This document discusses using frequency domain equalization (FDE) instead of cyclic prefixes in OFDM systems to improve transmission efficiency. It provides background on OFDM, how cyclic prefixes mitigate multipath interference, and the disadvantages of cyclic prefixes reducing efficiency. The study aims to apply FDE to address this issue. FDE could provide diversity benefits over cyclic prefixes but also introduces new challenges like inter-symbol interference that require further evaluation through computer simulation.

1. WATANABE・FUJII ・HATANO LAB.
A STUDY ON FREQEENCY DOMAIN EQUALIZATION FOR
OFDM SYSTEM TO GAIN HIGH TRANSMISION EFFICENCY
WATANABE・FUJII・HATANO LAB
CHAMARA SASANKA SALGADO

2. WATANABE・FUJII ・HATANO LAB.
Introduction to OFDM
1
 Multi-carrier modulation
 Method of transmitting data by splitting into
several components
 Sending each of these components over separate
carrier signals
 OFDM(Orthogonal frequency division multiplexing)
 One of the multi-carrier modulation techniques
that transmit signals using multiple carriers.
 These subcarriers are orthogonal to each other.
 Applications of OFDM
 Digital television broadcasting
 Wireless local area networks
 Asymmetric Digital Subscriber Line(ADSL)

3. WATANABE・FUJII ・HATANO LAB.
BASIC OFDM SYSTEM
2
F
F
Receiving
Filter
Data
each symbol is
assigned to a
carrier frequency
IFFT converts
frequency domain
data into
corresponding time
domain data
Generate samples
of a waveform with
orthogonal
frequency
components
creates the OFDM
signal by
sequentially
outputting the time
domain samples
Multipath, noise
etc.
OFDM data are
split from a serial
stream into
parallel sets
converts the time
domain samples
back into a
frequency domain
converts the parallel
data into a serial
stream to recover
the original input
data
Data
K×K
K×K
Transmitte
r
Receiver
No. of
subcarriers(K)

4. WATANABE・FUJII ・HATANO LAB.
MULTIPATH CHANNEL
3
 More than one transmission path between
transmitter and receiver
 Reflections from buildings, mountains or
other reflective surfaces

5. WATANABE・FUJII ・HATANO LAB.
MULTIPATH PROBLEM
4
Part from the
previous symbol
Direct
wave
Reflected
waves
Receiving
signal
delay
Time
Interference
from the
previous
symbol

6. WATANABE・FUJII ・HATANO LAB.
MULTIPATH DELAY SPREAD TOLERANCE
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 Cyclic Prefix(CP) is used in OFDM systems to
avoid the interference occurred by multipath
fading.
 End of the symbol is copied to beginning
CP
Receiving part
Direct wave
Reflected
waves
delay
Time
CP
CP CP
COPY

7. WATANABE・FUJII ・HATANO LAB.
OFDM WITH CYCLIC PREFIX
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F
F
K×K
K×K
Transmitte
r
Receiver
No. of
subcarriers(K)
copy of last part
of OFDM symbol
is placed in front
of each symbol
CP is removed

8. WATANABE・FUJII ・HATANO LAB.
TARGET OF THE RESEARCH
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 ADVANTAGE OF CP
 Helps to avoid inter symbol interference(ISI)
 DISADVANTAGE OF CP
 Cyclic prefix in an OFDM system usually results
an efficiency loss in an OFDM system
 CP, which is added at transmitter, is removed at
receiver.
 Energy and time using for CP is useless.
 TARGET
Applying Frequency Domain Equalization(FDE) instead
of CP to gain high transmission efficiency

9. WATANABE・FUJII ・HATANO LAB.
FREQUENCY DOMAIN EQULIZATION(FDE)(1/2)
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I
F
F
T
F
F
T
F
F
T
I
F
F
T
L K× L KL K×L K
K×K
K×K
Transmitte
r
Receiv
er
No. of
subcarriers(K)
No. of
symbols(L)

10. WATANABE・FUJII ・HATANO LAB.
FREQUENCY DOMAIN EQULIZATION(FDE)(2/2)
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L : No. of symbols
K : No. of subcarriers
Direct wave
Reflected
wave
CP CPCP
CP CPCP
CP
CP
FFT (L K×L K)FFT(K×K)
OFDM with CP OFDM with FDE
FFT(K×K) FFT(K×K)
 Advantages of the OFDM with FDE
 Effective than the OFDM with CP
 Diversity effect
 Disadvantages of the OFDM with FDE
 Inter symbol interference
 Little bit complex
e.g. L = 3
COPY

11. WATANABE・FUJII ・HATANO LAB.
SUMMARY AND FUTURE CHALLENGES
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 SUMMARY
 Basic OFDM system
 Multipath and multipath tolerance using
cyclic prefix
 Frequency domain equalization
 FUTURE CHALLENGES
 Evaluate the efficiency of an OFDM system
using FDE, by computer simulator.

12. WATANABE・FUJII ・HATANO LAB.
A STUDY ON FREQEENCY DOMAIN EQUALIZATION FOR
OFDM SYSTEM TO GAIN HIGH TRANSMISION EFFICENCY
WATHANABE・FUJII・HATHANO LAB
CHAMARA SASANKA SALGADO