1. Questions Concerning the PBCC-22 Proposal for High Rate 802.11b
March 2001
doc.: IEEE /162
March 2001
Questions Concerning the PBCC-22 Proposal for High Rate b
Christopher Hansen
Broadcom
Christopher Hansen, Broadcom
Christopher Hansen, Broadcom

2. Outline Introduction What does the cover code do?
March 2001
doc.: IEEE /162
March 2001
Outline
Introduction
What does the cover code do?
Simulation of the 22 Mbps system with and without the cover code
Is the PBCC-22 code the best choice?
Compare with published codes
Conclusions
Christopher Hansen, Broadcom
Christopher Hansen, Broadcom

3. What does the cover code do?
March 2001
What does the cover code do?
Simulated System
Random
Bits
256 State
Encoder and
Mapper 2
Channel
Model
Fractionally
Spaced Equalizer
Cover Code
AWGN
Measure Bit Errors
Viterbi Decoder
Remove Cover
Code
Christopher Hansen, Broadcom

4. What does the cover code do?
March 2001
What does the cover code do?
Christopher Hansen, Broadcom

5. What does the cover code do?
March 2001
What does the cover code do?
Christopher Hansen, Broadcom

6. What does the cover code do?
March 2001
What does the cover code do?
Christopher Hansen, Broadcom

7. Is the PBCC-22 Code the best choice?
March 2001
Is the PBCC-22 Code the best choice?
PBCC-22 Code
256 State, Rate 2/3, 8-PSK constellation
Dfree^2/Es = 8.6 dB
Ungerboeck Code
IEEE Communications Magazine, Feb. 1987
Dfree^2/Es = 8.75 dB
Christopher Hansen, Broadcom

8. Is the PBCC-22 Code the best choice?
March 2001
Is the PBCC-22 Code the best choice?
Higher Dfree will yield lower bit and frame error rates for a given SNR
Many published trellis codes available
Significant coding gain is possible with low levels of complexity
For Example: Ungerboeck 64 state code with Dfree^2/Es = 8.01 dB
Christopher Hansen, Broadcom

9. March 2001
Conclusions
PBCC-22 cover code does not appear to provide any performance gain
PBCC-22 trellis code is not necessarily the best for high rate b
Given the proposal of a new code for high rate b, the PBCC-22 authors should present more information to justify their design choice.
Christopher Hansen, Broadcom