KR100589897B1 - Open loop power control method - Google Patents

Abstract

The present invention relates to a method for controlling open power of a mobile station in an orthogonal frequency division multiple access-time division duplexing system. According to the present invention, when there is transmission data, the mobile station allocates initial reference power of the mobile station according to a given environment and condition, and controls the reverse transmission power of the frame unit according to the forward signal characteristics of the frame unit based on the allocated power. . This enables effective high speed power control in time division duplexing systems and ensures communication reliability even in a multipath environment.

OFDMA, TDD, RSSI, CINR, Open Power Control

Description

Open Power Control Method {OPEN LOOP POWER CONTROL METHOD}

1 is a diagram illustrating an open power control method of a code division multiple access (CDMA) system.

2 illustrates a frame structure of a time division duplexing (TDD) system.

3 is a state transition diagram of a mobile station.

4 is a control flowchart for open power control of a mobile station according to an embodiment of the present invention.

5 is a view showing a power gain factor in consideration of mobility according to an embodiment of the present invention.

6 is a control flowchart for open power control of a mobile station considering mobility according to an embodiment of the present invention.

The present invention relates to an Orthogonal Frequency Division Multiplexing Access-Time Division Duplex (OFDMA-TDD) system, and more particularly, to an open transmission power control method in a mobile station of an OFDMA-TDD system. .

In general, in a frequency division duplex (FDD) scheme such as a code division multiple access (CDMA) mobile communication system, a base station signal is a temporally continuous signal as shown in FIG. 1. Therefore, in such a system, an open power control method which always measures the reception strength of a signal and sets a transmission power using Equation 1 in the transmission process of the mobile station.

However, a typical time division duplexing (TDD) system performs reverse power control in the form of a message. In addition, in the time division duplexing (TDD) system, unlike the CDMA system, as shown in FIG. 2, reception and transmission of packets that are not continuous in time occur. That is, since there is no received data at the time of transmission of the mobile station, it is impossible to accurately determine the channel characteristics at the time of transmission, and in a system requiring adaptive modulation and coding (AMC) or the like, it is generally used in a CDMA system. Open power control is not applicable. In addition, the power control scheme in the form of a message of the conventional TDD system includes a large delay time, making it difficult to adapt to changes in the real-time channel environment.

 SUMMARY OF THE INVENTION The present invention has been made in an effort to solve the above problems, and to provide an open power control method of a mobile station capable of performing reliable communication in an OFDMA-TDD system and providing optimal performance.

An open power control method according to an aspect of the present invention for achieving the technical problem is a method for controlling open power of a mobile station in an orthogonal frequency division multiple access system,

a) determining whether reference power is allocated; b) if it is determined that reference power allocation is necessary in step a), confirming whether power adjustment is performed by the base station to perform power adjustment or a channel indicating a channel state for a first time; C) assigning initial power by measuring a state factor; and c) if it is determined that reference power allocation is not necessary in step a), it is determined whether a transmission packet exists to measure the signal reception strength of the current frame, and the measured signal And transmitting the packet after setting the transmission power based on the reception strength.

In addition, the step b),

i) checking whether the power is adjusted by the base station; ii) performing power adjustment if power adjustment by the base station is necessary as a result of the check in step i); and iii) performing the power adjustment in the step i). Measuring the channel state factor and allocating initial power based on the measured channel state factor if power adjustment is not required.

C),

i) checking whether the transmission packet exists, ii) returning to the standby state before determining whether to allocate the power if the transmission packet does not exist as a result of the check in step i), and iii) the i (B) measuring the signal reception strength of the base station signal received in the current frame if the transmission packet exists and setting a power control value according to the difference between the channel state factor and the signal reception strength; and iv) And transmitting the packet after setting a value obtained by adding the power control value to the reference power as the transmission power.

A method of controlling transmit power of a mobile station in an orthogonal frequency division multiple access system according to another aspect of the present invention,

C),

i) checking whether the transmission packet exists, ii) returning to the standby state before determining whether to allocate the power if the transmission packet does not exist as a result of the check in step i), and iii) the i (B) measuring signal reception strength of the base station signal received in the current frame when the transmission packet exists, and setting a power control value in consideration of the difference between the channel state factor and the signal reception strength and the mobility factor; And iv) transmitting the packet after setting a value obtained by adding the power control value to the reference power as the transmission power.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

Hereinafter, an open power control method of a mobile station according to an embodiment of the present invention will be described in detail with reference to FIG. 3.

