158
M. El Ghzaoui and S. Das
7 Advantages and Drawback of OFDM System
OFDM modulation is an old technology with recent success which consists in
transmitting data in parallel on several different carrier frequencies.
The OFDM is particularly well suited to long-distance radio transmission channels without multiple wave transmissions (echoes), so it significantly reduces
inter-symbol interference. However, OFDM also has a number of drawbacks.
7.1 Advantages
The OFDM modulation process has been mainly designed to fight against multiple
paths with fading, by minimizing inter-symbol interference (ISI), and it guarantees us
sufficiently high bit rates. Spectral congestion has been optimized, the transmission
channel appears locally invariant, and frequency equalization is carried out in a very
simple manner.
7.1.1 Low ISI
Using a guard interval enhances the robustness of the OFDM signal against
frequency-selective channel. This allows an acceptable ISI to be received, i.e., OFDM
symbols arriving at the receiver do not interfere with the sampling times.
7.1.2 Optimal Spectral Bulk
OFDM offer an effective use of frequency properties in comparison with conventional
frequency multiplexing solutions. This is due to the fact that in OFDM, the subcarriers
overlap while maintaining perfect orthogonality as shown in Fig. 10, and therefore
optimizing the spectral occupancy of the modulated signal.
f k − f k+1 = 1/T B
7.1.3 Frequency-Selective Channel
We can consider that the transfer function of the transmission channel is flat at the
level of each subcarrier as shown in Fig. 11.
M. El Ghzaoui and S. Das
7 Advantages and Drawback of OFDM System
OFDM modulation is an old technology with recent success which consists in
transmitting data in parallel on several different carrier frequencies.
The OFDM is particularly well suited to long-distance radio transmission channels without multiple wave transmissions (echoes), so it significantly reduces
inter-symbol interference. However, OFDM also has a number of drawbacks.
7.1 Advantages
The OFDM modulation process has been mainly designed to fight against multiple
paths with fading, by minimizing inter-symbol interference (ISI), and it guarantees us
sufficiently high bit rates. Spectral congestion has been optimized, the transmission
channel appears locally invariant, and frequency equalization is carried out in a very
simple manner.
7.1.1 Low ISI
Using a guard interval enhances the robustness of the OFDM signal against
frequency-selective channel. This allows an acceptable ISI to be received, i.e., OFDM
symbols arriving at the receiver do not interfere with the sampling times.
7.1.2 Optimal Spectral Bulk
OFDM offer an effective use of frequency properties in comparison with conventional
frequency multiplexing solutions. This is due to the fact that in OFDM, the subcarriers
overlap while maintaining perfect orthogonality as shown in Fig. 10, and therefore
optimizing the spectral occupancy of the modulated signal.
f k − f k+1 = 1/T B
7.1.3 Frequency-Selective Channel
We can consider that the transfer function of the transmission channel is flat at the
level of each subcarrier as shown in Fig. 11.