6,971 research outputs found
Stochastic Multipath Model for the In-Room Radio Channel based on Room Electromagnetics
We propose a stochastic multipath model for the received signal for the case
where the transmitter and receiver, both with directive antennas, are situated
in the same rectangular room. This scenario is known to produce channel impulse
responses with a gradual specular-to-diffused transition in delay. Mirror
source theory predicts the arrival rate to be quadratic in delay, inversely
proportional to room volume and proportional to the product of the antenna beam
coverage fractions. We approximate the mirror source positions by a homogeneous
spatial Poisson point process and their gain as complex random variables with
the same second moment. The multipath delays in the resulting model form an
inhomogeneous Poisson point process which enables derivation of the
characteristic functional, power/kurtosis delay spectra, and the distribution
of order statistics of the arrival delays in closed form. We find that the
proposed model matches the mirror source model well in terms of power delay
spectrum, kurtosis delay spectrum, order statistics, and prediction of mean
delay and rms delay spread. The constant rate model, assumed in e.g. the
Saleh-Valenzuela model, is unable to reproduce the same effects.Comment: 14 pages, Manuscript Submitted to IEEE Transaction on Antennas and
Propagatio
A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles
In recent years, there has been a dramatic increase in the use of unmanned
aerial vehicles (UAVs), particularly for small UAVs, due to their affordable
prices, ease of availability, and ease of operability. Existing and future
applications of UAVs include remote surveillance and monitoring, relief
operations, package delivery, and communication backhaul infrastructure.
Additionally, UAVs are envisioned as an important component of 5G wireless
technology and beyond. The unique application scenarios for UAVs necessitate
accurate air-to-ground (AG) propagation channel models for designing and
evaluating UAV communication links for control/non-payload as well as payload
data transmissions. These AG propagation models have not been investigated in
detail when compared to terrestrial propagation models. In this paper, a
comprehensive survey is provided on available AG channel measurement campaigns,
large and small scale fading channel models, their limitations, and future
research directions for UAV communication scenarios
Simultaneous Transmission and Reception: Algorithm, Design and System Level Performance
Full Duplex or Simultaneous transmission and reception (STR) in the same
frequency at the same time can potentially double the physical layer capacity.
However, high power transmit signal will appear at receive chain as echoes with
powers much higher than the desired received signal. Therefore, in order to
achieve the potential gain, it is imperative to cancel these echoes. As these
high power echoes can saturate low noise amplifier (LNA) and also digital
domain echo cancellation requires unrealistically high resolution
analog-to-digital converter (ADC), the echoes should be cancelled or suppressed
sufficiently before LNA. In this paper we present a closed-loop echo
cancellation technique which can be implemented purely in analogue domain. The
advantages of our method are multiple-fold: it is robust to phase noise, does
not require additional set of antennas, can be applied to wideband signals and
the performance is irrelevant to radio frequency (RF) impairments in transmit
chain. Next, we study a few protocols for STR systems in carrier sense multiple
access (CSMA) network and investigate MAC level throughput with realistic
assumptions in both single cell and multiple cells. We show that STR can reduce