3 shows a state transition diagram of a mobile station when there is a transport packet in a general packet communication system.

As shown in FIG. 3, the mobile station determines the service type according to the modulation and coding scheme through negotiation with the base station periodically when there is a new transmission packet or even when the state of the channel changes rapidly. The mobile station also allocates a transmission reference power in consideration of the transmission power level of the base station and the channel conditions of the current mobile station and the base station. At this time, the transmission reference power allocation of the mobile station follows Equation 2 below.

In the above equation, the initial allocation power f1 (x) is a function of the power level of the base station, the service type and channel state factor of the mobile station as variables, and the adjusted power is the amount of power separately adjusted by the base station through ranging.

In the process of allocating the transmission reference power of the mobile station, a channel state factor such as the average received signal strength (MEAN [RSSI] _T1 ), which measures the received signal strength (RSSI) of the base station for a predetermined time (T1), is essential. This channel state factor can be easily measured at the mobile station.

In addition, when there is a channel state factor such as MEAN [RSSI] _T1 used in the initial reference power allocation and a transmission packet, the RSSI of the base station signal received in the current frame is measured and compared, and the transmission power of the mobile station is controlled accordingly. Power can be controlled at a high speed of the same period as the frame period.

4 is a flowchart illustrating a fast power control method of a mobile station according to an embodiment of the present invention.

As shown in Fig. 4, the mobile station first determines whether reference power is allocated (S401). As a result of the determination, when power allocation is required, such as periodically or when the characteristics of the channel change suddenly, it is checked whether the power adjustment by the base station is necessary (S402). In this case, when the mobile station first attempts communication or periodically needs to adjust power with the base station through a ranging process, it is determined that the power allocation is necessary.

If it is determined that power adjustment by the base station is not necessary, a channel state factor such as MEAN [RSSI] _T1 indicating an average channel state for a predetermined time T1 is measured (S403), and the transmission power level of the base station and the service of the mobile station are measured. Initial power is allocated in consideration of the type and channel state (S404). In addition, when the power adjustment by the base station is required to adjust the constant power required by the base station (reference power = initial allocation power + adjustment power) (S405). The mobile station then returns to the standby state S400.

On the other hand, if it is determined in step S401 that reference power allocation is not necessary, it is checked whether there is a transmission packet (S406), and if there is no transmission packet as a result of the check, the process returns to the standby state (S400). If there is a transmission packet, the channel state in the current frame is checked to measure the signal reception strength (RSSI) (S407), and the difference between the channel state factor and the signal reception strength of the current frame is obtained (S408). After the transmission power is set based on the difference (S409), the packet is transmitted (S410).

At this time, the transmission power is calculated by the following equation (3).

In the above equation, RSSI is the signal reception strength in the current frame, and MEAN [RSSI] _T1 is a channel state factor indicating an average channel state during T1 time.

On the other hand, when the mobility is strong, there may be a large difference in the forward transmission section and the reverse transmission section in one frame according to the multipath fading, and when the channel change is severe, an error due to power control may be intensified.

In this case, MEAN [RSSI] _T1 , which is a channel state factor, and STD [RSSI] _T2 , which is a mobility factor representing the standard deviation of the channel state during a short period (T2) indicating mobility, in the process of allocating a channel. _T2, etc. should be measured to determine the channel status according to the mobility of the mobile station. Such channel characteristic factors can be easily measured in the RF section and the modem section of the mobile station.

)를 1로 유지하며, 이동성 인자가 특정값(TH1) 이상인 경우, 즉 과도한 이동성을 가지는 경우에는 이로 인한 전력 제어 오류가 크므로 이러한 오류를 감소시키기 위하여 전력 이득 인자를 1 이하의 값(=TH1/이동성 인자)으로 설정한다.However, when the measured mobility factor is less than or equal to the specific value TH1, that is, when the mobility is inadequate, the power control error is insufficient.

