This paper is divided into three parts: firstly, the rapid development trend of wireless mobile communication and wired fixed communication is expounded; then
This paper focuses on the rapid development process and future trend of wireless mobile communication cellular network from analog to digital and about to enter the third generation system
Finally, it is simply explained that microwave communication of wireless satellite communication must accelerate its pace and continue to develop if it wants to play an important role.
[Keywords:] wireless communication; Mobile communication; Cellular network; satellite communication
1 Wireless mobile communication and wired fixed communication develop together.
People usually regard wired fixed communication and wireless mobile communication as two major components of information infrastructure (NII/GII). near
In recent years, their development speed has obviously accelerated, and they will develop even faster after entering this prosperous information age in the new century.
Make a contribution. The traditional wired fixed communication network is Public Switched Telephone Network (PSTN).
Network), which has been steadily expanding for a long time, has prompted people to install fixed terminal telephones generally. However, since the 1990s.
Since the mid-1990s, the Internet has mushroomed, which has brought unprecedented impact to traditional communication networks around the world. vast
More than 60% communication users have started to install computers, and the business volume of data communication is growing rapidly every year, far exceeding the growth rate of traditional telephones.
Annual growth rate of. According to this trend, after entering the new century, the global data and information business will catch up in about five years.
The total number of telephone information services will increase in the future. Therefore, the future communication transmission network will be dominated by data information.
Point of Packet Switching network (packet switching), and undertake the transmission of telephone communication, no longer use the original circuit switching.
(circuit-switched), but still ensure the unique quality of service (QoS) index of the phone. With the progress of computer technology and
With more functions, data communication will be extended to multimedia communication including audio and video information. In this way, the future wired fixed communication.
Information network, a unified communication network that can undertake all information business transmission, is bound to be a large-capacity communication network.
Wireless mobile communication network is mainly the cellular network of cities around the world, and each city is divided into several cells.
District,
A radio base station is set in each regional center, and all mobile terminals and personal wireless handsets in the region are directly connected with the base station.
Connecting by wireless line is called wireless access. Mobile communication used to be only mobile phones, but it has also been available recently.
Like wired networks, mobile users can connect to the Internet to transmit data and information when necessary. With the development of computer,
In the future, multimedia communication including audio and video information will also be transmitted. The mobile terminal is connected to the base station through wireless access.
To the mobile communication switching center MSC.
the same
Besides other radio base stations of the cellular network, it is also connected to the city exchange office of the wired fixed communication network. This means wireless mobile communication.
The network should be connected with the fixed communication network in the city. If a mobile terminal and a personal portable mobile phone want to communicate with a mobile terminal in the same cell or city
Terminals or personal mobile phones communicate with each other directly, but they can also be connected through wireless mobile communication networks. But the wireless mobile communication network is limited to this city.
Cellular networks in different cities still need to be connected through the national wired fixed communication network. If any wireless phone wants to be real.
At present, domestic or international communication must be connected by wireless access and then by the city's fixed network. Therefore, the wired fixed communication network not only
Undertake all kinds of communication services for wired access, including those required by original PSTN users, and also undertake wireless access.
Into a variety of communication services, so the total number of fixed-line communication services is very large, and it is increasing year by year, which is in the future design.
In the case of fixed communication network, it is necessary to calculate carefully and consider the trend of large capacity and increasing capacity year by year. This requires transmission lines and
The internal devices in the communication network can easily increase the capacity as needed.
In view of the great contribution of TDM in digital communication network in the past, digital system has developed from PDH to SDH, but
Its highest digital rate has been difficult to improve, which has become an "electronic bottleneck" for communication networks to continue to improve their capacity. Fortunately, optical fiber is used as
Transmission lines have huge potential capacity, which can be developed and utilized. Moreover, since the mid-1990s, wavelength division multiplexing/dense wavelength division multiplexing.
(WDM/DWDM) has been put into commercial use on optical fiber lines, showing unparalleled advantages. Therefore, almost all the trunk lines in wired communication networks are
The Ministry adopts optical fiber and is equipped with wavelength division multiplexing system, and in the communication network itself, in order to facilitate future expansion, it has begun to consider power.
