{"id":85029,"date":"2020-06-12T13:43:50","date_gmt":"2020-06-12T11:43:50","guid":{"rendered":"https:\/\/prohoster.info\/blog\/administrirovanie\/glubokoe-pogruzhenie-v-princzipy-raboty-wi-fi-6-ofdma-i-mu-mimo"},"modified":"2020-06-12T13:43:50","modified_gmt":"2020-06-12T11:43:50","slug":"glubokoe-pogruzhenie-v-princzipy-raboty-wi-fi-6-ofdma-i-mu-mimo","status":"publish","type":"post","link":"https:\/\/prohoster.info\/cs\/blog\/administrirovanie\/glubokoe-pogruzhenie-v-princzipy-raboty-wi-fi-6-ofdma-i-mu-mimo","title":{"rendered":"Hlubok\u00e9 pono\u0159en\u00ed do princip\u016f fungov\u00e1n\u00ed Wi-Fi 6: OFDMA a MU-MIMO","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Ve sv\u00fdch v\u00fdvoj\u00edch Huawei s\u00e1z\u00ed na Wi-Fi 6. Ot\u00e1zky od koleg\u016f a z\u00e1kazn\u00edk\u016f ohledn\u011b nov\u00e9 generace standardu n\u00e1s p\u0159ivedly k tomu, abychom napsali p\u0159\u00edsp\u011bvek o teoretick\u00fdch z\u00e1kladech a fyzik\u00e1ln\u00edch principech, kter\u00e9 jsou do n\u011bj zakotveny. Od historie p\u0159ejdeme k fyzice, podrobn\u011b se zam\u011b\u0159\u00edme na to, pro\u010d jsou technologie OFDMA a MU-MIMO pot\u0159ebn\u00e9. P\u0159edstav\u00edme i to, jak z\u00e1sadn\u011b p\u0159epracovan\u00e9 fyzick\u00e9 prost\u0159ed\u00ed p\u0159enosu dat umo\u017enilo dos\u00e1hnout zaru\u010den\u00e9 propustnosti kan\u00e1l\u016f a takov\u00e9ho sn\u00ed\u017een\u00ed celkov\u00e9 \u00farovn\u011b zpo\u017ed\u011bn\u00ed, \u017ee se staly srovnateln\u00fdmi s \u201eoper\u00e1torsk\u00fdmi\u201c. A to i p\u0159esto, \u017ee modern\u00ed s\u00edt\u011b na b\u00e1zi 5G jsou n\u00e1kladn\u011bj\u0161\u00ed (v pr\u016fm\u011bru 20\u201330kr\u00e1t) ne\u017e obdobn\u00e9 indoor s\u00edt\u011b na Wi-Fi 6.<\/p>\n

\"Hlubok\u00e9
\n<\/a><\/noindex>
\nPro Huawei nen\u00ed toto t\u00e9ma zanedbateln\u00e9: \u0159e\u0161en\u00ed s podporou Wi-Fi 6 pat\u0159\u00ed mezi na\u0161e nejprogresivn\u011bj\u0161\u00ed produkty v roce 2020, do nich\u017e byly investov\u00e1ny obrovsk\u00e9 zdroje. Tady je jen jeden p\u0159\u00edklad: v\u00fdzkumy v oblasti materi\u00e1lov\u00e9ho in\u017een\u00fdrstv\u00ed n\u00e1m umo\u017enily vybrat slitinu, jej\u00ed\u017e pou\u017eit\u00ed v r\u00e1diov\u00fdch prvc\u00edch p\u0159\u00edstupov\u00e9ho bodu zv\u00fd\u0161ilo pom\u011br \u201esign\u00e1l \u2013 \u0161um\u201c o 2\u20133 dB: smek\u00e1me klobouk p\u0159ed Doronem Ezrim za toto dosa\u017een\u00ed.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Trocha historie<\/h2>\n

\nHistorii Wi-Fi m\u00e1 smysl po\u010d\u00edtat od roku 1971, kdy na Havajsk\u00e9 univerzit\u011b profesor Norman Abramson se skupinou koleg\u016f vyvinul, postavil a spustil bezdr\u00e1tovou s\u00ed\u0165 paketov\u00e9ho p\u0159enosu dat ALOHAnet.<\/p>\n

V roce 1980 byla schv\u00e1lena skupina standard\u016f a protokol\u016f IEEE 802, popisuj\u00edc\u00edch organizaci dvou spodn\u00edch vrstev sedmivrstv\u00e9 s\u00ed\u0165ov\u00e9 modelu OSI. Na zve\u0159ejn\u011bn\u00ed prvn\u00ed verze 802.11 se \u010dekalo dlouh\u00fdch 17 let.<\/p>\n

S p\u0159ijet\u00edm standardu 802.11 v roce 1997, dva roky p\u0159ed vznikem organizace Wi-Fi Alliance, prvn\u00ed generace dnes nejpopul\u00e1rn\u011bj\u0161\u00ed technologie bezdr\u00e1tov\u00e9ho p\u0159enosu dat vstoupila do velk\u00e9ho sv\u011bta. <\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Standard IEEE 802. Generace Wi-Fi<\/h2>\n

