OFDM for Terahertz Wireless Communication Systems
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each symbol being transmitted on one of the N carrier frequencies orthogonal to one
another and modulated at low speed. This technique has the advantage of converting a
frequency-selective channel into a non-selective subchannel [13]. For these reasons,
OFDM has been adopted for high data rate applications, such as worldwide interoperability for microwave access (WIMAX) and 3GPP long-term evolution (LTE) [14].
However, the technology does impose some drawbacks which must be considered
when designing an OFDM modem.
The work carried out in this chapter consists of studying OFDM systems to obtain
the best possible spectral efficiency while keeping a high performance in terms of
transmission errors. Indeed, the key objective of this chapter is the reduction of BER
under the rate constraint and the robustness of THz systems with multiple carriers.
The research aims of our work is to explore the OFDM approach on a THz channel.
We applied OFDM techniques to the THz network in order to achieve reliable transmission on this network. We also made a detailed study on the parameters of the
modulations used in this work in order to improve the transmission quality on this
network. The implementation of the theoretical model and the simulations are carried
out using MATLAB software.
2 Principe of OFDM
OFDM system consists in distributing the data to be transmitted over a big number of
carriers in parallel, individually modulated at low speed. The spectra of all the subcarriers resulting from a filtering of rectangular formatting are cardinal sinuses which
overlap each other. This gives excellent spectral efficiency. And since the OFDM
signal verifies the crucial condition of orthogonality, the information carried by each
subcarrier can be extracted without suffering from interference due to the neighboring carrier. The orthogonality between the subcarriers requires that the spacing
between two adjacent subchannels is equal to the inverse of the OFDM block time.
An OFDM symbol duration is generally much greater than the duration of the
delay spread by a channel, thus limiting the effect of inter-symbol interference (ISI)
on a small part of each OFDM symbol. To completely avoid ISI, a prefix cyclic is
inserted between successive OFDM symbols. Its duration is selected to be extended
than the maximum delay induced by the transmission channel, and it is formed by
a cyclic extension of the OFDM symbol. The guard interval also makes it possible
to maintain the orthogonality between the subcarriers and thus to avoid interference
between subcarriers (ICI).
3 Description of Signal OFDM
To be able to transmit information, the carrier frequency is must be modulated,
i.e., Bu is the useful or necessary bandwidth of the signal. If the useful band Bu
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each symbol being transmitted on one of the N carrier frequencies orthogonal to one
another and modulated at low speed. This technique has the advantage of converting a
frequency-selective channel into a non-selective subchannel [13]. For these reasons,
OFDM has been adopted for high data rate applications, such as worldwide interoperability for microwave access (WIMAX) and 3GPP long-term evolution (LTE) [14].
However, the technology does impose some drawbacks which must be considered
when designing an OFDM modem.
The work carried out in this chapter consists of studying OFDM systems to obtain
the best possible spectral efficiency while keeping a high performance in terms of
transmission errors. Indeed, the key objective of this chapter is the reduction of BER
under the rate constraint and the robustness of THz systems with multiple carriers.
The research aims of our work is to explore the OFDM approach on a THz channel.
We applied OFDM techniques to the THz network in order to achieve reliable transmission on this network. We also made a detailed study on the parameters of the
modulations used in this work in order to improve the transmission quality on this
network. The implementation of the theoretical model and the simulations are carried
out using MATLAB software.
2 Principe of OFDM
OFDM system consists in distributing the data to be transmitted over a big number of
carriers in parallel, individually modulated at low speed. The spectra of all the subcarriers resulting from a filtering of rectangular formatting are cardinal sinuses which
overlap each other. This gives excellent spectral efficiency. And since the OFDM
signal verifies the crucial condition of orthogonality, the information carried by each
subcarrier can be extracted without suffering from interference due to the neighboring carrier. The orthogonality between the subcarriers requires that the spacing
between two adjacent subchannels is equal to the inverse of the OFDM block time.
An OFDM symbol duration is generally much greater than the duration of the
delay spread by a channel, thus limiting the effect of inter-symbol interference (ISI)
on a small part of each OFDM symbol. To completely avoid ISI, a prefix cyclic is
inserted between successive OFDM symbols. Its duration is selected to be extended
than the maximum delay induced by the transmission channel, and it is formed by
a cyclic extension of the OFDM symbol. The guard interval also makes it possible
to maintain the orthogonality between the subcarriers and thus to avoid interference
between subcarriers (ICI).
3 Description of Signal OFDM
To be able to transmit information, the carrier frequency is must be modulated,
i.e., Bu is the useful or necessary bandwidth of the signal. If the useful band Bu