Time Division Multiplexing Scheme Research Articles

Broadband High-Linear FMCW Light Source Based on Spectral Stitching

The key to realizing a high-performance frequency-modulated continuous wave (FMCW) laser frequency-sweeping light source is how to extend the frequency-swept bandwidth and eliminate the effect of nonlinearity. To solve these issues, this paper designs a broadband high-linear FMCW frequency-sweeping light source system based on the combination of fixed temperature control and digital optoelectronic phase-locked loop (PLL), which controls the temperatures of the two lasers separately and attempts to achieve the coarse spectral stitching based on a time-division multiplexing scheme. Furthermore, we uses the PLL to correct the frequency error more specifically after the coarse stitching, which achieves the spectrum fine stitching and, meanwhile, realizes the nonlinearity correction. The experimental results show that our scheme can successfully achieve bandwidth expansion and nonlinearity correction, and the sweeping bandwidth is twice as much as that of the original single laser. The full-width half-maximum (FWHM) of the FMCW output is reduced from 150 kHz to 6.1 kHz, which exhibits excellent nonlinear correction performance. The relative error of the FMCW ranging system based on this frequency-swept light source is also reduced from 1.628% to 0.673%. Therefore, our frequency-swept light source with excellent performance has a promising application in the FMCW laser ranging system.

Multiplexed Surface Electrode Arrays Based on Metal Oxide Thin-Film Electronics for High-Resolution Cortical Mapping.

Electrode grids are used in neuroscience research and clinical practice to record electrical activity from the surface of the brain. However, existing passive electrocorticography (ECoG) technologies are unable to offer both high spatial resolution and wide cortical coverage, while ensuring a compact acquisition system. The electrode count and density are restricted by the fact that each electrode must be individually wired. This work presents an active micro-electrocorticography (µECoG) implant that tackles this limitation by incorporating metal oxide thin-film transistors (TFTs) into a flexible electrode array, allowing to address multiple electrodes through a single shared readout line. By combining the array with an incremental-ΔΣ readout integrated circuit (ROIC), the system is capable of recording from up to 256 electrodes virtually simultaneously, thanks to the implemented 16:1 time-division multiplexing scheme, offering lower noise levels than existing active µECoG arrays. Invivo validation is demonstrated acutely in mice by recording spontaneous activity and somatosensory evoked potentials over a cortical surface of ≈8×8mm2 . The proposed neural interface overcomes the wiring bottleneck limiting ECoG arrays, holding promise as a powerful tool for improved mapping of the cerebral cortex and as an enabling technology for future brain-machine interfaces.

Vector-switched digital predistortion for concurrent dual-band transmitters with hybrid time-division multiplexing scheme

In a concurrent dual-band digital predistortion (DPD) system, due to the large number of two-dimensional (2D) polynomial-based model coefficients and the existence of cross-modulation terms, the hardware realization usually requires a lot of resources. To alleviate this problem, this paper proposes a hardware-efficient field programmable gate array (FPGA)-based piecewise vector-switched (PVS) DPD method. With the PVS method, a 2D memory polynomial (MP) model with fewer coefficients can be used as a sub predistorter model for each region. Furthermore, a new hybrid time-division multiplexing (HTDM) scheme is proposed for the 2D-MP predistorter architecture, which enables sharing of cross-modulated lookup tables (LUTs) and complex multipliers in a hybrid way. Experimental results show that the proposed method improves the adjacent channel power ratio (ACPR) and normalized mean square error (NMSE) by 18.74 dB and 13.23 dB, respectively, and saves about 30% and 80% of RAM and DSP resources, respectively.

Improving the Timeliness of Two-Source Status Update Systems in Internet of Vehicles With Source-Dedicated Buffer: Resource Allocation

Age of information (AoI) is a pertinent metric for characterizing the timeliness of status updates in Internet of Vehicles (IoV). Resources allocated to update transmission would significantly affect the timeliness of status update observed at the receiver end. This work investigates the sum average AoI of a two-source wireless updating system in IoV by modeling the system as a non-preemptive queue with a size-two source-dedicated buffer. Two bandwidth allocation schemes, i.e., an asynchronous time division multiplexing (ATDM) scheme and a dynamic bandwidth allocation (DBA) scheme, are proposed for the system. In the ATDM scheme, status updates are transmitted using all available bandwidth sequentially while in the DBA scheme, the server fractionally allocates the available bandwidth for transmitting the arrived update based on the buffer state. By analyzing the age evolution of each update stream based on stochastic hybrid systems, the closed-form per-source average AoI and the sum average AoI of the two proposed schemes are derived. In particular, the per-source average AoI when the system provides priority for serving one update stream is also given. It is demonstrated that by employing the ATDM scheme and the DBA scheme with optimized bandwidth allocation factor, the system can achieve a significant improvement in terms of sum average AoI, enhancing the update freshness.

