Things you must not know about WiFi
- Categories:Technical Topics
- Time of issue:2018-02-01 16:36
Things you must not know about WiFi
The editor is very long-winded, let's take you through more than 100 years ago, starting from the touching love story of Jack and Rose.
April 14, 1912.
22:55: The Californian near the Titanic found an iceberg ahead and issued a warning to all nearby sailing ships. When the radio signal reached the Titanic, the iceberg warning was interrupted and a rude response was given: " Don't bother! Stop it! You have interfered with my signal! I am sending a telegram to Cape Rais!"
Because at that time, the telegrapher of the Titanic was busy helping the passengers to send telegrams to Cape Reese.
23:30: The Californian telegrapher turns off the telegraph and gets off work and takes a break.
11:40: The Titanic hits an iceberg.
After Heinrich Hertz invented radio waves in 1887, radio was first used for navigation. Maritime wireless telegraphy, hailed as the first killer application of wireless technology, was messed up this time.
At that time, the wireless telegraphy used a spark-gap transmitter, which was mainly used to transmit Morse code. Strictly speaking, it is an ultra-wideband UWB wireless technology. It occupies the entire frequency band and puts all the transmitting and receiving devices in a shared channel. The telegrapher can only listen before sending signals (this is probably the earliest listen before talk mechanism).
Objectively speaking, it was already a very advanced technology at the time, but its shortcomings were also very prominent. For example, encountering the very busy and rude Titanic telegraph operator, the trouble is big.
Later, people invented the resonant circuit, which can choose to receive signals in a specific frequency band, and radio receivers can distinguish signals at different frequencies.
At the same time, with the advent of AM (Amplitude Modulation) technology, people can listen to music and sound through AM radio. In the 1920s, AM radio stations sprung up like mushrooms.
The problem comes again.
The more radio stations there are, the more and more serious wireless interference becomes. The radio broadcasts in some cities are almost paralyzed and cannot be listened to at all.
The government began to regulate wireless broadcasting and issued authorized frequency bands.
This is the origin of the spectrum authorization system.
Later, FM and TV signals were also included in the spectrum authorization system. In the 1970s, with the rise of two-way wireless transmission technology (both radio and television broadcasts belong to one-way wireless transmission), the spectrum authorization scope was expanded to the field of cellular mobile communications.
However, the original spectrum authorization system was very crude.
In the United States, the government issued a decree that requires all wireless devices to obtain spectrum authorization and restricts the range of wireless signal propagation. There was also a joke: As AM signals travel farther at night, in order to control cross-area coverage, many radio stations have to turn off signal transmission when night falls.
What a psychological shadow of these radio stations!
Later, the FCC (U.S. Communications Commission) finally let go. This decree only applies to those wireless devices that have high transmit power and interfere with other wireless signals. This decision has also been recognized by other countries in the world: devices with low transmit power can work on unlicensed spectrum.
There is finally unlicensed spectrum in the world!
Although the FCC opened a window to unlicensed spectrum, the development of unlicensed spectrum equipment was slow before the 1980s, and there were very few communication devices, that is, some applications such as automatic garage doors and analog cordless phones. The main reason is that in order to fully protect the licensed spectrum from interference, the FCC is very conservative on the transmission power limits of these unlicensed spectrum devices.
Since 1980, the world of wireless communication has begun to change.
At this time, with the development and application of technologies such as microcircuits and digital signal processing, the cost of wireless devices has been greatly reduced.
At this time, a figure called the "Godfather of WiFi" appeared.
The godfather of WiFi-Michael Marcus, then an FCC engineer, one day, he made a suggestion to his boss: I hope that some unlicensed spectrum can be used for communication, and the transmission power of these unlicensed spectrum devices should be appropriately increased to make it It can cover a range of tens to hundreds of meters, which will encourage technology companies to innovate more and bring more economic benefits.
The FCC adopted Michael Marcus's suggestions and sought comments from all walks of life. The feedback was completely irresponsible:
As long as you don't occupy my frequency band, you can play whatever you want!
This is difficult to handle, and no one wants to release the frequency band in their hands.
