WO2016153244A9 - Cooperative communication method in small cell network environment - Google Patents

Abstract

An embodiment of the present invention relates to a method for selecting a base station for performing communication in a wireless network environment including small cells, the method comprising the steps of: evaluating the utilization for base stations which can communicate with a terminal of a user; selecting base stations which have the lowest utilization among the base stations; in consideration of a signal-to-interference-plus-noise ratio (SINR) at which communication with the terminal of the user can be performed, additionally selecting a base station so as to satisfy the SINR; and performing cooperative communication with the terminal of the user through joint transmission of the base stations. Therefore, the present invention enables a user to preferentially select a base station having relatively low throughput in an environment where users and networks are densely deployed, so that even in a situation where a user density is temporarily high or there is high service demand from a user, a stable network connection can be achieved and the performance of the network can be maintained at a certain level.

Description

Cooperative Communication Method in Small Cell Network Environment

The present invention relates to a cooperative communication method in a small cell network environment, and more particularly, to a communication method for selecting a base station capable of providing an optimal network environment to a user in a small cell environment in which base stations are concentrated.

Information dealt with in modern society is increasing exponentially, and network capacity and processing speed are important issues. Therefore, user equipment requires a lot of traffic, and securing a large number of base stations to meet such a requirement can be a solution. Therefore, many small cells are placed in a macro cell, and network cells are becoming increasingly dense. have.

Due to the characteristics of a cellular communication system, each cell may use the same frequency resource around a cell boundary, and in this case, mutual interference may exist. Recently, in order to increase system capacity, cellular communication systems are oriented toward small cells by moving away from macro cells, and networks have evolved in such a manner that small cells of various sizes exist in macro cells. It is an important issue. In order to overcome the inter-cell interference and improve the performance of the UE located at the cell boundary, a method of transmitting data through mutual cooperation between neighboring base stations has been proposed.

In this method, a base station adjacent to a specific terminal located at a cell boundary transmits the same data at the same time, and each serving base station forms a sharp beam toward the terminal to reduce interference and reduce the interference of the signal to be received from the serving base station at the terminal. There is a way to maximize strength. The above technique for overcoming cell-to-cell interference is problematic in that the amount of information exchanged for mutual cooperation increases and requires complicated calculations. In addition, when the terminal efficiently selects its own serving base station, there is a limit to the initial cell search method based on the reception strength of the existing base station pattern signal.

Accordingly, there is a need for a method capable of performing cooperative communication between base stations while improving network performance and effectively reducing the effects of interference.

An object of the present invention is to provide a method for selecting an optimal base station for a user in a network environment based on small cell cooperative communication.

It is an object of the present invention to provide a method for preventing an error due to interference caused by a non-cooperative network in an environment in which various networks are concentrated.

An embodiment of the present invention is a cooperative communication method for selecting a base station for performing communication in a wireless network environment consisting of a small cell, comprising the steps of: evaluating the utilization (utilization) of the base station that can communicate with the user terminal; Selecting base stations among the base stations which have the lowest usability; Additionally selecting a base station to satisfy the SINR in consideration of a signal-to-noise ratio (SINR) in which communication with a user terminal may be performed; And performing cooperative communication with the user's terminal through the joint transmission of the base stations, wherein the usability is a ratio of the number of users currently served by the base station to the service capacity that the base station can perform at maximum. Characterized in that represents.

According to the present invention, the user terminal preferentially selects a base station having relatively low usability by the user in an environment in which the user and the network are concentrated, thereby stably accessing the network even in a situation where the user is temporarily crowded. You can keep performance at a constant level.

According to the present invention, it is possible to provide a certain quality of service to a user connected to a network by using a method of additionally selecting a base station to compensate for channel measurement uncertainty caused by interference propagated in an uncooperating base station.

1 illustrates a model of a dense small cell network

2 is a graph showing the serviceability of user equipment in a network

3 is a graph illustrating the use of resources when a base station cooperatively provides a service to a user terminal, (a) shows an average transmission power when the base station provides a service to a user terminal, and (b) shows a user. Graph showing average usability of base station serving terminal

4 is a graph showing a comparison result of Jain's fairness index

5 is a flowchart illustrating a cooperative communication method in a small cell network environment according to an embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, but are not limited or limited by the embodiments of the present invention. In describing the present invention, a detailed description of known functions or configurations may be omitted to clarify the gist of the present invention.

The user terminal receives a lot of signal information from a plurality of base stations, and the base stations cooperatively distribute channel and message information to the user equipment through the various lines. However, in a hotspot area, a particular base station may be over-selected and overloaded with multiple user equipment.

The present embodiment is based on the premise that small cells are performed in a dense network environment, and provides a method for improving processing performance of a network in a situation where a plurality of networks perform cooperative communication with each other.

