1. for Wireless Communications
OFDM
for Wireless Communications
By Frank Shao

2. Road Map Modulation Analog Digital FM TDM AM FDM
Orthogonal Frequency Division Multiplexing

3. Symbol Generation
a1(t)
a2(t)
a3(t)

4. To take k-th subcarrier:
Orthogonality
To take k-th subcarrier:
If i = j, then result is aK

5. Advantages Guard Interval
High bandwidth efficiency
Resilience to multipath delays
Guard Interval
FFT time interval

6. Advantages No Guard Interval With Guard Interval FFT time interval
Symbol period

7. Phase Rotation ?
FFT time interval

8. Phase Rotation Take the i-th subcarrier’s 4 QAM constellation:
Showing the effect of a timing offset of T/8. Each i-th subcarrier has rotation:

9. Phase noise produces ICI Frequency offset produces ICI
Disadvantages
Phase noise produces ICI
Frequency offset produces ICI
Requires that the receiver have accurate synchronization

10. Applications: a

11. Applications: a

12. Methods on correcting the timing offset (phase rotation)
Further Research
Methods on correcting the timing offset (phase rotation)
Methods of synchronizing frequency offset
SNR of receivers