Practical, real-time, full duplex wireless

Abstract

This paper presents a full duplex radio design using signal inversion and adaptive cancellation. Signal inversion uses a simple design based on a balanced/unbalanced (Balun) transformer. This new design, unlike prior work, supports wideband and high power systems. In theory, this new design has no limitation on bandwidth or power. In practice, we find that the signal inversion technique alone can cancel at least 45dB across a 40MHz bandwidth. Further, combining signal inversion cancellation with cancellation in the digital domain can reduce self-interference by up to 73dB for a 10MHz OFDM signal.This paper also presents a full duplex medium access control (MAC) design and evaluates it using a testbed of 5 prototype full duplex nodes. Full duplex reduces packet losses due to hidden terminals by up to 88%. Full duplex also mitigates unfair channel allocation in AP-based networks, increasing fairness from 0.85 to 0.98 while improving downlink throughput by 110% and uplink throughput by 15%. These experimental results show that a redesign of the wireless network stack to exploit full duplex capability can result in significant improvements in network performance.

Error rates of a full-duplex system over EGK fading channels subject to laplacian interference

“…Furthermore, the CHF of Z is independent of the angle between the real and imaginary components. Consequently, (4) shows that Z follows a circularly symmetric complex Laplace distribution. Theorem 1.…”

“…FD communication relies on the recently developed self-interference (SI) cancellation techniques that enable simultaneous transmission and reception on the same frequency band, which offer better spectral utilization compared to the half-duplex (HD) system [3], [4]. However, implementing SI cancellation at the user's equipment (UE) can be expensive in terms of complexity, power consumption, and/or terminal price.…”

Compact Antennas With Reduced Self Interference for Simultaneous Transmit and Receive

“…Avoiding the issue of the transmitting signal interfering with the receiving signal requires operation at either different times or at different frequencies. However, prospects for creating an in-band full-duplex system, which would allow for transmitting and receiving on the same frequency at the same time, have shown that full-duplex is feasible [1][2][3][4][5][6]. Ideally, this would allow twice as many devices to make use of a given spectrum at any time.…”

Experimental evaluation of interference reduction effect; Eigen-beamforming and digital subtraction by using MIMO-OFDM signals

“…Therefore, the self-interference needs to be suppressed before the RF front-end at the receiver. To combat this, three methods have been studied [5,6,7]. Antenna cancellation uses an additional transmitting antenna to form a null point at the receiving antenna [5].…”

“…Antenna cancellation uses an additional transmitting antenna to form a null point at the receiving antenna [5]. Balun cancellation places a balun circuit between the transmitting and receiving antennas to subtract the self-interference signals from the received signals [6]. Note that these methods cannot be directly applied to MIMO systems because the interference among all combinations of transmitting and receiving antennas must be considered and implementation is difficult.…”