SoFunction
Updated on 2025-04-09

Introduction to Wireless LAN

Wireless Local Area Networks (WLAN) is a very convenient data transmission system. It uses radio frequency (RF) technology to replace the old hindered twisted copper wire (Coaxial), so that wireless local area networks can use a simple access architecture to allow users to achieve the ideal state of "information is carried through it and convenient to travel around the world."


Why use wireless LAN

For one of the main tasks of local network management, time-consuming tasks such as laying cables or checking whether the cable is broken are easy to make people irritated, and it is not easy to find out where the broken wire is in a short time. Furthermore, due to the continuous updating and development of the enterprise and application environment, the original enterprise network must be re-layouted and the network lines need to be reinstalled. Although the cable itself is not expensive, the cost of hiring technicians to distribute wiring is very high, especially for old buildings, the wiring project costs are even higher. Therefore, setting up a wireless LAN is the best solution.


What are the situations that require wireless LAN

Wireless LAN is by no means used to replace wired LAN, but to make up for the shortcomings of wired LAN to achieve the purpose of network extension. The following situations may require wireless LAN.

◆ Users without fixed workplaces

◆ The establishment of wired LANs is subject to environmental restrictions

◆ As a backup system for wired LAN


Wireless LAN access technology

Currently, when manufacturers design wireless LAN products, there are quite a few access design methods, which can be roughly divided into three categories: Narrowband Microwave technology, Spread Spectrum technology, and Infrared technology. Each technology has its advantages and disadvantages, limitations, and comparison. Next is a detailed discussion of these technical methods.

Expanding technology

The wireless LAN products of spread frequency technology are based on ISM (Industrial Scientific, and Medical) stipulated by the FCC (Federal Communications Committee), with a frequency range of 902M~928MHz and 2.4G~2.484GHz, so there is no limit on so-called use authorization. Frequency spreading technology is mainly divided into two ways: "frequency hopping technology" and "direct sequence". These two technologies are technologies used by the army in World War II. The purpose is to maintain the stability and confidentiality of communication signals in a harsh war environment.

1. Frequency hopping technology (FHSS)

Frequency-Hoping Spread Spectrum (FHSS) receives both ends in synchronous and simultaneous manner to transmit signals with specific types of narrow frequency carriers. For a non-specific receiver, the jump signal generated by FHSS is only considered impulse noise to it. The signals deployed by the FHSS can be specially designed to avoid noise or non-repetitive channels of One-to-Many, and these frequency hopping signals must comply with the FCC requirements, using more than 75 frequency hopping signals, and the maximum time interval (Dwell Time) of frequency hopping to the next frequency is 400ms.

2. Direct Sequence Spreading Technology (DSSS)

Direct Sequence Spread Spectrum (DSSS) uses more than 10 chips to represent the "1" or "0" bits, so that the original higher power and narrower frequency becomes a low power frequency with a wider frequency. How many chips are used per bit is called Spreading chips. A higher Spreading chips can increase noise interference, while a lower Spreading Ration can increase the number of users.

Basically, Spreading Ration is quite small in DSSS, for example, in almost all 2.4GHz wireless LAN products, there are less than 20 Spreading Ration used. In the IEEE802.11 standard, its Spreading Ration is about 100.

3. Differences in FHSS VS DSSS modulation

The performance and capability differences of wireless LANs mainly depend on whether FHSS or DSSS is used to implement it, and the modulation method adopted. However, the choice of modulation method is not entirely arbitrary. For example, FHSS does not force a specific modulation method. Moreover, most existing FHSSs use certain different forms of GFSK, but the draft IEEE 802.11 stipulates that GFSK should be used. As for DSSS, by using variable phase modulation (such as PSK, QPSK, DQPSK), the highest reliability and high data rate performance can be achieved.

In terms of noise resistance, compared with FHSS using QPSK modulation method, it can be found that the advantages of these two different technologies have respectively. The reason why FHSS systems use FSK modulation is because of the simplicity of the inherent architecture of FHSS and FSK. The FSK wireless signal can use nonlinear power amplifiers, but this sacrifices the range of action and noise immunity. The DSSS system requires a slightly more expensive linear amplifier, but it can get more feedback.

