On Full-Duplex Radios With Modulo-ADCs

Wireless full-duplex (FD) transceivers have become more commonplace in the recent years, enabled by improvements in hardware as well as in signal processing algorithms dedicated to self-interference (SI) mitigation. A key design target for any FD radio is to limit the analog-to-digital converter (ADC) quantization noise affecting the signal of interest (SoI), which results from the difference in dynamic range between the SI and the SoI at the input of the ADC. Indeed, when using conventional ADCs, since the SI power is much larger than that of the SoI, the SI spans most of the ADC's dynamic range and the SoI becomes distorted by a large quantization noise. Reducing the power of the SI before the ADC, for example via analog domain SI cancellation, is so far the only means to mitigate this undesired effect. In this paper we consider the use of so-called modulo ADCs as a new tool to reduce the quantization noise that affects the SoI in the presence of SI. We demonstrate theoretically and numerically that by substituting the conventional ADCs with modulo-ADCs, which fold the analog input signal before analog-to-digital conversion, and by using appropriately designed analog gain control and digital-domain SI cancellation, one can reduce the quantization noise that affects the SoI. As such, the work in this paper provides a new technique for counteracting the detrimental effect of SI in analog-to-digital conversion and, thus, provides a new route to be explored in order to enhance the performance of FD radios.