80 research outputs found
Deep Ensemble of Weighted Viterbi Decoders for Tail-Biting Convolutional Codes
Tail-biting convolutional codes extend the classical zero-termination
convolutional codes: Both encoding schemes force the equality of start and end
states, but under the tail-biting each state is a valid termination. This paper
proposes a machine-learning approach to improve the state-of-the-art decoding
of tail-biting codes, focusing on the widely employed short length regime as in
the LTE standard. This standard also includes a CRC code.
First, we parameterize the circular Viterbi algorithm, a baseline decoder
that exploits the circular nature of the underlying trellis. An ensemble
combines multiple such weighted decoders, each decoder specializes in decoding
words from a specific region of the channel words' distribution. A region
corresponds to a subset of termination states; the ensemble covers the entire
states space. A non-learnable gating satisfies two goals: it filters easily
decoded words and mitigates the overhead of executing multiple weighted
decoders. The CRC criterion is employed to choose only a subset of experts for
decoding purpose. Our method achieves FER improvement of up to 0.75dB over the
CVA in the waterfall region for multiple code lengths, adding negligible
computational complexity compared to the circular Viterbi algorithm in high
SNRs
Feedback Communication Systems with Limitations on Incremental Redundancy
This paper explores feedback systems using incremental redundancy (IR) with
noiseless transmitter confirmation (NTC). For IR-NTC systems based on {\em
finite-length} codes (with blocklength ) and decoding attempts only at {\em
certain specified decoding times}, this paper presents the asymptotic expansion
achieved by random coding, provides rate-compatible sphere-packing (RCSP)
performance approximations, and presents simulation results of tail-biting
convolutional codes.
The information-theoretic analysis shows that values of relatively close
to the expected latency yield the same random-coding achievability expansion as
with . However, the penalty introduced in the expansion by limiting
decoding times is linear in the interval between decoding times. For binary
symmetric channels, the RCSP approximation provides an efficiently-computed
approximation of performance that shows excellent agreement with a family of
rate-compatible, tail-biting convolutional codes in the short-latency regime.
For the additive white Gaussian noise channel, bounded-distance decoding
simplifies the computation of the marginal RCSP approximation and produces
similar results as analysis based on maximum-likelihood decoding for latencies
greater than 200. The efficiency of the marginal RCSP approximation facilitates
optimization of the lengths of incremental transmissions when the number of
incremental transmissions is constrained to be small or the length of the
incremental transmissions is constrained to be uniform after the first
transmission. Finally, an RCSP-based decoding error trajectory is introduced
that provides target error rates for the design of rate-compatible code
families for use in feedback communication systems.Comment: 23 pages, 15 figure
A FEC Decoding in LTE and WiMAX Systems
Abstract: Recent wireless systems such as EDGE, WIMAX, LTE are using LDPC, tail biting and turbo convolution codes as the forward error correction codes (FEC) for the data and overhead channels. Therefore many decoding algorithms are introduced for decoding these codes. Using different decoding approaches lead to different hardware architectures. As, in new wireless systems these codes work side by side a single universal decoder which is efficient in handling decoding of all the codes
Information-Coupled Turbo Codes for LTE Systems
We propose a new class of information-coupled (IC) Turbo codes to improve the
transport block (TB) error rate performance for long-term evolution (LTE)
systems, while keeping the hybrid automatic repeat request protocol and the
Turbo decoder for each code block (CB) unchanged. In the proposed codes, every
two consecutive CBs in a TB are coupled together by sharing a few common
information bits. We propose a feed-forward and feed-back decoding scheme and a
windowed (WD) decoding scheme for decoding the whole TB by exploiting the
coupled information between CBs. Both decoding schemes achieve a considerable
signal-to-noise-ratio (SNR) gain compared to the LTE Turbo codes. We construct
the extrinsic information transfer (EXIT) functions for the LTE Turbo codes and
our proposed IC Turbo codes from the EXIT functions of underlying convolutional
codes. An SNR gain upper bound of our proposed codes over the LTE Turbo codes
is derived and calculated by the constructed EXIT charts. Numerical results
show that the proposed codes achieve an SNR gain of 0.25 dB to 0.72 dB for
various code parameters at a TB error rate level of , which complies
with the derived SNR gain upper bound.Comment: 13 pages, 12 figure
Feasibility study of 5G low-latency packet radio communications without preambles
This thesis deals with the feasibility of having lower latency for radio communication of short packets, which is the major traffic in the fifth generation (5G) of cellular systems. We will examine the possibility of using turbo synchronization instead of using a long preamble, which is needed for Data-Aided (DA) synchronization. The idea behind this is that short packets are required in low-latency applications. The overhead of preambles is very significant in case of short packets. Turbo synchronization allows to work with short or null preambles. The simulations will be run for a turbo synchronizer which has been implemented according to the Expectation Maximization (EM) formulation of the problem. The simulation results show that the implemented turbo synchronizer outperforms or attains the DA synchronizer in terms of reliability, accuracy and acquisition range for carrier phase synchronization. It means that the idea of eliminating the preamble from the short packet seems practical. The only downward is that there is a packet size limitation for the effective functionality of turbo synchronizer. Simulations indicate that the number of transmitted symbols should be higher than 128 coded symbols
