1 research outputs found
Coded-OFDM for PLC systems in non-Gaussian noise channels
PhD ThesisNowadays, power line communication (PLC) is a technology that uses the power
line grid for communication purposes along with transmitting electrical energy, for
providing broadband services to homes and offices such as high-speed data, audio,
video and multimedia applications. The advantages of this technology are to eliminate
the need for new wiring and AC outlet plugs by using an existing infrastructure,
ease of installation and reduction of the network deployment cost. However,
the power line grid is originally designed for the transmission of the electric power
at low frequencies; i.e. 50/60 Hz. Therefore, the PLC channel appears as a harsh
medium for low-power high-frequency communication signals. The development
of PLC systems for providing high-speed communication needs precise knowledge
of the channel characteristics such as the attenuation, non-Gaussian noise and selective
fading. Non-Gaussian noise in PLC channels can classify into Nakagami-m
background interference (BI) noise and asynchronous impulsive noise (IN) modelled
by a Bernoulli-Gaussian mixture (BGM) model or Middleton class A (MCA)
model. Besides the effects of the multipath PLC channel, asynchronous impulsive
noise is the main reason causing performance degradation in PLC channels.
Binary/non-binary low-density parity check B/NB-(LDPC) codes and turbo codes
(TC) with soft iterative decoders have been proposed for Orthogonal Frequency
Division Multiplexing (OFDM) system to improve the bit error rate (BER) performance
degradation by exploiting frequency diversity. The performances are investigated
utilizing high-order quadrature amplitude modulation (QAM) in the presence
of non-Gaussian noise over multipath broadband power-line communication (BBPLC)
channels. OFDM usually spreads the effect of IN over multiple sub-carriers
after discrete Fourier transform (DFT) operation at the receiver, hence, it requires
only a simple single-tap zero forcing (ZF) equalizer at the receiver.
The thesis focuses on improving the performance of iterative decoders by deriving
the effective, complex-valued, ratio distributions of the noise samples at the zeroforcing
(ZF) equalizer output considering the frequency-selective multipath PLCs,
background interference noise and impulsive noise, and utilizing the outcome for
computing the apriori log likelihood ratios (LLRs) required for soft decoding algorithms.
On the other hand, Physical-Layer Network Coding (PLNC) is introduced to help
the PLC system to extend the range of operation for exchanging information between
two users (devices) using an intermediate relay (hub) node in two-time slots
in the presence of non-Gaussian noise over multipath PLC channels. A novel detection
scheme is proposed to transform the transmit signal constellation based on
the frequency-domain channel coefficients to optimize detection at the relay node
with newly derived noise PDF at the relay and end nodes. Additionally, conditions
for optimum detection utilizing a high-order constellation are derived. The closedform
expressions of the BER and average BER upper-bound (AUB) are derived for
a point-to-point system, and for a PLNC system at the end node to relay, relay to
end node and at the end-to-end nodes. Moreover, the convergence behaviour of
iterative decoders is evaluated using EXtrinsic Information Transfer (EXIT) chart
analysis and upper bound analyses. Furthermore, an optimization of the threshold
determination for clipping and blanking impulsive noise mitigation methods are
derived. The proposed systems are compared in performance using simulation in
MATLAB and analytical methods.Ministry of
Higher Education in Ira