Simultaneous transmit and receive (STAR) allows full-duplex operation of a radio, which leads to doubled capacity for a given bandwidth. A circulator with high-isolation between transmit and receive ports, and low-loss from the antenna to receive port is typically required for achieving STAR. Conventional circulators do not offer wideband performance. Although wideband circulators have been proposed using parametric, switched delay-line/capacitor, and N-path filter techniques using custom integrated circuits, these magnet-free devices have non-linearity, noise, aliasing, and switching noise injection issues. In this paper, a STAR front-end based on passive linear microwave circuit is proposed. Here, a dummy antenna located inside a miniature RF-silent absorption chamber allows circulator-free STAR using simple COTS components. The proposed approach is highly-linear, free from noise, does not require switching or parametric modulation circuits, and has virtually unlimited bandwidth only set by the performance of COTS passive microwave components. The trade-off is relatively large size of the miniature RF-shielded chamber, making this suitable for base-station side applications. Preliminary results show the measured performance of Tx/Rx isolation between 25-60 dB in the 1.0-3.0 GHz range, and 50-60 dB for the 2.4-2.7 GHz range.
The availability of large unused spectrum at millimeter wave (mmWave) frequency bands has steered the future 5G research towards these bands. However, mmWave signals are attenuated severely in the non-lineof-sight (NLOS) scenarios, thereby leaving the strong link quality by a large margin to line-of-sight (LOS) links. In this paper, a passive metallic reflector is used to enhance the coverage for mmWave signals in an outdoor, NLOS propagation scenarios. The received power from different azimuth and elevation angles are measured at 28 GHz in a parking lot setting. Our results show that using a …
Propagation channel characteristics are substantially different in sub-6 GHz and millimeter-wave (mmWave) bands. A typical mmWave link experiences more than an order-of-magnitude larger path loss and is more susceptible to blockages than a traditional sub-6 GHz link. Therefore, extensive measurement campaigns with efficient channel sounders are needed for a complete understanding of the mmWave propagation channel characteristics. In addition, solutions should be sought to overcome the outage problems associated with the mmWave bands and to achieve acceptable communication performance. In this …
Modern radio systems and transceivers utilize carrier aggregation (CA) to meet the demands for higher and higher data rates. However, the adoption of CA in the existing Long Term Evolution (LTE)-Advanced and emerging 5G New Radio (NR) mobile networks, in case of frequency division duplexing (FDD), may incur self-interference challenges with certain band combinations. More specifically, the nonlinear distortion products of the transmit signals or component carriers (CCs), stemming from the passive radio frequency (RF) front-end components of the transceiver, can appear in one or more of the con…
Neural Network Based Framework for Passive Intermodulation Cancellation in MIMO Systems
School of Mathematical Sciences, Institute of Natural Sciences, MOE-LSC, Shanghai Jiao Tong University（数学科学学院、自然科学院、MOE-LSC、上海交通大学）；Huawei Technologies Co., Ltd., Shenzhen, Guangdong, China（华为技术有限公司，深圳，广东，中国）
This paper proposes an active radio frequency (RF) cancellation solution to suppress the transmitter (TX) passband leakage signal in radio transceivers supporting simultaneous transmission and reception. The proposed technique is based on creating an opposite-phase baseband equivalent replica of the TX leakage signal in the transceiver digital front-end through adaptive nonlinear filtering of the known transmit data, to facilitate highly accurate cancellation under a nonlinear TX power amplifier (PA). The active RF cancellation is then accomplished by employing an auxiliary transmitter chain, …
Multiple-input multiple-output (MIMO) techniques can help in scaling the achievable air-to-ground (A2G) channel capacity while communicating with drones. However, spatial multiplexing with drones suffers from rank deficient channels due to the unobstructed line-of-sight (LoS), especially in millimeter-wave (mmWave) frequencies that use narrow beams. One possible solution is utilizing low-cost and low-complexity metamaterial-based intelligent reflecting surfaces (IRS) to enrich the multipath environment, taking into account that the drones are restricted to fly only within well-defined drone co…
We propose and experimentally demonstrate an interference management system that removes wideband wireless interference by using photonic signal processing and free space optical communication. The receiver separates radio frequency interferences by upconverting the mixed signals to optical frequencies and processing the signals with the photonic circuits. Signals with GHz bandwidth are processed and separated in real-time. The reference signals for interference cancellation are transmitted in a free space optical communication link, which provides large bandwidth for multi-band operation and …
As the spectrum under 6 GHz is being depleted, pushing wireless communications onto millimeter wave (mmWave) frequencies is a trend that promises multi-Gbps data rate. mmWave is therefore considered as a key technology for 5G wireless systems and has attracted tremendous research efforts. The booming research on mmWave necessitates a reconfigurable mmWave testbed that can be used to prototype and validate new research ideas in real wireless environments. In this paper, we develop an easy-to-use mmWave testbed using commercial off-the-shelf devices (USRP and 60 GHz Tx/Rx RF frontends) and open-…
We design and experimentally demonstrate a radio frequency interference management system with free-space optical communication and photonic signal processing. The system provides real-time interference cancellation in 6 GHz wide bandwidth.
