One document matched: draft-perkins-manet-rsw-00.xml
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<rfc ipr="trust200902" category="std" docName='draft-perkins-manet-rsw-00.txt' >
<front>
<title abbrev="RSW Cost Metric">
Received Signal Weakness (RSW) Metric</title>
<author fullname="Charles E. Perkins" initials="C.E." surname="Perkins">
<organization abbrev="Futurewei">Futurewei Inc. </organization>
<address>
<postal>
<street>2330 Central Expressway</street>
<city>Santa Clara</city>
<code>95050</code>
<region>CA</region>
<country>USA</country>
</postal>
<phone>+1-408-330-4586</phone>
<email>charliep@computer.org</email>
</address>
</author>
<date/> <!-- day="25" month="October" year="2010" /> -->
<area>Routing</area>
<workgroup>Mobile Ad Hoc Networks [manet]</workgroup>
<keyword>Mobility</keyword>
<keyword>Metric</keyword>
<abstract>
<t>
The Received Signal Weakness (RSW) metric is a simple cost metric that
enables selection of a route with the high end-to-end signal strength.
</t>
</abstract>
</front>
<middle>
<section anchor='intro' title='Introduction'>
<t>
It is often desirable to identify which of several available routes
offers the best signal strength for data transmission, de-emphasizing
other considerations such as number of hops. However, signal strength
is in certain ways less suitable for use as a routing metric; in
particular, the signal strength of a path with several hops is not
as easy to calculate as cost metrics such as hop count.
</t>
<t>
Instead of signal strength, we calculate a metric proportional to the
weakness of the signal, in order to obtain a cost metric. The route
having the links with the best signal strength is then chosen in
preference to other routes, by choosing the route presenting the
lowest cost as measured by the Received Signal Weakness (RSW) metric.
The total signal weakness cost for a route is the sum of
the signal weakness measurements at each hop, so that the RSW cost
metric is additive, monotonic, and easy to calculate.
</t>
</section>
<section anchor='def'
title='Received Signal Weakness Metric'>
<t>
The received signal strength for packets received from a neighbor
is an important factor relevant to the reliability of the link
between the receiving node and its neighbor. Notice that the received
signal strength can vary over time even if the neighboring devices
are not moving.
</t>
<t>
For a route R as follows composed of links between nodes N_1 ... N_k:
<list style="empty">
<t>N_1 <--> N_2 <--> N_3 <--> .... <--> N_k</t>
</list>
denote the link between
N_{i} and N_{i+1} by L_{i,i+1} and the received signal weakness over
link L_{i,i+1} by RSW_{i,i+1}.
The RSW cost for route R is the
sum of the RSW costs for each link, or in other words
M_rsw(R) = SUM M_rsw(L_{i,i+1}) [i == 1..k-1], where M_rsw is the
metric value for the RSW metric.
</t>
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http://www.gs1.org/gsmp/kc/epcglobal/tds/tds_1_1_rev_1_27-standard-20050510.pdf
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</section>
<section anchor='units'
title='Units for RSW metric'>
<t>
The received power as measured (say, in mW) for incoming packets may
have quite a large dynamic range, but the measurements are also quite
variable and so great precision is unlikely to be required. In order
to fit in eight bits, the received power measurement is normalized to
be within the range from 0 to 1, where the minimum measurable power
P_min maps to 1 (the highest cost value) and the maximum measurable
power P_max maps to 0 (the lowest cost value). In other words, the
measured received power P_meas maps to a normalized value
P_norm = (P_max - P_meas) / (P_max - P_min).
</t>
<t>
It is desirable to increase the cost of low signal strength so
that weak signals are strongly disfavored. For this purpose, P_norm,
which is a positive number no greater than 1, can be exponentiated.
Using RSW_exponent = (1/8) is proposed for this purpose, and
effectively reduces the cost associated with using links that have
good measured values for the received signal strength.
</t>
<t>
For the purposes of this initial draft, it is proposed to use
a precision that can be carried in an 8 bit metric. That would
allow Max_RSW to attain the value 255, but that value should be
reserved to indicate a route cost of "infinity"; i.e., the route
cost is too large to be represented. For that reason, Max_RSW is
defined to be 254. In addition, we define Min_RSW to be 1, so that
there is some nonzero RSW cost for every link even if the measurement
of the received signal strength is the same as P_min.
These definitions of Max_RSW and Min_RSW determine the scaling
factor for P_norm, namely (Max_RSW - Min_RSW).
</t>
<!--
RSW is a metric which measures the cost of a path due to reductions in signal
strength and has the following properties:
1) As signal strength degrades, the value of the metric increases. In other
words, the metric measures signal weakness instead of signal strength.
