Shulou(Shulou.com)06/01 Report--

The first part records the foundation of WLAN wireless network. This article writes about the communication foundation of WLAN.

First of all, WLAN is a kind of radio communication technology, which should talk about the working frequency.

Now the working frequency of WLAN is mainly concentrated in two main bands, 2.4GHz and 5GHz. Why are these two main bands used? This is mainly because these two bands are open to all countries free of charge.

The 2.400-2.500GHz and ISM bands mean Industrial, Scientific and Medical bands respectively in Chinese, so as the name implies, the ISM band is open to industrial, scientific and medical institutions free of charge. There is no need to obtain a license in advance to use these frequency bands, only to comply with certain transmission power requirements and not to cause interference to other frequency bands.

5.000-5.875GHZz, this band mainly consists of U-NII and ISM bands. U-NII, or Unlicensed National Information Infrastructure (U-NII), translates to the National Information Infrastructure (U-NII) band without permission.

UNII-1,5.150-5.250 GHz (100 MHz)

UNII-2,5.250 GHz-5.350 GHz (100 MHz)

UNII-2e,5.470 GHz-5.725 GHz (5.725 MHz)

UNII-3,5.725 GHz-5.850 GHz (125MHz)

ISM,5.725 GHz-5.875 GHz (150 MHz)

Secondly, the channel of signal transmission

In the working band mentioned above, WLAN uses different channels to transmit.

WLAN channels in 2.4GHz include CH1 (2.412GHz), CH2 (2.417GHz), CH3 (2.422GHz), CH4 (2.427GHz), CH5 (2.432GHz), CH6 (2.437GHz), CH7 (2.442GHz), CH8 (2.447GHz), CH9 (2.452GHz), CH10 (2.457GHz), CH11 (2.462GHz), CH12 (2.467GHz), CH13 (2.472GHz), CH14 (2.484GHz)

The channels used by WLAN in 5.GHz are

UNII-1:CH36 (5.180GHz), CH40 (5.200GHz), CH44 (5.220GHz), CH48 (5.240GHz)

UNII-2:CH52 (5.260GHz), CH56 (5.280GHz), CH60 (5.300GHz), CH64 (5.320GHz)

UNII-2e:CH100 (5.500GHz), CH104 (5.520GHz), CH108 (5.540GHz), CH112 (5.560GHz), CH116 (5.580GHz), CH120 (5.600GHz), CH124 (5.620GHz), CH128 (5.640GHz), CH132 (5.660GHz), CH136 (5.680GHz), CH140 (5.700GHz), CH144 (5.720GHz)

UNII-3:CH149 (5.745GHz), CH153 (5.765GHz), CH157 (5.785GHz), CH161 (5.805GHz), CH165 (5.825GHz)

ISM:CH149 (5.745GHz), CH153 (5.765GHz), CH157 (5.785GHz), CH161 (5.805GHz), CH165 (5.825GHz)

Third, let's talk about how information is transmitted. Let's start with two-week basic spread spectrum technology.

In computer language, binary we have to mention, the so-called binary is to use 0 and 1 to represent information.

FHSS, or Frequency-Hopping Spread Spectrum, or frequency hopping spread spectrum in Chinese, is a kind of spread spectrum technology, which quickly switches between different frequencies via carrier and uses a pseudorandom process at the same time at the receiver and transmitter.

DSSS, namely Direct-Sequence Spread Spectrum, is called direct sequence spread spectrum in Chinese, or direct spread spectrum (DS) for short, is a modulation technology. At the transmitting end, the spectrum of the signal is spread directly with a high bit rate spreading code sequence, and at the receiving end, the signal is despreaded with the same spreading code sequence, and the broadened signal is restored to the original state. The "spread spectrum" in its name comes from the fact that the transmission frequency of the carrier signal generating device is full of the entire bandwidth (spectrum).

OFDM, namely Orthogonal frequency-division multiplexing, is called orthogonal frequency division multiplexing in Chinese, sometimes it is also called separated multi-frequency modulation technology. Here OFDM is not spread spectrum technology, because it uses a large number of adjacent orthogonal subcarriers (Orthogonal sub-carrier), each subcarrier uses the traditional modulation scheme for low symbol rate modulation. It can be regarded as a combination of modulation technology and multiplexing technology. It can be regarded as a special case of multicarrier transmission, which has the ability of high-speed data transmission and can effectively combat frequency selective attenuation, so it has been gradually valued and adopted.

After talking about spread spectrum technology, let's talk about coding and modulation.

Coding is the process of converting information from one form or format to another. Decoding is the inverse process of coding. Because 802.11 wireless transmission is vulnerable to interference, resulting in data destruction, in order to reduce the data received due to RF interference in the process of transmission and can not be recovered, each effective data bit will be encoded and transmitted as multiple bits.

Modulation is a technique that mixes one or more periodic carriers into the signal to be transmitted, which is often used in radio wave propagation and communication, data communication using telephone lines, and so on. Different modulations are techniques that synthesize signals and carriers in different ways. The inverse process of modulation is called "demodulation", which is used to decipher the original signal.

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