A digital-assisted photonic analog wideband radio-frequency multipath self-interference cancellation (SIC) and frequency downconversion method based on a dual-drive Mach-Zehnder modulator and the recursive least square (RLS) algorithm is proposed and demonstrated for in-band full-duplex systems. Besides the reference for the direct-path self-interference (SI) signal, the RLS algorithm is used to construct another reference for the residual SI signal from the direct path and the SI signals from the reflection paths. The proposed method can solve the performance limitation in the previously repo…
One of the main obstacles in full-duplex radios is analog-to-digital converter (ADC) saturation on a receiver due to the strong self-interference (SI). To solve this issue, researchers have proposed two different types of analog self-interference cancellation (SIC) methods -- i) passive suppression and ii) regeneration-and-subtraction of SI. For the latter case, the tunable RF component, such as a multi-tap circuit, reproduces and subtracts the SI. The resolutions of such RF components constitute the key factor of the analog SIC. Indeed, they are directly related to how well the SI is imitated…
A digitally-assisted photonic analog domain self-interference cancellation (SIC) and frequency downconversion method is proposed for in-band full-duplex multiple-input multiple-output (MIMO) systems using the least square (LS) algorithm with adaptive order. The SIC and frequency downconversion are achieved in the optical domain via a dual-parallel Mach-Zehnder modulator (DP-MZM), while the downconverted signal is processed by the LS algorithm with adaptive order that is used to track the response of the multipath self-interference (SI) channel and reconstruct the reference signal for SIC. The …
In this paper, we propose a closely spaced multi-antenna system with \textit{passive} self-interference cancellation (\textit{p}-SIC) of $\approx 90$ dB between the transmitter and receiver antenna for full-duplex application. The \textit{p}-SIC is achieved by field confinement near individual antennae using shorted metallic vias and the application of U-shaped perturbation in the ground plane. The \textit{p}-SIC technique is initially implemented in a 1-Tx and 1-Rx antenna system and explained using transmission line-based theory. Further, it is extended to 1-Tx and 2-Rx configurations. Here …
This paper presents an analysis of the Orthogonal Time Frequency Space (OTFS) modulation scheme when applied to realistic vehicular channel situations. OTFS modulates symbols in delay-Doppler domain, hoping to exploit diversity in both. The penalty for doing this is the requirement of complex interference cancellation equalizers, as this domain incurs a strong amount of intercarrier and intersymbol interference. We conduct this analysis using measured millimeter wave vehicular channels, and we assume typical physical layer settings for a performance analysis. Our results show that there is a c…
The millimeter wave spectra at 71-76GHz (70GHz) and 81-86GHz (80GHz) have the potential to endow fifth-generation new radio (5G-NR) with mobile connectivity at gigabit rates. However, a pressing issue is the presence of incumbent systems in these bands, which are primarily point-to-point fixed stations (FSs). In this paper, we first identify the key properties of incumbents by parsing databases of existing stations in major cities to devise several modeling guidelines and characterize their deployment geometry and antenna specifications. Second, we develop a detailed uplink interference framew…
Millimeter wave (mmWave) full-duplex (FD) is a promising technique for improving capacity by maximizing the utilization of both time and the rich mmWave frequency resources. Still, it has restrictions due to FD self-interference (SI) and mmWave's limited coverage. Therefore, this study dives into FD mmWave MIMO with the assistance of reconfigurable intelligent surfaces (RIS) for capacity improvement. First, we demonstrate the angular-domain reciprocity of FD antenna arrays under the far-field planar wavefront assumption. Accordingly, a strategy for joint downlink-uplink (DL-UL) channel estimat…
CubeSounder: Low SWaP-C 180 GHz Radiometer for Atmospheric Sensing Tested on High Altitude Balloons
National Radio Astronomy Observatory（国家射电天文台）；Arizona State University School of Earth and Space Exploration（亚利桑那州立大学地球与空间探索学院）；Arizona State University School of Electrical, Computer, and Energy Engineering（亚利桑那州立大学电气、计算机与能源工程学院）