) Is maintained at 1, and the power gain factor is less than 1 (= TH1) in order to reduce the error because the power control error is large when the mobility factor is greater than or equal to a certain value (TH1), that is, when the mobility factor is excessive. / Mobility factor).

At this time, the specific value TH1 is set using the function f2 (x) as shown in Equation 4.

In the above equation, the function f2 (x) is a function that uses carrier frequency and frame size of carrier, maximum allowable speed of mobile station, and allowable correlation coefficient as variables.

5 illustrates an example of a power gain factor considering mobility according to an embodiment of the present invention.

 Hereinafter, a high speed power control method of a mobile station including such a mobility factor will be described.

6 is a flowchart for performing fast power control of a mobile station including a mobility factor according to an embodiment of the present invention.

Steps S600 to S606 of FIG. 6 are the same as steps S400 to S406 of FIG. 4, and thus redundant descriptions thereof will be omitted.

Next, as a result of checking whether a transmission packet exists in step S606, if there is a transmission packet, the channel state of the current frame is determined to measure a signal reception strength (RSSI), and the mobility factor is determined using STD [RSSI] _T2 . In consideration of setting the power gain factor (S607). Then, the control power amount ΔP is calculated in consideration of the difference between the channel state factor, the signal reception intensity of the current frame, and the power gain factor (S608). Then, the transmission power is set according to the allocated reference power and the control power amount ΔP (S609), and then the packet is transmitted (S610).

In general, T1>T2> T _FRAME , and the transmission power can be expressed by Equation 5 below.

이다.In the above expression

to be.

P2)을 증가시키거나 감소시킴으로써 이동국의 송신 전력을 제어할 수 있다. 이와 같이 하면 간단하면서도 프레임 주기와 동일한 주기의 고속 전력 제어가 가능하다. As another method, when there is a transmission packet with MEAN [RSSI] _T1 , which is a channel state factor used in initial power allocation, it measures and compares the strength of the base station signal (RSSI) received in the current frame. According to the sign of the comparison value,

By increasing or decreasing P2), the transmission power of the mobile station can be controlled. In this way, high-speed power control in the same period as the frame period is simple.

In another method, the transmission power of the mobile station is controlled in accordance with the sign of the comparison value as shown in Equation (7).

)을

로 설정하고, 채널상태인자 RSSI가 MEAN[RSSI]_T1 보다 작은 경우에는 오차의 범위가 크므로 이득(

)을

로 설정한다. 이와 같이 하면 프레임 주기와 동일한 주기의 고속의 정밀한 오류를 감소시킬 수 있다. 일반적으로

이다.That is, if the channel state factor RSSI of the current frame is larger than MEAN [RSSI] _T1 , the gain range is small.

)of

If the channel condition factor RSSI is smaller than MEAN [RSSI] _T1 , the error range is large.

)of

Set to. In this way, high-speed precise errors of the same period as the frame period can be reduced. Generally

to be.

As another method, as shown in Equation 8, the transmission power of the mobile station is controlled according to the time difference between the symbol measured RSSI in the received frame and the transmitted symbol.

는 현재 프레임의 채널상태인자 RSSI를 측정한 심볼과 송신 해야할 데이터가 위치하는 심볼의 위치에 따라 설정한 이득을 나타낸다. 즉, 하나의 프레임은 다수의 DL 심볼과 다수의 UL 심볼로 구성된다. 이러한 구성에서 RSSI를 측정한 심볼과 송신 데이터가 위치하는 심볼의 시간차이는 결과적으로 두 신호의 상관관계를 나타낸다. 그러므로, 두 신호의 상관관계 따라 이득을 조절함으로써 오류 확률을 감소시킬 수 있다.In the above formula,

Represents the gain set according to the position of the symbol for measuring the channel state factor RSSI of the current frame and the symbol where the data to be transmitted is located. That is, one frame is composed of a plurality of DL symbols and a plurality of UL symbols. In this configuration, the time difference between the symbol for which the RSSI is measured and the symbol in which the transmission data is located represents a correlation between the two signals. Therefore, the error probability can be reduced by adjusting the gain according to the correlation of the two signals.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited thereto, and various other changes and modifications are possible.

