17,208 research outputs found
Crosstalk-free Conjugate Networks for Optical Multicast Switching
High-speed photonic switching networks can switch optical signals at the rate
of several terabits per second. However, they suffer from an intrinsic
crosstalk problem when two optical signals cross at the same switch element. To
avoid crosstalk, active connections must be node-disjoint in the switching
network. In this paper, we propose a sequence of decomposition and merge
operations, called conjugate transformation, performed on each switch element
to tackle this problem. The network resulting from this transformation is
called conjugate network. By using the numbering-schemes of networks, we prove
that if the route assignments in the original network are link-disjoint, their
corresponding ones in the conjugate network would be node-disjoint. Thus,
traditional nonblocking switching networks can be transformed into
crosstalk-free optical switches in a routine manner. Furthermore, we show that
crosstalk-free multicast switches can also be obtained from existing
nonblocking multicast switches via the same conjugate transformation.Comment: 10 page
Architecture, design, and modeling of the OPSnet asynchronous optical packet switching node
An all-optical packet-switched network supporting multiple services represents a long-term goal for network operators and service providers alike. The EPSRC-funded OPSnet project partnership addresses this issue from device through to network architecture perspectives with the key objective of the design, development, and demonstration of a fully operational asynchronous optical packet switch (OPS) suitable for 100 Gb/s dense-wavelength-division multiplexing (DWDM) operation. The OPS is built around a novel buffer and control architecture that has been shown to be highly flexible and to offer the promise of fair and consistent packet delivery at high load conditions with full support for quality of service (QoS) based on differentiated services over generalized multiprotocol label switching
A systematic analysis of equivalence in multistage networks
Many approaches to switching in optoelectronic and optical networks decompose the switching function across multiple stages or hops. This paper addresses the problem of determining whether two multistage or multihop networks are functionally equivalent. Various ad-hoc methods have been used in the past to establish such equivalences. A systematic method for determining equivalence is presented based on properties of the link permutations used to interconnect stages of the network. This method is useful in laying out multistage networks, in determining optimal channel assignments for multihop networks, and in establishing the routing required in such networks. A purely graphical variant of the method, requiring no mathematics or calculations, is also described
Investigation of FACTS devices to improve power quality in distribution networks
Flexible AC transmission system (FACTS) technologies are power electronic solutions
that improve power transmission through enhanced power transfer volume and stability,
and resolve quality and reliability issues in distribution networks carrying sensitive
equipment and non-linear loads. The use of FACTS in distribution systems is still in
its infancy. Voltages and power ratings in distribution networks are at a level where
realistic FACTS devices can be deployed. Efficient power converters and therefore loss
minimisation are crucial prerequisites for deployment of FACTS devices.
This thesis investigates high power semiconductor device losses in detail. Analytical
closed form equations are developed for conduction loss in power devices as a function
of device ratings and operating conditions. These formulae have been shown to predict
losses very accurately, in line with manufacturer data. The developed formulae enable
circuit designers to quickly estimate circuit losses and determine the sensitivity of those
losses to device voltage and current ratings, and thus select the optimal semiconductor
device for a specific application.
It is shown that in the case of majority carrier devices (such as power MOSFETs), the
conduction power loss (at rated current) increases linearly in relation to the varying rated
current (at constant blocking voltage), but is a square root of the variable blocking voltage
when rated current is fixed. For minority carrier devices (such as a pin diode or IGBT),
a similar relationship is observed for varying current, however where the blocking voltage
is altered, power losses are derived as a square root with an offset (from the origin).
Finally, this thesis conducts a power loss-oriented evaluation of cascade type multilevel
converters suited to reactive power compensation in 11kV and 33kV systems. The cascade
cell converter is constructed from a series arrangement of cell modules. Two prospective
structures of cascade type converters were compared as a case study: the traditional type
which uses equal-sized cells in its chain, and a second with a ternary relationship between
its dc-link voltages. Modelling (at 81 and 27 levels) was carried out under steady state
conditions, with simplified models based on the switching function and using standard
circuit simulators. A detailed survey of non punch through (NPT) and punch through
(PT) IGBTs was completed for the purpose of designing the two cascaded converters.
Results show that conduction losses are dominant in both types of converters in NPT
and PT IGBTs for 11kV and 33kV systems. The equal-sized converter is only likely to
be useful in one case (27-levels in the 33kV system). The ternary-sequence converter
produces lower losses in all other cases, and this is especially noticeable for the 81-level
converter operating in an 11kV network
Digital Switching in the Quantum Domain
In this paper, we present an architecture and implementation algorithm such
that digital data can be switched in the quantum domain. First we define the
connection digraph which can be used to describe the behavior of a switch at a
given time, then we show how a connection digraph can be implemented using
elementary quantum gates. The proposed mechanism supports unicasting as well as
multicasting, and is strict-sense non-blocking. It can be applied to perform
either circuit switching or packet switching. Compared with a traditional space
or time domain switch, the proposed switching mechanism is more scalable.
Assuming an n-by-n quantum switch, the space consumption grows linearly, i.e.
O(n), while the time complexity is O(1) for unicasting, and O(log n) for
multicasting. Based on these advantages, a high throughput switching device can
be built simply by increasing the number of I/O ports.Comment: 24 pages, 16 figures, LaTe
- …