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Caracterização de Canais sem Fio com Correlator Deslizante – Parte I: Fundamentos
Abstract
A pesquisa e o desenvolvimento de sistemas de
comunicação sem fio são sempre precedidos pela caracterização
do canal através do qual o sinal é transmitido. Tal caracterização
abrange os domínios do tempo, frequência e espaço, podendo
ser estocástica, empírica, determinística ou uma combinação
destas. Ela fornece subsídios para que o canal seja modelado e o
sistema seja dimensionado de forma a viabilizar a comunicação
frente às possíveis adversidades desse canal, podendo também
fornecer dados para a elaboração de modelos de predição de
cobertura. É comum que os modelos de canal sejam construídos
com o auxílio de medidas em campo, as quais são obtidas por
meio de técnicas de sondagem que processam o sinal recebido
a partir da transmissão de um sinal de sondagem conhecido.
O correlator deslizante (sliding correlator) é uma das técnicas
mais utilizadas para sondagem, permitindo que se obtenham as
informações estocásticas que caracterizarão o canal. Este artigo
tutorial compõe uma série em que a sondagem por correlator
deslizante é abordada em três partes: na primeira, alvo do
presente texto, abordam-se os fundamentos teóricos que permitem
o entendimento sobre o correlator deslizante; na segunda parte é
dado enfoque no procedimento de análise de medidas simuladas
pelo correlator deslizante para a caracterização estocástica do
canal; na terceira parte são descritos os detalhes do projeto de
um correlator deslizante na plataforma USRP (universal software
radio peripheral).
... C omo enfatizado nas Partes I [1] e II [2] desta série de artigos sobre o correlator deslizante, as mais fortes condições de contorno em relação ao projeto de sistemas de comunicação sem fio são impostas pelo canal de comunica- ção, o que significa que tal projeto é sempre precedido pela caracterização do meio através do qual o sinal será transmitido. O correlator deslizante [3] vem sendo utilizado há décadas Artigo recebido em outubro de 2017. ...
... O principal objetivo deste trabalho é apresentar uma imple- mentação do sistema de sondagem por correlator deslizante uti- lizando placas universal software radio peripheral (USRP) [7] e validar as medidas obtidas por meio da utilização de um emulador de canal. Para isso, utilizarem-se os fundamentos da técnica de sondagem por correlator deslizante abordados na Parte I [1], assim como a análise das medidas simuladas obtidas pelo sistema de sondagem e apresentadas na Parte II [2]. As principais vantagens da sondagem com USRP são o baixo custo destas placas em relação a outros equipamentos e a flexibilidade de configurações de sondagem devido à utilização da técnica de rádio definido por software (SDR, software defined radio) [8]. ...
... Como detalhado na Parte I [1] e ilustrado na Fig. 1, a sondagem de canal é realizada por meio da transmissão de um sinal conhecido e sua recepção em algum local de interesse distante do transmissor. Existem diversos tipos de equipamentos que podem realizar essa tarefa, como o analisador vetorial de rede [22] e o gerador e analisador de sinais [17]. ...
A pesquisa e o desenvolvimento de sistemas de comunicação
sem fio são sempre precedidos pela caracterização do canal
através do qual o sinal é transmitido. Tal caracterização abrange os
domínios do tempo, frequência e espaço, podendo ser estocástica,
empírica, determinística ou uma combinação destas. Ela fornece
subsídios para a modelagem do canal para que o sistema seja
então dimensionado de forma a viabilizar a comunicação frente às
possíveis adversidades do canal, podendo também fornecer dados
para a elaboração de modelos de predição de cobertura. É comum
que os modelos de canal sejam construídos com o auxílio de
medidas em campo, as quais são obtidas por meio de técnicas de
sondagem que processam o sinal recebido a partir da transmissão
de um sinal de sondagem conhecido. O correlator deslizante
(sliding correlator) é uma das técnicas mais utilizadas para sondagem,
permitindo que se obtenham as informações estocásticas que
caracterizam o canal. Este artigo tutorial compõe uma série em que
a sondagem por correlator deslizante é abordada em três partes:
no primeiro artigo da série foram abordados os fundamentos
teóricos necessários ao entendimento sobre o correlator deslizante;
o segundo artigo foi direcionado à análise das medidas obtidas
pelo correlator deslizante para a caracterização do canal; já o
presente artigo é voltado à implementação do sistema de sondagem
por correlator deslizante utilizando placas universal software radio
peripheral (USRP). Com o auxílio de um emulador de canal, a
sondagem é realizada em um ambiente totalmente controlado, o
que permite verificar a capacidade do correlator deslizante de
obter as estatísticas do canal conforme os parâmetros previamente
configurados no emulador. Por intermédio do teste estatístico
Kolmogorov–Smirnov e do erro quadrático médio normalizado, a
envoltória discreta da resposta ao impulso estimada pelo correlator
deslizante é comparada com aquela gerada pelo emulador de canal.
Com este processo objetiva-se validar o correto funcionamento do
sistema de sondagem proposto. Além da envoltória, apresentam-se
comparações envolvendo o espectro de potências Doppler, o
perfil de atraso de potência, a banda de coerência e os ganhos dos
múltiplos percursos.
... II. FUNDAMENTOS SOBRE O CORRELATOR DESLIZANTE Esta seção tem por objetivo apenas tornar o artigo auto- contido. Detalhes sobre o funcionamento do correlator des- lizante e de toda a cadeia de processamento do sinal de sondagem e de sua recepção podem ser obtidos em [6], referência em que esta seção está baseada. A Fig. 1 mostra o diagrama de blocos simplificado de um sistema de sondagem com correlator deslizante. ...
... Neste caso, y(t) = x(t) e x (t) são aplicados às entradas do mixer do ramo superior do correlator deslizante, o qual servirá como referência para esta análise inicial. À entrada do correspondente filtro é aplicado o sinal p(t) = x(t)x (t) que, após algum algebrismo [6], pode ser representado por ...
