Analog Least Mean Square Loop for Self-Interference Cancellation: A Practical Perspective

Abstract

Self-interference (SI) is the key issue that prevents in-band full-duplex (IBFD) communications from being practical. Analog multi-tap adaptive filter is an efficient structure to cancel SI since it can capture the nonlinear components and noise in the transmitted signal. Analog least mean square (ALMS) loop is a simple adaptive filter that can be implemented by purely analog means to sufficiently mitigate SI. Comprehensive analyses on the behaviors of the ALMS loop have been published in the literature. This paper proposes a practical structure and presents an implementation of the ALMS loop. By employing off-the-shelf components, a prototype of the ALMS loop including two taps is implemented for an IBFD system operating at the carrier frequency of 2.4 GHz. The prototype is firstly evaluated in a single carrier signaling IBFD system with 20 MHz and 50 MHz bandwidths, respectively. Measured results show that the ALMS loop can provide 39 dB and 33 dB of SI cancellation in the radio frequency domain for the two bandwidths, respectively. Furthermore, the impact of the roll-off factor of the pulse shaping filter on the SI cancellation level provided by the prototype is presented. Finally, the experiment with multicarrier signaling shows that the performance of the ALMS loop is the same as that in the single carrier system. These experimental results validate the theoretical analyses presented in our previous publications on the ALMS loop behaviors.

Unbalanced Hybrid AOA/RSSI Localization for Simplified Wireless Sensor Networks

“…The simulation results show that the 1AOA/nRSSI LS estimator is suitable when more accurate RSSI measurements are available, while the subspace method is more suitable in a shadowing environment with an acceptable increase in the number of anchors and computational complexity. Possible future directions include improving the precision of 1AOA/nRSSI localization algorithms using different approaches listed in Section 4 and adopting an analog least mean square loop presented in [ 29 , 30 , 31 , 32 ] for a more accurate ranging estimation. Additionally, we might consider orthogonal frequency division multiplexing (OFDM) for correlated multipath fading channels [ 33 ] in the localization and positioning contexts.…”

Outage Probability and Throughput Analyses in Full-Duplex Relaying Systems With Energy Transfer

“…The future work would be the extension of our proposed system to the case of multiple antennas [33], multiple users [34], and multiple relays [8]. We might also consider nonlinear RF EH models [22], [23] and examine other SI cancellation techniques, such as the analog least mean square loops [35]- [38], to cancel the SI at the relay. .…”

Analog Least Mean Square Adaptive Filtering for Self-Interference Cancellation in Full Duplex Radios

“…Therefore, as long as a sufficiently high loop gain is provided, the ALMS loop achieves a substantial SIC, typically about 40 to 60 dB based on practical prototyping [12].…”

“…Additionally, although the structure of the ALMS loop is relatively simple, its implementation is still a challenge, since no high-gain multiplier is available in practical RF bands at high carrier frequencies. These problems are tackled in [12] as follows. The pair of multipliers in each tap of the ALMS loop are replaced by a quadrature demodulator and a modulator, respectively.…”

“…Practical imperfections of the ALMS loop, such as its I/Q imbalance in the I/Q modulators and demodulators, on its performance were analyzed in [11]. An experimental prototype was also developed for verifying the theoretical results and for demonstrating the ALMS loops potential for efficient SIC [12].…”