Multichannel $\Sigma \Delta$ ADCs With Integrated Feedback Beamformers to Cancel Interfering Communication Signals

In multiuser multiantenna communication receivers, the use of high resolution ADCs is costly. In the presence of (strong) interference, more bits are used than would be necessary for quantizing only the signal of interest. Thus, if it is possible to cancel the interference in the analog domain, considerable savings can be realized. In this paper, we exploit the fact that a multiantenna receiver consists of a bank of ADCs and propose a new architecture, wherein a feedback beamformer (FBB) takes a linear combination of the ADC outputs and feeds back the result to be subtracted at the input. This ADC architecture is especially compatible with existing ΣΔ ADCs, that already consist of a digital-to-analog converter (DAC) in the feedback loop and enables sophisticated source separation algorithms designed in the digital baseband to cancel the interfering users in the analog domain. Subsequently, the ΣΔ ADCs digitize only the desired user signals and achieve considerable savings in power consumption. Using a mean squared error criterion and assuming that a training sequence is available, we present an algorithm to design the weights of the FBB. The interference suppression and power savings of the proposed approach are demonstrated via simulation results.