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Wi-Fi (802.11) PHY Data Rates

 Tech  1121  6 分钟

Modulation with DSSS/CCK

DSSS/CCK data symbol is formed by spreading and modulating the data bits. The data rate depends on:

  • Chips per second (CSec) = 11,000,000

  • Chips per symbol (CSym) = 11 (DSSS) or 8 (DSSS with CCK)

  • Bits per symbol (NBits) = 1 or 2 (DSSS), 4 or 8 (DSSS with CCK)

Wi-Fi 0 and 1 use this technology.

  • Wi-Fi 0

    • IEEE standard: 802.11 (1997)
    • Maximum link rate (Mbit/s): 1 to 2
    • Radio frequency (GHz): 2.4

  • Wi-Fi 1

    • IEEE standard: 802.11b (1999)
    • Maximum link rate (Mbit/s): 1 to 11
    • Radio frequency (GHz): 2.4
Chips per second Chips per symbol Bits per symbol Data Rate (Mbps)
11,000,000 11 1 1
11,000,000 11 2 2
11,000,000 8 4 5.5
11,000,000 8 8 11

Modulation with OFDM

DSSS/CCK uses the entire available bandwidth as one single channel. OFDM divides the channel into multiple(overlapping) sub-channels. The data rate depends on:

  • Symbol duration (in other words symbols per second) (SDur)

    • Symbol duration depends on "Guard Interval" between symbols.

    • OFDM Symbol Duration is 3.2us and Guard Interval Duration is 0.4us or 0.8us, so SDur is equal 3.6us or 4us

  • Bits per symbol (NBits)

  • Coding rate (CRate)

    • Some bits are used for error correction and do not carry data

  • Number of sub-channels (NChan)

    • Depends on channel width(20/40/80/160)

    • 11n/11ac have more sub-channels in the same bandwidth compared to 11a/11g

The formula for data rate is:

​ $Data Rate = (1/SDur)\times(NBits\times CRate)\times NChan$

11a/11g

  • Wi-Fi 2

    • IEEE standard: 802.11a (1999)
    • Maximum link rate (Mbit/s): 6 to 54
    • Radio frequency (GHz): 5

  • Wi-Fi 3

    • IEEE standard: 802.11g (2003)
    • Maximum link rate (Mbit/s): 6 to 54
    • Radio frequency (GHz): 2.4
Modulation NBits CRate NChan SDur (micro sec) Data Rate (Mbps)
BPSK 1 1/2 48 4 6
BPSK 1 3/4 48 4 9
QPSK 2 1/2 48 4 12
QPSK 2 3/4 48 4 18
16-QAM 4 1/2 48 4 24
16-QAM 4 3/4 48 4 36
64-QAM 6 2/3 48 4 48
64-QAM 6 3/4 48 4 54

Note: The above table shows date rates for 20MHz channel width. 5,10 MHz channel widths are not shown.

11n/11ac

  • Wi-Fi 4
    • IEEE standard: 802.11n (2008)
    • Maximum link rate (Mbit/s): 72 to 600
    • Radio frequency (GHz): 2.4/5
Channel Width NBits CRate NChan Data Rate (Mbps) SDur=3.6us (Nss=1) 11n Max Rate (Nss=4)
20 Mhz 6 5/6 52 72.2 288.8
40 Mhz 6 5/6 108 150 600

  • Wi-Fi 5

    • IEEE standard: 802.11ac (2014)

    • Maximum link rate (Mbit/s): 433 to 6933

    • Radio frequency (GHz): 5

Channel Width NBits CRate NChan Data Rate (Mbps) SDur=3.6us (Nss=1) 11ac Max Rate (Nss=8)
20 Mhz 8 5/6 52 96.3 577.8 (Nss=6)
40 Mhz 8 5/6 108 200 1600
80 Mhz 8 5/6 234 433.3 3467
160 Mhz 8 5/6 468 866.7 6933

Modulation with OFDMA

There are some chagne in OFDMA compared to OFDM:

  • A new symbol duration is used: 12.8µs

  • Different Guard Intervals are used: 0.8µs, 1.6µs and 3.2µs

  • The size and number of data subcarriers is not the same (especially with the different RU sizes introduced by OFDMA).

