Part 2 Wireless Communication
Technologies
Wireless Communication Technologies Chapter 2
1
Outline
2.5.1 Introduction
2.5.2 OFDM Basics
2.5.3 Performance Sensitivity for Imperfect Circuit
2.5.4 Timing and Frequency Synchronization
2.5.5 Example Coherent Detection and Channel
Estimation
2.5.6 The Peak Power Problem
2.5.7 Summary
References
Problems
Wireless Communication Technologies 2.5.1
2
Introduction
 The most suitable modulation choice for wireless broadband
multimedia communication systems (WBMCS) seems to be
orthgonal frequency division multiplexing (OFDM).
 The principle of OFDM is to split high-rate data-streams into
a number of lower rate streams that are transmitted
simultaneously over a number of sub-carriers.
 The dispersion in time from multi-path delay spread is
relatively decreased per sub-carrier.
Wireless Communication Technologies 2.5.1
3
Introduction
 The inter-symbol interference (ISI)
can be eliminated by guard time
and the inter-carrier interference
(ICI) can be avoided by using cycle
extension.
Cyclic Prefix
15
10
5
0
-5
-10
-15
0
0.5
1
1.5
2
2.5
3
3.5
4
OFDM symbol time
Guard Time
Serial
to
parallel
IFFT
Parallel
to
serial
Add
guard
time
Wireless Communication Technologies 2.5.1
OFDM
signal
4