What Is 3G CDMA?

3G is the third generation mobile communication technology, which refers to the cellular mobile communication technology that supports high-speed data transmission. 3G services are capable of transmitting both voice and data information. 3G is a generation of mobile communication systems that combines wireless communications with multimedia communications such as the Internet.

Chinese name: Third generation mobile communication technology
Foreign name: 3rd-Generation

Foreign language abbreviations: 3G
Provide services: Digital voice and data

3G Introduction

The so-called third-generation mobile communication technology, that is, 3G network technology, compared with the first-generation mobile communication technology (that is, 1G) and the second-generation digital mobile communication technology (that is, 2G), 3G mobile phones are mainly wireless communications and the Internet. The communication technology is comprehensively combined to form a brand new mobile communication system. This mobile technology can handle media formats such as images and music. In addition, it also includes some business functions such as conference calls. In order to support the functions described above, the wireless network can fully support different data transmission speeds, that is, it can provide a minimum of 2Mbps, 384kbps, and 144kbps data transmission speeds, whether outdoors, indoors or in a driving environment. ^[1]

The third generation of mobile communication technology (3G), 3G network technology is inevitable for the development of this field. 3G defines mobile communication technology standards, uses higher frequency bands and CDMA technology to transmit data for related technical support, and has a high operating frequency band. The main characteristics are fast speed, high efficiency, stable signals, low cost, and good security performance. Compared with the previous two generations of communication technology, the most obvious feature is that 3G network technology fully supports more diverse multimedia technologies. ^[2]

3G Technology Origins

In 1940, American actress Heidi Rama and her composer husband George Ansell proposed a concept of Spectrum technology, which is called "spread spectrum technology" (also known as code division spread spectrum technology). Technology theory has brought changes to this world since then. It is this technology theory that eventually evolved into our 3G technology today. Spread spectrum technology is the fundamental principle of 3G technology. Spread spectrum is a communication technology that spreads the spectrum of a transmission signal to a wider range than its original bandwidth, and is often used in the field of wireless communications.

After the Nazis officially invaded Austria in March 1938, she also fled to London to stay away from her failed marriage and numerous Nazi "friends." By the way, the "military secrets" of Nazi wireless communications were brought to the allies. These secrets are mainly "command-oriented guidance" systems based on radio-secret communications, which are used to automatically control weapons and strike targets accurately. She educated secretly assimilated many valuable forward-looking concepts.

But in the end of August 1942, she still got a U.S. patent. At the U.S. Patent Office, there was such a patent: the "secret communication system" patent with the patent number of 2,292,387. On August 11, 1942, the application time was June 10, 1941, and spread spectrum technology (spread spectrum technology) was spread. This technology patent is archived on the National Patent Office's website for military use.

Heidi Rama originally researched this technology to help the US military create a military communication system capable of dealing with radio interference or anti-eavesdropping in Nazi Germany. Therefore, this technology was originally used in the military. After the end of World War II, the United States military sealed up this technology because it temporarily lost its value, but its concept has attracted interest from many countries. Many countries began to study this technology in the 1960s, but little progress was made.

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

In May 2008, the International Telecommunication Union officially announced the third-generation mobile communication standard. TD-SCDMA submitted by China has officially become an international standard, and it has become one of the three most mainstream technologies in the 3G era with European WCDMA and US CDMA2000.

3G Important factors for 3G 3G development success

With the development and development of mobile communication network technology, the application of this type of technology in various fields is indispensable, but the standards set by various communication companies for related technical methods are different, which has greatly inhibited the development of this technology. Later 3G services The emergence of the Internet has changed this chaotic situation. In addition, 3G services have many high-quality features such as higher speed, smarter, more stable, more diversified, and gradually transitioned to all-IP networks. The biggest difference between the future network and today's IP is that it can cost-effectively provide multiple services and support end-to-end quality of service. MPLS is a gradually clear development trend. ^[2]

3G technology is an integration of three key technologies: wireless, data (IP and ATM), and telephony (circuit switched and packet switched). The elements that guarantee the success of 3G networks include the open interface standards and unified management advocated by relevant networks in international standards organizations, and the timely commercialization of user terminals. The repeated delays in the release of GPRS terminals have caused some concern. In fact, this worry is not unreasonable. Looking at the individual handset manufacturers of the entire 3G terminal, they have not formed a unified standard like the 3G service platform. In addition, for this, The research on a new type of multimedia terminal equipment also suffers from some setbacks, and its related technologies also need to be replaced and replaced in a large amount. But in fact, for 3G business, the most important thing is whether the developer can get the due benefits. After all, this is a commercial use. Without interest, it means that the process fails. ^[2]