... em que q d (t) é a representação temporal da parte central do espectro de P (f ), aqui denotada como parcela desejada, e q i (t) é a correspondente representação das partes à direita e à esquerda da parte central, denotadas como indesejadas. Demonstra-se em [6] que a parcela central do espectro ilustrado na Fig. 2 é a densidade espectral de potência de x(t) comprimida na frequência de um fator de compressão (ou dilatação, conforme a referência) γ = R c /(R c − R c ); esse fator é usualmente denominado de sliding factor na literatura em Inglês. A transformada de Fourier inversa dessa parcela corresponde à função de autocorrelação R x (τ ) da sequência x(t), porém dilatada no tempo, ou seja, q d (t) = R x (t/γ). ...
Sliding correlators are commonly used for probing wireless communication channels, resulting in high interference rejection capability and reduced hardware requirements for broadband measurements when compared to other techniques. This paper presents results of an experimental analysis on the influence of the cut-off frequency and the form factor of the low-pass filters composing the sliding correlator, as well as the signal-to-noise ratio, on the performance of the sounding system. The results presented serve as design guidelines for such filters, based on the dynamic range and mean squared error achieved by the system. These results confirm some design rules recommended in the literature and rectify or complement others.
Correlatores deslizantes são comumente utilizados para sondagem de canais de comunicação sem fio, resultando em grande capacidade de rejeição de interferências e redução nas exigências de hardware para medidas em banda larga quando comparados com outras técnicas. Este artigo apresenta resultados de uma análise experimental sobre a influência da frequência de corte e do fator de forma dos filtros passa-baixas que compõem o correlator deslizante, e também da relação sinal-ruído, no desempenho do sistema de sondagem. Os resultados apresentados servem como diretrizes de projeto de tais filtros, com base na faixa dinâmica e no erro quadrático médio alcançados pelo sistema. Tais resultados ratificam algumas regras de projeto recomendadas na literatura e retificam ou complementam outras.
... A ssim como enfatizado na Parte I desta série de artigos sobre o correlator deslizante [1], as mais fortes condições de contorno em relação ao projeto de sistemas de comuni- cação sem fio são impostas pelo canal de comunicação, o que significa que tal projeto é sempre precedido pela carac- terização do meio através do qual o sinal é transmitido. O correlator deslizante vem sendo utilizado há décadas para esse fim, permitindo que se obtenham, por meio de medidas, os parâmetros estocásticos que caracterizam o canal nos domínios temporal, da frequência e espacial. ...
... O principal objetivo deste trabalho é apresentar uma forma de obter parâmetros estatísticos temporais, espaciais e em frequência do canal por meio de medidas realizadas pela técnica de sondagem por correlator deslizante estudada na Parte I [1]. Entre esses parâmetros podem ser citados o perfil de atraso de potência, o espalhamento de retardo, a banda e o tempo de coerência, o espalhamento Doppler, o perfil angular de potência e o espalhamento angular de potência. ...
... Com o intuito de facilitar a leitura, o diagrama simplificado do receptor do sistema de sondagem por correlator deslizante apresentado em [1] é reproduzido na Fig. 1, com uma ligeira modificação: um atenuador variável foi adicionado para fins de calibração do sistema de sondagem, conforme é abordado mais adiante. ...
A pesquisa e o desenvolvimento de sistemas de comunicação sem fio são sempre precedidos pela caracterização do canal através do qual o sinal é transmitido. Tal caracterização abrange os domínios do tempo, frequência e espaço, podendo ser estocástica, empírica, determinística ou uma combinação destas.
Ela fornece subsídios para modelagem do canal para que o sistema seja então dimensionado de forma a viabilizar a comunicação frente às possíveis adversidades do canal, podendo também fornecer dados para a elaboração de modelos de predição de cobertura. É comum que os modelos de canal sejam construídos com o auxílio de medidas em campo, as quais são obtidas por meio de técnicas de sondagem que processam o sinal recebido a partir da transmissão de um sinal de sondagem conhecido. O correlator deslizante (sliding correlator) é uma das técnicas mais utilizadas para sondagem, permitindo que se obtenham os parâmetros estocásticos que caracterizam o canal. Este artigo tutorial compõe uma série em que a sondagem por correlator deslizante é abordada em três partes: no primeiro artigo da série são abordados os fundamentos teóricos necessários ao entendimento sobre o correlator deslizante; o presente artigo é direcionado à análise das medidas obtidas por simulação para a caracterização do canal; no terceiro artigo são descritos os detalhes do projeto de um correlator deslizante na plataforma USRP (universal software radio peripheral).
This paper investigates the characteristics of the shadowed fading observed in off-body communications channels at 5.8 GHz. This is realized with the aid of the κ−µ / gamma composite fading model which assumes that the transmitted signal undergoes κ−µ fading which is subject to multiplicative shadowing. Based on this, the total power of the multipath components, including both the dominant and scattered components, is subject to non-negligible variations that follow the gamma distribution. For this model, we present an integral form of the probability density function (PDF) as well as important analytic expressions for the PDF, cumulative distribution function, moments and moment generating function. In the case of indoor off-body communications, the corresponding measurements were carried out in the context of four explicit individual scenarios namely: line of sight (LOS) and non-LOS (NLOS) walking, rotational and random movements. The measurements were repeated within three different indoor environments and considered three different hypothetical body worn node locations. With the aid of these results, the parameters for the κ − µ / gamma composite fading model were estimated and analyzed extensively. Interestingly, for the majority of the indoor environments and movement scenarios, the parameter estimates suggested that dominant signal components existed even when the direct signal path was obscured by the test subject’s body. Additionally, it is shown that the κ−µ / gamma composite fading model provides an adequate fit to the fading effects involved in off-body communications channels. Using the Kullback-Leibler divergence, we have also compared our results with another recently proposed shadowed fading model, namely the κ−µ / lognormal LOS shadowed fading model. It was found that the κ − µ / gamma composite fading model provided a better fit for the majority of the scenarios considered in this study.