\nPrvn\u00edm standardem, kter\u00fd byl masivn\u011b podporov\u00e1n v\u00fdrobci za\u0159\u00edzen\u00ed, se stal 802.11b. Jak vid\u00edte, frekvence inovac\u00ed od konce 20. stolet\u00ed byla pom\u011brn\u011b stabiln\u00ed: pro kvalitn\u00ed zm\u011bny je pot\u0159eba \u010das. V posledn\u00edch letech se ve\u0161ker\u00e1 pr\u00e1ce zam\u011b\u0159ila na zlep\u0161en\u00ed fyzick\u00e9ho prost\u0159ed\u00ed p\u0159enosu sign\u00e1lu. Abychom l\u00e9pe pochopili sou\u010dasn\u00e9 probl\u00e9my Wi-Fi, vr\u00e1t\u00edme se k jeho fyzick\u00fdm z\u00e1klad\u016fm.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Vzpom\u00ednejme na z\u00e1klady!<\/h2>\n

\nR\u00e1diov\u00e9 vlny jsou zvl\u00e1\u0161tn\u00edm p\u0159\u00edpadem elektromagnetick\u00fdch vln, kter\u00e9 se \u0161\u00ed\u0159\u00ed od zdroje ru\u0161en\u00ed elektrick\u00e9ho a magnetick\u00e9ho pole. Charakterizuj\u00ed se t\u0159emi z\u00e1kladn\u00edmi parametry: vlnov\u00fdm vektorem a vektory intenzity elektrick\u00e9ho a magnetick\u00e9ho pole. V\u0161echny t\u0159i jsou navz\u00e1jem kolm\u00e9. Frekvenc\u00ed vlny se obvykle rozum\u00ed po\u010det opakuj\u00edc\u00edch se kmit\u016f, kter\u00e9 se vejdou do jednotky \u010dasu.<\/p>\n

V\u0161echna tato jsou obecn\u011b zn\u00e1m\u00e1 fakta. Abychom v\u0161ak do\u0161li a\u017e na konec, mus\u00edme za\u010d\u00edt \u00fapln\u011b na za\u010d\u00e1tku.<\/p>\n

\"Hlubok\u00e9
\n
\nNa hypotetick\u00e9 \u0161k\u00e1le frekven\u010dn\u00edch p\u00e1sem elektromagnetick\u00e9ho z\u00e1\u0159en\u00ed zab\u00edr\u00e1 r\u00e1diov\u00e9 p\u00e1smo nejni\u017e\u0161\u00ed (n\u00edzkofrekven\u010dn\u00ed) \u010d\u00e1st. Pat\u0159\u00ed sem elektromagnetick\u00e9 vlny s frekvencemi kmit\u00e1n\u00ed od 3 Hz do 3000 GHz. V\u0161echna ostatn\u00ed p\u00e1sma, v\u010detn\u011b viditeln\u00e9ho sv\u011btla, maj\u00ed mnohem vy\u0161\u0161\u00ed frekvenci.<\/p>\n

\"Hlubok\u00e9
\n
\n\u010c\u00edm vy\u0161\u0161\u00ed je frekvence, t\u00edm v\u011bt\u0161\u00ed energii lze r\u00e1diov\u00e9 vln\u011b p\u0159edat, nicm\u00e9n\u011b z\u00e1rove\u0148 h\u016f\u0159e obch\u00e1z\u00ed p\u0159ek\u00e1\u017eky a rychleji zanik\u00e1. Plat\u00ed i opak. S ohledem na tyto zvl\u00e1\u0161tnosti byly pro pr\u00e1ci s Wi-Fi zvoleny dv\u011b hlavn\u00ed frekven\u010dn\u00ed p\u00e1sma \u2014 2,4 GHz (frekven\u010dn\u00ed rozsah od 2,4000 do 2,4835 GHz) a 5 GHz (frekven\u010dn\u00ed p\u00e1sma 5,170\u20145,330, 5,490\u20145,730 a 5,735\u20145,835 GHz).<\/p>\n

\"Hlubok\u00e9
\n
\nR\u00e1diov\u00e9 vlny se \u0161\u00ed\u0159\u00ed v\u0161emi sm\u011bry, a aby se vlivy zpr\u00e1v navz\u00e1jem neovliv\u0148ovaly kv\u016fli interferen\u010dn\u00edmu efektu, je obvykl\u00e9 rozd\u011blit frekven\u010dn\u00ed p\u00e1smo na jednotliv\u00e9 \u00fazk\u00e9 \u00faseky \u2014 kan\u00e1ly s touto \u010di onou propustnost\u00ed<\/a><\/noindex>. Na sch\u00e9matu v\u00fd\u0161e je vid\u011bt, \u017ee sousedn\u00ed kan\u00e1ly 1 a 2 s propustnost\u00ed 20 MHz si vz\u00e1jemn\u011b br\u00e1n\u00ed, zat\u00edmco 1 a 6 si nebr\u00e1n\u00ed.<\/p>\n

Sign\u00e1l v r\u00e1mci kan\u00e1lu se p\u0159en\u00e1\u0161\u00ed pomoc\u00ed r\u00e1diov\u00e9 vlny na ur\u010dit\u00e9 nosn\u00e9 frekvenci. Pro p\u0159enos informac\u00ed mohou b\u00fdt parametry vlny modulov\u00e1ny<\/a><\/noindex> podle frekvence, amplitudy nebo f\u00e1ze.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Rozd\u011blen\u00ed kan\u00e1l\u016f ve frekven\u010dn\u00edch p\u00e1smech Wi-Fi<\/h2>\n

