Communication Technology and Mobile Communication 

 

Mobile communication is a communication technology in which one or both parties are in motion. Including land, sea, and airmobile communications. The frequency bands used are low frequency, mid-frequency, high frequency, very high frequency, and ultra-high frequency. A mobile communication system consists of a mobile station, a base station, and a mobile switching office. To communicate with a certain mobile station, the mobile switching office sends a call to the whole network through each base station, and the called station sends a response signal after receiving the response. Send signaling to make it ring.

 

Communication Technology and Mobile communication 

Introduce

Mobile communication is communication between mobile bodies or communication between mobile bodies and fixed bodies. The moving body can be a person or an object in a moving state such as a car, a train, a ship, a radio, etc.

From January to March 2013, China's domestic sales of mobile communication handsets reached 163.16 million units, a growth rate of 39%. The production and sales of mobile communication handsets are accelerating towards smartphones. Smartphones accounted for 77% of new models launched in March, and domestic sales increased by 62.5% year-on-year, accounting for 58% of domestic mobile phone sales. 

Communication Technology and Mobile communication 

 Mobile communication technology system consists of two parts:

 (1) Space system;

 (2) Ground system: â‘  satellite mobile radio station and antenna; â‘¡ gateway station and base station.

 Since the mobile communication system was born in the 1980s, it will roughly go through five generations of development by 2020, and by 2010, it will transition from the third generation to the fourth generation (4G). By 4G, in addition to cellular phone systems, broadband wireless access systems, millimeter-wave LANs, intelligent transport systems (ITS) and stratospheric platform (HAPS) systems will be put into use. The most obvious trend in the future generations of mobile communication systems is to require high data rates, high mobility, and seamless roaming. Achieving these requirements will be technically more challenging. In addition, system performance (such as cell size and transmission rate) will be highly dependent on the frequency. Taking into account these technical issues, some systems will focus on providing high data rates, while others will focus on enhancing mobility or extending coverage.

 From the user's point of view, the access technologies that can be used include cellular mobile wireless systems, such as 3G; cordless systems, such as DECT; short-range communication systems, such as Bluetooth and DECT data systems; wireless local area network (WLAN) systems; fixed wireless Access or wireless local loop systems; satellite systems; broadcasting systems such as DAB and DVB-T; ADSL and Cable Modem.

Communication Technology and Mobile communication 

Features 

(1) Mobility.

 It is to maintain the communication of objects in a moving state, so it must be wireless communication or a combination of wireless communication and wired communication.

 (2) The radio wave propagation conditions are complex

 . Because the moving body may move in various environments, the electromagnetic wave will produce reflection, refraction, diffraction, Doppler Effect, and other phenomena during propagation, resulting in multipath interference, signal propagation delay and broadening, and other effects.

 (3) Serious noise and interference.

 In the urban environment, car spark noise, various industrial noises, intermodulation interference between mobile users, adjacent channel interference, co-channel interference, etc.

 (4) The system and network structure are complex.

 It is a multi-user communication technology system and network, which must enable users to work in unison without interfering with each other. In addition, the mobile communication technology system should also be interconnected with the local telephone network, satellite communication network, data network, etc. The entire network structure is very complicated.

 (5) High-frequency band utilization and good equipment performance are required.

Communication Technology and Mobile communication 

Classification 

There are many types of mobile communications. It can be divided into the following types according to different user requirements and work situations.

 Trunking

 Trunking mobile communication, also known as regional mobile communication. It is characterized by only one base station, the antenna height is tens to hundreds of meters, the coverage radius is 30 kilometers, and the transmitter power can be as high as 200 watts. The number of users is about tens to hundreds, which may be vehicle-mounted radios or handheld radios. They can communicate with the base station, and can also communicate with other mobile stations and local users through the base station, and the base station is connected to the wired network of the local station.

 Cellular

 Cellular mobile communication is also known as cell-based mobile communication. Its characteristic is that the entire large-scale service area is divided into many cells, and each cell is set with a base station, which is responsible for the contact and control of each mobile station in the cell. Utilizing the characteristics of limited propagation distance of ultra-short wave radio waves, the cells at a certain distance can reuse the frequency so that the frequency resources can be fully utilized. The number of users in each cell is more than 1,000, and the final capacity of the entire coverage area can reach 1 million users.

 Satellite

 Satellite mobile communications. Mobile communication can also be achieved by using satellite relay signals. For vehicle-mounted mobile communication, equatorial fixed satellites can be used, and for handheld terminals, it is more beneficial to use multiple constellation satellites in medium and low orbits.

 Cordless phone

 Cordless phone. For the communication of indoor and outdoor slow-moving handheld terminals, light-weight cordless telephones with low power, short communication distances are used. They can communicate unidirectionally or bidirectionally with the local subscriber through the communication point.