The FCC can only "tactfully" release three unpopular "junk bands" for unlicensed spectrum communications. These three frequency bands include the 2.4GHz and 5.8GHz bands of today's WiFi. At the time, none of these "junk bands" were used for communications, but for other applications, such as microwave ovens that use radio waves to heat food.
In terms of equipment transmission power, the FCC stipulates that these new unlicensed frequency bands can reach 1W. Although only 1W, this is an unprecedented step in the history of human communication. No one thought that this 1W, these frequency bands used in microwave ovens, made today's various short-distance spread spectrum communication technologies such as WiFi, Bluetooth, and ZigBee.
In order to avoid interference between devices, the FCC also requires products in these new unlicensed frequency bands to use spread spectrum technology. The so-called spread spectrum technology means that the bandwidth used to transmit information is much larger than the bandwidth of the information itself. Spread-spectrum modulation is performed at the transmitting end with spread-spectrum coding, and the relevant demodulation technology is used at the receiving end to receive information. Spread spectrum technology was first applied in the military field, with high reliability, high confidentiality and not easily interfered.
Although it seems today that the FCC has a foresight in this new regulation, nothing happened afterwards. A dead letter cannot promote the development of communication technology.
What is driving WiFi to become a widely adopted standard?
At first, there was no uniform standard in the entire industry. LAN wireless product and equipment vendors such as Proxim and Symbol all worked on their own, specializing in their own special equipment. No one is a bird, and the equipment between different manufacturers is simply incompatible. .
In 1980, under the lobbying of 3com, the Ethernet standard was promulgated, and it succeeded like a spring tide. Encouraged by the successful case of the wired network standard ---- Ethernet, several equipment manufacturers began to realize the necessity of establishing a unified wireless standard.
In 1988, NCR wanted to use unlicensed frequency bands to make wireless cash registers (NCR was the first company in the world to make mechanical and electric cash registers). NCR approached their engineer Victor Hayes and asked him what the matter should be. How to do?
Victor Hayes believes that there must first be a unified standard. Victor Hayes approached IEEE with Bruce Tuch, another engineer at Bell Labs, hoping to establish a common unlicensed spectrum standard. Thus, the IEEE established the 802.11 working group, chaired by Victor Hayes.
The next story is still very tortuous.
The fragmented market of unified technology is a very tortuous and long process, just like within 3GPP, there are endless debates and fierce tears. At that time, the definition of each standard needed to be approved by 75% of the members.
Finally, in 1997, the IEEE 802.11 working group reached a consensus on the basic standard. It defines a data transmission rate of 2Mbps and uses two spread spectrum techniques: frequency hopping and direct sequence spread spectrum.
After the standard was introduced, engineers began to verify on various prototypes. In this process, two different standard versions were produced: 802.11b (working in the 2.4GHz band) and 802.11a (working in the 5.8GHz band), which were approved in December 1999 and January 2000, respectively.
Some companies found that this standard is too complicated when testing 802.11b compatible devices. The Nima standard has more than 400 pages, and it is difficult to solve the compatibility problems of devices between different manufacturers. In August 1999, in order to promote the IEEE 802.11b standard, six companies including Intersil, 3Com, Nokia, Aironet, Symbol and Lucent formed the Wireless Ethernet Compatibility Alliance (WECA).
This is the predecessor of the WiFi Alliance. In October 2002, it was renamed the Wi-Fi Alliance (Wi-Fi Alliance). The main purpose of WECA was to carry out compatibility certification for products of different manufacturers and to achieve interoperability between equipment of different manufacturers.
The alliance was established, but for the market to accept it, it first needs a strong name. "WECA compatible" and "IEEE802.11b compatible" are difficult to make people blurt out. For this matter, they also consulted brand experts, who gave them many suggestions, such as "FlankSpeed", "DragonFly" and so on.
In the end, "Wi-Fi" won. The reason why it is called "WiFi" is because it sounds a bit like "HiFi", which makes people think that CD players from different manufacturers can be compatible with any power amplifier device. Later, someone said that "WiFi" is the abbreviation of "wireless fidelity", which is actually just what people later imagined.
Technology has been standardized, and there is a resounding name. Now, WiFi needs to hold your thigh.