\nFrekven\u010dn\u00ed p\u00e1smo 2,4 GHz je rozd\u011bleno na 14 \u010d\u00e1ste\u010dn\u011b se p\u0159ekr\u00fdvaj\u00edc\u00edch kan\u00e1l\u016f optim\u00e1ln\u00ed \u0161\u00ed\u0159ky \u2014 20 MHz. D\u0159\u00edve se pova\u017eovalo, \u017ee to je zcela dostate\u010dn\u00e9 pro uspo\u0159\u00e1d\u00e1n\u00ed slo\u017eit\u00e9 bezdr\u00e1tov\u00e9 s\u00edt\u011b. Brzy se v\u0161ak uk\u00e1zalo, \u017ee kapacita p\u00e1sma se rychle vy\u010derp\u00e1v\u00e1, a proto bylo p\u0159id\u00e1no p\u00e1smo 5 GHz, jeho\u017e spektr\u00e1ln\u00ed kapacita je mnohem vy\u0161\u0161\u00ed. V n\u011bm, krom\u011b 20MHz kan\u00e1l\u016f, je mo\u017en\u00e9 vy\u010dlenit kan\u00e1ly o \u0161\u00ed\u0159ce 40 a 80 MHz.<\/p>\n

\"Hlubok\u00e9
\n
\nPro zv\u00fd\u0161en\u00ed efektivity vyu\u017e\u00edv\u00e1n\u00ed r\u00e1diov\u00e9ho frekven\u010dn\u00edho spektra se v sou\u010dasnosti \u0161iroce uplat\u0148uje technologie v\u00edcerozm\u011brn\u00e9ho multiplexov\u00e1n\u00ed s ortogon\u00e1ln\u00edm d\u011blen\u00edm frekvenc\u00ed (OFDM<\/a><\/noindex>).<\/p>\n

) znamen\u00e1 pou\u017eit\u00ed nejen nosn\u00e9 frekvence, ale tak\u00e9 n\u011bkolika podnosn\u00fdch frekvenc\u00ed ve stejn\u00e9m kan\u00e1le, co\u017e umo\u017e\u0148uje paraleln\u00ed p\u0159enos dat. OFDM umo\u017e\u0148uje distribuovat provoz dostate\u010dn\u011b pohodln\u00fdm \u201egranul\u00e1rn\u00edm\u201c zp\u016fsobem, ale vzhledem k sv\u00e9mu v\u011bku si zachov\u00e1v\u00e1 \u0159adu z\u00e1sadn\u00edch nev\u00fdhod. Mezi nimi jsou principy fungov\u00e1n\u00ed podle s\u00ed\u0165ov\u00e9ho protokolu CSMA\/CA (Carrier Sense Multiple Access with Collision Avoidance), podle kter\u00e9ho m\u016f\u017ee v ur\u010dit\u00e9m okam\u017eiku na jedn\u00e9 nosn\u00e9 a podnosn\u00e9 frekvenci pracovat pouze jeden u\u017eivatel.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Prostorov\u00e9 toky<\/h2>\n

\nD\u016fle\u017eit\u00fdm zp\u016fsobem, jak zv\u00fd\u0161it propustnost bezdr\u00e1tov\u00e9 s\u00edt\u011b, je vyu\u017eit\u00ed prostorov\u00fdch tok\u016f.<\/p>\n

Bod p\u0159\u00edstupu nese n\u011bkolik r\u00e1diomodul\u016f (jeden, dva nebo v\u00edce), kter\u00e9 jsou p\u0159ipojeny k ur\u010dit\u00e9mu po\u010dtu ant\u00e9n. Tyto ant\u00e9ny vyza\u0159uj\u00ed podle ur\u010dit\u00e9ho sch\u00e9matu a modulace, a my dost\u00e1v\u00e1me informace p\u0159enesen\u00e9 bezdr\u00e1tov\u00fdm prost\u0159ed\u00edm. Prostorov\u00fd tok m\u016f\u017ee b\u00fdt vytv\u00e1\u0159en mezi konkr\u00e9tn\u00ed fyzickou ant\u00e9nou (r\u00e1diomodulem) bodu p\u0159\u00edstupu a u\u017eivatelsk\u00fdm za\u0159\u00edzen\u00edm. D\u00edky tomu se celkov\u00fd objem p\u0159en\u00e1\u0161en\u00fdch informac\u00ed z bodu p\u0159\u00edstupu zvy\u0161uje n\u00e1sobn\u011b podle po\u010dtu tok\u016f (ant\u00e9n). <\/p>\n

Podle aktu\u00e1ln\u00edch standard\u016f je v p\u00e1smu 2,4 GHz mo\u017en\u00e9 realizovat a\u017e \u010dty\u0159i prostorov\u00e9 toky, v p\u00e1smu 5 GHz - a\u017e osm.<\/p>\n

\"Hlubok\u00e9
\n
\nD\u0159\u00edve, p\u0159i pr\u00e1ci v p\u00e1smech 2,4 a 5 GHz, jsme se orientovali pouze na po\u010det r\u00e1diov\u00fdch modul\u016f. P\u0159\u00edtomnost druh\u00e9ho r\u00e1diov\u00e9ho modulu poskytovala dodate\u010dnou flexibilitu, proto\u017ee umo\u017e\u0148ovala star\u00fdm u\u017eivatelsk\u00fdm za\u0159\u00edzen\u00edm fungovat na frekvenci 2,4 GHz, zat\u00edmco nov\u00fdm na frekvenci 5 GHz. S p\u0159\u00edchodem t\u0159et\u00edho a dal\u0161\u00edch r\u00e1diov\u00fdch modul\u016f se objevily ur\u010dit\u00e9 probl\u00e9my. Vyza\u0159uj\u00edc\u00ed prvky maj\u00ed tendenci vz\u00e1jemn\u011b se ovliv\u0148ovat, co\u017e zvy\u0161uje n\u00e1klady za\u0159\u00edzen\u00ed v souvislosti s nutnost\u00ed p\u0159esn\u011bj\u0161\u00edho n\u00e1vrhu a vybaven\u00ed p\u0159\u00edstupov\u00e9ho bodu kompenza\u010dn\u00edmi filtry. Tak\u017ee teprve ned\u00e1vno bylo mo\u017en\u00e9 sou\u010dasn\u011b podporovat 16 prostorov\u00fdch tok\u016f na jeden p\u0159\u00edstupov\u00fd bod.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Praktick\u00e1 a teoretick\u00e1 rychlost<\/h2>\n

