Joint Beam Steering and Nulling Angle Perturbation for Tx-Rx Isolation Enhancement in FD mMIMO

Strain imaging has been performed using 1D, 2D and 3D ultrasound data. Usually, strain is only estimated in the beam direction, because of the availability of phase information. However, strain estimates in other directions are also desired, since most tissues are anisotropic. Beam steering enables measurement of different projections of the 2D displacement field while using phase information. The full 2D displacement field and strain tensor can be derived using multiple projections. This study aims at deriving the full 2D strain tensor by estimating only displacement along the beam while steering the beam at three angles, i.e. 0?, a positive, and a negative beam steering angle. Displacements were iteratively estimated using 2D cross-correlations. The 0? acquisition yielded the vertical displacement vector. Projection of the other measured displacements yielded the horizontal (lateral) vector. The full 2D strain tensor was derived using 1D least squares strain estimators. Since horizontal displacements and strains are usually the least accurate, these were first focused on. Horizontal displacements were estimated for simulated radiofrequency (rf) data of a block with a four times stiffer cylindrical inclusion before and after application of 2% vertical compression. Root mean squared error (RMSE) of the horizontal displacements were calculated for every symmetric pair of beam steering angles in the range of -30 to 30? with angular increments of 5?. The RMSE analysis was performed for signal-to-noise (SNR) levels of 5, 10, 20 and 50 dB. Beam steering combinations of about -25? and 25? were found to be most optimal. The technique's performance was maintained regardless of the SNR level. For an SNR of 5 dB a reduction in RMSE of up to 70% was observed. In analogy with the simulations, experiments were performed with a similar inclusion phantom made of polyvinyl alcohol. Using data from beam steering angles of -25?, 0? and 25? strain images were constructed for all strain components and compared to strain images constructed without beam steering. The horizontal and shear strain images improved clearly with beam steering. Finally, the technique was also applied to derive radial and circumferential strain images for a homogeneous vessel phantom made of gelatin. Radially, SNR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> and CNR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> increased with 2.2 dB and 8 dB and circumferentially with 2.6 dB and 9.2 dB compared to non steered strain estimates. To conclude, the full 2D strain tensor can be accurately measured by using three beam steering angles.

Underwater acoustic (UWA) communication suffers from the limited available bandwidth of acoustic links. We consider in-band full-duplex (FD) communication in UWA channels, which has the potential of doubling the channel capacity. The key challenge of FD operation is the strong self-interference (SI) introduced by the near-end transmission. For a time-invariant UWA channel, the SI can be efficiently cancelled using an adaptive filter. In practice, the time-varying reflections particularly introduced by the moving sea surface limit the cancellation performance. In this paper, we propose a two-stage SI cancellation scheme with a transceiver structure comprising one projector and two hydrophones. In the first stage, the stable SI path from each hydrophone is cancelled using a digital canceller based on the recursive least-squares (RLS) algorithm with dichotomous coordinate descent (DCD) iterations. In the second stage, the scheme tries to cancel the residual SI using an RLS-DCD-based adaptive beamformer. The beamformer combines the residual signals at the hydrophones in such a way to minimize the final residual SI. The cancellation performance of the proposed scheme is investigated using the Waymark simulator and with lake experiments. As demonstrated by the simulation results, the SI can be efficiently cancelled with the proposed two-stage SI cancellation scheme. The experimental results also demonstrate the capability of the adaptive beamformer in reducing the residual SI after digital cancellation.

Requiring a single frequency band for transmission, full-duplex (FD) systems can ideally double the spectral efficiency. However, in addition to the information signal, radiated from user's own transmit antenna generates a strong self-interference (SI). To eliminate effects of SI, active and passive cancellation techniques are used in the literature. However, omitted in these studies is the fact that the time dispersion in the SI channel may cause an error floor. In this paper, it is verified that the SI channel is time dispersive via measurements. Later, we present an analysis in order to determine the error performance. Following these results, a fractionally spaced SI canceler is proposed to eliminate the error floor. We verify our analytical results via simulations, showing that the proposed SI canceler can critically enhance the performance of FD systems.

