A Digital Self-Interference Cancellation Scheme for In-Band Full-Duplex-Applied 5G System and Its Software-Defined Radio Implementation

Abstract

The development of mobile communication technology toward 6G is difficult because the required spectrum resources have already been allocated to existing systems. Therefore, new communication systems must have high spectral efficiency to effectively utilize the available resources. This article proposes a digital self-interference (SI) canceller that can be applied to full-duplex cellular systems based on the current 5G signal format (5G-FDC) to introduce in-band full-duplex systems beyond 5G. Specifically, we reorganize the 5G demodulation reference signal (DMRS) and define a novel DMRS configuration, in which the DMRSs for uplink and downlink communications do not interfere with each other. The proposed DMRS configuration effectively improves the accuracy of the SI channel estimation. Moreover, we propose a channel extrapolation scheme that suppresses the channel estimation degradation, which deteriorates the block error rate performance. Additionally, we propose a noise estimation method to improve the low-density parity check decoding performance of the desired signal in 5G-FDC systems. The effectiveness of the proposed method is demonstrated through computer simulations and experimentally by using our developed and implemented software-defined radio-based 5G-FDC prototype. Digital SI cancellation performances of 50 dB and 30.6 dB are observed in the simulation and experimental evaluations, respectively.INDEX TERMS 5G, full-duplex cellular, in-band full-duplex, self-interference, software-defined radio.

Inter-User Interference Cancellation Scheme for 5G-Based Dynamic Full-Duplex Cellular System

“…where 𝑋 DLD and 𝑋 ULD denote the transmitted DL-DMRS and UL-DMRS, respectively. First, the estimated noise power, 𝜎 2 ̃, is obtained using DL-DMRS, following a procedure similar to 5G-based SI cancellation [12]. Subsequently, the powers of DL-DMRS, 𝑃 DL , and UL-DMRS, 𝑃 IUI , are calculated as follows: where E[•] represents the expected value.…”

“…However, in the current 5G systems, which do not operate as FDC systems, the UL/DL signals may interfere with the DMRSs contained in the DL/UL signal (DL-DMRS/UL-DMRS). Hence, we adopted the DMRS configuration proposed for 5G-based SI cancellation [12].…”

“…The rationale here is that when the demodulation accuracy of the IUI signal is sufficiently high, IUI and SI cancellations can be considered equivalent. Therefore, only the estimated noise power term is utilized [12]. The noise terms are replaced as follows:…”

“…For instance, the SI cancellation performance of wireless fidelity (Wi-Fi) systems can reach up to 110 dB [10]. Digital SI cancellation schemes have been proposed for 5G (referred to as 5G-based SI cancellation) and long-term evolution (LTE) signals in [12] and [13], respectively, significantly enhancing the feasibility of FDC systems.…”

“…The DL-UE firstly demodulates the IUI signal and subtracts it from the received signal. Considering the coexistence of IUIC and SI cancellations, the proposed IUIC leverages the configuration of a demodulation reference signal (DMRS), as originally proposed for SI cancellation [12], to estimate the IUI channel. Subsequently, it removes the IUI signal by demodulating and subtracting it from the received signal.…”