The Wi-Fi Alliance found Apple, hoping that their products can introduce WiFi. Apple is very powerful, and the same is true in 10 years. They told Lucent: If the price of your wireless adapter can drop below $100, we can consider designing a WiFi slot in our laptop.
In July 1999, Apple introduced WiFi for the first time in its new generation of iBook notebooks, but it is not a standard configuration, but an option.
However, it is this "optional" that quickly attracted other computer manufacturers to follow suit. Since then, the wireless network landscape has continued to expand until today, WiFi is in full swing.
WiFi quickly occupied the home broadband market, and began to move from home to public places. Some coffee shops, shops, etc. began to have wireless hotspots to provide free WiFi access. At this time, the EEE802.11 working group re-adjusted the IEEE802.11 protocol standard and introduced a new physical layer standard IEEE802.11g, which uses a more advanced spread spectrum technology called Orthogonal Frequency Division Multiplexing (OFDM) modulation technology. Its rate can reach 54Mbps on the 2.4GHz frequency band.
WiFi is a success, some people say it is a miracle in wireless history. WiFi is considered by many to be a disruptor of the rules of the game. From the day it was born, it has planted the disruptor gene. It has overturned the "crude" spectrum authorization system and created a vast space between technology and regulations.
This success has left countless people with a huge space for beautiful imagination, yes, it seems that everything is possible.
Rule makers and technical experts began to rethink the spectrum authorization system.
With the transition from traditional analog TV to digital TV, some frequency resources in the licensed frequency bands originally allocated to broadcast TV are released, but are not actually used. These frequency bands are called White Space (TVWS). Encouraged by the success of WiFi, the FCC considers making full use of White Space, exempting these frequency bands from authorization, and everyone can use it, hoping to trigger a new wave of wireless innovation.
In order to avoid White Space’s interference with the licensed TV frequency bands in use, around 2000, advocates envisaged two sets of solutions: One is to establish a national white spectrum database, and TVWS terminals determine which frequency band to use by querying the database. According to the location of the TVWS terminal, the database tells the TVWS terminal which frequency bands are free and available; another solution is that the TVWS terminal senses its location's spectrum status through cognitive radio technology and selects an available channel.
It is said that the radio and television also considered this kind of scheme. (Nonsense, don't believe it!)
Subsequently, Google plans to build White Space into super wifi (super wifi) and established the "White Space Alliance" because this frequency band has wider coverage and stronger penetration.
Yes, the territory of WiFi continues to expand. It has moved from homes to commercial venues. This gives enthusiastic supporters of WiFi see boundless hope. They dream of WiFi moving from indoors to outdoors, sweeping away all other wireless communication technologies.
The objects they want to subvert also include cellular mobile communication technologies, such as 3G/4G technology.
In June 2004, the IEEE formally approved the 802.16 standard, and the WiMAX Forum promoted this standard. WiMAX is called the wide-area coverage version of WiFi. At that time, the maximum rate of WiMAX was up to 70Mbps, and the maximum coverage was 50 kilometers, achieving carpet-like coverage like 3G technology.
WIMAX has received full support from giants such as Intel, Motor, Nortel, and successfully squeezed into the fourth international 3G standard.
The latter thing is well known.
Nortel sold WCDMA and started playing WiMAX. It went bankrupt by accident!
Intel announced the abolition of the WiMAX division.
Subsequently, Japan quickly switched to TDD, and South Korea was not slow. Taiwan, which wanted to stay the course to the end, finally couldn't hold it anymore, holding the wall towards LTE. \Looking back on this history, the editor would once again pay tribute to those great wireless pioneers. They have done a lot of things and screwed up a lot of things, but what does it matter? We don’t judge heroes by success or failure. Behind WiFi, I saw the fanaticism and innovation in technology, and the subversion of the rules of the game.
In addition, I have also seen the importance of unified standards. It is no exaggeration to say that technology cannot control the market. There is nothing that can't be broken by technological fragmentation. Only standards and alliances can create a market.
Today, 5G is coming. Although the industry is calling for tolerance and unity, who knows how many more stories will be staged?