WO2017018593A1

WO2017018593A1 - Device and method for determining transmission power in device-to-device communication system

Info

Publication number: WO2017018593A1
Application number: PCT/KR2015/009814
Authority: WO
Inventors: 이웅섭; 반태원; 정방철
Original assignee: 경상대학교산학협력단
Priority date: 2015-07-27
Filing date: 2015-09-18
Publication date: 2017-02-02
Also published as: KR101662505B1

Abstract

A technique for determining transmission power in device-to-device (D2D) communication is disclosed. According to the disclosed transmission power technique, the total sum of interference signals transmitted from a terminal to a base station can be controlled to be a threshold value or less even while maximally improving a data transmission rate of the D2D communication.

Description

Apparatus and method for determining transmission power in an end-to-end communication system

The following embodiments are related to an apparatus and method for determining transmission power in an inter-terminal communication system. Specifically, the present invention relates to a transmission power for maximizing data transmission speed between terminals while maintaining the influence of interference on a base station below a threshold. The present invention relates to determining.

Recently, with the spread of smartphones and tablet PCs and the activation of high-capacity multimedia communications, mobile traffic is rapidly increasing. Since most of this mobile traffic is transmitted through base stations, telecommunications service providers are faced with serious network load issues at the moment. As a result, service providers have increased network facilities to handle increasing traffic, and hastened to commercialize next-generation mobile communication standards that can efficiently handle large amounts of traffic such as mobile WiMAX and Long Term Evolution (LTE). But it's time for another solution to handle the ever-increasing volume of traffic.

Device-to-device (D2D) communication is a distributed communication technology that directly passes traffic between adjacent nodes without using infrastructure such as base stations. In a D2D communication environment, each node, such as a mobile terminal, finds another terminal physically adjacent to itself, establishes a communication session, and transmits traffic. Since D2D communication can solve the traffic overload problem by distributing the traffic concentrated at the base station, it is getting the spotlight as an element technology of the next generation mobile communication technology after 4G.

However, if the terminals perform D2D communication, the interference signal generated during the communication degrades the performance of the base station. That is, while the terminals perform the D2D communication, a technique for maintaining the performance of the base station is required.

An object of the following embodiments is to determine the transmission power for D2D communication between terminals without degrading the performance of the base station.

According to an exemplary embodiment, a terminal located within the coverage of a base station, wherein the third terminal located within the coverage of the base station to the second terminal paired with the terminal during the time for transmitting the first data to the base station; Provided is a terminal including a transmitter for directly transmitting second data at a transmission power determined in consideration of a first channel state from the base station to the base station.

The apparatus may further include a channel state estimator and a receiver configured to estimate a second channel state from the second terminal to the terminal, wherein the transmitter transmits the second channel state to the base station and the receiver transmits the second channel state. The transmission power determined in consideration of the state may be received from the base station.

The apparatus may further include a transmit power determiner configured to update and transmit the transmit power according to Equation 1 below.

[Equation 1]

here,

Is the value of the updated transmit power,

Is the following equation

Is updated as shown in 2.

Is the first channel state,

Is the effect of the multipath fading channel of the channel from the terminal to the base station,

Is the channel gain according to the distance from the terminal to the base station.

Is a second channel state which is a channel state from the second terminal to the terminal,

Is the influence of the multipath fading channel of the channel from the terminal to the second terminal,

Is a channel gain according to the distance from the second terminal to the terminal.

Is the power of thermal noise,

Is the strength of the interference transmitted from the terminal to the base station,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 2]

here,

Updated

Is the value of,

Is a threshold of the sum of interference signals received by the base station.

Is the number of terminals transmitting interference to the base station,

Is the value of the previous transmit power.

Is any constant.

The apparatus may further include a transmit power determiner configured to determine the transmit power according to Equation 3 below.

[Equation 3]

here,

Is determined according to the following equation (4).

Is the first channel state,

Is the effect of the multipath fading channel of the channel from the terminal to the second terminal,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 4]

here,

Is a threshold of the sum of interference signals received by the base station.

Here, the transmission power to determine the transmission power according to the following equation (5)

It may further include wealth.

[Equation 5]

here,

Is determined according to the following equation (6).

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 6]

here,

Is a threshold of the sum of interference signals received by the base station.

According to still another exemplary embodiment, a base station in which terminals located within coverage directly transmit data to each other, the pilot receiving unit receiving a pilot signal from a first terminal among the terminals, and using the received pilot signal; A channel state estimator for estimating a first channel state from a first terminal to the base station, and a channel state receiver for receiving a second channel state from the first terminal to a second terminal included in the terminals from the first terminal And a transmission power determiner for determining a transmission power for the first terminal in consideration of the first channel state and the second channel state, and a transmitter for transmitting the determined transmission power to the first terminal. When the third terminal located within the coverage of the first data is transmitted to the base station While, according to the transmission power of the transmission of the first station is a base station directly transmits the second data to the second terminal is provided.

