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PSEUDO ERROR DETECTION IN SMART ANTENNA/DIVERSITY SYSTEMSHaghdad, Mehdi, Feher, Kamilo 10 1900 (has links)
International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / An implementation of a Pseudo Error Detection (PSED) system is presented and its
performance in conjunction with smart antenna and smart diversity systems tested and
evaluated. Non redundancy, instant response and relative simplicity make the Pseudo
Error Detectors excellent real time error monitoring systems in smart antenna and smart
diversity systems. Because of the Non-redundant Error Detection mechanism in Pseudo
Error Detectors, we can monitor the error quality without any coding or overhead. The
output of the pseudo error detector in AWGN, selective fading Doppler shift and other
interference environments is directly correlated to the BER and BLER. This direct
correlation makes it a great tool for online error monitoring of a system and can have
numerous applications
In a PSED the Eye diagram from the demodulator is sampled once per symbol. By
monitoring and comparison of the eye at sampled intervals at different thresholds, we
would know if an error has occurred. By integrating this result over a period of time we
can get the averaged error level. The results provided in this paper were obtained and
verified by both MatLab simulations using dynamic simulation techniques and hardware
measurements over dynamic channels.
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SMART ANTENNA (DIVERSITY) AND NON-FEEDBACK IF EQUALIZATION TECHNIQUES FOR LEO SATELLITE COMMUNICATIONS IN A COMPLEX INTERFERENCE ENVIRONMENTHaghdad, Mehdi, Feher, Kamilo 10 1900 (has links)
International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / An improved performance smart diversity was invented to improve the signal performance in a
combined selective fading, Additive White Gaussian Noise (AWGN), Co-channel interference
(CCI) and Doppler shift environment such as the LEO satellite channel. This system is also
applicable to aeronautical and telemetry channels. Smart diversity is defined here as a
mechanism that selects at each moment the best branch in a n-branch diversity system based on
the error quality with no default branch and no prioritization. The predominant novelty of this
discovery is the introduction of multi level analog based Pseudo Error Detectors (PSED) in every
branch. One of the advantages of PSED is that it is a non redundant error detection system, with
no requirement for overhead and no need for additional valuable spectrum.
This research was motivated by problems in LEO satellite systems due to low orbit and high
relative speed with respect to the ground stations. The system is independent of the modulation
techniques and is applicable to both coherent and non-coherent detections. The results from
simulations using dynamic simulation techniques and hardware measurements over dynamic
channels show significant improvement of both the Bit Error Rate (BER) and the Block Error
Rate (BLER).
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[en] BLIND RECEPTION OF SEQUECIES EXPLORING OVERSAMPLING / [pt] RECEPÇÃO CEGA DE SEQUÊNCIAS EXPLORANDO SUPERAMOSTRAGEMERNESTO LEITE PINTO 12 December 2005 (has links)
[pt] Propõe-se alternativas para exploração da amostragem a
taxas múltiplas da taxa símbolos (superamostragem) em
receptores cegos com decisão de sequências de símbolos, a
fim de se obter melhoria de desempenho em canais com
desvanecimento rápido e seletivo em frequência. O trabalho
se centra em esquemas de recepção do tipo MLSE/PSP
(maximum likelihood sequence estimation/per-survivor
processing) baseados na modelagem estocástica do canal.
Deduz-se um modelo em espaço de estado para a geração das
amostras do sinal recebido, cujos parâmetros podem ser
facilmente associados ao sistema de transmissão. Investiga-
se também uma estratégia de ataque ao problema de recepção
diante de ruído colorido, intrinsecamente associado à
superamostragem. O desempenho dos esquemas de recepção
propostos é avaliado através de simulação computacional.
