To meet rapidly growing traffic demands and accommodate large number of devices, more radio spectrum is needed for future wireless communications. Considering the scarcity of radio spectrum, it is needed to enhance the utilization of radio spectrum licensed exclusively to specific users. In cognitive radio, an unlicensed user, called a secondary user, is permitted to access the spectrum allocated to a licensed user, called a primary user. When the primary and secondary users transmit their signals simultaneously, interference occurs at both users which degrades their performance. Interference at the primary user can be avoided by spectrum sensing technique which prohibits a secondary user from transmitting its signal when it detects a primary user’s signal. Also, interference level at the primary user can be limited below a certain threshold by spectrum sharing technique in which the secondary user adjusts its transmit power accordingly. Some recent results on cognitive radio are introduced, and its applications and future research subjects are shown.
Date: 8th June at 11:00 am.
Local: Lecture Hall A4, Department of Electrical and Computer Engineering, Faculty of Science and Technology, University of Coimbra.
GPS coordinates (Latitude: 40°11'10.38"N, Longitude: 8°24'59.13"W).
Jae Hong Lee
Professor, Department of Electrical and Computer Engineering
Seoul National University
(Distinguished Speaker of the IEEE Vehicular Technology Society)
Sungoh Kwon, Ulsan University, Republic of Korea
Date & Time: Thursday, June 7, 16:00
Location: Instituto Superior Técnico, Lisbon, Abreu Faro Amphitheatre, Interdisciplinary Building
Milimeter-wave links can provide Gbit/s data rates but are highly susceptible to blockage. In case a direct line-of-sight communication path becomes blocked, communication via a reflected path may allow to maintain connectivity. A common approach is to switch to such an alternative path whenever the first path becomes blocked. However, this requires detecting the blockage and then reconfiguring the transceiver to use the new path, which incurs latency. For traffic with strict latency or reliability requirements, or in highly dynamic environments where path switching would be frequent, using both paths concurrently can be more beneficial. In this work, we consider using multiple paths and dividing the transmission power over those paths, instead of path switching. We propose an algorithm to allocate power among the different mmWave communication paths to overcome link blockage under randomly distributed obstacles. The power allocation algorithm is based on analysis of the blockage probabilities of the direct and reflected paths using geometric probability, to statistically maximize the overall capacity of the path between two nodes. We evaluate the performance of the proposed algorithm via simulation for various wireless environments. More Information..