Secondary Transceiver Design in the Presence of Frequency Offset between OFDM-Based Primary and Secondary Systems

In a cognitive network where both primary and secondary systems are Orthogonal Frequency Division Multiplexing modulated, carrier frequency offset between the two systems is inevitable and may cause harmful interference. In this paper, we jointly optimize the transceiver for the secondary system considering the frequency offset between secondary transmitter (ST) and primary receiver (PR). We first derive unified interference constraints with different information of inference channels known at ST, and formulate the transceiver design problem based on minimum mean square criterion as a convex optimization problem. To reveal the structure of secondary transceiver, we derive closed-form pre- processors in two special cases. It is shown from the simulations that with the increase of frequency offset, the performance of primary system degrades evidently when its bandwidth is smaller than that of secondary system, whereas the performance of secondary system using the proposed transceiver improves due to frequency diversity.