Was ist der Grund für das drastische Wachstum der WLAN-Geschwindigkeit, obwohl wir dieselben Frequenzen und Kanäle verwenden?

344
xoX_Zeus_Xox

Ich habe mich kürzlich gefragt, warum sich die gewöhnliche WLAN-Geschwindigkeit heutiger WLAN-Standards so stark von älteren unterscheidet.

Als Beispiel verwenden wir 802.11b und 802.11ac. Die maximale Downloadrate von 802.11ac liegt bei 1,6 Gigabit / s. Dies entspricht etwa dem 150-fachen der Downloadrate von 802.11b, die bei 11 Megabit / s liegt.
Beide nutzen das 2,4-GHz-Frequenzband mit etwa 11 bis 14 Kanälen, je nachdem, wo Sie leben.

Welcher Faktor macht jetzt den Unterschied?
Oder fehlt mir etwas offensichtliches?

1
Informieren Sie sich einfach über die Besonderheiten dieser Standards [802.11ac] (https://en.wikipedia.org/wiki/IEEE_802.11ac). Es kann viele Dinge geben. Normalerweise hat es etwas mit Signalmodulation und Signalisierung im Allgemeinen zu tun. Seth vor 6 Jahren 0
Besseres Verständnis der Funkemissionen, kompliziertere Sender, gekoppelt mit empfindlicheren Empfängern, die Signalphasen unterscheiden können. Mehrere Antennen ermöglichen mehr gerichtete Übertragung und bessere Rauschunterdrückung. Es gab * viele * Verbesserungen bei der Signalqualität und bei der Verwendung der Signale. Neuere Technologien ermöglichen es uns immer, das, was wir haben, effektiver und effizienter einzusetzen. Mokubai vor 6 Jahren 0

1 Antwort auf die Frage

1
Spiff

We don't use the same frequencies or channels. 802.11ac uses 5GHz exclusively, and typically uses 80MHz-wide channels, whereas 802.11b used 2.4GHz exclusively, and used 20MHz-wide channels.

Basically, speed improvements have come from 3 sources:

  • Modulation improvements. Fancier signaling schemes allowing more bits to be sent per "symbol" or per unit of time. After 802.11g (2003) these improvements have been modest compared to the other two below.
  • Channel width doubling, quadrupling, and future potential octupling. 802.11n can use 40MHz-wide channels, 802.11ac can use 80MHz-wide channels, and may expand in the future to 160MHz-wide channels. Doubling the channel width also allows efficiency gains so you get slightly better than a 2x speedup.
  • Adding a second, third, fourth...and potentially up to eighth radio chain. 2x the radio chains can mean 2x the speed, 3x radios means 3x speed, etc.

Here's a more detailed summary of how each generation of 802.11 has gotten its speed increase:

  • 802.11-1997 DSSS: This is the baseline at 1 and 2 Mbps via DBPSK and DQPSK modulation. 20MHz-wide channels in 2.4GHz.
  • 802.11b (1999): Added 5.5 and 11 Mbps via modulation improvements (CCK). The spec contained provisions for a 22 Mbps modulation, but it was encumbered by Texas Instruments patents, and very few vendors licensed the 22Mbps mode from TI.
  • 802.11a/g (2002/2003): Added several rates up to 54 Mbps. Cheated the Shannon Limit by stuffing 48 orthogonal subcarriers into the same 20MHz-wide channel. Added 16-QAM and 64-QAM modulation.
  • 802.11n (2007): Doubled channel width to 40MHz. Added MIMO (multiple transmit and receive radio chains, multiple "spatial streams"). Added a faster coding rate for 64-QAM. Note that when operating in 20MHz channels with only a single radio chain (for maximum comparability to 802.11a/b/g), 802.11n's modulation improvements only allowed it to get to 72.2 Mbps, so not that much higher than a/g's 54 Mbps. 802.11n's big speed advancements were mostly from doubling the channel width, and from doubling, tripling, or potentially quadrupling the number of radios (radio chains) on each end of the link. The spec contained provisions for up to 4 spatial streams (4x4:4) for a 600Mbps PHY rate, but I'm not aware of anyone shipping a 4 spatial stream 802.11n chipset.
  • 802.11ac (2012/2013): Doubled channel width again to 80MHz. Added 256-QAM modulation. The spec contains provisions for another channel width doubling to 160MHz, and up to 8 spatial streams (8x8:8), for a nearly 7 Gbps max PHY rate, but I'm not aware of anyone shipping anything better than 4x4:4 in 80MHz-wide channels as of spring 2017. Just like 802.11ac came along and took away the need to do 4x4:4 in 802.11n, it looks like 802.11ax may come along and provide newer/better/more-practical ways to do faster data rates, so I doubt we'll see anyone actually ship 8x8:8 in 160MHz (7 Gbps) 802.11ac. Also note that if we limit 802.11ac to a single radio chain in a 20MHz-wide channel, it only gets 86.7 Mbps, because its only advantage is 256-QAM modulation.

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