3G is the third generation mobile communication technology, which refers to the cellular mobile communication technology supporting high-speed data transmission. 3G services can transmit voice and data information simultaneously. 3G is a new generation of mobile communication system which combines wireless communication with multimedia communication such as Internet.

The so-called third generation mobile communication technology is 3G network technology. Compared with the first generation mobile communication technology (1G) and the second generation digital mobile phone communication technology (2G), 3G mobile phone mainly combines wireless communication and Internet communication technologies to form a new mobile communication system. This mobile technology can handle media forms such as images and music, as well as business functions such as teleconferencing.In order to support the above functions, the wireless network can fully support different data transmission speeds, that is, the wireless network can provide data transmission speeds of at least 2Mbps, 384kbps and 144kbps whether indoors, outdoors or in a driving environment.

The third generation mobile communication technology (3G), 3G network technology is the inevitable development in this field. 3G has made the definition to the mobile communication technology standard, uses the higher frequency band and the CDMA technology to transmit the data to carry on the related technical support, the working frequency band is high, the main characteristic is the speed is quick, the efficiency is high, the signal is stable, the cost is low and the security performance is good and so on, compared with the previous two generation of communication technologies, the most obvious characteristic is that the 3G network technology supports the more diverse multimedia technology comprehensively.

The origin of technology

In 1940, Hedy Lamarr, an American actress, and her husband George Ansel, a composer, put forward a technical concept of Spectrum, which was called "spread spectrum technology" (also known as code division spread spectrum technology) and brought changes to the world thereafter. It is this technical theory that eventually evolved into today's 3G technology. Spread spectrum technology is the fundamental principle of 3G technology. Spread spectrum is a communication technology that spreads the spectrum of the transmitted signal to a wider bandwidth than its original bandwidth, which is often used in the field of wireless communication.

In March 1938, the Nazis officially invaded Austria, and she fled to London to escape her failed marriage and many Nazi "friends". By the way, it also brought the "military secrets" of Nazi wireless communication to the allies.These secrets are mainly based on the "command guidance" system of radio secure communication, which is used to automatically control weapons and accurately attack targets. However, in order to prevent radio commands from being stolen by the enemy, it is necessary to develop a series of radio communication security technologies. She is well educated and has secretly absorbed many valuable forward-looking concepts.

But in August 1942, she finally got the patent of the United States. In the patent office of the United States, there was a dust-laden patent: Patent No.2,292,387 for "Secure Communication System", which was passed on August 11, 1942 and applied on June 10, 1941. Spread Spectrum technology (spread spectrum technology). The technology, which is archived on the National Patent Office's website, was originally patented for military use.

Heidi Lamarr originally developed the technology to help the U.S. military create a military communications system that could deal with Nazi Germany's radio jamming or anti-eavesdropping, so the technology was initially used for military purposes. After the end of World War II, the U.S. military mothballed the technology because it temporarily lost its value, but its concept has made many countries interested in it, and many countries have studied the technology in the 1960s, but little progress has been made.

Until 1985, a small company named "Qualcomm" was established in San Diego of the United States (now the world's top 500). This company used the "spread spectrum technology" lifted by the US military to develop a new technology named "CDMA", which directly led to the birth of 3G. The three major standards of 3G technology in the world, CDMA2000 in the United States, WCDMA in Europe and TD-SCDMA in China, are all developed on the basis of CDMA technology. CDMA is the fundamental principle of 3G, and spectrum distribution technology is the basis of CDMA.

On May 5, 2000, the International Telecommunication Union officially announced the third generation mobile communication standard, and TD-SCDMA submitted by China formally became an international standard, becoming one of the three most mainstream technologies in the 3G era with WCDMA in Europe and CDMA2000 in the United States.

Important factors for the success of 3G development

With the development of mobile communication network technology, the application of this technology in various fields is indispensable, but the standards of related technical means formulated by various communication enterprises are different, which greatly curbs the development of this technology, and then the emergence of 3G services has changed this chaotic situation. In addition, 3G services have many excellent characteristics, such as higher speed, more intelligent, more stable and more diversified, and gradually transit to the all-IP network.The biggest difference between the future network and today's IP is that it can provide a variety of services economically and effectively and support end-to-end quality of service. MPLS is a gradually clear development trend.

