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dei80211mr
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Overview |
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The dei80211mr library - nicknamed 'multirate' for short - provides a
802.11 implementation for the Network Simulator Version 2. This
implementations is derived from the 802.11 implementation included in
NS 2.29 and aims at solving some known bugs as well as providing
enhanced functionality.
The dei80211mr library relies on the Dynamic Library patch. Thanks to
the functionalities introduced by this patch, dei80211mr can be used
with different versions of ns2. We have tested it with ns-2.29 and
ns-2.31, and we expect it to work with future ns2 releases as well.
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Features |
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The following functionalities are provided by the dei80211mr library:
- support for multiple PHY modes is included; in particolar,
dei80211mr simulation of the different transmission rates, modulation
and coding schemes defined in the IEEE802.11b/g standards.
- a SINR-based packet level error model is introduced:
- the RX Threshold variable which was used in the 802.11
implementation included in standard NS to determine successful
receptions has been removed. Instead, Packet Error Rate (PER) is
used to determine random packet losses.
- PER is calculated using pre-determined curves (PER
vs SINR and packet size); the curves can be specified by the user
via TCL. Some default curves for both 802.11g and 802.11b are provided.
- SINR is calculated using received signal strength, noise and
interference
- interference is calculated using a gaussian model to account for
all transmissions which happen simultaneously to the one which is
considered for reception
- noise power is set via TCL
- the capture model, i.e. the determination of whether a packet can be
received when there are other concurrent transmissions are
simultaneously ogoing, is now embedded in the above mentioned
interference model (no more Capture Threshold)
- Some well-known bugs of the 802.11 implementation in NS have been
resolved. With reference to [1], we solved the following bugs:
- direct access denial
- random backoff time
- capture model (note: this is different from the point above since,
as per the description in [1], it is actually a synchronization issue)
- In the wireless channel, the affected nodes distance is no more
determined using the CS threshold, but we used a fixed value in
meters (distInterference_) which can be set at the beginning of the
simulation. The reason is that, since we use a gaussian interference
model, nodes well below the CS threshold often still provide a
non-negligible contribution to interference. The default value for
the affected nodes distance (distInterference_) is very
conservative, so that all nodes are considered for interference
calculation. This default value therefore yields accurate but
computationally intensive simulations. The value can be adjusted via
TCL to achieve different trade-offs between computational load and
simulation accuracy.
[1] Ilango Purushotaman and Sumit Roy,
IEEE802.11 implementation Issues in Network Simulator 2
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