After comprehensive comparison and analysis, there are significant differences among CDMA2000, WCDMA and TD-SCDMA. TD-SCDMA proposed by China is an international standard based on China's independent intellectual property rights, which has the following five outstanding advantages.

1. Technical advantages

TD-SCDMA is a perfect combination of TDD, CDMA and TDMA technologies, and has the following technical advantages:

First, time division duplex (TDD) technology is adopted, which only needs 1.6MHz bandwidth and does not need paired frequency bands, so it is suitable for multi-operator environment; While CDMA2000 of FDD needs 1.25×2 MHz, and WCDMA needs 5×2 MHz bandwidth.

Secondly, advanced technologies such as smart antenna, joint detection and uplink synchronization can reduce transmission power, reduce multiple access interference and improve system capacity; Using "relay handover" technology can overcome the disadvantage that soft handover takes up a lot of resources.

Thirdly, TDMA is adopted, which is suitable for asymmetric Internet services with downlink data rate higher than uplink data rate. WCDMA is not suitable, so it was upgraded to HSDPA in R5 version.

Fourthly, using software radio technology, it is easy to realize multi-mode base stations and multi-mode terminals, and the system can be upgraded to HSDPA for free.

Fifthly, it is easier to support PTT service by adopting TDD and TDMA, and realize a new generation of digital trunking.

2. Frequency advantage

First of all, TD-SCDMA has abundant frequency resources. China's 3G frequency planning has more than tripled compared with the internationally divided 50 MHz time division duplex frequency band, reaching 105MHz, which is rich in frequency resources, laying a resource foundation for promoting the industrialization of TD-SCDMA.

WCDMA and CDMA2000 share 90MHz×2 frequency band, so the frequency resources are scarce.

Secondly, the spectrum efficiency is high. TD-SCDMA can effectively eliminate the interference due to the comprehensive adoption of the above advanced technologies, so that the system can work under the condition of full code channel, and can support the 144 12.2kbit/s voice channel, covering 7,200 users. Its voice spectrum utilization ratio is 2.2 times higher than WCDMA, and the data spectrum utilization ratio is even as high as 3. 1 times.

Third, it is suitable for global roaming. TD-SCDMA enjoys the same frequency division as TDD in the world. Among the valid licenses issued worldwide, TDD accounts for 104, which creates a unique resource condition for global promotion and roaming. WCDMA and CDMA2000, which are both FDD modes, are inevitably different in the actual spectrum division of different countries, and it is impossible for them to realize global roaming directly.

3. Advantages of the network

First of all, it has no effect on the respiratory system. The phenomenon that the network coverage radius decreases due to the increase of the number of users or business volume is called "respiratory effects". CDMA is a self-jamming system. When the number of users increases significantly, self-interference increases exponentially, so "respiratory effects" is its natural defect.

Each carrier of TD-SCDMA is similar to GSM network, and most of the interference of the system is eliminated by dividing the time slots of low-bandwidth FDMA and TDMA. Due to the small number of users in a single time slot, there is less self-interference; Moreover, this part of self-interference is further suppressed by joint detection and smart antenna technology, so TD-SCDMA is no longer an interference-limited system, but a code-limited system, and the coverage radius does not shrink with the increase of users.

Secondly, it can ensure continuous coverage of various services at the same time. According to the link budget, WCDMA services have different spreading factor and coverage radius, so they can only "concentric coverage", which can not solve the contradiction between continuous coverage of high-speed services and serious interference of low-speed services, and bring trouble to network planning. The backward compatibility of WCDMA network topology is poor, and the previous network base stations need to be relocated, which has a great impact on the stability of network quality.

TD-SCDMA is rich in frequency resources, and there is no "respiratory effects", which makes the coverage radius of its services almost the same, that is, "same-path coverage", so all services can be covered continuously at the same time, and the network topology is closest to the ideal cellular structure. According to the market demand in different periods, corresponding network planning can be carried out to ensure the synchronization of network construction and market demand and avoid resource cost. By adding frequency points, the capacity and business requirements in different periods and situations can be met without changing the site and coverage, so as to maintain the mutual independence between plans. The later network construction does not affect the earlier network, which makes the network develop steadily.

