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RF Self-interference Cancellation for Full-duplex Communication by Using Photonic Technique
Abstract
A photonic approach based on phase modulation and optical sideband filtering for cancelling the RF self-interference in full-duplex communication system is proposed and experimentally demonstrated with good cancellation performance.
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The wireless research community aspires to conceive full duplex operation by supporting concurrent transmission and reception in a single time/frequency channel for the sake of improving the attainable spectral efficiency by a factor of two as compared to the family of conventional half duplex wireless systems. The main challenge encountered in implementing FD wireless devices is that of finding techniques for mitigating the performance degradation imposed by self-interference. In this article, we investigate the potential FD techniques, including passive suppression, active analog cancellation, and active digital cancellation, and highlight their pros and cons. Furthermore, the troubles of FD medium access control protocol design are discussed for addressing the problems such as the resultant end-to-end delay and network congestion. Additionally, an opportunistic decode-and-forward- based relay selection scheme is analyzed in underlay cognitive networks communicating over independent and identically distributed Rayleigh and Nakagami-m fading channels in the context of FD relaying. We demonstrate that the outage probability of multi-relay cooperative communication links can be substantially reduced. Finally, we discuss the challenges imposed by the aforementioned techniques and a range of critical issues associated with practical FD implementations. It is shown that numerous open challenges, such as efficient SI suppression, high-performance FD MAC-layer protocol design, low power consumption, and hybrid FD/HD designs, have to be tackled before successfully implementing FD-based systems.
In this paper, we design a self-interference cancellation (SIC) scheme for in-band full-duplex (IBFD) radio-over-fiber (RoF) systems based on wavelength division multiplexing passive optical network (WDM-PON) architectures. By using a single dual-drive Mach-Zehnder modulator (DDMZM), over various bands up to 25 GHz, this proposed SIC system can simultaneously cancel the in-band downlink (DL) self-interference and modulate the recovered uplink (UL) radio frequency (RF) signal. OFDM-RF signals are used to study the cancellation performances of optical SIC system for the first time. Experimental results show more than 32-dB cancellation depth over 250-MHz bandwidth within 1-GHz RF band, as well as 300-MHz within 2.4-GHz and 400-MHz within 5-GHz band. As for 2.4-GHz RF band, 390.63-Mbps 16-QAM OFDM UL signal buried by strong in-band DL OFDM signal is well recovered. For broadband applications, more than 27-dB cancellation depth is achieved over 10 MHz~25 GHz wideband, so that up to 25 GHz RF band can be expanded for this IBFD WDM-RoF system.
A wideband co-site co-channel interference cancellation system (ICS), based on hybrid electrical and optical techniques, is proposed and is experimentally demonstrated. The demonstrated cancellation system subtracts the in-band wideband interfering signal from the received signal, such that the weak signal of interest (SOI) can be recovered. Our system utilizes a broadband radio frequency (RF) Balun transformer to invert the phase of the interfering signal, while electro-absorption modulated lasers are used for converting the RF signals into the optical domain to enable fine adjustment with the hybrid ICS. We experimentally achieve 45 dB of cancellation over a 220 MHz bandwidth, and over 57 dB of cancellation for a 10 MHz bandwidth, at a center frequency of 900 MHz. The proposed system also experimentally shows good cancellation (30 dB) over an enormously wide bandwidth of 5.5 GHz. To the best of our knowledge, this is the first demonstration of such a wide bandwidth cancellation with good cancellation depth. This property is extremely useful when there are multiple interference signals at various frequency bands. The proposed hybrid ICS has a spurious-free dynamic range of . Moreover, a SOI is recovered from a strong interfering signal, sweeping over 3 GHz bandwidth. A widely open eye diagram, as well as error-free bit-error rate measurements, is experimentally achieved, with the use of the hybrid ICS. The approach also works well for various frequency bands that are within the bandwidth of the Balun transformer and electro-absorption modulated lasers.
