The following article was written by the team at IK4-Ikerlan.
One of the main issues in wireless communications is the availability of the link, with most of the development efforts directed towards the maximization of the robustness of the wireless communication system. The aim of this work has been to develop a cognitive wireless communication system with frequency diversity, for harsh industrial environments where the propagation and interference characteristics must be taken into account. The challenges to be met have been:
A fully reconfigurable cognitive radio platform has been designed and developed. This platform is able to achieve reconfiguration at all levels of the physical layer (i.e. FPGA baseband processing, RF front-end and antenna), enabling both in-band channel change and dual-band reconfiguration in the Industrial, Scientific and Medical (ISM) bands of 868 MHz and 2.4 GHz. As a consequence, this platform provides a suitable framework for reliable wireless communications.
The developed cognitive radio platform consists of a transmitter and a receiver that make up a cognitive wireless communication at 1.6 Mbps. The system is based on QPSK modulation and is able to change its transmission frequency depending on the availability of the channel. The following picture shows a block diagram.
Block Diagram of the Cognitive Radio Platform
This platform is reconfigurable at the three main parts of the physical layer, namely baseband processing, RF front-end and antenna:
1. Reconfiguration of the FPGA baseband processing has been carried out via dynamic partial reconfiguration of a Xilinx Virtex-6 FPGA. This feature enables the change of functionality of part of the FPGA while the rest continues unaltered, which leads to a reduction in the required amount of FPGA resources and, consequently, in its size. The implemented baseband processing is mainly divided into two tasks, present both in the transmitter and receiver.
a) Data Modulation/Demodulation: this task performs the QPSK modulation of the input data in the transmitter and recovers it in the receiver. This is the task where FPGA dynamic partial reconfiguration is applied.
b) Dynamic Spectrum Access (DSA): this task carries out a spectrum sensing algorithm to look for channel availability in the transmitter, prior to any transmission. It is also in charge of searching the signal in the receiver.
2. The reconfigurable RF front-end has been based on Nutaq’s Radio420S module, which allows an easy translation of the baseband signal to the desired ISM bands of 868 MHz and 2.45 GHz (up-conversion), and vice versa (down-conversion). An external RF switch has been added to use a single antenna for both transmission and reception; this switch has been controlled by a signal coming from the FPGA.
3. Finally, a frequency-reconfigurable microstrip antenna has been designed, which operates in 868 MHz or 2.45 GHz depending on the status of the PIN diodes mounted on its surface; the status of the diodes has been controlled by a signal coming from the FPGA. In order to ensure the required bandwidth in both bands, a reconfigurable matching network (RMN) has been designed and added to the antenna.
The following picture shows the fully reconfigurable cognitive platform.
Image Of The Fully Reconfigurable Platform
More details can be found in the following publication:
Casado F., Torrego R., Arriola A., and Val I., “Fully Reconfigurable FPGA-based Cognitive Radio Platform for Reliable Communications”, Wireless Innovation Forum European Conference on Communications Technologies and Software Defined Radio (SDR-WInnComm-Europe 2013), Munich, Germany, June 11th-13th 2013.
Why IK4-Ikerlan Chose Nutaq’s Radio420X
Nutaq’s platforms speed up the development process by allowing the testing and improvement of DSP algorithms in a rapid way. In addition, the Radio420X RF modules are convenient for SDR/Cognitive radio based system, especially since their wide RF range allows to switch between different bands sufficiently apart from each other; this way, it is possible to take advantage of the frequency diversity using two bands which are uncorrelated from the point of view of the multipath propagation and interferences.
IK4-IKERLAN (www.ikerlan.es) is a Spanish private non-profit Technological Research Centre, member of the IK4 Research Alliance and set up in 1974.
IK4-IKERLAN is the key technological R&D actor within the Mondragon Corporation (www.mondragon-corporation.com), Spain’s sixth-largest industrial corporation. With a staff of more than 200 qualified researchers and engineers, IK4-IKERLAN is a reference for innovation, advanced technology transfer to industry, and comprehensive product development for a wide variety of domains such as transportation, automation, industrial, or healthcare.