The key technology of TD-LTE is composed of some loaded signals. Due to the special way of the signal, how its co-frequency networking is organized and how to operate is placed in a very important position. Here Including some resource blocks and some PRB situations, Datang has proposed several methods and mechanisms for reducing co-frequency interference to reduce the interference of the cell to achieve the final co-frequency networking for co-frequency networking.
Consider the following method of centralized co-frequency networking when designing. The first is scrambling, the second is frequency hopping transmission, and power control; inter-cell interference coordination, and the beam assignment method proposed by Datang.
Let's look at scrambling first. It uses random sequences to randomize data after encoding. The impact on the system is relatively small, but the gain it provides for reducing interference is not very obvious.
The second is frequency hopping. The frequency-hopping method is used to randomize inter-cell interference. At present, all downlink physical control channel resources in LTE except CH are affected by the cell ID. Such frequency hopping transmission can be achieved. POSCH uses frequency hopping transmission between pointers to reduce interference. For the sub-needle tip method, the frequency hopping transmission method uses a fixed frequency to perform frequency hopping transmission, and the sub-needle uses a medium needle to perform frequency hopping transmission. The frequency-hopping transmission is relatively simpler, the frequency-hopping transmission between sub-pins is more complicated, and the effect may be worse. In general, the gain of frequency-hopping transmission to reduce interference from the current point of view, from the current simulation situation 1 To about 2 DBs.
The third method is beam assignment. The first is to improve the user ’s interference ratio. At the same time, the beam assignment method can also be used to reduce the desired intensity of the interfered user. When we do beam assignment, we adjust the beam Adjust the position of the neutral line to reduce interference.
Looking at the fourth mechanism for reducing inter-cell interference, inter-cell interference coordination, from the current point of view, the method of interference coordination is mainly for inter-cell resources, different resources between two different cells, video resources and even It is the way that the power resources coordinate and control each other between such cells, and here includes static inter-cell interference coordination and semi-static inter-cell interference coordination. This is fixed for the interference coordination of static cells. It is fixed to set what frequency resources my edge users can use. This does not need to be further strengthened in the standard and written into the standard. It can be achieved through the parameters and configuration of each system manufacturer. For semi-static inter-cell interference coordination, it requires a cell base station through the X2 interface Exchange PRB usage information, power allocation information, and overload indication information between cells.
Finally, power control, power control also has an inter-cell power control and power space within the cell, the inter-cell is often periodically tell the LT information of the cell to the neighboring cell, control the LT of the cell to achieve the LT between the cells To reduce the interference between cells, the power control in the cell is obvious. We reduce the transmission power of the terminal in TD-LTE, so as to reduce the interference to other cells, so that the LT of this cell remains at Below a certain level.
For the above-mentioned control methods for reducing inter-cell interference, the gain for reducing inter-cell interference by adding Rao and frequency hopping is not very obvious, that is, 1 to 2 DBs. For inter-cell interference coordination and power control methods to reduce interference In this way, when the cell load is very light, it is effective to reduce inter-cell interference in this case. If the cell load is relatively heavy, information interaction is also required. The real-time nature of this information interaction is in This kind of cell can not be guaranteed when it meets the heavy requirements. In this case, coordination is very difficult. At the same time, the two methods of inter-cell coordination also bring a certain system complexity, so this method also has certain The room for improvement is more obvious for the beam assignment to reduce the inter-cell interference, but we still need to improve it and put forward two enhanced solutions for co-frequency networking. The first solution is BR-OFDMA, which is Small cells can share the same video resource, but different cells use the same repetitive code for the same video resource to reduce inter-cell interference .
The operation of the same video resource through the repetitive code is 8 to get the corresponding video running map. This repetitive code can be adjusted according to the interference situation. For example, the interference is more serious, and there are multiple cells at a certain point that repeat at this point. At this time, the interference factor can be adjusted from 4 to 8 or 8 to 16, so as to realize the identification and frequency division and then perform code division to match different interference scenarios, this way it can be more in the contact section The joint detection of the users of the cell to make full use of the interference signal to cancel the interference can also further reduce the interference between the cells. This method is mainly for the inter-cell coordination we mentioned earlier. This method is relatively heavy in the cell load. Under the circumstances, we can not achieve the purpose of effectively reducing interference.
In the case of relatively heavy cell interference, this advantage can be greatly improved, just mentioned the first method. In the second aspect, the enhanced beam attribute we mentioned, the technology of beam assignment that has been supported can effectively improve the throughput of the system and improve the throughput of edge users. The mechanism of multi-cell cooperative transmission introduced later, beam Attributes enter the cell coordination method to improve cell interference.
Here, the following methods can be used to reduce cell interference. The first is interference avoidance. The idea of ​​interference avoidance is mainly for different beam properties. It can transmit the same resources, and the same beam does not apply the same resources. And, the same resources are allocated to different directions, try to make the video resources be used in different directions, which also realizes the space resources to achieve interference reduction to achieve this purpose, which is a method of interference avoidance.
Interference suppression, considering the joint scheduling method of multiple cells, when the cell resumes, it should be considered that the interfering users of the external cell avoid the interference of the external cell through the line-by-line method. This is the way to avoid interference suppression. The final method is The way of signal enhancement, this way is to enhance the signal strength of edge users through the interaction and coordination of the information of multiple neighboring cells.
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