TD-SCDMA has unique advantages in spectrum utilization, frequency flexibility, service support diversity and cost.
TD-SCDMA adopts time division duplex, and the uplink and downlink channel characteristics are basically the same. Therefore, it is easier for the base station to estimate the uplink and downlink channel characteristics from the received signals. In addition, TD-SCDMA has inherent advantages in using smart antenna technology, which introduces the advantages of SDMA, which can reduce the interference between users and improve the spectrum utilization.
TD-SCDMA also has the advantages of TDMA, which can flexibly set the ratio of uplink and downlink time slots and adjust the ratio of uplink and downlink data rates, and is especially suitable for occasions with less uplink data and more downlink data in Internet services. However, the variability of uplink and downlink switching points increases the complexity of co-frequency networking.
TD-SCDMA is time division duplex, and it doesn't need paired frequency bands. Therefore, compared with the other two 3G standards of frequency division duplex, it is more flexible in the division of frequency resources.
It is generally believed that TD-SCDMA can greatly simplify the complexity of the system by adopting smart antenna and synchronous CDMA technology, and is suitable for adopting software radio technology, so the equipment cost is expected to be lower.
However, due to the shortcomings of the time division duplex system, TD-SCDMA is considered to lag behind the frequency division duplex system in terms of terminal allowable moving speed and cell coverage radius. At the same time, compared with other 3G systems, it has a narrower bandwidth and fewer scrambling codes, so it is theoretically possible to identify cells by scrambling codes on the network side. At present, only nine frequency points can be used to distinguish cells, and each carrier has only a bandwidth of 1.6M, resulting in an air interface rate much lower than that of CDMA and CDMA2000. According to the actual test, the TD-SCDMA network deployed by China Mobile is not as fast and stable as W-CDMA network and CDMA2000 network.
TD-SCDMA adopts TDD duplex mode with unmatched frequencies and multiple access mode combining FDMA/TDMA/CDMA, with low chip rate of 1.28 Mcps and spread spectrum bandwidth of 1.6 MHz (the theoretical peak rate can reach 2.8 Mbps within the bandwidth of 1.6 MHz). At the same time, smart antenna, joint detection, uplink synchronization, relay switching and other technologies are adopted.
TD-SCDMA technology features: comprehensive addressing (multiple access).
TD-SCDMA air interface adopts four multiple access technologies: TDMA, CDMA, FDMA and SDMA (smart antenna).
By comprehensively utilizing the degrees of freedom of the four technologies in resource allocation from different angles, the optimal resource allocation can be dynamically adjusted. Flexible configuration of uplink and downlink time slots
Flexible time slot uplink and downlink configuration can meet users' needs of calling, web browsing, downloading files and video services at any time, and ensure users to enjoy 3G services clearly and smoothly. Overcoming respiratory effects and Near-Far Effects
Respiratory effects means that in CDMA system, when the interference signal of a cell is strong, the actual effective coverage area of the base station will decrease; When the interference signal of a cell is weak, the actual effective coverage area of the base station will increase. The main reason of respiratory effects is that CDMA system is a self-jamming system, and the increase of users leads to the increase of interference and affects coverage. At the same time, TD can only online 500 people at the same time, which is a problem. China will issue TD-SCDMA, WCDMA and CDMA2000, which belong to China Mobile, China Unicom and China Telecom.
20 12 1 China mobile TD-SCDMA 3G users increased to 53.94 million. China Unicom WCDMA 3G users increased to 43.07 million. China Telecom CDMA2000 3G subscribers increased to 38.7 million. The statistics of 3G users of China Mobile include TD wireless Internet access, TD wireless fixed telephone and so on. In 3G networks, China Unicom has the fastest growth rate, ranking first in the industry. Features: The full name is time division-synchronous code division multiple access, which has unique advantages in spectrum utilization and flexibility of service support.
Advantages: China has its own 3G technology and government support. Features: the full name of wideband CDMA, also known as CDMA direct spread spectrum, means wideband code division multiple access. This is a 3G technical specification based on GSM network development. WCDMA is the most widely used 3G standard in countries and regions with the richest terminal types. 538 WCDMA operators have opened WCDMA networks in 246 countries and regions, and the commercial market share of 3G is over 80%. The backward compatible GSM network of WCDMA has covered 184 countries and spread all over the world. The number of WCDMA users has exceeded 600 million.
Advantages: high spread spectrum gain, large development space, the strongest global roaming ability and the best technical maturity. Features: CDMA2000 is a wideband CDMA technology developed from the wideband CDMA(CDMA IS95) technology, also known as CDMA multicarrier, which was proposed by Qualcomm.
Advantages: It can be directly upgraded from the original CDMA 1X to 3G with low construction cost.
It is not entirely right to say that Unicom's WCDMA is better than mobile TD, and each has its own characteristics.
TD-SCDMA is an independent 3G standard in China. In May, 2000, ITU (International Telecommunication Union) announced that TD-SCDMA officially became an integral part of the third generation mobile communication standard 3G international standard of ITU, and it was listed as the three mainstream 3G international standards along with WCDMA in Europe and CDMA2000 in the United States. TD-SCDMA was put into commercial trial on April 1 2008.
TD-HSDPA is the next evolution technology of TD-SCDMA, adopting TDD mode. As a post-3G HSDPA technology, it can be applied to both WCDMA and TD-SCDMA.
After TD-HSDPA, TD will also realize TD-HSUPA with an uplink rate of 2.2Mbps, and will eventually evolve to LTE TDD.
WCDMA is an upgraded version of GSM (GSM is 2G technology, which evolved into GSM, GPRS, EDGE and WCDMA), and it is also the most widely used 3G technology in the world (GSM technology has 85% mobile users in the world), with the most mature technology and commercial application. WCDMA operators follow the evolution routes of WCDMA, HSPA and LTE.
HSDPA and HSUPA are collectively referred to as HSPA, and the latter has a faster uplink speed. China Unicom adopts HSPA technology, and big cities adopt HSUPA, which can be deployed in June and July 2009.
After HSPA, Australia, Singapore and other places also began to build HSPA+ technology, with a speed as high as 2 1 Mbps.