Search

Predmet ove doktorske disertacije je kalibracija distribuiranog vixekanalnog prijemnog sistema beiqnim putem, tako xto se vrxi obrada primljenih radio signala. Distribuirani prijemnici imaju nezavisne analognodigitalne konvertore i lokalne oscilatore, te su vremenski, frekvencijski i fazno nesinhronizovani. Pod kalibracijom se podrazumijeva procjena i kompenzacija vremenskih, frekvencijskih i faznih pomaka izmeu signala u prijemnim kanalima u cilju postizanja vremenske, frekvencijske i fazne sinhronizacije, koja je preduslov za pravilno funkcionisanje obrade signala sa antenskih nizova. Pretpostavlja se da postoji prostorna koherencija signala, xto znaqi da se faza nosioca predvidivo mijenja po prostoru tako xto je linearna funkcija vremena propagacije talasa i frekvencije nosioca. Pored toga, smatra se da se snaga reflektovanih komponenti signala (Non-Line-of-Sight { NLoS) moe zanemariti u odnosu na direktnu komponentu (Line-of-Sight { LoS). Ove pretpostvake vae pri prenosu u mmWave opsegu u malim elijama, xto je karakteristiqno za nadolazeu petu generaciju mobilne telefonije, gdje se oqekuje primjena rezultata istraivanja u tezi. Pretpostavlja se da se predajnici i prijemnici ne kreu. Prijemnici su povezani sa fuzionim centrom putem digitalnih linkova, posredstvom kojih nije mogu prenos analognih referentnih signala za sinhronizaciju. Zbog jednostavnosti, teza se najveim dijelom bavi dvokanalnim prijemnim sistemima, a proxirenje na vixekanalne sisteme moe se postii posmatranjem parova kanala. Analizirana su dva scenarija. U prvom scenariju, izmeu prijemnih kanala postoje konstantni vremenski pomak, poqetni fazni pomak i promjenljivi frekvencijski pomak. Cilj je razvoj i ispitivanje performansi metoda koje, procjenom i kompenzacijom pomaka izmeu primljenih signala, omoguuju distribuirani digitalni beamforming (BF) i lokalizaciju izvora radio signala korixenjem datog sistema. Sa tom namjerom je u tezi predloena procedura za kalibraciju. U sluqaju lokalizacije, procedura obuhvata zdruenu procjenu i kompenzaciju vremenskog i trenutnog faznog pomaka izmeu prijemnih kanala. U tu svrhu se koristi predajnik za kalibraciju, beacon, koji xalje uskopojasni i xirokopojasni pilot. U sluqaju beamforming-a, procedura obuhvata zdruenu procjenu i kompenzaciju vremenskog i trenutnog faznog pomaka izmeu primljenih korisnih signala i, opciono, ekvalizaciju korisnog signala. Pored uskopojasnog i xirokopojasnog pilota koje xalje beacon, koriste se i uskopojasni pilot (ako se vrxi ekvalizacija) i xirokopojasna preambula, poslati od strane korisniqkog predajnika. Poxto je frekvencijski pomak promjenljiv, ne procjenjuje se eksplicitno, ve je formulisan novi adaptivni algoritam za procjenu trenutnog faznog pomaka. Nekoherentni algoritam tipa maksimalne vjerodostojnosti (Maximum Likelihood { ML), predstavljen u drugom dijelu teze, vrxi procjenu vremenskih pomaka. Numeriqki prost algoritam baziran na korelaciji signala koristi se za procjenu konstantnog faznog pomaka. U svrhu evaluacije predloene procedure i algoritama vrxene su Monte-Karlo simulacije i eksperimenti sa softverski definisanim radio-ureajima. Rezultati eksperimenata su pokazali odliqno slaganje sa rezultatima simulacija, xto potvruje ispravnost matematiqkog modela i usvojenih pretpostavki... The dissertation deals with over-the-air calibration of a distributed multichannel receiving system, by processing the received radio signals. Distributed receivers have independent analog-digital converters and local oscillators, so they are time, frequency, and phase unsynchronized. The calibration includes estimation and compensation of time, frequency, and phase offsets between the signals in the receiving channels with the aim of achieving time, frequency, and phase synchronization, which is a prerequisite for proper operation of array processing. Spatial coherence of signals is assumed, meaning that the carrier phase changes predictably over the space, being the linear function of the propagation delay and the carrier frequency. Additionally, we assume that the Non-Line-of-Sight components (NLoS) are negligible compared to the Line-of-Sight (LoS) components. These assumptions are valid for communication in mmWave range in small cells, which are typical of 5G, where the application of the investigation in the thesis is expected. All of the transmitters and receivers are assumed to be stationary. The receivers are connected to a fusion center via digital links, which are incapable of conveying analog reference signals for the synchronization. For the sake of simplicity, the thesis mostly addresses twochannel receiving systems, but the generalization to multichannel systems can be achieved by dealing with pairs of the channels. Two scenarios are analyzed. In the first scenario there is a constant time offset, an initial phase offset and a variable frequency offset between the receiving channels. The goal is to develop and investigate the performance of the methods that, by estimating and compensating for the offsets between the received signals, enable distributed digital beamforming (BF) and the radio source localization using that system. To this end a procedure for calibration is proposed in the dissertation. In the localization case, the procedure includes joint estimation and compensation of the time offset and instantaneous phase offset between the receiving channels. For that purpose a calibration transmitter, the beacon, sends a narrowband and a wideband pilot. In the BF case, the procedure includes joint estimation and compensation of the time offset and instantaneous phase offset between the received signals, and, optionally, equalization of a user signal. For that purpose a narrowband pilot (if the equalization takes place) and a wideband preamble sent by the user transmitter are used, in addition to the beacon signals. Since the frequency offset is time-variable, it is not estimated explicitly, but a new adaptive algorithm for instantaneous phase offset estimation is formulated. A non-coherent maximum likelihood (ML) algorithm, presented in the second part of the dissertation, is used for the time shifts estimation. A numerically cheap algorithm based on signal correlation is used for the constant phase offset estimation. Monte-Carlo simulations and experiments using software defined radio devices have been carried out to evaluate the procedure and algorithms. The results of the experiments have shown excellent matching with the simulation results, which confirms the correctness of the signal model and adopted assumptions. The adaptive algorithm for instantaneous phase offset estimation has shown capability of following abrupt changes in frequency offsets. The obtained accuracies show that the proposed procedure and algorithms are especially suited to receive BF and non-coherent/semi-coherent localization. If the frequency offset changes slowly enough, application in transmit BF is also possible. The proposed procedure is modular, i.e. every algorithm can be replaced by another algorithm of the same type...

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 eliji 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.