Here, the transmission power determiner may determine the transmission power according to Equation 7 and Equation 8 below.

[Equation 7]

here,

Is a threshold of the sum of interference signals received by the base station.

Transmit power

Is a set of terminals having a value of 0,

Transmit power

Has a value of

Is a set of terminals.

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 8]

The transmission power determiner may update the transmission power by repeating Equation 7 and Equation 8 until the determined transmission power satisfies Equation 9 below.

[Equation 9]

According to another exemplary embodiment, in a method of operating a terminal located within the coverage of a base station, the third terminal located within the coverage of the base station is paired with the terminal during the time for transmitting the first data to the base station A method of operating a terminal is provided, comprising directly transmitting second data to a second terminal at a transmission power determined in consideration of a first channel state from the terminal to the base station.

Estimating a second channel state from the second terminal to the terminal, wherein the transmitter is further configured to transmit the second channel state to the base station and the transmission power determined in consideration of the second channel state. The method may further include receiving from a base station.

The method may further include updating and determining the transmission power according to Equation 10 below.

[Equation 10]

here,

Is the value of the updated transmit power,

Is updated as in Equation 11 below.

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 11]

here,

Updated

Is the value of,

Is a threshold of the sum of interference signals received by the base station.

Is the number of terminals transmitting interference to the base station,

Is the value of the previous transmit power.

Is any constant.

The method may further include determining the transmission power according to Equation 12 below.

[Equation 12]

here,

Is determined according to the following equation (13).

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 13]

here,

Is a threshold of the sum of interference signals received by the base station.

Here, the method may further include determining the transmission power according to Equation 14 below.

[Equation 14]

here,

Is determined according to the following equation (15).

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 15]

here,

Is a threshold of the sum of interference signals received by the base station.

According to the following embodiments, it is possible to determine the transmission power for D2D communication between terminals without degrading the performance of the base station.

1 is a diagram illustrating a concept of D2D communication according to an exemplary embodiment.

2 is a flowchart illustrating a step-by-step method of D2D communication according to an exemplary embodiment.

3 is a block diagram illustrating a structure of a terminal for performing D2D communication according to another exemplary embodiment.

Fig. 4 is a flowchart illustrating a step-by-step method of operating a terminal performing D2D communication according to another exemplary embodiment.

Fig. 5 is a block diagram showing the structure of a base station for determining transmission power for D2D communication according to another exemplary embodiment.

Fig. 6 is a flowchart illustrating step by step a D2D communication method according to yet another exemplary embodiment.

[Equation 1]

here,

Is the value of the updated transmit power,

Is updated as in Equation 2 below.

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 2]

here,

Updated

Is the value of,

Is a threshold of the sum of interference signals received by the base station.

Is the number of terminals transmitting interference to the base station,

Is the value of the previous transmit power.

Is any constant.

[Equation 3]

here,

Is determined according to the following equation (4).

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 4]

here,

Is a threshold of the sum of interference signals received by the base station.

Here, the transmission power may further include a transmission power determination unit to determine according to the following equation (5).

[Equation 5]

here,

Is determined according to the following equation (6).

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 6]

here,

Is a threshold of the sum of interference signals received by the base station.

[Equation 7]

here,

Is a threshold of the sum of interference signals received by the base station.

Transmit power

Is a set of terminals having a value of 0,

Transmit power

Has a value of

Is a set of terminals.

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 8]

[Equation 9]

[Equation 10]

here,

Is the value of the updated transmit power,

Is updated as in Equation 11 below.

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 11]

here,

Updated

Is the value of,

Is a threshold of the sum of interference signals received by the base station.

Is the number of terminals transmitting interference to the base station,

Is the value of the previous transmit power.

Is any constant.

[Equation 12]

here,

Is determined according to the following equation (13).

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 13]

here,

Is a threshold of the sum of interference signals received by the base station.

[Equation 14]

here,

Is determined according to the following equation (15).

Is the first channel state,

Is the power of thermal noise,

Is the maximum transmit power of the terminal.

Is

It is the larger of internal value and '0'.

[Equation 15]

here,

Is a threshold of the sum of interference signals received by the base station.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings.

Several terminals

121, 122, 131, 132, 140 are located within the coverage of the base station 110. Each of the

terminals

121, 122, 131, 132, and 140 may transmit data according to a device-to-device (D2D) communication method of directly transmitting data to other terminals, or via the base station 110 to another terminal. You can also send data.

