Currently there are two 4G standards based on LTE, namely LTE FDD and LTE TDD (the domestic custom of LTE TDD is called Td-lte). See the name you will have an intuitive impression, the two standards are based on the different branches of LTE, the similarity of more than 90%. Next we use traffic to illustrate the difference between the two:
One, Td-lte province resources, FDD speed fast
LTE FDD uses frequency division duplex, Td-lte is time division duplex. Let's put aside these jerky terms and explain in a simpler way:
First of all, mobile phones want to surf the Internet, you have to build up and down the channel: for example, you click on the micro-letter, hand opportunity to send a request through the uplink channel, and then the micro-trust server through the downlink channel, your latest unread message to your phone. In general, we use the downlink (download) more time, and the uplink (upload) time is very small.
In order to establish uplink and downlink channels, FDD is segmented by frequency, at two symmetrical frequencies, one tube is downloaded and one tube is uploaded. It's like a two-lane, two-direction car with no interference, unimpeded. Acting on your phone is a quick feeling.
Td-lte in a different way. It uses only one frequency, both for uploading and for downloading. The advantage is that more than FDD province a frequency occupancy, resource utilization is higher (in fact td-lte in order to avoid interference, need to reserve a large protection belt, will also consume some resources); TDD's shortcomings are also obvious, because it is "one-way street" running two-way "traffic", Td-lte only through time to control traffic (TDMA), one will let the download flow through, and then let the upload of traffic through. Performance in the mobile phone, will be slower than the FDD speed.
At present, the theory of LTE FDD downlink speed of 150mbps,td-lte theory downward speed of 100Mbps.
Second, td-lte suitable for hot area coverage, FDD suitable for wide area coverage
We have encountered this situation in our lives: Rush hour, traffic congestion in the direction of the city, next to the road in the direction of the town is scarce traffic. This is undoubtedly a waste of resources.
In the process of mobile Internet, this phenomenon is more common: people use mobile phones, more reading, viewing and downloading, little time for uploading. Therefore, if the mobile phone's wireless network is visible, you will find that there is a stream of data on the download channel, and the upload channel is rarely used.
The advantage of Td-lte is that he merges the upload and download channels into one, then controls the time flexibly, such as 70% of the time allotted to the download, and 30% for uploads, so you will find that the traffic is always full and resource utilization is higher.
Since Td-lte is so economical, it cannot be fully adopted.
In the user-intensive hotspot area, the frequency band resources are very tight, at this time, FDD's "two lanes" is very wasteful, TDD more suitable. However, because TDD is limited in the uplink and the base station coverage is less than FDD, TDD needs to build more base stations than FDD in the non hot areas (suburbs, towns and highways), and the cost is too high.
Three, finish the difference, Td-lte and FDD can mix network?
FDD and Td-lte, the two LTE branch standards have their own strengths, but the basic technology is very similar to each other. Some experts said that Td-lte and LTE FDD can be regarded as a system, only in the business implementation of a certain technical differences.
Therefore, there is an international model of TD-LTE and FDD mixed network, play their respective strengths, Td-lte for hot area coverage, FDD for wide area coverage.
Because of the common Technical Foundation, TD-LTE and FDD have a very good prospect in the mixed networking. This is what ITU hoped to achieve when it developed the 4G standard-that is, to minimize the differences between the physical layers of the different standards, so that the network standards eventually converge.
Mobile in Hong Kong's 4G network is the use of Td-lte and FDD hybrid network approach, accumulated experience in this area. From the current news, the Ministry of Information will also be the organization of operators to carry out a hybrid network verification.
Td-lte and LTE FDD essentially share a set of standard bases, which have a certain difference in the technical implementation of the business. Td-lte saves channel resources and is suitable for hot spot area coverage; FDD's theory has the highest speed, the base station cover wider, suitable for suburban, road and railway wide area coverage. The combination of the two networks is a better choice.