1. Pseudo-Pilot OFDM Scheme for 802.11a and R/A in DSRC Applications
Salvador Sibecas, Celestino A. Corral, Shahriar Emami, Glafkos Stratis, Gregg Rasor --Motorola Labs
VTC 2003
Advisor: Yung-an kao
Student:Chian Young

2. outline Why use a new pilot-scheme? Pseudo-Pilot Scheme
Simulation description
Simulation result

3. Why use a new pilot-scheme?
802.11a’s pilot structure can’t correct for large Doppler frequency spread typically encounter in high-mobility DSRC

4. Pseudo-Pilot Scheme
802.11a/RA Pilot structure
Pseudo-Pilot scheme

5. Pseudo-Pilot Scheme
In TX, known pilots replace the symbols prior to IFFT
At RX, the pilots are removed and random data symbols are placed back in their original locations

6. Pseudo-Pilot Scheme 2-D interpolated version is used
Receiver places complex data symbol, Obtained from a uniform distribution, into the location of each pilot
Block diagram of pseudo-pilot scheme for mobility enhancement in a and R/A.

7. Pseudo-Pilot Scheme
The receiver does not differentiate between the newly replaced complex symbol and the rest of the data symbol sent
The number of inserted pilots is minimized to reduce number of unintentional error by using single pilot per symbol

8. Simulation description
Distance between access point and mobile is
100m, peak velocity is 45 mph(72km/h) corresponding a max Doppler freq.=397Hz
Bits are modulated using 4-QAM(?),and convolutional coding is used
Max rms delay =108ns,and a maximum delay=1.6us
Assume ICI, ISI is eliminated, and perfect symbol and freq. synchronization

9. Simulation description
WSSUS(WSS uncorrelated scattering) channel model is used
Assuming the channel to be constant over one OFDM symbol, the instantaneous freq. response of Mth path at time t is:
:Doppler freq.
:delay of nth path

10. Simulation result
802.11a/RA standard
Pseudo-pilot Scheme