The Real-Time System for Distribution of Clock, Control and Monitoring Commands With Fixed Latency of the LHCb Experiment at CERN

The Large Hadron Collider beauty (LHCb) experiment has gone through a major upgrade for LHC Run 3 at European Organization for Nuclear Research (CERN), scheduled to start in the middle of 2022. The entire readout system of the experiment has been replaced by front-end and back-end electronics that are able to record LHC events at the full LHC bunch crossing rate of 40 MHz. To maintain synchronicity across the full system, clock and control commands are originated from a single readout supervisor (SODIN) and distributed downstream through a passive optical network (PON) infrastructure, reaching all the back-end cards of the readout system, via a two-level hierarchy and using PON splitters. A field programmable gate arrays (FPGA) firmware core, called LHCb-PON and based on the CERN timing, trigger, and control (TTC)-PON, is instantiated on SODIN and all back-end cards and provides the communication protocol while ensuring a stable distribution of control commands within the readout period of 25 ns and a clock signal with fixed and deterministic latency with a precision of a few hundreds of picoseconds. This is achieved by the firmware backbone that provides clock recovery and ensures the transmission of a control word downstream with fixed latency. In addition, the LHCb-PON also provides monitoring functionalities over the upstream link, with less strict timing requirements, connecting multiple back-end cards to the central SODIN. This is achieved by having each back-end card send data upstream through a time-division multiplexing (TDM) scheme. This article describes the implementation, measurements, and results from the usage of the system during the startup of the LHC Run 3.

Configurable Hybrid Energy Synchronous Extraction Interface With Serial Stack Resonance for Multi-Source Energy Harvesting

Conventional multi-source energy harvesters use the time-division multiplexing (TDM) scheme, where the inductor operates in discontinuous current mode (DCM) and fails to perform well in continuous current mode (CCM). This article presents a single-inductor hybrid energy synchronous extraction circuit with serial stack resonance (SSR) for multi-source energy harvesting. The proposed circuit incorporates a synchronous electric charge extraction (SECE) circuit for ac energy and two buck–boost circuits for dc energy with a single inductor, which can operate either in a TDM mode to harvest energy from different sources separately or in an SSR mode to extract energy from multiple sources synchronously. The proposed harvester is fabricated in a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process. It is configured with a photovoltaic (PV) cell, a thermoelectric generator (TEG), and two piezoelectric transducers (PZTs), where the number of PZTs is flexible to meet different application needs.

High Data Density Absolute Electromagnetic Encoders Based on Hybrid Time/Frequency Domain Encoding

This article presents a novel concept for the implementation of electromagnetic encoders exhibiting very high data density per unit length (DPL), a figure of merit (FoM) of such systems. Encoding is based on a hybrid scheme that exploits both the frequency and time domains. The encoders consist of rows of inclusions (linear strips) of different sizes, periodically arranged to form a chain (with four columns). The bits corresponding to each row are read sequentially in a time-division multiplexing scheme, whereas the size of the inclusions provides frequency encoding. The main relevant aspect of the proposed system concerns the reader, based on a power splitter architecture with either two outputs (prototype A) or four outputs (prototype B). It is shown that the data capacity per row in one of the encoders read through prototype B is 8.78 bits, whereas the data density is as high as DPL = 29.26 bit/cm, an unprecedented value in this type of encoders. The proposed system can be used as a near-field synchronous chipless-radio frequency identification (RFID) system, or as a position and velocity sensor. In the latter case, the system is able to provide the absolute encoder position, provided the number of bits per row (or position) is enough to discern the different number of encoder positions (up to 440 different positions for prototype B, corresponding to the indicated number of bits).