Ultra-wideband millimeter-wave (mmWave) propagation measurements were conducted in the 28- and 73-GHz frequency bands in a typical indoor office environment in downtown Brooklyn, New York, on the campus of New York University. The measurements provide large-scale path loss and temporal statistics that will be useful for ultra-dense indoor wireless networks for future mmWave bands. This paper presents the details of measurements that employed a 400 Megachips-per-second broadband sliding correlator channel sounder, using rotatable highly directional horn antennas for both co-polarized and crosspolarized antenna configurations. The measurement environment was a closed-plan in-building scenario that included a line-of-sight and non-line-of-sight corridor, a hallway, a cubicle farm, and adjacent-room communication links. Well-known and new single-frequency and multi-frequency directional and omnidirectional large-scale path loss models are presented and evaluated based on more than 14 000 directional power delay profiles acquired from unique transmitter and receiver antenna pointing angle combinations. Omnidirectional path loss models, synthesized from the directional measurements, are provided for the case of arbitrary polarization coupling, aswell as for the specific cases of co-polarized and cross-polarized antenna orientations. The results show that novel large-scale path loss models provided here are simpler and more physically based compared to previous 3GPP and ITU indoor propagation models that require more model parameters and offer very little additional accuracy and lack a physical basis. Multipath time dispersion statistics formmWave systems using directional antennas are presented for co-polarization, crosspolarization, and combined-polarization scenarios, and show that the multipath root mean square delay spread can be reduced when using transmitter and receiver antenna pointing angles that result in the strongest received power. Raw omnidirectional path l- ss data and closed-form optimization formulas for all path loss models are given in the Appendices.
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=7109864
The relatively unused millimeter-wave (mmWave) spectrum offers excellent opportunities to increase mobile capacity due to the enormous amount of available raw bandwidth. This paper presents experimental measurements and empirically-based propagation channel models for the 28, 38, 60, and 73 GHz mmWave bands, using a wideband sliding correlator channel sounder with steerable directional horn antennas at both the transmitter and receiver from 2011 to 2013. More than 15,000 power delay profiles were measured across the mmWave bands to yield directional and omnidirectional path loss models, temporal and spatial channel models, and outage probabilities. Models presented here offer side-by-side comparisons of propagation characteristics over a wide range of mmWave bands, and the results and models are useful for the research and standardization process of future mmWave systems. Directional and omnidirectional path loss models with respect to a 1 m close-in free space reference distance over a wide range of mmWave frequencies and scenarios using directional antennas in real-world environments are provided herein, and are shown to simplify mmWave path loss models, while allowing researchers to globally compare and standardize path loss parameters for emerging mmWave wireless networks. A new channel impulse response modeling framework, shown to agree with extensive mmWave measurements over several bands, is presented for use in link-layer simulations, using the observed fact that spatial lobes contain multipath energy that arrives at many different propagation time intervals. The results presented here may assist researchers in analyzing and simulating the performance of next-generation mmWave wireless networks that will rely on adaptive antennas and multiple-input and multiple-output (MIMO) antenna systems.
The global bandwidth shortage facing wireless carriers has motivated the exploration of the underutilized millimeter wave (mm-wave) frequency spectrum for future broadband cellular communication networks. There is, however, little knowledge about cellular mm-wave propagation in densely populated indoor and outdoor environments. Obtaining this information is vital for the design and operation of future fifth generation cellular networks that use the mm-wave spectrum. In this paper, we present the motivation for new mm-wave cellular systems, methodology, and hardware for measurements and offer a variety of measurement results that show 28 and 38 GHz frequencies can be used when employing steerable directional antennas at base stations and mobile devices.
Wireless data traffic is projected to skyrocket 10 000 fold within the next 20 years. To tackle this incredible increase in wireless data traffic, a first approach is to further improve spectrally efficient systems such as 4G LTE in bands below 6 GHz by using more advanced spectral efficiency techniques. However, the required substantial increase in system complexity along with fundamental limits on hardware implementation and channel conditions may limit the viability of this approach. Furthermore, the end result would be an extremely spectrally efficient system with little room for future improvement to meet the ever-growing wireless data usage. The second approach is to move up in frequency, into an unused nontraditional spectrum where enormous bandwidths are available, such as at millimeter wave (mmWave). The mmWave option enables the use of simple air interfaces since large bandwidths can be exploited (e.g., 2 GHz) to achieve high data rates rather than relying on highly complex techniques originally aimed at achieving a high spectral efficiency with smaller bandwidths. In addition, mmWave systems will easily evolve to even higher system capacities, because there will be plenty of margin to improve the spectral efficiency as data demands further increase. In this paper, a case is made for using mmWave for a fifth generation (5G) wireless system for ultradense networks by presenting an overview of enhanced local area (eLA) technology at mmWave with emphasis on 5G requirements, spectrum considerations, propagation and channel modeling, air-interface and multiantenna design, and network architecture solutions.
Existing cellular network analyses, and even simulations, typically use the
standard path loss model where received power decays like
over a distance . This model leads to tractable analysis of coverage
probability and other metrics for downlink cellular networks with base stations
distributed by a Poisson point process. However, it is widely known that this
standard path loss model is quite idealized, and that in most scenarios the
path loss exponent is itself a function of , typically an
increasing one. Enforcing a single path loss exponent can lead to orders of
magnitude differences in received and interference powers versus the true
values. In this paper we study multi-slope path loss models, where different
distance ranges are subject to different path loss exponents. We focus on the
dual-slope path loss function, which is piece-wise power law and continuous,
and derive the coverage probability and potential throughput. The exact
mathematical results show that the SIR monotonically decreases with network
density and (consequently) network coverage is maximized at some finite
density. With ultra-densification (network density goes to infinity), there
exists a phase transition at the near-field path loss exponent : if
unbounded potential throughput can be achieved asymptotically; if
, ultra-densification leads to zero throughput.
