Digital Compensation of Transmitter Leakage in FDD zero-IF Receivers

Transmitter Leakage (Tx Leakage, TxL) has a significant impact on the performance of frequency division duplex (FDD) devices using zero-IF receivers and thus, requires a suitable compensation. In contrast to analog approaches, digital Tx Leakage compensation approaches can easily be reconfigured and therefore, are highly attractive for multi-band mobile devices. In this contribution we present a system model, describing the Tx Leakage impact on the received digital baseband signal. Furthermore, we show analytically that Tx Leakage causes an additional, irreversible SNR loss due to the quantization in the analog-to-digital converter, which limits the applicability of a digital Tx Leakage compensation. However, this SNR loss remains negligible small as long as the TxL interference does not exceed significantly the desired received signal. To compensate Tx Leakage digitally, the TxL channel needs be estimated. In this work we present two TxL channel estimation approaches, suitable for frequency flat and frequency selective channels. It is shown, that the usage of these approaches mitigates effectively the Tx Leakage impact on the system performance. Thus, the system designer can allow much stronger Tx Leakage, which significantly relaxes the requirements on the Tx-Rx isolation of the duplexer and the linearity of the analog receiver frontend. Copyright c 2010 John Wiley & Sons, Ltd.