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Impact of interconnected architectures on near-term quantum algorithms

June 1, 2025
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Conference Paper
Author:
Eric Bersin
…
Topic:
quantum
R&D area:
R&D group:

Summary

Scaling quantum computers requires interconnected processors; however, the interconnected architecture's effect on computing performance is not well quantified. We assess the impact of architectures on algorithm performance and identify performance benefits relative to interconnect-free architectures.
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Summary

Scaling quantum computers requires interconnected processors; however, the interconnected architecture's effect on computing performance is not well quantified. We assess the impact of architectures on algorithm performance and identify performance benefits relative to interconnect-free architectures.

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Impact of interconnected architectures on near-term quantum algorithms

Capacity-based analysis of physical-layer and link-layer techniques for reliable communication over free-space optical fading channels

January 23, 2025
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Conference Paper
Author:
Curt M. Schieler
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Topic:
laser communications
R&D area:
R&D group:

Summary

Free-space optical communication links can experience signal power fluctuations due to channel effects such as turbulence and pointing jitter. Systems can ensure reliable, error-free communication over fading channels by using physical-layer techniques (e.g., forward error correction with codeword interleaving) and link-layer techniques (e.g., erasure coding or ARQ). In this work, Shannon capacity analysis is used to compare the fundamental performance of different coding architectures in a variety of link conditions. For systems using coherent receivers we find that, in channels with benign to moderate fade statistics, there can be a ~3 dB link budget advantage to using physical-layer interleaving instead of deferring fade mitigation to the link layer. On the other hand, in very strong fluctuations or when system robustness is paramount, it can be advantageous to use link layer codes.
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Summary

Free-space optical communication links can experience signal power fluctuations due to channel effects such as turbulence and pointing jitter. Systems can ensure reliable, error-free communication over fading channels by using physical-layer techniques (e.g., forward error correction with codeword interleaving) and link-layer techniques (e.g., erasure coding or ARQ). In this work...

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Capacity-based analysis of physical-layer and link-layer techniques for reliable communication over free-space optical fading channels

Covariance estimation with scanning arrays: FY23 RF Systems Technical Investment Program

December 21, 2023
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Project Report
Author:
Keith W. Forsythe
Published in:
MIT Lincoln Laboratory Report TIP-194
Topic:
RF systems
R&D area:
R&D group:

Summary

Analog arrays with steerable beams can be capable of angle estimation and sometimes even adaptive beamforming based on power measurements taken at the outputs of multiple beam dwells. In the interesting case of a reflectarray, where beams are formed using a large collection of programmable, passive phase shifters, it is possible to use multiple dwells to estimate signal correlations among the phase shifters. These correlations form an estimated covariance matrix at the phase centers of the shifters. Adaptive beamforming and geolocation can be based on this covariance matrix. Various methods for estimating full-rank and approximately rank-deficient covariance matrices using power measurements from multiple dwells are introduced and evaluated. In some cases, the performance of an estimator can be shown to be optimal in the sense of achieving Cramer-Rao bounds for the estimated covariance parameters.
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Summary

Analog arrays with steerable beams can be capable of angle estimation and sometimes even adaptive beamforming based on power measurements taken at the outputs of multiple beam dwells. In the interesting case of a reflectarray, where beams are formed using a large collection of programmable, passive phase shifters, it is...

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Covariance estimation with scanning arrays: FY23 RF Systems Technical Investment Program

Network performance of pLEO topologies in a high-inclination Walker Delta Satellite Constellation

March 4, 2023
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Conference Paper
Author:
Thomas H. Shake
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Published in:
IEEE Aerospace Conf. Proc., 4-11 March 2023, 188722.
Topic:
satellites
R&D area:
R&D group:

Summary

Low-earth-orbit satellite constellations with hundreds to thousands of satellites are emerging as practical alternatives for providing various types of data services such as global networking and large-scale sensing. The network performance of these satellite constellations is strongly dependent on the topology of the inter-satellite links (ISLs) in such systems. This paper studies the effects of six different ISL topologies, coupled with three configurations of ground relay terminals, on path failure rate, path latency, and link transmission efficiency in an example highly-inclined Walker Delta constellation with 360 satellites. These network performance parameters are calculated in the presence of satellite failures in the constellation. Trade-offs between ISL connection density and overall performance are examined and quantified. Topologies with 4 active ISLs per satellite are shown to perform significantly better than topologies requiring fewer, especially as the average number of active ISLs per satellite becomes significantly less than three. Latencies for a topology requiring 3 active ISLs per satellite are shown to be between 15 and 60% higher than for a 4-ISL reference topology. Path availabilities for the 3-ISL topology are shown to be on the order of 30% lower for a benchmark case of 10 satellite failures. The performance of near-minimal topologies (e.g., an average of 2.2 active ISLs per satellite) is much worse. Latency reductions of 10-30% and path failure rate improvements on the order of 45% are shown to be obtainable by the inclusion of 2 to 5 strategically located ground relay stations
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Summary

Low-earth-orbit satellite constellations with hundreds to thousands of satellites are emerging as practical alternatives for providing various types of data services such as global networking and large-scale sensing. The network performance of these satellite constellations is strongly dependent on the topology of the inter-satellite links (ISLs) in such systems. This...