As the mobile cellular carriers are currently facing a spectrum crunch, researchers are concentrating on higher carrier frequency bands, such as E-band (71–76 GHz and 81–86 GHz) for the next generation wireless communication systems. The E-band is promising due to its large available, continuous bandwidth and robust weather resilience. In this paper, we demonstrate a spread spectrum sliding correlator channel sounder operating at a center frequency of 73.5 GHz with an 800 MHz null-to-null bandwidth. The channel sounder provides a multipath time resolution of 2.33 ns. 72 GHz millimeter wave propagation and penetration characteristics in an indoor office environment are investigated using the sliding correlator channel sounding system. Data collected and processed from the measurements shows that strong received power can be achieved from the multipath-rich indoor environment, in the presence of multiple obstructions. The data obtained from this measurement campaign may be utilized for the design of future fifth generation millimeter wave indoor cellular systems.
Wireless systems are getting deployed in many new environments with different
antenna heights, frequency bands and multipath conditions. This has led to an
increasing demand for more channel measurements to understand wireless
propagation in specific environments and assist deployment engineering. We
design and implement a rapid wireless channel sounding system, using the
Universal Software Radio Peripheral (USRP) and GNU Radio software, to address
these demands. Our design measures channel propagation characteristics
simultaneously from multiple transmitter locations. The system consists of
multiple battery-powered transmitters and receivers. Therefore, we can set-up
the channel sounder rapidly at a field location and measure expeditiously by
analyzing different transmitters signals during a single walk or drive through
the environment. Our design can be used for both indoor and outdoor channel
measurements in the frequency range of 1 MHz to 6 GHz. We expect that the
proposed approach, with a few further refinements, can transform the task of
propagation measurement as a routine part of day-to-day wireless network
engineering.
The Lee method, which was recommended by the International Telecommunications Union (ITU) and the European Conference of Postal and Telecommunications Administrations (CEPT) to obtain the local mean values of the received signal along a route, was developed for a Rayleigh distribution in the ultrahigh-frequency (UHF) band. This paper describes the generalization of this method to any propagation channel and frequency band and describes the methodology to obtain the parameters involved. The Generalized Lee Method is based on field data samples, which allows estimating the mean values without the requirement of a priori knowing the distribution function that better fits the propagation channel. The accuracy in obtaining the averaging interval is also improved. The Generalized Lee Method is solved for ground-wave propagation at the medium-wave (MW) band, taking data from field trials of a Digital Radio Mondiale (DRM) transmission. The results show that the values considerably differ from those obtained for a Rayleigh channel and prove that the method allows the adequate differentiation of long-term and short-term signals. The Generalized Lee Method completes the results obtained by Lee and Parsons and makes better characterization of the spatial variability possible.
In this paper two new fading distributions, the α-η-μdistribution and α-κ-μ distribution, are presented. The α-η-μdistribution includes the α-μ, Nakagami-m, Nakagami-g, Weibull, Hoyt, Rayleigh, Exponential, and the one-sided Gaussian distributions as special cases. The α-κ-μ distribution includes the α-μ, Nakagami-m, Weibull, Rice, Rayleigh, exponential, and the one-sided Gaussian distributions as special cases. Furthermore, it proposes estimators for the involved parameters and uses field measurements to validate the distributions.
In this paper, we consider a relatively new small scale multipath fading model, namely; the � µ fading distribu- tion. We derive expressions for the amount of fading and the average channel capacity for this channel model and show the generalized attribute of this fading model. The obtained expres- sions for the performance metrics reduce to other expressions for other channel models as special cases. Numerical results for the obtained expressions are provided and some conclusions are also drawn. Index Terms—Channel capacity, generalized fading model, amount of fading, the � µ model. I. INTRODUCTION
It has been shown that the capacity of a multiple-input multiple-output system increases linearly with the number of antennas, provided that the environment is rich scattering. However, this increase in the capacity is substantially degraded if the multiple input multiple output channels are correlated. In this paper, the capacity of correlated multiple input multiple output fading channel is investigated for laplacian and uniform angular energy distributions that implicitly represent two different scatterer distributions. The effect of the spatial correlation of a uniform circular antenna array is considered. Optimal power allocation is implemented to maximize the capacity. Through extensive Monte Carlo simulations, the results show that multiple input multiple output channel capacity is a function of the angle spread and antenna spacing. These two parameters play a major role in dictating the spatial correlation which in turn affects on the capacity. Large angle spread leads to lower correlation between the antenna elements and consequently higher capacity. The degradation in the capacity can be reduced by increasing the spacing between the antenna elements.
