HISTORY OF WIFI PART 1
1. Introduction Wireless LAN Network (Local network without cables)
We already know and know about Local Area Network (LAN), where it is a network formed from a combination of several computers connected via a physical channel (cable). Along with the development of technology and the need for mobile network access (moving) that does not require the cable as a transmission medium, it appears Wireless Local Area Network (Wireless LAN / WLAN).
A wireless local network or WLAN is a wireless local area network where the transmission media uses radio frequency (RF) and infrared (IR), to provide a network connection to all users within the immediate area.The coverage area can be spaced from classrooms to the entire campus or from offices to other offices and different buildings. Devices commonly used for WLAN networks include PCs, Laptops, PDAs, cell phones, and so on. This WLAN technology has a lot of usabilities. For example, mobile users can use their mobile phones to access e-mail.Meanwhile, travelers with their laptops can connect to the internet while they're at airports, cafes, trains and other public places.
The specification used in WLANs is 802.11 from the IEEE where it is also commonly referred to as the standard WiFi (Wireless Fidelity) associated with data access speeds. There are several types of 802.11 specifications of 802.11b, 802.11g, 802.11a, and 802.11n as shown in the following table:
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| Table 1. Specification of 802.11 |
2. History of Wireless LAN
In the late 1970s IBM released their experimental results in designing WLANs with IR technology, other companies such as Hewlett-Packard (HP) tested WLANs with RF. Both companies only achieve 100 Kbps data rate. Because it does not meet IEEE 802 standards for LAN that are 1 Mbps then the product is not marketed. New in 1985, (FCC) established the Industrial, Scientific, and Medical (ISM band) bands of 902-928 MHz, 2400-2483.5 MHz and 5725-5850 MHz unlicensed so that commercial WLAN development enters a serious stage. It was not until 1990 that WLANs could be marketed using products using spread spectrum (SS) techniques on the ISM band, licensed 18-19 GHz frequencies and IR technology with data rate> 1 Mbps.
In 1997, an independent agency called IEEE created the first WLAN specification/standard coded 802.11. Equipment that complies with the 802.11 standard works on a 2.4GHz frequency, and a maximum theoretical throughput rate of 2Mbps.
In July 1999, the IEEE re-issued a new specification named 802.11b. The maximum theoretical data transfer speed that can be achieved is 11 Mbps. The data transfer rate of this magnitude is proportional to traditional Ethernet (IEEE 802.3 10Mbps or 10Base-T). Equipment that uses the 802.11b standard also works on a 2.4GHz frequency. One drawback of wireless equipment working at this frequency is the possibility of interference with cordless phones, microwave ovens or other equipment that uses radio waves of the same frequency.
At almost the same time, IEEE makes 802.11a specifications that use different techniques. The frequency used is 5Ghz and supports maximum theoretical data transfer speeds up to 54Mbps. Radio waves emitted by 802.11a equipment are relatively difficult to penetrate walls or other obstructions. The range of radio waves is relatively shorter than 802.11b. Technically, 802.11b is not compatible with 802.11a. But at this time quite a lot of hardware manufacturers that make equipment that supports both standards.
In 2002, IEEE created a new specification that could combine the advantages of 802.11b and 802.11a. The 802.11g coded specification works on a 2.4GHz frequency with a maximum theoretical data transfer rate of 54Mbps. 802.11g equipment is compatible with 802.11b so it can be interchangeable. Let's say a computer that uses 802.11g network card can take advantage of the 802.11b access point, and vice versa.
In 2006, 802.11n was developed by incorporating 802.11b, 802.11g technology. The technology is known as MIMO (Multiple Input Multiple Output) is the latest Wi-Fi technology. MIMO is based on the Pre-802.11n specification. The word "Pre-" states "Prestandard versions of 802.11n".MIMO offers increased throughput, reliability advantages, and increased number of connected clients. MIMO's penetrating power of the barrier is better, in addition to its wider reach so you can place your laptop or Wi-Fi client at will. Access Point MIMO can reach various Wi-Fi equipment available in every corner of the room. Technically MIMO is superior to its elder brother 802.11a / b / g. The Access Point MIMO can recognize radio waves emitted by the Wi-Fi 802.11a / b / g adapter. MIMO supports backward compatibility with 802.11 a / b / g. MIMO Wi-Fi equipment can generate data transfer speeds of 108Mbps.
3. WLAN Transmission Media
There are 2 transmission media used by this wireless local network that is:
3.1. Radio Frequency (RF)
The use of RF is no stranger to us, examples of its use are on radio stations, TV stations, cordless phones etc. RF is always faced with a limited spectrum problem, so it should be considered how to efficiently utilize the spectrum. WLAN uses RF as a transmission medium because its range is far away, can penetrate the wall, support high mobility, the cover area much better than IR and can be used outdoors. WLANs, here, use the ISM band (Table 2) and utilize spread spectrum (DS or FH) techniques.
* DS is a technique that modulates the information signal directly with certain codes (pseudo code line / PN with chip unit).
* FH is a technique that modulates information signals with frequency jumps (not constant). This variable frequency is chosen by certain codes (PN)
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| Table 2. ISM Bands. |
3.2. Infrared (IR)
Infrared is widely used in close-range communication, the most common example of IR usage is the remote control (for television). IR waves are easy to make, cheap, more directional, cannot penetrate walls or dark objects, have high power fluctuations and can be interfered with sunlight. The IR sender and receiver uses Light Emitting Diode (LED) and Photo Sensitive Diode (PSD). WLAN uses IR as a transmission medium because IR can offer high data rate (100s Mbps), its power consumption is small and its price is cheap. WLANs with IRs have three kinds of techniques: Directed Beam IR (DBIR), Diffused IR (DFIR) and Quasi Diffused IR (QDIR).
1. DFIR
This technique utilizes communication through reflection. The advantage is not requiring Line Of Sight (LOS) between the sender and receiver and creating terminal portables. The disadvantage is that it requires high power, a data rate is limited by multipath, dangerous for the naked eye and the risk of interference in the simultaneous state is high.
2. DBIR
This technique uses the principle of LOS, so the direction of radiation must be arranged. The advantages are low power consumption, high data rate and no multipath. The downside is the terminal must be fixed and the communication must be LOS.
3. QDIR
Each terminal communicates with a reflector so that the radiation pattern must be directional. QDIR is located between DFIR and DBIR (power consumption is smaller than DFIR and runs much longer than DBIR)Click here to open HISTORY OF WIFI PART 2
Source: Google