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Network performance of pLEO topologies in a high-inclination Walker Delta Satellite Constellation

Rate control with autoregressive forecasting for high frequency communication

November 28, 2022
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Conference Paper
Author:
Allan Ko
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Published in:
2022 IEEE Military Communications Conf., MILCOM, 28 November - 2 December 2022.
Topic:
communications
R&D area:
R&D group:

Summary

This work introduces a data-driven framework for rate control and applies it to high frequency (HF) communication systems that propagate via the Earth’s ionosphere. The rate control approach uses statistical techniques to forecast channel state with an autoregressive (AR) model, which has previously been applied to different forms of wireless fading, including "medium" timescale fading at HF. The objective of rate control is to maximize the data rate while constraining the rate of packets decoded in error. We show that under ideal assumptions, the rate controller selects the rate by backing off from the forecast average signal-to-noise ratio (SNR) by a factor of sigmaQ^-1(Beta), where sigma^2 correlates with fading variance, Beta denotes a constraint on decoder errors, and Q(.) is the complementary cumulative distribution function of the Gaussian distribution. Simulation results on an HF channel model show that compared with naive schemes, AR forecasting provides a good balance between achieving high rate and ensuring reliability.
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Summary

This work introduces a data-driven framework for rate control and applies it to high frequency (HF) communication systems that propagate via the Earth’s ionosphere. The rate control approach uses statistical techniques to forecast channel state with an autoregressive (AR) model, which has previously been applied to different forms of wireless...

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Rate control with autoregressive forecasting for high frequency communication

Failure resilience in proliferated low earth orbit satellite network topologies

November 28, 2022
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Conference Paper
Author:
Thomas H. Shake
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Published in:
2022 IEEE Military Communications Conf., MILCOM, 28 November - 2 December 2022.
Topic:
satellites
R&D area:
R&D group:

Summary

The vision of continuous network connectivity for users located anywhere on Earth is increasingly being enabled by satellite constellations with hundreds to thousands of satellites operating in low altitude orbits (typically somewhere between a few hundred and two thousand km). These constellations are often referred to as proliferated Low Earth Orbit (pLEO) constellations. Potential military use of such constellations would require a high degree of resilience against various types of failures. This paper examines how resilience to satellite failures in particular is affected by topology and topology management for a moderate-sized constellation of 360 low-earth-orbit satellites providing 2X-redundant global coverage. We present simulations quantifying the effects of two vs. four inter-satellite links (ISLs) per satellite, and of dynamic post-failure topology reconfiguration vs static topology management. Simulations show differences of 65-80% in mission connectivity between 4-ISL topologies with dynamic topology reconfiguration and 2-ISL topologies with static topology using two different traffic scenarios.
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Summary

The vision of continuous network connectivity for users located anywhere on Earth is increasingly being enabled by satellite constellations with hundreds to thousands of satellites operating in low altitude orbits (typically somewhere between a few hundred and two thousand km). These constellations are often referred to as proliferated Low Earth...

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Failure resilience in proliferated low earth orbit satellite network topologies

Contingent routing using orbital geometry in proliferated low-earth-orbit satellite networks

November 28, 2022
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Conference Paper
Author:
Thomas H. Shake
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Published in:
2022 IEEE Military Communications Conf., MILCOM, 28 November - 2 December 2022.
Topic:
satellites
R&D area:
R&D group:

Summary

Optimum adaptive routing in proliferated low-earth-orbit (pLEO) satellite networks requires intensive computation. The very small size, light weight, and low power of individual satellites in such networks makes a centralized, terrestrial, SDN-like approach to routing computation an attractive solution. However, it is highly desirable to have a distributed backup routing capability onboard each satellite that can maintain service if the central computational node(s) fail or lose their pathway(s) to upload routing data frequently to each satellite. This paper presents a routing algorithm based on orbital geometry that has a very low computation and storage requirements and is suitable as a backup routing capability in the event of failure of a centralized routing calculation node or nodes. Path failure rate, path latency, and link resource usage are simulated for a 360-satellite Walker Delta constellation with 4 inter-satellite link (ISL) terminals per satellite, and with up to 10% of the satellites having failed. For the fully intact satellite constellation, path failure rate is zero (identical to a shortest path routing algorithm), while mean latency and average link resource usage are shown to be approximately 12% and 13% higher, respectively, than with shortest path routing. With 10 random satellite failures in the constellation, the geometric algorithm has a path failure rate of less than 0.5%, while the mean latency and link resource usage are approximately 12% and 16% higher, respectively, than with shortest path routing.
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Summary

Optimum adaptive routing in proliferated low-earth-orbit (pLEO) satellite networks requires intensive computation. The very small size, light weight, and low power of individual satellites in such networks makes a centralized, terrestrial, SDN-like approach to routing computation an attractive solution. However, it is highly desirable to have a distributed backup routing...

