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Shalabh Gupta

Publications and source records attributed to Shalabh Gupta.

36 records · Page 2Linked to original sources
arXiv2020

Rapid Path Planning for Dubins Vehicles under Environmental Currents

This paper presents a rapid (real time) solution to the minimum-time path planning problem for Dubins vehicles under environmental currents (wind or ocean currents). Real-time solutions are essential in time-critical situations (such as replanning under dynamically changing environments or tracking fast moving targets). Typically, Dubins problem requires to solve for six path types; however, due to the presence of currents, four of these path types require to solve the root-finding problem involving transcendental functions. Thus, the existing methods result in high computation times and their applicability for real-time applications is limited. In this regard, in order to obtain a real-time solution, this paper proposes a novel approach where only a subset of two Dubins path types (LSL and RSR) are used which have direct analytical solutions in the presence of currents. However, these two path types do not provide full reachability. We show that by extending the feasible range of circular arcs in the LSL and RSR path types from $2π$ to $4π$: 1) full reachability of any goal pose is guaranteed, and 2) paths with lower time costs as compared to the corresponding $2π$-arc paths can be produced. Theoretical properties are rigorously established, supported by several examples, and evaluated in comparison to the Dubins solutions by extensive Monte-Carlo simulations.

cs.RO↗
arXiv2020

POSE.R: Prediction-based Opportunistic Sensing for Resilient and Efficient Sensor Networks

The paper presents a distributed algorithm, called Prediction-based Opportunistic Sensing for Resilient and Efficient Sensor Networks (POSE.R), where the sensor nodes utilize predictions of the targets positions to probabilistically control their multi-modal operating states to track the target. There are two desired features of the algorithm: energy-efficiency and resilience. If the target is traveling through a high node density area, then an optimal sensor selection approach is employed that maximizes a joint cost function of remaining energy and geometric diversity around the targets position. This provides energy-efficiency and increases the network lifetime while preventing redundant nodes from tracking the target. On the other hand, if the target is traveling through a low node density area or in a coverage gap (e.g., formed by node failures or non-uniform node deployment), then a potential game is played amongst the surrounding nodes to optimally expand their sensing ranges via minimizing energy consumption and maximizing target coverage. This provides resilience, that is the self-healing capability to track the target in the presence of low node densities and coverage gaps. The algorithm is comparatively evaluated against existing approaches through Monte Carlo simulations which demonstrate its superiority in terms of tracking performance, network-resilience and network-lifetime.

eess.SY↗
arXiv2020

$ε^*$+: An Online Coverage Path Planning Algorithm for Energy-constrained Autonomous Vehicles

This paper presents a novel algorithm, called $ε^*$+, for online coverage path planning of unknown environments using energy-constrained autonomous vehicles. Due to limited battery size, the energy-constrained vehicles have limited duration of operation time. Therefore, while executing a coverage trajectory, the vehicle has to return to the charging station for a recharge before the battery runs out. In this regard, the $ε^*$+ algorithm enables the vehicle to retreat back to the charging station based on the remaining energy which is monitored throughout the coverage process. This is followed by an advance trajectory that takes the vehicle to a near by unexplored waypoint to restart the coverage process, instead of taking it back to the previous left over point of the retreat trajectory; thus reducing the overall coverage time. The proposed $ε^*$+ algorithm is an extension of the $ε^*$ algorithm, which utilizes an Exploratory Turing Machine (ETM) as a supervisor to navigate the vehicle with back and forth trajectory for complete coverage. The performance of the $ε^*$+ algorithm is validated on complex scenarios using Player/Stage which is a high-fidelity robotic simulator.

cs.RO↗
arXiv2020

T$^{\star}$-Lite: A Fast Time-Risk Optimal Motion Planning Algorithm for Multi-Speed Autonomous Vehicles

