With this post, I want to shift your attention to the technology challenges and directions that might bring us to 5G. The timing of this post couldn’t be better, as the latest publication of Communication magazine contains a significant number of 5G articles  and is highly recommended.
Let’s start with two disruptive technologies for 5G: cognitive radio networks and device-to-device communications (D2D).
Cognitive radio networks
Cognitive radio networks is a potential solution to improve the utilization of congested RF spectrum. It’s a fact that large portions of the radio spectrum are not fully utilized. We want to let secondary users take advantage of it. The key problem to solve is how to manage the mutual interferences from both primary and secondary users. In principle, a secondary user needs to detect free spectrum (white spaces) and, based on regulations or policies, decide where to transmit. Monitoring of the spectrum usage is done with a combination of spectrum sensing and geolocational databases. Once a cognitive radio selects the right channel, the next challenge is to make the network protocols adaptive to the available spectrum (which requires spectrum-aware communication protocols).
A lot of work still needs to be done, both in terms of technology and regulations. Current studies have shown that the performance of this approach is very sensitive to user density, interference thresholds, and the transmission behavior of the licensed systems. Researchers around the world are using Nutaq’s PicoSDR and μSDR platforms, including CorteXlab in France  , to develop new algorithms for cognitive radio networks.
D2D communication enables interaction between user equipment without the need for a base station or core network access. This approach opens the door to new proximity-based communications, for use in social networking applications and public safety communication during emergency situations without network coverage. Also, D2D can greatly improve system performance by reusing cellular resources.
With Nutaq’s ZeptoSDR, you can start working on the new L1/L2/L3 layer protocols. Rapid prototyping can be done on a PC as well but the ARM processor on the ZeptoSDR with embedded GNU Radio lets you easily and efficiently verify your algorithms on portable devices in a mesh network .
What’s next on the list?
Millimeter-wave beamforming, massive MIMO, new PHY waveforms, HetNets, and device-centric architectures will be covered in my next blog posts. Stay tuned.
In the meantime, I encourage you to join the quickly growing Towards 5G LinkedIn group. With it, you can discuss with your peers the challenges you face when working on future wireless systems.
 Model Based Design Kit
 IEEE Communication Magazine, February 2014, Vol. 52, No. 2 Nutaq’s PicoSDR Selected By FIT/CorteXlab For Large Cognitive Radio Testbed
 Setting up Nutaq’s PicoSDR platform at CorteXlab
 GNU Radio embedded on an ARM-based SoC FPGA for portable SDR designs