Ralink RT2880 User Manual page 69

3. Guard Interval:
a. Definition:
T : 4 s
sym
T : 3.6 s ;Symbol interval of Short GI.
syms
b. Ratio of symbol interval on GI, refer to below EWC PHY
Tsym / Tsyms = 4 sec / 3.6 sec = 10/9
c. Example:
MCS=15, 40MHz Bandwidth, and 400ns Short Guard Interval.
270.0 * (10/9) = 300.0 for Short GI.
d. Reference:
1) IEEE 802.11n draft 2.04, page 316 and
Table 211—MCS parameters for optional
MCS
Modulation
Index
8 BPSK
9 QPSK
10 QPSK
11 16-QAM
12 16-QAM
13 64-QAM
14 64-QAM
;Symbol Interval
40 MHz, NSS = 2, NES = 1, EQM
R NBPSCS(iSS) NSD
1/2 1 108
1/2 2 108
3/4 2 108
1/2 4 108
3/4 4 108
2/3 6 108
3/4 6 108
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RALINK AP SDK 3.3.0.0 User's Manual
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NSP NCBPS NDBPS
6 216 108
6 432 216
6 432 324
6 864 432
6 864 648
6 1296 864
6 1296 972
Data rate (Mb/s)
800 ns 400 ns
GI GI
27.0 30.0
54.0 60.0
81.0 90.0
108.0 120.0
162.0 180.0
216.0 240.0
243.0 270.0