Os resultados obtidos mostram que a exploração da
superamostragem produz ganhos significativos de desempenho
na recepção cega de sequências, em relação aos esquemas de
recepção MLSE/PSP com amostragem síncrona (taxa de
amostragem igual à taxa de símbolos). / [en] In this work we propose exploting the received signal
oversampling in order to improve the performance of blind
receivers over fast fequency selective fading channels.The
work focus attention on MLSE/PSP (maximum-likelihood
sequence estimation/per survivor processing) receivers and
statistical modeling of the channel output. A state-space
model for oversampled received signal in developed from a
generic continous time transmission system model. Two
MLSE/PSP receiving schemes relying on this model are
proposed. One of them is specially suitable for dealing
with the colored noise produced by oversampling. Computer
simulations were conducted in order to evaluate the
performance of the proposed blind receivers. The results
thus obtained show that these schemes significantly
outperform the synchronous MLSE/PSP receiver (for which
the sampling rate is equal to the sysmbol rate).
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The Impact of Channel Estimation Error on Space-Time Block and Trellis Codes in Flat and Frequency Selective ChannelsChi, Xuan 22 July 2003 (has links)
Recently multiple antenna systems have received significant attention from researchers as a means to improve the energy and spectral efficiency of wireless systems. Among many classes of schemes, Space-Time Block codes (STBC) and Space-Time Trellis codes (STTC) have been the subject of many investigations.
Both techniques provide a means for combatting the effects of multipath fading without adding much complexity to the receiver. This is especially useful in the downlink of wireless systems. In this thesis we investigate the impact of channel estimation error on the performance of both STBC and STTC.
Channel estimation is especially important to consider in multiple antenna systems since (A) for coherent systems there are more channels to estimate due to multiple antennas and (B) the decoupling of data streams relies on correct channel estimation. The latter effect is due to the intentional cross-talk introduced into STBC. / Master of Science
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[en] EFFECTS OF ATMOSPHERIC MULTIPATH IN LINE-OF -SIGHT MICROWAVE SYSTEMS / [pt] EFEITOS DE MULTIPERCURSOS ATMOSFÉRICOS EM ENLACES DE MICROONDAS EM VISIBILIDADEROQUE ANDRE CIUFO POEYS 20 December 2004 (has links)
[pt] As variações que ocorrem na estrutura da troposfera ao
longo do tempo em
relação à sua condição mediana provocam diversos fenômenos
que fazem variar
aleatoriamente o nível de sinal recebido num enlace rádio.
Estas variações
aleatórias são denominadas desvanecimentos. Os
desvanecimentos são
normalmente classificados em rápidos e lentos. Os
desvanecimentos rápidos estão
geralmente associados ao efeito de multipercurso
atmosférico que é fortemente
dependente da freqüência, sendo por isto denominados
desvanecimentos seletivos,
e são a principal causa de degradação do desempenho de
enlaces rádio digitais de
alta capacidade. Os modelos existentes para a
caracterização estatística do
desvanecimento por multipercurso são semi-empíricos e
baseados em dados
experimentais obtidos em regiões de clima temperado,
acarretando uma má
estimativa quando aplicados a regiões de clima tropical e
equatorial. Neste
trabalho é apresentada uma avaliação dos métodos existentes
para previsão do
desempenho de enlaces rádio digitais de alta capacidade, a
partir da utilização de
dados reais de desempenho extraídos de medidas em um tronco
rádio de alta
capacidade numa região tropical. / [en] The variations which happen in the troposphere layers
throughout the time
in relation to the median condition of the signal cause
various phenomena that
change the received signal level at digital radio relay
systems randomly. The
random changes are named fading. Fading is normally
classified as fast or slow.
The former is normally associated with the atmospheric
multipath propagation
and is strongly dependent on frequency; therefore, this is
named selective fading
and it is normally the cause of performance degradation in
high capacity digital
radio relays. The existing models for statistics of
multipath fading are semi -
empirical and based on experimental data extracts from
regions the climate of
which is temperate; and this gives a rough estimate with
respect to the tropical and
equatorial zones. This work presents an evaluation of
existing methods of
performance prediction for high capacity digital radio
relay systems using real
performance data obtained from measures of a high capacity
digital radio link in
operation in the tropical region.
