With the continuous development of mobile value-added services, moving towards 3G (3rd Generation, third generation mobile communications) is an inevitable choice for major mobile operators. Compared with the first two generations of systems, the main features of the third generation mobile communications system are It can provide a variety of mobile multimedia services. Its transmission rate supports 144kb/s in a high-speed mobile environment, 384kb/s in a slow-moving walking environment, and 2Mb/s in a stationary state. Its design goal is to provide greater system capacity and better communication quality than the second-generation system, and to better achieve seamless roaming around the world and provide users with voice, data and multimedia services. various services, and good compatibility with existing second-generation systems must also be considered.              signal jammer

There are currently three main 3G standards accepted by the ITU: WCDMA, CDMA2000 and TDSCDMA. CDMA is the abbreviation of CodeDivisionMultipleAccess (code division multiple access) and is the technical basis of the third generation mobile communication system. The first generation mobile communication system uses the analog modulation method of frequency division multiple access (FDMA). The main disadvantage of this system is spectrum utilization. The rate is low, and signaling interferes with voice services. The second-generation mobile communication system mainly uses time division multiple access (TDMA) digital modulation, which increases system capacity and uses independent channels to transmit signaling, which greatly improves system performance. However, TDMA The system capacity is still limited, and the handover performance is still imperfect. The CDMA system is characterized by its simple frequency planning, large system capacity, high frequency reuse coefficient, strong anti-multipath ability, good communication quality, soft capacity, and soft handover. Huge development potential.

The full name of WCDMA is WidebandCDMA. This is a 3G technical specification developed based on GSM network. It is a broadband CDMA technology proposed by Europe. It is basically the same as the broadband CDMA technology proposed by Japan and is currently being further integrated. This standard proposes the evolution strategy of GSM (2G)-GPRS-EDGEWCDMA3G. GPRS is the abbreviation of General Packet Radio Service (General Packet Radio Service), and EDGE is the abbreviation of Enhanced Datarate for GSMEvolution (GSM Evolution with Enhanced Data Rate). These two technologies are called 2.5-generation mobile communication technologies. According to the restructuring plan, the new China Unicom will rebuild its 3G network according to the plan.

CDMA2000 is a broadband CDMA technology developed from narrowband CDMA (CDMAIS95) technology. It is mainly promoted by the United States. This standard proposes an evolution strategy from CDMAIS95 (2G) CDMA20001 CDMA20003 (3G). CDMA20001x is called the 2.5th 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. Before the reorganization, China Unicom was using this plan to transition to 3G and had built a CDMA IS95 network. According to the reorganization plan, the entire network will be transferred to "New China Telecom".

The full name of TD-SCDMA is TimeDivision-SynchronousCDMA. It is a 3G standard proposed by my country Datang Telecom Company. This standard proposes a direct transition to 3G without the intermediate link of 2.5 generations. It is very suitable for the upgrade of GSM system to 3G. . According to the reorganization plan, "New China Mobile" will be constructed according to this standard and has been initially completed and put into trial operation in some areas.

Comparison of three technical standards
WCDMA, CDMA2000 and TDSCDMA are all broadband CDMA technologies. Broadband CDMA advances the standard CDMA concept, extending the signal over a relatively wider frequency band, thereby reducing propagation problems caused by multipath and attenuation, with greater capacity, and can use different bandwidths according to different needs. It has strong anti-fading and anti-interference capabilities, supports multi-channel simultaneous calls or data transmission, and is compatible with existing equipment. WCDMA, CDMA2000 and TD-SCDMA can all provide a data transmission rate of 2Mbit/s in a static state, but there are still big differences in some key technologies among the three, and the performance is also different.

duplex mode
WCDMA and CDMA2000 both adopt FDD (frequency division digital duplex) mode, and TD-SCDMA adopts TDD time division digital duplex) mode. WCDMA and CDMA2000 can support normal communication of mobile terminals at a speed of about 500 kilometers per hour, while 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.

Chip rate and carrier bandwidth
A high chip rate can effectively utilize frequency selective diversity and spatial receiving and transmitting diversity, and can effectively solve multipath problems and fading problems. WCDMA has the most advantage in this regard. In terms of carrier bandwidth, the higher the bandwidth, the more users can be supported, and the less likely network congestion will occur during communication. In this regard, WCDMA has obvious advantages. The TD-SCDMA system adopts TDD duplex mode, so it only needs to occupy a single 1.6M bandwidth, so TD-SCDMA has the highest utilization rate of frequency resources. Smart antenna technology.

Smart antenna technology is a key technology used by TD-SCDMA and has been patented by Datang Telecom. Currently, neither WCDMA nor CDMA2000 has adopted this technology. A smart antenna is a bidirectional antenna installed on the base station site to obtain directivity, and can also reduce interference between and within cells. These characteristics of smart antennas can significantly improve the spectral efficiency of mobile communication systems.

handover technology
Both WCDMA and CDMA2000 use handover "soft handover" technology, that is, when the mobile phone moves or the base station currently communicating with the mobile phone is busy and the mobile phone needs to communicate with a new base station, the connection with the original base station is not interrupted first. , but first connects to the new base station, and then interrupts the connection with the original base station. TD-SCDMA uses cross-area "relay switching" technology. Smart antennas can roughly locate the user's position and distance. The base station and base station control
The controller can determine whether the user has moved to a nearby area that should be handed over to another base station based on the user's orientation and distance information. If the user enters the handover area, the base station controller will notify the other base station to prepare for handover to achieve the purpose of relay handover.