In 802.11, L-STF is used for signal detection, AGC, and Diversity Selection ( what is this) ?
It consists of 10 OFDM symbols (1,0,1,0,1,0,1,0,1,0) , each symbol is 0.8us, a total of 8us, equivalent to a slot size (9us). So the sub-carrier width is 1.25MHz with BPSK modulation. The rate is 6Mbps.
( How is this calculated? Isn't it 1*12/0.8=15Mbps? ) Note that the subcarriers used here are -24, -20, -16, -12, -8, -4, 4, 8, 12, 16, 20, 24, the interval is 4*312.5khz=1.25MHz, and a total of 12 subcarriers within 20MHz are used (64 in total, 12 used).
The L-LTF is composed of two symbols, each symbol is 3.2us, and the sub-carrier width is 312.5KHz. Compared with L-STF, its sub-carrier width is reduced, occupying -26-26 All sub-carriers, so more accurate frequency acquisition can be performed. And can perform channel estimation.
The Pilot subcarrier is a carrier other than the data carrier used to support channel decoding. Compared with 802.11a/g, 802.11n/ac has higher sub-carrier utilization. Under 80MHz bandwidth, the rate can be increased by 5 times compared with Legacy's 20MHz, and under 160MHz, it can be increased by nearly 10 times.
