[Abstract] The content of this paper is divided into three parts: firstly, it explains the trend of the rapid development of wireless mobile communication along with wired fixed communication; then
focuses on the rapid development of wireless mobile communication cellular network from analog to digital and is about to enter into the third generation of the system and the future tendency;
finally briefly explains that wireless satellite communications microwave communications also need to accelerate the pace to continue to move forward in order to play an important role.
[ Keywords ] wireless communication; mobile communication; cellular network; satellite communication
1 wireless mobile communication and wired fixed communication along with the development
People often take wired fixed communication and wireless mobile communication as the two major components of the information infrastructure (NII/GII). They have been advancing at a remarkably rapid pace in recent years, and are expected to grow even more rapidly into the new century, contributing to a thriving information age
. The traditional wired fixed communications network, the "Public Switched Telephone Network" (PSTN), has been steadily expanding for a long time, leading to the widespread installation of fixed-terminal telephones. However, since the mid-1990s, the rise of the Internet has caused an unprecedented impact on traditional communication networks around the world. The vast number of communication users began to use computers, and the volume of data communication services rose sharply every year, with a growth rate that far exceeded the annual growth rate of traditional telephony
. According to this momentum, about five years into the new century, the world's total volume of data information services will catch up with
the total volume of telephone information services, and more and more in the future. Therefore, the future communication transmission network will be a packet switching network (Packet Switching), which focuses on data information and undertakes the transmission of telephone communications, no longer utilizing the original circuit switching
(Circuit Switching), but still guaranteeing the quality of service (QoS) indicators specific to telephony. With the improvement of computer technology and
more functions, data communication will be extended to include multimedia communication with audio and video information. In this way, the future wired fixed communication network
Communication network, will be able to undertake all the information business transmission of the unified communication network, will be a high-capacity communication network.
Wireless mobile communication network is mainly around the city's cellular network (Cellul Network), each city is divided into a number of cellular
districts,
the center of each district to set up a radio base station (Base Station), all the mobile terminals in the area and personal wireless handsets and the base station directly through
by the wireless line connection, called Wireless Access (Wireless Access). Known as wireless access (Wireless Access). Mobile communication was originally only cell phone, but recently also
and wired network, allowing mobile users to connect to the Internet when needed, the transmission of data information, and with the improvement of computers,
in the future will also be transmitted to include audio, video information with the multimedia communication. Mobile terminals are connected to the MSC (Mobile-communication Switching Center) through the wireless access base station, and are connected to the city switching office of the wired fixed communication network in addition to other radio base stations in the same
cellular network through the base station. This means that the wireless mobile communications
network is connected to the wired fixed communications network. Mobile terminals and personal portable cellular phones that wish to communicate directly with each other and with mobile terminals or personal cellular phones in the same cellular area or in the same city can, of course, be connected by a wireless cellular network. However, the wireless cellular network is limited to the cellular network of the city, and the cellular networks of different cities still need to be connected by the national wired fixed communication network. Any wireless cell phone that wants to realize
national or international communications, must go through the wireless access, and then by the city fixed network connection. It can be seen that the wired fixed communication network not only
take all kinds of communication services by wired access, including the original PSTN users need communication services, but also to undertake wireless access
into a variety of communication services, so the total volume of fixed network communication services is very large, and year by year to increase in the design of the future of the national wired
wire fixed communication network, it must be fine calculation, taking into account the high-capacity fixed communication network, the future of the country's
wire fixed communication network. When designing the future national fixed communication network, it is necessary to make fine calculations and consider the trend of large capacity and increasing capacity year by year. This requires that transmission lines and
equipment within the network can be easily increased in capacity as needed.
In view of the past digital communications network using time-division multiplexing TDM, although a great contribution to the digital system from the evolution of PDH to SDH, but
its highest digital rate has been difficult to increase, and thus become a communications network to continue to increase the capacity of the "electronic bottleneck". Fortunately, fiber optics as a
transmission line has a huge potential capacity can be exploited. Moreover, since the mid-1990s, the wavelength-division multiplexing/dense wavelength-division multiplexing
(WDM/DWDM) has been commercially available on fiber-optic lines, and has demonstrated its unparalleled superiority. As a result, almost all of the trunk lines in the wired communication network were fiber-optic and equipped with WDM systems, and within the communication network itself, in order to facilitate future expansion of capacity, consideration was given to evolving from an electric
network to an optical network (optical networking), which employs a variety of WDM-based optical devices/components to achieve wavelength routing
and switching functions, thus allowing for further expansion of the capacity. switching, etc., so that the capacity of the network can be further increased.
