Survey of Spectrum Sharing for Inter-Technology Coexistence

Increasing capacity demands in emerging wireless technologies are expected to be met by network densification and spectrum bands open to multiple technologies. These will, in turn, increase the level of interference and also result in more complex inter-technology interactions, which will need to be managed through spectrum sharing mechanisms. Consequently, novel spectrum sharing mechanisms should be designed to allow spectrum access for multiple technologies, while efficiently utilizing the spectrum resources overall. Importantly, it is not trivial to design such efficient mechanisms, not only due to technical aspects, but also due to regulatory and business model constraints. In this survey we address spectrum sharing mechanisms for wireless inter-technology coexistence by means of a technology circle that incorporates in a unified, system-level view the technical and non-technical aspects. We thus systematically explore the spectrum sharing design space consisting of parameters at different layers. Using this framework, we present a literature review on inter-technology coexistence with a focus on wireless technologies with equal spectrum access rights, i.e. (i) primary/primary, (ii) secondary/secondary, and (iii) technologies operating in a spectrum commons. Moreover, we reflect on our literature review to identify possible spectrum sharing design solutions and performance evaluation approaches useful for future coexistence cases. Finally, we discuss spectrum sharing design challenges and suggest future research directions

Analysis of Radar Doppler Signature from Human Data

This paper presents the results of time (autocorrelation) and time-frequency (spectrogram) analyses of radar signals returned from the moving human targets. When a radar signal falls on the human target which is moving toward or away from the radar, the signals reflected from different parts of his body produce a Doppler shift that is proportional to the velocity of those parts. Moving parts of the body causes the characteristic Doppler signature. The main contribution comes from the torso which causes the central Doppler frequency of target. The motion of arms and legs induces modulation on the returned radar signal and generates sidebands around the central Doppler frequency, referred to as micro-Doppler signatures. Through analyses on experimental data it was demonstrated that the human motion signature extraction is better using spectrogram. While the central Doppler frequency can be determined using the autocorrelation and the spectrogram, the extraction of the fundamental cadence frequency using the autocorrelation is unreliable when the target is in the clutter presence. It was shown that the fundamental cadence frequency increases with increasing dynamic movement of people and simultaneously the possibility of its extraction is proportional to the degree of synchronization movements of persons in the group

Scardinius knezevici Bianco & Kottelat, 2005 and Alburnus scoranza Bonaparte, 1845: New species of ichthyofauna of Serbia and the Danube basin

Research into the ichthyofauna of the Vlasina Lake reservoir in south Serbia, which is part of the Danube basin, was carried out in 1993, 40 years after its formation. The results of the research reveal the presence of several species of fish belonging to the Adriatic and Aegean basin, such as Alburnus albidus, Rutilus basak, Scardinius graecus and Pachychilon macedonicus. These findings are of great importance from the aspect of conservation, because the species Scardinius graecus and Alburnus albidus are on the European list of endangered fish species. In the latest study of the Vlasina Lake reservoir ichthyofauna (70 years after its formation), the above-mentioned species were not found. However, the presence of naturalized populations of two species from the Adriatic basin were confirmed: Scardinius knezevici and Alburnus scoranza. These findings represent the first known areal expansion of these species, which are new to the ichthyofauna of Serbia, from the Adriatic into the Danube (Black Sea) basin.[Acknowledgments. The present work was supported by the Ministry of Education and Science of the Republic of Serbia (Projects No. 43002 and 173025).

LTE in Unlicensed Bands is neither Friend nor Foe to Wi-Fi

Proponents of deploying LTE in the 5 GHz band for providing additional cellular network capacity have claimed that LTE would be a better neighbour to Wi-Fi in the unlicensed band, than Wi-Fi is to itself. On the other side of the debate, the Wi-Fi community has objected that LTE would be highly detrimental to Wi-Fi network performance. However, there is a lack of transparent and systematic engineering evidence supporting the contradicting claims of the two camps, which is essential for ascertaining whether regulatory intervention is in fact required to protect the Wi-Fi incumbent from the new LTE entrant. To this end, we present a comprehensive coexistence study of Wi-Fi and LTE-in-unlicensed, surveying a large parameter space of coexistence mechanisms and a range of representative network densities and deployment scenarios. Our results show that, typically, harmonious coexistence between Wi-Fi and LTE is ensured by the large number of 5 GHz channels. For the worst-case scenario of forced co-channel operation, LTE is sometimes a better neighbour to Wi-Fi - when effective node density is low - but sometimes worse - when density is high. We find that distributed interference coordination is only necessary to prevent a "tragedy of the commons" in regimes where interference is very likely. We also show that in practice it does not make a difference to the incumbent what kind of coexistence mechanism is added to LTE-in-unlicensed, as long as one is in place. We therefore conclude that LTE is neither friend nor foe to Wi-Fi in the unlicensed bands in general. We submit that the systematic engineering analysis exemplified by our case study is a best-practice approach for supporting evidence-based rulemaking by the regulator.Comment: accepted for publication in IEEE Acces