Terminals using the D2D communication scheme form a pair (pair, 120, 130) with other terminals for transmitting and receiving data. In FIG. 1, the terminal 121 configures a first D2D pair 120 with the terminal 122, and the terminal 121 directly transmits data to the terminal 122 according to a D2D communication scheme. In addition, the terminal 131 forms a second D2D pair 130 with the terminal 132, and the terminal 131 directly transmits data to the terminal 132 according to a D2D communication scheme. The terminal 140 transmits data to the other terminal through the base station 110.

For convenience of description, a terminal for transmitting data using a D2D communication method is referred to as a D2D transmitting terminal and a terminal for receiving data using a D2D communication method is referred to as a D2D receiving terminal.

In FIG. 1, each

pair

120, 130 is

Assume that they are spaced apart by the above distance. Also, in each

D2D pair

120, 130, the

D2D transmitting terminals

121, 131 are connected to the

D2D receiving terminals

122, 132 in another D2D pair.

Assume that we transmit as much interference.

According to one side, the D2D transmitting terminal (121, 131) transmits data to the D2D receiving terminal (122, 132) at the same time as the terminal 140 for transmitting data to the base station. Therefore, the

D2D transmission terminals

121 and 131 transmit the interference signal to the base station 140, and as a result, the data reception performance of the base station 140 is degraded.

According to one side, the base station 140 may determine the transmission power of the D2D transmitting terminals to maximize the data rate of each D2D pair while maintaining the strength of the interference signal received from all the D2D transmitting terminals to a certain level or less.

In FIG. 1, a channel gain according to a distance from a D2D transmitting terminal (called an i-th D2D transmitting terminal) included in an i-th D2D pair to a base station 140 is calculated.

The effects of multipath fading channels

, The channel state from the i-th D2D transmitting terminal to the base station 140

Can be expressed as

In addition, the channel gain according to the distance from the ith D2D transmitting terminal to the ith D2D receiving terminal

The effects of multipath fading channels

, The channel state from the i th D2D transmitting terminal to the i th D2D receiving terminal

Can be expressed.

The effects of multipath fading channels

Can be expressed.

Where the effect of multipath fading

,

Is a value that changes relatively quickly, and the channel gain over distance

,

Is a value that changes relatively slowly.

transmit power of the i-th D2D transmitting terminal

In this case, the sum of normalized data rates of each D2D pair may be expressed by Equation 1 below.

[Equation 1]

Where K is the number of D2D pairs,

Power of thermal noise,

Is the base 2 log (

).

In addition, the threshold value of the strength of the interference signal received by the D2D base station 140

In this case, the base station 140 receives a certain level (the strength of the interference signal received from all the D2D transmitting terminals).

Keeping below) can be expressed as Equation 2 below.

[Equation 2]

In addition, the transmission power of each D2D transmission terminal

Has a limiting condition as shown in Equation 3 below. here,

Transmit power

Is the maximum value that can have.

[Equation 3]

As described above, the base station 140 determines the transmission power of the D2D transmission terminals so that the data rate of each D2D pair is maximized while maintaining the strength of the interference signal received from all the D2D transmission terminals below a certain level. Satisfying Equations 2 and 3

To maximize Equation 1

It can be modeled as yielding a combination of these. To satisfy these conditions

A specific method for calculating the combination of these will be described in detail with reference to FIGS. 2 to 7.

The transmission power determination method according to an exemplary embodiment can be largely divided into four embodiments according to a subject that determines the transmission power and a parameter that is considered for determining the transmission power.

Example 1 Centralized Power Control Scheme

2 is a flowchart illustrating a step-by-step method of D2D communication according to an exemplary embodiment. In FIG. 2, the base station 110 considers a channel state from the

D2D transmitting terminals

121 and 131 to the base station 110 and a channel state from the

D2D transmitting terminals

121 and 131 to the

D2D receiving terminals

122 and 132. An embodiment of determining the transmission power of the

D2D transmission terminals

121 and 131 is shown.

In step 230, the D2D transmitting terminal 210 transmits a pilot signal to the base station 220.

In step 231, the base station estimates a first channel state from the D2D transmitting terminal 210 to the base station 220 using the pilot signal received from the D2D transmitting terminal 210. According to one side, the first channel state is a channel gain according to the distance from the D2D transmitting terminal 210 to the base station 220

And multipath fading channel effects

Considering

It can be expressed as

In operation 240, the D2D transmitting terminal 210 estimates a second channel state from the D2D transmitting terminal 210 to the D2D receiving terminal (not shown). According to one side, the second channel state is a channel gain according to the distance from the D2D transmitting terminal 210 to the D2D receiving terminal

And multipath fading channel effects

Considering

It can be expressed as

In step 241, the D2D transmitting terminal 210 transmits the second channel state to the base station 220.