This paper presents a simple formula relating multipath angular
spread to small-scale fading statistics. This formula is then applied to
find an approximate spatial cross-correlation function for received
voltage envelopes. The analytical approach is compared to 67
cross-correlation functions simulated with non-omnidirectional
multipath. The equations in this paper provide insight for applying
spatial diversity techniques to receivers operating in the presence of
non-omnidirectional multipath
The paper addresses Rayleigh fading, primarily in the UHF band, that affects mobile systems such as cellular and personal communication systems (PCS). The paper itemizes the fundamental fading manifestations and types of degradation. Two types of fading, large-scale and small-scale, are described. Two manifestations of small-scale fading (signal dispersion and fading rapidity) are examined, and the examination involves two aspects: time and frequency. Two degradation categories are defined for dispersion: frequency selective fading and flat fading. Two degradation categories are defined for fading rapidity: fast and slow. A mathematical model using correlation and power density functions is presented. This model yields a symmetry to help view the Fourier transform and duality relationships that describe the fading phenomena
To statistically model time-variant vehicle-to-vehicle (V2V) channels, the dynamic multi-path components (MPCs) are characterized based on suburban measurements conducted at 5.3 GHz. The correlation matrix distance (CMD) is used to determine the size of local wide-sense stationary (WSS) region. Within each WSS time window, MPCs are extracted using wideband spatial spectrum of Bartlett beamformer. A MPC distance (MCD)-based tracking algorithm is used to identify the »birth» and »death» of MPCs over different WSS regions, and the lifetime of MPC is modeled with a truncated Gaussian distribution. Distributions of number of MPCs and their positions are statistically modeled. The MPC characterization considers both angular and delay domain properties as well as the dynamic evolution of MPCs over different WSS regions. The results shows insight into the dynamic behaviors of MPCs in V2V environments, and is useful for the scatterer modeling in the geometry-based stochastic channel modeling.
The spectrum congestion experienced in today's common cellular bands has led to research and measurements to explore the vast bandwidths available at millimeter waves (mmWaves). NYU WIRELESS conducted E-band propagation measurements for both mobile and backhaul scenarios in 2013 in the dense urban environment of New York City using a sliding correlator channel sounder, by transmitting a 400 Mega chip per second (Mcps) PN sequence with a power delay profile (PDP) multipath time resolution of 2.5 ns. Measurements were made for more than 30 transmitter-to-receiver location combinations for both mobile and backhaul scenarios with separation distances up to 200 m. This paper presents results that support the use of directional steerable antennas at mmWave bands in order to achieve comparable path loss models and channel statistics to today's current cellular systems and at 28 GHz. These early results reveal that the mmWave spectrum, specifically the E-band, could be used for future cellular communications by exploiting multipath in urban environments with the help of beam-steering and beam combining.
This article presents empirically-based largescale propagation path loss models for fifthgeneration cellular network planning in the millimeter-wave spectrum, based on real-world measurements at 28 GHz and 38 GHz in New York City and Austin, Texas, respectively. We consider industry-standard path loss models used for today??s microwave bands, and modify them to fit the propagation data measured in these millimeter-wave bands for cellular planning. Network simulations with the proposed models using a commercial planning tool show that roughly three times more base stations are required to accommodate 5G networks (cell radii up to 200 m) compared to existing 3G and 4G systems (cell radii of 500 m to 1 km) when performing path loss simulations based on arbitrary pointing angles of directional antennas. However, when directional antennas are pointed in the single best directions at the base station and mobile, coverage range is substantially improved with little increase in interference, thereby reducing the required number of 5G base stations. Capacity gains for random pointing angles are shown to be 20 times greater than today??s fourth-generation Long Term Evolution networks, and can be further improved when using directional antennas pointed in the strongest transmit and receive directions with the help of beam combining techniques.
In this paper we analyze the characteristics of a crosscorrelation method for measuring the impulse response of an unknown system. This analysis may also be of some interest in the area of synchronization of pseudonoise systems. In the first part of the paper a closed-form expression for the main component of the probing pulse is derived. This result may be used to quickly estimate the effect of various system parameters on the measurement's accuracy. In the second part results are presented for two system configurations.
Networks based on WiMAX (Worldwide Interoperability for Microwave Access) provide efficient packet radio interface. These networks enable high data transmission rates. WiMAX is the newest wireless broadband Internet technology based on IEEE 802.16 standard. Based on OFDM (Orthogonal Frequency Division Multiplexing), this system uses radio frequency range from 2 to 11 GHz. Calculation of path loss is very important, because it gives approximate values compared to any, obtained from real measurements. So it is helpful for initial deployment of WiMAX networks, providing an opportunity for cell planning. In this paper I discuss and compare following path loss models - Free Space Path Loss Model (FSPL Model), Hata-Okumura Extended Model (called also ECC-33 Model), Cost 231 Walfish-Ikegami Model and Stanford University Interim Model. In this paper I take the information on the location of buildings, the height of the transmitting antenna, receiving antenna and the others, consistent with conditions in Bulgaria. In each country, there are portions of the spectrum set aside for commercial purposes. In Europe and much of Asia, the 3.5 GHz spectrum range is used for broadband wireless, so I make calculations for 3.5 GHz. From calculations, that I made, can be concluded, that FSPL model, gives the lowest path loss, in all type of terrains - rural, suburban and rural areas. Model ECC-33 can predict path loss in urban and suburban areas, but it is unusable in rural areas. Also I can conclude, that model SUI, has approximately the same values of path loss with those, computed with FSPL model. My research shows that all four models for calculating the path loss are applicable to various areas, and we must compromise between coverage area and low interference of the transmitted signals, when we design WiMAX network.
The millimeter wave frequency spectrum offers unprecedented bandwidths for future broadband cellular networks. This paper presents the world's first empirical measurements for 28 GHz outdoor cellular propagation in New York City. Measurements were made in Manhattan for three different base station locations and 75 receiver locations over distances up to 500 meters. A 400 megachip-per-second channel sounder and directional horn antennas were used to measure propagation characteristics for future mm-wave cellular systems in urban environments. This paper presents measured path loss as a function of the transmitter - receiver separation distance, the angular distribution of received power using directional 24.5 dBi antennas, and power delay profiles observed in New York City. The measured data show that a large number of resolvable multipath components exist in both non line of sight and line of sight environments, with observed multipath excess delay spreads (20 dB) as great as 1388.4 ns and 753.5 ns, respectively. The widely diverse spatial channels observed at any particular location suggest that millimeter wave mobile communication systems with electrically steerable antennas could exploit resolvable multipath components to create viable links for cell sizes on the order of 200 m.