4. Pros and cons of DSSS VS FHSS

Up to now, if you compare the existing product parameters in detail, it can be seen that DSSS technology has better advantages in applications that require optimal reliability, while FHSS technology has more advantages in applications that require low cost. Although we can see that various manufacturers speak in the Internet network, what we really need to pay attention to is that the choice of manufacturers in DSSS and FHSS frequency spreading technology must be carefully determined by the product's positioning in the market, because it can solve the transmission capabilities and characteristics of wireless local area networks, including: anti-interference ability, usage distance range, bandwidth size, and transmission data size.

Generally speaking, DSSS uses full-band data transmission and is faster, and the potential for developing higher transmission frequencies in the future is also greater. DSSS technology is suitable for applications in fixed environments or with high requirements for transmission quality. Therefore, applications such as wireless factories, wireless hospitals, network communities, and branch networking mostly use DSSS wireless technology products. FHSS is mostly used for endpoints that require fast movement. For example, mobile phones use FHSS technology in the wireless transmission technology part; and because the FHSS transmission range is small, in the same transmission environment, the FHSS technology equipment is often needed to be more FHSS technology equipment than DSSS technology equipment, and the overall price may also be higher. According to the current enterprise needs, high-speed mobile endpoints are less used, and most of them pay more attention to transmission rates and transmission stability. Therefore, the future development of wireless network products should be based on DSSS technology as the mainstream.


When purchasing wireless LANs, consumers need to pay special attention to the following features to determine their suitable products, including:

◎ Coverage scope;

◎ Transmission rate;

◎ The degree of influence of Multipath;

◎ Provide the degree of data integration;

◎ Interoperability with wired infrastructure;

◎ Interoperability with other wireless infrastructures;

◎ Anti-interference degree;

◎Simple and easy to operate;

◎ Confidentiality ability;

◎ Low cost;

◎ Current consumption.


Information about IEEE 802.11

In response to the strong demand for wireless LANs, the International Society of Electronic and Electrical Engineering in the United States held the 802.11 committee in November 1990 to begin formulating wireless LAN standards.

Inheriting the IEEE802 series, 802.11 regulates the medium access control (MAC) layer and physical (Physical; PHY) layer of wireless local area networks. This is more special because of the different actual wireless transmission methods. IEEE802.11 regulates various entity layers under the unified MAC layer to meet the current situation and future technological developments. Currently, three media entities have been formulated in 802.11, and for the expansion of future technology, they also provide the function of multiple rates (Mulitiple Rates). These three entities are:

1. 2.4GHz Direct Sequence Spread Spectrum

Use DBPSK to adjust the speed at 1Mbps (Difference By Phase Shift Keying)

DQPSK is used to adjust the speed at 2Mbps (Difference Quarter Phase Shift Keying)

Receive sensitivity –80dbm

Use Barker code of length 11 as the spread frequency PN code

2. 2.4GHz Frequency Hopping Spread Spectrum

Use 2-level GFSK to adjust the rate at 1Mbps, and the reception sensitivity is –80dbm,

At a rate of 2Mbps, use 4-level GFSK to adjust the reception sensitivity –75dbm,

Jump 2.5 hops per second

Hopping Sequence has 22 groups in Europe and the United States and 4 groups in Japan

3. Diffused IR

At 1Mbps, the speed is 16ppm, and the reception sensitivity is 2 × 10-5mW/square centimeter

At 2Mbps, the speed is 4ppm to adjust, and the reception sensitivity is 8 × 10-5mW/square centimeter

Wavelength 850nm~950nm

The first two RF methods at 2.4GHz are based on the ISM band, which can be used without authorization without authorization. The use of this band is open to major countries around the world, including the United States, Europe, Japan and *. The third item infrared ray is also free to use since there is no control (except for safety regulations) in use.

