460 research outputs found
On Time-Variant Distortions in Multicarrier Transmission with Application to Frequency Offsets and Phase Noise
Phase noise and frequency offsets are due to their time-variant behavior one
of the most limiting disturbances in practical OFDM designs and therefore
intensively studied by many authors. In this paper we present a generalized
framework for the prediction of uncoded system performance in the presence of
time-variant distortions including the transmitter and receiver pulse shapes as
well as the channel. Therefore, unlike existing studies, our approach can be
employed for more general multicarrier schemes. To show the usefulness of our
approach, we apply the results to OFDM in the context of frequency offset and
Wiener phase noise, yielding improved bounds on the uncoded performance. In
particular, we obtain exact formulas for the averaged performance in AWGN and
time-invariant multipath channels.Comment: 10 pages (twocolumn), 5 figure
Channel estimation with TCH codes for machine-type communications
TCH codes possess several properties that allow us to use them efficiently in
various applications. One of these applications is channel estimation and, in this
dissertation, it is studied the performance of TCH codes to estimate the channel in
an Orthogonal Frequency Division Multiplexing system, regarding Machine-Type
Communications. Bit error rate performance results were obtained by executing
simulations that allowed the evaluation of the impact of using two different pilot
techniques, such as data multiplexed and implicit pilots, different pilot power levels
and different modulations, QPSK and 64-QAM. Pilots based on TCH codes are
also compared with other conventional pilots. Results show that TCH codes have
a very positive and reliable performance.
Joint timing synchronization and channel estimation is also performed using different sparse based approaches, such as Orthogonal Matching Pursuit, L1-
regularized and Iterative Reweighted L1. TCH codes are compared against different
sequence types, namely Zadoff-Chu sequences and pseudorandom codewords, and
variations in the pilot size, the channel length and the observation window size are
executed in order to understand their effects. Results ultimately illustrate that
TCH codes can be effectively used in joint channel estimation and synchronization,
managing to withstand worst simulation conditions better than its counterparts.
It is also proven that compressed sensing can successfully be utilized in joint synchronization and channel estimation, an area where its use has not been very
explored.Os códigos TCH possuem várias propriedades que nos permitem usá-los eficientemente em diversas aplicações. Uma delas é a estimação de canal e nesta
dissertação é estudado o desempenho dos códigos TCH em estimação de canal
num sistema OFDM, tendo em conta as comunicações Machine-Type. Resultados que ilustram a taxa de erro de bit foram obtidos através de simulações que
permitem avaliar o impacto de usar diferentes técnicas de pilotos, nomeadamente
multiplexados e implícitos, diferentes valores de potência para os pilotos e diferentes modulações, QPSK e 64-QAM. Também é feita a comparação entre os pilotos
TCH e pilotos convencionais. Os resultados mostram que os pilotos TCH tem um
desempenho muito positivo e confiável, dentro dos parâmetros testados.
Também é efetuado o estudo de sincronização e estimação de canal conjunta
usando métodos esparsos como o OMP, o L1-regularized e o Iterative Reweighted
L1. Os códigos TCH são comparados com outros tipos de sequências, tais como as
sequências Zadoff-Chu e os códigos pseudo-aleatórios. São consideradas variações
no tamanho dos pilotos, no comprimento do canal e no tamanho da janela de
observação para perceber quais são os seus efeitos no desempenho. Os resultados
demonstram que os códigos TCH podem ser utilizados com sucesso em estimação
de canal e sincronização conjunta e conseguem aguentar condições adversas de simulação melhor que os outros pilotos utilizados. Também é provado que compressed
sensing pode ser utilizado com sucesso em sincronização e estimação conjunta, que
é uma área onde o seu uso ainda não foi explorado aprofundadamente
Channel estimation techniques for filter bank multicarrier based transceivers for next generation of wireless networks
A dissertation submitted to Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering (Electrical and Information Engineering), August 2017The fourth generation (4G) of wireless communication system is designed based on the principles of cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) where the cyclic prefix (CP) is used to combat inter-symbol interference (ISI) and inter-carrier interference (ICI) in order to achieve higher data rates in comparison to the previous generations of wireless networks. Various filter bank multicarrier systems have been considered as potential waveforms for the fast emerging next generation (xG) of wireless networks (especially the fifth generation (5G) networks). Some examples of the considered waveforms are orthogonal frequency division multiplexing with offset quadrature amplitude modulation based filter bank, universal filtered multicarrier (UFMC), bi-orthogonal frequency division multiplexing (BFDM) and generalized frequency division multiplexing (GFDM). In perfect reconstruction (PR) or near perfect reconstruction (NPR) filter bank designs, these aforementioned FBMC waveforms adopt the use of well-designed prototype filters (which are used for designing the synthesis and analysis filter banks) so as to either replace or minimize the CP usage of the 4G networks in order to provide higher spectral efficiencies for the overall increment in data rates. The accurate designing of the FIR low-pass prototype filter in NPR filter banks results in minimal signal distortions thus, making the analysis filter bank a time-reversed version of the corresponding synthesis filter bank. However, in non-perfect reconstruction (Non-PR) the analysis filter bank is not directly a time-reversed version of the corresponding synthesis filter bank as the prototype filter impulse response for this system is formulated (in this dissertation) by the introduction of randomly generated errors. Hence, aliasing and amplitude distortions are more prominent for Non-PR.
