Disertacija se bavi problemom direktne koherentne lokalizacije izvora xirokopojasnih radio signala pomou masivnih vixeantenskih sistemima u prostorno koherentnom scenariju LOS (Line-OfSight) komponenti. Ovaj scenario je tipiqan za male elije u milimetarskom opsegu u petoj generaciji 5G elijskih sistema. Lokalizacija
se zasniva na obradi signala sa distribuiranih antenskih nizova koji
mogu imati podnizove sa faziranim antenskim rexetkama. Ideja ove
disertacije je da se infrastruktura buduih beiqnih sistema pete
generacije (5G) iskoristi, pored komunikacije, i za lokalizaciju koja
je predmet disertacije.
Cilj je da se ostvari prezicnost procene pozicije za 2 do 3 reda
veliqine bolju od talasne duine nosioca, xto klasiqne metode za dvokoraqnu i jednokoraqnu (direktnu) lokalizaciju ne omoguavaju. Da
bi se to postiglo, koriste se koherentne metode { one koje pored pomaka anvelopa koriste i informacije sadrane u fazama nosioca LOS
komponenti. Da bi se to moglo iskoristiti, potrebno je da u eli...ji postoji prostorna koherencija LOS komponenti. Zbog toga se istraivanje
pre svega oslanja na male elije (sa LOS uslovima) i milimetarski
(mmWave) opseg (koji ima povoljne uslove prostiranja), ali nije ograniqeno na njih dok god je prethodni uslov zadovoljen.
Korixene su sledee metode istraivanja. Matematiqki je modelovan prostorno koherentni scenario i za njega su izvedene teorijske
granice preciznosti lokalizacije. Zatim su predloene metode lokalizacije. Njihove performanse su analizirane simulacijama i eksperimentalno. Za eksperimente je korixen hardver koji je napravljen u
sklopu istraivanja.
Izvedene su Kramer-Raove granice preciznosti lokalizacije za model signala u prostorno koherentnom scenariju i pokazano je da su
obrnuto srazmerne kvadratu frekvencije nosioca. Predloeno je vixe
tipova metoda za lokalizaciju { nekoherentne, polukoherentne i koherentne; metode za poznatu sekvencu (kooperativan predajnik/korisnik)
i za nepoznatu (nekooperativan predajnik); metode maksimalne verodostojnosti izvedene za jednokorisniqki potpuni LOS sluqaj i potprostorne metode. Predloene koherentne metode su statistiqki efikasne
(njihova preciznost dostie izvedene teorijske granice) i ostvaruju
preciznost za 2 do 3 reda veliqine bolju od talasne duine nosioca.
Analiziran je i sluqaj vixestrukog prostiranja, a metode i tada ostvaruju preciznost za 2 reda veliqine bolju od talasne duine. Takoe
funkcionixu u scenariju sa vixe (i to prostorno bliskih) predajnika
pribline snage. Pritom, potprostorne metode funkcionixu i kad je
interferirajui predajnik za 30 dB vee snage od ciljanog. Svi ovi
rezultati su ostvareni za razumne vrednosti sistemskih parametara,
kao xto su odnosi signal-xum i broj odbiraka. Pored toga, algoritmi
funkcionixu i pri malim odnosima signal-xum, zahvaljujui tome xto
direktno na osnovu sirovih signala procenjuju poziciju, za razliku od
klasiqnih metoda koje gube informacije pravei meuprocene. Dodatna
povoljnost direktne lokalizacije je xto se izbegava numeriqki zahtevan
problem asocijacije. Algoritmi funkcionixu i za kratke opservacione
intervale, zahvaljujui zdruenoj obradi svih spektralnih komponenti
signala.
The thesis deals with the problem of direct coherent localization
of wideband radio signal sources, using massive MIMO (Multiple-Input-MultipleOutput) antenna systems in scenarios with spatially coherent LOS (Line-Of-Sight)
signal components. These scenarios are typically found in small cells in the mmWave
(millimeter wave) range in the fifth generation (5G) cellular systems. The localization is based on the processing of signals received by a distributed antenna array
which may include phased antenna subarrays. In this thesis, the idea is to use the
infrastructure of future 5G cellular systems for the localization in the thesis and for
communication as well.
The goal is to achieve position estimation accuracy by 2 to 3 orders of magnitude better than the carrier wavelength, which cannot be achieved by classical
methods for two-step and one-step (direct) localization. In order to achieve that,
coherent methods are used { those that, in addition to the information contained
in envelope ...shifts, also use the information contained in carrier phase shifts of the
LOS components. Spatial coherence of LOS components in the given cell is required
to allow this information to be used. Thus, the research deals mostly with small
cells (in LOS conditions) and the mmWave range (which has suitable propagation
conditions), but is not limited to them as long as the previous condition is satisfied.
The following research methods were used. A spatially coherent scenario was
mathematically modelled and theoretical localization accuracy bounds were derived
for it. Then, appropriate localization methods were proposed. Their performance
was analyzed by simulations and experimentally. A hardware platform built as a
part of the research was used in the experiments.
Cram´er-Rao bounds on the localization accuracy have been derived for the signal
model for the spatially coherent scenario and it has been shown that they are inversely proportional to the squared carrier frequency. Different types of localization
methods have been proposed { non-coherent, semi-coherent and coherent; knownsequence methods (cooperative transmitter/user) and unknown-sequence methods
(noncooperative transmitter); maximum-likelihood methods derived for the singleuser LOS-only scenario and subspace-based methods. The coherent methods are
statistically efficient (their accuracy approaches the derived theoretical bounds) and
an accuracy by 2 to 3 orders of magnitude better than the carrier wavelength isachieved. Multipath propagation is also analyzed and the methods achieve an accuracy by 2 orders of magnitude better than the carrier wavelength even in that case.
They also perform well in a scenario with multiple (even spatially close) transmitters with comparable powers. Additionally, the subspace-based methods perform
well even if the power of an interfering transmitter is 30 dB higher than that of the
selected one. All of these results are achieved for reasonable values of the system
parameters, such as the signal-to-noise ratio (SNR) and the number of used samples. Also, the algorithms perform well even at low SNRs, thanks to the fact that
they estimate the position directly based on the raw signals, as opposed to classical
methods which reduce the amount of useful information by making intermediate
estimates. Another advantage of direct localization is the fact that the numerically
complex data association problem is evaded. The algorithms also perform well even
for short observation intervals, owing to the joint processing of all the spectral signal
components.