Comparison of 3G technical characteristics

The first generation of mobile communication technology was analog mobile communication technology, which represented AMPS in the United States, TACS in the United Kingdom, and NMT450 / 900 in Northern Europe. The main features are analog frequency modulation (FM) and frequency division multiple access (FDMA). The first generation of mobile communication systems was limited to voice transmission. It used analog circuit units as the basic module to implement voice communication and adopted a cellular structure. The frequency band can be reused. To achieve uninterrupted communication with large area coverage and mobile environment. ^[3]

The second generation mobile communication system is a mobile communication system featuring time division multiple access (TDMA) and code division multiple access (CDMA). In addition to providing voice services, it also provides low-speed data services. Currently, there are three main types of TDMA systems: GSM in Europe, D-AMPS in the United States, and PDC in Japan. The main adopter of CDMA technology is American CDMA (IS95). Direct spread spectrum and anti-interference are the outstanding features of CDMA mobile communication technology. The core network of the second generation communication system is still based on circuit switching. ^[3]

GPRS (General Packet Radio Service) can be regarded as a 2.5-generation mobile communication system between the second and third generations. It is a new bearer service developed on the existing second-generation GSM voice communication system. Through software upgrade and adding necessary hardware modules, packet data transmission is realized by using the signaling channel of GSM's existing wireless voice communication system, so it can coexist with GSM and can smoothly transition. The most fundamental difference between GPRS wireless packet data communication and existing GSM voice communication is that GSM is a circuit-switched system, while GPRS's short-message service etc. use a packet-switched system. CDMA-2000-1x is the first phase of CDMA-2000, and it is also 2.5G. Its network part also attracts packet switching. ^[3]

The third generation mobile communication system is proposed by the International Telecommunication Union (ITU) for international mobile communications in 2000. It has multiple functions such as global mobile, integrated services, data transmission cellular, cordless, paging, and trunking, and can meet the spectrum utilization rate. , Mobile operating system, business capability and quality, flexible network, seamless coverage, compatibility and other requirements of the global mobile communication system, referred to as IMT-2000 system. The system works in the 2000MHz frequency band and can provide both circuit switched and packet switched services. The uplink and downlink frequency bands are 1890-2030MHz, 2110-2250MHz. ^[3]

Comparison of 3G standards

The third generation of mobile communication uses code division multiple access technology, and has now basically formed three major mainstream technologies, including: W-CDMA.CDMA-2000 and TD-SCDMA. All three technologies are broadband CDMA technologies, which can provide 2Mbius data transmission rate in the static state. However, these three technologies have different characteristics in terms of working modes and district-city switching. ^[3]

W-CDMA, full name 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 broadband CDMA technology proposed by Europe. Broadband CDMA technology is basically the same and is currently being further integrated. WCDMA supporters are mainly European manufacturers mainly based on GSM systems, and Japanese companies are more or less involved, including European and American Ericsson, Alcatel, Nokia, Lucent, Nortel, and Japanese NTT, Fujitsu, Sharp and other manufacturers . This standard proposes the evolution strategy of GSM (2G) -GPRS-EDGE-WCDMA (3G). This system can be set up on the existing GSM network, and it can be easily transitioned for system providers. 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 currently the most widely used 3G standard in countries and regions in the world and the most abundant terminal types, occupying more than 80% of the global market share.

CDMA-2000 is a broadband CDMA technology developed from narrow-band CDMA (CDMA IS95) technology, also known as CDMA Multi-Carrier. It is proposed by Qualcomm North America, and Motorola, Lucent, and later Samsung Samsung joined With participation, South Korea became the leader of the standard. This system is derived from the narrowband CDMAOne digital standard. It can be directly upgraded from the original CDMAOne structure to 3G, and the construction cost is low. However, only Japan, South Korea, and North America use CDMA, so CDMA2000 supporters are not as many as W-CDMA. However, CDMA2000's research and development technology is currently the fastest progress in various standards, many 3G mobile phones have already taken the lead. The standard proposes an evolution strategy from CDMAIS95 (2G) -CDMA20001x-CDMA20003x (3G). CDMA20001x is called 2.5 generation mobile communication technology. The main difference between CDMA20003x and CDMA20001x is that multi-carrier technology is applied, and the bandwidth is increased by using three carriers. China Telecom is adopting this solution to transition to 3G and has established a CDMAIS95 network.

