Mobile Communication 3G Technology Overview
Zheng Yi
China Mobile and China Unicom's competition in mobile communications markets is increasingly fierce, and the competition is developed from the original voice service to the value-added business. With the continuous development of mobile value-added services, it is a inevitable choice for two major mobile operators to 3G (3rd Generation, third-generation mobile communication). Compared with the first two generation systems, the main feature of the third generation mobile communication system is to provide colorful mobile multimedia services, and their transmission rate supports 144kb / s in a high-speed moving environment, and supports 384KB / s in walking slow moving environment. 2MB / s supports 2MB / s in stationary state. Its design goal is to provide a larger system capacity, better communication quality than the second generation system, and can better achieve seamless roaming in a global scale and provide users with voice, data and multimedia. A variety of business, but also consider good compatibility with the second generation system.
At present, the 3G standards accepted by ITU mainly have the following: WCDMA, CDMA2000 and TD-SCDMA. CDMA is the abbreviation of Code Division Multiple Access (Code Division Multiple Access), which is the technical foundation of the third generation mobile communication system. The first generation of mobile communication systems uses the simulation modulation modulation of frequency division multiple access (FDMA). The main disadvantage of this system is that the spectral utilization rate is low, and the signaling is interfering. The second generation mobile communication system mainly uses the digital modulation method of time division multi-access (TDMA), and the system capacity is improved, and the independent channel transmission signal is used to make system performance improvement, but TDMA system capacity is still limited, and the overcover switching Performance is still not perfect. The CDMA system is simple in its frequency planning, high system capacity, high frequency multiplexing coefficient, strong anti-multi-diameter capacity, good communication quality, soft capacity, soft switching, etc. show huge development potential.
1, WCDMA
It is a Wideband CDMA, which is a 3G technical specification developed by GSM network. It is a broadband CDMA technology proposed in Europe. It is basically the same as the broadband CDMA technology proposed by Japan. It is currently being further integrated. This standard proposes an evolutionary strategy for GSM (2G) -GPRS-EDGE-WCDMA (3G). GPRS is the abbreviation of General Packet Radio Service (General Packet Wireless Service), EDGE is a referred to as ENHANCED DATA RATE for GSM EVOLUTION (GSM Evolution of Enhanced Data Rate), which is called 2.5 generation mobile communication technology. At present, China Mobile is using this program to transition to 3G, and has upgraded the original GSM network to a GPRS network.
2, CDMA2000
The CDMA2000 is a broadband CDMA technology developed by narrow-band CDMA (CDMA IS95), which is pushed by the United States, which proposes an evolutionary strategy from CDMA IS95 (2G) -CDMA20001X-CDMA20003X (3G). CDMA20001x is called 2.5 generation mobile communication technology. The main difference between CDMA20003X and CDMA20001x is to apply multi-carrier technology, and increase bandwidth by using three carriers. At present, China Unicom is using this program to transition to 3G and has built a CDMA IS95 network.
3, TD-SCDMA
It is called Time Division-Synchronous CDMA (Time Synchronous CDMA), which is a 3G standard proposed by the Datang Telecom Company of my country. This standard is proposed without the 2.5-generation intermediate link, directly to the 3G transition, which is very suitable for the GSM system to upgrade to 3G. However, Datang Telecom has not yet been launched based on this standard for commercial products.