\nKv\u016fli mechanism\u016fm fungov\u00e1n\u00ed OFDM jsme nemohli dos\u00e1hnout maxim\u00e1ln\u00ed propustnosti s\u00edt\u011b. Teoretick\u00e9 v\u00fdpo\u010dty pro praktickou aplikaci OFDM byly provedeny ji\u017e d\u00e1vno a pouze se vztahem na ide\u00e1ln\u00ed prost\u0159ed\u00ed, kde se p\u0159edpokl\u00e1dalo dostate\u010dn\u011b vysok\u00e9 pom\u011br sign\u00e1l-\u0161um (SNR) a pravd\u011bpodobnost chyby na bitu (BER). V modern\u00edch podm\u00ednk\u00e1ch siln\u00e9ho ru\u0161en\u00ed v\u0161ech n\u00e1mi zaj\u00edmaj\u00edc\u00edch radiov\u00fdch frekven\u010dn\u00edch spekter jsou ukazatele propustnosti s\u00edt\u00ed zalo\u017een\u00fdch na OFDM znepokojiv\u011b mal\u00e9. A protokol nesl tyto nedostatky a\u017e do ned\u00e1vn\u00e9 doby, dokud nep\u0159i\u0161la na pomoc technologie OFDMA (ortogon\u00e1ln\u00ed v\u00edcerozm\u011brn\u00fd p\u0159\u00edstup k frekvenci). O t\u00e9 \u2014 pozd\u011bji.<\/p>\n

Poj\u010fme si promluvit o ant\u00e9n\u00e1ch<\/h2>\n

\"Hlubok\u00e9
\n
\nJak v\u00edte, ka\u017ed\u00e1 ant\u00e9na m\u00e1 sv\u016fj zisk, na z\u00e1klad\u011b jeho\u017e hodnoty je vytvo\u0159en prostorov\u00fd vzor \u0161\u00ed\u0159en\u00ed sign\u00e1lu (beamforming) s ur\u010ditou pokryt\u00edm (nebereme v \u00favahu odrazy sign\u00e1l\u016f atd.). Na tomto se v\u017edy zakl\u00e1daly \u00favahy projektant\u016f ohledn\u011b toho, kde p\u0159esn\u011b by m\u011bly b\u00fdt um\u00edst\u011bny p\u0159\u00edstupov\u00e9 body. Dlouho tvar vzoru z\u016fst\u00e1val nezm\u011bniteln\u00fd a pouze se zv\u011bt\u0161oval nebo zmen\u0161oval \u00fam\u011brn\u011b vlastnostem ant\u00e9ny.<\/p>\n

\"Hlubok\u00e9
\n
\nModern\u00ed ant\u00e9nn\u00ed prvky se st\u00e1vaj\u00ed st\u00e1le v\u00edce \u0159\u00edzen\u00fdmi a umo\u017e\u0148uj\u00ed dynamicky m\u011bnit prostorov\u00fd vzor \u0161\u00ed\u0159en\u00ed sign\u00e1lu v re\u00e1ln\u00e9m \u010dase.<\/p>\n

Na obr\u00e1zku vlevo naho\u0159e je zn\u00e1zorn\u011bn princip \u0161\u00ed\u0159en\u00ed r\u00e1diov\u00fdch vln p\u0159i pou\u017eit\u00ed standardn\u00ed v\u0161esm\u011brov\u00e9 ant\u00e9ny. Zvy\u0161ov\u00e1n\u00edm v\u00fdkonu sign\u00e1lu jsme mohli m\u011bnit pouze r\u00e1dius pokryt\u00ed, ani\u017e bychom mohli v\u00fdrazn\u011b ovlivnit kvalitu pou\u017e\u00edv\u00e1n\u00ed kan\u00e1lu \u2014 KQI (Kl\u00ed\u010dov\u00e9 kvalitativn\u00ed indik\u00e1tory). Tento ukazatel je nesm\u00edrn\u011b d\u016fle\u017eit\u00fd p\u0159i organizaci spojen\u00ed v podm\u00ednk\u00e1ch \u010dast\u00e9ho pohybu u\u017eivatelsk\u00e9ho za\u0159\u00edzen\u00ed v bezdr\u00e1tov\u00e9m prost\u0159ed\u00ed.<\/p>\n

\u0158e\u0161en\u00edm probl\u00e9mu bylo pou\u017eit\u00ed velk\u00e9ho mno\u017estv\u00ed mal\u00fdch ant\u00e9n, jejich\u017e zat\u00ed\u017een\u00ed lze regulovat v re\u00e1ln\u00e9m \u010dase, \u010d\u00edm\u017e se formuj\u00ed vzory \u0161\u00ed\u0159en\u00ed v z\u00e1vislosti na prostorov\u00e9m um\u00edst\u011bn\u00ed u\u017eivatele. <\/p>\n

