7,156 research outputs found
On the Decoding of Polar Codes on Permuted Factor Graphs
Polar codes are a channel coding scheme for the next generation of wireless
communications standard (5G). The belief propagation (BP) decoder allows for
parallel decoding of polar codes, making it suitable for high throughput
applications. However, the error-correction performance of polar codes under BP
decoding is far from the requirements of 5G. It has been shown that the
error-correction performance of BP can be improved if the decoding is performed
on multiple permuted factor graphs of polar codes. However, a different BP
decoding scheduling is required for each factor graph permutation which results
in the design of a different decoder for each permutation. Moreover, the
selection of the different factor graph permutations is at random, which
prevents the decoder to achieve a desirable error-correction performance with a
small number of permutations. In this paper, we first show that the
permutations on the factor graph can be mapped into suitable permutations on
the codeword positions. As a result, we can make use of a single decoder for
all the permutations. In addition, we introduce a method to construct a set of
predetermined permutations which can provide the correct codeword if the
decoding fails on the original permutation. We show that for the 5G polar code
of length , the error-correction performance of the proposed decoder is
more than dB better than that of the BP decoder with the same number of
random permutations at the frame error rate of
Polar codes combined with physical layer security on impulsive noise channels
Ph. D. ThesisThe need for secure communications is becoming more and more impor-
tant in modern society as wired and wireless connectivity becomes more
ubiquitous. Currently, security is achieved by using well established
encryption techniques in the upper layers that rely on computational
complexity to ensure security. However, processing power is continu-
ally increasing and well-known encryption schemes are more likely to be
cracked. An alternative approach to achieving secure communication is
to exploit the properties of the communication channel. This is known as
physical layer security and is mathematically proven to be secure. Phys-
ical layer security is an active research area, with a significant amount
of literature covering many different aspects. However, one issue that
does not appear to have been investigated in the literature is the effect
on physical layer security when the noise in the communication channel
is impulsive. Impulsive noise adds large spikes to the transmitted signal
for very short durations that can significantly degrade the signal. The
main source of impulsive noise in wireless communications is electromag-
netic interference generated by machinery. Therefore, this project will
investigate the effect of impulsive noise on physical layer security.
To ensure a high level of performance, advanced error-correcting codes
are needed to correct the multiple errors due to this harsh channel. Turbo
and Low-Density Parity-Check (LDPC) codes are capacity-approaching
codes commonly used in current wireless communication standards, but
their complexity and latency can be quite high and can be a limiting fac-
tor when required very high data rates. An alternative error-correcting
code is the polar code, which can actually achieve the Shannon capacity
on any symmetric binary input discrete memoryless channel (B-DMC).
Furthermore, the complexity of polar codes is low and this makes them
an attractive error-correcting code for high data rate wireless commu-
nications. In this project, polar codes are combined with physical layer
security and the performance and security of the system is evaluated on
impulsive noise channels for the first time.
This project has three contributions:
Polar codes designed for impulsive noise channels using density evo-
lution are combined with physical layer security on a wire-tap chan-
nel experiencing impulsive noise.
The secrecy rate of polar codes is maximised. In the decoding of
polar codes, the frozen bits play an important part. The posi-
tions of the frozen bits has a significant impact on performance and
therefore, the selection of optimal frozen bits is presented to opti-
mise the performance while maintaining secure communications on
impulsive noise wire-tap channels.
Optimal puncturing patterns are investigated to obtain polar codes
with arbitrary block lengths and can be applied to different modu-
lation schemes, such as binary phase shift keying (BPSK) and M-
ary Quadrature Amplitude Modulation (QAM), that can be rate
compatible with practical communication systems. The punctured
polar codes are combined with physical layer security, allowing the
construction of a variety of different code rates while maintaining
good performance and security on impulsive noise wire-tap chan-
nels.
The results from this work have demonstrated that polar codes are ro-
bust to the effects of impulsive noise channel and can achieve secure
communications. The work also addresses the issue of security on im-
pulsive noise channels and has provided important insight into scenarios
where the main channel between authorised users has varying levels of
impulsiveness compared with the eavesdropper's channel. One of the
most interesting results from this thesis is the observation that polar
codes combined with physical layer security can achieve good perfor-
mance and security even when the main channel is more impulsive than
the eavesdropper's channel, which was unexpected. Therefore, this thesis
concludes that the low-complexity polar codes are an excellent candidate
for the error-correcting codes when combined with physical layer security
in more harsh impulsive wireless communication channels
A Survey of Physical Layer Security Techniques for 5G Wireless Networks and Challenges Ahead
Physical layer security which safeguards data confidentiality based on the
information-theoretic approaches has received significant research interest
recently. The key idea behind physical layer security is to utilize the
intrinsic randomness of the transmission channel to guarantee the security in
physical layer. The evolution towards 5G wireless communications poses new
challenges for physical layer security research. This paper provides a latest
survey of the physical layer security research on various promising 5G
technologies, including physical layer security coding, massive multiple-input
multiple-output, millimeter wave communications, heterogeneous networks,
non-orthogonal multiple access, full duplex technology, etc. Technical
challenges which remain unresolved at the time of writing are summarized and
the future trends of physical layer security in 5G and beyond are discussed.Comment: To appear in IEEE Journal on Selected Areas in Communication
Polar Codes over Fading Channels with Power and Delay Constraints
The inherent nature of polar codes being channel specific makes it difficult
to use them in a setting where the communication channel changes with time. In
particular, to be able to use polar codes in a wireless scenario, varying
attenuation due to fading needs to be mitigated. To the best of our knowledge,
there has been no comprehensive work in this direction thus far. In this work,
a practical scheme involving channel inversion with the knowledge of the
channel state at the transmitter, is proposed. An additional practical
constraint on the permissible average and peak power is imposed, which in turn
makes the channel equivalent to an additive white Gaussian noise (AWGN) channel
cascaded with an erasure channel. It is shown that the constructed polar code
could be made to achieve the symmetric capacity of this channel. Further, a
means to compute the optimal design rate of the polar code for a given power
constraint is also discussed.Comment: 6 pages, 6 figure
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