Propagation measurements at 28 GHz were conducted in outdoor urban environments in New York City using four different transmitter locations and 83 receiver locations with distances of up to 500 m. A 400 mega- chip per second channel sounder with steerable 24.5 dBi horn antennas at the transmitter and receiver was used to measure the angular distributions of received multipath power over a wide range of propagation distances and urban settings. Measurements were also made to study the small-scale fading of closely-spaced power delay profiles recorded at half-wavelength (5.35 mm) increments along a small-scale linear track (10 wavelengths, or 107 mm) at two different receiver locations. Our measurements indicate that power levels for small- scale fading do not significantly fluctuate from the mean power level at a fixed angle of arrival. We propose here a new lobe modeling technique that can be used to create a statistical channel model for lobe path loss and shadow fading, and we provide many model statistics as a function of transmitter- receiver separation distance. Our work shows that New York City is a multipath-rich environment when using highly directional steerable horn antennas, and that an average of 2.5 signal lobes exists at any receiver location, where each lobe has an average total angle spread of 40.3° and an RMS angle spread of 7.8°. This work aims to create a 28 GHz statistical spatial channel model for future 5G cellular networks.
As the cost of massively broadband® semiconductors continue to be driven down at millimeter wave (mm-wave) frequencies, there is great potential to use LMDS spectrum (in the 28-38 GHz bands) and the 60 GHz band for cellular/mobile and peer-to-peer wireless networks. This work presents urban cellular and peer-to-peer RF wideband channel measurements using a broadband sliding correlator channel sounder and steerable antennas at carrier frequencies of 38 GHz and 60 GHz, and presents measurements showing the propagation time delay spread and path loss as a function of separation distance and antenna pointing angles for many types of real-world environments. The data presented here show that at 38 GHz, unobstructed Line of Site (LOS) channels obey free space propagation path loss while non-LOS (NLOS) channels have large multipath delay spreads and can exploit many different pointing angles to provide propagation links. At 60 GHz, there is notably more path loss, smaller delay spreads, and fewer unique antenna angles for creating a link. For both 38 GHz and 60 GHz, we demonstrate empirical relationships between the RMS delay spread and antenna pointing angles, and observe that excess path loss (above free space) has an inverse relationship with transmitter-to-receiver separation distance.
We propose a new model for a cognitive radio in the scenario of centralized data-fusion cooperative spectrum sensing. The model is grounded on a direct-conversion receiver architecture and was applied to four detection methods: the eigenvalue-based generalized likelihood ratio test, the maximum-minimum eigenvalue detection, the maximum eigenvalue detection and the energy detection. It is shown that the sensing performance under the conventional model typically adopted in the above scenario is overestimated when compared with the proposed one, which suggests that our model better suits for the spectrum sensing design and its performance assessment.
The spectrum crunch currently experienced by mobile cellular carriers makes the underutilized millimeter-wave frequency spectrum a sensible choice for next-generation cellular communications, particularly when considering the recent advances in low cost sub-terahertz/millimeter-wave complementary metal-oxide semiconductor circuitry. To date, however, little is known on how to design or deploy practical millimeter-wave cellular systems. In this paper, measurements for outdoor cellular channels at 38 GHz were made in an urban environment with a broadband (800-MHz RF passband bandwidth) sliding correlator channel sounder. Extensive angle of arrival, path loss, and multipath time delay spread measurements were conducted for steerable beam antennas of differing gains and beamwidths for a wide variety of transmitter and receiver locations. Coverage outages and the likelihood of outage with steerable antennas were also measured to determine how random receiver locations with differing antenna gains and link budgets could perform in future cellular systems. This paper provides measurements and models that may be used to design future fifth-generation millimeter-wave cellular networks and gives insight into antenna beam steering algorithms for these systems.
A wireless channel sounder based upon the conventional spread spectrum sliding correlator implementation uses unfiltered pseudo-random noise (PN) at both the transmitter and receiver to generate a time-dilated copy of the channel's impulse response. However, in addition to this desired impulse response, the sliding correlator also produces a noise-like, wideband distortion signal that decreases the measurement system's dynamic range. Careful selection of the sliding correlator's low-pass filter can significantly reduce this distortion, but no amount of filtering will remove it completely. In contrast, using filtered PNs at both the transmitter and receiver enables one to remove this distortion in entirety and realize a measurement system whose dynamic range closely approximates the theoretical ideal for spread spectrum systems.
The sliding correlator is widely used in channel sounders employed
to measure the impulse response of the radio channel. Cross-correlation
of two pseudonoise (PN) sequences with slightly different chip rates
gives the channel impulse response. However, the slight difference in
chip rates creates various distortions in the cross-correlation
response, compared with the autocorrelation function of the same PN
sequence. The most significant of these is a reduction in dynamic range.
Using a novel algorithm, this paper quantifies the dynamic range as a
function of N (the PN sequence length) and k (the time scaling factor,
or the inverse of the fractional difference in chip rates), allowing a
sliding correlator with up to N=2047, and k=100000 to be fully
simulated. A design method based on the results presented in the paper
is described
Millimeter wave (mm-wave) channel models for outdoor wireless systems with adaptive antennas are needed to exploit the massive bandwidths available at frequencies above 30 GHz. In this paper, we describe 60 GHz wideband propagation measurements in cellular peer-to-peer outdoor environments and in-vehicle scenarios. We present a channel sounder that operates at 38 and 60 GHz with a passband bandwidth of 1.9 GHz. The channel sounder provides sub-ns RMS delay spread measurement resolution and angle-of-arrival (AOA) capabilities. AOA multipath measurements for cellular peer-to-peer communications in an outdoor campus setting show that in all measured locations, some non-Line of Sight (NLOS) antenna orientations can exploit beamforming to create links using scattering in the channel. Measurements using rotating directional antennas in NLOS antenna pointing scenarios found links with up to 36.6 ns RMS delay spread and an average propagation path loss exponent of 4.19, whereas LOS channels provided sub-nanosecond RMS delay spreads and an average path loss exponent of 2.23 (close to free space). Measurements into a vehicle showed similarities to outdoor peer-to-peer environments for LOS channels, but in NLOS situations there was significantly greater path attenuation due to the vehicle interior, vehicle body, windows, and passengers in the vehicle.
