Temat: OFDM - Katalog OPAC zbiorów

Skocz do pozycji: 1.

Tytuł:: Blind frequency offset estimation for overlap PCC-OFDM systems in presence of phase noise
Autorzy:: Shentu, J.
Armstrong, J.
Powiązania:: https://bibliotekanauki.pl/articles/307668.pdf
Data publikacji:: 2003
Wydawca:: Instytut Łączności - Państwowy Instytut Badawczy
Tematy:: OFDM
frequency offset
estimation
phase noise
overlap PCC-OFDM
Opis:: This paper presents a technique for frequency offset estimation for polynomial cancellation coded orthogonal frequency division multiplexing with symbols overlapped in the time domain (overlap PCC-OFDM) in the presence of phase noise. The frequency offset estimator is designed based on the subcarrier pair imbalance (SPI) caused by frequency offset. The estimation is performed in the frequency domain at the output of the receiver discrete Fourier transform (DFT). No training symbols or pilot tones are required. Simulations show that this estimator is an approximately linear function of frequency offset. Phase noise does not significantly affect the variance performance of the estimator.
Źródło:: Journal of Telecommunications and Information Technology; 2003, 2; 17-27
1509-4553
1899-8852
Pojawia się w:: Journal of Telecommunications and Information Technology
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Subcarrier Gain Based Power Allocation in Multicarrier Systems
Autorzy:: Abd-Elnaby, M.
Sedhom, G. G.
Messiha, N. W.
Abd El-Samie, F. E.
Zhu, X.
Powiązania:: https://bibliotekanauki.pl/articles/958110.pdf
Data publikacji:: 2014
Wydawca:: Instytut Łączności - Państwowy Instytut Badawczy
Tematy:: GPA
OFDM
QAM
SNR
Opis:: The Orthogonal Frequency Division Multiplexing (OFDM) transmission is the optimum version of the multicarrier transmission scheme, which has the capability to achieve high data rate. The key issue of OFDMsystem is the allocation of bits and power over a number of subcarriers. In this paper, a new power allocation algorithm based on subcarrier gain is proposed to maximize the bit rate. For OFDM systems, the Subcarrier Gain Based Power Allocation (SGPA) algorithm is addressed and compared with the standard Greedy Power Allocation (GPA). The authors demonstrate by analysis and simulation that the proposed algorithm reduces the computational complexity and achieves a near optimal performance in maximizing the bit rate over a number of subcarrier.
Źródło:: Journal of Telecommunications and Information Technology; 2014, 1; 62-67
1509-4553
1899-8852
Pojawia się w:: Journal of Telecommunications and Information Technology
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Enhancement of Power Efficiency in OFDM System by SLM with Predistortion Technique
Autorzy:: Sharma, P. K.
Nagaria, R. K.
Sharma, T. N.
Powiązania:: https://bibliotekanauki.pl/articles/308396.pdf
Data publikacji:: 2011
Wydawca:: Instytut Łączności - Państwowy Instytut Badawczy
Tematy:: nonlinear HPA
OFDM
PAPR
SLM
Opis:: Orthogonal Frequency Division Multiplexing (OFDM) is considered as a strong candidate for future wireless communication because it is marked by its higher frequency multiplicity and greater immunity to multipath fading. However, the main drawback of OFDM is its high amplitude fluctuations measured by peak-to-average power ratio (PAPR), which leads to power inefficiency and requires expensive high power amplifier (HPA) with very good linearity. In this paper, we propose selected mapping (SLM) with predistortion technique to decrease the nonlinear distortion and to improve the power efficiency of the nonlinear HPA. In the proposed method SLM reduces the PAPR and improves the power efficiency, the predistorter improves the bit error rate (BER) performance of the system. The PAPR reduction is possible with SLM when compared with original OFDM. After reducing the PAPR with SLM the data goes into the HPA with and without predistorter. The BER performance curves of SLM method with or without predistorter shows that, predistorter operates more effectively in SLM method than original OFDM system. At 4 dB IBO (input backoff) the conventional method with predistorter achieves 1.8 dB SNR gain than conventional method without a predistorter and at 6 dB IBO the BER performance is towards the ideal linear amplifier. The proposed system will be evaluated for OFDM system in the presence of a nonlinear power amplifier.
Źródło:: Journal of Telecommunications and Information Technology; 2011, 4; 86-91
1509-4553
1899-8852
Pojawia się w:: Journal of Telecommunications and Information Technology
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: MIMO versus SISO : simulation results
Efektywność systemu MIMO względem SISO : wyniki badań symulacyjnych
Autorzy:: Michalak, J.
Ziółkowski, C.
Uljasz, B.
Powiązania:: https://bibliotekanauki.pl/articles/210912.pdf
Data publikacji:: 2012
Wydawca:: Wojskowa Akademia Techniczna im. Jarosława Dąbrowskiego
Tematy:: MIMO
Alamouti
OFDM
SISO
STBC
Opis:: Results of computer simulation tests of the STBC Alamouti MIMO 2×2 system in comparison to SISO were presented in this paper. The aim was to assess effectiveness of MIMO versus SISO in assumed propagation conditions. Depending on subscriber motion, propagation conditions as well as antenna system configuration, different results were received. In each configuration, MIMO system was not worse than SISO and many times it is significantly better than SISO with gain from a few to a dozen or so dB.
W artykule zaprezentowano wyniki symulacji komputerowej systemu wieloantenowego MIMO 2×2 (ang. Multiple Input Multiple Output) z koderem STBC (ang. Space Time Block Coding) Alamoutiego w porównaniu do systemu SISO (ang. Single Input Single Output). Celem badania było określenie stopnia efektywności układu MIMO zależnie od prędkości i kierunku ruchu korespondenta, warunków propagacji oraz konfiguracji anten. Zależnie od założeń symulacyjnych uzyskano wyniki potwierdzające przewagę MIMO nad SISO w zakresie od kilku do kilkunastu dB.
Źródło:: Biuletyn Wojskowej Akademii Technicznej; 2012, 61, 1; 223-239
1234-5865
Pojawia się w:: Biuletyn Wojskowej Akademii Technicznej
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 5.

