Single Transmitter Research Articles

Impact of Random Receiver Orientation on Visible Light Communications Channel

Visible light communications (VLC) has been studied thoroughly in recent years as an alternative or complementary technology to radio frequency communications. The reliability of VLC channels highly depends on the availability and alignment of line of sight links. In this paper, we study the effect of random receiver orientation for mobile users over VLC downlink channels, which affects the existence and quality of line of sight links. Based on the statistics of the receiver location and relative orientation with respect to the transmitter LED, we develop an analytical framework to characterize the statistical distribution of VLC downlink channels, which is then utilized to obtain the outage probability and the bit error rate. Our analysis is generalized for arbitrary distributions of relative orientation and location for a single transmitter, and extended to multiple transmitter case for some certain scenarios. Extensive Monte Carlo simulations show a perfect match between the analytical and the simulation data in terms of both the statistical channel distribution and the resulting bit error rate. Our results also characterize the channel attenuation due to random receiver orientation and location for various scenarios of interest.

Transmitters and receivers in SiGe BiCMOS technology for sensitive gas spectroscopy at 222 - 270 GHz

This paper presents transmitter and receiver components for a gas spectroscopy system. The components are fabricated in IHP’s 0.13 μm SiGe BiCMOS technology. Two fractional-N phase-locked loops are used to generate dedicated frequency ramps for the transmitter and receiver and frequency shift keying for the transmitter. The signal-to-noise ratio (SNR) for the absorption line of gaseous methanol (CH3OH) at 247.6 GHz is used as measure for the performance of the system. The implemented mixer-first receiver allows a high performance of the system due to its linearity up to an input power of -10 dBm. Using a transmitter-array with an output power of 7 dBm an SNR of 4660 (integration time of 2 ms for each data point) was obtained for the 247.6 GHz absorption line of CH3OH at 5 Pa. We have extended our single frequency-band system for 228 – 252 GHz to a 2-band system to cover the range 222 – 270 GHz by combining corresponding two transmitters and receivers with the frequency bands 222 – 256 GHz and 250 – 270 GHz on single transmitter- and receiver-chips. This 2-band operation allows a parallel spectra acquisition and therefore a high flexibility of data acquisition for the two frequency-bands. The 50 GHz bandwidth allows for highly specific and selective gas sensing.

Expectation–Maximization-Based Passive Localization Relying on Asynchronous Receivers: Centralized Versus Distributed Implementations

This paper considers a passive localization scenario relying on a single transmitter, several receivers, and multiple moving targets to be located. The so-called “passive” targets equipped with RFID reflectors are capable of reflecting the signals from the transmitter to the receivers. Existing approaches assume that the transmitter and receivers are synchronous or quasi-synchronous, which is not always realistic in practical scenarios. Hence, an asynchronous wireless network is considered, where different clock offsets are assumed at different receivers. We propose a centralized expectation–maximization-based passive localization method for asynchronous receivers (EMpLaR) by treating the clock offsets as hidden variables. Thereby, the proposed algorithm makes use of Taylor expansions to arrive at a closed-form maximization. Furthermore, to improve the robustness to link failures and to reduce the energy consumption, we propose a distributed localization approach based on average consensus formulation to locate the target at each receiver. By applying a quadratic polynomial approximation of the function on which consensus has to be reached, both the computational complexity and the communications overhead are significantly reduced. The Cramer–Rao bound of the target location is derived as a benchmark of our proposed algorithms. Our simulation results show that the proposed centralized and distributed EMpLaR algorithms match the Cramer–Rao bound and significantly improve the localization performance compared with the conventional methods.

Transmitter-Selection Aided Adaptive Consensus-Based Data Sharing for UAV Swarms

The unmanned aerial vehicle (UAV) swarm systems rely on wireless communications for data sharing and coordination. Recently, both the lazy and eager consensus-based algorithms were proposed to enable swarm-wide data sharing. However, our analysis and experiments show that the performance of both algorithms may degrade drastically in dynamic and heterogeneous network environments. The reason is attributed to the fixed transmitter selection strategies adopted in the algorithms. Therefore, in this paper, we propose a novel adaptive consensus data sharing algorithm by adopting single best transmitter selection to strike a beneficial tradeoff between convergence rate and payload cost. Then, we propose and implement a UAV swarm simulation platform to facilitate simulations in dynamic and heterogeneous environment. Numerical results reveal that the proposed adaptive consensus-based data sharing algorithm performs well across different network scenarios in terms of convergence rate and payload cost.

