Richard J. Barron

The duality between information embedding and source coding with side information and some applications

Aspects of the duality between the information-embedding problem and the Wyner-Ziv (1976) problem of source coding with side information at the decoder are developed and used to establish a spectrum new results on these and related problems, with implications for a number of important applications. The single-letter characterization of the information-embedding problem is developed and related to the corresponding characterization of the Wyner-Ziv problem, both of which correspond to optimization of a common mutual information difference. Dual variables and dual Markov conditions are identified, along with the dual role of noise and distortion in the two problems. For a Gaussian context with quadratic distortion metric, a geometric interpretation of the duality is developed. From such insights, we develop a capacity-achieving information-embedding system based on nested lattices. We show the resulting encoder-decoder has precisely the same decoder-encoder structure as the corresponding Wyner-Ziv system based on nested lattices that achieves the rate-distortion limit. For a binary context with Hamming distortion metric, the information-embedding capacity is developed, along with its relationship to the corresponding Wyner-Ziv rate-distortion function. In turn, an information-embedding system for this case based on nested linear codes is constructed having an encoder-decoder that is identical to the decoder-encoder structure for the corresponding system that achieves the Wyner-Ziv rate-distortion limit. Finally, based on these results, a simple layered joint source-channel coding system is developed with a perfectly symmetric encoder-decoder structure. Its application and performance is discussed in a broadcast setting in which there is a need to control the fidelity experienced by different receivers. Among other results, we show that such systems and their multilayer extensions retain attractive optimality properties in the Gaussian-quadratic case, but not in the binary-Hamming case.

781 Mbit/s photon-counting optical communications using a superconducting nanowire detector

We demonstrate 1550 nm photon-counting optical communications with a NbN-nanowire superconducting single-photon detector. Source data are encoded with a rate-1/2 forward-error correcting code and transmitted by use of 32-ary pulse-position modulation at 5 and 10 GHz slot rates. Error-free performance is obtained with -0.5 detected photon per source bit at a source data rate of 781 Mbits/s. To the best of our knowledge, this is the highest reported data rate for a photon-counting receiver.

Channel equalization for self-synchronizing chaotic systems

Most strategies proposed for utilizing chaotic signals for communications exploit the self-synchronization property of a class of chaotic systems. Any realistic communication channel will introduce distortion including time-dependent fading, dispersion, and modification of the frequency content due to channel filtering and multipath effects. All of these distortions will affect the ability of the chaotic receiver to properly synchronize. This paper develops and illustrates some specific approaches to channel equalization to compensate for these distortions for self-synchronizing chaotic systems. The approaches specifically exploit the properties of chaotic drive signals and the self-synchronization properties of the receiver.

Analysis of capacity and probability of outage for free-space optical channels with fading due to pointing and tracking error

Free-space laser communications systems experience fading due to quasi-static pointing error and tracking error that impairs communications performance. Under a block fading model we show that using forward error correcting codes and interleaving - a simple non-mechanical data processing technique - much of the harmful effect of tracking error on communications performance can be removed. Using the concepts of fading capacity and outage capacity, we provide analytical tools that quantify the effects of fading on communications performance with and without interleaving. A link budget based on this analysis includes three loss terms due to pointing and tracking error: 1) static loss, which is primarily a function of pointing error; 2) capacity loss, which is the power difference between fading capacity and fade-free capacity; and 3) finite interleaver loss, which is the power difference between the probability of outage curve and fading capacity. Assuming pulse-position modulation and a Poisson channel, we derive closed-form solutions for the probability of outage of interleaved systems using a Gaussian beam with circularly symmetric Gaussian tracking error.

1.5-photons/bit photon-counting optical communications using Geiger-mode avalanche photodiodes

We demonstrate a photon-counting communications link using Geiger-mode avalanche photodiodes. High-efficiency pulse-position modulation and forward error correcting codes are used to demonstrate a receiver sensitivity of 1.5 incident photons/bit.

Channel Equalization For Communication with Chaotic Signals

Chaotic signals and synchronized systems are potentially useful as modulation or masking waveforms for communications systems. This paper explores the effect on synchronization of frequency dependent channel gain, i.e., linear filtering. Several approaches to compensating for these effects are also discussed.

Superconducting nanowire single-photon detectors

We present our ongoing work on superconducting NbN-nanowire photodetectors, which deliver both high speed ( 50% at 1550 nm), promising access to new regimes in ultrafast photon counting applications.

Binary shaping for low-duty-cycle communications

We develop a method called binary shaping for transmitting low-duty-cycle sequences robustly over binary-input channels, that employs a convolutional shaping code and a serially-concatenated convolutional code (SCCC) for forward error correction. Binary shaping is closely related to the nested linear coding scheme for coding over channels with known interference.

High-data-rate photon-counting optical communications using a NbN-nanowire superconducting detector

We demonstrate photon-counting communications using a NbN-nanowire superconducting detector. The fast response time of this detector enables error-free communications using pulse-position modulated data at 10-GHz slot rates and data rates >780 Mbit/s.

1.25-Gbit/s photon-counting optical communications using a two-element superconducting nanowire single photon detector

The sensitivity of a high-rate photon-counting optical communications link depends on the performance of the photon counter used to detect the optical signal. In this paper, we focus on ways to reduce the effect of blocking, which is loss due to time periods in which the photon counter is inactive following a preceding detection event. This blocking loss can be reduced by using an array of photon counting detectors or by using photon counters with a shorter inactive period. Both of these techniques for reducing the blocking loss can be employed by using a multi-element superconducting nanowire single-photon detector. Two-element superconducting nanowire single-photon detectors are used to demonstrate error-free photon counting optical communication at data rates of 781 Mbit/s and 1.25 Gbit/s.