Tytuł:: An adaptive hidden Markov model for indoor OFDM based wireless systems
Autorzy:: Verikoukis, Ch.V.
Powiązania:: https://bibliotekanauki.pl/articles/308130.pdf
Data publikacji:: 2004
Wydawca:: Instytut Łączności - Państwowy Instytut Badawczy
Tematy:: hidden Markov model
OFDM
multicarrier transmission
Opis:: Detailed physical layer simulation of orthogonal frequency division multiplexing (OFDM) systems requires programs that execute too slowly due to long coherence time of the indoor mobile channel. Evaluation of higher layers of such systems is simplified if suitable models for reproduction of channel errors statistics are available. An adaptive hidden Markov model (HMM) for indoor OFDM based systems that accurately reproduces error statistics of the real system with less computational effort than the exact simulation is presented in this paper. The standard HMM methodology has been modified in order to reproduce the periodicity in the error positions of the OFDM systems. The proposed model is validated by comparison of three statistical parameters: number of errors, length of the errors run and length of the error-free intervals in a frame of bits.
Źródło:: Journal of Telecommunications and Information Technology; 2004, 2; 61-65
1509-4553
1899-8852
Pojawia się w:: Journal of Telecommunications and Information Technology
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 6.

Tytuł:: Improvement of LTE Downlink Channel Estimation Performance by Using an Adaptive Pilot Pattern
Autorzy:: Youssefi, M. A.
Abbadi, J. E.
Powiązania:: https://bibliotekanauki.pl/articles/307570.pdf
Data publikacji:: 2015
Wydawca:: Instytut Łączności - Państwowy Instytut Badawczy
Tematy:: channel estimation
LTE
MIMO
OFDM
pilot pattern
Opis:: This paper proposes an adaptive pilot pattern to improve channel estimation performance for LTE downlink system with high mobility. The downlink pilot positions are predefined in the time and frequency domain with fixed pilot pattern in LTE standard. However, that pilot structure is not efficient in a fast time varying channel, and leads to a decrease of channel estimation performance. The authors propose and evaluate the performance of LTE downlink channel estimation using an adaptive pilot scheme to optimally use pilot tones over time varying channels. It is shown that only seven bits of additional wide-band feedback per frame and per user are required to optimally support adaptive pilot pattern. Simulation results show that the proposed method allows high performance in terms of throughput and channel estimation error. This analysis shows that LTE downlink throughput could be increased over 4%.
Źródło:: Journal of Telecommunications and Information Technology; 2015, 2; 59-63
1509-4553
1899-8852
Pojawia się w:: Journal of Telecommunications and Information Technology
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 7.