Zonal-Based GrEEn Algorithm for Augmenting the Battery Life in Spectrum Shared Networks via D2D Communication

This paper proposes a zone-based approach referred to as zone-based GrEEn (ZBGrEEn) algorithm, for energy-efficient spectrum sharing (SS) networks. The SS network is considered to encompass device-to-device (D2D) transmissions between a single primary transmitter (PT) and multiple primary receivers (PRs), placed in distinctive zones around the PT. Power allocation is performed optimally so that the target rate of each application demanded by the PRs are adequately met. When the PT fails to meet the target rates over ${\rm{PT}} \to {\rm{PR}}$ D2D links, it transmits cooperatively through an appropriate secondary transmitter (ST) in the SS network, which acts as an amplify-and-forward (AF) relay. The ST's basis for selection is the ${\rm{PT}} \to {\rm{ST}}$ channel state and power level at the ST. Use of game theory for solving the energy efficiency (EE) maximization problem has also been quantified. ZBGrEEn introduces zone factor for determining the transmission time for each zone in the SS network. This time determines the energy consumption at the user terminals, thereby impacting its battery lifetime. The efficiency of the proposed scheme has been validated through simulation results, with the enhancement in battery lifetime of up to 46.28% achievable for the PT. Game theory is also observed to be rewarding in battery lifetime augmentation, especially for ultradense networks (UDNs). Performance of other user terminals in the network can be similarly evaluated.

Cooperative OSIC System to Exploit the Leakage Power of MU-MIMO Beamforming based on Maximum SLR for 5G

This study investigated the crucial—but not welldiscussed—issues involved in designing beamforming for all receivers, subject to leakage power constraints. Our assumption is that all users use ordered successive interference cancellation (OSIC) detection when the channel state information (CSI) is available. The problem of interest is to find beamforming that can improve OSIC performance of a multi-user scheme without significantly increasing the complexity. This study considers the transceiver design for multi-user MIMO (MU-MIMO) communications, in which a single transmitter adopts beamforming to simultaneously transmit information at first time-slot. During the second time-slot, receivers cooperate to share specific results of OSIC detection in each user. We propose the maximum-likelihood (ML) to estimate the received symbols.The estimated symbols will be used in OSIC detection to detect interference symbols. Promising results show that our cooperative OSIC scheme of the MU-MIMO beamforming system based on maximum signal-to-leakage ratio (SLR) realizes the diversity order of OSIC. Also, by utilizing leakage power as a useful power and not just as an interference power, the performance of the proposed scheme over Rayleigh and Rician channels is significantly better than the performance of classical MU-MIMO beamforming system based on SLR at a high signalto-noise ratio (SNR).

The WARR Machine: System Design, Implementation and Data

In this paper, we describe a ground penetrating radar (GPR) system called the wide angle reflection and refraction (WARR) machine, outline the design and discuss the implementation challenges. WARR and the closely related common-mid-point (CMP) GPR soundings have been standard survey methods to measure velocity since GPR first existed. Earliest efforts demonstrated the variation in ice sheet velocity versus depth. Although GPR multi-offset soundings are valuable survey methods, they have seen little adoption since many systems are not bistatic. In addition, surveys most often use a single transmitter with a single receiver deployed sequentially at varying antenna separations, making data acquisition slow. Modern instrumentation with recent advances in GPR timing and control technology has enabled deployment of systems with multiple concurrent sampling receivers. This development has resulted in the ability to continuously acquire multi-offset WARR data at the same rate as two dimensional (2D) common offset reflection surveys in the past. The concomitant issues of survey design plus organizing the WARR data storage, documentation and analysis present numerous challenges. The extraction of velocity information from the large volumes of GPR WARR/CMP data demands automated analysis techniques. We have explored the use of normal move out (NMO) stacking at creating enhanced zero offset section from multi-offset data. Furthermore, we investigated the use of semblance analysis at estimating move-out velocities in order to apply in the NMO stack. These traditional seismic processing steps have proven to be less effective with GPR. These conclusions point to the differences in data character between seismic and GPR. Results of in-field deployment are used to illustrate advances to date and point the way to further advancements.

