AgileRF Overview AgileRF is our current RF platform. The main objective is to show that a highly reconfigurable RF transceiver can be designed with commercial off-the-shelf components. The prototype is very ambitious in term of frequency bands, since we target carrier frequencies from 200 MHz to 7.5 GHz, with a maximum channel bandwidth of 20 MHz. Hence, we are able to receive and transmit almost all the existing commercial Radio Access Technologies. Concerning the transmitted power, the target is comparable to existing GSM terminals (+21 dBm). On the receiver side, the objective is to have a noise figure from 8 to 12 dB, depending on the frequency band. Since OpenAirInterface considers Multiple Antenna Processing, the RF equipment will include up to 4 antennas and 4 RF chains. Three key features to be demonstrated with the prototype are: - tight integration with baseband DSP (ExpressMIMO) for
- advanced re-sampling
- fine frequency adjustment
- I/Q amplitude/phase compensation
- PA linearization
- concurrent communication in different bands and with different waveforms
- time-division and frequency-division duplex with the same components
The board is Time Division Duplex based in its default configuration. This means that the same carrier frequency is used for Rx and Tx on one chain, and that a switch is used at the front end at the antenna. In other words, one can only either transmit or receive at any given instant in time. In order to implement a Frequency Division Duplex system, one has to use 2 chains, one for the uplink, and one for the downlink. The first prototypes of the three boards making up the AgileRF front-end have been fabricated and are currently being tested with respect to the their performance characteristics in order to complete a preliminary specification document. The cards were designed by EURECOM. Nextel France (Le Rouret, France) was involved in the drafting schematics, BETECH (St-Jeannet, France) in routing the design along with our RF engineer and Synergie CAD (Carros, France) fabricated the prototypes. Basic Characteristics and documents | Frequency Tuning Range | 200 MHz – 7.5 GHz | | Frequency raster | 500 kHz | | Baseband Channel Bandwidth | 20 MHz | | Transmit Power (for 35 dB OFDM ACLR) | 15 dBm | | Receiver Noise Figure | 8 dB |
More details can be found in the following documents:
Architecture Concretely, the overall RF board is comprised of 3 sections: - carrier frequency synthesis
- Transmitter section
- Receiver section
Each part has a control interface that comes from the digital mother board. More over, TX and RX parts have an I/Q signal interface to the mother board, for AD/DA conversion. OL part feed the 2 other parts in term of Local Oscillators for modulation/demodulation and frequency conversion.
agileRF architecture A. Frequency Synthesis Since we address a very wide frequency band, the local oscillator generation is a key feature of the RF transceiver. The LO generation is based on a wide band frequency synthesizer (1.9 to 4.1 GHz) and a frequency doubler. Hence the LO range is from 3.8 GHz to 8.2 GHz. The drawback of this solution is that the frequency step is quite large (500 kHz), but it can be compensated with baseband DSP (ExpressMIMO). B. Transmitter section The base band signal (zero IF or low-IF) is in I/Q format, and fed to a quasi direct modulator. The chosen component allows one to generate a signal directly from base band to a frequency range from 4 to 8 GHz. The modulated signal is then filtered and amplified. Afterwards, a switch is used to separate low and high frequencies, if the signal shall be transmitted between 4 to 7.5 GHz For signals below 4 GHz, a downconverter is used with the second 8.2 GHz synthesizer. C. Receiver section This part is certainly the most difficult, due to the very wide addressed frequency band (from 400 MHz to 7.5 GHz). As explained in section V, the LNA is a critical part, since the performance of existing wide band LNAs are not yet adequate (relatively high noise figure, non constant gain vs. frequency). Hence, the overall frequency band is divided (by a switch) into 2 sub-bands, one from 400 MHz to 2 GHz, and another one from 2 GHz to 7.5 GHz. After the LNA stage, the signal is filtered and the frequency bands are again spitted in 2 sub bands. It gives us 4 sub-bands : - 400 MHz to 1.2 GHz - 1.2 GHz to 2 GHz - 2 GHz to 4 GHz - 4 GHz to 7.5 GHz. This approach is used to decrease the amount off outer band interference (one has to keep in mind that basically all existing RATs are received at the antenna level, sometimes with huge level of signal). After this part, the architecture uses basically the same principle as for the transmitter section. We up convert the signal into a frequency range of 4 to 7.5 GHz and the signal is converted into base band thanks to an I/Q MMIC mixer. The base band signal is finally filtered and amplified. 
AgileRF board desmonstrated in March 2008 during the E2R2 final audit Related Projects AgileRF was/will be used/developped in the following projects: | 
