In the Wireless IP project, improvements of TCP/IP traffic over
wireless fading links are studied. A simulation tool is under development
in which computationally demanding algorithms for ARQ with adaptive
channel coding and modulation are used. This thesis describes a model
that can replace these non-real-time computations. The model in question
consists of a fast accessible statistical table for each (re)transmission
attempt. Three attempts are allowed. The tables holds the packet error
rates corresponding to all investigated combinations of channel coding
rate, modulation and channel signal to noise ratio (SNR). All the
combinations will form a very large combinatorial tree.
The work was performed in three steps. First, the system model and
the simulation tool were studied in order to implement an effective
program package for the creation and utilization of statistical tables.
Then large simulations were run for all chosen transmission combinations.
Finally, the statistical data and the retrieval of data from resulting
tables were evaluated.
The main conclusions are: 1) It is possible to do the simulations
in a reasonable amount of time (< 35 days) using a smaller cluster
of modern computers, if the statistical resolution for the third transmission
attempt is allowed to be low, and if the investigated transmission
combinations are carefully selected so that the number of combinations
is limited. The latter also implies that the retrieval of data from
tables will be fast enough to run the simulation tool in real-time.
2) The computed statistical data is reasonable and reliable. 3) Using
a limited number of investigated transmission combinations gives only
an approximation of the true system behaviour. The accuracy of this
approximation should be studied further.
