36 research outputs found
Low-Complexity Puncturing and Shortening of Polar Codes
In this work, we address the low-complexity construction of shortened and
punctured polar codes from a unified view. While several independent puncturing
and shortening designs were attempted in the literature, our goal is a unique,
low-complexity construction encompassing both techniques in order to achieve
any code length and rate. We observe that our solution significantly reduces
the construction complexity as compared to state-of-the-art solutions while
providing a block error rate performance comparable to constructions that are
highly optimized for specific lengths and rates. This makes the constructed
polar codes highly suitable for practical application in future communication
systems requiring a large set of polar codes with different lengths and rates.Comment: to appear in WCNC 2017 - "Polar Coding in Wireless Communications:
Theory and Implementation" Worksho
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
Problems on q-Analogs in Coding Theory
The interest in -analogs of codes and designs has been increased in the
last few years as a consequence of their new application in error-correction
for random network coding. There are many interesting theoretical, algebraic,
and combinatorial coding problems concerning these q-analogs which remained
unsolved. The first goal of this paper is to make a short summary of the large
amount of research which was done in the area mainly in the last few years and
to provide most of the relevant references. The second goal of this paper is to
present one hundred open questions and problems for future research, whose
solution will advance the knowledge in this area. The third goal of this paper
is to present and start some directions in solving some of these problems.Comment: arXiv admin note: text overlap with arXiv:0805.3528 by other author
Performance Improvement of Space Missions Using Convolutional Codes by CRC-Aided List Viterbi Algorithms
Recently, CRC-aided list decoding of convolutional codes has gained attention thanks to its remarkable performance in the short blocklength regime. This paper studies the convolutional and CRC codes of the Consultative Committee for Space Data System Telemetry recommendation used in space missions by all international space agencies. The distance spectrum of the concatenated CRC-convolutional code and an upper bound on its frame error rate are derived, showing the availability of a 3 dB coding gain when compared to the maximum likelihood decoding of the convolutional code alone. The analytic bounds are then compared with Monte Carlo simulations for frame error rates achieved by list Viterbi decoding of the concatenated codes, for various list sizes. A remarkable outcome is the possibility of approaching the 3 dB coding gain with nearly the same decoding complexity of the plain Viterbi decoding of the inner convolutional code, at the expense of slightly increasing the undetected frame error rates at medium-high signal-to-noise ratios. Comparisons with CCSDS turbo codes and low-density parity check codes highlight the effectiveness of the proposed solution for onboard utilization on small satellites and cubesats, due to the reduced encoder complexity and excellent error rate performance
Combined Time, Frecuency and Space Diversity in Multimedia Mobile Broadcasting Systems
El uso combinado de diversidad en el dominio temporal, frecuencial y espacial constituye una valiosa herramienta para mejorar la recepci贸n de servicios de difusi贸n m贸viles. Gracias a la mejora conseguida por las t茅cnicas de diversidad es posible extender la cobertura de los servicios m贸viles adem谩s de reducir la infraestructura de red. La presente tesis investiga el uso de t茅cnicas de diversidad para la provisi贸n de servicios m贸viles en la familia europea de sistemas de difusi贸n terrestres estandarizada por el prpoyecto DVB (Digital Video Broadcasting). Esto incluye la primera y segunda generaci贸n de sistemas DVB-T (Terrestrial), DVB-NGH (Handheld), y DVB-T2 (Terrestrial 2nd generation), as铆 como el sistema de siguiente generaci贸n DVB-NGH. No obstante, el estudio llevado a cabo en la tesis es gen茅rico y puede aplicarse a futuras evoluciones de est谩ndares como el japon茅s ISDB-T o el americano ATSC.
Las investigaciones realizadas dentro del contexto de DVB-T, DVB-H y DVBT2 tienen como objetivo la transmisi贸n simult谩nea de servicios fijos y m贸viles en redes terrestres. Esta Convergencia puede facilitar la introducci贸n de servicios m贸viles de TB debido a la reutilizaci贸n de espectro, contenido e infraestructura. De acuerdo a los resultados, la incorporaci贸n de entrelazado temporal en la capa f铆sica para diversidad temporal, y de single-input multiple-output (SIMO) para diversidad espacial, son esenciales para el rendimiento de sistemas m贸viles de difusi贸n. A pesar de que las t茅cnicas upper later FEC (UL-FEC) pueden propocionar diversidad temporal en sistemas de primera generaci贸n como DVB-T y DVB-H, requieren la transmisi贸n de paridad adicional y no son 煤tiles para la recepci贸n est谩tica. El an谩lisis en t锟矫眅rminos de link budjget revela que las t茅cnicas de diversidad noson suficientes para facilitar la provision de servicios m贸viles en redes DVB-T y DVB-T2 planificadas para recepci贸n fija. Sin embargo, el uso de diversidad en redes planificadas para recepci贸n portableGoz谩lvez Serrano, D. (2012). Combined Time, Frecuency and Space Diversity in Multimedia Mobile Broadcasting Systems [Tesis doctoral no publicada]. Universitat Polit猫cnica de Val猫ncia. https://doi.org/10.4995/Thesis/10251/16273Palanci