Tytuł:: Complex Signal Mapping for Improving Spectral Eﬃciency of Li-Fi Systems
Autorzy:: Sileh, Ibrahim K.
Abdulkaﬁ, Ayad A.
Hussein, Mohammed K.
Hardan, Saad M.
Powiązania:: https://bibliotekanauki.pl/articles/958061.pdf
Data publikacji:: 2019
Wydawca:: Instytut Łączności - Państwowy Instytut Badawczy
Tematy:: Li-Fi
OFDM
signal mapping
PAPR
BER
Opis:: Light ﬁdelity (Li-Fi) systems based on the orthogonal frequency division multiplexing (OFDM) scheme have gained more attention in the communications circles, as a means to provide high spectral eﬃciency and ensure stricter data rate requirements for visible light communication (VLC) systems. However, common OFDM schemes employ Hermitian symmetry to obtain a real-valued signal which is necessary in intensity modulation and direct detection (IM/DD) optical systems, at the expense of doubling the required bandwidth. In this paper, a novel transmission scheme for an OFDM-based Li-Fi system is proposed to tackle the issue in question. A new approach to complex signal mapping (CSM), based on the pairing function method, has been developed for Li-Fi systems. It does not require Hermitian symmetry and, hence, saves about 50% of the required bandwidth. Unlike existing OFDM-based VLC approaches, the proposed scheme employs CSM to ensure a real and positive signal without Hermitian symmetry in order to fully utilize the bandwidth available to Li-Fi networks. Simulation results show that the proposed scheme signiﬁcantly outperforms other systems in terms of spectral eﬃciency. The CSM-OFDM based Li-Fi system also achieves a good peak-to-average power ratio (PAPR) reduction with acceptable bit-error-rate (BER) performance, compared to conventional approaches.
Źródło:: Journal of Telecommunications and Information Technology; 2019, 3; 58-62
1509-4553
1899-8852
Pojawia się w:: Journal of Telecommunications and Information Technology
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 8.

Tytuł:: Algorithm Based New Tone Reservation Method for Mitigating PAPR in OFDM Systems
Autorzy:: Saha, S.
Chakrabarty, S.
Bhattacharjee, S.
Sil, S.
Powiązania:: https://bibliotekanauki.pl/articles/963815.pdf
Data publikacji:: 2017
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:: BER
CCDF
OFDM
PAPR
tone reservation algorithm
Opis:: There are abundant methods to mitigate PAPR in OFDM signals among which algorithm based tone reservation is of great popularity owing to its low complexity as well as decent BER. Here we have put forward a new distinct algorithm based Tone Reservation technique which is not only less complex and calculates its own threshold as well as PRT signal (unlike other algorithms requiring predetermined threshold and PRT) but also aptly modifies the data by bit by bit comparison with a modified copy of itself (algorithm modified) thus scaling the peaks as and providing a decent BER and good PAPR reduction.
Źródło:: International Journal of Electronics and Telecommunications; 2017, 63, 3; 293-298
2300-1933
Pojawia się w:: International Journal of Electronics and Telecommunications
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 9.

Tytuł:: A DFT-based Low Complexity LMMSE Channel Estimation Technique for OFDM Systems
Autorzy:: Patra, Jyoti P.
Pradhan, Bibhuti Bhusan
Singh, Poonam
Powiązania:: https://bibliotekanauki.pl/articles/2058504.pdf
Data publikacji:: 2022
Wydawca:: Instytut Łączności - Państwowy Instytut Badawczy
Tematy:: channel estimation
LMMSE
mean square error
OFDM
Opis:: The linear minimum mean square error (LMMSE) channel estimation technique is often employed in orthogonal frequency division multiplexing (OFDM) systems because of its optimal performance in the mean square error (MSE) performance. However, the LMMSE method requires cubic complexity of order O(N 3 p ), where Np is the number of pilot subcarriers. To reduce the computational complexity, a discrete Fourier transform (DFT) based LMMSE method is proposed in this paper for OFDM systems in the frequency selective channel. To validate the proposed method, the closed form mean square error (MSE) expression is also derived. Finally, a computer simulation is carried out to compare the performance of the proposed LMMSE method with the classical LS and LMMSE methods in terms of bit error rate (BER) and computational complexity. Results of the simulation show that the proposed LMMSE method achieves exactly the same performance as the conventional LMMSE method, with much lower computational complexity.
Źródło:: Journal of Telecommunications and Information Technology; 2022, 1; 72--78
1509-4553
1899-8852
Pojawia się w:: Journal of Telecommunications and Information Technology
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 10.

