Evolved Packet System (EPS): The LTE and SAE Evolution of 3G UMTS

3.2 OFDM (Orthogonal Frequency Division Multiplex)

The OFDM principles were elaborated in the early 1960s with the first multi-carrier systems, especially military systems but without massive impact because of the lacunas of the electronic circuits and signal processing available at this date.

This technology came back in the 1980s for the application to multipath channels. Such channels are characterized by a non-flat frequency response which includes deep holes known as ‘selective fading’. The basic idea for OFDM is, as we will see, to spread the information on a lot of sub-carriers in order to create very narrow band channels, experimenting in each of them a frequency response that can be considered as uniform or ‘flat’.

These multi-carrier modulations became practically interesting, since a completely numerical structure of a modulator was highlighted based on Fast Fourier Transform (FFT). Apart from the projects of future use of the OFDM for the applications of E-UTRAN radio communication, the OFDM is used particularly in the digital audio broadcast system (DAB, ‘Digital Audio Broadcasting’), and digital video broadcast system (DVB, ‘Digital Video Broadcasting’), High data rate local area networks, and DSL type wire line networks. In addition, this technology is used in the broadband wireless packet access of radio called WiMAX.

The OFDM technology is thus a well known technique which consists of multiplexing on frequency subcarriers some information to be transmitted on a ...