-OFDM reduces throughput: for MPEG packets (188 byte)
PBCC 22 has higher throughput than CCK-OFDM 26.4
PBCC 33 has higher throughput than CCK-OFDM 52.8
PBCC 33 Mbps has a 2 dB signal-to-noise ratio advantage over CCK-OFDM 26.4 Mbps
Sean Coffey, Texas Instruments

8. Time to market / solution feasibility
TI has produced a chip implementing all mandatory parts of its proposal.
PBCC proposed mandatory mode will work with existing b radios.
The CCK-OFDM proposal requires design of a new radio
Long delay in market availability of IEEE g products.
Sean Coffey, Texas Instruments

9. Overall approach The fundamentals of the respective approaches:
there is no fundamental performance difference between single-tone and multi-tone systems.
TI is developing a-compliant hardware.
Both single-tone and multi-tone make sense; it does not make sense to do both!
as is required for backward compatibility in CCK-OFDM proposal.
Sean Coffey, Texas Instruments

10. IP issues
TI has offered a royalty-free license for all its inventions required to implement the mandatory portions of the standard if its solution is adopted as the standard
There are serious third-party IP issues with CCK-OFDM proposal
Sean Coffey, Texas Instruments

11. Comparison to MBCK
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12. Performance advantage
Based on MBCK submission
In Gaussian noise, Eb/N0:
MBCK 22 Mbps: 8.0 dB, vs. PBCC: 5.5 dB
PBCC advantage 2.5 dB
Variable, 100 ns, MBCK dB, vs. PBCC dB
PBCC advantage 4.0 dB
Fixed, 25 ns: 7.2 dB vs PBCC 8.1 dB
difference –0.9 dB
Fixed, 100 ns: 16.2 dB vs PBCC 8.75 dB
difference 7.45 dB
Fixed, 250 ns: 17.5 dB vs. PBCC 9.75 dB
difference 7.75 dB
Sean Coffey, Texas Instruments

13. Discussion
Essential components of MBCK proposal not currently revealed
MBCK proposal beats CCK-OFDM in AWGN but is still well short of PBCC’s solution
From MBCK submission, PBCC’s solution has advantage in most channel conditions
Sean Coffey, Texas Instruments

14. Details
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15. Performance advantage
PBCC-22 uses a novel 256-state, rate 2/3 binary convolutional code matched to 8-PSK
CCK-OFDM adopts a standard 64-state, rate 1/2 convolutional code
widely known to all coding practitioners since 1972
existing PBCC 11 Mbps option in b standard is a variation of this type of code
A major component of overall 2.95 dB advantage comes from differences between the codes
Sean Coffey, Texas Instruments

16. Performance curve
/24
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17. Performance curve (cont)
/24
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18. Performance curve (cont)
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19. Performance curve (cont)
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20. Performance gain (cont)
CCK-OFDM solution spends 20% of transmission time on cyclic extension of every OFDM symbol
non-information-carrying, performance cost
CCK-OFDM solution has 4 pilot tones out of 52 tones overall
spends 1/13 of energy on non-information-carrying signal
Bottom line: PBCC advantage of 1.6 (coding) (cyclic extension) (pilot tones) = 2.95 dB
Sean Coffey, Texas Instruments

21. Performance gain (cont)
Required Eb/N0, experimental:
Assume 1000 byte packets, PER = 0.01:
CCK-OFDM Eb/N0 = 8.4 dB (document 00/392r1)
PBCC Eb/N0 = 5.5 dB
Documented difference: 2.9 dB
Sean Coffey, Texas Instruments

22. Performance difference
CCK-OFDM 26.4 Mbps vs. PBCC 22 Mbps
Difference in received power must be 3.75 dB
PBCC’s 22 Mbps has 130% more coverage, or battery life, or cell density than CCK-OFDM 26.4 Mbps
(3.35dB, 115% 24 Mbps)
CCK-OFDM 26.4 Mbps vs. PBCC’s 33 Mbps
Difference in received power must be 2.0 dB
CCK-OFDM requires more!
( Mbps)
PBCC’s 33 Mbps mode has 60% more coverage, or battery life, or cell density, than CCK-OFDM 26.4 Mbps
(45% 24 Mbps)
Sean Coffey, Texas Instruments

23. Multipath performance:
Variable, 100 ns
PBCC 22 Mbps Eb/N0 = dB
CCK-OFDM 26.4 Mbps Eb/N0 = 15 dB
Difference 3.25 dB
Fixed, 25 ns
8.1 dB vs. 11 dB, difference 2.9 dB
Fixed, 100 ns
8.75 dB vs. 12 dB, difference 3.25 dB
Fixed, 250 ns
9.75 dB vs dB, difference 3.55 dB
Sean Coffey, Texas Instruments