 Comparison of technical features

The first generation of mobile communication technology is analog mobile communication technology, which is represented by AMPS in the United States, TACS in the United Kingdom and NMT450/900 in Northern Europe. The first generation mobile communication system is mainly characterized by analog frequency modulation (FM) and frequency division multiple access (FDMA), which is limited to voice transmission. It uses analog circuit unit as the basic module to realize voice communication, and adopts cellular structure, so the frequency band can be reused, and the uninterrupted communication of large area coverage and mobile environment is realized.

 The third generation (3G) mobile communication system is the global mobile communication system proposed by the International Telecommunication Union (ITU) for the international mobile communication in 2000, which has many functions such as global mobility, integrated services, data transmission cellular, cordless, paging, trunking, etc. It can also meet the requirements of spectrum efficiency, operational environment, service capacity and quality, network flexibility and seamless coverage, compatibility, etc. IMT-2000 system for short. The system operates in the 2000MHz frequency band and can provide circuit switching and packet switching services at the same time. The uplink and downlink frequency bands are 1890-2030MHz and 2110-2250MHz.

 Comparison of three standards

The full name of CDMA is Wideband CDMA, also known as CDMA Direct Spread, which means Wideband Code Division Multiple Access. This is a 3G technical specification developed based on the GSM network. It is a wideband CDMA technology proposed by Europe, which is basically the same as the wideband CDMA technology proposed by Japan, and is currently being further integrated.The supporters of WCDMA are mainly European manufacturers based on GSM system, and Japanese companies are more or less involved, including Ericsson, Alcatel, Nokia, Lucent and Nortel in Europe and the United States, as well as NTT, Fujitsu and Sharp in Japan. The standard proposes an evolution strategy of GSM (2G) -GPRS-EDGE-WCDMA (3G).This system can be installed on the existing GSM network, and it is easy for the system provider to make the transition. It is expected that in Asia, where the GSM system is quite popular, the acceptance of this new technology will be quite high. Therefore, WCDMA has inherent market advantages. WCDMA is the most widely used 3G standard in the world with the most abundant terminal types, accounting for more than 80% of the global market share.

CDMA-2000 is a wideband CDMA technology developed from narrowband CDMA (CDMA IS95) technology, also known as CDMA Multi-Carrier. It was proposed by Qualcomm North America Company of the United States, with the participation of Motorola, Lucent and Samsung of South Korea. South Korea became the leader of the standard.This system is derived from the narrowband CDMAOne digital standard, which can be upgraded directly from the original CDMAOne structure to 3G, with low construction cost. But CDMA is only used in Japan, Korea and North America, so there are not as many supporters of CDMA2000 as there are of W-CDMA. However, the development of CDMA2000 technology is currently the fastest progress in all standards, and many 3G mobile phones have been the first to appear.The standard proposes an evolution strategy from CDMAIS95 (2G) -CDMA2000 1x-CDMA2000 3x (3G). CDMA2000 1x is known as the 2.5 generation mobile communication technology. The main difference between CDMA20003x and CDMA20001x is the application of multi-carrier technology, which increases the bandwidth by using three carriers.China Telecom is using this scheme to transition to 3G and has built a CDMAIS95 network.

 Working mode

W-CDMA can work in both FDD and TDD modes, and use the same clock with GSM system to realize the dual-mode operation of CDMA and GSM system mobile phones, which is a compatible system. FDD is a duplex mode that implements uplink and downlink transmissions using two separate symmetric frequency bands. It requires pairs of frequencies to distinguish the up and down rows by frequency. W-CDMA can support the normal communication of mobile terminals at a speed of about 500 kilometers per hour.In TDD mode, the spreading gain of W-CDMA is unchanged, and multi-code transmission can be used to realize high-speed data communication. Its most important feature is that it has uplink multiuser detection technology, which can eliminate the mutual interference among multiple users by measuring the non-orthogonality between the spreading codes of each user and using the matrix inversion method or iteration method. While CDMA-2000 only supports FDD mode of operation.

