Interference reduction with relay beacon in cognitive radio networks

Open Access
Banik, Arnab Kumar
Area of Honors:
Electrical Engineering
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Dr Sven Bilén, Thesis Supervisor
  • Sven G Bilen, Thesis Supervisor
  • Jeffrey Louis Schiano, Honors Advisor
  • cognitive radio
  • spectrum scanning
  • SU
  • secondary user
  • primary user
  • PU
  • sdr
  • software defined radio
  • signal relaying
  • usrp
The existing static frequency allocation policy, controlled by the Federal Communications Commission (FCC) in the United States, is fast approaching an apparent spectral crisis, owing to consistent and rapid increase in spectrum demand by wireless users. In such an inevitable spectrum scarcity scenario, opportunistic use of the idle spectrum bands that are otherwise licensed to primary users is one key solution approach. Cognitive radio (CR) arises to be a tempting solution to this spectral congestion. The purpose of a cognitive radio network is to efficiently detect spectrum holes so that secondary transmissions can optimally use the spectrum band without interfering with primary users. Misdetection of spectrum holes, owing to signal fading and path loss, however, will cause in concurrent transmission with primary users resulting in undesirable interference that violates the very basic philosophy of cognitive network transmission. Therefore, it is important to study how this interference level relates to design parameters such as the beacon detection threshold, and how it affects the primary users’ performance. Also, to improve spectrum sensing and to reduce interference, it is of key interest to formulate how a cooperative scheme of relay transmission of beacon signals suitably addresses the effect of signal fading and path loss, which often results in misdetection of spectrum holes. This work deals with the effect of interference owing to concurrent transmission by both primary and secondary user for the case of failed detection of a beacon transmitted by primary user. In such a scenario, beside theoretical study of the interference phenomena, we experiment with it by transmitting data from both primary and secondary user at the same frequency to allow channel interference. To avoid this, we introduce a beacon signal by the primary user to notify the secondary users to transmit data at a different frequency in the available frequency band. Further, that signal might still be lost due to fading, so to avoid this case we introduce a relaying method in which the secondary user retransmits the beacon to the second secondary user, hence minimizing interference even more. All the results were carried out with software-defined radio using the Universal Software Radio Peripheral and GNU radio platform in LINUX. It uses a number of GNU Radio modules along with other Python and C-Shell scripts giving a working baseline structure for a cognitive radio.