The network evolved into an optical network, and wavelength routing was realized by using various optical devices/components based on WDM.
And the capacity of the network can be further increased.
For people who use telephone communication, although the fixed terminal telephone installed in the past runs reliably, it is different from the portable telephone popularized in recent years.
Compared with wireless mobile phones, users feel that they have a mobile phone and a number with them, and they can call each other anytime and anywhere.
That is to say, the call is much more flexible and convenient than the fixed terminal in the past. Therefore, in recent years, the sales of mobile communication phones have increased dramatically. International speculation,
In less than 20 10 years, the total number of mobile wireless phones owned by global users will be equal to the total number of fixed telephone terminals, and users need
When you want to make a phone call, you prefer to use your mobile phone. Nowadays, wireless mobile communication networks not only provide telephones, but also try to make portable computers.
Interworking data information and even multimedia communication is only because radio spectrum resources are limited after all, and wireless mobile communication can provide every channel.
The bandwidth of signal is not as wide as that of wired fixed communication. Therefore, when users need communication services with large bandwidth,
For example, users need Internet/WWW to provide a large amount of data and information for a long time when surfing the Internet, or users need to watch specific programs at home.
It is necessary to use "cable" when using VOD/MOD service of high-quality entertainment TV programs or movies.
Visit ".
Generally speaking, less than ten years after entering the new century, there are two extremely important forecasts for the development of communication services: one is about 2005.
In, the global data and information service volume caught up with the traditional telephone service volume, and then exceeded it year by year; Second, about 20 1O years.
The total number of global wireless mobile communication users has increased as much as the total number of traditional wired fixed communication users. Whereby the wired fixed communication network
The capacity of mobile phone will become larger and larger, and the mobile phone of wireless mobile communication network will become more and more common. In the future, these two communication network technologies will continue to coexist.
-rapid development.
Cellular network will enter the third generation from analog to digital.
The most basic and main way of wireless mobile communication is to use cellular network. It prevents a city from using high-power wireless.
The area covered by the electric transmitting station is 40km in diameter, and a city is divided into several hexagons close to each other according to the shape of the cellular network.
Cell, the radius of each cell can be less than 1km. A radio base station BS(base) is set in the center of such a cell.
Station), with low transmission power, can be used with all mobile terminals MS(mobilestation) or personal mobile phones.
Feel free to contact. When an MS moves from one area to an adjacent area, it changes to contact the BS in the adjacent area, and this "handover" is called "traversal"
Zone switching ". The wavelength used by a certain area BS is different from that of the adjacent area BS, but it can be the same as that of one or two other areas.
"Frequency reuse" will not cause interference, which is the advantage of cellular network and saves the use of radio spectrum resources. In the early 1980s,
Cellular mobile communication began to be commercialized. At that time, analog phones were used. Because of the rapid progress of integrated circuits, speech coding and digital communication.
The development of information technology is very successful. In the second half of 1980s, the cellular network developed to digital, which was called the second generation ZG(second
During the transition period, mobile phones can be used in dual mode, and both analog phones and digital phones can be used. at that time
There is a standard organization GSM (Mobile Task Force) in Europe. Later, it was called the second generation of 900MHz spectrum.
GSM (Global System for Mobile Communications). At the beginning, digital mobile phones used "Time Division Multiple Access".
Address "tdma (Time Division Multiple Access). In the mid-1990s, CDMA reappeared.
(code
Division Multiple access), also in the mid-1990s, the United States designated the width of 1850- 1990 MHz as 14 MHz.
about
Spectrum, used by Personal Communication Service (PCs), has been going on.
By the late 1990s, it maintained a sustained development momentum.
In the period when the technology of 2G system continues to flourish, the third generation mobile communication 3G(third) is being discussed internationally.
), it is necessary to adopt foreseeable advanced technology as far as possible, and to take care of the installed systems and equipment before making a reservation.
Set a world-recognized standard, commonly known as IMT-2000 (International Mobile Communication), set
prepare
Using 2000MHz spectrum, the experiment began in 2000. This 3G system not only guards the mobile phone, but also attaches great importance to the development of data.
According to communication, wireless systems and wired communication networks attach equal importance to data transmission, including Internet/Internet Protocol IP and broadband services.
