Digital compensation of transmitter leakage in FDD zero‐IF receivers

Abstract

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.

Performance of a digital transmitter leakage LMS-based cancellation algorithm for multi-standard radio-frequency transceivers

“…In such a case, the fractional delay estimated by our algorithm is expected to converge to the position of the maximum of the time impulse response of the synthesized filter (this position is denoted as 'expected fractional delay'). We want to now compare our method with the TxL compensation method presented by [15] (and variations of this method can be found in [16,22,31]), based on a multitap LMS canceller. Figure 13 compares the performances of this multitap-LMS (with 8 taps) and the performance of the proposed scheme for the synthesized filter, with several values of the expected fractional delay.…”

Transmitter leakage analysis when operating USRP (N210) in duplex mode

“…There are implementations of transmitter leakage estimation and cancellation in the digital front end which is independent of the RF front-end used. Though these cancellation techniques are capable of cancelling the leakage, they fail when the transmitter leakage is significant such that the Low Noise Amplifier (LNA) gets saturated and there is no room to retrieve the information from its output [10] [11]. Even if the transmitter leakage is not enough to saturate the LNA, they will be amplified and still increase the difficulty in retrieving the information.…”

Optimum Single Antenna Full Duplex Using Hybrid Junctions

“…Digital cancellation [6], [7], [11]- [13], although effective and easy to implement in baseband DSP, cannot prevent self-interference from overloading the receiver front end, which would prevent any recovery of the receive signal. Analog cancellation [4]- [6], [8], [10], [14], [15], can provide significant isolation prior to the receiver, reducing selfinterference and preventing receiver overloading, making it a requirement in most practical systems [4].…”