Di Meo, Gennaro Digital Cancellation Techniques Toward Full-Duplex Radios. [Tesi di dottorato]

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Abstract

In this thesis, the Least Mean Square (LMS) based adaptive filters are analyzed with the aim to design a digital cancellation algorithm able to suppress the self-interference (SI) in the In-Band Full-Duplex (IBFD) transceiver. The LMS algorithm updates its impulse response by minimizing the mean square error (MSE) between its output and an external, reference solicitation, thus allowing operations as system identification, channel equalization, and noise cancellation. The intensive usage of arithmetic circuits and registers in the updating process makes the hardware realization challenging from a power consumption point of view. With the aim to overcome this point, four low-power implementations are proposed in which (i) approximate multipliers are used in the FIR section, (ii) the coefficients smaller than an external threshold are stuck at zero, (iii) a variable rounding is used to change the precision of the input samples in the feedback, and (iv) the approximation of the input samples is used along with the absolute value of the error signal for the learning. The first and the second approaches allow a power improvement up to 32% at the cost of a degradation of the regime MSE, whereas the third and the fourth methods exhibits the best trade-off between energy dissipation and quality of results. In particular, the approximate technique with the error absolute value achieves a power reduction of about 45-50% with regime MSE practically unchanged with respect to the exact implementation. Also experimental results, obtained by measuring a chip designed in TSMC 28nm CMOS technology, confirmed the simulation analyses. In the last part of this work, the digital cancellation algorithm for the IBFD transceiver is realized by using a Delayed LMS and two filtered-x LMS and filters. The design is also able to overcome the issues due to the nonlinearities of the power amplifier. The simulation results show the possibility to reduce the SI to the level of the receiver noise floor with a cancellation of about 58dB. The electrical performances, obtained by means of post-place and route analyses, benefit from the low-power technique with module error and approximate inputs. Each AF dissipates the 20% of the total power and occupy about 30% of the total core area.

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