  • Wi-Fi 6

    • IEEE standard: 802.11ax (2019)
    • Maximum link rate (Mbit/s): 574 to 9608
    • Radio frequency (GHz): 2.4/5/6
    • 6GHz only avaliable in Wi-Fi 6E proposed at 2020
Channel Width NBits CRate NChan Data Rate (Mbps) SDur=13.6us (Nss=2) 11ax Max Rate (Nss=8)
20 Mhz 10 5/6 234 287 1147
40 Mhz 10 5/6 468 574 2294
80 Mhz 10 5/6 980 1201 4804
160 Mhz 10 5/6 1960 2402 9608
  • Wi-Fi 7
    • IEEE standard: 802.11be (2024)
    • Maximum link rate (Mbit/s): 1376 to 46120
    • Radio frequency (GHz): 2.4/5/6
Channel Width NBits CRate NChan Data Rate (Mbps) SDur=13.6us (Nss=4) 11be Max Rate (Nss=16)
20 Mhz 12 5/6 234 688 2753
40 Mhz 12 5/6 468 1376 5506
80 Mhz 12 5/6 980 2882 11529
160 Mhz 12 5/6 1960 5765 23059
320 Mhz 12 5/6 3920 11529 46118
Generation NBits (log2) CRate Channel Width NChan Symbol Duration (micro sec) Number of Spatial Streams Data Rate (Mbps)
802.11a/g(2003) 6 3/4 20 MHz 48 4 1 54
802.11n(2008) 6 5/6 40 MHz 108 3.6 4 600
802.11ac(2014) 8 5/6 160 MHz 468 3.6 8 6933
802.11ax(2019) 10 5/6 160 MHz 1960 13.6 8 9608
802.11be(2024) 12 5/6 320 MHz 3920 13.6 16 46118

The parameters in the table are now represented as follows:

  • NBits (log2): number of bits used for modulation
  • CRate: rate at which redundant bits are added for error correction
  • Channel Width: bandwidth of the channel
  • NChan: number of non-overlapping channels available
  • Symbol Duration (micro sec): time taken for a symbol to be transmitted
  • Number of Spatial Streams: number of independent data streams that can be transmitted simultaneously
  • Data Rate: theoretical maximum data rate

MCS

MCS Index Modulation Scheme Bits per Symbol Coding Rate
0 BPSK 1 1/2
1 QPSK 2 1/2
2 QPSK 2 3/4
3 16-QAM 4 1/2
4 16-QAM 4 3/4
5 64-QAM 6 2/3
6 64-QAM 6 3/4
7 64-QAM 6 5/6
8 256-QAM 8 3/4
9 256-QAM 8 5/6
10 1024-QAM 10 3/4
11 1024-QAM 10 5/6
12 4096-QAM 12 3/4
13 4096-QAM 12 5/6

Advertised speeds for Xiaomi Router

Type 2.4 GHz band Mbit/s 2.4 GHz band config [all 40 MHz] 5 GHz band Mbit/s 5 GHz band config Remark
AC2100 300[1] 2 streams 1733 4 streams @ 80MHZ
AX1800 574 2 streams 1201 2 streams @ 80MHz
AX3000 574 2 streams 2402 2 streams @ 160MHz
AX5400 574 2 streams 4804 4 streams @ 160MHz
AX6000 574 2 streams 4804 4 streams @ 160MHz +AIoT:583[2]
AX6000 1148 4 streams 4804 4 streams @ 160MHz
AX9000 1148 4 streams 4804+2402 4 streams @ 160MHz+ 4 streams @80MHz[3] +AIoT:5832
BE10000 1376.4 4 streams 5764.8+2882.4 4 streams @ 160MHz+ 4 streams @80MHz3 @4096QAM

Reference

More to read

  1. 802.11ac specifies operation in the 5 GHz band, hence operation in the 2.4 GHz band is specified by 802.11n for 802.11ac. 

  2. By utilizing a dual-frequency design comprising of 2.4GHz (150Mbps at 802.11n@40MHz1) and 5GHz (433Mbps at 802.11ac@80MHz), the AIoT antenna is capable of adding 583Mbps speed. Nonetheless, it is not possible to have both the 574Mbps in 2.4GHz and the 150Mbps at the same time due to the limited availability of a 40MHz channel in 2.4GHz.  ↩︎

  3. Although the AX9000 and BE10000 routers enable dual-band connectivity in the 5GHz frequency range using channels in both the 5.2GHz and 5.8GHz bands, China has only one available 160MHz channel and it is in the 5.2GHz band. Therefore, having two 5GHz bands utilizing 160MHz channels simultaneously in this country is not feasible. Consequently, users in China must opt for a 160MHz + 80MHz channel configuration rather than a 160MHz + 160MHz combination.  ↩︎

updatedupdated2023-06-052023-06-05
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