1 is a diagram illustrating a model of a dense small cell network.

Referring to FIG. 1, as a model of a dense wireless network, it is assumed that N base stations defined by X are scattered, and a wireless connection service is provided to L user equipments (terminals) defined by U. Neighbor base stations for the k-th (arbitrary) user terminal may be defined as X _k included in X, and the k-th user terminal communication is possible.

If the size of X _k is large, it may be possible to perform cooperative communication with more base stations at a higher level, but interference between base stations occurs in a situation in which cooperative communication is not properly performed. The base stations share CSI with the transmitted data, i-th base station transmits mi signal at the power of Pi, and it is assumed that the base stations are connected to the high-speed wireless network. However, message exchange overhead may occur when X _k is large.

The set of base stations included in X _k is defined as S _k (t) and is selected to jointly participate in signal transmission at the k th user equipment (terminal) (hereinafter referred to as UE) for the time t. Can be. In the embodiment, u _i (t), which is an index indicating a service rate performed at the i-th base station relative to the maximum service capacity for the time t, is defined, and this will be referred to as utilization. Here, the service rate being performed may be described as the number of users currently serving the base station. For example, if the i-th base station is used to have a maximum service rate by a plurality of UEs, it may be referred to as u _i = 1, and u _i = 0 when the i-th base station is not in operation.

In FIG. 1, a signal received at a k th UE during a time t may be represented by the following equation.

[Correction under Rule 91 13.09.2016]

Where h _{i, k} (t) is the channel gain from the i th base station to the k th UE, m _i (t) is the transmission message from the i th base station, and n is white Gaussian noise with a variance of. When X = Sk ∪ (Xk | Sk) ∪ (X | Xk), R _k (t) of Equation 1 may be represented again by the following equation.

[Correction under Rule 91 13.09.2016]

Here, r _{i, k} (t) = h _{i, k} (t) p _i , and the SINR of the k-th UE is expressed as follows.

[Correction under Rule 91 13.09.2016]

Here, the operator of Equation 3 does not include the interference from the base station, because the selected base station is controlled so as not to interfere with the user's terminal (kth UE) using the precoding matrix in the cooperative communication environment.

In other words, the plurality of base stations BS may perform cooperative communication with each other to improve processing performance of the user equipment UE. The cooperating base stations X _k provide a radio connection service and are superior in performance than simply when one neighboring base station exists. However, because the cooperative base station is large, there is a message exchange overhead because cooperative base stations must share CSI and transmission data.

If the k-th UE is being serviced from the cooperating base station X _k , a portion of the cooperating base station Sk (t) may be selected to participate in the joint signal transmission to the K-th UE. In selecting S _k (t) defined as a cooperative base station, a method of minimizing the sum of the total transmit power of the base station while satisfying the threshold of SINR may be considered. The method of considering the minimum power is defined as a MIN-POWER technique, and can be expressed by the following equation.

[Correction under Rule 91 13.09.2016]

However, in the embodiment, unlike the above description in the selection of the base station, base stations having low utilization for the common signal transmission to the k-th UE are selected. An embodiment can improve service capacity by determining cooperative bases in consideration of usability.

On the other hand, some base stations in close proximity to the UE may be over-selected and overloaded in the hotspot area, reducing QoS and BS. Rather than being excessively used, it is desirable to improve the processing performance of the network by selecting several base stations with less usability and cooperatively serving the UE.

Therefore, in the embodiment, a process of selecting S _k (t) corresponding to the base station may be performed to minimize the sum of ui (t) indicating usability within a range in which the SINR threshold is guaranteed. This is defined as a MIN-UTIL technique, and the base station selection method may be expressed by the following equation.

[Correction under Rule 91 13.09.2016]

Here, any UE may be provided with a service for t times by the base stations Sk selected by Equation 5.

The embodiment also provides an optimization technique for compensating for parameters due to channel uncertainty by base stations that do not collaborate in multiple base stations. G _{i, k} in Equation 5 is a parameter to be verified, allowing interference from an uncooperative base station in any UE. If the threshold of SINR is not satisfied by the uncertainty of verification, the joint transmission by the selected base stations increases the likelihood that the communication of the network will not be successful since any UE does not have enough SINR value for transmission. G _{i, k} (t) _, which represents the value of SINR, is a nominal value for validation and optimization, but is the actual value of the parameters of uncertainty g ' _{i, k} (t) and j ∈ S _k (t) Can be assumed in the range [g _{i, k} (t) -g ' _{i, k} (t), g _{i, k} (t) + g' _{i, k} (t)]. If S _k , the set of base stations, is defined as C, then β _{Sk (t)} (Γ) = max _{{C | C⊆ Sk (t), | C | = Γ}} {∑ _{i∈ C} g _{i, k (} t) m _i (t)}, the optimization method of Equation 5 can be expressed by the following equation, it is defined as ROBUST-MIN-UTIL.