Comparison of three technical standards
WCDMA, CDMA2000 and TD-SCDMA are part of broadband CDMA technology. Broadband CDMA further expands the standard CDMA concept, expands signals on a relatively wider frequency band, thereby reducing the propagation problems caused by multipath and attenuation, with larger capacity, can use different bandwidth according to different needs, Has strong anti-fading ability and anti-interference ability, support multi-channel synchronous call or data transmission, and is compatible with existing equipment. WCDMA, CDMA2000 and TD-SCDMA can provide 2 mbit / s data transfer rates in a stationary state, but some key technologies in the three still have a large difference, and there is also different performance. 1, duplex mode
Both WCDMA and CDMA2000 use FDD (frequency division digital duplex) mode, TD-SCDMA uses TDD (Time Digital Duplex) mode. FDD is a duplex mode of two symmetrical bands that use separate (send) and downlink (received) transmission, requires a pair of frequencies, distinguishes, down, down, for symmetrical services (such as speech) The spectra of up and down lines, but for the non-configurable packet switched data traffic (such as the Internet), the spectral utilization is greatly reduced due to the low load load. TDD is a duplex mode of the uplink and downlink transmission using the same frequency band. According to the time, down, down and switch, the time slot of the physical layer is divided into upper, downlink two parts, no need to pair, up and down The link service shares the same channel, which can be unassigned, especially suitable for non-confiTemark exchange data services (such as the Internet). The spectral utilization rate of TDD is high, and the cost is low, but due to the non-continuous transmission of multi-time slots, the ratio of the peak power and the average power is high, resulting in a large base station power consumption, and the base station covers the radius of the base station smaller, and also cause Anti-fading and anti-Doppler frequency shift are poor, and when the phone is in a state where the mobile phone is moved, the communication capacity is poor. WCDMA and CDMA2000 can support normal communication when the mobile terminal is about 500 kilometers of speed, while TD-SCDMA can only support normal communication when the mobile terminal is about 120 kilometers per hour. TD-SCDMA is in a disadvantage in high-speed moving in highways and railways.
2, chip rate and carrier bandwidth
WCDMA (FDD-DS) uses a direct sequence spread spectrum mode, and its chip rate is 3.84 MCHIP / s. The difference between CDMA20001x and CDMA20003X is that the number of carriers is different. The CDMA20001x is a single carrier, and the chip rate is 1.2288 MCHIP / S, and the CDMA20003X is three carriers, and the chip rate is 1.2288 × 3 = 3.6864 MCHIP / S. The chip rate of TD-SCDMA is 1.28 MChip / s. The chip rate high energy efficiently utilizes frequency selective diversity and space reception and emission diversity, which can effectively solve multipath problems and fading problems, and WCDMA is the most advantageous in this regard.
In terms of carrier bandwidth, WCDMA adopts direct sequence expanded technology with 5MHz carrier bandwidth. The CDMA20001x uses a 1.25 MHz carrier bandwidth, and the CDMA20003X utilizes three 1.25 MHz carriers to form a 3.75 MHz carrier bandwidth. TD-SCDMA is designed with a three carrier, each carrier having a bandwidth of 1.6M. The higher the carrier bandwidth, the more the number of supported users, the smaller the possibility of a mesh when communication is in communication. WCDMA in this area has a more obvious advantage.
The TD-SCDMA system uses only 1.28 MCHIP / s chip rate, which uses the TDD duplex mode, so only the single 1.6M bandwidth can transmit 2 Mbit / s data services. WCDMA and CDMA2000 need to transmit 2 Mbit / s data services, both symmetrical bandwidth, as top, downlink band, respectively, thus the utilization of TD-SCDMA to frequency resources is the highest. 3, intelligent antenna technology
Intelligent antenna technology is a key technique adopted by TD-SCDMA. It has been applied by Datang Telecom. The current WCDMA and CDMA2000 have not been adopted. The intelligent antenna is a bidirectional antenna mounted on the base station on-site, through a set of fixed antenna units with programmable electron phase relationships, and can simultaneously acquire the directional characteristics of each link between the base station and the mobile station. The high efficiency of the TD-SCDMA intelligent antenna is obtained based on the symmetry of the uplink and the downlink wireless path (the same wireless environment, and transmission conditions). The smart antenna can also reduce interference between cells and cells. These features of the intelligent antenna can significantly improve the spectral efficiency of the mobile communication system.
