
PowerLossChannel |
ptolemy.domains.wireless.lib.PowerLossChannel |
This is a model of a wireless channel with a specified power propagation
formula. The power propagation is given as an expression that is evaluated
and then multiplied by the power field of the transmit properties before
delivery to the receiver. For convenience, a variable named "distance"
is available and equal to the distance between the transmitter and the
receiver when the power propagation formula is evaluated. Thus, the
expression can depend on this distance. The value of the power field should
be interpreted as power at the transmitter but power density at the receiver.
A receiver may multiply the power density with its efficiency and an
area(typically the antenna area). A receiver can then use the resulting
power to compare against a detectable threshold, or to determine
signal-to-interference ratio, for example.
<p>
The default value of <i>powerPropagationFactor</i> is
<pre>
1.0 / (4 * PI * distance * distance).
</pre>
This assumes that the transmit power is uniformly distributed
on a sphere of radius <i>distance</i>. The result of multiplying
this by a transmit power is a power density (power per unit area).
The receiver should multiply this power density by the area of the
sensor it uses to capture the energy (such as antenna area) and
also an efficiency factor which represents how effectively it capture
the energy.
<p>
The power field of the transmit properties can be supplied by
the transmitter as a record with a <i>power</i> field of type double.
The default value provided by this channel is Infinity, which when
multiplied by any positive constant will yield Infinity, which
presumably will be above any threshold. Thus, the default behavior
is to encounter no power loss and no limits to communication due
to power.
<p>
In addition, this channel can have a specified limited transmission
range. If a transmission range less than Infinity (the default)
is specified, then receivers outside the specified range will
not be notified of transmission, irrespective of power loss.
The transmission range can be specified in one of two ways.
Either it is the value of the <i>range</i> field in the
<i>defaultProperties</i> parameter (a record) of this
channel, or it is provided by the transmitter on each call to
transmit() as a property argument. To use the latter mechanism,
it is necessary that the property token be an instance of RecordToken
with a field named "range" that can be converted to a double
(i.e., it can be a double, an int, or a byte).
The default value for <i>range</i> is Infinity, which
indicates that by default, there is no range limit.
<p>
Any receiver that is within the specified range when transmit()
is called will receive the transmission, unless the <i>lossProbability</i>
parameter is set to greater than zero.
<p>
Author(s): Edward A. Lee
Version:$Id: PowerLossChannel.doc.html,v 1.1 2006/02/22 18:41:22 mangal Exp $
Pt.Proposed Rating:Green (cxh)
Pt.Accepted Rating:Yellow (cxh)
powerPropagationFactor
The default formula for the power loss factor.
This value, when multiplied by the transmit power, yields
the power density (per unit area) at a receiver. It can
be an expression that depends on a variable "distance,"
which has the value of the distance between a transmitter
and receiver when this parameter is evaluated. This is
a double that defaults to
"1.0 / (distance * distance))".