Recent wireless cellular systems, like 3GPP’s Long Term Evolution (LTE) and LTE-Advanced (LTE-A), benefit from many enhancements of wireless techniques. These include multicarrier modulation schemes, fast link adaptation, forward error correction with HARQ, powerful turbo codes and mutiple antenna techniques. System level simulators usually use link
abstraction models for capturing the effects of these enhancements from link level simulators. This reduces both time and
complexity of large system simulations. Also the link abstraction models are used in the mobile stations for an efficient feed-
back of instantaneous channel quality indicator in real systems.
Therefore, it is extremely important for a link abstraction model
to not only have low complexity but also very good accuracy.
However modeling the effects of incremental redundancy (IR)-
HARQ in LTE-based systems is a challenging and interesting
task. In LTE-based systems two types of gains can be achieved
with IR-HARQ at the receiver. These are coding gain, which is
achieved through the transmission of new parity bits in each of
the retransmission, and an SNR gain, which is achieved due to
repetition of coded bits in each of the retransmission. A good
link abstraction model should be able to abstracts the effects IR-
HARQ and other enhancements with as much low complexity
as possible and reasonable accuracy. In this paper we propose a
low complexity link abstraction which abstracts the performance
of LTE-based link level simulators with multiple antennas,
incremental redundancy (IR) HARQ and other enhancements.
The complexity is reduced by the fact that our proposed scheme
only uses three reference curves corresponding to the mother
code rate for each type of QAM modulation. Then we show
that how the reference curves for an arbitrary code rate can be
generated by using these three reference curves and an offset.
This offset is based on the effective code rate after combining the
transmissions from different HARQ rounds. To strengthen the
case for our proposed link abstraction model we show the results
for LTE-based wireless system. The results show that our method
provides reasonably accurate results with very low complexity
and even no calibration of adjustment factors is performed. For
all the simulations we used Eurecom’s OpenAirInterface platform
which implements physical layer of LTE release 8 as per the
standards of 3GPP.
