{"id":"https://openalex.org/W3092787052","doi":"https://doi.org/10.1109/vtc2021-spring51267.2021.9448802","title":"Passive RIS vs. Hybrid RIS: A Comparative Study on Channel Estimation","display_name":"Passive RIS vs. Hybrid RIS: A Comparative Study on Channel Estimation","publication_year":2021,"publication_date":"2021-04-01","ids":{"openalex":"https://openalex.org/W3092787052","doi":"https://doi.org/10.1109/vtc2021-spring51267.2021.9448802","mag":"3092787052"},"language":"en","primary_location":{"id":"doi:10.1109/vtc2021-spring51267.2021.9448802","is_oa":false,"landing_page_url":"https://doi.org/10.1109/vtc2021-spring51267.2021.9448802","pdf_url":null,"source":null,"license":null,"license_id":null,"version":"publishedVersion","is_accepted":true,"is_published":true,"raw_source_name":"2021 IEEE 93rd Vehicular Technology Conference (VTC2021-Spring)","raw_type":"proceedings-article"},"type":"conference-paper","indexed_in":["arxiv","crossref","datacite"],"open_access":{"is_oa":true,"oa_status":"green","oa_url":"https://arxiv.org/pdf/2010.06981","any_repository_has_fulltext":true},"authorships":[{"author_position":"first","author":{"id":"https://openalex.org/A5066906982","display_name":"Rafaela Schroeder","orcid":"https://orcid.org/0000-0002-1119-5224"},"institutions":[{"id":"https://openalex.org/I98381234","display_name":"University of Oulu","ror":"https://ror.org/03yj89h83","country_code":"FI","type":"education","lineage":["https://openalex.org/I98381234"]}],"countries":["FI"],"is_corresponding":false,"raw_author_name":"Rafaela Schroeder","raw_affiliation_strings":["Centre for Wireless Communications, University of Oulu, Finland","University of Oulu,Centre for Wireless Communications,Finland,FI-90014"],"raw_orcid":null,"affiliations":[{"raw_affiliation_string":"Centre for Wireless Communications, University of Oulu, Finland","institution_ids":["https://openalex.org/I98381234"]},{"raw_affiliation_string":"University of Oulu,Centre for Wireless Communications,Finland,FI-90014","institution_ids":["https://openalex.org/I98381234"]}]},{"author_position":"middle","author":{"id":"https://openalex.org/A5039927858","display_name":"Jiguang He","orcid":"https://orcid.org/0000-0002-6227-2138"},"institutions":[{"id":"https://openalex.org/I98381234","display_name":"University of Oulu","ror":"https://ror.org/03yj89h83","country_code":"FI","type":"education","lineage":["https://openalex.org/I98381234"]}],"countries":["FI"],"is_corresponding":false,"raw_author_name":"Jiguang He","raw_affiliation_strings":["Centre for Wireless Communications, University of Oulu, Finland","University of Oulu,Centre for Wireless Communications,Finland,FI-90014"],"raw_orcid":null,"affiliations":[{"raw_affiliation_string":"Centre for Wireless Communications, University of Oulu, Finland","institution_ids":["https://openalex.org/I98381234"]},{"raw_affiliation_string":"University of Oulu,Centre for Wireless Communications,Finland,FI-90014","institution_ids":["https://openalex.org/I98381234"]}]},{"author_position":"last","author":{"id":"https://openalex.org/A5029534229","display_name":"Markku Juntti","orcid":"https://orcid.org/0000-0002-5413-1896"},"institutions":[{"id":"https://openalex.org/I98381234","display_name":"University of Oulu","ror":"https://ror.org/03yj89h83","country_code":"FI","type":"education","lineage":["https://openalex.org/I98381234"]}],"countries":["FI"],"is_corresponding":false,"raw_author_name":"Markku Juntti","raw_affiliation_strings":["Centre for Wireless Communications, University of Oulu, Finland","University of Oulu,Centre for Wireless Communications,Finland,FI-90014"],"raw_orcid":null,"affiliations":[{"raw_affiliation_string":"Centre for Wireless Communications, University of Oulu, Finland","institution_ids":["https://openalex.org/I98381234"]},{"raw_affiliation_string":"University of Oulu,Centre for Wireless Communications,Finland,FI-90014","institution_ids":["https://openalex.org/I98381234"]}]}],"institutions":[],"countries_distinct_count":1,"institutions_distinct_count":1,"corresponding_author_ids":[],"corresponding_institution_ids":["https://openalex.org/I98381234"],"apc_list":null,"apc_paid":null,"fwci":null,"has_fulltext":false,"cited_by_count":4,"citation_normalized_percentile":null,"cited_by_percentile_year":null,"biblio":{"volume":null,"issue":null,"first_page":"1","last_page":"7"},"is_retracted":false,"is_paratext":false,"is_xpac":false,"primary_topic":{"id":"https://openalex.org/T11458","display_name":"Advanced