Improving the performance of LoRa based wireless transceivers

Abstract

The use of wireless technologies dominates the everyday life of a modern society. Internet of Things, the new paradigm of interaction between humans and their environment, unlocks advanced scenarios of collecting information from the real world using various sensors. One of the recently developed technologies, that is a potential candidate to become a prevalent technology exploited in the Internet of Things arena, is LoRa. The technology has been extensively explored in numerous theoretical and experimental studies, and a signicant insight has been gained. However, to provide a deeper insight into LoRa technology capabilities, the novel LoRa transceiver with improved characteristics in terms of sensitivity and immunity to external interferences has been developed. This work presents the development methodology, as well as the laboratory experiments that veried the transceiver's superior characteristics. In addition, it provides performance comparison with two widely adopted commercial solutions. The results have shown that the novel LoRa transceiver has an improved sensitivity of 15{25 dB, while the eld experiments revealed higher immunity to external interferences. The second part of the thesis explores LoRa capabilities and limitations by deploying the novel transceiver along with the two commercial transceivers in various experimental scenarios. Namely, the transceivers were deployed in very long and ultra-long distance links providing two propagation conditions: line-of-sight over land and line-of-sight over seawater. In addition, obstructed line-of-sight scenario over sea water has been investigated. The results indicate that 112km long links over land are fully feasible using low-cost, rubber-duck, omnidirectional antennas and standard output powers in two ISM frequency bands, 868MHz and 434 MHz, provided that line-of-sight is guaranteed. Furthermore, it has been shown that such links can be established for virtually any combination of LoRa parameters, since the experiments were carried out deploying three dierent, characteristic, set of LoRa parameters, namely: for spreading factors of SF 2 f7; 10; 12g, within a xed bandwidth of BW = 125 kHz, and deploying xed coding rate of CR = 4=6. The short and long-term temporal analysis of the links revealed that the main cause of packet reception rate deterioration are multipath propagation eects, while the i radio-interference has negligible eects on packet reception rate. Furthermore, it has been demonstrated that ultra-long distance links of 316 km are also possible, in both ISM bands of interest, but using only novel LoRa transceiver. The signicance of the results is amplied by the fact that omnidirectional antennas were used in the experiments with standard output powers. Finally, the experiments over seawater revealed that links up to 22 km in line-ofsight mode are fully feasible using low-cost, rubber-duck, omnidirectional antennas and standard output powers with link margin yielding more than 15 dB in both ISM frequency bands. Moreover, the links in obstructed line-of-sight mode over 28 km are also possible in ISM 434MHz band; however, there are certain limitations when it comes to their practical implementations since costly and bulky antennas are needed on both sides and transmission reliability is not guaranteed.

Savremene bežične tehnologije značajno utiču na svakodnevni život modernog društva. Internet stvari, nova paradigma interakcije čoveka sa njegovom okolinom, omogućava brzo prikupljanje i selektovanje informacija iz realnog sveta koristeći različite vrste senzora. Jedna od novih tehnologija, koja je potencijalni kandidat da postane najmasovnije upotrebljavana tehnologija u takvim sistemima jeste upravo LoRa. Ova tehnologija je, do sada, ispitivana kroz brojne teoretske i eskperimentalne studije. Da bi se obezbedio dublji uvid u mogućnosti tehnologije, razvijen je novi LoRa primopredajnik sa poboljšanim karakteristikama u smislu osetljivosti i imunosti na smetnje. U tezi je prikazana metodologija razvoja novog primopredajnika i dati su rezultati laboratorijskih ispitivanja koji verikuju poboljšane performanse. Takodje su uradjena uporedna ispitivanja novorazvijenog primopredajnika sa dva veoma rasprostranjena komercijalna primopredajnika. Rezultati ispitivanja su pokazali, da novi LoRa primopredajnik ima poboljsanu osetljivost u opsegu 15 {25 dB, dok su rezultati ispitivanja u realnim uslovima dodatno utvrdili i veću imunost na spoljnje smetnje. U drugom delu teze su dati rezultati eksperimenta izvršenih u realnim uslovima. Novi LoRa primopredjanik je ispitivan na vrlo dugačkim i izuzetno dugačkim trasama u dva karakteristična propagaciona scenarija: kada je zadovoljen uslov optičke vidljivosti i kada je optička vidljivost blokirana izmedju prijemnika i predajnika. U ovim eksperimentima linkovi su formirani iznad kopna i iznad mora. Rezultati eksperimenata su pokazali da, ukoliko je obezbedjena optička vidljivost izmedju prijemnika i predajnika, linkovi u dužini od 112 km iznad kopna u potpunosti su izvodljivi, koristeći omnidirekcione antene i standardnu izlaznu snagu u oba ISM opsega, 868MHz i 434 MHz. Takodje, pokazano je da takvi linkovi mogu biti uspostavljeni za bilo koju kombinaciju LoRa parametara, ukljućujući i komercijalne primopredajnike, s obzirom na to da su eksperimenti izvršeni za tri karakteristična seta LoRa parametara, naime: koristeći faktore širenja SF 2 f7; 10; 12g unutar ksnog LoRa opsega od BW = 125 kHz i upotrebom zaštitnog kodovanja iii CR = 4=6. Analiza parametara linka u vremenskom domenu je pokazala da je glavni uzrok gubitka paketa mulitpath propagacija signala, dok je radio-interferencija imala zanemariv doprinos gubitku paketa. Dalje je pokazano da su izuzetno dugački linkovi, dužine 316 km, izvodljivi koristeći novorazvijeni primopredajnik u oba ISM opsega od interesa, upotrebljavajuci omnidirekcione antene i standardne izlazne snage. Konačno, eksperimenti iznad morske površine su pokazali da, ukoliko postoji optička vidljivost izmedju prijemnika i predajnika, linkovi u dužini od 22 km su mogući i to u oba ISM opsega od interesa, koristeći omnidirekcione antene i standardne izlazne snage; margina linka od 15 dB u oba frekvencijska opsega implicira da su moguća i veća rastojanja. Eksperimentalno je utvrdjeno i da, ukoliko je optička vidljivost preko morske površine izmedju prijemnika i predajnika blokirana, moguće je uspostaviti link u dužini od 28 km na frekvenciji od 434 MHz, upotrebom antena sa većim pojačanjem, ali kvalitet prenosa u ovom slučaju ne može biti garantovan.