KR20160112762A - Coordinated Transmission Method for Small Cell Network - Google Patents

Abstract

The present invention relates to a cooling and moistureproof distribution box (100). The cooling and moistureproof distribution box (100) according to the present invention comprises: a box-type main body (110) for containing a control unit; and a cooling moistureproof unit (120), mounted on an outer side of the main body (110), for providing cool air and warm air for the inside of the main body (110), wherein the cooling moistureproof unit (120) can provide cool air and warm air via a thermoelectric element (127). Accordingly, since the main body (110) is cooled when heat generated from a distribution board inside the main body (110) is greater than or equal to the stated temperature, the efficiency is improved and the accuracy of outputting voltage is enhanced, and a contact unit of a cable terminal connected to the distribution board is melted and separated therefrom via the heat greater than or equal to the stated temperature, thereby preventing a power supply disconnection phenomenon from occurring. Moreover, since dew condensation occurs inside the main body (110) in the winter, the dew condenses into water drops as time goes on and then the water drops fall on the distribution board, thereby preventing a short circuit from occurring.

Description

{Coordinated Transmission Method for Small Cell Network}

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 that can provide an optimal network environment to a user in a small cell environment in which the base station is concentrated.

Information handled in modern society is increasing exponentially, and capacity and processing speed of network are becoming important issues. Therefore, a large amount of traffic is required in the user equipment. In order to satisfy such a demand, it is one of measures to secure a large number of base stations. Therefore, various small cells are arranged in the macro cell, and the network cells become increasingly dense have.

Due to the characteristics of the cellular communication system, each cell can use the same frequency resources around the cell boundary, in which case mutual interference may exist. In recent years, in order to increase system capacity, a cellular communication system has moved away from a macro cell to aim at a small cell, and a network has evolved in the form of small cells of various sizes within a macro cell, It is becoming an important issue. In order to overcome inter-cell interference and improve the performance of a terminal located at a cell boundary, a method of transmitting data through mutual cooperation among 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, There is a way to maximize the century. The above technique for overcoming the inter-cell interference has a problem in that the amount of information exchanged for mutual cooperation increases and complex calculation is required. Also, when the mobile station efficiently selects its serving base station, there is a limit to the initial cell search method based on the reception strength of the base station pattern signal.

Accordingly, there is a need for a method that can perform cooperative communications between base stations while improving network performance and effectively reducing the impact of interference.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of selecting an optimal base station for a user in a network environment based on a small-cell cooperative communication.

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

An embodiment of the present invention provides a cooperative communication method for selecting a base station for performing communication in a wireless network environment comprising a small cell, the method comprising: evaluating utilization of base stations capable of communicating with a user terminal; Selecting the base stations with the lowest usability among the base stations; Further selecting a base station to satisfy the SINR in consideration of a signal-to-noise ratio (SINR) at which communication with a user terminal can be performed; And performing cooperative communication with a user's terminal through joint transmission of the base stations, wherein the usability is determined based on a ratio of the number of users currently serving by the base station to a service capacity that the base station can maximally perform .

According to the present invention, a user terminal selects a base station having a low usability by a user relatively in an environment where a user and a network are concentrated, so that a user can stably access the network even in a situation where the user is temporarily crowded, Performance can be maintained at a certain level.

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

1 shows a model of a compact cell network
Figure 2 is a graph showing the serviceability of user equipment in a network;
FIG. 3 is a graph illustrating the use of resources when a base station cooperatively provides a service to a user terminal. FIG. 3 (a) shows an average transmission power when a base station provides a service to a user terminal, A graph showing the average usability of the base stations servicing the terminal
FIG. 4 is a graph showing a comparison result of the Jain's fairness index
5 is a flowchart illustrating a cooperative communication method in a small cell network environment according to an embodiment

The embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited to these embodiments. In describing the present invention, a detailed description of well-known functions or constructions may be omitted for the sake of clarity of the present invention.

A user terminal receives a large amount of signal information from a plurality of base stations, and the base stations cooperatively distribute the channel and message information to user equipment through a plurality of lines. However, in a hotspot region, a particular base station can be overloaded with a large selection of user equipment.

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

1 is a diagram showing a model of a compact cell network.

Referring to FIG. 1, it is assumed that N base stations defined as X are scattered and a wireless connection service is provided to L user equipments (terminals) defined as U, as a model of a dense wireless network. The neighboring 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 available.

If the size of X _k is large, cooperative communication can be performed at a higher level with a larger number of base stations, but in a situation where cooperative communication is not properly performed, interference occurs between the base stations. The BSs share the CSI with the transmission data, and the i-th BS transmits the mi signal to the power of Pi, and the BSs are assumed to be connected to the high-speed wireless network. However, message exchange overhead can 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 participate in a signal transmission jointly in the kth user equipment (UE) . In the embodiment, U _i (t), which is an index indicating the rate of service being performed in comparison with the maximum service capacity at the i th base station during the time t, is defined and referred to as utilization. Here, the service ratio being performed can be described by the number of users currently serving by the base station. For example, if the i-th base station is used to have the maximum service rate by a plurality of UEs, u _i = 1, and u _i = 0 when the i-th base station is not in operation.