Wireless Communication Technologies","score":0.9998999834060669,"subfield":{"id":"https://openalex.org/subfields/2208","display_name":"Electrical and Electronic Engineering"},"field":{"id":"https://openalex.org/fields/22","display_name":"Engineering"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},"topics":[{"id":"https://openalex.org/T11458","display_name":"Advanced Wireless Communication Technologies","score":0.9998999834060669,"subfield":{"id":"https://openalex.org/subfields/2208","display_name":"Electrical and Electronic Engineering"},"field":{"id":"https://openalex.org/fields/22","display_name":"Engineering"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},{"id":"https://openalex.org/T10936","display_name":"Millimeter-Wave Propagation and Modeling","score":0.998199999332428,"subfield":{"id":"https://openalex.org/subfields/2208","display_name":"Electrical and Electronic Engineering"},"field":{"id":"https://openalex.org/fields/22","display_name":"Engineering"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},{"id":"https://openalex.org/T10069","display_name":"Antenna Design and Analysis","score":0.9979000091552734,"subfield":{"id":"https://openalex.org/subfields/2202","display_name":"Aerospace Engineering"},"field":{"id":"https://openalex.org/fields/22","display_name":"Engineering"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}}],"keywords":[{"id":"https://openalex.org/keywords/telecommunications-link","display_name":"Telecommunications link","score":0.7609996199607849},{"id":"https://openalex.org/keywords/transceiver","display_name":"Transceiver","score":0.6382678151130676},{"id":"https://openalex.org/keywords/computer-science","display_name":"Computer science","score":0.6274611353874207},{"id":"https://openalex.org/keywords/channel","display_name":"Channel (broadcasting)","score":0.5800547003746033},{"id":"https://openalex.org/keywords/channel-state-information","display_name":"Channel state information","score":0.5539752244949341},{"id":"https://openalex.org/keywords/mimo","display_name":"MIMO","score":0.5233139991760254},{"id":"https://openalex.org/keywords/electronic-engineering","display_name":"Electronic engineering","score":0.49592408537864685},{"id":"https://openalex.org/keywords/overhead","display_name":"Overhead (engineering)","score":0.4823291003704071},{"id":"https://openalex.org/keywords/beamforming","display_name":"Beamforming","score":0.48189789056777954},{"id":"https://openalex.org/keywords/spectral-efficiency","display_name":"Spectral efficiency","score":0.46225613355636597},{"id":"https://openalex.org/keywords/telecommunications","display_name":"Telecommunications","score":0.254705548286438},{"id":"https://openalex.org/keywords/wireless","display_name":"Wireless","score":0.2052563726902008},{"id":"https://openalex.org/keywords/engineering","display_name":"Engineering","score":0.18189460039138794}],"concepts":[{"id":"https://openalex.org/C138660444","wikidata":"https://www.wikidata.org/wiki/Q5607897","display_name":"Telecommunications link","level":2,"score":0.7609996199607849},{"id":"https://openalex.org/C7720470","wikidata":"https://www.wikidata.org/wiki/Q954187","display_name":"Transceiver","level":3,"score":0.6382678151130676},{"id":"https://openalex.org/C41008148","wikidata":"https://www.wikidata.org/wiki/Q21198","display_name":"Computer science","level":0,"score":0.6274611353874207},{"id":"https://openalex.org/C127162648","wikidata":"https://www.wikidata.org/wiki/Q16858953","display_name":"Channel (broadcasting)","level":2,"score":0.5800547003746033},{"id":"https://openalex.org/C148063708","wikidata":"https://www.wikidata.org/wiki/Q5072511","display_name":"Channel state information","level":3,"score":0.5539752244949341},{"id":"https://openalex.org/C207987634","wikidata":"https://www.wikidata.org/wiki/Q176862","display_name":"MIMO","level":3,"score":0.5233139991760254},{"id":"https://openalex.org/C24326235","wikidata":"https://www.wikidata.org/wiki/Q126095","display_name":"Electronic