152
M. El Ghzaoui and S. Das
Fig. 5 DSP of OFDM with guard interval for128 subcarriers
approximately) which implies a relatively significant loss of power outside the signal
band.
The case of OFDM with guard interval (duration equal to 25% of the symbol
time) is different as shown in Fig. 5. There are slight fading of power in the band
which can be a handicap for certain applications such as THZ channels. This is due
to the fact that the symbol time is extended compared to the equivalent conventional
OFDM system while the intercarrier gap does not vary. Also the longer the chosen
guard interval, the more this phenomenon becomes accentuated.
6 Characteristics of the OFDM Signal
The fact that the time signal is a superposing of N subcarriers implies that amplitude
variations of this signal can be very large. An important property of the OFDM
signal is that it has a wide dynamic range. Thus, the parts of the signal having a
high amplitude risk of being affected by the nonlinearities of the analog elements
in particular those of analog to digital or analog digital converter and of the power
amplifier. In the next subsection, we study the dynamics of the OFDM signal by
studying its amplitude or power distribution, then we will analyze its PAPR.
M. El Ghzaoui and S. Das
Fig. 5 DSP of OFDM with guard interval for128 subcarriers
approximately) which implies a relatively significant loss of power outside the signal
band.
The case of OFDM with guard interval (duration equal to 25% of the symbol
time) is different as shown in Fig. 5. There are slight fading of power in the band
which can be a handicap for certain applications such as THZ channels. This is due
to the fact that the symbol time is extended compared to the equivalent conventional
OFDM system while the intercarrier gap does not vary. Also the longer the chosen
guard interval, the more this phenomenon becomes accentuated.
6 Characteristics of the OFDM Signal
The fact that the time signal is a superposing of N subcarriers implies that amplitude
variations of this signal can be very large. An important property of the OFDM
signal is that it has a wide dynamic range. Thus, the parts of the signal having a
high amplitude risk of being affected by the nonlinearities of the analog elements
in particular those of analog to digital or analog digital converter and of the power
amplifier. In the next subsection, we study the dynamics of the OFDM signal by
studying its amplitude or power distribution, then we will analyze its PAPR.