The CWNA exam exists of some MCS questions. In this article i’ll explain you how to memorize this table without much hassle.
This table only takes 802.11n rates into account. I’ll might update the table on a later stage to include the 802.11ac MCS ratest, however to memorize it, there’s no need to add the 802.11ac rates.
The only rates you should truly memorize are the ones in MCS0.
These are 6.5, 7.2, 13.5 and 15.
All calculations can be made with these values.
The rule of thumb is the following formulate. BPSK+ BPSK +BPSK +BPSK +QPSK +QPSK +BPSK +BPKS +BPSK (or simply B+ (B+B+B+Q+Q+B+B)).
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I would like to know the MCS6 rate of a 20Mhz Short GI rate, then you apply the following rule:
B+ (B+B+B+Q+Q+B) = 7.2 (+7.2 + 7.2 +7.2 + 14.4 +14.4 + 7.2) = 64.8 which rounds up to 65!
If you want to calculate the MCS7 rate of a 40Mhz LONG GI, this is even easier. You start with the BPSK of the 40Mhz LONG GI and multiply it with 10.
MCS0 of 40Mhz LONG GI = 13.5 * 10 = 135 !
The above rules are only for 1 spatial streams. If you go higher and need to calculate 2 spatial streams (eg MCS 13 for 40Mhz LONG GI), you double the initial BPSK value for the 40Mhz LONG GI and again use the formula B +( B +B +B +Q +Q +B +B).
For ex MCS 14 with 40Mhz and a LONG GI =
2*B +( 2B +2B +2B + 2Q +2Q +2B) =
(2*13.5) +((2*13.5) +(2*13.5) +(2*13.5) +(2*27) +(2*27) +(2*13.5)) =
27 +27 +27 +27 +54 +54 +27 = 243 !
- CWNA notes part 1 : 802.11 standards
- Free CWNA support and design booklet