Chapter 1 aims at revisiting the mathematical basement on probability, random
variables and random processes, since these topics are extensively used throughout
the book. In Chap. 2, signals typically encountered in communication systems
are studied, aiming the analysis of their deterministic and random characteristics.
While writing these first two chapters, I was wondering if I was being repetitive
and exaggeratedly concise, trying to condense a material vastly available in all good
books on Probability and Stochastic Processes and Signals and Systems. Eventually,
I have decided to run into the risk and give a condensed review of some of the main
concepts on these two areas. Some topics were in fact covered in a very simplistic
way and I did this motivated by my students. During the past few years, I detected
several “holes” in their basic knowledge, and this was the main reason for covering
such simple and basic topics in Chaps. 1 and 2. By doing this, the students are not
forced to resort to other references if some (not heavy) stone shows up in their way
when studying the main chapters of the book.
Chapter 3 covers the communication channels over which most of the communication
systems convey information. The importance of this chapter and its location
resides in the fact that it is virtually impossible to design a communication system
without knowing the characteristics and behaviour of the channel through which the
information will flow.
In Chap. 4 the study of digital communication systems starts with one of its
simplest forms: baseband transmission. The concepts drawn from the discussion
about baseband transmission are applied in the study of passband transmission (or
digital modulation), a topic covered in Chap. 6.
Chapter 5 can be viewed as an interface or preparation for Chap. 6. Some tools
are developed so that a smooth transition is made between baseband and passband
transmission. Additionally, most of the concepts discussed in Chap. 4 are generalized
in Chap. 6 by applying the tools developed in Chap. 5.
Spread spectrum, multi-carrier, and ultra wideband are covered in Chap. 7. This
chapter can be viewed as an application of fundamental concepts presented in previous
chapters. However, several new concepts are presented in this chapter.
As a complementary and final part of the book, notions about information theory
and error-correcting codes are discussed in Chap. 8.
The material presented in this book can be more adequately explored depending
on the content of the curriculum of the course where it is intended to be applied.
Chapters 1 and 2 can be skipped if there are courses on Probability and Stochastic
Processes and on Signals and Systems. Nevertheless, it can be of help to recommend
to the students a review of such topics before entering into the specifics of
digital transmission. In this case the book can be covered in two 4-month terms in
an undergraduate course and in one 4-month term in a graduate course. We must
not forget that the computer experiments can be explored as laboratory activities to
complement the theoretical studies. The majority of details and deeper analysis are
concentrated in Chaps. 3, 4, 5, 6, and 7, since these chapters can be considered the
most relevant from the perspective of an introductory study about digital transmission.
Information theory and error-correcting codes normally are part of graduate
courses in communication systems. If this is the case, Chap. 8 can also be skipped
and treated as a review.
In recent years, cognitive radio has drawn extensive research attention due to its ability to improve the efficiency of spectrum usage by allowing dynamic spectrum resource sharing between primary and secondary users. The concept of cognitive radio was first presented by Joseph Mitola III and Gerald Q. Maguire, Jr., in which either network or wireless node itself changes particular transmission and reception parameters to execute its tasks efficiently without interfering with the primary users [1]. Such a transceiving mechanism and network environment is called the dynamic spectrum access (DSA) network. The Federal Communications Commission (FCC) allows any type of transmission in unlicensed bands at any time as long as their transmit power level obeys specific FCC regulations. Performing channel sounding as a secondary user in such an environment becomes a challenge due to the rapidly changing network environment and also the limited transmission power. Moreover, to obtain the long term behavior of the channel in the DSA network is impractical with conventional channel sounders due to frequent changes in frequency, transmission bandwidth, and power. Conventional channel sounding techniques need to be adapted accordingly to be operated in the DSA networks. In this dissertation, two novel channel sounding system frameworks are proposed. The Multicarrier Direct Sequence Swept Time-Delay Cross Correlation (MC-DS-STDCC) channel sounding technique is designed for the DSA networks aiming to perform channel sounding across a large bandwidth with minimal interference. It is based on the STDCC channel sounder and Multicarrier Direct Sequence Code Division Multiple Access (MC-DS-CDMA) technique. The STDCC technique, defined by Parsons [2], was first employed by Cox in the measurement of 910 MHz band [3{6]. The MC-DS-CDMA technique enables the channel sounder to be operated at different center frequencies with low transmit power. Hence, interference awareness and frequency agility are achieved. The OFDM-based channel sounder is an alternative to the MC-DS-STDCC technique. It utilizes user data as the sounding signal such that the interference is minimized during the course of transmission. Furthermore, the OFDM-based channel sounder requires lower sampling rate than the MC-DS-STDCC system since no spreading is necessary.
Channel sounding is an important step in the development of any wireless communication system in order to determine small-scale fading effects. We present measurements taken with a direct sequence spread spectrum sliding correlator on TV band I (centre frequency: 59.5 MHz) at 15 locations across the Australian Capital Territory and surrounding regions. The measurements were made over various types of terrain at distances ranging from approximately 1– 50 km. The RMS delay spread was calculated from the channel impulse response and found to be between 0.24 − 4.88μs.