\"Hlubok\u00e9
\n
\nTak se poda\u0159ilo p\u0159ibl\u00ed\u017eit k aplikaci technologie MU-MIMO (Multi-User Multiple Input, Multiple Output). S jej\u00ed pomoc\u00ed vytv\u00e1\u0159\u00ed p\u0159\u00edstupov\u00fd bod v ka\u017ed\u00e9m okam\u017eiku tok z\u00e1\u0159en\u00ed zam\u011b\u0159en\u00fd p\u0159\u00edmo na u\u017eivatelsk\u00e1 za\u0159\u00edzen\u00ed.<\/p>\n

Od fyziky ke standard\u016fm 802.11<\/h2>\n

\"Hlubok\u00e9
\n
\nS rozvojem standard\u016f Wi-Fi se m\u011bnily principy pr\u00e1ce s fyzickou vrstvou s\u00edt\u011b. Pou\u017eit\u00ed jin\u00fdch modula\u010dn\u00edch mechanism\u016f dalo mo\u017enost \u2014 po\u010d\u00ednaje verzemi 802.11g\/n \u2014 vm\u011bstnat do \u010dasov\u00e9ho okna mnohem v\u00edce informac\u00ed a t\u00edm p\u00e1dem pracovat s v\u011bt\u0161\u00edm po\u010dtem u\u017eivatel\u016f. Krom\u011b toho bylo toho dosa\u017eeno i d\u00edky pou\u017eit\u00ed prostorov\u00fdch tok\u016f. A nov\u011b z\u00edskan\u00e1 flexibilita ohledn\u011b \u0161\u00ed\u0159ky kan\u00e1lu umo\u017enila vytv\u00e1\u0159et v\u00edce zdroj\u016f pro MIMO.<\/p>\n

Na p\u0159\u00ed\u0161t\u00ed rok se pl\u00e1nuje schv\u00e1len\u00ed standardu Wi-Fi 7. Co se s jeho p\u0159\u00edchodem zm\u011bn\u00ed? Krom\u011b obvykl\u00e9ho n\u00e1r\u016fstu rychlosti a p\u0159id\u00e1n\u00ed p\u00e1sma 6 GHz se objev\u00ed mo\u017enost pracovat s \u0161irok\u00fdmi agregovan\u00fdmi kan\u00e1ly, jako je 320 MHz. To je zvl\u00e1\u0161\u0165 zaj\u00edmav\u00e9 v kontextu pr\u016fmyslov\u00e9ho vyu\u017eit\u00ed.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Teoretick\u00e1 propustnost Wi-Fi 6<\/h2>\n

\nTeoretick\u00fd vzorec pro v\u00fdpo\u010det nomin\u00e1ln\u00ed rychlosti Wi-Fi 6 je dost slo\u017eit\u00fd a z\u00e1vis\u00ed na mnoha parametrech, po\u010d\u00ednaje po\u010dtem prostorov\u00fdch tok\u016f a kon\u010de informacemi, kter\u00e9 m\u016f\u017eeme vlo\u017eit do podnosn\u00e9 (nebo podnosn\u00fdch, pokud jich je n\u011bkolik) za jednotku \u010dasu.<\/p>\n

Jak vid\u00edte, prostorov\u00e9 toky maj\u00ed velk\u00fd vliv na v\u00fdkon. P\u0159edt\u00edm v\u0161ak zvy\u0161ov\u00e1n\u00ed jejich po\u010dtu v kombinaci s pou\u017eit\u00edm STC (Space-Time Coding) a MRC (Maximum Ratio Combining) zhor\u0161ovalo funk\u010dnost bezdr\u00e1tov\u00e9ho \u0159e\u0161en\u00ed jako celku.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Nov\u00e9 kl\u00ed\u010dov\u00e9 technologie fyzick\u00e9 \u00farovn\u011b<\/h2>\n

\nP\u0159ejdeme k kl\u00ed\u010dov\u00fdm technologi\u00edm fyzick\u00e9 \u00farovn\u011b \u2014 a za\u010dneme s prvn\u00ed \u00farovn\u00ed s\u00ed\u0165ov\u00e9ho modelu OSI.<\/p>\n

\"Hlubok\u00e9
\n
\nP\u0159ipome\u0148me, \u017ee v OFDM se pou\u017e\u00edv\u00e1 ur\u010dit\u00e9 mno\u017estv\u00ed podnosn\u00fdch, kter\u00e9 mohou p\u0159en\u00e1\u0161et ur\u010dit\u00fd objem informac\u00ed, ani\u017e by se vz\u00e1jemn\u011b ovliv\u0148ovaly. <\/p>\n

\"Hlubok\u00e9
\n
\nV tomto p\u0159\u00edkladu pou\u017e\u00edv\u00e1me frekven\u010dn\u00ed p\u00e1smo 5,220 GHz, kter\u00e9 zahrnuje 48 podkan\u00e1l\u016f. Agregac\u00ed tohoto kan\u00e1lu z\u00edsk\u00e1me v\u00edce podnosn\u00fdch, na ka\u017ed\u00e9 z nich\u017e se pou\u017e\u00edv\u00e1 vlastn\u00ed modula\u010dn\u00ed sch\u00e9ma.<\/p>\n

