The Cross-Channle Gain Estimation Techniques Between Layers For Spectrum Sharing

In recent years, in order to alleviate the problems of spectrum resources shortage and low spectrum utilization rate, the concept of cognitive radio is put out. The spectrum sharing technology of cognitive radio technology is becoming a popular technology in cognitive radio system. In the spectrum sharing, the cross-channel gain estimation between Cognitive Transmitter and the Primary Receivers is an important factor influencing the cognitive ability. The traditional spectrum sensing methods are mainly passive detections, though it doesn’t cause interference to the Primary Receivers, but needs to closely cooperate with the primary system, which is obviously impractical. Nowadays, some researchers proposes a new category of estimation methods, called proactive estimation of spectrum sensing technology, but when the cognitive users trying to access into the spectrum, interference follows. The main contributions of this thesis are providing the methods about cross-channel gain estimation between layers for spectrum sharing.First, the thesis proposes a method about relay-assisted cross-channel gain estimation with interference-free. In this method, we design different estimators based on the arrival time difference between Primary Transmitter-Primary Receiver link and Primary Transmitter-Cognitive Transmitter-Primary Receiver link. To avoid the signal interference to the Primary Receiver, Cognitive Transmitter acts as a full-duplex relay forwarding and amplifying the signal from the Primary Transmitter to the Primary Receiver,which triggers the close-loop power control between Primary Transceivers. By measuring the power adjustment of the primary signal, the Cognitive Transmitter estimates the cross-channel gain. Simulation results show that under the premise of keeping the same estimation error, the interference probability of our method can reduced to 5% from 100%in the traditional method.Then, the thesis proposes a method about relay-assisted cross-channel gain estimation with interference-free under complex environment, this method is more suitable for the primary system in a dynamic target signal noise ratio scenario. In this method, we first estimate the target signal noise ratio by the relationship between the amplify-and-forward gain and the ratio of Primary Receiver target signal noise ratio to Cognitive Transmitter Receives signal to noise ratio. Unlike the first method, we let the cognitive Transmitter add a time delay which forces the arriving time difference between Primary TransmitterPrimary Receiver link and the Primary Transmitter-Cognitive-Transmitter-Primary Receiver link arrival time difference to be large enough, and the estimator design can be more simplified. Simulation results demonstrate that the proposed method can reduce the interference to the PR and improve the successful estimation probability in comparison with the existing methods.Finally, we introduce the contribution of this thesis, and analyses the future works.