The full name of TD-SCDMA is Time Division-Synchronous CDMA (Time Division Synchronous CDMA), which is a 3G standard developed by China alone. It was proposed, but the technical invention started from Siemens. TD-SCDMA has the characteristics of low radiation and is known as green 3G. This standard integrates today's leading international technologies such as smart wireless, synchronous CDMA, and software radio, with unique advantages in spectrum utilization, service support flexibility, frequency flexibility, and cost. In addition, due to the huge market in mainland China, the standard has been valued by major telecommunications equipment manufacturers, and more than half of the equipment manufacturers worldwide have announced that they can support the TD-SCDMA standard. The standard proposes to directly transition to 3G without going through the intermediate link of 2.5 generations, which is very suitable for the GSM system to upgrade to 3G. Military communication network is also the core task of TD-SCDMA. Compared to the other two major 3G standards, CDMA2000 and WCDMA, it started late and the technology is not mature enough.

3G working mode

W-CDMA can work in both FDD and TDD modes and uses the same clock as the GSM system to achieve dual-mode operation of CDMA and GSM mobile phones. It is a compatible system. FDD is a duplex mode that uses two separate symmetrical frequency bands to implement uplink and downlink transmissions. It needs paired frequencies to distinguish up and down 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 achieve high-speed data communication. Its biggest feature is that it has uplink multi-user detection technology. Multi-user detection technology can measure the non-orthogonality between the spreading codes of each user, and use matrix inversion method or iterative method to eliminate mutual interference between multiple users. . CDMA-2000 only supports FDD operation mode. ^[3]

TD-SCDMA is an IMT-2000 system design scheme proposed by China, which uses TDD mode. TDD is a duplex mode that uses the same frequency band for uplink and downlink transmissions, and distinguishes between uplink and downlink based on time. The physical time slot is divided into uplink and downlink. There is no need for paired frequencies. Link services share the same channel and can be unevenly distributed, which is especially suitable for asymmetric packet-switched data services. TDD has high spectrum utilization and low cost, but because of the multi-slot discontinuous transmission method, the ratio of the peak power to the average power of the base station is high, resulting in large power consumption of the base station and a small coverage radius of the base station. The performance of fading and anti-Doppler shift is poor, and the communication ability is poor when the mobile phone is moving at a high speed. TD-SCDMA can only support normal communication of mobile terminals at a speed of about 120 kilometers per hour. TD-SCDMA is at a disadvantage in high-speed moving environments such as highways and railways. ^[3]

3G area switching

W-CDMA uses "soft handover" technology between sectors and between cells, that is, when the mobile phone is moving or the base station business currently communicating with the mobile phone is busy and the mobile phone needs to communicate with a new base station, it should first connect to the new base station and then interrupt the For the connection of the original base station, the handover of W-CDMA is performed by asynchronous soft handover. There is no need for synchronization between W-CDMA base stations and no special synchronization reference source. The handover between carrier frequencies is a hard handover, that is, the connection with the original base station is interrupted before the new base station is connected. ^[3]

CDMA-2000 also uses cross-zone "soft handover" technology. CDMA-2000 requires strict synchronization between base stations. Therefore, GPS and other equipment must be used to determine the location of the mobile phone and calculate the distance to the two base stations. Hard switching is used between carrier frequencies. ^[3]

TD-SCDMS uses crossover "relay switching" technology. Smart antennas can roughly locate the user's position and distance. The base station and the base station controller can determine whether the user has moved to another base station based on the user's position and distance information Proximity area. If entering the handover zone, the base station controller will notify the other base station to prepare for handover. Before the handover, the mobile station will synchronize with the identified base station and report to the network. The network will control the mobile station to complete the handover. This method is applicable to both intra-frequency switching and inter-frequency switching. Relay handover is an improved hard handover technology, which reduces the dropped call rate and improves the handover success rate. Compared with soft handover, the signaling and resources used are very small. TD-SCDMA requires strict synchronization between base stations. GPS or network synchronization is used to reduce interference between base stations. ^[3]

3G resource utilization

W-CDMA uses a direct sequence spreading method, and its chip rate is 3.84Mchip / s. The chip rate can effectively use frequency selective diversity and spatial receive and transmit diversity, which can effectively solve multipath problems and fading problems. Each carrier of W-CDMA only occupies 5MHz bandwidth. The higher the carrier bandwidth, the greater the number of users supported, and the smaller the possibility of network congestion during communication. ^[3]

