52,499 research outputs found
Evaluation of Frame Synchronization Algorithms for Wireless Communications
In this document, we study the synchronization between the sent frame and the received
frame in a communications system for a good recovery of the data and its probability of
success. It is a important due to the channel introduces impairments, and the signal is
di erent when arrives to the nish.
Studying Massey algorithm for real sequences, and improving it for complex sequences
used in Long Term Evolution, we see success of a correct detection or not.
The results show for big SNRs a great detection, with a very high percentage of success,
but adding the di erent impairments produced during the transmission in the channel,
the errors grow up, so in a perfect situation, the algorithm works for LTE.Tárrega Alonso, J. (2013). Evaluation of Frame Synchronization Algorithms for Wireless Communications. http://hdl.handle.net/10251/29043.Archivo delegad
Node Synchronization for the Viterbi Decoder
Motivated by the needs of NASA's Voyager 2 mission, in this paper we describe an algorithm which detects and corrects losses of node synchronization in convolutionally encoded data. This algorithm, which would be implemented as a hardware device external to a Viterbi decoder, makes statistical decisions about node synch based on the hard-quantized undecoded data stream. We will show that in a worst-case Voyager environment, our method will detect and correct a true loss of synch (thought to be a very rare event) within several hundred bits; many of the resulting outages will be corrected by the outer Reed-Solomon code. At the same time, the mean time between false alarms is on the order of several years, independent of the signal-to-noise ratio
Wireless Software Synchronization of Multiple Distributed Cameras
We present a method for precisely time-synchronizing the capture of image
sequences from a collection of smartphone cameras connected over WiFi. Our
method is entirely software-based, has only modest hardware requirements, and
achieves an accuracy of less than 250 microseconds on unmodified commodity
hardware. It does not use image content and synchronizes cameras prior to
capture. The algorithm operates in two stages. In the first stage, we designate
one device as the leader and synchronize each client device's clock to it by
estimating network delay. Once clocks are synchronized, the second stage
initiates continuous image streaming, estimates the relative phase of image
timestamps between each client and the leader, and shifts the streams into
alignment. We quantitatively validate our results on a multi-camera rig imaging
a high-precision LED array and qualitatively demonstrate significant
improvements to multi-view stereo depth estimation and stitching of dynamic
scenes. We release as open source 'libsoftwaresync', an Android implementation
of our system, to inspire new types of collective capture applications.Comment: Main: 9 pages, 10 figures. Supplemental: 3 pages, 5 figure
TS-MUWSN: Time synchronization for mobile underwater sensor networks
Time synchronization is an important, yet challenging, problem in underwater sensor networks (UWSNs). This challenge can be attributed to: 1) messaging timestamping; 2) node mobility; and 3) Doppler scale effect. To mitigate these problems, we present an acoustic-based time-synchronization algorithm for UWSN, where we compare several message time-stamping algorithms in addition to different Doppler scale estimators. A synchronization system is based on a bidirectional message exchange between a reference node and a slave one, which has to be synchronized. Therefore, we take as reference the DA-Sync-like protocol (Liu et al., 2014), which takes into account node's movement by using first-order kinematic equations, which refine Doppler scale factor estimation accuracy, and result in better synchronization performance. In our study, we propose to modify both time-stamping and Doppler scale estimation procedures. Besides simulation, we also perform real tests in controlled underwater communication in a water test tank and a shallow-water test in the Mediterranean Sea.Peer ReviewedPostprint (author's final draft
Impact of topology on layer 2 switched QoS sensitive services
High-bandwidth QoS sensitive services such as large scale video surveillance generally depend on provisioned capacity delivered by circuit-switched technology such as SONET/SDH. Yet development in layer 2 protocol sets and manageability extensions to Ethernet standards propose layer 2 packet switching technology as a viable, cheaper alternative to SONET/SDH. Layer 2 switched networks traditionally offer more complex topologies; in this paper we explain general QoS issues with layer 2 switching and show the impact of topology choice on service performance
Synchronization in two-level quantum systems
Recently, it was shown that dissipative quantum systems with three or more
levels are able to synchronize to an external signal, but it was stated that it
is not possible for two-level systems as they lack a stable limit cycle in the
unperturbed dynamics. At the same time, several papers, demonstrate, under a
different definition of what is synchronization, that the latter is possible in
qubits, although in different models which also include other elements. We show
how a quantum two-level system can be understood as containing a valid limit
cycle as the starting point of synchronization, and that it can synchronize its
dynamics to an external weak signal. This is demonstrated by analytically
solving the Lindblad equation of a two-level system coupled to an environment,
determining the steady state. This is a mixed state with contributions from
many pure states, each of which provides a valid limit cycle. We show that this
is sufficient to phase-lock the dynamics to a weak external signal, hence
clarifying synchronization in two-level systems. We use the Husimi Q
representation to analyze the synchronization region, defining a
synchronization measure which characterizes the strength of the phase-locking.
Also, we study the stability of the limit cycle and its deformation with the
strength of the signal in terms of the components of the Bloch vector of the
system. Finally, we generalize the model of the three-level system from in
order to illustrate how the stationary fixed point of that model can be changed
into a limit cycle similar to the one that we describe for the two-level
system.Comment: 7 pages, 6 figure
Visual to Sound: Generating Natural Sound for Videos in the Wild
As two of the five traditional human senses (sight, hearing, taste, smell,
and touch), vision and sound are basic sources through which humans understand
the world. Often correlated during natural events, these two modalities combine
to jointly affect human perception. In this paper, we pose the task of
generating sound given visual input. Such capabilities could help enable
applications in virtual reality (generating sound for virtual scenes
automatically) or provide additional accessibility to images or videos for
people with visual impairments. As a first step in this direction, we apply
learning-based methods to generate raw waveform samples given input video
frames. We evaluate our models on a dataset of videos containing a variety of
sounds (such as ambient sounds and sounds from people/animals). Our experiments
show that the generated sounds are fairly realistic and have good temporal
synchronization with the visual inputs.Comment: Project page:
http://bvision11.cs.unc.edu/bigpen/yipin/visual2sound_webpage/visual2sound.htm
The Function of the Second Postulate in Special Relativity
Many authors noted that the principle of relativity, together with space-time
symmetries, suffices to derive Lorentz-like coordinate transformations between
inertial frames. These contain a free parameter, , (equal to in
special relativity) which is usually claimed to be empirically determinable, so
that special relativity does not need the postulate of constancy of the speed
of light. I analyze this claim and find that all methods destined to measure
fail without further assumptions, similar to the second postulate.
Specifically, measuring requires a signal that travels identically in
opposite directions (this is unrelated to the conventionality of
synchronization, as the one-postulate program implicitly selects the standard
synchronization convention). Positing such a property about light is logically
weaker than Einstein's second postulate but suffices to recover special
relativity in full
Mark 4-A DSCC (Magellan-era) telemetry system description
An update to the description of the Deep Space Communications Complex portion of the Mark 4-A Telemetry system is given. This system is currently implemented at all signal processing centers. The upgrade of the telemetry system was undertaken primarily in support of the Voyager-Neptune Encounter and the Magellan mission. The Mark 3 Telemetry System is the predecessor of the Mark 4-A system
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