[ns] Multirate 802.11 implementation is now available

[Federico Maguolo]

Hi all,
I would like to announce the publication of a new 802.11 that we
developed at the SIGNET lab, University of Padova, Department of
Information Engineering (DEI), downloadable  at

http://www.dei.unipd.it/wdyn/?IDsezione=5090

This 802.11 implementation, named dei80211mr, permits the simulation of rate 
adaptation algorithm (in the distribution an implementation of ARF  is already 
included) with an enhanced physical layer with respect to those 
in the ns distribution. In particular:

- support for multiple PHY modes is included; in particolar,
  dei80211mr supports 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.

- Several useful 802.11 MAC MIB counters described in [3], Annex D, have 
  been added to the MACMIB C++ class

- dei80211mr can be used within the classical ns-2 MobileNode



dei80211mr is distributed as a dynamic library using the Dynamic Library
patch [2]. 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.


[1] Ilango Purushotaman and Sumit Roy,
"IEEE802.11 implementation Issues in Network Simulator 2",
Dept. of Electrical Engineering, University of Washington, US
http://ee.washington.edu/research/funlab/

[2] Patch for Loading Dynamic Modules in ns-2,
http://mailman.isi.edu/pipermail/ns-users/2007-June/060486.html
http://www.dei.unipd.it/~rossi/ns2-patch.html

[3] IEEE LAN MAN Standards, Part 11: Wireless LAN
Medium Access Control (MAC) and Physical Layer
(PHY) specifications¿, ANSI/IEEE Std., March 1999.