1. Chapter 4 of Hiroshi Harada Book (OFDM Transmission)
EE578 Assignment #4
Chapter 4 of Hiroshi Harada Book  (OFDM Transmission)
Abdul-Aziz .M Al-Yami
Nov 1st 2010

2. OUTLINE OVERVIEW ABOUT OFDM DEFINITION AND PRINCIPLES
OFDM ADVANTAGES & DRAWBACKS
APPLICATIONS
CONCLUSIONS AND PERSPECTIVES
RESULTS

3. OVERVIEW ABOUT OFDM OFDM was invented more than 40 years ago.
OFDM has been adopted for several technologies:
Asymmetric Digital Subscriber Line (ADSL) services.
IEEE a/g, IEEE a.
Digital Audio Broadcast (DAB).
Digital Terrestrial Television Broadcast: DVD in
Europe, ISDB in Japan
4G, IEEE n, IEEE , and IEEE

4. WHY OFDM ?
High bit rate needs are clumped by the nature of communication channels.
Multi-path Propagation effects forbid increasing of transmission rates.

5. OFDM DEFINITION OFDM = Orthogonal FDM
Carrier centers are put on orthogonal frequencies
ORTHOGONALITY - The peak of each signal coincides with trough of other signals
Subcarriers are spaced by 1/Ts

6. Modulation

7. PRINCIPLES
BASIC IDEA : Channel bandwidth is divided into multiple subchannels to reduce ISI and frequency-selective fading.
Multicarrier transmission : Subcarriers are orthogonal each other in frequency domain.

8. PRINCIPLES Time-domain spreading:
Spreading is achieved in the time-domain by repeating the same information in an OFDM symbol on two different sub-bands => Frequency Diversity.
Frequency-domain spreading:
Spreading is achieved by choosing conjugate symmetric inputs for the input to the IFFT (real output)
Exploits frequency diversity and helps reduce the transmitter complexity/power consumption.

9. FDM  OFDM Frequency Division Multiplexing OFDM frequency dividing
EARN IN SPECTRAL EFFICIENCY

10. OFDM THEORY The baseband OFDM signals can be written as
Where is the central frequency of the mth sub-channel and is the corresponding transmitted symbol.
The signals are orthogonal over [0, T ] as illustrated below:

11. Generic OFDM Transmitter
OFDM symbol
bits
Serial to
Parallel
Pulse shaper
FEC
IFFT
Linear PA
&
DAC
add cyclic extension fc
view this as a time to
frequency mapper
Complexity (cost) is transferred back from the digital to the analog domain!

12. (of all tones sent in one OFDM symbol)
Generic OFDM Receiver
Slot &
Timing
AGC
Sync.
P/S and
Detection
Error
Sampler
FFT
Recovery fc
gross offset
VCO
Freq. Offset
fine offset
Estimation
(of all tones sent in one OFDM symbol)

13. OFDM ADVANTAGES OFDM is spectrally efficient
IFFT/FFT operation ensures that sub-carriers do not interfere with each other.
OFDM has an inherent robustness against narrowband interference.
Narrowband interference will affect at most a couple
of subchannels.
Information from the affected subchannels can be
erased and recovered via the forward error
correction (FEC) codes.
Equalization is very simple compared to Single-Carrier systems

14. OFDM ADVANTAGES
OFDM has excellent robustness in multi-path environments.
Cyclic prefix preserves orthogonality between sub-
carriers.
Cyclic prefix allows the receiver to capture multi-
path energy more efficiently.
Ability to comply with world-wide regulations:
Bands and tones can be dynamically turned on/off
to comply with changing regulations.
Coexistence with current and future systems:
for enhanced coexistence with the other devices.

15. OFDM DRAWBACKS High sensitivity inter-channel interference, ICI
OFDM is sensitive to frequency, clock and phase offset
The OFDM time-domain signal has a relatively large peak-to-average ratio
tends to reduce the power efficiency of the RF amplifier
non-linear amplification destroys the orthogonality of the OFDM signal and introduced out-of-band radiation

16. Standards Digital Audio Broadcasting (DAB)
Digital Video Broadcasting (DVB)
Asymmetric Digital Subscriber Line (ADSL)
Wireless LAN IEEE a
Wireless networking, device connectivity
Proposed for standard
Connection between subscriber's transceiver station and a base transceiver station

17. COFDM Transmitter
Digital Radio
Coded OFDM Transmitter

18. DRM For HF Frequencies 4.5 – 5 kHz for half channel
Data Rates of 4 – 14.5 kbit/s
9 – 10 kHz for full channel
Data Rates of 8 – 35kbit/s
18-20 kHz for double channel
Data Rates of 31 – 72kbit/s

19. (V-OFDM) of Cisco, Iospan,etc.
Proprietary OFDM Flavours
Wideband-OFDM
(W-OFDM) of Wi-LAN
Flash OFDM
from Flarion
Vector OFDM
(V-OFDM) of Cisco, Iospan,etc.
-- Freq. Hopping for
CCI reduction, reuse
to 5.0MHz BW
-- mobility support
GHz band
Mbps in 40MHz
-- large tone-width
(for mobility, overlay)
-- MIMO Technology
-- non-LoS coverage,
mainly for fixed access
-- upto 20 Mbps in MMDS
Wi-LAN leads the OFDM Forum -- many proposals submitted to
IEEE Wireless MAN
Cisco leads the Broadand Wireless Internet Forum (BWIF)

20. MATLAB Results
Program 4.2 (ofdm_fading)