engineering","level":1,"score":0.49592408537864685},{"id":"https://openalex.org/C2779960059","wikidata":"https://www.wikidata.org/wiki/Q7113681","display_name":"Overhead (engineering)","level":2,"score":0.4823291003704071},{"id":"https://openalex.org/C54197355","wikidata":"https://www.wikidata.org/wiki/Q5782992","display_name":"Beamforming","level":2,"score":0.48189789056777954},{"id":"https://openalex.org/C137246740","wikidata":"https://www.wikidata.org/wiki/Q583970","display_name":"Spectral efficiency","level":3,"score":0.46225613355636597},{"id":"https://openalex.org/C76155785","wikidata":"https://www.wikidata.org/wiki/Q418","display_name":"Telecommunications","level":1,"score":0.254705548286438},{"id":"https://openalex.org/C555944384","wikidata":"https://www.wikidata.org/wiki/Q249","display_name":"Wireless","level":2,"score":0.2052563726902008},{"id":"https://openalex.org/C127413603","wikidata":"https://www.wikidata.org/wiki/Q11023","display_name":"Engineering","level":0,"score":0.18189460039138794},{"id":"https://openalex.org/C111919701","wikidata":"https://www.wikidata.org/wiki/Q9135","display_name":"Operating system","level":1,"score":0.0}],"mesh":[],"locations_count":4,"locations":[{"id":"doi:10.1109/vtc2021-spring51267.2021.9448802","is_oa":false,"landing_page_url":"https://doi.org/10.1109/vtc2021-spring51267.2021.9448802","pdf_url":null,"source":null,"license":null,"license_id":null,"version":"publishedVersion","is_accepted":true,"is_published":true,"raw_source_name":"2021 IEEE 93rd Vehicular Technology Conference (VTC2021-Spring)","raw_type":"proceedings-article"},{"id":"pmh:oai:arXiv.org:2010.06981","is_oa":true,"landing_page_url":"http://arxiv.org/abs/2010.06981","pdf_url":"https://arxiv.org/pdf/2010.06981","source":{"id":"https://openalex.org/S4306400194","display_name":"arXiv (Cornell University)","issn_l":null,"issn":null,"is_oa":true,"is_in_doaj":false,"is_core":false,"host_organization":"https://openalex.org/I205783295","host_organization_name":"Cornell University","host_organization_lineage":["https://openalex.org/I205783295"],"host_organization_lineage_names":[],"type":"repository"},"license":null,"license_id":null,"version":"submittedVersion","is_accepted":false,"is_published":false,"raw_source_name":"","raw_type":"text"},{"id":"mag:3092787052","is_oa":true,"landing_page_url":"https://arxiv.org/pdf/2010.06981.pdf","pdf_url":null,"source":{"id":"https://openalex.org/S4306400194","display_name":"arXiv (Cornell University)","issn_l":null,"issn":null,"is_oa":true,"is_in_doaj":false,"is_core":false,"host_organization":"https://openalex.org/I205783295","host_organization_name":"Cornell University","host_organization_lineage":["https://openalex.org/I205783295"],"host_organization_lineage_names":[],"type":"repository"},"license":null,"license_id":null,"version":"submittedVersion","is_accepted":false,"is_published":false,"raw_source_name":"arXiv (Cornell University)","raw_type":null},{"id":"doi:10.48550/arxiv.2010.06981","is_oa":true,"landing_page_url":"https://doi.org/10.48550/arxiv.2010.06981","pdf_url":null,"source":{"id":"https://openalex.org/S4306400194","display_name":"arXiv (Cornell University)","issn_l":null,"issn":null,"is_oa":true,"is_in_doaj":false,"is_core":false,"host_organization":"https://openalex.org/I205783295","host_organization_name":"Cornell University","host_organization_lineage":["https://openalex.org/I205783295"],"host_organization_lineage_names":[],"type":"repository"},"license":null,"license_id":null,"version":null,"is_accepted":false,"is_published":null,"raw_source_name":null,"raw_type":"Preprint"}],"best_oa_location":{"id":"pmh:oai:arXiv.org:2010.06981","is_oa":true,"landing_page_url":"http://arxiv.org/abs/2010.06981","pdf_url":"https://arxiv.org/pdf/2010.06981","source":{"id":"https://openalex.org/S4306400194","display_name":"arXiv (Cornell University)","issn_l":null,"issn":null,"is_oa":true,"is_in_doaj":false,"is_core":false,"host_organization":"https://openalex.org/I205783295","host_organization_name":"Cornell University","host_organization_lineage":["https://openalex.org/I205783295"],"host_organization_lineage_names":[],"type":"repository"},"license":null,"license_id":null,"version":"submittedVersion","is_accepted":false,"is_published":false,"raw_source_name":"","raw_type":"text"},"sustainable_development_goals":[],"awards":[],"funders":[{"id":"https://openalex.org/F4320321108","display_name":"Academy