A comparison of wi-fi and wimax with case studies - Florida State ...

for the channel, timing and fine frequency offset estimation. The Head contains two parts, the
signal and data’s service section. The head is 40 bits long (signal is 24 bits plus service 16 bits).
The signal field is always transmitted with BPSK at 6 Mbps.
Figure 3-11 OFDM PLCP Structure
In the OFDM-PMD sub-layer, to maintain the speed 6, 12 and 24 Mbps is required. An
operation channel (20 MHz bandwidth) is divided into 52 sub-channels (sub-carriers). Four of
them are pilot carriers; the rest of the 48 sub-channels are used to transmit data. The data will be
divided and modulated into sub-channels, then transmitted parallel. [17][21][29]
3.3.1.6. IEEE 802.11g and the Physical Layer
3.3.1.6.1. Background and Backward Compatibility
As 802.11b became more and more popular, people started to notice the convenience of
wireless LAN. At that time, 802.11b could only provide a maximum 11Mbps. Compared to
Ethernet, this was not a good performance – it was just barely acceptable. When 802.11a started
to join the market, end users also wanted 802.11b to become faster. In fact, 54 Mbps really was
not very fast and most of the time, in a wonderful environment, the performance could only
achieve 50% of the possible speed. However WLAN has its own advantages and “wireless” has
become a trend gradually. Under these conditions, 802.11g is the answer. It has the same speed
with 802.11a, but it has a longer area of coverage. Moreover, it operates in the 2.4 GHz band.
According to 802.11g clause, this standard is not a “new” standard. It is an integrated
standard using many existing technologies. Its physical layer is called ERP (Extended Rate PHY)
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