On the Generalized Degrees of Freedom of the Noncoherent Interference Channel

We study the generalized degrees of freedom (gDoF) of the block-fading <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">noncoherent</i> 2-user interference channel (IC) with a coherence time of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T$ </tex-math></inline-formula> symbol durations and symmetric fading statistics. We demonstrate that a standard training-based scheme for the noncoherent IC is suboptimal in several regimes. We study and analyze several alternate schemes: the first is a new noncoherent scheme using rate-splitting. We also consider a scheme that treats interference-as-noise (TIN) and a time division multiplexing (TDM) scheme. We show that a standard training-based scheme for the noncoherent IC is outperformed by one of these schemes in several regimes: our results demonstrate that in the very weak interference regime, the TIN scheme is the best; in the strong interference regime, the TDM scheme and the noncoherent rate-splitting scheme give better performance; in other cases either of the TIN, TDM or noncoherent rate-splitting scheme could be preferred. We also study the noncoherent IC with feedback and propose another noncoherent rate-splitting scheme. Again for the feedback case, our results demonstrate that a standard training-based scheme can be outperformed by other schemes.

Noise Power Minimization in CMOS Brain-Chip Interfaces.

This paper presents specific noise minimization strategies to be adopted in silicon–cell interfaces. For this objective, a complete and general model for the analog processing of the signal coming from cell–silicon junctions is presented. This model will then be described at the level of the single stages and of the fundamental parameters that characterize them (bandwidth, gain and noise). Thanks to a few design equations, it will therefore be possible to simulate the behavior of a time-division multiplexed acquisition channel, including the most relevant parameters for signal processing, such as amplification (or power of the analog signal) and noise. This model has the undoubted advantage of being particularly simple to simulate and implement, while maintaining high accuracy in estimating the signal quality (i.e., the signal-to-noise ratio, SNR). Thanks to the simulation results of the model, it will be possible to set an optimal operating point for the front-end to minimize the artifacts introduced by the time-division multiplexing (TDM) scheme and to maximize the SNR at the a-to-d converter input. The proposed results provide an SNR of 12 dB at 10 µVRMS of noise power and 50 µVRMS of signal power (both evaluated at input of the analog front-end, AFE). This is particularly relevant for cell–silicon junctions because it demonstrates that it is possible to detect weak extracellular events (of the order of few µVRMS) without necessarily increasing the total amplification of the front-end (and, therefore, as a first approximation, the dissipated electrical power), while adopting a specific gain distribution through the acquisition chain.

Power Packet Router With Power and Signal Switches for a Single Power Packet

This brief proposes a power packet router (router) and experimentally verifies its operation. A power packet is a unit of DC power and an information tag. When the tag is attached to the power directly, a power packet ensures their simultaneity during the transmission. The router sends and receives power packets in Time Division Multiplexing scheme. Since the beginning of our research project, the router has generated a power packet with a single switch. The switch ensures the simultaneity of power and information during transmission. On the other hand, the switch limits the capacities of power and information of a power packet. The proposed router ensures the simultaneity by its power packet generation method. It lets the switches operate in sync for power and information to generate a single power packet. The operation is experimentally verified. The results make it confirmed the possibility to combine the individually optimized subunits for packet generation.

Trilateration‐based indoor localization engineering technique for visible light communication system

SummaryThis article is aimed at designing positioning system using visible light communication technology by incorporating three different diversity schemes, namely, transmit diversity (TD), receive diversity (RD), and angle diversity. For the TD, multiple transmitters with single receiver (MISO) is used to obtain the target location using frequency division multiplexing (FDM) and variable phase approach. To deploy RD, the proposed system comprises multiple receivers and single transmitter (SIMO). Only one transmitter's absolute coordinates are required to obtain the location coordinates of optical receivers. FDM and time division multiplexing access schemes have been utilized to transmit the unique signals by light‐emitting diodes (LEDs). To implement angle diversity, orientation of transmitter and receiver is considered for positioning purposes. Under this environment, there is no constraint for the LEDs to be installed on ceiling; they can be at any point within the room or at different heights. The information regarding spherical coordinates (representing the orientation) of LEDs (single or multiple) is used to determine the coordinates or the orientation of receiver having multiple or single photodiodes, respectively. Under multiple orientations, this system is analyzed with both scenarios, that is, MISO and SIMO.

