The Research Of Pahse Synchronization For Distributed Beamforming In Cognitive Radio Networks

With the substantial increase in user demand for wireless communications, the existing rae spectrum resources have faced increasingly serious challenges. And unreasonable division of private and public spectrum made this problem even worse. For this case, cognitive radio networks has been proposed by Joeseph Mitola in1999. In cognitive radio networks, Secondary User (SU) need to communicate with each other, not interferencing with Primary Users (PU) or causeing the interference below certain threshold by finding spectrum hole, or doing beamforming(BF) via antenna array.For this special need of SU, beamforming (BF) just right fit this demand in which several antennas combine to form an antenna array, adjusting their complex beamforming weightings to change the Receive Signal Strength (RSS) at different positions, resulting in high RSS in certain positions and low RSS in others. The principle of BF in cognitive radio networks is to increase the RSS of receive SU and decrease the RSS of PU. BF is divided into centralized beamforming and distributed beamforming (DBF). DBF is a cooperative communication technology in wireless system, which describes the situation that a cluster of distributed source nodes emulate a virtual antenna array, adjusting their beamforming weights so as to transmit their common message to the target destination node. The advantage of DBF is the low complecity of hardware device where one terminal is at least equipped with one single antenna, making it possible for DBF in small terminal.However, the biggest difference of DBF and BF is the antennas are divided in to a cluster of SUs, not centralized. Since they are equipped in different SU and every SU has a different Local Oscillator (LO), the carrier phases of each SU are different from each other. Without phase synchronization, the received signal at SU may cancel each other out, result in low RSS which may not reach the threshold. Not only that, the interference of SU cluster to PU should be considered in cognitive radio networks as well. So. phase synchronization is of great importance to the performance of DBF.This paper focuses on the phase synchronization algorithm of distributed beamforming in cognitive radio networks in order to work out efficient and fast phase synchronization algorithm. An algorithm named GAP(Gradualiy Adjust Phase) is proposed which has less overheads, less energy consumption, and lower complicity compared with the previous algorithms. RRI(Rapid Reduce Interference) algorithm is proposed for reducing interference of PU. SUs can use GAP and RRI algorithm to do DBF, making high RSS at receive SU and suppressing interference on the PU effectively at the same time.