For people using telephone communications, although the past installation of the fixed terminal telephone runs reliably, but with the promotion of portable
wireless cell phones in recent years, compared to the user feels that each carry a cell phone, a number, at any time, anywhere you can make a phone call to find each other immediately
that is, call, than in the past, fixed terminals, flexible and convenient much more. Therefore, in recent years, the sales of mobile communication cell phone has increased dramatically. International speculation,
less than 2010, the world's users have a mobile wireless cell phone will be equal to the total number of installations and fixed telephone terminals, and users need to
to call the phone, more happy to use the cell phone. Now the wireless mobile communication network not only provide telephone, but also trying to make portable computers
interoperable data information and even multimedia communications, simply because the radio spectrum resources are limited, wireless mobile communications can provide each way
signal bandwidth is not as wide as wired fixed communications. Therefore, in the case of communication services where users need to use a large bandwidth,
such as users need Internet/WWW to provide a particularly large amount of data information for a long time, or users need to watch a specific
high-quality entertainment TV programs or movies at home using "on-demand TV/movie" VOD/MOVIE. Movie" VOD/MOD service, it is necessary to utilize "cable
access".
In summary, less than a decade into the new century, there are two extremely important predictions for the development of communications services: First, the world's total volume of data and information services in about 2005
to catch up with the total volume of traditional telephone services, and then exceeded year by year; and the second is that the world's total number of wireless mobile subscribers in about 201O
increase as much as the total number of traditional wired fixed communications subscribers. fixed communications subscribers. As a result, the capacity of wired fixed communication network
will be more and more large, while the wireless mobile communication network of cell phones more and more common, the future of the two types of communication network technology will continue to
-rapid development together.
2 cellular network from analog to digital, will enter the third generation
Wireless mobile communications, the most basic and the most important one is to use the cellular network approach. It avoids the use of high-power wireless
electricity transmitters in a city, covering an area of 40km in diameter of the old idea, and a city according to the shape of the cellular network is divided into a number of close to each other hexagonal
shaped area (cell), each area of the graphic radius can be less than 1km. In the center of such a cellular area, a radio base station (BS) is set up, with low transmitter power, which can be used to contact with all mobile terminals MS (mobilestation) or cell phones carried by individuals
at any time. When an MS moves from a zone to a neighboring zone, it will contact the BS in the neighboring zone, and this "handover" is called "zone switching". The wavelength used by the BS in one area is different from the wavelength of the BS in the neighboring area, but can be the same wavelength as the wavelength of the next one or two areas, which is known as
"Frequency reuse", and will not cause interference, which is an advantage of the cellular network, and saves the use of the radio spectrum resources.In the early 80's, the cellular network of mobile communication began to be commercially available, and at that time analog phones were used. In the early 1980s, cellular mobile communications became commercially available, using analog telephones, due to rapid advances in integrated circuits, and due to the successful development of both voice coding and digital communications
technology. In the second half of the 1980s, the cellular network evolved to digital, known as the second generation (second
generation). During the transition period cell phones could be used in dual mode, for both analog and digital telephony. At that time
Europe had the standards organization GSM (Groupe Special Mo-bile), and the second generation, which became common in the 900 MHz spectrum, was called
GSM (Global System for Mobile Communications). In the beginning, digital mobile telephony utilized Time Division Multiple Access (TDMA), and in the mid-1990s, Code Division Multiple Access (CDMA)
(Code
).
(Code
Division Multiple Ac- cess), and also in the mid-1990s, the United States designated a 14MHz width
of 1850-1990MHz
spectrum for "Personal Communication Services
(PCS). " (Personal Communication Service), and these continued
until the late 1990s, maintaining constant momentum.
While the 2G system technology continued to flourish, the international community began to discuss the future of the third generation of mobile communications 3G (third
generation), not only to maximize the use of foreseeable advanced technology, but also to take care of the system equipment that is now installed, and then to set
determine the standard recognized by the whole world, commonly known as IMT-2000 (International MobileTelecommunications), which is the most advanced technology available. 2000 (International Mobile Telecommunication), set
prepared
using 2000MHz spectrum, and started trial in 2000. This 3G system not only maintains mobile telephony, but also places great emphasis on the development of digital
data communications, so that the wireless system and the wired communications network as much emphasis on the transmission of data, including Internet/Internet Protocol IP and broadband services,
to the data rate of 2Mb / s multimedia communications. The International Organization for Standardization has reviewed the radio transmission schemes submitted by various countries, including
including China's scheme, there are frequency division duplex FDD (Frequency Duplex) CDMA, TDMA, and time `division duplex TDD (Time
Division Duplex) CDMA. always unable to make the wireless communication in terms of performance, cost and capacity are obvious, cost, and capacity.
