20.500.12556/RUL-142905 Sinhronizacija nosilnega signala v radijskem sistemu s sočasno oddajo in sprejemom Carrier signal synchronization in radio system with simultaneous transmission and reception NFC naprava imenovana tudi značka ali tag, vsebuje vrsto specifičnih podsestavov, ki omogočajo znački, da generira lastno magnetno polje in tako aktivno modulira antenski nihajni krog. Imenujemo jo aktivna bremenska modulacija (ang. Active Load Modulation ALM). Ta potrebuje referenčni takt oziroma uro, ekstraktor zunanje ure (nosilne frekvence izpraševalnika) za obnovitev te ure, frekvenčno-fazni sledilnik, ki usklajuje frekvenco in fazo obnovljene ure. Tako dobimo sinhrono ali asinhrono delovanje. Potek faze je v veliki meri odvisen od prenosa podatkov iz značke (protokola oz. dolžine trajanja prenosa). Struktura značke, ki aktivno oddaja, postane lahko izjemno kompleksna, zato je raziskava, kako sinhronizirati ALM modulacijo z nosilno frekvenco izpraševalnika ključna za doseganje skladnosti z obstoječimi standardi, ki obravnavajo aktivno oddajo. Induktivni sklop med antenami izpraševalnika in značke omogoča izpraševalniku, da zazna modulacijo iz značke pri NFC komunikaciji. Ker je v tipični aplikaciji emulatorja kartice v mobilniku antena značke zelo majhna in ima posledično majhen sklopni faktor, je nujno izvajati aktivno oddajo (ALM), kjer se modulirani signal aktivno oddaja. Sklop se dodatno zmanjša zaradi okolja, kjer značka deluje (kovinski deli, baterija, množica drugih vezij itd). Pri tem je potrebna sinhronizacija oddaje z nosilno frekvenco izpraševalnika. Idealno bi bilo popolno izenačenje nosilnih frekvenc in faze. Ideja je torej izvajati povsem enako modulacijo, kot jo omogoča pasivna bremenska modulacija (PLM), vendar pri veliko manjšem sklopnem faktorju. ALM ne izvaja direktne bremenske modulacije, temveč s podatki modulira lastno polje s frekvenco podnosilca in tako proizvede signal, ki ima enak frekvenčni spekter kot modulacija bremena. Pri tem se lahko uporabijo različne modulacijske sheme skladno z NFC standardi. Problem, ki ga je treba rešiti, je pripraviti sistem za ALM tako, da bo skladen z dosedanjimi standardi in pripravljen na prihodnje zahteve, kjer se pričakuje vedno večja zanesljivost in hitrost komunikacije. Težava ALM modulacije je v nepopolni sinhronizaciji moduliranega signala z nosilcem izpraševalnika. To pa zato, ker je nosilni signal izpraševalnika zakrit z aktivnim signalom modulacije značke in je tako oteženo opazovanje nosilne frekvence izpraševalnika med izvajanjem modulacije. Posledično izpraševalnik sprejema signal s faznim zamikom in pri daljših oddajnih sekvencah tudi z lezenjem faze. Raziskovali smo rešitve problema sinhronizacije s šibkim nosilcem izpraševalnika v močnem ozadju modulirane nosilne frekvence značke. Oddaja značke je asinhrona, saj ni mogoče ves čas kontrolirati frekvence lokalnega nosilca, ki ga proizvaja značka. Možna rešitev bi bila delna sinhronizacija nosilnih frekvenc (znotraj toleranc ±7 kHz) in popolna fazna sinhronizacija v začetku oddajne sekvence. Fazna sinhronizacija se lahko izvaja kontinuirano z vzporedno digitalno zanko, kar zmanjša zakasnitve, ki bi jo sicer zahtevale stabilne analogne zanke. Digitalne izvedbe prinašajo razvoj digitalnih faznih interpolatorjev (PI), pretvornik časa v digitalno obliko (TDC), fazni selektor (PS) itd. Ključni podsestavi za natančno sledenje frekvence in faze so fazno in frekvenčno sklenjene zanke z ustreznimi detektorji, frekvenčnimi delilniki, kontroliranim nizkošumnim oscilatorjem, selektorjem faz itd. Rešitve smo iskali v hitrosti sledenja frekvence in faze, v stabilnosti nastavljene frekvence in faze ter hitri nastavitvi pravilne faze pri oddaji. Uvedli smo paralelno digitalno procesiranje sledenja faze ter interferenčno merjenje fazne razlike med sprejetim šibkim nemoduliranim nosilcem izpraševalnika in oddanim fazno moduliranim nosilcem. Uvedli smo fazno interpolacijo ter ortogonalno fazno moduliranje aktivne oddaje. S tem smo delno popravili spekter oddaje, zmanjšali vpliv lezenja faze in izboljšali zanesljivost komunikacije. An NFC device, or a label or tag, as it is called, contains a series of specific subblocks that allow the tag to generate its own magnetic field and thus actively modulate the antenna loop. It is composed of a reference clock, an extractor of the external clock (carrier frequency of the reader) in order to recover it and a frequency-phase tracker that performs tracking