Even for multimedia communication with a data rate of 2MB/s, the International Organization for Standards has reviewed the radio transmission schemes and data packets submitted by various countries.
Including China's schemes, there are frequency division duplex FDD (frequency duplex) CDMA, TDMA, time division duplex TDD (time
Frequency division duplex) CDMA. It is always impossible for wireless communication to show advantages in performance, cost and capacity.
In wireless digital mobile communication, in order to make full use of spectrum, speech coding technology is very heavy.
Yes This is very different from wired communication. Wired digital phones use pulse code modulation (PCM), 64kb/s per phone, or adaptive pulse code modulation.
AD-PCM modulation, 32kB/s per channel, has no difficulty in the capacity of communication network. Speech coding of wireless communication, from the early "linear"
Predictive coding "LPC (linear predictive coding) and" code-excited linear prediction "CELP in 1980s.
(code-excited linear prediction), the digital rate of each speech is reduced to 5 ~13kb/s. At the same time, in coding
In this process, we should also consider overcoming the damage and background noise caused by radio wave propagation to ensure the quality of the call. In the 3G system, it also
It is necessary to consider the audio and video coding technology required for multimedia communication, which not only saves the frequency spectrum, but also ensures the communication quality.
Usually, each radio base station needs to be equipped with several sets of RF transceivers. Now it is transitioning from analog to digital.
Digitalization will make full use of digital signal processing DSP and ASIC, and tend to use more and more new types.
The software that leads to the programmable base station allows the use of various air interface standards.
The base station will use broadband linear power amplifier and broadband RF equipment to increase digital content and make digital processing as close as possible to the antenna.
It can handle multiple radio frequencies at the same time, and enable the software to complete more functions. Since digital mobile communication supports multiple users to use CDMA or
Compared with analog communication, digital TDMA multi-access communication can reduce the number of radio transceivers, can process in a wider frequency band, and allow communication in the Internet.
Higher frequency processing from baseband to IF to RF uses digital processing. When the base station makes full use of the programmable device in this way,
They are called "software radios". Radio), becomes quite flexible and allows base station equipment to be more easily equipped.
Smart antenna or smart antenna. Mobile terminals and wireless mobile phones will also tend to
Software radio. When the service and standard technology change, software radio can quickly adapt to the new technology without a lot of replacement.
Equipment, so the investment cost can be reduced.
More use of digital signal processing can promote the development of smart antenna technology in wireless communication. Smart antenna requirements
Use multiple antennas. A base station usually has several directional antennas, and each antenna is responsible for a sector, which is used for wireless access to mobile terminals in the area.
It is particularly advantageous that multiple beams can be quickly switched through the adaptive process to obtain the best aperture gain and diversity gain.
Benefit, and suppress interference, thereby improving performance. If the receiving antenna adopts two antenna branches, there is enough space.
Get the benefits of spatial diversity. If there is only one radio station, you can also benefit from using polarization diversity. In the adaptive smart antenna,
More benefits can be obtained by installing multiple antennas for transmission. For TDMA systems, smart wireless can increase the communication capacity of the reverse line.
Processing the signal from the road can adjust the beam of the front line to the best. For CDMA systems, all mobile terminals use
Same frequency band, but different coding. In 3G systems, if users use higher data rates, they can specify a special symbol (pilot).
Symbol) to control adaptive antenna processing to reduce interference between users, thereby increasing communication capacity, that is, when there are several users.
When using high-speed data, more users are still allowed to make phone calls.
Due to public safety reasons, wireless mobile communication networks sometimes need to measure a mobile terminal or individual in a certain place quite accurately.
Moving to one geographical location at a time is called geographical positioning. Now there is an independent handheld function.
With enough additional equipment, we can use the Global Positioning System (GPS) to measure outdoor mobile individuals.
Your own position. In the future, in the 3G era, the personal mobile wireless phone itself may have a positioning function, assisted by the network.
You don't need to carry an independent GPS handheld device for positioning in this environment. That is to say, the new mobile communication mobile phone is auxiliary.
AGPS (Auxiliary Global Positioning System), to determine your geographical location outdoors or even indoors. When needed, the communication handset is provided by the network.