The basic access method of IEEE 802.11 MAC is called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), and it becomes Collision Avoidance with CSMA/CD (Collision Detection) used in Ethernet networks. The difference is very big. Because sensing carriers and collision detection are unreliable in wireless transmission, it is difficult to sense carriers. In addition, when the radio waves are usually sent out through the antenna, they cannot monitor them, so collision detection is essentially impossible. In 802.11, sense carriers are achieved in two ways. The first is to actually listen to whether there are radio waves transmitted and the concept of priority. The other is a virtual sensing carrier, which tells you how long it will take to send things to prevent collisions.


Product introduction of wireless LAN

Access Point
It is commonly known as a network bridge, as the name implies, as the name suggests, it is used as a bridge between traditional wired LAN and wireless LAN. Therefore, any PC equipped with a wireless network card can share resources of wired LAN or even wide area networks through AP. In addition, the AP itself also has the function of network management, which can be used as necessary control management for PCs connected to wireless network cards.

Wireless LAN Card
It is generally called a wireless network card. The difference between it and the traditional Ethernet network card is that the data transmission of the former is through radio waves, while the latter is through a general network line.

Currently, the specifications of wireless network cards can be roughly divided into three types: 2M, 5M, 11M, and the applicable interfaces can be divided into three types: PCMCIA, ISA, and PCI.

Antenna

Generally called an antenna. This antenna is different from the antenna used by general TV, ham family, and big brothers. The reason is that the frequency used by WLAN is in the higher 2.4GHz frequency band.

The function of an antenna is to transmit the source signal to a distance through the characteristics of the antenna itself. As for how far it can be transmitted, in addition to considering the output power strength of the source, another important factor is the dBi value of the antenna itself, which is commonly known as the gain value. The higher the dB value, the longer the distance it can be transmitted. Usually, every 8dB increase, the relative distance can be increased to half of the original distance.

Generally, antennas have so-called Uni-direction and Omni-direction. The former is more suitable for long-distance use, while the latter is more suitable for regional applications.


Product Q & A

Q1: What is wireless network?

ANS: Generally speaking, wireless, as the name suggests, uses radio waves as the transmission of data. However, at the application level, it is completely similar to a wired network. The biggest difference between the two is that the medium of transmitting data is different. In addition, because it is wireless, the maneuverability of hardware installation or use is much better than that of wired networks.



Q2: What are the advantages of wireless networks compared to wired networks?

ANS: Its mobility and convenience are beyond the reach of wired networks. In terms of cost, it can save a considerable wiring cost and modification and decoration cost, and basically the space used is much more flexible.



Q3: Will wireless network affect the human body?

ANS: Because the transmitting power of wireless networks is much weaker than that of ordinary mobile phones, the transmitting power of wireless networks is about 60~70mW, while the transmitting power of mobile phones is about 200mW, and the usage method is not like mobile phones that directly contact the human body, so there is no security consideration.



Q4: To build a wireless network, what are the most basic equipment?

ANS: Generally, the basic equipment for setting up wireless networks is a wireless network card and a bridge (AP), so that network resources can be shared in a wireless mode and with the existing wired architecture.



Q5: Will the use of wireless networks be interfered with or affect the operation of other devices?

ANS: Basically, the frequency band used by wireless networks belongs to the high frequency range of ISM 2.4GHz. Electrical equipment used in daily life, offices, etc. will not interfere with each other, because there are many frequency differences, and the wireless network itself has 12 channels for adjustment, so there is no need to worry about natural interference.



Q6: What is the ISM frequency band?

ANS: ISM (Industrial Scientific Medical) Band, this frequency band (2.4~2.4835GHz) is mainly open to three major institutions for industry, science, medicine. This frequency band is defined by the Federal Communications Commission (FCC) and belongs to Free License. There are no restrictions on so-called use authorization.



Q7: What is Spread Spectrum?

ANS: Frequency spreading technology is mainly divided into two ways: "frequency hopping technology" and "direct sequence". These two technologies are technologies used by the army in World War II. The purpose is to maintain the stability and confidentiality of communication signals in a harsh war environment. For a non-specific receiver, the jump signal generated by Spread Spectrum is only impulse noise. Therefore, it is a relatively safe communication technology overall.



Q8: What is frequency hopping (Frequency-Hoping Spread Spectru Article entry: aaadxmmm      Editor: aaadxmm