In this paper, we develop a new algorithm, called T$^{\star}$-Lite, that enables fast time-risk optimal motion planning for variable-speed autonomous vehicles. The T$^{\star}$-Lite algorithm is a significantly faster version of the previously developed T$^{\star}$ algorithm. T$^{\star}$-Lite uses the novel time-risk cost function of T$^{\star}$; however, instead of a grid-based approach, it uses an asymptotically optimal sampling-based motion planner. Furthermore, it utilizes the recently developed Generalized Multi-speed Dubins Motion-model (GMDM) for sample-to-sample kinodynamic motion planning. The sample-based approach and GMDM significantly reduce the computational burden of T$^{\star}$ while providing reasonable solution quality. The sample points are drawn from a four-dimensional configuration space consisting of two position coordinates plus vehicle heading and speed. Specifically, T$^{\star}$-Lite enables the motion planner to select the vehicle speed and direction based on its proximity to the obstacle to generate faster and safer paths. In this paper, T$^{\star}$-Lite is developed using the RRT$^{\star}$ motion planner, but adaptation to other motion planners is straightforward and depends on the needs of the planner

cs.RO↗
arXiv2020

All-Analog Adaptive Equalizer for Coherent Data Center Interconnects

In a high-speed coherent optical transmission system, typically the signals obtained at the receiver front-end are digitized using very high-speed ADCs and then processed in the digital domain to remove optical channel impairments. In this work, we show that these signals can instead be processed in the analog domain itself, which can significantly reduce the power consumption as well as the complexity of the receiver. The first all-analog adaptive equalizer for receivers of coherent dual-polarization optical links has been presented with its detailed architecture and measurement results. The proof-of-concept equalizer uses the constant modulus algorithm for blind adaptation of its weight coefficients to implement a 4x4 2-tap FIR filter in 130 nm SiGe BiCMOS technology. Its functionality is evaluated experimentally for 40 Gb /s data rate and 10 km standard single-mode fiber channel. This demonstration shows that the use of all-analog processing for short-reach data-center interconnects is feasible and is a much simpler solution than the use of the high-speed ADC+DSP based approach. Moreover, when implemented in advanced CMOS or FinFET technologies, the power consumption of the equalizer is expected to be significantly lower than the DSP based implementations in similar process technologies.

eess.SP↗
arXiv2019

Demonstration of an LO-less, DSP-free QPSK Receiver for Data Center Interconnects

We present the first demonstration of a local oscillator (LO)-less digital signal processing (DSP)-free coherent receiver for high-capacity short distance optical links. Experimental results with an analog domain constant modulous algorithm (CMA)-based equalizer chip for the self-homodyne quadrature phase shift keying (SH-QPSK) system validate the employability of an all-analog and LO-less receiver for low-power interconnects.

eess.SP↗
arXiv2019

High-Capacity Coherent DCIs using PolMuxed Carrier and LO-Less Receiver

A PAM4 based direct detection system has been standardized for short-distance data center interconnects because of its simple architecture. Performance of the PAM4 systems is limited for high dispersion values or demands complicated signal processing for further increase in data rates. A polarization multiplexed carrier based self-homodyne (PMC-SH) link with adaptive polarization control is a practical approach with an laser oscillator (LO)-less and carrier phase recovery (CPR)-free coherent receiver that can replace PAM4 links for achieving high data rates. We analytically find that PMC-SH scheme results in a significantly better BER for a given transmission rate or can achieve doubling of the data rate for given bandwidth of electronics and laser power (when compared with PAM4). Practical implementation of the proposed system with adaptive polarization control is also discussed. Presented theoretical frame work highlights the advantages of such self-homodyne systems over PAM4 based systems in terms of SNR requirements and capacity.

eess.SP↗
arXiv2019

CARE: Cooperative Autonomy for Resilience and Efficiency of Robot Teams for Complete Coverage of Unknown Environments under Robot Failures