In step 250, the base station 220 determines the transmit power of the D2D transmitting terminal 210 in consideration of the first channel state and the second channel state. According to one side, the base station maintains the transmission power of the D2D transmission terminals to the maximum data rate of each D2D pair while maintaining the strength of the interference signal received from all the D2D transmission terminals for a K terminal pair below a certain level. You can decide.

This satisfies Equations 2 and 3

To maximize Equation 1

It can be thought of as yielding a combination of these.

According to one side, the base station 220 using the following equation (4) and (5), according to the following algorithm

Can be calculated.

Step 1:

reset

(According to one side, base station 220 is

To the empty set (

Can be initialized to here,

Transmit power

Is a set of D2D transmitting terminals with a value of 0.)

Step 2:

reset

(According to one side, base station 220 is

To the empty set (

Can be initialized to here,

Transmit power

Has a value of

Is a set of D2D transmission terminals.)

Step 3: According to Equation 4 below

Calculation

[Equation 4]

Here, K is a set of D2D transmission terminals.

Step 4: According to Equation 5 below

Calculation

[Equation 5]

here,

Is the transmit power of the i-th D2D transmitting terminal determined according to the centralized power control scheme. Also,

Is

It is the larger of internal value and '0'.

Step 5: Determine whether the following inequality (Equation 6) is satisfied

[Equation 6]

If the inequality is satisfied in step 5, the determined

The value is finally determined as the transmission power of the D2D transmitting terminal. If the inequality is not satisfied, the following steps 6 and 9 are repeated until the inequality is satisfied.

Step 6:

update

(Calculated in step 4

According to the value

Update it.)

Step 7:

update

(Calculated in step 4

According to the value

Update it.)

Step 8: According to Equation 4

Calculation

(Updated in steps 6 and 7

,

Using

Calculation)

Step 9: According to Equation 5

Calculation

(Updated in steps 6 and 7

,

And updated in step 8

Using

Calculate

In step 260, the base station 220 calculates the calculated transmit power

To the D2D transmitting terminal 210.

In step 261, the D2D transmitting terminal 210 receives the received transmit power.

The second data is transmitted to the D2D receiving terminal (second terminal, not shown). The interference signal is transmitted to the base station 220, but the total sum of the interference signals received by the base station 220 is kept below the threshold. Therefore, even when the base station 220 receives the first data at the same time as the D2D transmitting terminal 210, the performance of the base station 220 is maintained.

3 is a block diagram illustrating a structure of a terminal for performing D2D communication according to another exemplary embodiment. The terminal according to the exemplary embodiment includes a channel state estimator 310, a transmitter 320, and a receiver 330.

In FIG. 3, the terminal 300 and the second terminal 350 are terminals included in the same terminal pair, the terminal 300 operates as a D2D transmitting terminal, and the second terminal 350 operates as a D2D receiving terminal.

The transmitter 320 transmits a pilot signal to the base station 340. The pilot signal transmitted to the base station 340 is used to estimate the first channel state from the terminal 300 to the base station 340.

The channel state estimator 310 estimates a second channel state from the second terminal 350 to the terminal 300. According to one side, the receiver 330 receives a pilot signal from the second terminal 350, the channel state estimator 310 using the pilot signal received from the second terminal 350, the second terminal 350 The second channel state from the terminal to the terminal 300 can be estimated.

The transmitter 320 transmits the second channel state to the base station 340. The second channel state may be used by the base station 340 to determine the transmit power of the terminal 300. According to one side, the base station 340 may determine the transmission power of the terminal 300 in consideration of both the first channel state and the second channel state. According to another aspect, the base station 340 maintains the strength of the interference signal received from all the D2D transmitting terminals for the K terminal pairs below a certain level, so that the data rate of each D2D pair to the maximum D2D transmitting terminal Can determine their transmit power. According to another aspect, the base station 340 may determine the transmit power of the terminal 300 by using the algorithm according to the steps 1 to 9 described above.

The receiver 330 receives the transmission power determined by the base station 340 from the base station 340.

Although not shown in FIG. 3, a third terminal may be additionally located within the coverage of the base station 340. The third terminal may transmit the first data to the base station without directly transmitting the data to another terminal.

The transmitter 320 transmits the second data to the second terminal 350 while the third terminal transmits the first data to the base station 340. The transmitter 320 may transmit the second data with the received transmission power. In this case, the interference signal is transmitted from the terminal 300 to the base station 340. However, the total sum of the interference signals received by the base station 340 is maintained below the threshold.