This work introduces a novel full-duplex hybrid beamforming (FD-HBF) technique for the millimeter-wave (mmWave) multi-user massive multiple-input multiple-output (MU-mMIMO) systems, where a full-duplex (FD) base station (BS) simultaneously serves half-duplex (HD) downlink and uplink user equipments over the same frequency band. Our main goal is jointly enhancing the downlink/uplink sum-rate capacity via the successful cancellation of the strong self-interference (SI) power. Furthermore, FD-HBF remarkably reduces the hardware cost/complexity in the mMIMO systems by interconnecting the radio frequency (RF) and baseband (BB) stages via a low number of RF chains. First, the RF-stage is constructed via the slow time-varying angular information, where two schemes are proposed for both maximizing the intended signal power and canceling the SI power. Particularly, orthogonal RF beamformer (OBF) scheme only aims canceling the far-field component of SI, while non-orthogonal RF beamformer (NOBF) scheme applies perturbations to the orthogonal beams for also suppressing the near-field component of SI channel. Considering the high computational complexity during the search for optimal perturbations, we apply swarm intelligence to find the optimal perturbations. Second, the BB-stage is designed based on only the reduced-size effective intended channel matrices, where the BB precoder/combiner solutions are obtained via regularized zero-forcing (RZF) and minimum mean square error (MMSE). Hence, the proposed FD-HBF technique does not require the instantaneous SI channel knowledge. It is shown that FD-HBF with NOBF+MMSE achieves 78.1 dB SI cancellation (SIC) on its own. Additionally, FD-HBF with the practical antenna isolation can accomplish more than 130 dB SIC and reduce the SI power below the noise floor. The numerical results present that FD-HBF greatly improves the sum-rate capacity by approximately doubling it compared to its HD counterpart.

Full duplex (FD) communications, which increases spectral efficiency through simultaneous transmission and reception on the same frequency band, is a promising technology to meet the demand of next generation wireless networks. In this paper, we consider the application of such FD communication to self-backhauled small cells. We consider a FD capable small cell base station (BS) being wirelessly backhauled by a FD capable macro-cell BS. FD communication enables simultaneous back-haul and access transmissions at small cell BSs, which reduces the need to orthogonalize allocated spectrum between access and backhaul. However, in such simultaneous operations, all the links experience higher interference, which significantly suppresses the gains of FD operations. We propose an interference-aware scheduling method to maximize the FD gain across multiple UEs in both uplink and downlink directions, while maintaining a level of fairness between all UEs. It jointly schedules the appropriate links and traffic based on the back-pressure algorithm, and allocates appropriate transmission powers to the scheduled links using Geometric Programming. Our simulation results show that the proposed scheduler nearly doubles the throughput of small cells compared to traditional half-duplex self-backhauling, even when the uplink/downlink traffic is asymmetric.

This paper presents a kernel-based adaptive filter that is applied for the digital domain self-interference cancellation (SIC) in a transceiver operating in full-duplex (FD) mode. In FD, the benefit of simultaneous transmission and receiving of signals comes at the price of strong self-interference (SI). In this work, we are primarily interested in suppressing the SI using an adaptive filter namely adaptive projected subgradient method (APSM) in a reproducing kernel Hilbert space (RKHS) of functions. Using the projection concept as a powerful tool, APSM is used to model and consequently remove the SI. A low-complexity and fast-tracking algorithm is provided taking advantage of parallel projections as well as the kernel trick in RKHS. The performance of the proposed method is evaluated on real measurement data. The method illustrates the good performance of the proposed adaptive filter, compared to the known popular benchmarks. They demonstrate that the kernel-based algorithm achieves a favorable level of digital SIC while enabling parallel computation-based implementation within a rich and nonlinear function space, thanks to the employed adaptive filtering method.