This paper addresses the problem of Multi-robot Coverage Path Planning (MCPP) for unknown environments in the presence of robot failures. Unexpected robot failures can seriously degrade the performance of a robot team and in extreme cases jeopardize the overall operation. Therefore, this paper presents a distributed algorithm, called Cooperative Autonomy for Resilience and Efficiency (CARE), which not only provides resilience to the robot team against failures of individual robots, but also improves the overall efficiency of operation via event-driven replanning. The algorithm uses distributed Discrete Event Supervisors (DESs), which trigger games between a set of feasible players in the event of a robot failure or idling, to make collaborative decisions for task reallocations. The game-theoretic structure is built using Potential Games, where the utility of each player is aligned with a shared objective function for all players. The algorithm has been validated in various complex scenarios on a high-fidelity robotic simulator, and the results demonstrate that the team achieves complete coverage under failures, reduced coverage time, and faster target discovery as compared to three alternative methods.

cs.RO↗
arXiv2018

A Polarization Multiplexed Carrier based Coherent Link with Adaptive Polarization Control

Transmitting polarization multiplexed carrier makes the receiver of a coherent system local oscillator-less and frequency offset-free. A polarization multiplexed carrier based self-homodyne (PMC-SH) system with an adaptive polarization control (PC) can replace pulse amplitude modulation (PAM- 4) data center interconnects. An adaptive PC technique is practically implemented by using an electrically controlled PC along-with control circuitry for PMC-SH systems. The de-multiplexing of the carrier and the modulated signal by using this technique is validated through simulations for a 50 Gbaud PMC-SH quadrature phase shift keying (QPSK) system with 20km standard single mode fiber (SSMF). We successfully demonstrate 16 Gbaud PMC-SH systems with adaptive PC for 10km SSMF channel. A bit error rate (BER) of 5.9 x 10^(-5) is achieved with 32 Gb/s PMC-SHQPSK system without any signal processing while a BER of 8.7 x 10^(-3) is achieved with a 64 Gb/s PMC-SH quadrature amplitude modulation (16QAM) system after equalization.

eess.SP↗
arXiv2018

A Phase Lookahead DTC for Fast Settling Switched Loop DPLL

In most digital-to-time converter (DTC) based applications, apart from maintaining low integral non-linearity (INL), it is also required of the system to achieve a wide frequency translation range. To achieve this performance, we present a dual-phase direct digital synthesizer (DDS) based DTC with phase-lookahead mechanism. The proposed technique of variable phase-advancement enhances the frequency translation range, without excessive power consumption. A 5-GHz digital phase locked loop (DPLL) with switched loop, incorporating this DDS based DTC, is implemented in CMOS65nm-LL technology. The proposed DDS based DTC is able to perform fractional shift upto 80MHz with 100MHz reference clock, using 3mW of power from 1.2V supply. A simple look-up table based foreground-calibration of phase-to-amplitude converter (PAC) in DDS improves the peak INL of the DTC to 0.25ps. Hence, with the proposed DTC and a proportional-integral-derivative (PID) controller based loop, we are able to achieve a low-jitter fractional-N DPLL with fastest settling time of 1us reported until now for fractional-N PLLs.

physics.ins-det↗
arXiv2018

Stability Analysis for Fast Settling Switched DPLL

In current generation digital phase locked loop (DPLL) architectures, techniques like adaptive loop bandwidth with loop order switching and switched phase-detection are employed to achieve better lock time and jitter performance. This work derives stability conditions for such DPLL architectures using Multiple Lyapunov Functions (MLFs) for switched systems. The loop-parameters chosen on the basis of these stability conditions ensure that chattering phenomenon does not occur during switching between different subsystems. A 5GHz fractional-N DPLL designed with these loop-parameter values is fabricated in CMOS65nm-LL technology. The measured settling time of the implemented DPLL is within 1us. The efficiency of switching rule and stability conditions used for this DPLL is validated with the fast settling response, which is the best lock time reported until now for fractional-N DPLLs.

