Adaptive rate and power transmission in spectrum-sharing systems with statistical interference constraint

The present study attempted to investigate the capacity gains in a spectrum-sharing system where the transmit power and rate of the secondary user (SU) are adapted based on the spectrum sensing information about activity of primary user (PU) and statistical channel fading gain between the SU transmitter (SUT) and PU receiver (PUR). It was assumed that the SU can use the spectrum band originally allocated to PU, based on the definition that when the PU is present in the spectrum band, the SU must consider the peak transmit power and statistical interference constraints. In addition, when the PU is absent at the spectrum band, the SU can only consider the peak transmit power constraint. The main advantage of using statistical interference constraint is that it does not require the instantaneous feedback channel between SUT and PUR. Furthermore, to maximise the achievable capacity of the SU, the average transmit power was first calculated. Then the adaptive rate and power policy were inspected for maximising the achievable capacity under said constraints and bit error rate requirements in multilevel quadrature amplitude modulation. Numerical and comparison results representing the efficiency of the proposed system are also provided.