Tytuł:: Influence of a real radio channel parameters on the quality of the OFDM signal in mobile applications. Estimation of parameters of the channel as an element of improvement of the transmission quality
Autorzy:: Bożek, K.
Powiązania:: https://bibliotekanauki.pl/articles/385028.pdf
Data publikacji:: 2007
Wydawca:: Sieć Badawcza Łukasiewicz - Przemysłowy Instytut Automatyki i Pomiarów
Tematy:: OFDM
radio transmission
multi-path
radio channel estimation
Opis:: The article deals with issues related to transmission of a signal with the OFDM multitude modulation in a real radio channel. Following short characteristics of the OFDM modulation, the article includes an analysis of typical radio channels from the angle of amplitude and phase on the basis of delay profiles referred to in the literature. The study contains results of simulated receipt of the OFDM signal in the multi-path conditions. On the basis of diagrams of constellation of the modulation symbols, the author presented differences in the quality of the signal before and after the phase correction and improvement in the quality due to application of cyclic prefix. Influence of noise as well as the fact that the terminals are non-stationary on operation of the frequency characteristics estimation algorithm was analyzed. At the end, an example was presented of application of a linear model of estimation of phase characteristics of a channel with the shift in frequency occurring in mobile systems as a consequence of the Doppler effect being compensated.
Źródło:: Journal of Automation Mobile Robotics and Intelligent Systems; 2007, 1, 3; 64-68
1897-8649
2080-2145
Pojawia się w:: Journal of Automation Mobile Robotics and Intelligent Systems
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 11.

Tytuł:: Normalized Gaussian Approach to Statistical Modeling of OFDM Signals
Autorzy:: Rudziński, A.
Powiązania:: https://bibliotekanauki.pl/articles/308010.pdf
Data publikacji:: 2014
Wydawca:: Instytut Łączności - Państwowy Instytut Badawczy
Tematy:: M-PSK
OFDM
sample value distribution
statistical model
Opis:: This article concerns modeling of statistical properties of OFDM signals with the help of “normalized Gaussian” model, proposed by Kotzer et al. In this paper there is provided an extended formulation of the model, supplemented by an expression for probability density, extending possible applications of the model in theoretical works. Numerical results for verification of the model are provided and a more accurate alternative is suggested.
Źródło:: Journal of Telecommunications and Information Technology; 2014, 1; 54-61
1509-4553
1899-8852
Pojawia się w:: Journal of Telecommunications and Information Technology
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 12.

Tytuł:: New OSTBC for Blind Channel Estimation and Tracking in MIMO-OFDM Systems
Autorzy:: Tami, Abdelkader
Keche, Mokhtar
Bouazza, Boubaker S.
Powiązania:: https://bibliotekanauki.pl/articles/958059.pdf
Data publikacji:: 2019
Wydawca:: Instytut Łączności - Państwowy Instytut Badawczy
Tematy:: MIMO
OFDM
blind channel estimation
OSTBC
SS-KCE
Opis:: Applying orthogonal space time block coding (OSTBC) to multiple-input multiple-output (MIMO) systems helps reduce receiver complexity. However, this approach has been applied only to ﬂat fading channels, as when the channel is a frequency selective fading MIMO channel, OSTBC cannot be used directly since its orthogonal propriety may be lost. Furthermore, the MIMO channel is not always known. To deal with this problem, many techniques were proposed to estimate the channel using a training sequence. Unfortunately, these techniques reduce the useful spectral bandwidth. This paper proposes OSTBC for blind channel estimation and data detection in the case of a MIMO frequency selective channel. The aim of this new OSTBC is twofold: to solve the ambiguity of channel estimation and to reduce the complexity of the detector. By exploiting the well-known technique of orthogonal frequency division multiplexing (OFDM), the frequency selective fading MIMO channel is split into a set of ﬂat fading subchannels. Moreover, to accommodate the fact that a MIMO channel can be time varying, the steady state Kalman channel estimator (SS-KCE) is extended to track the channel’s fast variations. The performance of the proposed blind algorithm is related by the adequate choice of the number of subcarriers and it is compared with other existing approaches by means of Monte Carlo simulations.
Źródło:: Journal of Telecommunications and Information Technology; 2019, 3; 49-57
1509-4553
1899-8852
Pojawia się w:: Journal of Telecommunications and Information Technology
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 13.