Performance difference between zero‐forcing and maximum likelihood detectors in massive MIMO systems

In massive multiple-input multiple-output (MIMO) systems with hundreds of antennas at the base station (BS) and few users with a single transmitter antenna, linear detectors, such as zero-forcing (ZF), achieve near-optimum performance due to the property of asymptotically orthogonal channel matrix. However, how far away is ZF from the optimum performance. To answer this question, in this Letter, closed-form bit error rate (BER) expressions are derived. These BER expressions are subsequently used to evaluate the performance difference between ZF and the optimum detector, which is a function of the number of antennas at the BS and the number of users. Numerical results verify the tightness of the performance difference.

VTEM ET: An improved helicopter time-domain EM system for near surface applications

Sampling the earliest possible transient EM decay in time-domain airborne electromagnetic data (TDEM) is critical for shallow near surface applications. In an effort to further improve near-surface resolution, starting in late 2015 and into 2016, Geotech continued by developing its new VTEM ET system that uses a re-designed broadband receiver sensor, a re-configured transmitter system, and a new digital acquisition system to achieve precise, distortion free measurements of the time-domain EM decay as early as 0.005 msec after the transmitter turn-off. The new receiver features a much larger frequency bandwidth for lower distortion measurements. The new transmitter delivers a sufficiently high dipole moment, a long pulse-width and faster turn-off time than previous systems, but similarly using a single transmitter pulse. The new digital acquisition system operates at a much higher sampling rate, with significantly more decay channels, particularly in early times, and with low noise levels. The result is a new category of VTEM system that is specifically is designed for precise near-surface applications, such as groundwater and environmental problems, but also with sufficient depth of investigation. We present forward modelling and field survey test results comparing the VTEM ET system with our standard VTEM Plus system with full-waveform processing over a groundwater project with ground geophysical and borehole controls in the upper 30-50 metres.

Biologically‐inspired wideband target localisation

In this study, the authors present two biologically-inspired angular localisation techniques for radar which separately use the magnitudes and phases of the wideband received signals as the cues for angular target localisation. By comparison with predetermined map functions, the angle to a target may be estimated with good accuracy and over a wide angular range of operation. These techniques are implemented in a radar system with a single transmitter and two offset receiving antennas, allowing us to draw upon cues derived from biological systems that are often only explored in psychology, biology, and psychoacoustics.

Cooperative Cognitive Non-Orthgonal Multiple Access Under Unreliable Backhaul Connections

In this paper, we investigate the performance of energy-harvesting communications with decode-and-forward relay in the presence of non-orthogonal multiple access (NOMA) multiple access and cognitive radio spectrum sharing. We study three cases of single transmitter single relay and various transmitters and relays with two selection strategies (called as RTST1 and RTST2). Specifically, one source node (macro base station) transmits two symbols to two respective destinations via multiple transmitters and multiple relays under the power constraint of a primary user. We derived the closed-form expressions for the outage probability at two destinations and overall system. The outcomes revealed that the system performances are improved when increases the maximum transmit power at the transmitters, the threshold power affect to the primary user, the backhaul reliability. The system performance is lightly decreased when the power splitting ratio is at too low or too high value.

A Multifrequency Superposition Methodology to Achieve High Efficiency and Targeted Power Distribution for a Multiload MCR WPT System

Magnetically coupled resonant (MCR) wireless power transfer (WPT) is one of the most promising WPT technologies for its remarkable capability of simultaneous noncontact power transfer for multiple independent loads. Nevertheless, diverse energy requirements of different loads and efficiency quota make it difficult to design and optimize the multiload system. In this paper, a novel driver configuration for the MCR WPT system with multiple loads is proposed, in which the transmitting resonant tank is driven synchronously by multiple inverters operating at multiple switching frequency and sharing a common dc voltage source, then a multifrequency superposition methodology is presented to achieve high efficiency and targeted power distribution. The dominant features of the methodology are listed as follows: 1) the multifrequency power components from multiple inverters can be simultaneously delivered to multiple loads through a single transmitter; 2) the receiving coils are elaborately designed at different resonant frequencies that correspond to the operating frequencies of multiple inverters to achieve targeted power transfer and high efficiency; 3) the resonant frequency of the transmitter can be modulated within the adjacent area of multiple operating frequencies, and the power distribution to meet the requirements of selective loads will be realized; and 4) the resonant frequencies of receivers can also be adjusted to effectively realize the power distribution. In this paper, a double-frequency MCR WPT system with two loads is comprehensively investigated as a representative example, and the studied methodology has been experimentally verified by two prototypes of the proposed circuit configurations.