24. Achievable rates/throughputs
CCK-OFDM requires
extra OFDM preamble: 10.9 msec
extra SIFS time postamble: 6 msec
extra end-symbol pad time: up to 3.64 msec
Average extra overhead is 18.7 msec per packet
in addition to 96 msec 11b short preamble
Sean Coffey, Texas Instruments

25. Breakeven points
Below certain packet lengths, PBCC has higher throughput:
PBCC 22 vs. CCK-OFDM 26.4, no acks: bytes
PBCC 33 vs. CCK-OFDM 39.6, no acks: bytes
PBCC 33 vs. CCK-OFDM 52.8, no acks: bytes
PBCC 33 vs CCK-OFDM 59.4, no acks: bytes
Compare MPEG packet length of 188 bytes!
Sean Coffey, Texas Instruments

26. Breakeven points, contd.
PBCC 22 vs. CCK-OFDM 26.4, with acks: 466 bytes
PBCC 22 vs. CCK-OFDM 39.6, with acks: 176 bytes
PBCC 33 vs. CCK-OFDM 39.6, with acks: bytes
PBCC 33 vs. CCK-OFDM 52.8, with acks: bytes
PBCC 33 vs CCK-OFDM 59.4, with acks: bytes
Sean Coffey, Texas Instruments

27. Complexity requirements: Decoder
PBCC
decode a 256-state (1024-edge) BCC with an 11/16.5 MHz clock
CCK-OFDM
decode a 64-state (128-edge) BCC with a 60 MHz clock
if top optional mode implemented
Similar complexity and cost
TI’s PBCC 22 Mbps decoder has been implemented
its practicality is proven
Sean Coffey, Texas Instruments

28. Complexity requirements: Receiver
PBCC
a sophisticated single-tone receiver to handle multipath robustly
Same receiver as all IEEE b modes
CCK-OFDM
a large FFT based processor at both the transmitter and receiver
Similar complexity with TI’s single tone receiver
Plus, a single-tone receiver for backward compatibility
Undue extra cost, for what benefit?
TI’s 22 Mbps receiver has been implemented
its practicality is proven.
Sean Coffey, Texas Instruments

29. Required radio PBCC uses 8-PSK, with 802.11b’s 11 MHz clock
no problems of dynamic range or peak-to-average ratio.
CCK-OFDM proposal involves 16- and 64-QAM
much larger peak-to-average ratio
Poses problems with linearity and dynamic range...
… and is dramatically different as an interferer
CCK-OFDM proposal requires a new radio and baseband
a long delay in the debut of standardized products
recall HomeRF 10 Mbps products expected in 2001
Sean Coffey, Texas Instruments

30. Temporal Character: Peak to Average Power
Barker-2
PAR:
2.1 = 3.2 dB
CCK-11
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31. PAR (cont) PBCC-24: OFDM-26.4: PAR: 2.1 = 3.2 dB 11.5 = 10.6 dB
Sean Coffey, Texas Instruments

32. Overall approach
Both single-tone and multi-tone systems achieve “capacity” on the channels seen by wireless LANs.
“Which is better: many bits on one tone or few on many?”
Well studied in information theory, answer is well known: highest achievable performance in each system is exactly the same
This is neither obvious nor easy to show, but has been known since at least the 1960's.
Sean Coffey, Texas Instruments

33. IP issues
Wi-LAN and others claim broad patents covering use of OFDM in wireless LANs
Are attempting to enforce these patents via litigation
Are not participants in IEEE g
TI has offered a royalty-free license, without time limit, for all its inventions required to implement the mandatory portions of the standard, if its solution is adopted as the standard
Sean Coffey, Texas Instruments

34. Wi-LAN's Zaghloul:
"Wi-LAN is ready for the worst," he says, "and antcipates the best. We anticipate [Cisco] will pay without much of a fight, but if they don't, we're prepared to go all the way [in a legal fight to secure license payments.]”
Sean Coffey, Texas Instruments

35. Sean Coffey, Texas Instruments

36. Conclusions PBCC proposed mandatory 22 Mbps mode
Has large performance advantage (3.75 dB over 26.4 Mbps)
Works in same environment as IEEE b
Put PBCC-22 Mbps next to 11 Mbps CCK: if the CCK mode works, the PBCC-22 mode also works
Has been implemented, is ready for market now
Spectrally and temporally identical to existing b
Works with existing b radios
No new interference type
Royalty-free license offered
PBCC proposed optional 33 Mbps mode requires 2dB less SNR than the mandatory 26.4 Mbps OFDM
Sean Coffey, Texas Instruments