Paper
PHY Abstraction Methods
for OFDM and NOFDM Systems
Adrian Kliks, Andreas Zalonis, Ioannis Dagres, Andreas Poly d oros, and Hanna Bogucka
Abstract— In the paper various PHY abstraction methods for
both orthogonal and non- orthogonal systems are p resented,
which allow to predict the coded block error rate (BLER)
across the subcarriers transmitting this FEC-coded block for
any given channel realization. First the efficiency of the se-
lected methods is investigated and proved by the means of
computer simulations carried out in orthogonal muticarrier
scenario. Presented results are followed by the generalization
and theoretical extension of these methods for non-orthogonal
systems.
Keywords— orthogonal and non-orthogonal multicarrier sys-
tems, PHY abstraction methods.
1. Introduction
In the past where multi-modal operation was not an optio n,
the role of performance evaluation (an alytically or by sim-
ulation) was to simply check whether a given signal design
met the pre-specified performance requirements. The av-
erage performance of a system was quantified by using
the topology and the channel macro-characteristics in order
to compute a geometric (or average) signal-to-interference
plus noise ratio (SINR) distribution across the cell. If there
were degrees of freedom either for transmitter-based signal
design or for receiver-based algorithmic choice, then the
role of performance evaluation was to pick the right set of
parameter values so as to optimize a performance metric.
In that sense, performance evaluation started becoming an
integral part of the system design process itself, and the mo-
tivation thus arose to have simple analytic forms for these
performance results which would make them amenable to
easy pa rametric optimization .
Once the de sign aspect advances to become multi-modal
and multi-parametric at both sides of the transmission link
(e.g., current orthogonal fre quency division multiplexing
(OFDM) based systems: 3rd generation partnership project-
long term evolution (3GPP-LTE), worldwide interope rabil-
ity for microwave access (WiMAX)), the task of link-
performance evaluation becomes not only germane to the
design proce dure itself, but the effective and efficient rep-
resentation of this parameterized performance in ways that
are compact (parsimonious) yet accurate comprises a main
challenge of the optimization task.
Compact-description models are also of great interest in
the context of evaluation me thodologies (EVM’s) which
are currently being developed for various systems in the re-
spective standard iz a tion bodies (e.g., I EEE 802.16m Task
Group [1]). The goal of this type of physical-layer (PHY)
abstraction is to determine the performance of a given
link an d thus avoid the need for extensive simulation.
This “simulation-shortcut” accelera tes the corresponding
system- leve l simulations where a large number of physical-
layer-related links need to be taken into account. Th e ab-
straction should be accurate, compu ta tionally simple, rel-
atively independent of chan nel models, and extensible to
interference models and multi-antenna proc e ssing.
A very novel and challenging task is to define the proper
(PHY) abstraction methods for the non-orthogonal mutli-
carrier (NOMC) systems, which are gaining the interest in
the area o f considered future wireless communication tech-
niques. In the case of non-orthogonal frequency division
multiplexing (NOFDM) signals, the impu lses used at the
transmitter overlap each other both in time and in frequency
domain, thus they are not orthogonal. The shape and the
signaling time of the applied impulses can be chosen with-
out any r estrictions besides ensuring that the pulses used at
the receiver are biorthogonal to pulses used on the transmit-
ter side. The (NOFDM) systems are the part of the larger
set of generalized mutlica rrier (GMC) systems, where all
of the transmit p arameters can be in general chosen without
any specified restriction. Th us a GMC signal set includes
the o rthogon a l multicarrie r signals as well.
The remainder of the paper is organized as follows: first the
idea of (PHY) abstraction methodology is described an d
some possible abstraction methods are pre sented. These
are followed by some results obtained for (OFDM) sce-
nario. Finally, the main features of (NOFDM) systems are
presented and the proposals for modification of some ab-
straction methods for (NOFDM) case are described. The
whole paper is summarized in the last section.
2. PHY Abstraction Methodology
Physical-layer abstraction methodology for predicting in-
stantaneous link perfo rmance for OFDM systems has been
an active area of research and has received considerable
attention in the literature [ 2]–[11]. T he content in this sec-
tion is based on the evaluation methodology document [1]
of the ongoing work in IEEE 802.16m Task.
In a coded OFDM system, the coded block is transmitted
over many subcarriers usually over a frequency selective
channel, resulting in unequal channel gains for the subcarri-
ers, and thus non -uniform and time-varying post-processing
SINR values just prior to decoding . The task of the PHY
abstraction methodology is to pr edict the coded block error
rate (BLER) across the OFDM subcarriers transmitting this
forward erro r correction (FEC) coded block for any given
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