The Ministry of Industry and Information Technology recently issued 4G licenses for TD-LTE standards to three operators, and did not issue LTE FDD. What is the difference between these two standards? Is it true that FDD is faster? At present, there are two LTE-based 4G standards, namely LTE FDD and LTE TDD (domesticly used to call LTE TDD TD-LTE). Looking at the name, everyone will have an intuitive impression. The two standards are based on different branches of LTE, and the similarity is over 90%. Next, we use traffic as an example to analyze the difference between the two:
First, TD-LTE provincial resources, fast FDD
LTE FDD uses frequency division duplexing, while TD-LTE is time division duplexing. Let's put aside these oyster terms and explain them in a simpler way:
First of all, if the mobile phone wants to access the Internet, it must establish an uplink and downlink channel: for example, if you click on WeChat, the mobile phone will send a request through the uplink channel, and then the WeChat server will send your latest unread message to your mobile phone through the downlink channel. . In general, we use the downlink (download) for a lot of time, while the uplink (upload) time is very small.
In order to establish the uplink and downlink channels, FDD is divided by frequency. On two symmetric frequencies, one tube is downloaded and one tube is uploaded. It is like a two-lane car. The cars in both directions do not interfere with each other and are unimpeded. Expressed on your phone is a feeling of speed.
TD-LTE takes another approach. It uses only one frequency, both for uploading and for downloading. The advantage is that it saves one frequency occupation and more resource utilization than FDD (in fact, in order to avoid interference, TD-LTE needs to reserve a large protection band and consume some resources); the disadvantage of TDD is also obvious because it is " One-way street "runs two-way "car flow", TD-LTE can only control traffic by time (time division duplex), one will let the downloaded traffic pass, and then let the uploaded traffic pass. On the mobile phone side, it will be slower than the FDD network speed.
At present, the downlink speed of the LTE FDD theory is 150 MBPs, and the TD-LTE theoretical downlink speed is 100 Mbps.
Second, TD-LTE is suitable for hot area coverage, and FDD is suitable for wide area coverage.
We have encountered this kind of situation in our life: during the peak hours of work, the traffic in the direction of entering the city is very unbearable, but the traffic on the road in the direction of the city is rare. This is undoubtedly a waste of resources.
In the process of mobile Internet access, this phenomenon is more common: people use mobile phones, more are reading, watching and downloading, and less time for uploading. Therefore, if the wireless network of the mobile phone is visible, you will find that the data on the download channel is constantly flowing, and the upload channel is rarely used.
The advantage of TD-LTE is that he combines the upload and download channels into one, and then flexibly controls through time, for example, 70% of the time allocated for download and 30% of uploads, so that you will find that the traffic of the entire channel is always Full, resource utilization is higher.
Since TD-LTE is so economical, it cannot be used at all.
In the user-intensive hotspot area, the frequency band resources are very tight. At this time, the “dual lane†of FDD is very wasteful, and TDD is more suitable. However, because TDD is limited in uplink, the coverage of base stations is smaller than FDD. Therefore, in non-hotspots in wide coverage areas (suburban, township, and highway), TDD needs to build more base stations than FDD, and the cost is too high.
Third, after the difference, can TD-LTE and FDD be mixed?
The two LTE branching standards of FDD and TD-LTE have their own strengths, but the basic technologies are very similar. Some experts said that TD-LTE and LTE FDD can be regarded as a system, and there are certain technical differences in service implementation.
Therefore, there is a mode of hybrid networking between TD-LTE and FDD in the world, and the advantages of both are utilized. TD-LTE is used for hotspot coverage and FDD is used for wide-area coverage.
Due to the common technical foundation, TD-LTE and FDD have very good prospects in hybrid networking. This was also what ITU hoped to achieve when developing the 4G standard – that is, to minimize the differences in physical layers between different standards, and to eventually bring the network standards to convergence.
China Mobile has adopted the TD-LTE and FDD hybrid networking in the 4G network in Hong Kong and accumulated experience in this area. Judging from the news obtained so far, the Ministry of Industry and Information Technology is also about to organize operators to carry out verification of hybrid networking.
Finally, summarize:
TD-LTE and LTE FDD essentially share a set of standard foundations, and there are certain differences in the technology of service implementation. TD-LTE saves channel resources and is suitable for hotspot centralized area coverage; FDD has the highest theoretical speed and wider base station coverage, and is suitable for wide-area coverage such as suburban, highway and railway.
A hybrid network of the two is a better choice.
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