In step 410, the terminal transmits a pilot signal to the base station. The pilot signal transmitted to the base station is used to estimate the first channel state from the terminal to the base station.

In step 420, the terminal estimates a second channel state from the second terminal to the terminal. Here, the second terminal is a terminal included in the same terminal pair as the terminal. In this case, the terminal operates as a D2D transmitting terminal and the second terminal operates as a D2D receiving terminal.

In step 430, the terminal transmits a second channel state to the base station. The second channel state may be used by the base station to determine the transmit power of the terminal. According to one side, the base station maintains the transmission power of the D2D transmission terminals to the maximum data rate of each D2D pair while maintaining the strength of the interference signal received from all the D2D transmission terminals for a K terminal pair below a certain level. You can decide. According to another aspect, the base station may determine the transmit power of the terminal using the algorithm according to the steps 1 to 9 described above.

In step 440, the terminal receives the transmission power determined by the base station from the base station.

In step 450, the terminal transmits the second data to the second terminal during the time that the third terminal transmits the first data to the base station. The third terminal is a terminal located within the coverage of the base station and is a terminal for directly transmitting data to the base station.

In step 450, the terminal may transmit the second data at the received transmission power. In that case, the interference signal is transmitted from the terminal to the base station. However, the total sum of the interference signals received by the base station remains below the threshold.

Fig. 5 is a block diagram showing the structure of a base station for determining transmission power for D2D communication according to another exemplary embodiment. Another base station 500 according to the exemplary embodiment includes a pilot receiver 510, a channel state estimator 520, a channel state receiver 530, a transmit power determiner 540, and a transmitter 550.

The pilot receiver 510 receives a pilot signal from the terminal 560.

The channel state estimator 520 estimates a first channel state from the terminal 560 to the base station using the received pilot signal.

The channel state receiver 530 receives the second channel state from the terminal 560. The second channel state is a channel state from the second terminal 570 to the terminal 560. According to one side, the terminal 560 may receive a second pilot signal from the second terminal 570 and estimate the second channel state using the received second pilot signal.

The transmit power determiner 540 determines the transmit power of the terminal 560 using the second channel state and the first channel state. According to one side, the transmission power determiner 540 maintains the strength of the interference signal received from all the D2D transmission terminals for the K terminal pairs below a certain level, D2D so that the data rate of each D2D pair to the maximum It is possible to determine the transmit power of the transmitting terminals. According to another aspect, the transmit power determiner 540 may determine the transmit power of the terminal 560 by using the algorithm according to the steps 1 to 9 described above.

The transmitter 550 transmits the determined transmission power to the terminal 560.

The terminal 560 receives the transmission power from the base station 500. The third terminal may be located in the coverage of the base station 500. The third terminal may transmit data to the base station 500 without directly transmitting data to another terminal.

The terminal 560 transmits the second data to the second terminal 570 during the time when the third terminal transmits the first data to the base station 500. The terminal 560 may transmit the second data with the received transmission power. In this case, the interference signal is transmitted from the terminal 560 to the base station 500. However, the total sum of the interference signals received by the base station 500 remains below the threshold.

In step 630, the terminal 610 transmits a pilot signal to the base station 620.

In step 631, the base station estimates a first channel state from the terminal 610 to the base station 620 using the received pilot signal.

In step 640, the terminal 610 receives the first channel state from the base station 620.

In FIG. 6, an embodiment in which the terminal 610 receives the first channel state estimated by the base station 620 is described. According to another embodiment, the terminal 610 is downward from the base station 620 to the terminal 610. The link channel state may be used as the first channel state.

In step 650, the terminal 610 estimates a second channel state from the second terminal to the terminal 610. According to one side, the terminal 610 may receive a second pilot signal from the second terminal, and estimate the second channel state from the second terminal to the terminal 610 using the received second pilot signal.

In step 660, the terminal 610 determines the transmit power.

The terminal 610 determines the transmission power according to some assumptions of a distributed power control scheme, a power control scheme based on average, and a power average based on a channel average value. It can be classified into a technique (Power Control Scheme Based on Averaged Channel Value).

Example 2: Distributed Power Control Scheme

In the distributed power control scheme, the terminal 610 may determine the transmit power. Accordingly, the terminal 610 does not need to feed back the second channel state to the base station 620.

According to the distributed power control scheme, the terminal 610 is a utility for the i-th D2D pair according to Equation 7 below.

Can be defined.

[Equation 7]

In Equation 7, the first item is the data rate between the i-th D2D pair, and the second item is the influence of interference transmitted by the D2D transmitting terminal 610 included in the i-th D2D pair to the base station. here,

Is the normalized price of interference.

