OFDM — 802.11 Protocol Description
OFDM has been proposed in IEEE802.11a. Based on this method of modulation, we need to know what OFDM is to understand the different protocols.
What is OFDM?
OFDM is a special multi-carrier modulation technology. This technology aims to divide a channel into several orthogonal sub-channels, and then convert high-speed data signals into low-speed sub-data streams for parallel transmission, which are modulated and transmitted on each sub-channel. Each subcarrier is orthogonal to the other, and the frequency channels after spread spectrum modulation can overlap, reducing the interference between subcarriers and improving spectrum utilization.
How to understand orthogonal no interference: when one subcarrier reaches the peak, the amplitude of the other subcarrier is 0. That is, the two subcarriers are orthogonal without interference. As shown in the figure below, when the blue arrival amplitude is the highest, the other subcarrier is 0.
Also, OFDM can use subcarriers that overlap because subcarriers are defined in a way that makes them easy to tell apart.
The signal is divided into three subcarriers, from left to right. Each subcarrier peak is used for data coding, as shown in the red dot in the figure, which corresponds to the 0 scale line below. One reaches the peak, and the rest reaches 0. These subcarriers are deliberately designed to maintain an orthogonal relationship with each other. The peak of each subcarrier At this time, the amplitude of the other two subcarriers is 0.
5GHz OFDM channel:
The 5GHz channel has 52 subcarriers, and each subcarrier has 312.5 kHz. There are 48 channels for transmitting data, and 4 channels are used for phase reference.
The OFDM subchannel modulation technology uses QAM (QAM is the abbreviation of quadrature amplitude modulation, which is translated as “quadrature amplitude modulation” in Chinese). QAM uses the amplitude and phase of the carrier wave to transmit information.
The above is the knowledge explanation of the OFDM-802.11 protocol brought to you by Shenzhen HDV Phoelectron Technology Co., Ltd. hope this article can help you to increase your knowledge. Besides this article if you’re looking for a good optical fiber communication equipment manufacturer company you may consider about us.
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