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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