Exploiting spatial dimension in cognitive radios and networks

This paper studies the maximum number of users that can be allocated in the same frequency band in case of using beamforming in a transmitter and a receiver by simulations. With the use of smart antennas the spectrum can be used efficiently, and at the same time the quality of service (QoS) of secondary users is increased in comparison with omnidirectional antennas. The results indicate that more users can transmit in the same area while fulfilling QoS constraints. The obtained results regarding spectrum sensing state that beamforming gives a great improvement in comparison with detection with omnidirectional antennas. Beamforming leads to power savings because the transmission power is sent to the wanted direction. In addition, directional antennas decrease the time needed for sensing and therefore more time for secondary transmission is left than with omnidirectional antennas.