hidden node problem in CSMA network and produce gains of up to 279% in maximum
throughput in such networks. Finally, we investigate the application of STR in
cellular systems and study two new unique interferences introduced to the
system due to STR, namely BS-BS interference and UE-UE interference. We show
that these two new interferences will hugely degrade system performance if not
treated appropriately. We propose novel methods to reduce both interferences
and investigate the performances in system level.Comment: 20 pages. This manuscript will appear in the IEEE Transactions on
Wireless Communication
Spatial Identification Methods and Systems for RFID Tags
DisertaÄnĂ prĂĄce je zamÄĆena na metody a systĂ©my pro mÄĆenĂ vzdĂĄlenosti a lokalizaci RFID tagĆŻ pracujĂcĂch v pĂĄsmu UHF. Ăvod je vÄnovĂĄn popisu souÄasnĂ©ho stavu vÄdeckĂ©ho poznĂĄnĂ v oblasti RFID prostorovĂ© identifikace a struÄnĂ©mu shrnutĂ problematiky modelovĂĄnĂ a nĂĄvrhu prototypĆŻ tÄchto systĂ©mĆŻ. Po specifikaci cĂlĆŻ disertace pokraÄuje prĂĄce popisem teorie modelovĂĄnĂ degenerovanĂ©ho kanĂĄlu pro RFID komunikaci. DetailnÄ jsou rozebrĂĄny metody mÄĆenĂ vzdĂĄlenosti a odhadu smÄru pĆĂchodu signĂĄlu zaloĆŸenĂ© na zpracovĂĄnĂ fĂĄzovĂ© informace. Pro ĂșÄely lokalizace je navrĆŸeno nÄkolik scĂ©nĂĄĆĆŻ rozmĂstÄnĂ antĂ©n. Modely degenerovanĂ©ho kanĂĄlu jsou simulovĂĄny v systĂ©mu MATLAB. VĂœznamnĂĄ ÄĂĄst tĂ©to prĂĄce je vÄnovĂĄna konceptu softwarovÄ definovanĂ©ho rĂĄdia (SDR) a specifikĆŻm jeho adaptace na UHF RFID, kterĂĄ vyuĆŸitĂ bÄĆŸnĂœch SDR systĂ©mĆŻ znaÄnÄ omezujĂ. DiskutovĂĄna je zejmĂ©na problematika prĆŻniku nosnĂ© vysĂlaÄe do pĆijĂmacĂ cesty a poĆŸadavky na signĂĄl lokĂĄlnĂho oscilĂĄtoru pouĆŸĂvanĂœ pro smÄĆĄovĂĄnĂ. PrezentovĂĄny jsou tĆi vyvinutĂ© prototypy: experimentĂĄlnĂ dotazovaÄ EXIN-1, mÄĆicĂ systĂ©m zaloĆŸenĂœ na platformÄ Ettus USRP a antĂ©nnĂ pĆepĂnacĂ matice pro emulaci SIMO systĂ©mu. ZĂĄvÄreÄnĂĄ ÄĂĄst je zamÄĆena na testovĂĄnĂ a zhodnocenĂ popisovanĂœch lokalizaÄnĂch technik, zaloĆŸenĂœch na mÄĆenĂ komplexnĂ pĆenosovĂ© funkce RFID kanĂĄlu. Popisuje ĂșzkopĂĄsmovĂ©/ĆĄirokopĂĄsmovĂ© mÄĆenĂ vzdĂĄlenosti a metody odhadu smÄru signĂĄlu. Oba navrĆŸenĂ© scĂ©nĂĄĆe rozmĂstÄnĂ antĂ©n jsou v zĂĄvÄru ovÄĆeny lokalizaÄnĂm mÄĆenĂm v reĂĄlnĂœch podmĂnkĂĄch.The doctoral thesis is focused on methods and systems for ranging and localization of RFID tags operating in the UHF band. It begins with a description of the state of the art in the field of RFID positioning with short extension to the area of modeling and prototyping of such systems. After a brief specification of dissertation objectives, the thesis overviews the theory of degenerate channel modeling for RFID communication. Details are given about phase-based ranging and direction of arrival finding methods. Several antenna placement scenarios are proposed for localization purposes. The degenerate channel models are simulated in MATLAB. A significant part of the thesis is devoted to software defined radio (SDR) concept and its adaptation for UHF RFID operation, as it has its specialties which make the usage of standard SDR test equipment very disputable. Transmit carrier leakage into receiver path and requirements on local oscillator signals for mixing are discussed. The development of three experimental prototypes is also presented there: experimental interrogator EXIN-1, measurement system based on Ettus USRP platform, and antenna switching matrix for an emulation of SIMO system. The final part is focused on testing and evaluation of described positioning techniques based on complex backscatter channel transfer function measurement. Both narrowband/wideband ranging and direction of arrival methods are validated. Finally, both proposed antenna placement scenarios are evaluated with real-world measurements.
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