In wireless digital mobile communications, Speech Coding is very important in order to fully utilize the spectrum
. This is very different from wired communications, wired digital telephony using pulse code modulation PCM, 64kb/s per call, or adaptive pulse code
modulation AD-PCM, 32kb/s per call, there is no difficulty in the capacity of the communication network. Voice coding for wireless communications, from the early "linear
predictive coding" LPC (Linear Predictive Coding), to the "Code Excited Linear Predictive" CELP
(Code Excited Linear Predictive)
(Code Excited Linear Predictive), which began in the 80s.
(Code Excited Linear Pre-diction), the digital rate of each voice down to 5 ~ 13kb / s. At the same time, in the coding
process should also be considered to overcome the radio wave propagation process caused by the damage and background noise, to ensure that the call quality. In the 3G system, it is also
required to consider the coding technology of audio and video for multimedia communication, which saves spectrum and ensures the quality of communication.
Each radio base station generally needs to set up several sets of radio frequency transceiver (RF transceiver). Now the transition from analog to digital
Digital, will take full advantage of digital signal processing DSP and dedicated large-scale integrated chip ASIC, and tend to use more and more new
Software, resulting in programmable (programmable) base station, allowing the use of a variety of air interface (air interface) standards.
The base station will use broadband linear power amplification and broadband RF devices to facilitate the addition of digital content, keep digital processing as close to the antenna as possible,
enable simultaneous processing of multiple RFs, and enable software to perform more functions. As digital mobile communications to support multiple users using CDMA or
TDMA multi-access communications, digital can be compared to analog to reduce the number of radio transceivers, can be processed in a wider band, but also allowed in
higher-frequency processing, from the baseband to the IF to the RF are using digital processing. When base stations make full use of programmable devices in this way,
they are called "software radios" (software. Ra-dio), which become quite flexible and allow base station equipment to be more easily configured with
smart antennas (smart antennas). Mobile terminals and wireless handsets will also tend to be
software radios. As services and standard technologies change, software radios can be quickly adapted to the new technology without the need for extensive replacement of
equipment, and thus investment costs can be reduced.
Additional use of digital signal processing can lead to the favorable development of smart antenna technology for wireless communications. Smart antennas require
the use of multiple antennas. The base station often has several directional antennas, each branching off into a sector, which is particularly favorable for wireless access to mobile terminals within the sector
and may also allow multiple beam shots to undergo an adaptive process for rapid switching to obtain the best aperture gain, diversity gain
gain, and curbing of interference, resulting in improved performance. Receiving antennas with two antenna branches that are sufficiently spaced apart in space can
acquire the benefits of spatial diversity, or if there is only one radio, the benefits can be obtained using polarization diversity. In the case of adaptive smart antennas,
transmission mounts with multiple antennas can achieve even more benefits. For TDMA systems, smart radios can increase communication capacity, and signals coming from the reverse line
are processed so that beams from the forward line can be optimally adjusted. For the CDMA system, all mobile terminals use
the same frequency band, just with different codes. With 3G, users using higher data rates can specify a special symbol (pilot
symbol) to control adaptive antenna processing to minimize interference between users, thereby increasing communication capacity, i.e., allowing more users to make calls when several users
use high-speed data.
Wireless mobile communication networks sometimes need to determine quite accurately, for reasons of public ****security, where a mobile terminal or an individual is moving to geographically at a certain
time, known as positioning technology (geoloca-tion). Now there is a stand-alone handheld can
enough incidental equipment, the use of global positioning system (GPS, global positioning system), outdoor determination of mobile personal
their own position. In the future, in the 3G era, the personal mobile wireless cellular phone itself may be equipped with a positioning function, and it is possible to carry out positioning work with the assistance of the network
without the need to carry a separate independent GPS handheld. That is to say, the new mobile communication cell phone is equipped with assisted GPS (AGPS) to determine its own geographic position outdoors or even indoors. The cellular phone is provided by the network when needed
and it is not necessary for the cellular phone itself to continuously track the GPS satellites.