eess.SY↗
arXiv2018

Adaptive Polarization Control for Coherent Optical Links with Polarization Multiplexed Carrier

Self-homodyne systems with polarization multiplexed carrier offer an LO-less coherent receiver with simplified signal processing requirement that can be a good candidate for high-speed short-reach data center interconnects. The practical implementation of these systems is limited by the requirement of polarization control at the receiver end for separating the carrier and the modulated signal. In this paper, effect of polarization impairments in polarization diversity based systems is studied and modeled. A novel and practical adaptive polarization control technique based on optical power feedback from one polarization is proposed for polarization multiplexed carrier based systems and verified through simulation results. The application of the proposed concept is experimentally demonstrated also for a QPSK system with polarization multiplexed carrier.

eess.SP↗
arXiv2012

Trade-off between Settling Time and Jitter in Phase Locked Loop

Most PLL architectures have inherent trade-off between settling time and jitter. This trade-off is ignored by commonly used Figure of Merit (FoM) for PLL, which considers only jitter and power for benchmarking PLL performance. This work proposes new Figure of Merit for PLL, which considers settling time also as performance parameter, along with jitter and power. In this work, trade-off between settling time and jitter is analyzed in linear/non-linear/hybrid PLLs, theoretically and with behavioral simulations. Then, based on settling time vs. jitter relation obtained, currently used Figure of Merit for PLL is modified to consider all important specifications i.e. lock time, power and jitter.

physics.ins-det↗
arXiv2009

Power Scaling in High Speed Analog-to-Digital Converters using Photonic Time Stretch Technique

Factors that contribute to the rapid increase in power dissipation as a function of input bandwidth in high speed electronic Analog-to-Digital Converters (ADCs) are discussed. We find that the figure of merit (FOM), defined as the energy required per conversion step, increases linearly with bandwidth for high-speed ADCs with moderate to high resolution, or equivalently, the power dissipation increases quadratically. It is shown that by use of photonic time-stretch technique, it is possible to have ADCs in which this FOM remains constant for up to 10 GHz input RF frequency. Using this technique, it is also possible to overcome the barrier to achieving high resolution caused by clock jitter and speed limitations of electronics in such ADCs. Use of optics is actively being pursued for reducing power dissipation and achieving higher data-rates for board-level and chip-level serial communication links. In the same manner, we expect that optics will also help in reducing power dissipation in high-speed ADCs in addition to providing broader bandwidths.

physics.ins-det↗
arXiv2009

Automatic Analog Beamforming Transceiver for 60 GHz Radios

We propose a transceiver architecture for automatic beamforming and instantaneous setup of a multigigabit-per-second wireless link between two millimeter wave radios. The retro-directive architecture eliminates necessity of slow and complex digital algorithms required for searching and tracking the directions of opposite end radios. Simulations predict <5 micro-seconds setup time for a 2-Gbps bidirectional 60-GHz communication link between two 10-meters apart radios. The radios have 4-element arrayed antennas, and use QPSK modulation with 1.5 GHz analog bandwidth.

cs.NI↗
arXiv2008

Photonic Time Stretch Enhanced Recording Scope

We demonstrate a new mode of operation for the Time Stretched A/D converter. The technique is superior to the sampling scope in that it permits the capture of non periodic events such as clustered noise.

physics.ins-det↗
arXiv2008

Time Warps in Photonic Time Stretch ADC and Their Mitigation

We demonstrate a 10-GHz bandwidth digitizer with 7-effective bits of resolution and 52dB SFDR, using photonic time stretch technique. To the best of our knowledge, this is the highest resolution analog-to-digital converter (ADC) of the same bandwidth, with at least an order of magnitude higher SNR than previously achieved. This is made possible by correction of distortion due to time warps, and non-linearities due to wavelength dependent bias variation in the Mach-Zehnder modulator. We also demonstrate concatenation of 30 wavelength interleaved time segments with high fidelity on the path to achieving continuous time operation.

physics.ins-det↗