CDMA-2000 has two main channel structures in F-link: multi-carrier and direct spread spectrum. Multi-carrier downlink transmission generally uses 3 consecutive carriers in a 5 MHz bandwidth, and the chip rate of each carrier is 122288 Mchip / s; for downlink transmission in the direct spread spectrum mode, a code of 3.6864 Mchip / s is usually used Slice rate. When the multi-carrier method is adopted, different radio frequency channel bandwidths can be used to support multiple radio frequency bandwidths. It can transmit data at a rate of 1.2 kbps to 2 Mbps 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. ^[3]

The chip rate of TD-SCDMA is 1.28Mchip / s. TD-SCDMA uses a three-carrier design, each carrier has a bandwidth of 1.6M. Because it uses TDD duplex mode, it only needs a single 1.6M bandwidth to transmit 2Mbps data services. For W-CDMA and CDMA-2000 to transmit 2 Mbps data services, two symmetrical bandwidths need to be assigned, which are respectively used as uplink and downlink frequency bands. Therefore, TD-SCDMA has the highest utilization of frequency resources. ^[3]

3G signal modulation and coding

W-CDMA uses BPSK for uplink and QPSK for downlink. The uplink of the spread spectrum coding adopts Walsh (channelization) + Gold sequence 241-1 (to distinguish users), and the downlink uses Walsh (channelization) + Gold sequence 218-1 (to distinguish cells). The channel coding is a convolutional code and an RS cascade code, and the diversity uses RAKE reception plus antenna diversity. Power control adopts open-loop K slow-closed loop (1.6K). Pilot symbols assist coherent detection of RAKE during joint detection. The uplink uses dedicated pilot symbols, and the downlink uses perch channels + dedicated pilot symbols. ^[3]

The signal modulation of CDMA-2000 uses the BPSK modulation method on the uplink and the QPSK modulation method on the downlink. Spread-spectrum coding adopts Walsh (channelization) + Gold sequence 241-1 (differentiation of users) on the uplink, and uses Walsh (channelization) + Gold sequence 215-1 (downcoming of cells) on the downlink. In joint detection, the common pilot channel is used for uplink The downlink uses a dedicated pilot channel. The signal modulation method of TD-SCDMA is QPSK / BPSK modulation. Spread-spectrum coding adopts Walsh (channelization) + time slot number (to distinguish users) on the uplink, and uses Walsh (channelization) + Gold sequence (to distinguish cells) on the downlink. Power control uses open loop + fast closed loop (0-200Hz). Joint detection , Uplink / downlink synchronization signal Gold code + training sequence. ^[3]

The key technology used in TD-SCDMA is smart antenna technology. Smart antennas use array antennas at the base station to adaptively form multiple beams and track multiple users who share the same channel. During reception, spatial-domain filtering is used to suppress co-channel interference and separate each user; during transmission, multi-beamforming is used to maximize the power of the signal received by the desired user and minimize interference to undesired users at other locations. In this way, the transmission power of the signal can be reduced, and interference from other users can be reduced, thereby improving the system capacity and communication quality. The high efficiency of the TD-SCDMA smart antenna is obtained based on the symmetry of the wireless path of the uplink and downlink (same wireless environment and transmission conditions). Smart antennas can also reduce interference between cells and cells. These characteristics of smart antennas can significantly improve the spectral efficiency of mobile communication systems. ^[3]

TD-SCDMA system uses smart antenna and low chip rate signal transmission. The signal has a high spectrum utilization rate. It can solve the problem of tight frequency resources in high population density areas. It is used in Internet browsing, asymmetric mobile data transmission, and video on demand. Multimedia services have outstanding advantages. ^[3]

TD-SCDMA uses software radio technology. When the operation department increases its business, it can use software to process baseband signals on the same hardware platform and load different software to achieve different service performance. ^[3]

When synchronous CDMA communication is used, the signals arriving at each mobile station in the downlink are synchronized, and the signals arriving at each base station in the uplink are also synchronized. The mobile station signal can be obtained by measuring the accurate propagation delay of the signal from the base station to the mobile station. Accurate sending time. TD-SCDMA uses uplink synchronous CDMA technology to make the uplink signal fully synchronized with the base station demodulator, which not only reduces the interference between uplink users and the width of the protection time slot, but also increases the system capacity, which simplifies the hardware and significantly costs reduce. ^[3]