Signal Detection for Superposition Transmission Protocols for Optical Wireless Scattering Broadcast Channel

Due to the scattering events in the ultra-violet (UV) spectrum, UV optical wireless communication enables transmission from a single transmitter to multiple receivers, which forms a broadcast channel. In this paper, we address the transmission protocols for such a broadcast channel. Based on the degradeness of such a broadcast channel, we propose time-dilation and time-shrinking superposition transmission. For the former, the duration of the base-layer symbols is shorter than that of the enhancement-layer symbols; while for the latter, the duration of the base-layer symbols is longer. We propose the signal detection of the two types of superposition transmission protocols, analyze the detection error probability and the associated upper bounds, and formulate the problems of power allocation among the signal layers. The numerical results on the sum power obtained from the exact detection error probability and the upper bounds are provided. It is shown that for the superposition with two signal layers, the sum power based on the upper bounds can be close to that based on the exact detection error probability.

Development and Validation of a Chip Integration Concept for Multi-Die GaAs Front Ends for Phased Arrays up to 60 GHz

High-gain steerable antenna arrays in the K-, Ka-, and V-frequency bands have the potential to facilitate high-bandwidth satellite communication for a variety of applications. Copper-core printed circuit boards (PCBs) can offer a cost-effective integration platform for such systems by simultaneously addressing both the high frequency and thermal challenges. Integrating GaAs dies into test vehicles has shown that copper-core PCBs can be automatically assembled and provide high-frequency systems that show adequate reliability during thermal cycling. A single 60-GHz transmitter front end, designed to drive a single element of a phased array, with a 2-GHz bandwidth signal, composed of four GaAs dies, including a phase shifter, integrated onto a copper-core PCB produces an output power of −4 dBm and maintains an on-chip temperature under 51 °C.

A Multi-site Heart Pacing Study Using Wirelessly Powered Leadless Pacemakers.

In this work, we report an energy-efficient switched capacitor based millimeter-scale pacemaker (5 mm ×7.5 mm) and a multi-receiver wireless energy transfer system operating at around 200 MHz, and use them in a proof-of-concept multi-site heart pacing study. Two pacemakers were placed on two beating Langendorff rodent heart models separately. By utilizing a single transmitter positioned 20-30 cm away, both Langendorff hearts captured the stimuli simultaneously and were electromechanically coupled. This study provides an insight for future energy-efficient and distributed cardiac pacemakers that can offer cardiac resynchronization therapies.

Resolution Analysis of Spatial Modulation Coincidence Imaging Based on Reflective Surface

The spatial modulation coincidence imaging (SMCI), as a novel kind of microwave coincidence imaging method, is proposed in this paper. The SMCI system provides a new way to produce the time-space independent signal instead of multitransmitter architecture with wideband randomly modulated signal in radar coincidence imaging. Due to some special features, metamaterial plate is utilized as the reflective surface to modulate the incident signal to construct random radiation field. The resolution of SMCI system is analyzed under large viewing angle with two different transmitting signals. Reflective surface is nonuniformly divided to derive the expression of resolution. The analysis results show that the resolution of SMCI system is mainly determined by the size of reflective surface and center frequency, which is similar to the traditional aperture. The SMCI system is low cost and flexible in design. Simultaneously, it can avoid the synchronization problem between subsources. Moreover, the SMCI system can achieve the resolution of space target through single transmitter–single receiver radar system. High-resolution image can be reconstructed since the tests are nonlinear. Finally, a series of simulation experiments is presented based on the nondirect-viewing scene we proposed. Using the algorithm based on a compressed sensing theory, we reconstructed the target image with high resolution.

Coherent MIMO to Improve Aperture Synthesis Radar Imaging of Field-Aligned Irregularities: First Results at Jicamarca