The cellular 3G system is aligned with the future packet-switched wireline network, and focuses on providing the highest possible speed for data communications. Cellular networks
are also expected to provide asymmetric digital transmission. Like ADSL, the asymmetric digital subscriber line of the wireline network, the radio base station-to-subscriber direction
provides higher-rate data transmission. Wireline network is set up in the switching office multi-carrier discrete multi-tone (DMF, Discrete
Multi-Tone) equipment, while the wireless network is set up in the base of the multi-carrier Orthogonal Frequency Division Multiplex (OFDM, Orthogonal
Frequency Division Multiplex) equipment, which for the
Frequency Division Multiplex (OFDM) equipment is installed in the base station, which is very necessary for mobile users to access the Internet to request a large amount of information
.
3 Satellite and microwave communications play an important role
Wireless mobile communications in addition to most of the reliance on urban cellular networks, as described in the previous section, there are also satellite communications is also very important, a large
has a future. Synchronous satellites for fixed communications and broadcasting has been many years of practice has proved to be extremely reliable, but also can be advantageous to provide long-range mobile
mobile communications, low-orbit channel, medium-orbit satellite communications. If in-depth research is conducted on technology, equipment, and cost, it can still play a significant role in global personal mobile communications.
Synchronous satellites have been proven to be extremely reliable for fixed communications and broadcasting for many years. Stratospheric (stratospheric) wireless communication program has been put forward, if we continue to study,
Fixed communications and mobile communications have a unique role. In addition, wireless fixed communications, including the familiar microwave digital relay communications
and recently advocated wireless subscriber loop (WSL, Wireless Subscriber Loop), in less populated areas is very suitable, it
they with the construction of fiber-optic cable and wired municipal telephone subscriber line compared to the construction of the advantages of faster construction, less investment. Millimeter wave radio
communication and wireless infrared communication has been installed in a number of tests, proved beneficial to short-distance communication. In short, a number of international practical application
use and experimental experience shows that wireless communication has many advantages, it is worth expanding the scope of practical use. It can be asserted that in the new century,
Wireless communication will be rapid development and mutual application with wired communication, worthy of the two major components of the information infrastructure.
Satellites operating in synchronous orbits have enjoyed a strong reputation in the past for providing reliable international communications and television transmission. In recent years, the development has been strengthened, especially
its transponder inside the satellite, broadening the transmission band, increasing the transmission power, improving the efficiency of antenna, and even
adding ATM equipment to expand the business function, so that more and more applications on the ground. One application is the installation of "very small aperture
antenna" satellite stations on the ground, known as VSAT, to facilitate wide-area private communications for large enterprises. Synchronous satellites may also be able to provide mobile communications to the ground over long distances, but mobile terminals on the ground require larger antennae and are difficult to transmit over the airwaves in high-rise city centers. For this reason, the global mobile communications on the ground, there has been a separate development and launch of low orbit, several hundred to one thousand kilometers from the ground
dozens of mobile satellite family, known as LEO (Low Earth Or-bit). In addition, a family of ten mobile satellites in medium orbit, about 10,000 kilometers above the ground, called MEO (Medium Earth Orbit), was also developed and launched. [Accordingly, a family of three satellites that were originally 36,000 km above the ground and synchronized with the Earth
was called GEO (Geostationary Earth Or-bi). While the LEO system
Iridium recently suffered a setback shortly after it was opened for commercial use, and another system, Globalstar, is being opened for commercial use and may be going well,
it should be treated with equanimity. The theory and technology of these LEO/MEO global wireless mobile communication systems are correct, but the operators seem to have not given enough thought in advance to
the conditions of users' needs, the equipment and cost of mobile handsets, and the issues of charging the users not to be too expensive
. If we can seriously learn from the experience and carefully analyze the reasons, it is likely to be a complete success, and we can enthusiastically look forward to a beautiful
good future. Wireless fixed communications should also move forward to take full advantage of the unique advantages of wireless, but wireless communications by radio frequency
spectrum resource constraints, in order to continue the development of applications, we must consider increasing the use of frequency or shorten the use of wavelengths, i.e., from the microwave (centimeter
wave) extended to millimeter waves, and even infrared waves. In the process of such an extension, will certainly encounter new wave propagation problems and devices
problems, are to be properly resolved one by one, should be supported and encouraged by all parties concerned.