4, Vietnam Switching Technology
Both WCDMA and CDMA2000 use the "soft switch" technology, that is, when the mobile phone moves or currently communicating with the mobile phone, it is not necessary to interrupt the contact with the original base station when the mobile phone communicates with the mobile phone needs to communicate with a new base station. However, after connecting to the new base station, interrupt the connection with the original base station, which is a classic CDMA technology. "Soft switch" is relative to "hard switching". Both FDMA and TDMA systems use "hard switching" technology, first interrupt the connection with the original base station, and then connect to the new base station, and it is easy to generate a drop. Since soft switching is connected to two base stations at the same time, the channel resource takes up. The TD-SCDMA is a transcendental "relay switching" technology, and the smart antenna can generally locate the user's orientation and distance, the base station and the base station controller determine whether the user moves to the other according to the user's orientation and distance information. The adjacent area of a base station, if the switching area is entered, the base station controller notifies the other base station to do a good job, reach the relay switching. The relay switch is an improved hard switching technology that improves the switching success rate, which can reduce the occupancy time of the adjacent base station channel resource compared to soft switching.
In the process of switching, coordination operations between two base stations are required. WCDMA does not require synchronization between base stations, and complete soft switching through timed differential reports between two base stations. Both CDMA2000 and TD-SCDMA require strict synchronization between base stations, thus must determine the location of the phone with a device such as GPS (Global Positioning System, Global Positioning System) and calculate the distance to the two base stations. Since GPS depends on satellite, CDMA2000 and TD-SCDMA network departments will be limited, while WCDMA's network is easier to deploy in many environments, even if the GPS signal such as the subway cannot be reached, the base station can also be installed, realization Seamless covered. And GPS is a US system. If the mobile communication system is established in GPS reliably, it will be subject to the US GPS policy, there is a certain risk.
5, compatibility with the second generation system
WCDMA is transitioned by a GSM network, although the GSM core network can be retained, but the WCDMA access network must be re-established, and the GSM base station must be re-established. CDMA20003X transitions from CDMA IS95, CDMA20001X, can retain original CDMA IS95 devices. The construction of the TD-SCDMA system only needs to add TD-SCDMA devices on existing GSM networks. In the three technical standards, WCDMA has a maximum of the upgrade.
3G strategy for mobile operators
At present, 73 WCDMA operation licenses have been issued, and 13 CDMA2000 operation licenses have been issued. my country's 3G licenses have not been issued, China Mobile, China Unicom and other operators will adopt what technical standards are still not determined. Soonfore recently, the Ministry of Information Industry has planned the use frequency of WCDMA, CDMA2000, TD-SCDMA, indicating that these three criteria will be adopted in my country. 2.5 g technology was derived between 2g and 3 g. 2.5g technology Break through the restriction of 2G circuit switched technology on data transmission rate, introduced packet switching technology, so that the data transmission rate has a quality breakthrough, which is a transition technology between 2g and 3 g. At present, China Mobile has built a 2.5-generation GPRS network, which is moving toward WCDMA. China Unicom suddenly turned to the development of CDMA IS95 network after developing the GSM network, and was moving towards the direction of CDMA2000. Although the CDMA2000 saves investment in the upgrade process, because China Unicom has developed CDMA IS95 network by GSM network, its network cost investment is quite large. Since China Unicom's CDMA network construction started late, the 2.5-generation CDMA20001X network has not yet been completed, and it is disadvantageous in the competition with China Mobile's 2.5-generation business. On October 1 this year, China Mobile officially launched a 2.5-generation version of the MMS service (MMS, multimedia information service), which can load multimedia information such as sound, image, video in mobile phone text messages, and use GPRS network to reach about 40kbit. The transmission speed of / s unveil the prelude to the mobile multimedia era, and new features such as color screen and string digital cameras will immediately go to the market. In response to China Mobile's MMS business, Guangdong Unicom has launched a color e business, but China Unicom's CDMA IS95 network can only provide 14.4 kbit / s transmission speed, and form a bottleneck for multimedia information. Rapid Development 2.5 generation CDMA20001x network has become the urgent task of China Unicom.
