OFDM for Terahertz Wireless Communication Systems
151
We observe that this expression of the DSP was obtained without particular restriction concerning the waveform h. This expression is therefore a general formula of
the DSP for modulations with waveform, and it only depends on the waveform used.
5.2.2 Application and Simulation of DSP
As the Fourier transform of the gate function of length T B and centered at 0 is:
T F(Π T B (t)) = sinc(π T B f )
(20)
So, we get:
Φ OFDM ( f ) =
σ
2
c
T B
N
k=1
sinc(π T B ( f − f k ))
2
(21)
This expression is also found in [19]. Figure 4 shows the DSP of 128 subcarriers
OFDM system.
It should be noted that the spectrum presented is simulated in discrete time while
the DSP is expressed in continuous time. We also highlight one of the weaknesses
of OFDM. Indeed, the secondary lobes of the DSP go up relatively high (−25 dB
Fig. 4 DSP of OFDM with 128 subcarriers
151
We observe that this expression of the DSP was obtained without particular restriction concerning the waveform h. This expression is therefore a general formula of
the DSP for modulations with waveform, and it only depends on the waveform used.
5.2.2 Application and Simulation of DSP
As the Fourier transform of the gate function of length T B and centered at 0 is:
T F(Π T B (t)) = sinc(π T B f )
(20)
So, we get:
Φ OFDM ( f ) =
σ
2
c
T B
N
k=1
sinc(π T B ( f − f k ))
2
(21)
This expression is also found in [19]. Figure 4 shows the DSP of 128 subcarriers
OFDM system.
It should be noted that the spectrum presented is simulated in discrete time while
the DSP is expressed in continuous time. We also highlight one of the weaknesses
of OFDM. Indeed, the secondary lobes of the DSP go up relatively high (−25 dB
Fig. 4 DSP of OFDM with 128 subcarriers