Transmit and receive crosstalk cancellation

In modern mobile communication systems higher bandwidths are required by users. But higher bandwidths mean, that in Frequency Division Duplex (FDD) standard where uplink and downlink is separated, the receive band has to be protected against the transmit band. Violation of the receiver is caused by distortion coming from the transmitter, which is insufficiently suppressed by Transmit (TX) duplex filter in the receive (RX) band. Another type of distortion is called passive intermodulation (PIM). Reason for this is material nonlinearity and contact nonlinearity. The aim of this paper is to find a mathematical description of the passive nonlinearities and to reduce them in the digital baseband of the receiver. Two modeling techniques namely linear and nonlinear, the underlying algorithm and implementation of this algorithm on Gaussian Minimum Shift Keying (GMSK) modulated signals have been discussed and the results are presented. Firstly a brief introduction to intermodulation distortion is provided, followed by an overview of the hardware setup so that the reader can get acquainted to the hardware configuration used. An overview of the algorithm, which is the essence and underlying concept for intermodulation distortion suppression, is discussed, and finally implementation of this algorithm on GMSK signals along with its results is presented.