Digital compensation of transmitter leakage in FDD zero-IF receivers

Transmitter leakage (TxL) has a significant impact on the performance of frequency division duplex devices using zero-IF receivers and thus requires a suitable compensation. In contrast to analog approaches, digital TxL compensation approaches can easily be reconfigured and therefore are highly attractive for multiband mobile devices. In this contribution, we present a system model, describing the TxL impact on the received digital baseband signal. Furthermore, we show analytically that TxL causes an additional, irreversible signal-to-noise loss due to the quantisation in the analog-to-digital converter, which limits the applicability of a digital TxL compensation. However, this signal-to-noise ratio loss remains negligibly small as long as the TxL interference does not exceed significantly the desired received signal. For TxL to be compensated 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 TxL impact on the system performance. Thus, the system designer can allow much stronger TxL, which significantly relaxes the requirements on the transmitter–receiver isolation of the duplexer and the linearity of the analog receiver frontend. Copyright © 2011 John Wiley & Sons, Ltd. *Correspondence Andreas Frotzscher, Bell Labs, Alcatel-Lucent, Lorenzstr. 10, Stuttgart, Germany. E-mail: [email protected] Received 19 January 2011; Revised 10 August 2011; Accepted 29 August 2011