1,232 research outputs found
Phase-locked Loop Dynamics in the Presence of Noise by Fokker-planck Techniques
Phase error behavior of phase-locked loop tracking system in presence of gaussian noise determined by fokker-planck equatio
Duality of Channel Encoding and Decoding - Part I: Rate-1 Binary Convolutional Codes
In this paper, we revisit the forward, backward and bidirectional
Bahl-Cocke-Jelinek-Raviv (BCJR) soft-input soft-output (SISO) maximum a
posteriori probability (MAP) decoding process of rate-1 binary convolutional
codes. From this we establish some interesting explicit relationships between
encoding and decoding of rate-1 convolutional codes. We observe that the
forward and backward BCJR SISO MAP decoders can be simply represented by their
dual SISO channel encoders using shift registers in the complex number field.
Similarly, the bidirectional MAP decoding can be implemented by linearly
combining the shift register contents of the dual SISO encoders of the
respective forward and backward decoders. The dual encoder structures for
various recursive and non-recursive rate-1 convolutional codes are derived.Comment: 32 pages, 20 figures, to appear in ET
Coded spread spectrum digital transmission system design study
Results are presented of a comprehensive study of the performance of Viterbi-decoded convolutional codes in the presence of nonideal carrier tracking and bit synchronization. A constraint length 7, rate 1/3 convolutional code and parameters suitable for the space shuttle coded communications links are used. Mathematical models are developed and theoretical and simulation results are obtained to determine the tracking and acquisition performance of the system. Pseudorandom sequence spread spectrum techniques are also considered to minimize potential degradation caused by multipath
Convolutional coded dual header pulse interval modulation for line of sight photonic wireless links.
The analysis and simulation for convolutional coded dual header pulse interval modulation (CC-DH-PIM) scheme using a rate ½ convolutional code with the constraint length of 3 is presented. Decoding is implemented using the Viterbi algorithm with a hard decision. Mathematical analysis for the slot error rate (SER) upper bounds is presented and results are compared with the simulated data for a number of different modulation techniques. The authors show that the coded DH-PIM outperforms the pulse position modulation (PPM) scheme and offers >4 dB code gain at the SER of 10?4 compared to the standard DH-PIM. Results presented show that the CC-DH-PIM with a higher constraint length of 7 offers a code gain of 2 dB at SER of 10?5 compared to the CC-DH-PIM with a constraint length of 3. However, in CC-DH-PIM the improvement in the error performance is achieved at the cost of reduced transmission throughput compared to the standard DH-PIM
Concatenation of convolutional and block codes Final report
Comparison of concatenated and sequential decoding systems and convolutional code structural propertie
Study of information transfer optimization for communication satellites
The results are presented of a study of source coding, modulation/channel coding, and systems techniques for application to teleconferencing over high data rate digital communication satellite links. Simultaneous transmission of video, voice, data, and/or graphics is possible in various teleconferencing modes and one-way, two-way, and broadcast modes are considered. A satellite channel model including filters, limiter, a TWT, detectors, and an optimized equalizer is treated in detail. A complete analysis is presented for one set of system assumptions which exclude nonlinear gain and phase distortion in the TWT. Modulation, demodulation, and channel coding are considered, based on an additive white Gaussian noise channel model which is an idealization of an equalized channel. Source coding with emphasis on video data compression is reviewed, and the experimental facility utilized to test promising techniques is fully described
Nonlinear interactions with an ultrahigh flux of broadband entangled photons
We experimentally demonstrate sum-frequency generation (SFG) with entangled
photon-pairs, generating as many as 40,000 SFG photons per second, visible even
to the naked eye. The nonclassical nature of the interaction is exhibited by a
linear intensity-dependence of the nonlinear process. The key element in our
scheme is the generation of an ultrahigh flux of entangled photons while
maintaining their nonclassical properties. This is made possible by generating
the down-converted photons as broadband as possible, orders of magnitude wider
than the pump. This approach is readily applicable for other nonlinear
interactions, and may be applicable for various quantum-measurement tasks.Comment: 4 pages, 2 figures, Accepted to Phys. Rev. Let
Naturalistic Affective Expression Classification by a Multi-Stage Approach Based on Hidden Markov Models
In naturalistic behaviour, the affective states of a person
change at a rate much slower than the typical rate at which video or
audio is recorded (e.g. 25fps for video). Hence, there is a high probability
that consecutive recorded instants of expressions represent a same
affective content. In this paper, a multi-stage automatic affective expression
recognition system is proposed which uses Hidden Markov Models
(HMMs) to take into account this temporal relationship and finalize the
classification process. The hidden states of the HMMs are associated
with the levels of affective dimensions to convert the classification problem
into a best path finding problem in HMM. The system was tested on
the audio data of the Audio/Visual Emotion Challenge (AVEC) datasets
showing performance significantly above that of a one-stage classification
system that does not take into account the temporal relationship, as well
as above the baseline set provided by this Challenge. Due to the generality
of the approach, this system could be applied to other types of
affective modalities
The Globalstar mobile satellite system for worldwide personal communications
Loral Aerospace Corporation along with Qualcomm Inc. have developed a satellite system which offers global mobile voice and data services to and from handheld and mobile user terminals with omni-directional antennas. By combining the use of low-earth orbit (LEO) satellites with existing terrestrial communications systems and innovative, highly efficient spread spectrum techniques, the Globalstar system provides users with low-cost, reliable communications throughout the world. The Globalstar space segment consists of a constellation of 48 LEO satellites in circular orbits with 750 NM (1389 km) altitude. Each satellite communicates with the mobile users via the satellite-user links and with gateway stations. The gateway stations handle the interface between the Globalstar network and the OSTN/PLMN systems. Globalstar transceivers are similar to currently proposed digital cellular telephones in size and have a serial number that will allow the end user to make and receive calls from or to that device anywhere in the world. The Globalstar system is designed to operate as a complement to existing local, long-distance, public, private and specialized telecommunications networks. Service is primarily designed to serve the rural and thin route communications needs of consumers, government users, and private networks
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