Cognitive MIMO radio

Abstract

The supply of available radio frequency spectrum is in a state of shortage. Whereas demand for spectrum in the most useful frequencies exceeds supply and some statically allocated spectrum bands experience low utilization. Currently the spectrum assignment for the exclusive use to licensed services is highly inefficient. This is due to the high variability of the traffic statistics across time, space and frequency. Basically the spectrum usage is typically concentrated over certain portions of the spectrum, while a significant amount of the licensed bands (or idle slots in static time division multiple access (TDMA) systems with bursty traffic) remains unused or under-utilized for 90% of time. A Cognitive Radio (CR) is a technology that is capable of exploiting unused or lightly used spectrum and is a promising mechanism to achieve efficient use of the frequency resource by allowing the coexistence of licensed (primary) and unlicensed (secondary) users in the same bandwidth. This project was proposed with the aim to design a prototype for unlicensed secondary users (SUs) to dynamically access the unused white spaces in the licensed spectrum held by primary users (PUs) in order to increase the efficiency of spectrum utilization. Multiple Input Multiple Output (MIMO) technology is used in our Cognitive Radio system as MIMO system prominently increases the spectral efficiency of a wireless system. In our project, we consider a simple cognitive MIMO system, in which the cognitive link has two transmission antennas and two receive antennas. By monitoring the activity of the primary user through spectrum sensing technique, the cognitive link lets the secondary user to communicate when it senses an idle slot. MIMO uses spatial multiplexing as the transmission technique to provide additional data capacity. This prototype enables us to use the available natural frequency resource efficiently and allows the secondary user to transmit on the same available bandwidth without paying revenue.