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Ambient Backscatter Communication Systems: Design, Signal Detection and Bit Error Rate AnalysisDevineni, Jaya Kartheek 21 September 2021 (has links)
The success of the Internet-of-Things (IoT) paradigm relies on, among other things, developing energy-efficient communication techniques that can enable information exchange among billions of battery-operated IoT devices. With its technological capability of simultaneous information and energy transfer, ambient backscatter is quickly emerging as an appealing solution for this communication paradigm, especially for the links with low data rate requirements. However, many challenges and limitations of ambient backscatter have to be overcome for widespread adoption of the technology in future wireless networks. Motivated by this, we study the design and implementation of ambient backscatter systems, including non-coherent detection and encoding schemes, and investigate techniques such as multiple antenna interference cancellation and frequency-shift backscatter to improve the bit error rate performance of the designed ambient backscatter systems.
First, the problem of coherent and semi-coherent ambient backscatter is investigated by evaluating the exact bit error rate (BER) of the system. The test statistic used for the signal detection is based on the averaging of energy of the received signal samples. It is important to highlight that the conditional distributions of this test statistic are derived using the central limit theorem (CLT) approximation in the literature. The characterization of the exact conditional distributions of the test statistic as non-central chi-squared random variable for the binary hypothesis testing problem is first handled in our study, which is a key contribution of this particular work. The evaluation of the maximum likelihood (ML) detection threshold is also explored which is found to be intractable. To overcome this, alternate strategies to approximate the ML threshold are proposed. In addition, several insights for system design and implementation are provided both from analytical and numerical standpoints.
Second, the highly appealing non-coherent signal detection is explored in the context of ambient backscatter for a time-selective channel. Modeling the time-selective fading as a first-order autoregressive (AR) process, we implement a new detection architecture at the receiver based on the direct averaging of the received signal samples, which departs significantly from the energy averaging-based receivers considered in the literature. For the proposed setup, we characterize the exact asymptotic BER for both single-antenna (SA) and multi-antenna (MA) receivers, and demonstrate the robustness of the new architecture to timing errors. Our results demonstrate that the direct-link (DL) interference from the ambient power source leads to a BER floor in the SA receiver, which the MA receiver can avoid by estimating the angle of arrival (AoA) of the DL. The analysis further quantifies the effect of improved angular resolution on the BER as a function of the number of receive antennas.
Third, the advantages of utilizing Manchester encoding for the data transmission in the context of non-coherent ambient backscatter have been explored. Specifically, encoding is shown to simplify the detection procedure at the receiver since the optimal decision rule is found to be independent of the system parameters. Through extensive numerical results, it is further shown that a backscatter system with Manchester encoding can achieve a signal-to-noise ratio (SNR) gain compared to the commonly used uncoded direct on-off keying (OOK) modulation, when used in conjunction with a multi-antenna receiver employing the direct-link cancellation.
Fourth, the BER performance of frequency-shift ambient backscatter, which achieves the self-interference mitigation by spatially separating the reflected backscatter signal from the impending source signal, is investigated. The performance of the system is evaluated for a non-coherent receiver under slow fading in two different network setups: 1) a single interfering link coming from the ambient transmission occurring in the shifted frequency region, and 2) a large-scale network with multiple interfering signals coming from the backscatter nodes and ambient source devices transmitting in the band of interest. Modeling the interfering devices as a two dimensional Poisson point process (PPP), tools from stochastic geometry are utilized to evaluate the bit error rate for the large-scale network setup. / Doctor of Philosophy / The emerging paradigm of Internet-of-Things (IoT) has the capability of radically transforming the human experience. At the heart of this technology are the smart edge devices that will monitor everyday physical processes, communicate regularly with the other nodes in the network chain, and automatically take appropriate actions when necessary. Naturally, many challenges need to be tackled in order to realize the true potential of this technology. Most relevant to this dissertation are the problems of powering potentially billions of such devices and enabling low-power communication among them.