operation of the frequencies and phases of both clocks. In this way, the synchronous or asynchronous operation is obtained. Both phase mismatch and drift largely depend on the transfer of data from the tag (protocol and the duration of the data transmission). The structure of a tag that actively modulates the field and transmits data can become extremely complex; therefore, research work to synchronize the frequency and phase of ALM modulation with a reader’s carrier is key for achieving compliance with existing and future standards which address an active transmission. The challenge is to prepare the system for ALM modulation in a way that would comply with current standards and future requirements, where a higher speed of communication and increased reliability is expected. The problem with ALM modulation is the inability to completely synchronize the tag’s locally modulated signal with the reader carrier. This is because the carrier signal of the reader is obscured by the signal of the tag’s active modulation and thus it is difficult to observe the carrier frequency of the reader during the modulation and data transmitting procedure. Consequently, the reader receives the signal with a phase shift and, for longer transmission sequences, also with a phase drift, the result of which is a reduction of the transmitted data amplitude on the reader antenna or even zero amplitude. The transmission of the tag data becomes asynchronous, as it is almost impossible to completely and permanently synchronize the frequency of the local oscillator and the reader carrier. We investigated ALM solutions for the synchronization problem with a weak reader carrier in the background of the strongly modulated tag carrier frequency. A possible solution would be partial synchronization of carrier frequencies within tolerances and full phase synchronization at the beginning of the transmission sequence. Phase synchronization can be performed continuously with a parallel digital loop, which reduces the delay that would otherwise be present in stable analog loops. Digital implementations are based on the development of digital phase interpolators (PI), time to digital converters (TDC), phase selectors (PS), etc. The key sub-blocks for accurate frequency and phase tracking are phases and frequency lock loops composed of appropriate detectors, frequency dividers, voltage-controlled low noise oscillators, phase selectors, phase interpolators, etc. We looked for solutions in high-speed tracking of the frequency and phase, in the stability of the selected frequency and phase, and in the fast setting of the correct phase during data transmission. We have introduced parallel digital processing of phase tracking and an interference measurement of the phase difference between the received weak non-modulated reader carrier and the transmitted phase-modulated carrier. We introduced phase interpolation and differential modulation of an active transmission. These measures partially correct the transmission frequency spectrum, reduce the effect of phase drift during transmission, and further reduce noise by means of digital filtering. Simulations and measurements have shown that homodyne demodulation is a suitable way to demodulate the interference signal and calculate the phase drift on the test device even at a low ratio of the signal of the tested device and the reader. With the homodyne technique, the phase can be controlled and calculated, as the technique demodulates the signal by signal processing procedures. Sinhronizacija nosilnega signala v radijskem sistemu NFC RFID interferenčna meritev aktivna bremenska modulacija fazno sklenjena zanka Carrier signal synchronization in radio system NFC RFID interference measurement active load modulation phase locked loop true false false Slovenski jezik Angleški jezik Doktorsko delo/naloga 2022-12-01 12:30:00 2022-12-01 12:30:23 2022-12-02 14:04:19 0000-00-00 00:00:00 2022 0 0 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 1970-01-01 60970 132129539 Suhadolnik_Nejc_-_Sinhronizacija_nosilnega_signala_v_radijskem_sistemu_s_socasno_oddajo_in_sprej.pdf Suhadolnik_Nejc_-_Sinhronizacija_nosilnega_signala_v_radijskem_sistemu_s_socasno_oddajo_in_sprej.pdf 1 167749E82E6F3F354B02C5F67BFBEB96 fb9f8347d1d684c1efb3144666bc6b8df95a6cd5f6aad0e194e722b75d89deb6 66b242f3-716b-11ed-9c94-00155dcfd717 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=164445 Fakulteta za elektrotehniko 0 0 0