In this case, it is not necessary for the communication mobile phone itself to track the GPS satellite continuously.
The 3G system of cellular network is consistent with the future packet-switched wired network, focusing on providing data communication at the highest possible rate. Cellular network
Asymmetric digital transmission should also be provided. Like ADSL, an asymmetric digital subscriber line of a wired network, the direction from the radio base station to the user.
Provide high-speed data transmission. Wired network is to establish multi-carrier discrete multi-tone (DMF)
Multi-tone) devices, while wireless networks are based on multi-carrier orthogonal frequency division multiplexing (OFDM)
Frequency division multiplexing) equipment, which is very necessary for mobile users to access the Internet to request a large amount of information.
Yes
Satellite communication and microwave communication play an important role.
Besides relying mainly on urban cellular networks, as mentioned in the previous section, wireless mobile communication is also very important.
The future is bright. Over the years, synchronous satellites have proved to be extremely reliable for fixed communication and broadcasting, and can also advantageously provide long-distance movement.
Mobile communication, low orbit and medium orbit satellite communication. If we make in-depth research on technology, equipment and cost, we can still do a lot.
Play a role in global personal mobile communication. Stratospheric (stratospheric) wireless communication has been proposed. If we continue to carry out specific research,
It plays a unique role in both fixed communication and mobile communication. In addition, wireless fixed communication includes well-known microwave digital relay communication.
There is also the recently advocated WSL, Wireless Subscriber Loop (WSL), which is very suitable for areas with less population. it
Compared with the construction of optical cable and wired local telephone subscriber line, it has the advantages of fast construction speed and low investment. Millimeter wave radio
Communication and wireless infrared communication have been installed and tested in many places, which proves to be beneficial to short-distance communication. In a word, many international practices should
The application and test experience show that wireless communication has many advantages and is worth expanding the practical application scope. It can be asserted that after entering the new century,
Wireless communication is bound to develop rapidly and cooperate with wired communication, which deserves to be regarded as two major components of information infrastructure.
Geosynchronous orbit satellites once provided reliable international communication and television transmission and enjoyed a high reputation. Strengthen development in recent years, especially
It relaxes the transmission band, increases the transmission power, improves the antenna efficiency, and even
With the installation of ATM equipment and the expansion of business functions, there are more and more ground applications. One application is to install "very small aperture" on the ground.
Antenna satellite station, called VSAT, provides convenience for wide-area private communication of large enterprises. Synchronous satellites can also be provided to the ground.
Long-distance mobile communication, but the ground mobile terminal needs to be equipped with a large satellite antenna to transmit radio waves in the city center with many tall buildings.
It's hard to broadcast. For this reason, global mobile communication on the ground has been developed and launched in low orbit hundreds to 1000 km from the ground.
Dozens of mobile satellites are called LEO (Low Earth or -bit). It has also developed a medium orbit launch, about10,000 km above the ground.
These ten mobile satellite families are called MEO (Medium Earth Orbit). [Accordingly, the original distance from the ground is 36,000,000 000km, and the ground.
A family of three satellites, whose spheres run synchronously, is called GEO (geostationary orbit or -BI)]. Although LEO systems have recently
Iridium suffered a setback shortly after it was put into commercial use, and another system, Globalstar, is being put into commercial use, which may be very smooth.
But we should treat it calmly. The theories and technologies of these LEO/MEO global wireless mobile communication systems are correct, but the operators are correct.
It seems that the requirements of users, the equipment and cost of mobile phones have been considered in advance, and the charging of users should not be too expensive.
Not thoughtful enough. If we can learn from the experience and analyze the reasons carefully, we are likely to be a complete success, and we can look forward to the beauty with enthusiasm.
A bright future. Wireless fixed communication should also develop forward and make full use of the unique advantages of wireless, but wireless communication is affected by radio frequency.
Due to the limitation of spectrum resources, in order to continue the development and application, we must consider increasing the application frequency or shortening the application wavelength, that is, from microwave (cm
Wave) extends to millimeter waves and even infrared waves. In the process of such expansion, new radio wave propagation problems and equipment problems will be encountered.
Problems should be properly solved one by one and should be supported and encouraged by all parties concerned.