Ambient backscatter has emerged as a useful technology to handle the aforementioned challenges of the IoT networks due to its capability to support the simultaneous transfer of information and energy. This technology allows devices to harvest energy from the ambient signals in the environment thereby making them self-sustainable, and in addition provide carrier signals for information exchange. Using these attributes of ambient backscatter, the devices can operate at very low power which is an important feature when considering the reliability requirements of the IoT networks. That said, the ambient backscatter technology needs to overcome many challenges before its widespread adoption in IoT networks. For example, the range of backscatter is limited in comparison to the conventional communication systems due to self-interference from the power source at a receiver. In addition, the probability of detecting the data in error at the receiver, characterized by the bit error rate (BER) metric, in the presence of wireless multipath is generally poor in ambient backscatter due to double path loss and fading effects observed for the backscatter link. Inspired by this, the aim of this dissertation is to come up with new architecture designs for the transmitter and receiver devices that can improve the BER performance. The key contributions of the dissertation include the analytical derivations of BER which provide insights on the system design and the main parameters impacting the system performance.
The exact design of the optimal detection technique for a communication system is dependent on the channel behavior, mainly the time-varying nature in the case of a flat fading channel. Depending on the mobility of devices and scatterers present in the wireless channel, it can either be described as time-selective or time-nonselective. In the time-nonselective channels, coherent detection that requires channel state information (CSI) estimation using pilot signals can be implemented for ambient backscatter. On the other hand, non-coherent detection is preferred when the channel is time-selective since the CSI estimation is not feasible in such scenarios. In the first part of this dissertation, we analyze the performance of ambient backscatter in a point-to-point single-link system for both time-nonselective and time-selective channels. In particular, we determine the BER performance of coherent and non-coherent detection techniques for ambient backscatter systems in this line of work. In addition, we investigate the possibility of improving the BER performance using multi-antenna and coding techniques. Our analyses demonstrate that the use of multi-antenna and coding can result in tremendous improvement of the performance and simplification of the detection procedure, respectively. In the second part of the dissertation, we study the performance of ambient backscatter in a large-scale network and compare it to that of the point-to-point single-link system. By leveraging tools from stochastic geometry, we analytically characterize the BER performance of ambient backscatter in a field of interfering devices modeled as a Poisson point process.
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Δέκτες χωροχρονικής κωδικοποίησης για συχνοτικά επιλεκτικά συστήματαΧριστοδούλου, Κωνσταντίνος 14 September 2010 (has links)
Η χωροχρονική μπλοκ κωδικοποίηση (STBC) αποτελεί μία αποδοτική και ευρέως διαδεδομένη τεχνική διαφορετικότητας μετάδοσης για την αντιμετώπιση του φαινομένου της εξασθένησης στις ασύρματες επικοινωνίες. Χαρακτηριστικό παράδειγμα είναι ο ορθογώνιος κώδικας του σχήματος Alamouti, ο οποίος με δύο κεραίες μετάδοσης επιτυγχάνει τη μέγιστη χωρική διαφορετικότητα στο μέγιστο δυνατό ρυθμό μετάδοσης, για οποιονδήποτε (πραγματικό ή μιγαδικό) αστερισμό συμβόλων. Ωστόσο, το σχήμα Alamouti έχει σχεδιαστεί για συχνοτικά επίπεδα κανάλια. Στην παρούσα εργασία μελετούμε την εφαρμογή STBC σε κανάλια συχνοτικά επιλεκτικής εξασθένησης. Εστιάζουμε κυρίως στο συνδυασμό του σχήματος Alamouti με τεχνικές εξάλειψης της διασυμβολικής παρεμβολής, εξετάζοντας τα σχήματα OFDM-STBC, FDE-STBC και TR-STBC, που έχουν προταθεί στη βιβλιογραφία. Επιπρόσθετα των συμβατικών δεκτών, για τα δύο τελευταία σχήματα περιγράφουμε