\"Hlubok\u00e9
\n
\nVe Wi-Fi 5 se pou\u017e\u00edv\u00e1 kvadraturn\u00ed modulace 256 QAM (Quadrature Amplitude Modulation), kter\u00e1 umo\u017e\u0148uje vytv\u00e1\u0159et v r\u00e1mci nosn\u00e9 frekvence v jednom \u010dasov\u00e9m slotu pole 16 x 16 bod\u016f, kter\u00e9 se li\u0161\u00ed amplitudou a f\u00e1z\u00ed. Nev\u00fdhodou je, \u017ee v ka\u017ed\u00e9m okam\u017eiku m\u016f\u017ee na nosn\u00e9 frekvenci p\u0159en\u00e1\u0161et pouze jedna stanice.<\/p>\n

\"Hlubok\u00e9
\n
\nM multiplexing s ortogon\u00e1ln\u00edm frekven\u010dn\u00edm d\u011blen\u00edm kan\u00e1l\u016f (OFDMA) p\u0159i\u0161el ze sv\u011bta mobiln\u00edch oper\u00e1tor\u016f, roz\u0161\u00ed\u0159il se spolu s LTE a pou\u017e\u00edv\u00e1 se pro organizaci downlinku (kan\u00e1l spojen\u00ed k u\u017eivateli). Umo\u017e\u0148uje pracovat s kan\u00e1lem na \u00farovni tzv. zdrojov\u00fdch jednotek. Tyto jednotky pom\u00e1haj\u00ed rozd\u011blit blok na ur\u010dit\u00e9 mno\u017estv\u00ed komponent\u016f. V r\u00e1mci bloku m\u016f\u017eeme v ka\u017ed\u00e9m okam\u017eiku nepracovat pouze s jedn\u00edm vyza\u0159uj\u00edc\u00edm prvkem (u\u017eivatelem nebo p\u0159\u00edstupov\u00fdm bodem), ale kombinovat des\u00edtky prvk\u016f. To dovoluje dosahovat pozoruhodn\u00fdch v\u00fdsledk\u016f.<\/p>\n

\"Hlubok\u00e9
\n
\n\"Hlubok\u00e9
\n<\/p>\n

Jednoduch\u00e9 spojen\u00ed kan\u00e1l\u016f ve Wi-Fi 6<\/h2>\n

\nSpojen\u00ed kan\u00e1l\u016f (Channel Bonding) ve Wi-Fi 6 umo\u017e\u0148uje z\u00edsk\u00e1vat slou\u010den\u00e9 kan\u00e1ly o \u0161\u00ed\u0159ce od 20 do 160 MHz. Spojen\u00ed p\u0159itom nemus\u00ed b\u00fdt provedeno v sousedn\u00edch p\u00e1smech. Nap\u0159\u00edklad jeden blok m\u016f\u017ee b\u00fdt z p\u00e1sma 5,17 GHz a druh\u00fd z p\u00e1sma 5,135 GHz. To umo\u017e\u0148uje flexibiln\u011b vytv\u00e1\u0159et r\u00e1diov\u00e9 prost\u0159ed\u00ed i p\u0159i siln\u00fdch interferen\u010dn\u00edch faktorech nebo p\u0159i sousedstv\u00ed s jin\u00fdmi st\u00e1l\u00fdmi vys\u00edlac\u00edmi stanicemi.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Od SIMO k MIMO<\/h2>\n

\nMetoda MIMO nebyla s n\u00e1mi v\u017edy. V minulosti byla mobiln\u00ed komunikace omezena na re\u017eim SIMO, kter\u00fd vy\u017eadoval, aby u\u017eivatelsk\u00e1 stanice m\u011bla n\u011bkolik ant\u00e9n, kter\u00e9 sou\u010dasn\u011b pracovaly na p\u0159\u00edjmu informac\u00ed. <\/p>\n

\"Hlubok\u00e9
\n
\nMU-MIMO m\u00e1 za c\u00edl p\u0159en\u00e1\u0161et informace u\u017eivatel\u016fm, p\u0159i\u010dem\u017e vyu\u017e\u00edv\u00e1 ve\u0161ker\u00e9 aktu\u00e1ln\u00ed ant\u00e9nn\u00ed kapacity. To odstra\u0148uje d\u0159\u00edve uplat\u0148ovan\u00e1 omezen\u00ed protokolem CSMA\/CA, kter\u00e1 byla spojena s pos\u00edl\u00e1n\u00edm token\u016f pro p\u0159enos na u\u017eivatelsk\u00e1 za\u0159\u00edzen\u00ed. Nyn\u00ed se u\u017eivatel\u00e9 sdru\u017euj\u00ed do skupin a ka\u017ed\u00fd \u010dlen skupiny z\u00edsk\u00e1v\u00e1 svou \u010d\u00e1st zdroj\u016f ant\u00e9nn\u00ed kapacity p\u0159\u00edstupov\u00e9ho bodu, ani\u017e by \u010dekal na svou p\u0159\u00edle\u017eitost.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Tvorba r\u00e1diov\u00e9ho paprsku<\/h2>\n

\nD\u016fle\u017eit\u00fdm pravidlem MU-MIMO je udr\u017eov\u00e1n\u00ed takov\u00e9ho re\u017eimu pr\u00e1ce ant\u00e9n, kter\u00fd nezp\u016fsobuje vz\u00e1jemn\u00e9 p\u0159ekr\u00fdv\u00e1n\u00ed r\u00e1diov\u00fdch vln a ztr\u00e1tu informac\u00ed v d\u016fsledku slo\u017een\u00ed f\u00e1z\u00ed.<\/p>\n