[Correction under Rule 91 13.09.2016]

In Equation 6, the robustness of the system may be adjusted by an integer parameter Γ. The technique obtained by Equation 6 satisfies the threshold of SINR, which is possible if the discrepancy from the corresponding nominal value does not exceed Γ. Accordingly, the base stations obtained by Equation 6 may provide a more robust service to the UE than the base stations obtained by Equation 5 in an environment where parameter variability exists.

Optimization by Equation 6 is a method of minimizing the combined usability of the selected base station, which satisfies the SINR constraint with uncertainty.

Next, a method of performing cooperative communication by selecting a base station as in the embodiment of the present invention will be described with a specific example.

Base station	BS1	BS2	BS3	BS4	BS5	BS6	BS7
SINR	One	2	One	One	2	2	3
Utilization	0.1	0.1	0.2	0.3	0.1	0.3	0.5
Transmission power	0.1	0.1	0.1	0.1	0.1	0.1	0.1

Referring to Table 1, it shows the relative value of the signal-to-noise ratio (SINR), utilization (Utilization), and transmission power according to the base station. In order to perform successful communication with the user terminal, it is assumed that the relative value of the SINR value must satisfy at least 5.

First, when considering the transmission power of the base station, two base stations (BS6, BS7) can be selected to satisfy the SINR for communication with the user terminal, the sum of the transmission power is 0.2, the sum of usability is 0.8 Indicates. In this case, since the usability of the network is not taken into consideration, only a specific network may be excessively selected, resulting in relatively low communication performance with the user terminal.

Subsequently, when considering the usability of the base station as in the embodiment, BS1, BS2, BS5, which are the base stations with the lowest usability, may be selected among the base stations. In this case, the sum of transmission powers is 0.3, and the sum of usability represents 0.3.

At this time, the base stations are selected in the order of having the highest SINR value among the base stations BS1, BS2, BS5 selected on the basis of the usability only as many as?

As above based on the values of SINR due to the interference comprises an uncertain factor, g _{i, k} values from the uncooperative base station as shown in Equation (6) discussed _{[g i, k - g '} i, k, g i, k + g ' _{i, k} ]. Here, when g ' _{i, k} = g _{i, k} / 2, the SINR value of BS5 is 2, and when β is calculated when Γ is 1, β = 2/2 = 1. Therefore, in the embodiment, additional base stations are selected to perform cooperative communication so as to compensate for at least one SINR value by interference by non-cooperative base stations.

That is, BS3 is selected as the base station that satisfies the above conditions. Since BS3 has the lowest usability and the SINR value is 1 or more among the remaining base stations, BS3 performs a cooperative communication for jointly transmitting data to the user terminal. Processing performance can be improved. In other words, by selecting a base station in consideration of the usability of the network as well as the compensation value of the uncertain SINR, it is a robust cooperative communication that can guarantee the stability of the network more than the case of selecting the base station only considering the transmission power or only the usability. have.

FIG. 2 is a graph comparing performance in a cooperative communication method in a small cell network environment according to an embodiment, and is a graph showing serviceability indicating a ratio of user terminals in a network that can be serviced in detail.

Referring to (a), when 80 user terminals are used, the service performance of the ROBUST-MIN-UTIL method considering both the usability and the SINR compensation value in the cooperative communication method according to the embodiment is higher than other methods. This was found to be stable, and it may be determined that the specific base station is not excessively selected in the hot spot region in the process of selecting the base station based on the usability.

When the SINR value is increased to a certain level, the MIN-UTIL method considering transmission power has higher serviceability than the MIN-POWER method considering usability, which means that the base station can be easily overloaded as the number of required base stations increases. Because it can.

 Referring to (b), it can be seen that 120 user terminals are applied, and that serviceability is similar to that of 80 user terminals. However, although the serviceability gradually decreases in all methods, the serviceability of the method considering the transmission power decreases significantly compared with other methods. This is because the method considering the transmission power is caused by an overload phenomenon accelerated as the user terminal increases. However, it can be seen that the ROBUST-MIN-UTIL method of the embodiment has a good service performance on average compared to other methods.

3 is a graph illustrating the use of resources when a base station cooperatively provides a service to a user terminal. (a) shows the average transmission power when the base station provides a service to the user terminal. The MIN-POWER technique considering the transmission power is a method that requires the least amount of power, as shown in the graph, and can consider αγ for the limitation of SINR. Considering α in power consumption, the transmit power increased in the MIN-POWER and MIN-UTIL techniques as α increased. However, in the ROBUST-MIN-UTIL technique, the transmission power value was lower than those of the above two techniques, which may be determined because the uncertainty is compensated by the parameter evaluation according to the selected base station.