of Finland","ror":"https://ror.org/05k73zm37"}],"has_content":{"grobid_xml":false,"pdf":false},"content_urls":null,"referenced_works_count":32,"referenced_works":["https://openalex.org/W1541064563","https://openalex.org/W2111953900","https://openalex.org/W2113638573","https://openalex.org/W2116334496","https://openalex.org/W2195693430","https://openalex.org/W2945534522","https://openalex.org/W2950077417","https://openalex.org/W2953226670","https://openalex.org/W2968810373","https://openalex.org/W2969424089","https://openalex.org/W2981792785","https://openalex.org/W2994612022","https://openalex.org/W2995155092","https://openalex.org/W3006251808","https://openalex.org/W3010499839","https://openalex.org/W3015419519","https://openalex.org/W3033179367","https://openalex.org/W3038076970","https://openalex.org/W3043810557","https://openalex.org/W3047175607","https://openalex.org/W3081077581","https://openalex.org/W3092446067","https://openalex.org/W3102195069","https://openalex.org/W3133443365","https://openalex.org/W3134059753","https://openalex.org/W3144244478","https://openalex.org/W6762113363","https://openalex.org/W6772218483","https://openalex.org/W6774205530","https://openalex.org/W6780047104","https://openalex.org/W6781196761","https://openalex.org/W6782070025"],"related_works":["https://openalex.org/W3171953287","https://openalex.org/W3201584873","https://openalex.org/W3046670323","https://openalex.org/W3207187630","https://openalex.org/W3081518414","https://openalex.org/W3099478061","https://openalex.org/W3092049479","https://openalex.org/W3138516517","https://openalex.org/W3121406643","https://openalex.org/W3035697429","https://openalex.org/W3209927629","https://openalex.org/W3162440886","https://openalex.org/W3193557774","https://openalex.org/W3138360126","https://openalex.org/W3202266633","https://openalex.org/W2996403195","https://openalex.org/W3048730941","https://openalex.org/W3180635532","https://openalex.org/W3046925429","https://openalex.org/W3113261730"],"abstract_inverted_index":{"The":[0,130],"reconfigurable":[1],"intelligent":[2],"surface":[3],"(RIS)":[4],"plays":[5],"an":[6],"important":[7],"role":[8],"in":[9,13],"maintaining":[10],"the":[11,20,24,34,43,54,61,72,88,100,105,110,114,118,135,147,151,161,166],"connectivity":[12],"millimeter":[14],"wave":[15],"(mmWave)":[16],"MIMO":[17],"systems":[18],"when":[19],"direct":[21],"channel":[22,35,62,101],"between":[23],"transceivers":[25],"is":[26,30,40,80],"blocked.":[27],"However,":[28],"it":[29],"difficult":[31],"to":[32,97,146],"acquire":[33],"state":[36],"information":[37],"(CSI),":[38],"which":[39],"essential":[41],"for":[42,104,160],"design":[44],"of":[45,71],"RIS":[46,77,107,115,122,138,149,163],"phase":[47],"control":[48],"matrix":[49],"and":[50,66,75,127,142,164],"beamforming":[51],"vectors":[52],"at":[53,113],"transceivers.":[55],"In":[56],"this":[57],"paper,":[58],"we":[59,92,108],"compare":[60],"estimation":[63],"(CE)":[64],"performance":[65,144],"achieved":[67],"spectral":[68],"efficiency":[69],"(SE)":[70],"purely":[73,89,136],"passive":[74,90,137],"hybrid":[76,106,148,162],"architectures.":[78],"CE":[79,141],"done":[81],"via":[82],"atomic":[83],"norm":[84],"minimization":[85],"(ANM).":[86],"For":[87],"RIS,":[91],"follow":[93],"a":[94],"two-stage":[95],"procedure":[96],"sequentially":[98],"estimate":[99,109],"parameters,":[102],"while":[103],"individual":[111],"channels":[112],"based":[116],"on":[117],"observations":[119],"from":[120],"active":[121],"elements":[123],"assuming":[124],"alternating":[125],"uplink":[126],"downlink":[128],"training.":[129],"simulation":[131],"results":[132],"show":[133],"that":[134],"brings":[139],"better":[140],"SE":[143],"compared":[145],"under":[150],"same":[152],"training":[153],"overhead.":[154],"We":[155],"further":[156],"consider":[157],"different":[158],"setups":[159],"study":[165],"tradeoffs":[167],"among":[168],"them.":[169]},"counts_by_year":[{"year":2025,"cited_by_count":1},{"year":2023,"cited_by_count":1},{"year":2021,"cited_by_count":2}],"updated_date":"2026-07-14T23:27:15.235271","created_date":"2025-10-10T00:00:00"}