Tytuł:: Performance metrics in OFDM wireless networks supporting quasi-random traffic
Autorzy:: Panagoulias, P.
Moscholios, I.
Sarigiannidis, P.
Piechowiak, M.
Logothetis, M.
Powiązania:: https://bibliotekanauki.pl/articles/200360.pdf
Data publikacji:: 2020
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:: congestion
quasi random
OFDM
reservation
loss model
recursive
Opis:: We consider the downlink of an orthogonal frequency division multiplexing (OFDM) based cell that accommodates calls from different service-classes with different resource requirements. We assume that calls arrive in the cell according to a quasi-random process, i.e., calls are generated by a finite number of sources. To calculate the most important performance metrics in this OFDM-based cell, i.e., congestion probabilities and resource utilization, we model it as a multirate loss model, show that the steady-state probabilities have a product form solution (PFS) and propose recursive formulas which reduce the complexity of the calculations. In addition, we study the bandwidth reservation (BR) policy which can be used in order to reserve subcarriers in favor of calls with high subcarrier requirements. The existence of the BR policy destroys the PFS of the steady-state probabilities. However, it is shown that there are recursive formulas for the determination of the various performance measures. The accuracy of the proposed formulas is verified via simulation and found to be satisfactory.
Źródło:: Bulletin of the Polish Academy of Sciences. Technical Sciences; 2020, 68, 2; 215-223
0239-7528
Pojawia się w:: Bulletin of the Polish Academy of Sciences. Technical Sciences
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 14.

Tytuł:: Performance Improvements in SNR of a Multipath Channel Using OFDM-MIMO
Autorzy:: Enoch, Sharmini
Otung, Ifiok
Powiązania:: https://bibliotekanauki.pl/articles/27311959.pdf
Data publikacji:: 2023
Wydawca:: Polska Akademia Nauk. Czasopisma i Monografie PAN
Tematy:: WiMAX
fade mitigation
OFDM
MIMO
cyclic prefix
guard time
Opis:: The Non Line of Sight (NLOS) broadband wireless access provided by Worldwide Interoperability for Microwave Access (WiMAX) operating in 2-11 GHz frequency is susceptible to the effects of multipath propagation, diffraction fading, vegetation attenuation, shadowing loss etc. In order to overcome these effects effective fade mitigation techniques, have to be implemented. The Orthogonal Frequency Division Multiplexing- Multiple Input Multiple Output (OFDM-MIMO) is an efficient method that helps in combatting the fading and providing higher SNR to the WiMAX system. According to the IEEE 802.16 specification, for QPSK modulation, a threshold SNR of 6 dB is required for the link to operate. In the present work the use of OFDM-MIMO achieves a SNR above this operating threshold.
Źródło:: International Journal of Electronics and Telecommunications; 2023, 69, 4; 770--773
2300-1933
Pojawia się w:: International Journal of Electronics and Telecommunications
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 15.

Tytuł:: Shallow Water Experiment of OFDM Underwater Acoustic Communications
Autorzy:: Kochańska, Iwona
Schmidt, Jan H.
Marszal, Jacek
Powiązania:: https://bibliotekanauki.pl/articles/177592.pdf
Data publikacji:: 2020
Wydawca:: Polska Akademia Nauk. Czasopisma i Monografie PAN
Tematy:: underwater acoustic communications
UAC
orthogonal frequency-division multiplexing
OFDM
Opis:: The large variability of communication properties of underwater acoustic channels, and especially the strongly varying instantaneous conditions in shallow waters, is a challenge for the designers of underwater acoustic communication (UAC) systems. The use of phase modulated signals does not allow reliable data transmission through such a tough communication channel. However, orthogonal frequency-division multiplexing (OFDM), being a multi-carrier amplitude and phase modulation technique applied successfully in the latest standards of wireless communications, gives the chance of reliable communication with an acceptable error rate. This paper describes communication tests conducted with the use of a laboratory model of an OFDM data transmission system in a shallow water environment in Wdzydze Lake.
Źródło:: Archives of Acoustics; 2020, 45, 1; 11-18
0137-5075
Pojawia się w:: Archives of Acoustics
Dostawca treści:: Biblioteka Nauki

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