6 research outputs found
On the Capacity of Communication Channels with Memory and Sampled Additive Cyclostationary Gaussian Noise: Full Version with Detailed Proofs
In this work we study the capacity of interference-limited channels with
memory. These channels model non-orthogonal communications scenarios, such as
the non-orthogonal multiple access (NOMA) scenario and underlay cognitive
communications, in which the interference from other communications signals is
much stronger than the thermal noise. Interference-limited communications is
expected to become a very common scenario in future wireless communications
systems, such as 5G, WiFi6, and beyond. As communications signals are
inherently cyclostationary in continuous time (CT), then after sampling at the
receiver, the discrete-time (DT) received signal model contains the sampled
desired information signal with additive sampled CT cyclostationary noise. The
sampled noise can be modeled as either a DT cyclostationary process or a DT
almost-cyclostationary process, where in the latter case the resulting channel
is not information-stable. In a previous work we characterized the capacity of
this model for the case in which the DT noise is memoryless. In the current
work we come closer to practical scenarios by modelling the resulting DT noise
as a finite-memory random process. The presence of memory requires the
development of a new set of tools for analyzing the capacity of channels with
additive non-stationary noise which has memory. Our results show, for the first
time, the relationship between memory, sampling frequency synchronization and
capacity, for interference-limited communications. The insights from our work
provide a link between the analog and the digital time domains, which has been
missing in most previous works on capacity analysis. Thus, our results can help
improving spectral efficiency and suggest optimal transceiver designs for
future communications paradigms.Comment: accepted to the IEEE Transactions on Information Theor
Deep Space Telecommunications Systems Engineering
Descriptive and analytical information useful for the optimal design, specification, and performance evaluation of deep space telecommunications systems is presented. Telemetry, tracking, and command systems, receiver design, spacecraft antennas, frequency selection, interference, and modulation techniques are addressed
Treatise on Hearing: The Temporal Auditory Imaging Theory Inspired by Optics and Communication
A new theory of mammalian hearing is presented, which accounts for the
auditory image in the midbrain (inferior colliculus) of objects in the
acoustical environment of the listener. It is shown that the ear is a temporal
imaging system that comprises three transformations of the envelope functions:
cochlear group-delay dispersion, cochlear time lensing, and neural group-delay
dispersion. These elements are analogous to the optical transformations in
vision of diffraction between the object and the eye, spatial lensing by the
lens, and second diffraction between the lens and the retina. Unlike the eye,
it is established that the human auditory system is naturally defocused, so
that coherent stimuli do not react to the defocus, whereas completely
incoherent stimuli are impacted by it and may be blurred by design. It is
argued that the auditory system can use this differential focusing to enhance
or degrade the images of real-world acoustical objects that are partially
coherent. The theory is founded on coherence and temporal imaging theories that
were adopted from optics. In addition to the imaging transformations, the
corresponding inverse-domain modulation transfer functions are derived and
interpreted with consideration to the nonuniform neural sampling operation of
the auditory nerve. These ideas are used to rigorously initiate the concepts of
sharpness and blur in auditory imaging, auditory aberrations, and auditory
depth of field. In parallel, ideas from communication theory are used to show
that the organ of Corti functions as a multichannel phase-locked loop (PLL)
that constitutes the point of entry for auditory phase locking and hence
conserves the signal coherence. It provides an anchor for a dual coherent and
noncoherent auditory detection in the auditory brain that culminates in
auditory accommodation. Implications on hearing impairments are discussed as
well.Comment: 603 pages, 131 figures, 13 tables, 1570 reference
Collective analog bioelectronic computation
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 677-710).In this thesis, I present two examples of fast-and-highly-parallel analog computation inspired by architectures in biology. The first example, an RF cochlea, maps the partial differential equations that describe fluid-membrane-hair-cell wave propagation in the biological cochlea to an equivalent inductor-capacitor-transistor integrated circuit. It allows ultra-broadband spectrum analysis of RF signals to be performed in a rapid low-power fashion, thus enabling applications for universal or software radio. The second example exploits detailed similarities between the equations that describe chemical-reaction dynamics and the equations that describe subthreshold current flow in transistors to create fast-and-highly-parallel integrated-circuit models of protein-protein and gene-protein networks inside a cell. Due to a natural mapping between the Poisson statistics of molecular flows in a chemical reaction and Poisson statistics of electronic current flow in a transistor, stochastic effects are automatically incorporated into the circuit architecture, allowing highly computationally intensive stochastic simulations of large-scale biochemical reaction networks to be performed rapidly. I show that the exponentially tapered transmission-line architecture of the mammalian cochlea performs constant-fractional-bandwidth spectrum analysis with O(N) expenditure of both analysis time and hardware, where N is the number of analyzed frequency bins. This is the best known performance of any spectrum-analysis architecture, including the constant-resolution Fast Fourier Transform (FFT), which scales as O(N logN), or a constant-fractional-bandwidth filterbank, which scales as O (N2).(cont.) The RF cochlea uses this bio-inspired architecture to perform real-time, on-chip spectrum analysis at radio frequencies. I demonstrate two cochlea chips, implemented in standard 0.13m CMOS technology, that decompose the RF spectrum from 600MHz to 8GHz into 50 log-spaced channels, consume < 300mW of power, and possess 70dB of dynamic range. The real-time spectrum analysis capabilities of my chips make them uniquely suitable for ultra-broadband universal or software radio receivers of the future. I show that the protein-protein and gene-protein chips that I have built are particularly suitable for simulation, parameter discovery and sensitivity analysis of interaction networks in cell biology, such as signaling, metabolic, and gene regulation pathways. Importantly, the chips carry out massively parallel computations, resulting in simulation times that are independent of model complexity, i.e., O(1). They also automatically model stochastic effects, which are of importance in many biological systems, but are numerically stiff and simulate slowly on digital computers. Currently, non-fundamental data-acquisition limitations show that my proof-of-concept chips simulate small-scale biochemical reaction networks at least 100 times faster than modern desktop machines. It should be possible to get 103 to 106 simulation speedups of genome-scale and organ-scale intracellular and extracellular biochemical reaction networks with improved versions of my chips. Such chips could be important both as analysis tools in systems biology and design tools in synthetic biology.by Soumyajit Mandal.Ph.D