The TD-SCDMA with independent intellectual property rights will be held in the 3G technical standards. TD-SCDMA can effectively save spectrum resources, enabled from a cheap upgrade from the GSM system, but its communication quality is poor by WCDMA and CDMA2000. After all, it is only a matter of concern to the Government and operators, as users are always the first choice. Under the fierce competition in my country's mobile communication market, the need to meet the needs of users is always the goal of operators to pursue, and the TD-SCDMA may be applied in the low-end 3G market in the future. At present, TD-SCDMA technology has not been adopted by foreign operators. If there is only this standard in my country, this standard will make new problems on international roaming. Datang Telecom has not launched a mature product based on TD-SCDMA technology, and its research and development progress is behind WCDMA and CDMA2000. But soon, we would like to see the "TD-SCDMA Industry Alliance" established, Datang Telecom, Southern High School, Hua Li, Huawei, Lenovo, ZTE, China Electronics, China Putian and other 8 enterprises have formed the first core of the alliance. Make this technology to commercial support. TD-SCDMA is the first standard in China in mobile communication, and its emergence is a breakthrough in China's 100-year telecommunications history. We are happy to be mature.
At present, in the second generation of mobile communication systems, both GSM or CDMA IS95 have been able to provide basic satisfactory voice quality and communication stability, but its data transmission rate is low, and thus the third generation mobile communication system is the most attractive The place is not in terms of the improvement of voice quality and communication stability, but the significant increase in data transmission rates, which will greatly promote the development of mobile multimedia business. However, the main purpose of the mobile phone is a call, not other value-added services. Whether the huge investment in 3G can create benefits and is still an unknown. At present, the 2.5-generation business development can provide a certain help for our 3G strategy.
China Mobile's GPRS has been launched so far, and the more successful MMS business is based on GPRS bandwidth multimedia business, and the number of users who directly use GPRS mobile phones and computer connecting Internet users have not much. After all, people with mobile Internet needs are only a few. At present, the 2.5-generation GPRS or CDMA20001X can provide a data transfer rate of 40kbit / s, which can basically meet the bandwidth requirements of multimedia information transmission such as sound, image, short video. The main purpose of mobile Internet is to send and receive officials such as E-mail, rather than downloading video, etc., and current bandwidth can also be basically met. The theoretical transmission rate of GPRS or CDMA20001X is around 150kbit / s. In the future, with the continuous upgrade of 2.5G network, its actual transmission rate will gradually approach this value, and provide stronger support for mobile multimedia and mobile Internet services. The 3G network can have a data transfer rate of 2 mbit / s in the mobile phone stationary state. In terms of multimedia business, 3G compared to 2.5G is capable of providing more colorful video information; for mobile Internet access, mobile Internet access speed can basically reach the level of current wired broadband network. However, can a significant increase in bandwidth increase enough traffic to make 3G achieved profit? In terms of multimedia applications, you can use your mobile phone to quickly send a video to other mobile phones, which can be applied to an important party such as a reporter interview and wedding. This is a profit point of 3G, but the number of users is very few. In the mobile Internet, you can download the video on the Internet or watch online movies, live broadcast, etc. However, this kind of user Liao Liao is unique due to the rapid spread of wired broadband networks. Moreover, the cost of mobile communication is much higher than that of wired communication, and its tariff is norty, the price will also become an unfavorable factor in restricting the development of 3G business.
Considering the various factors above, my country does not have market conditions for development of 3G. The world's other countries have adopted 3G to the development. It has been postponed 3G development plans as a rapid development of WCDMA. The British Vodafone Group announced that the original plan of the 3G service launched in Germany today will postpone for about 6 months, while terminating 3G network infrastructure in the UK and other regions in Europe. Orange, France's Telecom is negotiating with the official official, requiring 3G services in Sweden. Spanish Telecom Telefonica and Finnish Sonra Telecom announced that it will provide 3G services to Germany, Italy, Austria and Switzerland. Suppliers of 6 general mobile communication systems in Germany have been forced to delay 3G commercial operations. In Hong Kong, my country, it is expected that 3G operators in today's two years have also postponed time to 2005 or 2006.
At present, mobile operators need to focus on how to build and further optimize 2.5G networks, provide better support for mobile multimedia and mobile Internet services, which is a small investment and profitable project. The development of 3G is a general trend, but should be in the blind comparison of the country or operator and operators with the maturity of potential markets. (2003.02)