This paper presents a new commercial wide-band channel sounder
(SARACOM). This instrument measures the complex envelope of the channel
impulse response by the use of a sliding correlator. The principles and
benefits of this technique are briefly reviewed. The hardware
architecture of the system is explained. The choice of key parameters
such as chip rate, pseudonoise sequence length versus sounder
performance are discussed and verified by laboratory tests. Measurement
results in the 2.45 GHz band in a large indoor environment are then
presented in order to demonstrate the performance of the equipment in a
realistic situation. The capabilities of the post-processing software
are then illustrated
A simple analysis leading to expressions for the multiplier output
spectrum and the effective probing signal of an impulse response
measurement system using sliding correlation is presented. Evaluation of
the expressions shows the presence of self-noise at the correlator
output and its dependence on the system parameters. The dynamic range of
the measurement can be studied using the expressions derived. The
incorporation of different correlation filter characteristics in the
expressions for the effective probing signal is easily achieved
The sliding correlator technique remains one of the most versatile and effective methods for sounding the radio propagation channel in next-generation wireless systems. Despite their utility, there has never been a comprehensive set of metrics and rules for the design of a sliding correlator channel sounder. This paper presents quantitative guidelines for balancing the many system parameters to achieve optimal levels of temporal resolution, dynamic range, processing gain, and Doppler resolution. The design procedure presented at the end of the paper will allow researchers to probe the new radioscapes that result as wireless systems are pushed to higher carrier frequencies, wider bandwidths, multiple antennas, and ubiquitous operation.
This paper presents two general fading distributions, the kappa-mu distribution and the eta-mu distribution, for which fading models are proposed. These distributions are fully characterized in terms of measurable physical parameters. The kappa-mu distribution includes the Rice (Nakagami-n), the Nakagami-m, the Rayleigh, and the one-sided Gaussian distributions as special cases. The eta-mu distribution includes the Hoyt (Nakagami-q), the Nakagami-m, the Rayleigh, and the one-sided Gaussian distributions as special cases. Field measurement campaigns were used to validate these distributions. It was observed that their fit to experimental data outperformed that provided by the widely known fading distributions, such as the Rayleigh, Rice, and Nakagami-m. In particular, the kappa-mu distribution is better suited for line-of-sight applications, whereas the eta-mu distribution gives better results for non-line-of-sight applications.
The results of indoor multipath propagation measurements using 10 ns, 1.5 GHz, radarlike pulses are presented for a medium-size office building. The observed channel was very slowly time varying, with the delay spread extending over a range up to about 200 ns and rms values of up to about 50 ns. The attenuation varied over a 60 dB dynamic range. A simple statistical multipath model of the indoor radio channel is also presented, which fits our measurements well, and more importantly, appears to be extendable to other buildings. With this model, the received signal rays arrive in clusters. The rays have independent uniform phases, and independent Rayleigh amplitudes with variances that decay exponentially with cluster and ray delays. The clusters, and the rays within the cluster, form Poisson arrival processes with different, but fixed, rates. The clusters are formed by the building superstructure, while the individual rays are formed by objects in the vicinities of the transmitter and the receiver.
This paper describes the results of frequency-domain channel sounding in residential environments. It consists of detailed characterization of complex frequency responses of ultra-wideband (UWB) signals having a nominal center frequency of 5 GHz. A path loss model as well as a second-order autoregressive model is proposed for frequency response generation of the UWB indoor channel. Probability distributions of the model parameters for different locations are presented. Also, time-domain results such as root mean square delay spread and percent of captured power are presented.
Statistical descriptions of the time delays and Doppler shifts associated with multipath propagation in a suburban mobile radio environment obtained from bandpass impulse response measurements are presented. The measuring equipment which has 0.1 mu s resolution in time delay and a data output bandwidth of less than 5 kHz is also described. For the first time small scale statistics of the multipath propagation for vehicle travel distances on the order of 30 m along streets are presented in the following forms: 1) average power-delay profiles made up of over 200 individual profiles, 2) cumulative distributions of signal amplitude at fixed delays, and 3) radio frequency Doppler spectra at fixed delays. Delay spreads for typical suburban streets are on the order of 0.25 mu s. Extreme cases have paths with significant amplitudes at excess delays of 5 to 7 mu s and the square root of the second central moment delay spreads up to about 2 mu s. Often the signal at fixed delays has a Rayleigh distributed amplitude but large departures from the Rayleigh distribution also occur. RF Doppler spectra at fixed delays indicate that some of the multipath is from one relatively discrete scattering center while at other delays several scattering centers distributed widely in angle are involved. The observed RF Doppler spectra are consistent with the cumulative amplitude distributions at the same delays.
Comparison of wideband channel sounding techniques
- X H Mao
- Y H Lee
- B C Ng
X. H. Mao, Y. H. Lee, and B. C. Ng, " Comparison of wideband
channel sounding techniques, " in Progress In Electromagnetics Research
Symposium Proceedings, Moscow, Russia, Aug. 2009, pp. 400–404.
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A sliding correlator channel sounder for ultra-wideband measurements
R. J. Pirkl, " A sliding correlator channel sounder for ultra-wideband
measurements, " MSc. Dissertation, Georgia Institute of Technology,
USA, Dept. of Electrical and Computer Engineering, Jun. 2007.
Design and implementation of an ultrabroadband millimeter-wavelength vector sliding correlator cahnnel sounder and inbuilding multipath measurements at 2.5-60 GHz
- C R Anderson
C. R. Anderson, " Design and implementation of an ultrabroadband
millimeter-wavelength vector sliding correlator cahnnel sounder and inbuilding multipath measurements at 2.5-60 GHz, " Master of Science
Dissertation, Virginia Polytechnic Institue and State University, USA,
May 2002.
Space-time Wireless Channels
- G Durgin
G. Durgin, Space-time Wireless Channels, 1st ed. Upper Saddle River,
NJ, USA: Prentice Hall Press, 2002.
Cognitive radio: Making software radios more personal
- J Mitola
- G Q Maguire Jr
J. Mitola III and G. Q. Maguire Jr., " Cognitive radio: Making software
radios more personal, " IEEE Personal Commun. Mag., vol. 6, no. 4, pp.
13–18, Aug. 1999.