2) The value of the metric increases rapidly with weakness of the signal, so
that links with better signal strength are greatly preferred. The RSW value
increases rapidly with loss of signal strength.
3) Links with very strong signals should have very low metric values,
close to zero.
4) Signal strength measurements are notoriously unstable and inaccurate,
so great precision is not needed.
-->
<!--
Make the following definitions:
Pmax the maximum feasible value for received signal strength, measured in mW
Pmin the minimum feasible value for received signal strength, measured in mW
Pmeas the measured value for received signal strength, measured in mW
P normalized received power ratio in the range (0, 1)
Max_RSW the maximum possible value for the RSW metric
Min_RSW the minimum possible value for the RSW metric
mu_0 calculated value for the received signal weakness metric
mu scaled value for the received signal weakness metric
Let P = (Pmax - Pmeas) / (Pmax - Pmin). P is a positive number in the
range (0, 1). The following formula satisfies properties (1) - (3) above:
mu_0 (P) = P8.
mu_0 also lies in the range (0, 1). In order for the RSW metric M_rsw
to be in the range (Min_RSW, Max_RSW), we multiply M_rsw 0 by the scaling
factor (Max_RSW-Min_RSW), convert to integer, and add Min_RSW:
mu(P) = floor((Max_RSW-Min_RSW) * (P_norm^RSW_exponent)) + MinRSW
For the RSW metric, Max_RSW = 254 and Min_RSW = 1, requiring only 8 bit
values for M_rsw (P). 255 is the maximum possible value of the metric, and
is reserved to mean infinity. To calculate the RSW metric over a multi-hop
route, the link values are summed; anything added to infinity results in
the same value, infinity.
-->
<t>
Given the scaling factor and shaping function P_norm^RSW_exponent as
above, the RSW metric is defined as
M_rsw = floor((Max_RSW-Min_RSW) * (P_norm^RSW_exponent)) + MinRSW
</t>
</section>
<section anchor='funcs'
title='Cost() and Loop_Free() functions for the RSW metric'>
<t>
To be useful with AODVv2 <xref target="I-D.ietf-manet-aodvv2"/>, it is
helpful to define functions Cost() and Loop_Free() for the RSW metric.
The purpose of the Loop_Free() function is to provide assurance that a
selected route is loop-free.
</t>
<t>
The definition of the Cost() function for RSW is exactly
the same as the RSW metric, M_rsw. In other words, using RSW,
Cost(L) = M_rsw(L) and Cost(R) = M_rsw(R) for a link L and a route R.
</t>
<t>
For routes R1 and R2, Loop_Free(R1, R2) for RSW is defined
as follows:
<list style="empty">
<t> LoopFree(R1,R2) := M_rsw(R1) < M_rsw(R2) </t>
</list>
or, in other words, LoopFree(R1,R2) returns TRUE if the cost of R1
is less than the cost of R2 (cost as measured by the RSW metric).
</t>
</section>
<section anchor='sec'
title='Security Considerations'>
<t>
This document does not introduce any security mechanisms,
and does not have any impact on existing security mechanisms.
</t>
</section>
<section anchor='iana' title='IANA Considerations'>
<t>
The routing metric defined in the document should
be assigned a value from the "AODVv2 Metric Types"
registry <xref target="I-D.ietf-manet-aodvv2"/>.
</t>
</section>
</middle>
<back>
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<reference anchor="IEEE_L2R_RSW">
<front>
<title>RSW for IEEE 802.15.10 Layer-2 Routing
(https://mentor.ieee.org/802.15/dcn/15/15-15-0925-03-0010-received-signal-weakness-rsw-metric-specification.docx)
</title>
<author initials="C.E." surname="Perkins"
fullname="Charles E. Perkins">
<organization>
https://mentor.ieee.org/802.15/dcn/15/15-15-0925-03-0010-received-signal-weakness-rsw-metric-specification.docx
</organization>
<address>
<uri>https://mentor.ieee.org/802.15/dcn/15/15-15-0925-03-0010-received-signal-weakness-rsw-metric-specification.docx</uri>
</address>
</author>
<date year="2015" />
</front>
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<date month="March" year="2009"/>
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EPC(TM) Generation 1 Tag Data Standards Version 1.1 Rev.1.27
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<author surname="EPCglobal Inc.">
<organization>
</organization>
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<date day='10' month="January" year="2005"/>
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<title>United States Department of Defense Suppliers Passive RFID
Information Guide (Version 15.0)</title>
<author surname="Department of Defense">
<organization>
</organization>
</author>
<date month="January" year="2010"/>
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<organization>
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<date year="2001"/>
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