


Adaptive Techniques for Multiuser
OFDM
PhD. Exit Seminar
Overview
Topics Covered in Thesis
Future of Communications
Current OFDM systems
OFDM systems, Hiperlan/2
OFDM
5 carrier OFDM signal
OFDM Transceiver
Inverse Fourier Transform
Subcarrier Modulation
Function of Guard Period
Multipath Propagation
Function Guard Period
Properties of OFDM
Overview
Short Term Fading
Frequency Selective Fading
Experimental Setup
Measurement Locations
Some of the Results
Some of the Results
Overview
Performance of Modulation
Schemes
Adaptive Modulation
Simulated Channel SNR for –8
dBm Tx. Power
Adaptive Modulation
Bit errors for Adaptive
Modulation
Location of bit errors for
fixed QPSK
Adaptive Modulation
Overview
Every user has a different
multipath response
Fixed Frequency Allocation
Fixed Frequency Allocation
Modulation at each frequency
Problems with fixed
modulation
Adaptive Frequency Hopping
Adaptive Frequency Hopping
Clashes in frequency
allocation
Adaptive User Allocation
Adaptive User Allocation
Modulation at each frequency
Adaptive User Allocation
Overview
How can we overcome
shadowing?
Access Point
Repeater
Configuration
Experimental Setup
Measurement Locations
Measured Results
Pathloss Probability
Distribution Over Area of Building
Simulated path loss
distribution for multiple transmitters
Interference rejection with
APRs
Signal to Interference with
1 APR
Signal to Interference with
8 APRs
Spectral Efficiency of WLAN
with mobile interferer
Coverage of the WLAN
building, with mobile interferer of equal power
Summary
Publications