Introduction to "Performance Analysis of the IEEE 802.11 DCF" - Bianchi
Simplifying Assumptions
Assumptions made to make analysis tractable:
Ideal channel conditions
No hidden nodes
No capture (one station monopolizes
the channel)
The number of stations is
fixed (constant)
(I.e., stations do not leave or join the wireless network)
Each stationalways
has packets to transmit
("Saturated condition")
(Key assumption)constant and
independent
(i.e., memory-less)
collision probability
of transmitted packets by stations
regardless
of the number of (re)transmission already
attempted
This assumption makes it possible to model
the 802.11 DCF function as a
Markov chain
(The author performed a
simulation study
and found that these
assumption does produce
very accurate results)
Note:
Always verify
analytical results
with simulation study
Overview of the performance study
The analysis procedure consists of
2 parts:
A study of the
behaviour of
a single station
using a
Markov model
The result of this analysis will be:
To obtain the
steady state probability τ
that a station
transmits a packet in a
arbitrary slot time
(This packet transmission probability
does not depend
on the packet transmission mechanism
This packet transmission probability is the same when a station
uses the
basic transmission scheme or
the RTS/CTS scheme)
A study of
all possible event
that can occur within
one slot time
This result will give us equations
for the throughput
of the basic transmission method
and of the
RTS/CTS transmission method