In Equation 7, a utility

Is proportional to the data rate between the D2D pairs and is inversely proportional to the effect of interference transmitted by the D2D transmitting terminal 620 to the base station 620. Thus, the normalization cost of interference

If appropriately determined, it is possible to control the effect of the interference on the base station 620 due to the D2D transmission.

According to one side, the terminal 610 is a utility

Transmit power to maximize

Can be determined. utility

Using the derivative of, the transmit power

May be updated as in Equation 8 below.

[Equation 8]

here,

Is a value determined by the base station 620 at time t, and may be determined as shown in Equation 9 below.

[Equation 9]

here,

Is

Constant that determines the update rate of.

Referring to Equations 8 and 9, in step 660, the terminal is defined in Equation 9 from the base station

And transmit power in accordance with Equation (8).

Can be updated.

According to the distributed power control scheme, the base station 620 may not know the second channel state between the terminal 610 and the second terminal.

Can be updated. Accordingly, the terminal 610 does not have to feed back the second channel state every time, and can greatly reduce the signaling overhead.

Example 3: Power Control Scheme Based on Expectation

In the average-based power control scheme, the transmission power may be determined according to average channel information, rather than instantaneous channel information.

According to the average-based power control scheme, the average data rate between the D2D pairs is maximized, and the average value of the interference transmitted to the base station is controlled below the threshold. Referring to Equations 1, 2, and 5, the average power control technique may be expressed as Equation 10 below.

[Equation 10]

here,

Is

Is a vector whose elements are

Is

Vector whose elements are elements.

Is the normalization cost of the interference taking the average value into account.

According to one side, the terminal 610 is optimal to satisfy the equation (10)

sign

The value of can be calculated according to the following equation (11).

[Equation 11]

The left side of the equation (11) can be expressed as shown in the following equation (12).

[Equation 12]

In Equation 12, the condition

Can be expressed as in Equation 13.

[Equation 13]

In a similar way,

Can be expressed as in Equation 14 below.

[Equation 14]

Using Equations 13 and 14, the first item of Equation 12 may be expressed as Equation 15 below.

[Equation 15]

In addition, the second item of Equation 12 may be expressed as Equation 16 below.

[Equation 16]

Here, the terminal 610 is optimal

May be calculated using Equations 11, 15, and 16.

According to another embodiment, the terminal 610 is

An approximation of can be calculated according to the following equation (17).

[Equation 17]

Using Equation 17, the terminal 610 is a threshold value of the sum of the number K of D2D pairs and the interference signal received by the base station.

Using bay

You can simply determine the approximation of.

Example 4 Power Control Scheme Based on Averaged Channel Value

According to the power control scheme based on the channel average value, the terminal 610 may be affected by multipath fading.

,

Can be assumed to be 1. In this case, the cost of interference

May be determined according to Equation 18 below.

Equation 18

The optimal solution of equation (18)

Can be summarized as a value satisfying Equation 19 below.

[Equation 19]

According to another embodiment, the terminal 610 is

An approximation of can be calculated according to the following equation (20).

[Equation 20]

Using Equation 20, the terminal 610 is a threshold value of the sum of the number K of D2D pairs and the interference signal received by the base station.

Using bay

You can simply determine the approximation of.

In operation 670, the terminal 610 may transmit second data to the second terminal at the determined transmission power. According to one side, the terminal 610 may transmit the second data during the time that the third terminal located in the coverage of the base station 620 transmits the first data to the base station 620. In this case, the interference signal is transmitted from the terminal 610 to the base station 620. However, the total sum of the interference signals received by the base station 620 remains below the threshold.

7 is a block diagram illustrating a structure of a terminal for performing D2D communication according to another exemplary embodiment. The terminal 700 according to an exemplary embodiment includes a transmission power determiner 710 and a transmitter 720.

The transmit power determiner 710 determines the transmit power of the terminal 700. According to one side, the transmission power determination unit 710 is a distributed power control scheme (Distributed Power Control Scheme) described above, a power control scheme based on the average (Power Control Scheme Based on Expectation) and a channel average value based on the power control scheme ( The transmission power may be determined according to any one of Power Control Scheme Based on Averaged Channel Value.

For example, the transmit power determiner 710 may determine transmit power according to a distributed power control technique. In this case, the terminal 700 costs the normalization cost of the interference from the base station (not shown).

Receive the received

The transmission power may be determined by substituting Equation (8).

According to another embodiment, the transmission power determiner 710 may determine the transmission power according to the average power control technique. In this case, the transmission power determiner 710 may use the equations 11, 15, and 16 to optimize

And calculate

The transmission power may be determined by substituting into Equation 10.