 TD-SCDMA is the IMT-2000 system design scheme proposed by our country, which adopts TDD mode. TDD is a duplex mode that uses the same frequency band for uplink and downlink transmissions, distinguished by time. The time slot of the physical layer is divided into an uplink part and a downlink part, and paired frequencies are not needed; uplink and downlink services share the same channel and can be unevenly distributed; and the method is particularly suitable for asymmetric packet-switched data services.TDD has high spectrum utilization and low cost, but due to the use of multi-slot discontinuous transmission mode, the ratio of peak power to average power transmitted by the base station is high, resulting in large power consumption of the base station, small coverage radius of the base station, and poor anti-fading and anti-Doppler frequency shift performance, and poor communication capability when the mobile phone is in a high-speed mobile state. TD-SCDMA can only support the normal communication of mobile terminals at about 120 kilometers per hour.TD-SCDMA is at a disadvantage in high-speed mobile environments such as highways and railways.

 Area switching

 W-CDMA adopts the "soft handover" technology between sectors and cells, that is, when the mobile phone moves or the base station currently communicating with the mobile phone is busy, so that the mobile phone needs to communicate with a new base station, it first connects with the new base station and then disconnects with the original base station. The handover of W-CDMA is carried out by asynchronous soft handover. W-CDMA does not require synchronization between base stations, nor does it require a special synchronization reference source. The handover between carrier frequencies is a hard handover, that is to say, the connection with the original base station is interrupted first and then the new base station is connected.

 CDMA-2000 also uses "soft handoff" technology. CDMA-2000 requires strict synchronization between base stations, so it must use GPS and other equipment to determine the location of the mobile phone and calculate the distance to two base stations. Hard handoff is used between carrier frequencies.

TD-SCDMA adopts the technology of "relay handover". The smart antenna can roughly locate the location and distance of the user. The base station and the base station controller can judge whether the user moves to the adjacent area of another base station according to the location and distance information of the user.If a handover area is entered, another base station is notified by the base station controller to be ready for handover. The mobile station synchronizes with the identified base station before handover and reports to the network, which controls the mobile station to complete the handover. The method is applicable to both same-frequency switching and different-frequency switching. Baton handover is an improved hard handover technology, which reduces the call drop rate and improves the handover success rate. Compared with soft handover, it uses less signaling and resources.TD-SCDMA requires strict synchronization between base stations. GPS or network synchronization is used to reduce the interference between base stations.

 Resource utilization

W-CDMA uses direct sequence spread spectrum, and its chip rate is 3.84 Mchip/s. It can efficiently use frequency selective diversity and space receive and transmit diversity, and can effectively solve the problems of multipath and fading. Each carrier of W-CDMA only occupies 5 MHz bandwidth. The higher the carrier bandwidth is, the more users are supported, and the smaller the possibility of network congestion occurs during communication.

CDMA-2000 has two main channel structures in the F-link: multicarrier and direct spread. Multi-carrier downlink transmission generally uses three consecutive carriers within a 5MHz bandwidth, and the chip rate of each carrier is 122288Mchip/s; for direct spread spectrum downlink transmission, the chip rate of 3.6864 Mchip/s is usually used.When the multi-carrier mode is adopted, a plurality of radio frequency bandwidths can be supported, different radio frequency channel bandwidths are adopted, and data can be transmitted at a rate of 1.2k bps-2Mbps or even higher. The CD-MA-2000 system can also be increased to use 6, 9 and 12 basic channels, and its signal bandwidth will be increased accordingly, and the data transmission rate will be higher.

The chip rate of TD-SCDMA is 1.28 Mchip/s. TD-SCDMA uses a three-carrier design, with each carrier having a bandwidth of 1.6m. Because of the TDD duplex mode, it only needs to occupy a single 1.6m bandwidth to transmit 2Mbps data services. W-CDMA and CDMA-2000 need two symmetrical bandwidths to transmit 2Mbps data services, which are used as uplink and downlink frequency bands respectively, so TD-SCDMA has the highest utilization rate of frequency resources.