Referring to (b), it is a graph showing the average usability of the base station serving the user terminal. The MIN-UTIL technique showed the lowest usability and the MIN-POWER technique showed the highest usability. Through this, it can be seen that the usability increases as the value of α or γ increases as the number of required base stations increases.

4 shows a graph comparing the results of Jain's fairness index. The result of Jain? S fairness index is represented by a value between 1 / | X _k | and 1, where 1 means that all base stations have the same usability. The results show that the MIN-UTIL and ROBUST-MIN-UTIL techniques are better in terms of 'fairness' in the hotspot area than the MIN-POWER technique. This may be determined that the MIN-UTIL technique and the ROBUST-MIN-UTIL technique balance the usability of the base station by selecting a base station having low usability instead of an overloaded base station compared to the MIN-POWER technique. That is, by selecting a base station in consideration of the usability of the base station, it is possible to prevent the specific base station from being excessively selected and overloaded (overloaded).

5 is a flowchart illustrating a cooperative communication method in a small cell network environment according to an embodiment. Referring to FIG. 5, the flow of a cooperative communication method in a small cell network environment according to an embodiment is as follows.

First, a step (S10) of evaluating usability of each base station for a plurality of base stations that can communicate with a user terminal is performed. Here, usability is defined as representing the ratio of the service capacity currently being performed to the service capacity that the base station can perform at the maximum.

Subsequently, step S20 of selecting the base stations among the base stations that have the lowest usability while satisfying the theoretical SINR value for performing communication with the user terminal is performed. At this time, a plurality of base stations with low usability are selected so that the sum of SINRs satisfies a theoretical SINR value for communication with a user terminal.

Subsequently, it is determined whether it is possible to communicate with the user terminal using SINR values of the selected base stations (S30). In step S20, the base station is theoretically selected to satisfy the SINR that can communicate with the user terminal, but the SINR value may not be satisfied due to channel uncertainty due to channel measurement error or interference from an uncooperated region.

Therefore, if the SINR value of the selected base stations does not satisfy the SINR value due to interference due to channel uncertainty, an additional base station selection step S40 may be performed to compensate for the SINR value.

If the SINR value between the user terminal and the base station satisfies the threshold through the above-described steps S30 and S40, the user terminal may perform cooperative communication between the selected base stations to improve the performance of the network.

As described above, the present embodiment allows users to preferentially select a base station having a relatively low usability in an environment in which users and networks are concentrated, thereby stably accessing the network even in a situation where users are temporarily crowded, and performing network performance. Can be maintained at a certain level. In addition, by using a technique of additionally selecting a base station to compensate for the uncertainty of the SINR caused by the interference propagated in the non-cooperation base station, it is possible to provide a certain quality of service to the user connected to the network.

The present invention has been described above with reference to the preferred embodiments, which are merely examples and are not intended to limit the present invention, and those skilled in the art to which the present invention pertains do not depart from the essential characteristics of the present invention. It will be appreciated that various modifications and applications are not possible that are not illustrated above. For example, each component specifically shown in the embodiment of the present invention can be modified. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

According to the present invention, it is possible to access the network stably even in a situation where users are temporarily crowded, and there is industrial applicability because the performance of the network can be maintained at a certain level.

Claims (5)

1. A method for selecting a base station for communicating in a wireless network environment consisting of small cells,

   Evaluating utilization for base stations that are capable of communicating with the user's terminal;

   Selecting base stations among the base stations which have the lowest usability;

   Additionally selecting a base station to satisfy the SINR in consideration of a signal-to-noise ratio (SINR) in which communication with a user terminal may be performed; And

   Performing cooperative communication with a user's terminal through co-transmission of the base stations;

   The usability is a cooperative communication method in a small cell network environment, characterized in that the ratio of the service capacity that is currently being performed relative to the service capacity that the base station can perform the maximum.
2. The method of claim 1,

   The step of selecting the base station of the lowest usage among the base stations,

   A method of cooperative communication in a small cell network environment, characterized in that the plurality of base stations are preferentially selected in consideration of the minimum SINR that can communicate with the user's terminal in the process of selecting a plurality of base stations with the lowest usability.
3. The method of claim 1,

   The step of additionally selecting a base station connected to the user terminal to compensate for the SINR due to interference transmitted from the non-cooperating base station,

   A method of cooperative communication in a small cell network environment comprising the step of selecting a predetermined number of base stations in order of the base station having the largest SINR among the selected base stations in consideration of usability.
4. The method of claim 3, wherein

   And determining a compensation value of the SINR according to the SINR value of the selected base station and the SINR value according to the range of the SINR.
5. The method of claim 4, wherein

   And performing co-communication with a user terminal by selecting a base station having a value equal to or greater than the compensation value and indicating minimum usability among unselected base stations.

Images