This paper describes the hardware implementation of real time configurable, electronically steered, transducer array for ultrasonic applications. In a transducer array radiation pattern of each of the elements are superimposed to get the resultant radiation pattern of the array. By applying progressive phase delay (time delay) to the driving signal of each of the transducer array elements the radiation beam of the transmitter can be steered to the intended direction. The implementation includes an graphical user interface for configuring the steering angle and other waveform parameters such as amplitude, frequency, modulation scheme etc. in real time. These parameters are communicated to the Digital Signal Processor (DSP) via. Serial Peripheral Interface (SPI). The programmable delay and waveform generation are done by Field Programmable Gate array (FPGA) so that the steering resolution is high. This implementation find application in radar systems where the beam steering angle needs to be dynamically varied on real time without any movement of mechanical masses.

In this paper, we investigate the energy harvesting (EH) technique and accordingly design transceivers for a K link multiple-input multiple-output interference channel. Each link consists of two full-duplex (FD) Internet of Things (IoT) nodes exchanging information simultaneously in a bi-directional communication channel. All the nodes suffer from interference, in particular strong self-interference and inter-node interference, due to operating in FD mode and simultaneous transmission at each link, respectively. Further, we divide the received signal at each node into two parts. While one part of the signal is used for information decoding, the other part is used for EH. We jointly design the transmit and receive beamforming vectors and receiver power splitting ratios by minimizing the total transmission power of the system, subject to both signal-to-interference-plus-noise ratio and EH threshold constraints. Furthermore, the case of multiple-input single-output interference channel is also included for the sake of comparison. We also revisit the above problems for the case when the available channel state information (CSI) at the transmitters is imperfect, where the errors of the CSI are assumed to be norm bounded. Simulation results show that the EH technique can harvest enough energy to support power consumption limited IoT devices by aiding in recharging their respective batteries.

The Spaceborne altimeter based on Interferometric Synthetic Aperture Radar (InSAR) can achieve high-resolution, wide-swath and high-accuracy height measurement of sea surface. The beam steering of the SAR systems in orbit is designed to access SAR images with the same noise equivalent sigma zero (NESZ) for near-range and far-range observation areas. However, for InSAR altimeters, the conventional method would result in the height accuracy of near-range areas much higher than the far-range ones. To achieve the required height accuracy in far-range areas, the SAR systems have to improve the transmission power or increase the size of antenna, improving the complexity in system designation. In this paper, a novel beam-steering method for spaceborne InSAR altimeters is proposed. The beam-steering angle is optimized according to the height accuracy in the whole scene. The performance of the proposed method over the conventional method is validated by the simulation.

Acquiring accurate channel state information (CSI) is essential for enabling reliable and efficient wireless transmission and reception. However, CSI is inherently stochastic, high-dimensional, and time-varying, which makes its acquisition particularly challenging. Motivated by the success of deep learning (DL) across many data modalities, this thesis explores DL-based solutions for CSI estimation, compression, and prediction.First, we study CSI estimation in full-duplex (FD) multiple-input multiple-output (MIMO) systems, where strong self-interference (SI) complicates channel acquisition. To reduce the pilot and computational burden of estimating both SI and user channels, we propose a pilot-sharing strategy together with a convolutional neural network that jointly estimates these channels.We further introduce a neural mapping that enables CSI acquisition at the transmit chain.Second, we investigate DL–based CSI compression and its limited robustness under distribution shifts. To address this issue, we adopt a full-model fine-tuning while explicitly accounting for model update signaling overhead. Specifically, we employ a spike-and-slab prior to promote sparsity in the model updates and fine-tune the pretrained network using a rate–distortion objective regularized by the update bit rate.Third, we tackle CSI prediction using a diffusion-based generative framework. The method consists of a temporal encoder that extracts latent features from past CSI and a diffusion generator that synthesizes future CSI. We also study a simplified encoder-free design to reduce latency, compare autoregressive and sequence-to-sequence inference, and explore multiple architectures for both temporal encoding and diffusion generation.