In-band full-duplex (IBFD) operation has emerged as an attractive solution
for increasing the throughput of wireless communication systems and networks.
With IBFD, a wireless terminal is allowed to transmit and receive
simultaneously in the same frequency band. This tutorial paper reviews the main
concepts about in-band full-duplex wireless .A key challenge behind IBFD
operation is mitigation of self-interference, i.e., the interference caused by
an IBFD node's own transmissions to its desired receptions. A wide array of
techniques proposed in the literature for IBFD self-interference suppression
are surveyed in this tutorial. Also discussed are numerous research challenges
and opportunities in the design and analysis of IBFD wireless systems
Full-Duplex (FD) wireless technology enables a radio to transmit and receive on the same frequency band at the same time, and it is considered to be one of the candidate technologies for the fifth generation (5G) and beyond wireless communication systems due to its advantages including potential doubling of the capacity and increased spectrum utilization efficiency. However, one of the main challenges of the FD technology is the mitigation of strong Self-Interference (SI). Recent advances in different SI cancellation techniques such as antenna cancellation, analog cancellation and digital cancellation methods have led to the feasibility of using FD technology in different wireless applications. Among potential applications, one important application area is Dynamic Spectrum Sharing (DSS) in wireless systems particularly 5G networks, where FD can provide several benefits and possibilities such as Concurrent Sensing and Transmission (CST), Concurrent Transmission and Reception (CTR), improved sensing efficiency and secondary throughput, and the mitigation of the hidden terminal problem. In this direction, first, starting with a detailed overview of FD-enabled DSS, we provide a comprehensive survey of recent advances in this domain. We then highlight several potential techniques for enabling FD operation in DSS wireless systems. Subsequently, we propose a novel communication framework to enable CST in DSS systems by employing a power control-based SI mitigation scheme and carry out the throughput performance analysis of this proposed framework. Finally, we discuss some open research issues and future directions with the objective of stimulating future research efforts in the emerging FD-enabled DSS wireless systems.
We perform a full radio frequency (RF) characterization of the first integrated microwave photonic interference canceller. The photonic integrated circuit is one of the first to possess only RF inputs and outputs, with monolithically integrated optical sources and detectors. The characterization is important to developing an in-depth understanding of the integrated circuit's effect on RF receivers. We characterize the circuit's gain, noise figure, input intercept point, 1-dB compression point, and spurious-free dynamic range as functions of ON-chip device bias points and frequency up to 6 GHz. We find that the circuit's RF properties are almost exclusively determined by the directly modulated laser. Link gain is primarily driven by the laser slope efficiency. The noise figure is dominated by signal attenuation and laser relative intensity noise. The circuit nonlinearity is the third-order intermodulation product limited. With the exception of link gain, all properties improved with increasing laser bias, saturating at 30 mA. Meanwhile, all properties degraded with increasing frequency. External optical feedback from the reflections OFF of waveguide transitions in the monolithic circuit created operating points of high noise figure and low gain, and should be avoided during operation. The circuit can be improved by implementing a balanced link architecture to suppress the laser relative intensity noise and using external modulators to improve the link linearity and bandwidth.
We demonstrate an analog optical self-interference cancellation system for over-the-air multipath cancellation in radio-frequency communications. Self-interference cancellation is achieved by subtracting a matched copy of the self-interference signal from the corrupted received signal. The system uses optical signal processing instead of traditional radio-frequency approaches to achieve wide instantaneous bandwidth and high precision. Channel matching is performed entirely in the optical domain with variable optical attenuators and tunable optical delays. A singlemode to multimode combiner enables the cancellation of up to 6 multipath components using just 2 optical sources. The system achieved 35 dB of narrowband cancellation and 30 dB of cancellation across 20 MHz of instantaneous bandwidth, with multipath cancellation contributing more than 10 dB of cancellation at the signal of interest frequency.