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Contingent routing using orbital geometry in proliferated low-earth-orbit satellite networks

Robust network protocols for large swarms of small UAVs

March 5, 2022
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Conference Paper
Author:
Thomas B. Stahlbuhk
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Published in:
2022 IEEE Aeropsace Conf., AERO 2022, 18 p.
Topic:
UAVs
R&D area:
R&D group:

Summary

In this work, we detail a synchronized channel hopping network for autonomous swarms of small unmanned aerial vehicles (UAVs) conducting intelligence, surveillance, and reconnaissance (ISR) missions in the presence of interference and jamming. The core component of our design is Queue Length Informed Maximal Matching (QLIMM), a distributed transmission scheduling protocol that exchanges queue state information between nodes to assign subdivisions of the swarm to orthogonal hopping patterns in response to the network’s throughput demands. QLIMM efficiently allocates channel resources across large networks without relying on any centralized control or pre-planned traffic patterns, which is in the spirit of a swarming capability. However, given that the control messaging must scale up with the swarm’s size and the challenging interference environments we consider, fragility could be a concern. To observe under what conditions control fails, we test our protocol against both simulated partial-band noise jamming and background interference. For the latter, we use data collected from a small unmanned aircraft system to characterize the interference seen by a UAV in the 2.4 and 5 GHz bands in both urban and rural settings. These measurements show that the interference can be 15 dB higher at a 50-meter flight altitude when compared to observations on the ground. Using this data, we conduct extensive network simulations of QLIMM in Riverbed Modeler to show that, under moderate jamming and interference, it outperforms traditional channel access methods as well as other scheduling protocols that do not pass queue state information.
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Summary

In this work, we detail a synchronized channel hopping network for autonomous swarms of small unmanned aerial vehicles (UAVs) conducting intelligence, surveillance, and reconnaissance (ISR) missions in the presence of interference and jamming. The core component of our design is Queue Length Informed Maximal Matching (QLIMM), a distributed transmission scheduling...

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Robust network protocols for large swarms of small UAVs

Capacity bounds for frequency-hopped BPSK

November 29, 2021
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Conference Paper
Author:
Frederick J. Block IV
Published in:
2021 IEEE Military Communications Conf., MILCOM, 29 November - 2 December 2021.
Topic:
communications
R&D area:
R&D group:

Summary

In some channels, such as the frequency-hop channel, the transmission may undergo abrupt transitions in phase. This can require the receiver to re-estimate the phase on each hop, or for the system to utilize modulation techniques that lend themselves to noncoherent detection. How well the receiver can estimate the phase depends on the channel signal-to-noise ratio and how long phase coherence can be assumed. Although prior work has shown that using any reference symbols to aid the phase estimation process is suboptimal with respect to capacity, their presence may be useful in practice as they can simplify the receiver processing. In this paper, the effects of per-pulse phase uncertainty are examined for systems using binary modulation. Both the fraction of the transmission that may be devoted to reference symbols without substantially reducing the overall channel capacity and the point at which it is better to forego coherent processing in favor of noncoherent demodulation are examined.
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Summary

In some channels, such as the frequency-hop channel, the transmission may undergo abrupt transitions in phase. This can require the receiver to re-estimate the phase on each hop, or for the system to utilize modulation techniques that lend themselves to noncoherent detection. How well the receiver can estimate the phase...

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Capacity bounds for frequency-hopped BPSK

Application of complex split-activation feedforward networks to beamforming

October 31, 2021
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Conference Paper
Author:
Swaroop Appadwedula
Published in:
55th Asilomar Conf. on Signals, Systems and Computers, ACSSC, 31 October - 3 November 2021.
Topic:
machine learning
R&D area:
R&D group:

Summary

In increasingly congested RF environments and for jamming at closer ranges, amplifiers may introduce nonlinearities that linear adaptive beamforming techniques can't mitigate. Machine learning architectures are intended to solve such nonlinear least squares problems, but much of the current work and available software is limited to signals represented as real sequences. In this paper, neural networks using complex numbers to represent the complex baseband RF signals are considered. A complex backpropagation approach that calculates gradients and a Jacobian, allows for fast optimization of the neural networks. Through simulations, it is shown that complex neural networks require less training samples than their real counterparts and may generalize better in dynamic environments.
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Summary

In increasingly congested RF environments and for jamming at closer ranges, amplifiers may introduce nonlinearities that linear adaptive beamforming techniques can't mitigate. Machine learning architectures are intended to solve such nonlinear least squares problems, but much of the current work and available software is limited to signals represented as real...

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Application of complex split-activation feedforward networks to beamforming
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