3G security architecture

3G client

Users mainly use mobile 3G technology to obtain communication services through mobile phones, and some users also use radio equipment to obtain signal sources. The most mainstream is the communication service requests for mobile phone ports. The most critical part in the distressing process is the stability of signal transmission. As well as signal strength, 3G technology can effectively implement high-intensity and stable call information services, realize stable and fast transmission of data, and at the same time implement data encryption. ^[4]

3G Security Management Server

There are two types of authentication services currently in use. One is to use Kerberos technology to verify the user identity of the cryptographic key; the other is to use public keys to encrypt the system and use the X.509 service protocol. To verify the identity of both parties and service requests. It is necessary to ensure that both authentications have reliable encryption and anti-malicious attacks to fully ensure that the user's personal privacy is not stolen. ^[4]

3G server

The server is a receiver that receives user service application content. It contains various special service signals and passwords, and transmits to the corresponding service resources according to the user's personalized request. It can be said that the server is a system that responds to and responds to requests and commands made by the client. ^[4]

3G 3G 3G- based Internet

3G 3G 3G- based data transmission

High-speed circuit-switched data has been widely used in wireless communications at this stage. The data rate in a single service channel has been increased from 9.6kb / s to 14.4kb / s, and four channels are multiplexed in the same time slot at the same time. In addition, the data operator can further transfer data at a transmission rate of 57.6kb / s, which is more than 6 times the current data transmission rate at the same time. However, the GPRS developed by Nokia can be bundled in 1 carrier frequency or 8 channels to increase the data transmission rate of each channel to 14.4kb / s. For this reason, the maximum transmission efficiency of GPRS can reach 115.2kb / s. This data transmission method mainly uses TDMA's voice transmission method, and the packet form is mainly data transmission. At the same time, it also means that users have been charging online according to the flow meter, which has reduced service costs rapidly. This technology is between 2G and 3G, and is generally referred to as a 2.5G wireless communication technology. The above three technologies are communication technologies based on the continuous transition of the third generation mobile communication technology. ^[1]

3G 3G 3G wireless interface standards and features

As early as 1999, Finland had met to adopt the wireless interface technology standard included in the third generation mobile communication system. It can also be known from this that the third generation of mobile communication technology mainly uses the broadband CDMA system as the main system, and CDMA is code division multiple access technology. The main feature of mobile communication is the use of multiple access technology, which is a base station. The base stations used by the mobile stations in the surrounding area enter the technology related to receiving signals. Only when the mobile station occupies a channel can mobile communication be performed. The Internet technology goal based on the third-generation mobile communication technology is mainly to achieve a global mobile integrated service digital network. This network not only integrates the basic functions of some mobile communication technologies such as cordless, mobile data, and mobile satellites, but also Able to provide compatible services for fixed telecommunications networks, as well as voice and non-voice services. ^[1]

3G 3G 3G infrastructure

The third generation mobile communication technology mainly includes four functional subsystems, which are a core network, a wireless access network, a mobile station, and a user identification module. Among them, the wireless access network mainly uses five access standards based on the ITU, but the core network uses the basic form of upgrading 2G circuit-switched lines to high-speed circuit switching and packet switching. The third generation core network covers two types of networks: mobile switching network and business service network. The mobile switching network is mainly responsible for the connection between the wireless network and the fixed network and the management of terminal mobile performance functions. The business service network is mainly Mobile users provide the same services and services as fixed users. For example, users can enjoy a series of services such as e-commerce, billing, and calling. ^[1]

3G progress

The third-generation mobile communication system is still a regional communication system based on different terrestrial standards. Although its transmission rate is under the mature WCDMA standard, the theoretical value at standstill is 7.2Mb / s. Actually, in the commercial network, resources and wireless Environmental limits are far below this value. It still cannot meet the requirements of many multimedia communications, and cannot support communications with higher speed requirements. Inadequate provision of dynamic range multi-rate services. In addition, the core networks supported by the three commercial air interfaces currently fail to have a unified standard, and it is difficult to provide multi-rate services with multiple QoS and performance. It is not really possible to achieve seamless roaming between different service environments in different frequency bands. For different service environments using different frequency bands, mobile terminals need to be configured with different related software and hardware modules, and 3G mobile terminals cannot implement different configurations of this service environment. It is the 3G system that has these limitations, so various companies and institutions have already begun research on LTE. ^[5]