RS Codes for Downlink LTE System over LTE-MIMO Channel
Nowdays, different applications require a modern generation of mobile communication systems; long term evolution (LTE) is a candidate to achieve this purpose. One important challenge in wireless communications, including LTE systems, is the suitable techniques of controlling errors that degrade system performance in transmission systems over multipath fading channels. Different forward Error correction (FEC) techniqes are required to improve the robustness of transmission channels. In this paper, Reed-Solomon (RS) codes were used with a downlink LTE system over a LTE-MIMO channel. This research contributes by combining RS codes that have low decoding complexity (by using hard decision decoding) with a LTE-MIMO channel to improve downlink LTE system performance. The results show that using RS codes clearly improves LTE system performance and thus decreases Bit Error Rates (BER) more than convolutional and turbo codes which have high decoding complexity. Lastly, the results show also extra improvements of downlink LTE system performance by increasing the number of antennas of the LTE-MIMO channel
CRC-Aided High-Rate Convolutional Codes With Short Blocklengths for List Decoding
Recently, rate-1/n zero-terminated (ZT) and tail-biting (TB) convolutional
codes (CCs) with cyclic redundancy check (CRC)-aided list decoding have been
shown to closely approach the random-coding union (RCU) bound for short
blocklengths. This paper designs CRC polynomials for rate- (n-1)/n ZT and TB
CCs with short blocklengths. This paper considers both standard rate-(n-1)/n CC
polynomials and rate- (n-1)/n designs resulting from puncturing a rate-1/2
code. The CRC polynomials are chosen to maximize the minimum distance d_min and
minimize the number of nearest neighbors A_(d_min) . For the standard
rate-(n-1)/n codes, utilization of the dual trellis proposed by Yamada et al.
lowers the complexity of CRC-aided serial list Viterbi decoding (SLVD).
CRC-aided SLVD of the TBCCs closely approaches the RCU bound at a blocklength
of 128. This paper compares the FER performance (gap to the RCU bound) and
complexity of the CRC-aided standard and punctured ZTCCs and TBCCs. This paper
also explores the complexity-performance trade-off for three TBCC decoders: a
single-trellis approach, a multi-trellis approach, and a modified
single-trellis approach with pre-processing using the wrap around Viterbi
algorithm.Comment: arXiv admin note: substantial text overlap with arXiv:2111.0792
Modelação comportamental da camada física de NB-IoT em downlink
Mestrado em Engenharia Eletrónica e TelecomunicaçõesThe Internet of Things (IoT) paradigm de nes a fully connected network of
devices enabling new forms of interaction between users and devices. The
constant growth of these networks, as well as an increasing demand for
more reliable, low bit rate and massive communication data
ows lead to
the emergence of new technologies and set of standards, such as, the Low
Power Wide Area Networks (LPWAN).
In June 2016, 3GPP, the consortium responsible for LTE development and
standardization, released a new licensed band based standard, named Narrow
Band (NB) IoT. NB-IoT was designed based on the same principles
of other LPWAN standards, providing better coverage and additionally an
easier integration on existing cellular systems.
In this dissertation a study on the NB-IoT Physical Layer is presented along
with an open source behavioral implementation in MATLAB of the downlink
transmission and reception chains.
The system generates and recovers one radio frame successfully performings
procedures such as MIB and SIB1-N extracting along with scheduling
and recovering data scheduled through control channels by higher layer
paramenters. The project models and executes the downlink transmission
(eNodeB) and reception (terminal) PHYs either in a pure simulation environment
using di erent channel models, as well as integrated with an USRP
software de ned radio device for co-simulation.
The simulation and co-simulation results are presented evaluating the transmission's
quality and performance of the implemented Zero Forcing equalizer.O paradigma da Internet of Things (IoT) define uma rede interligada de
dispositivos que permite o surgimento de novas formas de interacção entre
utilizadores e dispositivos. O constante crescimento destas redes assim
como a crescente demanda por uma fiabilidade maior, bit rates mais baixos
e circulação massiva de informação insurgiu o aparecimento de novas tecnologias
tais como as Low Power Wide Area Networks (LPWAN).
Em Junho de 2016 a 3GPP, o órgão responsável pelo LTE, lançou um novo
standard para bandas licenciadas o Narrowband (NB) -IoT. O NB-IoT foi
desenhado com base nos mesmos princípios que as outras LPWAN com o
acréscimo de uma maior cobertura assim como uma mais fácil integração
em sistemas celulares existentes.
Nesta dissertação aborda-se um estudo da sua camada física (PHY Layer)
juntamente com uma implementação comportamental open source em Matlab
das cadeias de transmissão e recepção em downlink. O projecto modela
e executa transmissões em downlink (eNodeB) e sua recepcção (terminal)
tanto em ambiente simulado como integrado com um dispositivo de software
defined radio, USRP, para validação laboratorial.
Os resultados obtidos tanto de simulação como co-simulação são apresentados
avaliando a qualidade de transmissão assim como o comportamento
do equalizador Zero Forcing implementado
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