2,131 research outputs found
Synchronization of a WDM Packet-Switched Slotted Ring
In this paper, we present two different strategies of
slot synchronization in wavelength-division-multiplexing (WDM)
packet-switched slotted-ring networks. Emphasis is given to the
architecture behind the WDM Optical Network Demonstrator
over Rings (WONDER) project, which is based on tunable
transmitters and fixed receivers. The WONDER experimental
prototype is currently being developed at the laboratories
of Politecnico di Torino. In the former strategy, a slotsynchronization
signal is transmitted by the master station on a
dedicated control wavelength; in the latter, slave nodes achieve
slot synchronization aligning on data packets that are received
from the master. The performance of both synchronization strategies,
particularly in terms of packet-collision probability, was
evaluated by simulation. The technique based on transmitting a
timing signal on a dedicated control wavelength achieves better
performance, although it is more expensive due to the need for an
additional wavelength. However, the technique based on aligning
data packets that are received from the master, despite attaining
lower timing stability, still deserves further study, particularly
if limiting the number of wavelengths and receivers is a major
requirement. Some experimental results, which were measured on
the WONDER prototype, are also shown. Measurement results,
together with theoretical findings, demonstrate the good synchronization
performance of the prototype
Implementation of QoS onto virtual bus network
Quality of Service (QoS) is a key issue in a multimedia environment because multimedia applications are sensitive to delay. The virtual bus architecture is a hierarchical access network structure that has been proposed to simplify network signaling. The network employs an interconnection of hierarchical database to support advanced routing of the signaling and traffic load. Therefore, the requirements and management of quality of service is important in the virtual bus network particularly to support multimedia applications. QoS and traffic parameters are specified for each class type and the OMNeT model has been described
A study of topologies and protocols for fiber optic local area network
The emergence of new applications requiring high data traffic necessitates the development of high speed local area networks. Optical fiber is selected as the transmission medium due to its inherent advantages over other possible media and the dual optical bus architecture is shown to be the most suitable topology. Asynchronous access protocols, including token, random, hybrid random/token, and virtual token schemes, are developed and analyzed. Exact expressions for insertion delay and utilization at light and heavy load are derived, and intermediate load behavior is investigated by simulation. A new tokenless adaptive scheme whose control depends only on the detection of activity on the channel is shown to outperform round-robin schemes under uneven loads and multipacket traffic and to perform optimally at light load. An approximate solution to the queueing delay for an oscillating polling scheme under chaining is obtained and results are compared with simulation. Solutions to the problem of building systems with a large number of stations are presented, including maximization of the number of optical couplers, and the use of passive star/bus topologies, bridges and gateways
Synchronous subnanosecond clock and data recovery for optically switched data centres using clock phase caching
The rapid growth in the amount of data being transferred within data centres, combined with the slowdown in Moore’s Law, creates challenges for the future scalability of electronically switched data-centre networks. Optical switches could offer a future-proof alternative, and photonic integration platforms have been demonstrated with nanosecond-scale optical switching times. End-to-end switching time is, however, currently limited by the clock and data recovery time, which typically takes microseconds, removing the benefits of nanosecond optical switching. Here we show that a clock phase caching technique can provide clock and data recovery times of under 625 ps (16 symbols at 25.6 Gb s−1). Our approach uses the measurement and storage of clock phase values in a synchronized network to simplify clock and data recovery versus conventional asynchronous approaches. We demonstrate the capabilities of our technique using a real-time prototype with commercial transceivers and validate its resilience against temperature variation and clock jitter
Multi-Tag Access for a High Precision Ultra-Wideband Localization System
Ultra-Wideband (UWB) wireless positioning systems have many advantages for track- ing and locating items in indoor environments. Surgical navigation and industrial process control are potential applications for high accuracy UWB localization systems with millimeter or sub-millimeter accuracy. I present improvements made to an existing high accuracy, multi-tag, UWB localization system. The goal of this thesis was to improve the multi-tag performance of this system while maintaining the high localization accuracy, and to utilize the UWB system for digital communications allowing the existing narrowband 2.4 GHz transceiver to be eliminated.
This thesis presents a proof-of-concept for a multi-tag, UWB localization system utilizing orthogonal time hopping multiple access (OTHMA). Asynchronous transmit- only UWB digital communication allows identification of tags without the use of a narrowband control channel, and time di↵erence of arrival (TDOA) accomplishes localization. A digital sampling circuit is used for both localization and digital communication. I address the inherent challenge of collisions in an asynchronous transmit-only system while maintaining high accuracy and high update rates. An experimental system was developed consisting of two base stations and two tags allowing measurement of 1-D localization accuracy along with system update rates. The experimental results for localization accuracy were equivalent to results from the existing system while update rates were improved by greater than 50%
Resilient Peer-to-Peer Ranging using Narrowband High-Performance Software-Defined Radios for Mission-Critical Applications
There has been a growing need for resilient positioning for numerous
applications of the military and emergency services that routinely
conduct operations that require an uninterrupted positioning service.
However, the level of resilience required for these applications is difficult
to achieve using the popular navigation and positioning systems available
at the time of this writing. Most of these systems are dependent on
existing infrastructure to function or have certain vulnerabilities that can
be too easily exploited by hostile forces. Mobile ad-hoc networks can
bypass some of these prevalent issues making them an auspicious topic for
positioning and navigation research and development. Such networks
consist of portable devices that collaborate to form wireless
communication links with one another and collectively carry out vital
network functions independent of any fixed centralized infrastructure.
The purpose of the research presented in this thesis is to adapt the
protocols of an existing narrowband mobile ad-hoc communications
system provided by Terrafix to enable range measuring for positioning.
This is done by extracting transmission and reception timestamps of
signals exchanged between neighbouring radios in the network with the
highest precision possible. However, many aspects of the radios forming
this network are generally not conducive to precise ranging, so the
ranging protocols implemented need to either maneuver around these
shortcomings or compensate for loss of precision caused. In particular,
the narrow bandwidth of the signals that drastically reduces the
resolution of symbol timing. The objective is to determine what level of
accuracy and precision is possible using this radio network and whether
one can justify investment for further development. Early experiments
have provided a simple ranging demonstration in a benign environment,
using the existing synchronization protocols, by extracting time data.
The experiments have then advanced to the radio’s signal processing to
adjust the synchronization protocols for maximize symbol timing
precision and correct for clock drift.
By implementing innovative synchronization techniques to the radio
network, ranging data collected under benign conditions can exhibit a
standard deviation of less than 3m. The lowest standard deviation
achieved using only the existing methods of synchronization was over two
orders of magnitude greater. All this is achieved in spite of the very
narrow 10−20kHz bandwidth of the radio signals, which makes producing
range estimates with an error less than 10−100m much more challenging
compared to wider bandwidth systems. However, this figure is beholden
to the relative motion of neighbouring radios in the network and how
frequently range estimates need to be made. This thesis demonstrates
how such a precision may be obtained and how this figure is likely to hold
up when applied in conditions that are not ideal
Implementation Aspects of a Transmitted-Reference UWB Receiver
In this paper, we discuss the design issues of an ultra wide band (UWB) receiver targeting a single-chip CMOS implementation for low data-rate applications like ad hoc wireless sensor networks. A non-coherent transmitted reference (TR) receiver is chosen because of its small complexity compared to other architectures. After a brief recapitulation of the UWB fundamentals and a short discussion on the major differences between coherent and non-coherent receivers, we discuss issues, challenges and possible design solutions. Several simulation results obtained by means of a behavioral model are presented, together with an analysis of the trade-off between performance and complexity in an integrated circuit implementation
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