1, the signal received at the k < th > UE during the time t may be expressed by the following equation.

Here, 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 the white Gaussian noise with variance of n. X = Sk ∪ (Xk | Sk ) ∪ | to as _{(X Xk), R k (} t) of equation (1) may be re-expressed by the equation as described below.

Here, ri, k (t) = hi, k (t) pi, and the SINR of the kth UE is expressed as follows.

Here, the operator of Equation (3) does not include interference from the base station because it is controlled not to interfere with the user's terminal (kth UE) using the precoding matrix in an environment where the selected base stations cooperate.

Again, multiple base stations (BSs) may perform cooperative communications with each other to improve the processing performance of the user equipment (UE). The cooperating base stations Xk provide wireless connection services and are superior in performance to the case where there is only one neighboring base station. However, since the size of the cooperative base station is large, a message exchange overhead is generated because the cooperative base stations must share the CSI with the transmission data.

The k-th UE, if receiving service from the cooperative base station (X _k), a part of the cooperative base station (Sk (t)) may be selected to participate for the common signal is transmitted to the K th UE. In selecting S _k (t) defined as the cooperative base station, a method of minimizing the sum of the total transmission power of the base station while satisfying the threshold of SINR may be considered. The method of considering the minimum power is defined as the MIN-POWER technique, and can be expressed by the following equation.

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

On the other hand, some base stations close to the UE may be overloaded and overloaded in the hotspot area, and QoS and BS may be reduced. Rather than excessive use of the base stations, it is desirable to improve the processing performance of the network by selecting several base stations with low usability and cooperatively providing services to the UE.

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

Here, any UE can be served for a time t by the base stations Sk selected by Equation (5).

라고 할 때, 수학식 5의 최적화 방법은 하기와 같은 수학식으로 표현될 수 있으며, 이를 ROBUST-MIN-UTIL이라 정의한다.Embodiments also provide an optimization technique for compensating for parameters due to channel uncertainty by a base station that does not cooperate at a plurality of base stations. In Equation 5, g _{i, k} is a parameter to be verified, allowing interference from non-cooperative base stations in any UE. If the threshold of the SINR is not satisfied by the uncertainty of the verification, the joint transmission by the selected base stations will not have a sufficient SINR value for the transmission of any UE, which increases the likelihood that the communication on the network will not be successful. G _{i, k} (t) representing the value of the SINR is, but the nominal value to be used after the optimization is validated, which is a parameter of the uncertainty g _'i, the actual value of _{k (t), j ∈ S} k (t) Can be assumed in the range of [g _{i, k} (t) - g ' _{i, k} (t), g _{i, k} (t) + g' _{i, k} (t)]. Defining the set of base stations S _k as C

, The optimization method of Equation (5) can be expressed by the following equation, which is defined as ROBUST-MIN-UTIL.

The robustness of the system in Equation (6) can be adjusted by an integer parameter Γ. The technique obtained by equation (6) satisfies the threshold of SINR, which is possible if the mismatch from the corresponding nominal value does not exceed Γ. Therefore, the base stations obtained by Equation (6) can provide a more robust service to the UEs than the base stations obtained by Equation (5) in an environment where parameter variability exists.

The optimization according to Equation (6) is a method for minimizing the combined usability of the selected base station, which satisfies the constraints of SINR with uncertainty.

A method of performing cooperative communication by selecting a base station as an embodiment of the present invention will be described with reference to specific examples.

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, the SINR (Signal to Noise Ratio) relative value, Utilization, and transmission power according to the base station are shown. In order to perform successful communication with the user terminal, it is assumed that the relative value of the SINR value satisfies a minimum of 5.

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

When the usability of the base station is considered, BS1, BS2, and BS5, which exhibit the least usability among the BSs, may be selected. In this case, the sum of the transmission power is 0.3, and the sum of the usability is 0.3.

At this time, the number of the base stations is selected in the order of having the highest SINR value among the base stations (BS1, BS2, BS5) selected only on the basis of usability.

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 the BS 5 is 2, so that when β is 1, β = 2/2 = 1. Therefore, in the exemplary embodiment, an additional base station is selected to perform cooperative communication so that the SINR value can be compensated by at least one by the interference by the non-cooperative base station.

That is, since BS3 is selected as the base station satisfying the above-mentioned conditions and BS3 has the lowest usability among the remaining base stations and the SINR value satisfies 1 or more, cooperative communication for jointly transmitting data to the user terminal is performed, The processing performance can be improved. That is, it can be said that robust cooperative communication can more secure the stability of the network than selecting the base station considering only the transmission power or usability only by selecting the base station considering the usability of the network as well as the compensation value of the uncertain SINR have.

FIG. 2 is a graph comparing performance in a cooperative communication method in a small cell network environment according to an embodiment, and specifically, a graph showing a service possibility indicating a ratio of user terminals in a serviceable network.

(a), there are 80 user terminals. In the case of the ROBUST-MIN-UTIL method considering both the usability and the SINR compensation value in the cooperative communication method according to the embodiment, , Which can be judged to be due to the fact that the base station is not selected excessively in the hot spot area based on usability.

