学步园

ttp://www.isi.edu/nsnam/ns/doc/node193.html

Prior to release ns-2.33, there was only one main-tree 802.11 model,
although other researchers were maintaining third-party patches
on the web. Starting with ns-2.33, there are multiple choices in
the main distribution.

The first extension described below (infrastructure mode) extends
the legacy model to include infrastructure mode. However, the last
two items (802.11Ext and dei802mr) are complete replacements for the
legacy model.

Therefore, researchers now have a choice of 802.11 models, and
should carefully read the documentation and code of each one to
understand which is the best fit for the job.

802.11 DCF from CMU

This model has been the only model available in the main ns
source
tree prior to release ns-2.33. See ~ns
/mac-802_11.{cc,h} for
implementation details. It uses a
RTS/CTS/DATA/ACK pattern for all unicast packets and simply sends out
DATA for all broadcast packets. The implementation uses both
physical and virtual carrier sense. The
Mac802_11../ns-2/mac-802_11.h is implemented in
~ns
/mac-802_11.{cc,h}.

802.11 infrastructure extensions

Ilango Purushothaman from the University of Washington has
implemented
infrastructure extensions to the above 802.11 model, and fixed some
bugs
along the way. The extensions include passive and active scanning,
authentication, association, inter-AP communications, and mobility
support (handoff). Please note that this model still supports
single-channel scenarios only.

• Documentation:

  http://ee.washington.edu/research/funlab/802_11/report_80211_IM.pdf

• Example script:
  tcl/ex/infra.tcl
• Test suite:
  tcl/test/test-suite-wireless-infra-mobility.tcl
  tcl/test/test-suite-wireless-infra.tcl

802.11Ext

A team from Mercedes-Benz Research and Development North America and
from University of Karlsruhe have collaborated to develop a completely
new 802.11 Mac and Phy model, called Mac802_11Ext and WirelessPhyExt,
respectively. The new model contains the following features:

• Structured design of MAC functionality modules: transmission,
  reception, transmission coordination, reception coordination, backoff
  manager, and channel state monitor
• Cumulative SINR computation
• MAC frame capture capabbilities
• Multiple modulation scheme support
• Packet drop tracing at the PHY layer
• Nakagami fading model

This model should be used as a replacement for the existing models. The
example scripts show how to do this.

• Key files:
  apps/pbc.{cc,h}, mac/mac-802_11Ext.{cc,h}, mac/wireless-phyExt.{cc,h},
  mobile/nakagami.{cc,h}
• Documentation:

  http://dsn.tm.uni-karlsruhe.de/Overhaul_NS-2.php

• Example scripts:
  tcl/ex/802.11/ directory: IEEE802-11a.tcl IEEE802-11p.tcl
  broadcast_validation.tcl unicast_validation.tcl
• Test suite:
  tcl/test/test-suite-wireless-lan-newnode-80211Ext.tcl

dei80211mr

The dei80211mr library - nicknamed 'multirate' for short - provides
an
802.11 derived from the CMU implementation.
This library depends on the Dynamic Library (Chapter 28
) and
is included in the ns-allinone distribution only (see the
top-level dei80211mr directory in the ns-allinone distribution or
see http://www.dei.unipd.it/wdyn/?IDsezione=5091).
For step-by-step installation instructions, please refer to the tutorial
at

http://www.dei.unipd.it/%7Ebaldo/nsmiracle-dei80211mr-howto.html

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)
• In the wireless channel, the affected nodes distance is no more
  determined using the CS threshold, but we used a fixed value in meters
  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 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.

• Documentation:

  http://www.dei.unipd.it/%7Ebaldo/nsmiracle-dei80211mr-howto.html

• Example script:
  dei80211mr-1.1.4/samples/adhoc_tcp.tcl
• Test suite:
  None

In addition, a patch (relating to the CMU implementation) improving
ns-2
802.11 wireless support is available at

http://www.telematica.polito.it/fiore/.

The patch introduces realistic channel propagation, concurrent multiple
data transmission rates among stations and ARF mechanisms, has been
tested with ns-2.29, and features the following contributions:

• channel propagation improvements by Wu Xiuchao
• ricean propagation model by Ratish J. Punnoose
• SNOOPy calendar scheduler by David X. Wei
• 802.11 bug fixes by Felix Schmidt-Eisenlohr
• multiple data transmission rates support by Marco Fiore
• Adaptive Auto Rate Fallback (AARF) by Marco Fiore.