Software & Hardware
In this demonstration, the radar prototype is designed on the principles of a sub-Nyquist collocated multiple-input multiple-output (MIMO) radar. The setup allows sampling in both spatial and spectral domains at rates much lower than dictated by the Nyquist sampling theorem. We use frequency division multiplexing (FDM) to achieve the orthogonality of MIMO waveforms and apply the Xampling framework for signal recovery. The prototype also implements a cognitive transmission scheme where each transmit waveform is restricted to those pre-determined subbands of the full signal bandwidth that the receiver samples and processes. Real-time experiments show reasonable recovery performance while operating as a 4×5 thinned random array wherein the combined spatial and spectral sampling factor reduction is 87.5% of that of a filled 8 × 10 array.
We present for the first time a design and implementation of a Xampling-based hardware prototype that allows sampling of radar signals at rates much lower than Nyquist. We demonstrate by real-time analog experiments that our system is able to maintain reasonable detection capabilities, while sampling radar signals that require sampling at a rate of about 30MHz at a total rate of 1Mhz, namely, at 1/30 of the Nyquist rate. Our board is based on a 4-channel crystal receiver. To evaluate the board we make use of National Instrument (NI) PXI equipment.
We demonstrate the first wideband sub-Nyquist receiver that can sample and process multiband signals at rates far below the Nyquist rate. Our prototype, referred to as the Modulated Wideband Converter (MWC), samples multiple narrowband transmissions at a rate proportional to the actual bandwidth occupation, without knowledge of the carrier positions. Our specific implementation uses a rate that is only 8% of the Nyquist rate. Various extensions to the MWC are also presented, among them collaborative processing, direction of arrival (DOA) estimation and modulated data reconstruction (PSK, OFDM). These prove that the MWC is both a viable and flexible solution for future communication systems.
We demonstrate a real-time fixed-point embedded implementation of the sub-Nyquist reconstruction algorithm in the modulated wideband converter. The embedded design enables, for example, fast spectrum sensing, in a time duration as low as several micro-seconds, which is essential to real-time cognitive radio applications. The system uses LabView and is implemented on an Altera Stratix III field-programmable gate array (FPGA) mounted on a Gidel PROCStar-III development board.