Channel estimation (CE) is used to predict the behaviour of the frequency selective channel and is usually adopted to ensure excellent reconstruction of the transmitted symbols. These techniques can be broadly classified as pilot based, semi-blind and blind channel estimation schemes. In this dissertation, two linear pilot based CE techniques namely the least square (LS) and linear minimum mean square error (LMMSE), and three adaptive channel estimation schemes namely least mean square (LMS), normalized least mean square (NLMS) and recursive least square (RLS) are presented, analyzed and documented. These are implemented while exploiting the near orthogonality properties of offset quadrature amplitude modulation (OQAM) to mitigate the effects of interference for two filter bank waveforms (i.e. OFDM/OQAM and GFDM/OQAM) for the next generation of wireless networks assuming conditions of both NPR and Non-PR in slow and fast frequency selective Rayleigh fading channel. Results obtained from the computer simulations carried out showed that the channel estimation schemes performed better in an NPR filter bank system as compared with Non-PR filter banks. The low performance of Non-PR system is due to the amplitude distortion and aliasing introduced from the random errors generated in the system that is used to design its prototype filters. It can be concluded that RLS, NLMS, LMS, LMMSE and LS channel estimation schemes offered the best normalized mean square error (NMSE) and bit error rate (BER) performances (in decreasing order) for both waveforms assuming both NPR and Non-PR filter banks.
Keywords: Channel estimation, Filter bank, OFDM/OQAM, GFDM/OQAM, NPR, Non-PR, 5G, Frequency selective channel.CK201
Deep Learning Based on Orthogonal Approximate Message Passing for CP-Free OFDM
Channel estimation and signal detection are very challenging for an
orthogonal frequency division multiplexing (OFDM) system without cyclic prefix
(CP). In this article, deep learning based on orthogonal approximate message
passing (DL-OAMP) is used to address these problems. The DL-OAMP receiver
includes a channel estimation neural network (CE-Net) and a signal detection
neural network based on OAMP, called OAMP-Net. The CE-Net is initialized by the
least square channel estimation algorithm and refined by minimum mean-squared
error (MMSE) neural network. The OAMP-Net is established by unfolding the
iterative OAMP algorithm and adding some trainable parameters to improve the
detection performance. The DL-OAMP receiver is with low complexity and can
estimate time-varying channels with only a single training. Simulation results
demonstrate that the bit-error rate (BER) of the proposed scheme is lower than
those of competitive algorithms for high-order modulation.Comment: 5 pages, 4 figures, updated manuscript, International Conference on
Acoustics, Speech and Signal Processing (ICASSP 2019). arXiv admin note:
substantial text overlap with arXiv:1903.0476
Single-Frequency Network Terrestrial Broadcasting with 5GNR Numerology
L'abstract è presente nell'allegato / the abstract is in the attachmen
A turbo FDE technique for reduced-CP SC-based block transmission systems
For conventional cyclic-prefix (CP)-assisted block transmission systems, the CP length is selected on the basis of the expected maximum delay spread. With regard to single-carrier (SC)-based block transmission implementations, a full-length CP
is recommendable, since it allows good performances through the
use of simple frequency-domain equalization (FDE) techniques.
In this letter, a soft-decision-directed correction (SDDC)-aided
turbo FDE technique is presented for reduced-CP SC-based block
transmission systems using conventional frame structures. The
relations with some already known iterative FDE techniques are
established, and a set of performance results is reported and discussed.
The advantages of the proposed approach are emphasized,
namely, the possibility of approximately achieving (besides the
obvious bandwidth efficiency gain) the maximum power efficiency
gain that a strong CP reduction allows.Fundação para a Ciencia e Tecnologia (FCT), Centro de Análise e processamento de Sinais (CAPS
- …