 Mobile communications using analog identification signals are called analog mobile communications. To solve the problem of increasing capacity, improving communication quality, and increasing service functions, most of them use digital identification signals, that is, digital mobile communication. In terms of standard, there are two kinds of time division multiple access (TDMA) and code division multiple access (CDMA). The former has the European GSM system (Global System for Mobile Communications), the North American dual-mode standard IS-54, and the Japanese JDC standard in the world. For code division multiple access, there is the IS-95 standard system developed by Qualcomm Company in the United States. Mobile communication will develop into personal communication. In the 21st century, it has turned into a significant piece of worldwide data interstate. Mobile communications will have a more brilliant future.

Technological development 

Communication Technology and Mobile communication 

The 1G

 Analog mobile communication systems benefited from two key breakthroughs in the 1970s: the invention of microprocessors and the digitization of switching and control links. AMPS is the world's first 1G mobile communication system launched by the United States, which makes full use of FDMA technology to realize domestic-wide voice communication.

 2G

 Is it "The former has the European GSM system (Global System for Mobile Communications), the North American dual-mode standard IS-54, and the Japanese JDC standard in the world." a digital cellular communication system that has swept the world for more than ten years and was developed in the late 1980s? 2G is a fully digital system including voice, and the new technology is reflected in the improvement of call quality and system capacity. GSM (Global System for Mobile Communication) is the first commercial 2G system, and GSM uses TDMA technology.

 2.5G

 2.5G provides enhanced services such as WAP based on 2G.

 3G

 3G is a mobile multimedia communication system that provides services including voice, fax, data, multimedia entertainment, and global seamless roaming. NTT and Ericsson began to develop 3G in 1996 (ETSI in 1998). In 1998, ITU launched two commercial standards, WCDMA and CDMA2000 (China launched the TD-SCDMA standard in 2000, and it was accepted by 3GPP in March 2001. SCDMA) The first 3G network was operated in Japan in 2001. 3G technology provides 2MBPS standard user rate (144KBPS rate under high-speed mobile).

 4G

 4G is a real high-speed mobile communication system with a user rate of 20Mbps. 4G supports interactive multimedia services, high-quality images, 3D animations, and broadband Internet access, and is a high-speed cellular system with broadband and large capacity. In early 2005, the 4G mobile communication system demonstrated by NTTDoCoMo achieved a real-time transmission rate of 1Gbps at 20KM/hour. The system adopted 4X4 antenna MIMO technology and VSF-OFDM access technology.

Communication Technology and Mobile communication 

Communication advantages

1. The system capacity is large. In a CDMA system, all users share a wireless channel. At the point when a few clients don't talk, any remaining clients in the channel will profit from the diminished impedance. The capacity of the CDMA digital mobile communication system is theoretically 20 times larger than that of an analog network, 10 times larger than that of an analog network in practice, and 4 to 5 times larger than that of GSM.
2. Communication quality is good. The CDMA system adopts the adaptive threshold technology to determine the vocoder rate, the high-performance error correction coding, the soft handover technology, and the multi-path fading resistance diversity receiving technology, which can provide extremely high communication quality that the TDMA system cannot match.
3. High-frequency band utilization. CDMA is a spread spectrum communication technology. Although the improvement of the anti-interference performance of the spread spectrum communication system is at the expense of occupying the frequency bandwidth, CDMA allows a single frequency band to be reused in the entire system area, allowing many users to share this frequency band at the same time. Calls, greatly improve the frequency band utilization. Although this spread-spectrum CDMA method needs to occupy a wider frequency band, it is calculated according to the average frequency band occupied by each user, and its frequency band utilization rate is very high.
4. Suitable for multimedia communication systems. CDMA systems can easily use multi-code channels and multi-frame modes to transmit multimedia service information with different rate requirements. The processing and synthesis methods are more flexible and simpler than TDMA and FDMA, which is beneficial to the application of multimedia communication systems.
5. The transmit power of the mobile phone is low. The CDMA system uses power control to reduce the transmit power of CDMA mobile phones as much as possible to reduce interference and improve network capacity.
6. Flexible frequency planning. Users are distinguished by different code sequences, sectors are distinguished by different pilot codes, and the same CDMA carrier can be used in adjacent cells, so the frequency planning of the CDMA network is flexible and easy to expand.

 

 CDMA communication technology

 CDMA (Code Division Multiple Access) as a multiple access technology has long appeared, initially only in anti-jamming and security performance and other aspects of people's attention, is used in military anti-jamming systems. In 1989, Qualcomm Company of the United States first introduced the idea of ​​the CDMA cellular mobile communication system.