Third, network optimization is the best. WCDMA and CDMA2000 can only use the "hard optimization" strategy of "adding stations on the same frequency to make up for blindness" to make up for blind spots and absorb traffic. This method not only solves local problems, but also introduces some problems such as increased interference and complex neighbor configuration, and even needs to adjust the network topology in the original plan and relocate some original sites.

TD-SCDMA network adopts the "soft optimization" strategy of "adding sites with different frequencies to make up for blindness" to solve the coverage blind area and capacity overload, which will not increase the interference of neighboring cells, and will not affect the performance of the original network because of adding new base stations. Soft optimization strategy also enables TD-SCDMA system to solve the problem of coverage blind area caused by environmental changes and capacity overload caused by business changes without changing the original site distribution. At the same time, the abundant wireless resources also enable TD-SCDMA networking to adopt different combinations such as omni-directional or directional, single carrier frequency or multi-carrier frequency, same frequency or different frequency, so as to adapt to different environments and business requirements. In addition, TD-SCDMA also uses software radio technology to adjust or upgrade the software algorithm of the system, so that the network can cope with the problems caused by the change of terrain or signal propagation characteristics, thus ensuring the best network quality at each stage.

4. Business advantage

TD-SCDMA service is a TDMA transmission mode based on TDD duplex mode. Each TDMA frame structure is divided into 8 time slots. By changing the switching points of uplink and downlink time slots, it can adapt to symmetric and asymmetric Internet services. TD-SCDMA has a rate of 384Kbit/s, which can meet the needs of videophone and general streaming media services. After the upgrade, the speed of HSDPA is increased to 2.8Mbit/s, which is comparable to ADSL. It can also provide MBMS mobile TV service.

5. Cost advantage

First of all, the cost of a single channel is half cheaper. The cost of 3G base station has become a symbol to measure the cost of system equipment. Compared with WCDMA and CDMA2000, TD-SCDMA has no obvious difference in the cost of core network and base station controller. However, the base station technology and cost of different standards vary greatly. The cost of TD-SCDMA single base station is slightly better than WCDMA. The cost of single channel is as low as 44% of WCDMA. For asymmetric data channels, TD-SCDMA can adjust the uplink and downlink switching points to further enhance the capacity, and its cost is much lower than 44%.

Secondly, the cost of network construction in each period has been greatly reduced. The initial stage of construction is the coverage drive period. TD-SCDMA has the same coverage radius for each service, which can cover a wide area and save more than 30% of the number of base stations. In the capacity-driven period, TD-SCDMA has no "respiratory effects", is rich in frequency points, and supports a variety of services flexibly, which makes the service type and capacity expand quite quickly, which can save a lot of time and cost and increase business income. In the mature period, TD-SCDMA has high spectrum efficiency, and the number of base stations is less than 15% under the same capacity. At the same time, combined with its software radio technology, it has great advantages in maintenance cost and upgrade cost.

In addition to system equipment, network construction also includes stations, computer rooms, transmission, power supply, antennas and iron towers. Because of the landscape and environmental protection problems in the community, it is difficult to obtain the site, so sharing the site and supporting resources has become the main topic of 3G construction. TD-SCDMA has low requirements for site distribution, and more than 90% can use the original site. The site reuse rate of WCDMA does not exceed 60%. At the same time, there is no need to adjust the original network in different stages of TD-SCDMA network construction, which significantly reduces the engineering quantity.

In addition, for operation, TDD is convenient to obtain a single frequency band, which can save a lot of frequency usage fees; The characteristics of controllable interference, supporting different frequency overlapping coverage and flexible code resource planning simplify the network planning and optimization design, which can save a lot of technical training fees and human capital expenses for operators. Coupled with the saving of patents and chips, the cost of TD-SCDMA deployment by operators will be greatly reduced compared with the other two 3G technologies.

Third, the terminal cost advantage is obvious. TDD does not need diplexers and high-power linear power amplifiers, which can simplify the RF circuit and make the cost of system equipment and mobile phones lower. TD-SCDMA chip has a low speed, which can reduce the cost of mobile phone chips. No matter which 3G standard is adopted in Europe and America, domestic enterprises have to pay high patent fees. However, TD-SCDMA has independent intellectual property rights, which will greatly reduce patent fees and terminal prices.

In short, by expanding the network scale, TD-SCDMA has been proved to have outstanding advantages over WCDMA and CDMA2000 in cost performance. (Text/Li Jinliang)