According to another embodiment, the transmission power determiner 710 using Equation 17

You can simply determine the approximation of.

According to another embodiment, the transmit power determiner 710 may determine the transmit power according to a power control scheme based on the channel average value. In this case, the transmission power determining unit 710 according to the equation (19) interference cost

And calculate

By substituting into Equation 18, the transmission power may be determined.

According to another embodiment, the transmission power determiner 710 using Equation 20

You can simply determine the approximation of.

The transmitter 720 transmits the second data to the second terminal 630 according to the determined transmission power. According to one side, the transmitter 720 may transmit the second data during the time that the third terminal located in the coverage of the base station transmits the first data to the base station. In this case, the interference signal is transmitted from the transmitter 720 to the base station. However, the total sum of the interference signals received by the base station remains below the threshold.

8 is a flowchart illustrating a method of operating a terminal for performing D2D communication according to another exemplary embodiment.

In step 810, the terminal determines the transmit power. According to one side, the terminal is a distributed power control scheme (Distributed Power Control Scheme) described above, a Power Control Scheme Based on Expectation and a power control scheme based on the channel average value (Power Control Scheme Based on Averaged) Channel Value) can be used to determine the transmit power according to any one of the techniques.

For example, the terminal may determine the transmit power according to a distributed power control technique. In this case, the terminal costs the normalization cost of the interference from the base station (not shown).

Receive the received

The transmission power may be determined by substituting Equation (8).

According to another embodiment, the terminal may determine the transmission power according to the average power control scheme. In this case, the terminal uses the equations 11, 15, and 16 to optimize

And calculate

The transmission power may be determined by substituting into Equation 10. According to another embodiment, the terminal uses Equation 17

You can simply determine the approximation of.

According to another embodiment, the terminal may determine the transmit power according to a power control scheme based on the channel average value. In this case, the terminal costs the interference according to equation (19).

And calculate

By substituting into Equation 18, the transmission power may be determined. According to another embodiment, the terminal uses Equation 20

You can simply determine the approximation of.

In step 820, the terminal transmits the second data to the second terminal according to the determined transmission power. According to one side, the terminal may transmit the second data during the time that the third terminal located in the coverage of the base station transmits the first data to the base station. In this case, the interference signal is transmitted from the terminal to the base station. However, the total sum of the interference signals received by the base station remains below the threshold.

The method according to the embodiment may be embodied in the form of program instructions that can be executed by various computer means and recorded in a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the media may be those specially designed and constructed for the purposes of the embodiments, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

Although the embodiments have been described by the limited embodiments and the drawings as described above, various modifications and variations are possible to those skilled in the art from the above description. For example, the described techniques may be performed in a different order than the described method, and / or components of the described systems, structures, devices, circuits, etc. may be combined or combined in a different form than the described method, or other components. Or even if replaced or substituted by equivalents, an appropriate result can be achieved.

Therefore, other implementations, other embodiments, and equivalents to the claims are within the scope of the claims that follow.

Disclosed is a technique for determining transmission power in device-to-device (D2D). According to the disclosed transmission power scheme, the total sum of the interference signals transmitted from the terminal to the base station can be controlled to a threshold or less while maximally improving the data rate of the terminal-to-terminal communication.

Claims

A terminal located within the coverage of a base station,

The third terminal located within the coverage of the base station transmits the first power to the second terminal paired with the terminal during transmission of the first data to the base station at a transmission power determined in consideration of the first channel state from the terminal to the base station. 2 Transmitter that sends data directly

Terminal comprising a.
The method of claim 1,

A channel state estimator for estimating a second channel state from the second terminal to the terminal; And

Receiver

More,

The transmitter transmits the second channel state to the base station.

The receiving unit receives a transmission power determined from the base station in consideration of the second channel state additionally.
The method of claim 1,

A transmission power determining unit which updates and determines the transmission power according to Equation 1 below

The terminal further comprising.

[Equation 1]

here,
Is the value of the updated transmit power,
Is updated as in Equation 2 below.
Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the influence of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station,
Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 2]

here,
Updated
Is the value of,
Is a threshold of the sum of interference signals received by the base station.
Is the number of terminals transmitting interference to the base station,
Is the value of the previous transmit power.
Is any constant.
The method of claim 1,

A transmit power determiner configured to determine the transmit power according to Equation 3 below

The terminal further comprising.

[Equation 3]

here,
Is determined according to the following equation (4).
Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the effect of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station,
Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 4]

here,
Is a threshold of the sum of interference signals received by the base station.
The method of claim 1,

A transmit power determiner configured to determine the transmit power according to Equation 5 below

The terminal further comprising.