και προσαρμοστικούς δέκτες, οι οποίοι παρακολουθούν τις μεταβολές του καναλιού, χωρίς να απαιτούν την ακριβή εκτίμησή του. Η έρευνα πάνω στα προηγούμενα σχήματα οδήγησε σε ορισμένα αξιόλογα αποτελέσματα. Κατ’ αρχήν, αποδεικνύουμε ότι τα σχήματα FDE-STBC και TR-STBC είναι ισοδύναμα, μολονότι καθένα εφαρμόζει διαφορετική κωδικοποίηση στα μεταδιδόμενα δεδομένα. Επίσης, σχεδιάζουμε έναν νέο δέκτη για το σχήμα TR-STBC, τον οποίο αναπτύσσουμε και σε προσαρμοστική μορφή. Βασικό πλεονέκτημα του προτεινόμενου δέκτη είναι ότι εκμεταλλεύεται τους κυκλικούς πίνακες συνέλιξης για τη μείωση της πολυπλοκότητας αποκωδικοποίησης. Τέλος, η απόδοση κάθε σχήματος και δέκτη αξιολογείται σε διάφορες συνθήκες εξασθένησης μέσω προσομοιώσεων σε υπολογιστικό περιβάλλον. / Space-time block coding (STBC) is an effective and widely used transmit diversity technique to combat multipath fading in wireless communication systems. A prominent example of STBC is the orthogonal code of Alamouti scheme, which achieves full spatial diversity at full transmission rate for two transmit antennas and any (real or complex) signal constellation. However, Alamouti scheme has been designed only for frequency-flat channels. In this thesis we study the application of STBC in frequency-selective channels. We mainly focus on combining Alamouti scheme with techniques for mitigating intersymbol interference, by studying several schemes (OFDM-STBC, FDE-STBC and TR-STBC) that have been proposed in literature. In addition to the conventional receivers, for FDE-STBC and TR-STBC we describe adaptive receivers too, which have the ability of tracking channel variations, without requiring explicit channel estimation. Research made upon the above schemes has come to some remarkable results. First, we prove that TR-STBC and FDE-STBC are equivalent, although each one encodes differently the transmitted data. Then, we design a new receiver for TR-STBC, which exploits the circulant convolution matrices, in order to reduce decoding complexity and we, also, develop an adaptive structure for the proposed receiver. At last, we evaluate the performance of all the described schemes and receivers in different fading conditions, by using computer simulations.
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Avalia??o de desempenho da codifica??o wavelet em canais seletivos em frequ?nciaCavalcante, Lucas Costa Pereira 14 February 2014 (has links)
Made available in DSpace on 2014-12-17T14:56:18Z (GMT). No. of bitstreams: 1
LucasCPC_DISSERT.pdf: 1619300 bytes, checksum: 97bb04f66b84a1ed1935715460aa2c22 (MD5)
Previous issue date: 2014-02-14 / Wavelet coding has emerged as an alternative coding technique to minimize the fading effects of wireless channels. This work evaluates the performance of wavelet coding, in terms of bit error probability, over time-varying, frequency-selective multipath Rayleigh fading channels. The adopted propagation model follows the COST207 norm, main international standards reference for GSM, UMTS, and EDGE applications. The
results show the wavelet coding s efficiency against the inter symbolic interference which characterizes these communication scenarios. This robustness of the presented technique
enables its usage in different environments, bringing it one step closer to be applied in practical wireless communication systems / A codifica??o wavelet surgiu como uma t?cnica de codifica??o de canal alternativa para minimizar os efeitos destrutivos dos canais de comunica??o sem fio caracterizados pelo desvanecimento. Esse trabalho avalia o desempenho de sistemas com codifica??o wavelet, em termos de probabilidade de erro de bit, sobre canais de comunica??o com desvanecimento
Rayleigh variante no tempo e m?ltiplos percursos seletivos em frequ?ncia. O modelo de propaga??o adotado segue a norma COST207, principal refer?ncia dos padr?es internacionais para aplica??es GSM, UMTS e EDGE. Os resultados demonstram a efici?ncia da t?cnica no combate a interfer?ncia inter-simb?lica, caracter?stica desses cen?rios de comunica??o. Essa robustez habilita o uso da t?cnica em diferentes ambientes, trazendo-a
um passo ainda mais pr?ximo de ser aplicada em sistemas pr?ticos de comunica??o sem fio
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