In China, the F-band is currently divided into 1880MHz-1920MHz with a total bandwidth of 40M. The existing F-band has not been delisted due to the PHS network, and the 20M frequency bandwidth of 1900MHz-1920MHz is temporarily unavailable. In China Mobile's current TD-LTE large-scale experimental network, Guangzhou, Shenzhen and Hangzhou are mainly based on F-band deployment, while other cities generally use D-band as the main deployment method. In this frequency band and its adjacent frequency bands, some GSM1800 networks, TD-S networks and a few PHS networks are also included.
Although the bandwidth of the F-band is very limited compared with the D-band, its importance, resources and market significance in the construction of mobile TD-LTE projects exist objectively. The D+F hybrid networking has also reached consensus in the industry. Regardless of whether the mobile group or the major suppliers attach great importance to the construction of the F-band network, there is no need to repeat them here. However, in the face of the recent hot debate on the F-band new construction or upgrade, is it inclined to more new stations, or more upgrade stations?
This paper will discuss the differences and characteristics of the specific implementation schemes for F-band construction mainly from the technical perspective and the relevant aspects of project implementation. Other factors affecting the evaluation of different networking schemes in the F-band are not discussed here.
The core issue of the F-bandIn the future of TD-LTE commercial network construction, the core problem of F-band application is undoubtedly how to solve the interference problem. In addition, there are problems such as the difficulty of project implementation and the construction period of the project. The construction of the TD-L experimental network moving in multiple first- and second-tier cities has been large, and some important cities have also expanded the scale of the experimental network. Project data and test results from various Trial sites are already abundant. So now it is time to explore the advantages of each new technology and upgrade. After analyzing and summarizing the interference types of the mobile multi-site TD-L experimental network, the main interference comes from the following aspects:
• Second harmonic interference in the GSM900MHz band • Third-order intermodulation interference in the GSM1800MHz band • Interference introduced by the existing TD-S network equipment with insufficient blocking capability in the F-band • Different levels of adjacent-frequency interference in the PHS network and spurious interference in GSM1800MHz
These interference problems have long been foreseen, and data acquisition and verification are obtained in the networks of major manufacturers in the initial stage of the experimental network test. Tests from a second-tier city experimental network found that some manufacturers' GSM network antennas are older, have different degrees of degradation, and generate strong second harmonic interference. At the same time, PHS base stations will cause larger neighbors in some areas. Frequency interference. The field test in Guangzhou found that the existing mobile TD-S network has low anti-blocking capability and some spurious interference. These complex interferences will cause the SINR to deteriorate and the network throughput (Throughput) to be greatly reduced. At this time, even if the RSRP (Reference Signal Received Power) is high, the expected high throughput cannot be obtained.
For the solution of the interference problem, let us look at the characteristics and effects of upgrading the existing TD-S system and the newly built TD-L site.
Upgrade plan analysisFirst look at the upgrade of the existing TD-S station. Regarding the existing TD-SCDMA base station and the antenna feeder system to upgrade TD-LTE, the solution directions of different manufacturers are basically the same. First, due to product performance reasons, some sites still need to replace the RRU, and then the two networks are aligned in time slots. And do the power distribution, increase the fiber at the same time, adjust the sky surface, and do the double network double adjustment work.
In network performance, the primary problem with upgrading an existing network is that the performance of the TD-L network after dual-network matching will decrease. In order to avoid uplink and downlink interference of the two networks, the ratio of the uplink and downlink of the TD-L to the special time slot must be coordinated with the TD-S. In view of the fact that the TD-S network has adopted the 2:4 uplink and downlink time slot ratio, the TD-L can only adopt the 1:3 uplink-downlink ratio. At this time, the special time slot (DW-PTS, GP, Up-PTS) can only use the slot ratio of 3:9:2. This brings up two problems: too many GPs and too few Dw-PTSs. Due to the limitation of the protocol specification, the Dw-PTS cannot carry PDSCH information at this time.
According to test results from several manufacturers, this will result in a drop in throughput of about 25%. Secondly, the models and powers of TD-S stations in different periods are different. When upgrading, there will be problems of increased adjustment difficulty and insufficient coverage. After the actual measurement, the uplink throughput failed to reach the standard, and the switching success rate was about 95%.
On the anti-blocking index, most RRUs in the original TD-S station are required to face the TD-L index requirements, and the anti-blocking performance is not enough. It is easy to be blocked by the 1800MHz frequency of the GSM network, resulting in a significant decrease in the rate. At this point, AGC technology can be used to reduce the impact, but it will lead to reduced sensitivity, which also affects the actual coverage and performance of the network. The minimum antenna isolation requirement of the equipment before TD-S 6 is 94dB, and the distance between stations in the same direction is 600m. Can withstand interference not higher than -40dBm.
In engineering projects, it is first necessary to add isolators. To upgrade some of the early sites, it is necessary to replace the RRUs or even replace the sky surface. At this time, the complexity of the new construction is not much different. When the dual network is optimized at the same time, the probability of unknown obstacles will increase. In addition, an additional series of work is needed, such as communication report with the original TD-S maintenance personnel and data collection of the work parameters. These objectively increase the workload and duration.
On the subsequent optimization, there is a significant problem that every time you do network optimization, you may want to double-network dual-optimal. For the upgrade scheme of the shared antenna and the RRU, the technical difficulty and workload will be doubled due to the problem of the antenna electric downtilt adjustment and the area interference optimization. Experiences at home and abroad have shown that the antenna downtilt angle of TD-LTE is 2-30 larger than that of the 2/3G system, so it is very difficult to achieve dual network dual optimization.
New plan analysisIn terms of network performance, the downlink capacity and performance of the new TD-L station are not affected, and the RRU power is not limited. The coverage, throughput and mobility are all measured by different first- and second-tier cities. The SRSP value exceeds the standard by 16dB, and the uplink and downlink rates exceed 9-13M and 4-5M respectively, and the switching success rate reaches 100%.
Anti-blocking, the new station has the advantage of product index and performance, and the minimum antenna isolation requirement can reach 36dB. The distance between the stations is only 1.5 meters. Can withstand interference intensity values ​​up to 15dBm.
The implementation of the new station on the project tends to be fast, flexible and efficient. Although there are many new construction links, there are mature models for technical implementation and project management. It will make the construction progress of the initial or long-term project construction faster.
The new station has lower requirements for subsequent optimization work. Independently adjusted TD-L and TD-S stations can meet new network optimization requirements faster and better. The operators in the region are positive and optimistic about the network optimization and expansion projects brought about by urban development and construction needs.
Conclusion Through the above analysis, it is not difficult to find that from the technical level and performance performance, the new construction should be better than the upgrade. Because it is technically easier to implement, the new station is also superior to the upgrade in terms of construction period and long-term operation and maintenance costs. Here we specifically explore the F-band network construction solution from a technical perspective, because technology is the most important industry driver for our communications industry. Especially in today's high-tech accelerated commercialization, good technology brings excellent network performance, and with good services and applications, it can greatly enhance the user experience and create new value for users. This will attract a large number of customers to join, thus forming a scale-effective reduction of high-tech application costs, which is crucial for the goal of mobile to build a TD-LTE boutique network.
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