The Signalion Hardware-in-the-Loop (HaLo) is a platform designated to simplifying the transition from simulation to implementation. To support cognitive radio setups that consider a primary/secondary user configuration, the LTE testbed has been extended by a HaLo node that can take the role of the secondary user. On the HaLo device, a novel modulation scheme called Generalized Frequency Division Multiplexing (GFDM) is now available.

This enables experimenters to consider experiment setups in LTE testbed, where the LTE system can act as a monitored primary system, while the GFDM system can run as an interfering secondary system.

HaLo Concept

The HaLo consists of a wireless transceiver that can operate in the 2.6 GHz frequency band. The concept is such, that complex valued data samples are transmitted to the device’s memory via USB from a control computer. The samples can be either read from a previously recorded file or generated on the fly e.g. by a Matlab script. The signal is transmitted over the air and received in a similar way. The device digitizes the signal and stores complex valued samples to an internal memory before they are fed back via USB to the control computer.

The HaLo setup

Note that due to limitations in the HaLo’s internal memory real-time operation is not possible.

GFDM Theory

The transmission scheme chosen to be implemented on the HaLo device to act as a secondary system in the testbed is a novel, non-orthogonal and flexible modulation scheme called GFDM. The concept is such that a multicarrier signal is transmitted, quite similar to the well know and established OFDM scheme, however one of the differences is in the pulse shaping of the individual subcarriers. This step allows shaping of transmissions and produces a signal with particularly low out-of-band radiation, which is a very desirable property in cognitive radio. For further details please refer to:

 https://mns.ifn.et.tu-dresden.de/Lists/nPublications/Attachments/826/Michailov_N_VTCfall12.pdf

GFDM transmitter and receiver block diagram