[Equation 5]

here,
Is determined according to the following equation (6).
Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the effect of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station,
Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 6]

Here, K represents the number of terminals (D2D terminal pair) which are located within the coverage of the base station and directly transmit data to each other.
The method of claim 1,

A transmit power determiner configured to determine the transmit power according to Equation 7 below

The terminal further comprising.

[Equation 7]

here,
Is determined according to the following equation (8).
Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the effect of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station,
Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 8]

here,
Is a threshold of the sum of interference signals received by the base station.
The method of claim 1,

A transmit power determiner configured to determine the transmit power according to Equation 9 below

The terminal further comprising.

[Equation 9]

here,
Is determined according to the following equation (10).
Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the effect of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station, Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 10]

Here, K represents the number of terminals (D2D terminal pair) which are located within the coverage of the base station and directly transmit data to each other.
A base station in which terminals located within coverage directly transmit data to each other,

A pilot receiver for receiving a pilot signal from a first terminal among the terminals;

A channel state estimator estimating a first channel state from the first terminal to the base station using the received pilot signal;

A channel state receiver configured to receive, from the first terminal, a second channel state from the first terminal to a second terminal included in the terminals;

A transmission power determination unit determining transmission power for the first terminal in consideration of the first channel state and the second channel state; And

Transmitter for transmitting the determined transmission power to the first terminal

Including,

The base station directly transmits the second data to the second terminal according to the transmitted power during the time that the third terminal located within the coverage of the base station transmits the first data to the base station.
The method of claim 8,

The base station for determining the transmission power according to the following equation (11) and (12).

[Equation 11]

here,
Is a threshold of the sum of interference signals received by the base station.

Transmit power
Is a set of terminals having a value of 0,
Transmit power
Has a value of
Is a set of terminals.

Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the influence of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station,
Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 12]
The method of claim 9,

And the transmission power determiner is configured to update the transmission power by repeating Equation 11 and Equation 12 until the determined transmission power satisfies Equation 13.

[Equation 13]
In the operating method of a terminal located within the coverage of the base station,

The third terminal located within the coverage of the base station transmits the first power to the second terminal paired with the terminal during transmission of the first data to the base station at a transmission power determined in consideration of the first channel state from the terminal to the base station. 2 Steps to Transfer Data Directly

Method of operation of a terminal comprising a.
The method of claim 11,

Estimating a second channel condition from the second terminal to the terminal;

The transmitting unit transmitting the second channel state to the base station; And

Receiving transmission power determined from the base station in consideration of the second channel state

Operation method of the terminal further comprising.
The method of claim 11,

Determining by updating the transmit power according to Equation 14

Operation method of the terminal further comprising.

[Equation 14]

here,
Is the value of the updated transmit power,
Is updated as in Equation 15 below.
Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the influence of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station,
Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 15]

here,
Updated
Is the value of,
Is a threshold of the sum of interference signals received by the base station.
Is the number of terminals transmitting interference to the base station,
Is the value of the previous transmit power.
Is any constant.
The method of claim 11,

Determining the transmit power according to Equation 16

Operation method of the terminal further comprising.

[Equation 16]

here,
Is determined according to the following equation (17).
Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the effect of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station,
Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 17]

here,
Is a threshold of the sum of interference signals received by the base station.
The method of claim 11,

Determining the transmit power according to Equation 18

Operation method of the terminal further comprising.

Equation 18

here,
Is determined according to the following equation (19).
Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the effect of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station,
Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 19]

Here, K represents the number of terminals (D2D terminal pair) which are located within the coverage of the base station and directly transmit data to each other.
The method of claim 11,

Determining the transmit power according to Equation 20

Operation method of the terminal further comprising.

[Equation 20]

here,
Is determined according to the following equation (21).
Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the effect of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station,
Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 21]

here,
Is a threshold of the sum of interference signals received by the base station.
The method of claim 11,

Determining the transmit power according to Equation 22

Operation method of the terminal further comprising.

[Equation 22]

here,
Is determined according to the following equation (23).
Is the first channel state,
Is the effect of the multipath fading channel of the channel from the terminal to the base station,
Is the channel gain according to the distance from the terminal to the base station.
Is a second channel state which is a channel state from the second terminal to the terminal,
Is the effect of the multipath fading channel of the channel from the terminal to the second terminal,
Is a channel gain according to the distance from the second terminal to the terminal.
Is the power of thermal noise,
Is the strength of the interference transmitted from the terminal to the base station,
Is the maximum transmit power of the terminal.
Is
It is the larger of internal value and '0'.

[Equation 23]

Here, K represents the number of terminals (D2D terminal pair) which are located within the coverage of the base station and directly transmit data to each other.
A computer-readable recording medium having recorded thereon a program for executing the method of any one of claims 11 to 17.