Mehanizmi reparacije kod ozračenih stanica

Many aspects of bacterial mutations which lead to enhanced sensitivity to UV and X radiations have been studied. Radiosensitivity appears to result from a loss of the capacity to repair damaged DNA. The genetic map of these mutations in the chromosome of E. coli is shown. Sofar the best known DNA repair mechanisms are by excision repair (excision of pyrimidine dimers controlled by nonlinked uvr genes) and by recombination repair (elimination of similar damage as a result of genetic recombination between undamaged regions of the DNA). The understanding of the lethal and mutagenic effects of radiation on cells rests on the quantitative and qualitative identification of the various lesions in the DNA. Exposure to UV irradiation causes the production of many different types of photoproducts, but pyrimidine dimers appear to be the most important damage causing biological inactivation. The study of biochemical defects of UV sensitive mutants has allowed a partial understanding of the repair mechanisms. Generally, they consist in removing the UV induced-pyrimidine dimers by cellular enzyme systems (monomerization through photoreactivation, excision or recombination by the action of endo and exonucleases, polymerases and polynucleotides ligases). The X-ray induced lesions arc very heterogenous and not yet as well defined and the mechanisms of recovery are far less understood than in the case of U. V.Mnogi aspekti mutacija koje vode povećanoj osjetljivosti na UV i X zračenje izučavani su u Escherichia coli i u velikom broju slučajeva povećanje osjetljivosti je smatrano kao gubitak kapaciteta za reparaciju DNK. Predstavljena je genetska karta ovih mutacija na kromosomu E. coli. Da bi se shvatio mehanizam biološkog učinka zračenja na živu stanicu, neophodno je dovesti u vezu kvalitativno i kvantitativno oštećenje DNK. Nakon zračenja UV, u zavisnosti od eksperimetalnih uvjeta i fizikalnog stanja DNK, otkriveni su različiti tipovi fotoprodukata. Dokazano je da je među ovim lezijama fotoprodukt pirimidinski dimer značajan u biološkoj inaktivaciji. Mehanizmi reparacije u stanicama koje sadrže enzime potrebne za ovaj proces, dovode do uklanjanja ovog fotoprodukta (»brisanje«) pa uslijed toga i do povećanog preživljavanja. Za razliku od oštećenja induciranih zračenjem UV, oštećenja inducirana jonizirajućim zračenjem su ne samo veoma heterogena već i velikim dijelom neidentificirana. Sudeći po mnogim rezultatima moglo bi se reći da letalno oštećenje nastaje zbog diskontinuiteta genoma prouzrokovanog jonizujućim zračenjem. Iznijeti su također radovi koji izučavaju biokemijske defekte mutanata koji su osjetljivi na UV zračenje, što dovodi do djelomičnog shvatanja mehanizma reparacije DNK. Ovaj mehanizam uključuje fotorestauraciju ("brisanje" lezije dimer pirimidina, monomerizacijom dimer pirimidina) i restauraciju (rekonstrukcija oštećenih regiona DNK uslijed procesa isijecanja (ekscizije) dimer pirimidina i reparativne sinteze DNK. Reparacija nakon X zračenja samo je djelomično shvaćena i odnosi se na uspostavljanje kontinuiteta DNK u jednom od lanaca dvolančane DNK. Postoje indikacije da restauracija pomoću isijecanja sinteze DNK (replikacije) i rekombinacije može biti uvjetovana enzimskim kompleksima. Letalne radiolezije razmatrane su u svjetlosti mehanizma reparacije

Risk-Informed Interference Assessment for Shared Spectrum Bands: A Wi-Fi/LTE Coexistence Case Study

Interference evaluation is crucial when deciding whether and how wireless technologies should operate. In this paper we demonstrate the benefit of risk-informed interference assessment to aid spectrum regulators in making decisions, and to readily convey engineering insight. Our contributions are: we apply, for the first time, risk assessment to a problem of inter-technology spectrum sharing, i.e. Wi-Fi/LTE in the 5 GHz unlicensed band, and we demonstrate that this method comprehensively quantifies the interference impact. We perform simulations with our newly publicly-available tool and we consider throughput degradation and fairness metrics to assess the risk for different network densities, numbers of channels, and deployment scenarios. Our results show that no regulatory intervention is needed to ensure harmonious technical Wi-Fi/LTE coexistence: for the typically large number of channels available in the 5 GHz band, the risk for Wi-Fi from LTE is negligible, rendering policy and engineering concerns largely moot. As an engineering insight, Wi-Fi coexists better with itself in dense, but better with LTE, in sparse deployments. Also, both main LTE-in-unlicensed variants coexist well with Wi-Fi in general. For LTE intra-technology inter-operator coexistence, both variants typically coexist well in the 5 GHz band, but for dense deployments, implementing listen-before-talk causes less interference

Analysis of diet of piscivorous fishes in Bovan, Gruža and Šumarice Reservoir, Serbia

Diet of adult pikeperch Sander lucioperca, Eurasian perch Perca fluviatilis, northern pike Esox lucius and European catfish Silurus glanis as top predators in aquatic ecosystems in Serbia was investigated during 2011, in order to understand their relationship to their prey and to investigate their food consumption, feeding and assimilation rate, cannibalism, and habitat segregation. Northern pike, Eurasian perch, pikeperch and European catfish were collected in three reservoirs in Serbia. Prey items that were found in all four species included fish, mollusks, insect larvae and crustaceans. A total of 11 taxonomic groups were found, but they were not all represented as a prey in all four species. Eurasian perch were present in the diet of all four predatory fish species, mollusks were recorded only in that of European catfish. Roach Rutilus rutilus and bleak Alburnus alburnus were prey to all species, except northern pike. Chub Squalius cephalus, bream Brama brama and Gammaridae were found only in stomach of pikeperch. Analysis of similarity showed that difference for diet between predatory fish species was significant for their due to significant differences existing between northern pike and pikeperch and northern pike and Eurasian perch

New record of endangered red alga Bangia atropurpurea (A. Roth) C. Aardh (Bangiales, Rhodophyta) in the Nišava River, Serbia

Bangia atropurpurea was found at two new localities in the Nišava River (Southern Serbia). In Serbia, this species is endangered. It has been found so far in the Trgoviški Timok River, the Gvozdovačka River and the Raška River. With the two new localities in the Nišava River, at present Bangia occupies four rivers (five localities). New findings are important for the protection of the biodiversity of red algal flora in the region, and provide useful information on the ecological preferences of the species in Serbia