Gabatarwa ga Fasahar PAM4

Kafin a fahimci fasahar PAM4, menene fasahar daidaitawa? Fasahar daidaitawa ita ce dabarar mayar da siginar baseband (siginar lantarki mai sauƙi) zuwa siginar watsawa. Domin tabbatar da ingancin sadarwa da kuma shawo kan matsalolin watsa siginar nesa, ya zama dole a canja wurin siginar zuwa tashar mita mai yawa ta hanyar daidaitawa don watsawa.

PAM4 wata dabara ce ta daidaitawa ta huɗu ta tsarin bugun bugun jini (PAM).

Siginar PAM sanannen fasahar watsa sigina ce bayan NRZ (Ba a Komawa zuwa Sifili ba).

Siginar NRZ tana amfani da matakan sigina guda biyu, babba da ƙarami, don wakiltar 1 da 0 na siginar dabaru ta dijital, kuma tana iya aika bayanai na dabaru guda 1 a kowane zagayen agogo.

Siginar PAM4 tana amfani da matakan sigina guda 4 daban-daban don watsa sigina, kuma kowane zagayen agogo zai iya aika bayanai guda 2 na dabaru, wato 00, 01, 10, da 11.
Saboda haka, a ƙarƙashin yanayin baud rate iri ɗaya, bit rate na siginar PAM4 ya ninka na siginar NRZ sau biyu, wanda ke ninka ingancin watsawa kuma yana rage farashi yadda ya kamata.

An yi amfani da fasahar PAM4 sosai a fannin haɗa sigina mai sauri. A halin yanzu, akwai na'urar transceiver mai gani ta 400G bisa fasahar daidaitawa ta PAM4 don cibiyar bayanai da kuma na'urar transceiver mai gani ta 50G bisa fasahar daidaitawa ta PAM4 don hanyar sadarwa ta 5G.

Tsarin aiwatar da tsarin transceiver na gani na 400G DML bisa tsarin PAM4 shine kamar haka: lokacin da ake watsa siginar naúrar, ana shigar da tashoshi 16 na siginar lantarki na 25G NRZ daga sashin haɗin lantarki, wanda mai sarrafawa na DSP ya riga ya sarrafa, PAM4 ya daidaita, kuma ya fitar da tashoshi 8 na siginar lantarki na 25G PAM4, waɗanda aka ɗora a kan guntu na direba. Ana canza siginar lantarki mai sauri zuwa tashoshi 8 na siginar gani na sauri na 50Gbps ta hanyar tashoshi 8 na lasers, tare da haɗin mai yawa na rabe-raben raƙuman ruwa, kuma an haɗa su zuwa tashoshi 1 na fitarwar siginar gani na sauri na 400G. Lokacin karɓar siginar naúrar, ana shigar da siginar gani na babban tashar 1 ta 400G da aka karɓa ta hanyar sashin haɗin gani, an canza shi zuwa siginar gani na babban tashar 8 ta 50Gbps ta hanyar demultiplexer, wanda mai karɓar gani ya karɓa, kuma an canza shi zuwa siginar lantarki. Bayan dawo da agogo, ƙara girma, daidaitawa, da kuma rage PAM4 ta hanyar guntu mai sarrafawa na DSP, siginar lantarki za ta koma tashoshi 16 na siginar lantarki ta 25G NRZ.

Aiwatar da fasahar daidaitawar PAM4 zuwa na'urorin gani na 400Gb/s. Na'urar hangen nesa ta 400Gb/s bisa ga tsarin daidaitawar PAM4 na iya rage adadin lasers da ake buƙata a ƙarshen watsawa kuma hakan zai rage adadin masu karɓa da ake buƙata a ƙarshen karɓa saboda amfani da dabarun daidaitawa mafi girma idan aka kwatanta da NRZ. Tsarin daidaitawar PAM4 yana rage adadin abubuwan gani a cikin na'urar hangen nesa, wanda zai iya kawo fa'idodi kamar ƙarancin farashin haɗuwa, rage amfani da wutar lantarki, da ƙaramin girman marufi.

Akwai buƙatar na'urorin gani na 50Gbit/s a cikin hanyoyin sadarwa na watsawa da dawowa na 5G, kuma an ɗauki mafita bisa ga na'urorin gani na 25G kuma an ƙara shi da tsarin daidaita amplitude na PAM4 don cimma buƙatun bandwidth masu rahusa da yawa.

Lokacin da ake bayanin siginar PAM-4, yana da mahimmanci a kula da bambanci tsakanin ƙimar baud da ƙimar bit. Ga siginar NRZ ta gargajiya, tunda alama ɗaya tana watsa bit ɗaya na bayanai, ƙimar bit da ƙimar baud iri ɗaya ne. Misali, a cikin 100G Ethernet, ta amfani da siginar 25.78125GBaud guda huɗu don watsawa, ƙimar bit akan kowace sigina ita ma 25.78125Gbps ce, kuma siginar huɗu suna cimma watsa siginar 100Gbps; Ga siginar PAM-4, tunda alama ɗaya tana watsa bit 2 na bayanai, ƙimar bit da za a iya watsawa ita ce sau biyu ƙimar baud. Misali, ta amfani da tashoshi 4 na siginar 26.5625GBaud don watsawa a cikin 200G Ethernet, ƙimar bit akan kowane tasha shine 53.125Gbps, kuma tashoshi 4 na siginar za su iya cimma watsa siginar 200Gbps. Ga 400G Ethernet, ana iya cimma shi da tashoshi 8 na siginar 26.5625GBaud.