Universal Software Radio Peripheral (USRP)

1. General description

The USRP is a flexible software defined radio developed by Ettus. It is composed of a motherboard that performs some baseband processing (sampling over 12 bits and down conversion of the received signals) and of daughter boards that do the RF part of the radio. The motherboard is connected to a host PC through a USB 2.0 link and transmit/receive in real time the base band samples. The signal design, its modulation and demodulation are hence done on the host PC. The following scheme resumes this system:

2. Main characteristics

Radio interface to computer	The USRP is connected to a computer with a USB 2.0 interface. Because of this interface, the USRP is limited to signals with at most 4 MHz of bandwidth.
Frequencies	The USRP is able to work in many bands of frequencies depending on your daughterboards. For example: RFX 2400: This board can address the 2.4GHz ISM bands (2400 à 2483 MHz) XCVR2450 : This board can address the 2.4GHz ISM bands (2400 à 2483 MHz) and the 5.2GHz ISM bands TVRX : This board works in the UHF bands
MIMO	Can be supported depending on your motherboards. Note that the available bandwidth has to be divided by the number of antennas.
ADC/DAC	12 bits
Baseband	The baseband processing consists in sampling the signal and performing the downconvertion.
Software	The USRP can either be used with GNU Radio or with the interface to Matlab developed by tools4SDR.

3. Processing digital communications signal with USRP

Because it is able to work in a large set of bands of frequencies, some signal processing can be performed on signal transmitted by base station. An example of processing of undersampled DVB-T signal is shown on Tools4SDR. Nevertheless, because of it bandwidth limitation, it is not possible to decode WiFi, UMTS, or DVB signals.

Note that it is still possible to generate signals to handle the whole transmission. An example about the transfer of an image is shown on tools4SDR.

4. External links

• Ettus: Ettus website