 Signal modulation coding

 W-The uplink signal modulation of CDMA is BPSK, and the downlink signal modulation is QPSK. Spread spectrum coding uses Walsh (channelization) + Gold sequence 241-1 (user differentiation) for uplink and Walsh (channelization) + Gold sequence 218-1 (cell differentiation) for downlink. The channel coding is convolutional code and RS concatenated code, and the diversity is RAKE reception plus antenna diversity. The power control uses an open-loop K slow closed-loop (1.6 K). During joint detection, the pilot symbol assists the coherent detection RAKE, the uplink uses the dedicated pilot symbol, and the downlink uses the perch channel + dedicated pilot symbol.

 The uplink signal modulation of CDMA-2000 adopts BPSK modulation mode and the downlink signal modulation adopts QPSK modulation mode. Spread-spectrum coding uses Walsh (channelization) + Gold sequence 241-1 (user differentiation) for uplink and Walsh (channelization) + Gold sequence 215-1 (cell differentiation) for downlink. During joint detection, the uplink uses a common pilot channel and the downlink uses a dedicated pilot channel.The signal modulation mode of TD-SCDMA is QPSK/BPSK. Uplink spread spectrum coding uses Walsh (channelization) + time slot number (distinguishing users), and downlink uses Walsh (channelization) + Gold sequence (distinguishing cells). Power control with open loop + fast closed loop (0-200 Hz). During joint detection, Gold code + training sequence of uplink/downlink synchronization signal.

The key technology of TD-SCDMA is smart antenna. Smart antenna uses array antenna to adaptively form multiple beams at the base station to track multiple users who share the same channel. During receiving, spatial filtering is used to suppress co-channel interference and separate each user; during transmitting, multi-beam forming is used to maximize the signal power received by the desired user and minimize the interference to undesired users at other locations.Therefore, the transmission power of the signal can be reduced, and the interference from other users can be reduced, so that the capacity and the communication quality of the system are improved. The high efficiency of the TD-SCDMA smart antenna is obtained based on the symmetry of the radio paths (the same radio environment and transmission conditions) of the uplink and downlink. Smart antennas can also reduce inter-cell and intra-cell interference. These characteristics of smart antennas can significantly improve the spectral efficiency of mobile communication systems.

TD-SCDMA adopts software radio technology. When the operation department adds services, it can use software to process baseband signals on the same hardware platform, and achieve different service performance by loading different software.

When the synchronous CDMA communication mode is adopted, the downlink signal arriving at each mobile station is synchronous, and the uplink signal arriving at each base station is also synchronous. The accurate transmission time of the mobile station signal can be obtained by measuring the accurate propagation delay of the signal from the base station to the mobile station. TD-SCDMA uses uplink synchronous CDMA technology, which makes the uplink signal completely synchronous with the demodulator of the base station. It not only reduces the interference between uplink users and the width of the protection time slot, but also improves the system capacity, simplifies the hardware and significantly reduces the cost.

 Security architecture

Client side

Users mainly use mobile 3G technology to obtain communication services through mobile phones, some users will also use radio equipment to obtain signal sources, the most mainstream is the communication service request of mobile phone ports, and the most critical in the communication process is the stability and signal strength of signal transmission, 3G technology can effectively achieve high-intensity and stable call information services. Realize the stable and fast transmission of data, and realize the encryption of data in this process.

 Security management server

At present, there are two kinds of identity authentication services, one is to use Kerberos technology to realize the user's identity authentication of password key, the other is to use public key to realize the encryption of the system, and to use X. 509 service protocol to verify the identity of both parties and service requests. It is necessary to ensure that both verifications have reliable encryption function and anti-malicious attack function, in order to fully ensure that the user's personal privacy is not stolen.

