Severe fading and outdated channel condition models in relay communication networks
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Date
2019-08-01
Authors
Jamaluddin Zakaria
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Abstract
Cooperative communication system is an attractive method which enhances the
performance diversity by introducing an intermediate relay for assisting the primary
communication between the source and the destination terminals. There are two main
issues regarding to the communication channel. The first one is the severe fading
channel where the analysis is performed mainly for investigating the direct source-todestination
(SD) link in wireless cooperative network. Most of the works omits SD
link by simply assuming deep fade with no consideration of partial contribution to
the overall system diversity. This is due to the imprecise classification of Rayleigh
fading as severe fading. The second issue is a relative movement in communication
terminals cause some delay in propagating the transmitted signals which is subject to
the established Jakes’ autocorrelation model. This is also known as outdated channel
condition. It causes the destination terminal unable to estimate or recover the source’s
information properly that will deteriorate the system performances. For the first issue,
the analytical expressions based on this severe fading channel model has come
to an approach of utilizing the moment generating function (MGF). The MGF expression
of the Weibull distribution model has to deal with a complex Meijer’s G-function
and due to the complexity and limitation in the existing MGF expression, it is scarce
to have performance analysis based on the expression. To overcome this limitation,
infinite series of MGF expression for the Weibull model is proposed. This expression
is then, utilized for evaluating the impact of severe fading channel on the direct
SD link in a three-terminal cooperative network by employing approximated variablegain
and fixed-gain amplify-and-forward (AF) relaying schemes associates with the
maximal ratio combining (MRC) and the selection combining (SC) schemes. Under
predefined parameters setting, it is found that when the direct SD link is in deep
fade, the diversity gain for both MRC and SC for AF variable-gain relaying system is
0.771. While the SD link behaves as Rayleigh channel then diversity gain is given by;
MRC:1.660, SC:1.602. The second issue is investigated in a three-terminal wireless
energy harvesting-based AF dual-hop cooperative system along with the assumption
of dynamic terminals’ movement where it is assumed that the relay terminal is energyconstrained.
New time-switching relaying protocol which considers the amount of
propagation delay due to the terminal’s movement is proposed. Then, two different
types of transmission mode are considered; delay-limited, DL (requires outage probability
evaluation) and delay-tolerant, DT (requires ergodic capacity evaluation). It
is found that when all the terminals are in static, the system achieves the maximum
throughput (DL: 0.83 bit/sec/Hz, and DT: 1.59 bit/sec/Hz).