When the SINR value increases to a certain level, the MIN-UTIL scheme considering the transmission power has higher serviceability than the MIN-POWER scheme considering usability. As the number of required base stations increases, the base station easily overloads It is because.

 (b), it can be seen that 120 user terminals are applied, and that the serviceability on the network is similar to the case where 80 user terminals are applied. However, despite the gradual decrease in serviceability in all methods, the serviceability of the method considering the transmission power shows a larger decrease than the other methods. This is because a method considering transmission power occurs due to acceleration of overload phenomenon as user terminals increase. However, it can be seen that the ROBUST-MIN-UTIL method of the embodiment has a better service performance on average than other methods.

3 is a graph illustrating the use of resources when a base station cooperatively provides services to a user terminal. (a) shows the average transmission power when a base station provides a service to a user terminal. The MIN-POWER technique considering transmission power is a method that requires a minimum amount of power as shown in the graph, and αγ for constraining the SINR can be considered. Considering α in power consumption, the transmission power increases in MIN-POWER and MIN-UTIL as α increases. However, in the ROBUST-MIN-UTIL technique, a smaller transmission power value than that of the above-mentioned two techniques appears. This is because it compensates the uncertainty through the parameter estimation depending on the selected base station.

(b) is a graph showing an average usability of a base station serving a user terminal. The MIN-UTIL method showed the lowest usability and showed the greatest usability in the MIN-POWER technique. It can be seen from this that usability increases with increasing α or γ values due to the increase in the number of required base stations.

FIG. 4 shows a graph comparing the results of the Jain's fairness index. The result value of Jain's fairness index is 1 / | X _k | to 1, and 1 means that the usability of all base stations is the same. The results show that the MIN-UTIL technique and the ROBUST-MIN-UTIL technique are better than the MIN-POWER technique in terms of 'fairness' in the hotspot area. It can be judged that the MIN-UTIL scheme and the ROBUST-MIN-UTIL scheme balance the usability of the base station by selecting the base station having low usability instead of the overloaded base station as compared with the MIN-POWER scheme. That is, by selecting a base station in consideration of the usability of the base station, it is possible to prevent a 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, a flow of the cooperative communication method in the small cell network environment according to the embodiment will be described below.

First, a step of evaluating the usability of each of the plurality of base stations communicable with the user terminal (S10) is performed. Herein, the usability is defined as a ratio of the service capacity currently being performed to the service capacity that the base station can maximally perform.

Next, a step S20 is performed to select base stations with the lowest usability while satisfying a theoretical SINR value for performing communication with the user terminal among the base stations. At this time, a plurality of base stations with low usability are selected and the sum of SINRs satisfies a theoretical SINR value for communication with the user terminal.

Next, a determination is made as to whether or not the user terminal can communicate with the SINR value of the selected base stations (S30). In step S20, although the BS is theoretically selected to satisfy the SINR that can communicate with the user terminal, the SINR value may not be satisfied due to the channel uncertainty due to channel measurement error or interference from the non-cooperative area.

Therefore, if the SINR value of the selected base stations does not satisfy the SINR value due to the interference due to the 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 value through steps S30 and S40 described above, the user terminal can perform cooperative communication with the selected base stations to improve the performance of the network.

As described above, according to the present embodiment, the user can preferentially select a relatively low-availability base station in an environment where the user and the network are concentrated, so that the user can stably access the network even in a situation where the user is temporarily concentrated, Can be maintained at a certain level. Further, by using a technique of selecting an additional base station to compensate for the uncertainty of the SINR caused by the interference propagated in the non-cooperative base station, it is possible to provide a service of a constant quality to a user connected to the network.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood that various modifications and applications other than those described above are possible. For example, each component specifically shown in the embodiments of the present invention can be modified and implemented. It is to be understood that all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (5)

A method of selecting a base station for performing communication in a wireless network environment comprising a small cell,
Evaluating utilization of base stations capable of communicating with a user terminal;
Selecting the base stations with the lowest usability among the base stations;
Further selecting a base station to satisfy the SINR in consideration of a signal-to-noise ratio (SINR) at which communication with a user terminal can be performed; And
Performing collaborative communication with a user's terminal through joint transmission of the base stations,
Wherein the usability indicates a ratio of a service capacity that is currently being performed in relation to a service capacity that the base station can maximally perform. The method according to claim 1,
Wherein the selecting of the BSs having the lowest usability among the BSs comprises:
Wherein a plurality of base stations are preferentially selected in consideration of a minimum SINR that can be communicated to a user's terminal in a process of selecting a plurality of base stations with minimal usability. The method according to claim 1,
The step of additionally selecting a base station connected to the user terminal to compensate for the SINR due to the interference transmitted from the non-
And selecting a predetermined number of base stations in order of a base station having the largest SINR among the selected base stations considering only usability. The method of claim 3,
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,
And selecting a base station having a value equal to or greater than the compensation value and indicating the minimum usability among the base stations that are not selected and performing common communication with the user terminal.

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