Multiple-input multiple-output (MIMO) radar techniques make use of multiple transmitters and multiple receivers to improve the spatial characterization of targets. In the case where the Bragg scattering $\vec {k}$ -vector can be assumed to be the same for all transmit–receive paths, MIMO methods can be seen as a way of increasing the number of effective receivers. In the last decades, there has been scientific interest in determining the spatial characteristics of ionospheric and atmospheric irregularities on the subtransmit beam scale, allowing the study of processes in their intrinsic scales, otherwise inaccessible using simple beamforming techniques. Interferometric methods, including aperture synthesis imaging, were used in the past with a single transmitter and multiple receivers [single-input multiple-output (SIMO)]. In this paper, we present the first implementation of MIMO techniques to improve the spatial resolution of aperture synthesis radar imaging of daytime equatorial electrojet irregularities observed using the Jicamarca Radio Observatory (JRO). Our implementation uses two spatially separated transmitters and four spatially separated receivers. In order to separate the contributions of each transmitter, time, code, and polarization diversity experiments have been tested. We find that all three diversity approaches can be used for ionospheric irregularities, but time and polarization diversity are not applicable in all situations due to the range and Doppler width of the echoes, and due to magnetoionic radio propagation effects. The results are evaluated by comparing new MIMO imaging results against the currently used SIMO imaging technique. We present and discuss the theoretical and practical aspects of the MIMO approach, so they can be applied to study other targets not only at JRO but also at other modular coherent scatter radars.

System Architecture and Signal Processing for Frequency-Modulated Continuous-Wave Radar Using Active Backscatter Tags

In this paper, we study a frequency-modulated continuous-wave based radio-frequency identification system, which is composed of a reader with single transmitter and multiple receiving antennas as well as multiple active backscatter tags. In particular, our contribution is twofold in this paper. First, we construct a general architecture for achieving the functionality of wireless positioning based on the principle of the switched injection-locked oscillator (SILO). Unlike the previous SILO-based schemes, some limitations on the pulsed waveform generated by the tags are overcome. In addition, only one reader set up with multiple receiving antennas is used to precisely localize tags based on the delay and direction-of-arrival estimates. Second, the developed algorithms make use of a shift invariant property among the baseband signal snapshots of intra- and/or intermodulation intervals, i.e., snapshots in one modulation period and/or sets of snapshots in multiple modulation periods. A new joint singular value decomposition based ESPRIT algorithm is developed for determining the number of multiple active tags and their positions by implementing the matrix reconstruction and stacking techniques. The proposed method has its basic foundation on the processing of received data with global fusion scheme. In this way, this method can improve the performance of parameter estimates in terms of accuracy and resolution without suffering from the pair matching problem. System simulations and experimental validations are carried out to verify the proposed system architecture associated with the signal processing technique.

3D forward modeling and response analysis for marine CSEMs towed by two ships

A dual-ship-towed marine electromagnetic (EM) system is a new marine exploration technology recently being developed in China. Compared with traditional marine EM systems, the new system tows the transmitters and receivers using two ships, rendering it unnecessary to position EM receivers at the seafloor in advance. This makes the system more flexible, allowing for different configurations (e.g., in-line, broadside, and azimuthal and concentric scanning) that can produce more detailed underwater structural information. We develop a three-dimensional goal-oriented adaptive forward modeling method for the new marine EM system and analyze the responses for four survey configurations. Oceanbottom topography has a strong effect on the marine EM responses; thus, we develop a forward modeling algorithm based on the finite-element method and unstructured grids. To satisfy the requirements for modeling the moving transmitters of a dual-ship-towed EM system, we use a single mesh for each of the transmitter locations. This mitigates the mesh complexity by refining the grids near the transmitters and minimizes the computational cost. To generate a rational mesh while maintaining the accuracy for single transmitter, we develop a goal-oriented adaptive method with separate mesh refinements for areas around the transmitting source and those far away. To test the modeling algorithm and accuracy, we compare the EM responses calculated by the proposed algorithm and semi-analytical results and from published sources. Furthermore, by analyzing the EM responses for four survey configurations, we are confirm that compared with traditional marine EM systems with only in-line array, a dual-ship-towed marine system can collect more data.

Distortion minimization for relay assisted wireless multicast

The paper studies the scenario of wireless multicast with a single transmitter and a relay that deliver scalable source symbols to the receivers in a decode-and-forward (DF) fashion. With the end-to-end mean square error distortion (EED) as performance metric, we firstly derive the EED expression for the L-resolution scalable source symbol for any receiver. An optimization problem in minimizing the weighted EED is then formulated for finding the power allocations for all resolution layers at the transmitter and the relay. Due to nonlinearity of the formulations, we solve the formulated optimization problems using a generalized programming algorithm for obtaining good sub-optimal solutions. Case studies are conducted to verify the proposed formulations and solution approaches. The results demonstrate the advantages of the proposed strategies in the relay-assisted wireless networks for scalable source multicast.