Robust Multidimensional Optical Modulation Based on Hybrid Subcarrier/Amplitude/Phase/Dual Polarization for Wavelength-Division Multiplexing Systems

Here, we propose a novel scheme based on advanced techniques of digital modulation in optical communications to achieve a single-channel transmission rate above 100 Gb/s. We utilize a hybrid scheme amplitude/phase/frequency/dual polarization, combined with multidimensional dual lattice and a low-density parity-check-coded modulation. The Stokes parameters are applied to the proposed scheme to map the four-dimensional classical polarization I X , Q X , I Y , Q Y in a three-dimensional space. In addition, in the proposed system, the packing theory is applied to the bit interleaver process. Three wavelengths are packaged before being transmitted over a wavelength-division multiplexing optical channel. This modulation process is carried out using symmetrical geometric shapes, such as a hypercube or a polyhedron, based on the molecular links theory using a grouping of 12 and 13/15 bits for the cubic and spherical lattices, respectively. The proposed technique is evaluated in the context of long-distance communications over distances up to 100km. The bit error rate (BER) results showed that the optical signal-to-noise ratio was approximately 4dB over a distance of 50km. In addition, the power spectral efficiency was found to be 3 lambdas, which is considered good performance considering the effects of distance and the non-linear effects influencing the number of lambdas. Also, we use an optical time-division multiplexing scheme (OTDM) in order to achieve a transmission rate beyond 1Tbit/s, where the speed effect is evaluated, taking into consideration that the power spectral efficiency is degraded.

A Mixed Circular/Linear Dual-Polarized Phased Array Concept for Automotive Radar—Planar Antenna Designs and System Evaluation at 78 GHz

A planar antenna array front end for automotive applications in the 78 GHz band is discussed and evaluated. Separate antenna arrays for transmit and receive are realized on RF substrate with the objective to provide a very cost-effective and compact design. The basic array column consists of 10 dual-polarized square patch elements and launches a fan beam that illuminates a wide sector in azimuth but a narrow sector in elevation. The orthogonal linear polarizations are combined via a microstrip quadrature power splitting network in order to excite a single circularly polarized wave on transmit. On receive, the array column is arranged multiple times next to each other to allow for digital beamforming in azimuthal direction. A prototype consisting of three receiving columns has been fabricated and measured. Grating lobes are reduced to an overall sidelobe level of less than −10 dB by a time-division multiplex scheme that switches through several transmit arrays in different locations. Radar system simulations based on the measured antenna patterns demonstrate a very good discrimination of elementary polarimetric scattering objects.

Precisely Automatic Time Window Locating for an Interferometric Fiber-Optic Sensor Array Based on a TDM Scheme.

Interferometric fiber-optic sensors are often organized in the form of large-scale arrays by lending the technique of time division multiplexing (TDM) to reduce the system cost. Discriminating the time windows for different sensor units is the prerequisite to successfully demodulate the sensing message, but it traditionally calls for a very time-consuming manual calibration process. To combat this problem, a novel automatic time window locating method is proposed in this paper. It introduces the concept of shape function and carries out the cross-correlation operation between the shape function and the sensor signal. The shape function is defined as the function whose curve profile reflects the main data characteristics of the sensor signal. The time window information is then extracted from the correlation result. This whole process is carried out automatically by the interrogation controller of the sensor system without any manual intervene. Experiments are conducted to validate this method. The proposed method can greatly reduce the complexity of locating time windows in large-scale TDM sensor arrays, and make the practical use of the TDM scheme much more convenient.

A Spread-Spectrum SQUID Multiplexer

The Transition-Edge Sensors (TES) is a mature, high-resolution x-ray spectrometer technology that provides a much higher efficiency than dispersive spectrometers such as gratings and crystal spectrometers. As larger arrays are developed, time-division multiplexing schemes operating at MHz frequencies are being replaced by microwave SQUID multiplexers using frequency-division multiplexing at GHz frequencies. However, the multiplexing factor achievable with microwave SQUIDs is limited by the high slew rate on the leading edge of x-ray pulses. In this paper, we propose a new multiplexing scheme for high-slew-rate TES x-ray calorimeters: the spread-spectrum SQUID multiplexer, which has the potential to enable higher multiplexing factors, especially in applications with lower photon arrival rates.

Block network structure layout based on time and space division multiplexing scheme in an indoor positioning system using light-emitting diode

In an indoor positioning system with numerous light emitting diodes (LEDs), one of the most critical issues that must be addressed is the design of a suitable layout for numerous LEDs. In the layout design, the neighbor interference and the long time delay are two of the main factors that limit the positioning accuracy of a moving device. In this study, we propose a novel layout design method of topological block network structure (BNS) based on time and space division multiplexing (TSDM) to accurately locate a large number of moving objects in an indoor environment under the condition of meeting lighting requirement. Performance indicator, the positioning accuracy, was focused on in this paper. The simulation results showed that with a suitable distance between adjacent LEDs adapted to the room height, the various illumination standards can be satisfied and the system time delay can be reduced to less than 500 ms. The results further demonstrated that positioning accuracy of less than 1 cm can be achieved by employing our BNS and TSDM scheme in 2D and 3D positioning algorithm with dimensions of 25 m by 25 m by 3 m.

