Two things can be said about today’s wireless spectrum. First, it’s a fact that the allocation of frequencies is currently static. Second, it’s getting pretty crowded! Since it’s pretty obvious that the number of wireless devices will continue to increase in the upcoming years, the current way in which the wireless medium is shared must be revisited. This will inevitably lead to drastic changes in the algorithms implemented at different layers of the digital processing chain.
The most promising approach to better spectrum sharing comes from the cognitive radio paradigm. For a system to be cognitive it must reconfigure itself in real-time, be aware of its wireless environment, and be capable of self-organization. So how and where can we evaluate our theory in regards to these criteria in a real environment?
At INSA-Lyon, in France, the solution has a name: CorteXlab. CorteXlab stands for Cognitive Radio Testbed Experimentation Lab. This lab will be connected to other labs as part of the Future Internet of Things (FIT) program (http://fit-equipex.frhttp://www.nutaq.comglish):
What is the main difference between this testbed and other existing cognitive radio testbeds? The experimentation is extended to the PHY layer and enables remote users to test their own PHY layer algorithms. Since it’s difficult to dissociate the actual radio hardware from the digital processing layers in a cognitive radio, the lab is open to industry third-parties who want to deploy their own front-end or baseband systems for testing and validation. The goal: To rocket the scientific progress forward by enabling users to design, benchmark, and tune their cognitive radio protocols in a real environment.
The CorteXlab is composed of a mix of heterogeneous radio nodes:
All software-defined radio (SDR) nodes must present a high degree of RF flexibility to enable dynamic reconfiguration of the frequency, bandwidth, emitted power, and waveform. These nodes are able to accept PHY layer implementations on both FPGA and general-purpose CPU hardware and are interconnected through an Ethernet link to enable sharing between nodes. With such a lab, many techniques can now be put to the test: spectrum sensing, dynamic spectrum access, ad-hoc/structured networks, and distributed computing for sensor networks, to name a few.
So where does Nutaq fit in with all this? The SDR nodes are divided in two categories: standard and high performance, and Nutaq’s PicoSDR system was selected to implement the high-performance SDR nodes in the CorteXlab. Here’s a list of the high performance SDR node requirements:
- Multi-carrier transmission
- MIMO-OFDM transmission types
- Fast and flexible RF module reconfiguration
- High digital signal processing capability
- MIMO 2×2 and 4×4 configuration
- High bandwidth data streaming to/from and host PC
- Linux and GNU Radio compatibility
From this list, it’s not a surprise that the Nutaq PicoSDR was selected. With the PicoSDR comes an orthogonal frequency-division multiplexing (OFDM) reference design. In this reference design, the PicoSDR enables MIMO-OFDM 2×2 transmissions from day one. Being entirely implemented in an FPGA (both the RX and TX), the PicoSDR provides a high level of digital signal processing capability. In regards to radio reconfiguration, the PicoSDR uses the LimeMicro LMS6002D RFIC as the RF front-end, making the dynamic reconfiguration of the frequencies and the gains easy to perform directly from the FPGA, thus reducing (at the minimum) the latency of reconfiguration. It’s still possible however to configure the RFIC and the PicoSDR from an host computer running either Linux or Windows. In the CorteXlab, the Linux environment is preferred due to GNU Radio compatibility, which improves the reusability of community-developed waveforms. Finally, the PicoSDR PCIe interface offers up to 650 MBps of throughput, which is more than enough to meet the requirement of high-bandwidth data streaming.
CorteXlab is an on-going project and the official version of the testbed is planned for October 2014 (beta version will be available on February 2014). Nutaq is proud to help promote cognitive radio research via our PicoSDR 2×2/4×4 product. Other CorteXlab partners include UPMC, INRIA, Strasbourg University, Mines-Telecom, and the CNRS. For more information, visit their website at http://www.cortexlab.fr/.