In a joint research project between DLR and FH OÖ F&E Gmbh, multi-carrier transmission methods are to be implemented and tested in practice. The best known multicarrier method is Orthogonal Frequency Division Multiplexing (OFDM) and is used in many current standards such as LTE, WLAN, 5G, to name only the most important. OFDM is: very powerful at long echo times of the signals, easy to implement with FFT, but has some serious disadvantages. These include the moderate spectral efficiency and the high linearity requirements of the transmit amplifier. These disadvantages lead to out-of-band radiation, which can interfere with adjacent channels. In order to reduce this out-of-band radiation, variants of OFDM have been proposed in the literature which operate under the keyword Filter Bank Modulation Carrier (FBMC). They use spectrally more compact modulation shapes.
The test system shall consist of a PC with GNU Radio and two ETTUS B210 SDRs. The communication line shall be tested by an interface with a real data stream. Therefore a prototype of the DLR and a GNU radio open-source IEEE 802.11a/g/p transceiver (WLAN) will be used. After commissioning, different procedures of the FBMC will be investigated with regard to spectral efficiency. A Spectrum Analyzer R&S FSQ is available for this purpose. The bit error rates (BER) are to be investigated for the different modulation forms. The out-of-band radiations caused by the non-linearity of the amplifier can also be reduced by means of digital pre-distortion. For this purpose, suitable methods for multi-carrier modulation forms are evaluated from the literature. In a second project stage, extensions for multi-antenna systems (MIMO) and suitable coding methods (e.g. soft-decision deocoding) in combination with FMBC will be investigated.
Orthongonal Frquency-Division Multiplexing is a Multi-Carrier Modulation. It is widely used in apllications such as DVB-T, 4G, Wifi, and Powerline Networks.
FBMC can be seen as an envolved form of OFDM which overcomes the limitations of OFDM .
The signal processing software Gnuradio was used for implementation and testing.
DVB-T is a standard for the transmission of terrestrial television signals. Since the transmission of DVB-T is based on OFDM, this project was used as a showcase for OFDM.
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