To vy\u017eaduje slo\u017eit\u00e9 matematick\u00e9 v\u00fdpo\u010dty na stran\u011b p\u0159\u00edstupov\u00e9ho bodu. Pokud termin\u00e1l tuto funkci podporuje, MU-MIMO mu umo\u017e\u0148uje informovat p\u0159\u00edstupov\u00fd bod o tom, s jak\u00fdm zpo\u017ed\u011bn\u00edm p\u0159ij\u00edm\u00e1 sign\u00e1l na ka\u017edou konkr\u00e9tn\u00ed ant\u00e9nu. A p\u0159\u00edstupov\u00fd bod na opl\u00e1tku p\u0159izp\u016fsobuje sv\u00e9 ant\u00e9ny pro vytvo\u0159en\u00ed optim\u00e1ln\u011b sm\u011brovan\u00e9ho paprsku.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Co n\u00e1m to celkov\u011b p\u0159in\u00e1\u0161\u00ed?<\/h2>\n

\nV tabulce jsou aktu\u00e1ln\u00ed sc\u00e9n\u00e1\u0159e pou\u017eit\u00ed Wi-Fi p\u0159edchoz\u00edch generac\u00ed ozna\u010deny b\u00edl\u00fdmi kole\u010dky s \u010d\u00edsly. Modr\u00e1 kole\u010dka (viz ilustrace v\u00fd\u0161e) popisuj\u00ed mo\u017enosti Wi-Fi 6, zat\u00edmco \u0161ed\u00e1 jsou z\u00e1le\u017eitost\u00ed bl\u00edzk\u00e9 budoucnosti.<\/p>\n

Hlavn\u00ed v\u00fdhody, kter\u00e9 nov\u00e1 \u0159e\u0161en\u00ed s podporou OFDMA p\u0159in\u00e1\u0161ej\u00ed, souvisej\u00ed se zdrojov\u00fdmi jednotkami implementovan\u00fdmi na \u00farovni srovnateln\u00e9m s TDM (\u010dasov\u00e1 d\u011blen\u00ed multiplexov\u00e1n\u00ed). D\u0159\u00edve n\u011bco takov\u00e9ho ve Wi-Fi nebylo. To umo\u017e\u0148uje jasn\u00e9 \u0159\u00edzen\u00ed p\u0159i\u0159azen\u00e9ho p\u00e1sma, zaji\u0161\u0165uj\u00edc\u00ed minim\u00e1ln\u00ed dobu pr\u016fchodu sign\u00e1lu prost\u0159ed\u00edm a po\u017eadovanou \u00farove\u0148 spolehlivosti. Nikdo nepochybuje o tom, \u017ee spolehlivost Wi-Fi pot\u0159ebuje zlep\u0161en\u00ed.<\/p>\n

Historie se vyv\u00edj\u00ed jako spir\u00e1la a sou\u010dasn\u00e1 situace se podob\u00e1 t\u00e9, kter\u00e1 nastala kolem Ethernetu. U\u017e tehdy bylo ust\u00e1leno, \u017ee p\u0159enosov\u00e9 prost\u0159ed\u00ed CSMA\/CD (Carrier Sense Multiple Access with Collision Detection) nezaru\u010duje \u017e\u00e1dnou garantovanou propustnost. A to trvalo a\u017e do p\u0159echodu na IEEE 802.3z.<\/p>\n

Pokud jde o obecn\u00e9 modely aplikac\u00ed, jak vid\u00edte, s ka\u017edou generac\u00ed Wi-Fi nar\u016fstaj\u00ed sc\u00e9n\u00e1\u0159e jeho pou\u017eit\u00ed, kter\u00e9 jsou st\u00e1le citliv\u011bj\u0161\u00ed na latence, celkov\u00fd jitter<\/a><\/noindex> a spolehlivost.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

A znovu o fyzick\u00e9m prost\u0159ed\u00ed<\/h2>\n

\nA nyn\u00ed o tom, co tvo\u0159\u00ed nov\u00e9 fyzick\u00e9 prost\u0159ed\u00ed. P\u0159i pou\u017eit\u00ed CSMA\/CA a OFDM zvy\u0161uj\u00edc\u00ed se po\u010det aktivn\u00edch bod\u016f (Active STA) vedl k v\u00fdrazn\u00e9mu poklesu propustnosti 20megahertzov\u00e9ho kan\u00e1lu. To bylo zp\u016fsobeno ji\u017e zm\u00edn\u011bn\u00fdmi, nikoli zcela nov\u00fdmi technologiemi STC (Space-Time Coding) a MRC (Maximum Ratio Combining).<\/p>\n

\"Hlubok\u00e9
\n
\nOFDMA d\u00edky pou\u017eit\u00ed zdrojov\u00fdch jednotek m\u016f\u017ee efektivn\u011b spolupracovat s vzd\u00e1len\u00fdmi a slab\u011b v\u00fdkonn\u00fdmi stanicemi. M\u00e1me mo\u017enost pracovat v jednom nosn\u00e9 frekvenci s u\u017eivateli, kte\u0159\u00ed spot\u0159ebov\u00e1vaj\u00ed r\u016fzn\u00e9 objemy zdroj\u016f. Jeden u\u017eivatel m\u016f\u017ee obsadit jednu jednotku, zat\u00edmco jin\u00fd m\u016f\u017ee vyu\u017e\u00edt v\u0161echny ostatn\u00ed.<\/p>\n

\"Hlubok\u00e9
\n<\/p>\n

Pro\u010d OFDMA nebylo d\u0159\u00edve?<\/h2>\n

\nA kone\u010dn\u011b, hlavn\u00ed ot\u00e1zka: pro\u010d OFDMA d\u0159\u00edve neexistovalo? Jak zvl\u00e1\u0161tn\u00ed, v\u0161e se to\u010dilo kolem pen\u011bz.<\/p>\n