 Server side

Internet based on 3G

Data transmission based on 3G

At present, high speed circuit switched data has been widely used in wireless communication. The data rate of a single traffic channel is increased from 9.6kb/s to 14.4kb/s, and four channels are multiplexed in the same time slot at the same time, so that the transmission rate of data operators can reach 57.6kb/s. At the same time, it is more than six times the data transmission rate at the present stage.However, the GPRS developed by Nokia can be bundled in one carrier frequency or eight channels, and the transmission rate of each channel data can be increased to 14.4kb/s. Therefore, the maximum transmission efficiency of GPRS can reach 115.2kb/s.This kind of data transmission mode mainly uses the voice transmission mode of TDMA, and the packet form is mainly data transmission. At the same time, it also represents that users have been charging online according to traffic, which reduces the service cost rapidly. This technology is between 2G and 3G, and is generally referred to as potential 2.5g wireless communication technology. The above three technologies are all communication technologies based on the continuous transition of the third generation mobile communication technology.

 3G wireless interface standard and characteristic

As early as 1999, Finland has held a meeting to adopt the radio interface technology standards included in the third generation mobile communication system.From this we can also know that the third generation mobile communication technology mainly uses the wideband CDMA system as the main system, CDMA is also the code division multiple access technology, and the main feature of mobile communication is the use of multiple access technology, which is the base station access and signal receiving technology used by mobile stations around the base station, only the mobile station occupies a channel. Only in this way can mobile communication be carried out.On the basis of the third generation mobile communication technology, the main goal of Internet technology is to realize a global mobile integrated service digital network, which not only integrates the basic functions of cordless, mobile data, mobile satellite and other mobile communication technologies, but also provides compatible services of fixed telecommunication networks, as well as voice and non-voice services.

 3G infrastructure

The third generation mobile communication technology mainly includes four functional subsystems: core network, radio access network, mobile station and subscriber identity module. Among them, the wireless access network mainly applies five access standards based on ITU, but the core network applies the basic form of upgrading 2G circuit switching to high-speed circuit switching and packet switching.The third generation core network includes two kinds of network forms: mobile switching network and service network. The mobile switching network is mainly responsible for the connection between the wireless network and the fixed network and the management of the terminal mobile performance function, while the service network is mainly responsible for providing the same services and services for mobile users and fixed users. For example, users can enjoy a series of services such as e-commerce, billing and calling.

 Progress

The third-generation mobile communication system is still a regional communication system based on different ground standards, although its transmission rate under the mature WCDMA standard, the theoretical value of 7.2Mb/ s at rest, and the actual commercial network by resources and wireless environment constraints far below the value. It still can not meet the requirements of many multi-media communication, and can not support the communication with high speed requirements. Insufficient provision for dynamic range multi-rate services. At present, the core network supported by the three commercial standard air interfaces cannot have a unified standard, and it is difficult to provide multi-rate services with multiple QoS and performance. Seamless roaming between different business environments in different frequency bands is not truly possible. For different service environments using different frequency bands, mobile terminals need to be configured with different software and hardware modules, and 3G mobile terminals cannot achieve different configurations of this service environment. It is because of these limitations of 3G systems that various companies and institutions have long embarked on LTE research.

Applied everywhere

UK

On December 8, 2021, according to British media reports, the British government said it would phase out 2G and 3G services by 2033 in order to give way to 5G and 6G services.

America

On December 31, 2022, Verizon, the mainstream telecom operator in the United States, will shut down its 3G network. Starting in 2023, there will be no more 3G networks in the United States.

China

In December 2023, the Ministry of Industry and Information Technology responded to the issues related to the withdrawal of 2G/3G networks concerned by users on the People's Network Leadership Message Board. According to the Ministry of Industry and Information Technology, 2G/3G withdrawal is an inevitable choice for the upgrading of mobile communication networks, and is also the main international practice. However, the withdrawal of mobile communication network is not simply a "retreat". It is necessary to improve user protection measures and fully protect the rights and interests of users in order to implement withdrawal from the network.[10] 3G network withdrawal can use limited frequency resources and network resources in the development of 5G and 4G mobile communication networks, which is conducive to reducing the overall cost of network operation and improving the efficiency of network operation in China. The Ministry of Industry and Information Technology will plan as a whole and advance reasonably, and at the same time require mobile communication enterprises to plan early and inform early, so as to create conditions for users to "be willing to retreat" and "be willing to retreat".