In this paper, the clutter rejection threshold corresponding to the maximum Doppler frequency of mainlobe clutter in high pulse repetition frequency airborne radar with frequency modulation (FM) ranging is proposed. The clutter spreading due to range-Doppler coupling in FM ranging radar is analyzed, and based on that, four clutter rejection thresholds corresponding to the maximum sidelobe/mainlobe clutter frequencies without/with FM ranging are presented. In particular, the clutter rejection threshold for achieving mainlobe clutter-free condition with FM ranging is derived by analyzing the mainlobe clutter boundaries for various beam steering angles. The detection capability corresponding to each of the four thresholds is analyzed, and it is shown that the detection capability can be improve by applying the clutter rejection threshold proposed in this work.

Atherosclerotic plaque rupture can initiate stroke or myocardial infarction. Lipid-rich plaques with thin fibrous caps have a higher risk to rupture than fibrotic plaques. Elastic moduli differ for lipid-rich and fibrous tissue and can be reconstructed using tissue displacements estimated from intravascular ultrasound radiofrequency (RF) data acquisitions. This study investigated if modulus reconstruction is possible for noninvasive RF acquisitions of vessels in transverse imaging planes using an iterative 2D cross-correlation based displacement estimation algorithm. Furthermore, since it is known that displacements can be improved by compounding of displacements estimated at various beam steering angles, we compared the performance of the modulus reconstruction with and without compounding. For the comparison, simulated and experimental RF data were generated of various vessel-mimicking phantoms. Reconstruction errors were less than 10%, which seems adequate for distinguishing lipid-rich from fibrous tissue. Compounding outperformed single-angle reconstruction: the interquartile range of the reconstructed moduli for the various homogeneous phantom layers was approximately two times smaller. Additionally, the estimated lateral displacements were a factor of 2–3 better matched to the displacements corresponding to the reconstructed modulus distribution. Thus, noninvasive elastic modulus reconstruction is possible for transverse vessel cross sections using this cross-correlation method and is more accurate with compounding.

A full-duplex MAC technique to improve spectrum-efficiency on 5G mobile wireless networks

Device-to-device (D2D) communication has been regarded as a promising technique for content dissemination in the fifth generation wireless network. To improve the efficiency of content dissemination, in this paper, we propose a content dissemination mechanism with proactive content fetching (PCF) and full-duplex (FD) D2D communication, referred to as PCF-FD mechanism. This mechanism is characterized by the proactive content requests of partial users that don’t request contents originally. FD communication is utilized to establish more D2D links and increase the area spectral efficiency (ASE). Based on stochastic geometry, we derive the recursive formula of content caching probability from the evolutionary perspective. In addition, the expressions of successful offloading probability (SOP), ASE and average energy consumption are also obtained. Computer experiments show that the analytical results match well with simulation results and our scheme outperforms the conventional scheme without PCF and FD communication by 45% in terms of SOP in a scenario with small user density and light load.

Full-duplex (FD) communications shall play an important role on the next generation (5G) mobile wireless networks as they are expected to enhance spectrum usage and throughput. It requires a proper design of medium access control (MAC) schemes to fully exploit the potential advantages of FD communications. Notwithstanding, main existing full-duplex MAC schemes relies on IEEE 802.11 building blocks, which was designed to operate with half-duplex communications. This work proposes Full-duplex Multiple Receiver MAC (FDMR-MAC), which was tailored to enhance throughput and channel use. FDMR-MAC uses an innovative channel reservation scheme that raises the probability of establishing a full-duplex communication where the sender and the receiver nodes have data payload to transmit to each other. To compare FDMR-MAC with state-of-art full-duplex communications mechanisms, an analytical model addressing the particular aspects of a FD communication is proposed. Numerical results indicate that FDMR-MAC achieved throughput up to \(67\%\) higher than a state-of-art full-duplex scheme, thus pointing the potential impact of FDMR-MAC use in FD communications.