Time-Division Multiplexing Wireless Power Transfer for Separately Excited DC Motor Drives

This paper proposes and implements the concept of time-division multiplexing (TDM) wireless power transfer (WPT) for separately excited dc motor drives. Essentially, the proposed WPT system has only one transmitter that can transfer power to multiple receivers simultaneously while the power transfer to individual receivers can be independently controlled. Thus, the armature and field currents of the separately excited dc motor can be independently controlled, hence achieving the desired constant torque operation and constant power operation. The key is to make use of the TDM scheme to simultaneously transfer powers to both the armature and field windings. Meanwhile, the burst firing control method is incorporated to independently regulate the power flows to the armature and field windings at the resonant frequency, hence retaining the maximum power transfer efficiency. Both finite element analysis and experimentation are given to verify the validity of the proposed system.

Motion compensation for TDM MIMO radar by sparse reconstruction

A motion-compensation method that applies sparse reconstruction (SR) to reconstruct the Doppler spectrum of targets based on a random transmission scheme is proposed for time-division multiplexing (TDM) multiple-input multiple-output (MIMO) radar. Since the random transmission can eliminate the characteristic of periodic time-delay in conventional TDM scheme between transmit cycles, the angle information of a target is not affected by its motion. Therefore, the angle and velocity are no longer coupled with each other and can be estimated separately. This method not only overcome the space–frequency coupling problem but also enhances the unambiguous Doppler interval. Another advantage is that the method is valid even when the estimated target velocity is ambiguous. The results reported here offer the possibility of utilising SR to solve conventional TDM MIMO problems. The effectiveness of the proposed method is demonstrated by experimental results.

Development of an atmospheric polarization Scheimpflug lidar system based on a time-division multiplexing scheme.

A polarization Scheimpflug lidar system based on the Scheimpflug principle has been developed by employing two linearly polarized 808nm laser diodes and a complementary metal-oxide-semiconductor (CMOS) image sensor. The polarization of one laser diode is rotated 90° by a half-wave plate. The two laser beams with orthogonal polarizations are combined by a polarization beam splitter and transmitted into the atmosphere. The corresponding parallel- and perpendicular-polarized backscattering echoes are detected by the 45° tilted CMOS sensor using a time-division multiplexing scheme. A 24h continuous atmospheric vertical profiling of the depolarization ratio has been performed by using the polarization Scheimpflug lidar system. The promising results successfully demonstrated that the present lidar system has potential for the polarization studies of atmospheric aerosols.

Digital Time-Division Multiplexing Readout Circuit for Sensor Arrays

We have devised a digital time-division multiplexing (TDM) scheme for minimizing the circuit complexity required for an array of sensors. As a proof-of-concept, we have designed, fabricated, and tested a four-channel digital TDM readout circuit. The proposed scheme can be generalized for a larger number of channels. The readout circuit comprises an array of ADCs to digitize sensor outputs, a multiplexing unit, a clock controller, and a counter with parallel-to-serial output interface. For demonstration purposes, we employed low-pass phase modulation–demodulation ADCs running in a synchronous mode of operation. To facilitate an independent verification of circuit operation, we also placed an on-chip pattern generator to apply a unique pattern to each channel. The multiplexing unit is based on an array of sequentially triggered switches, each controlling the flow of data from a single ADC to a common output bus. In our scheme, the switches are realized using RS-flip-flops with nondestructive (RSN) readout cells with only one RSN cell turned on at a time. Multiplexed output data were stored in ripple counter based on T-flip-flops and read out to room temperature electronics using a serial interface. The chip was immersed in liquid helium at 4.2-K temperature and extensively evaluated at sampling frequencies up to 12.8 GHz. By means of embedded pattern generators, we proved the correct operation of each channel and of all four channels combined. We also were able to perform reconstruction of a signal applied to individual ADC. The chip was fabricated using HYPRES’ 4.5-kA/cm2 process with four Nb metal layers. We briefly discuss the proposed scheme's scalability for higher current density and smaller feature size fab processes.