Dlouho se pova\u017eovalo, \u017ee cena Wi-Fi modulu by m\u011bla b\u00fdt minim\u00e1ln\u00ed. P\u0159i spu\u0161t\u011bn\u00ed protokolu do komer\u010dn\u00edho provozu v roce 1997 bylo rozhodnuto, \u017ee v\u00fdrobn\u00ed n\u00e1klady takov\u00e9ho modulu nemohou p\u0159ekro\u010dit 1 USD. Jako d\u016fsledek technologie se vyv\u00edjela suboptim\u00e1ln\u011b. Zde nezohled\u0148ujeme oper\u00e1torsk\u00e9 LTE, kde se OFDMA pou\u017e\u00edv\u00e1 u\u017e dlouho. <\/p>\n

Nakonec pracovn\u00ed skupina pro Wi-Fi rozhodla, \u017ee vezme tyto technologie ze sv\u011bta oper\u00e1tor\u016f a p\u0159enese je do sv\u011bta podnikov\u00fdch s\u00edt\u00ed. Hlavn\u00edm \u00fakolem byl p\u0159echod na pou\u017eit\u00ed kvalitn\u011bj\u0161\u00edch komponent\u016f, jako jsou filtry a oscil\u00e1tory.<\/p>\n

\"Hlubok\u00e9
\n
\nPro\u010d jsme m\u011bli takov\u00e9 pot\u00ed\u017ee s prac\u00ed ve star\u00fdch k\u00f3dov\u00e1n\u00edch MRC s interferenc\u00ed nebo bez n\u00ed? Proto\u017ee mechanismus formov\u00e1n\u00ed paprsku MVDR (Minimum Variance Distortionless Response) dramaticky zvy\u0161oval po\u010det chyb, jakmile jsme se pokusili zkombinovat velk\u00e9 mno\u017estv\u00ed vys\u00edlac\u00edch bod\u016f. OFDMA dok\u00e1zal, \u017ee je to \u0159e\u0161iteln\u00e9.<\/p>\n

\"Hlubok\u00e9
\n
\nBoj s interferenc\u00ed je nyn\u00ed zalo\u017een na matematice. Pokud je okno pro p\u0159enos informac\u00ed dostate\u010dn\u011b dlouh\u00e9, vznikaj\u00edc\u00ed dynamick\u00e1 interference zp\u016fsobuje probl\u00e9my. Nov\u00e9 algoritmy umo\u017e\u0148uj\u00ed se jim vyhnout, vylu\u010duj\u00edc\u00ed vliv nejen interferenc\u00ed spojen\u00fdch s p\u0159enosem Wi-Fi, ale i jak\u00fdchkoli jin\u00fdch, kter\u00e9 v tomto p\u00e1smu vznikaj\u00ed.<\/p>\n

\"Hlubok\u00e9
\n
\nD\u00edky adaptivn\u00edmu boji s interferenc\u00ed m\u016f\u017eeme z\u00edskat zisk a\u017e 11 dB, i v n\u00e1ro\u010dn\u00e9m nerovnom\u011brn\u00e9m prost\u0159ed\u00ed. Vyu\u017eit\u00ed vlastn\u00edch algoritmick\u00fdch \u0159e\u0161en\u00ed Huawei umo\u017enilo dos\u00e1hnout v\u00fdrazn\u00e9 optimalizace pr\u00e1v\u011b tam, kde je to pot\u0159eba \u2013 v indoor \u0159e\u0161en\u00edch. To, co funguje dob\u0159e v 5G, nemus\u00ed b\u00fdt nutn\u011b efektivn\u00ed v prost\u0159ed\u00ed Wi-Fi 6. P\u0159\u00edstupy Massive MIMO a MU-MIMO se li\u0161\u00ed v p\u0159\u00edpad\u011b indoor a outdoor \u0159e\u0161en\u00ed. Tam, kde je to pot\u0159eba, je vhodn\u00e9 pou\u017e\u00edt n\u00e1kladn\u00e1 \u0159e\u0161en\u00ed, jako v 5G. Ale jsou zapot\u0159eb\u00ed i jin\u00e9 mo\u017enosti, jako Wi-Fi 6, kter\u00e9 mohou zajistit latence a dal\u0161\u00ed parametry, na kter\u00e9 jsme si zvykli o\u010dek\u00e1vat od oper\u00e1tor\u016f komunikac\u00ed.<\/p>\n

P\u0159ij\u00edm\u00e1me od nich ty n\u00e1stroje, kter\u00e9 budou u\u017eite\u010dn\u00e9 pro n\u00e1s jako pro firemn\u00ed z\u00e1kazn\u00edky, a to v\u0161e za \u00fa\u010delem poskytnout fyzick\u00e9 prost\u0159ed\u00ed, na kter\u00e9 se lze spolehnout.<\/p>\n

***<\/h2>\n

\nMimochodem, nezapome\u0148te na na\u0161e \u010detn\u00e9 webin\u00e1\u0159e k novink\u00e1m Huawei z roku 2020, kter\u00e9 se konaj\u00ed nejen v rusk\u00e9m segmentu, ale i na glob\u00e1ln\u00ed \u00farovni. Seznam webin\u00e1\u0159\u016f na nadch\u00e1zej\u00edc\u00ed t\u00fddny je k dispozici na odkazu<\/a><\/noindex>.
\n
Zdroj: habr.com<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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