As described above, according to the present invention, the initial reference power is allocated using the channel state factor, the mobility factor, the power gain factor, etc. measured by the mobile station itself, and the power of the frame unit is controlled based on the allocated power. do. In this way, effective high-speed power control is possible in an OFDMA system and communication reliability can be guaranteed even in a multipath environment.

Claims (16)

A method for controlling open power of a mobile station in an orthogonal frequency division multiple access system, a) determining whether reference power is allocated; b) if it is determined that the reference power allocation is necessary in step a), it is determined whether to adjust the power by the base station to perform power adjustment or to measure the channel state factor indicating the channel state during the first time to allocate initial power. step; And c) If it is determined in step a) that reference power allocation is not necessary, it is determined whether a transmission packet exists to measure the signal reception strength of the current frame, and the transmission power is set based on the measured signal reception strength. Sending Open power control method comprising a. The method of claim 1, B), i) checking whether the power is adjusted by the base station; ii) performing power adjustment if power adjustment by the base station is required as confirmed in step i); And iii) measuring the channel state factor and allocating initial power based on the measured channel state factor if the power adjustment by the base station is not necessary as confirmed in step i). Open power control method comprising a. The method of claim 1, C), i) checking whether the transmission packet exists; ii) returning to the standby state before determining whether to allocate the power if the transmission packet does not exist as a result of checking in step i); iii) If the transmission packet is present as a result of the step i), the signal reception strength of the base station signal received in the current frame is measured, and the power control value is set according to the difference between the channel state factor and the signal reception strength. step; And iv) transmitting the packet after setting the transmission power by adding the power control value to the reference power; Open power control method comprising a. The method of claim 1, In step a), Determining that the power allocation is necessary when the mobile station first attempts communication or needs to adjust power with the base station through a ranging process periodically Open power control method. The method according to claim 1 or 2, In step b), The reference power is variable according to the power level of the base station, the service type of the mobile station and the channel state factor. Open power control method. The method of claim 1, C), i) checking whether the transmission packet exists; ii) returning to the standby state before determining whether to allocate the power if the transmission packet does not exist as a result of checking in step i); iii) If the transmission packet is present as a result of checking in step i), the signal reception strength of the base station signal received in the current frame is measured, and the power control value considering the difference value and the mobility factor between the channel state factor and the signal reception strength. Setting up; And iv) transmitting the packet after setting the reference power plus the power control value as a transmission power; Open power control method comprising a. The method of claim 6, In step c), The mobility factor includes a factor representing a standard deviation of the channel state during the second time which is a short time indicating the mobility and a factor representing an average value of the channel state during the second time. Open power control method. The method of claim 7, wherein The second time is longer than the frame period and is shorter than the first time. Open power control method. The method of claim 6, In step iii), If the mobility factor is less than or equal to the reference value, the power gain factor is set to 1, and if the mobility factor is greater than or equal to the reference value, the power gain factor is set to a value less than or equal to 1 to reduce power control error due to high mobility. The value obtained by multiplying the difference value by the power gain factor is set to the power control value. Open power control method. The method of claim 9, The reference value is set in consideration of the size of the frame, the carrier frequency and the maximum allowable speed of the mobile station. Open power control method. The method of claim 1, C), i) checking whether the transmission packet exists; ii) returning to the standby state before determining whether to allocate the power if the transmission packet does not exist as a result of checking in step i); iii) If the transmission packet is present as a result of checking in step i), the signal reception strength of the base station signal received in the current frame is measured, and the power is based on a preset power amount according to the difference between the channel state factor and the signal reception strength. Setting a control value; And iv) transmitting the packet after setting the reference power plus the power control value as a transmission power; Open power control method comprising a. The method of claim 11, In step iii), When the difference value is less than 0, a value obtained by multiplying a preset power value by -1 is set as the power control value. When the difference value is 0 or more, the preset power value is set as the power control value. Open power control method. The method of claim 1, C), i) checking whether the transmission packet exists; ii) returning to the standby state before determining whether to allocate the power if the transmission packet does not exist as a result of checking in step i); iii) In step i), if the transmission packet is present, the signal reception strength of the base station signal received in the current frame is measured, and the difference between the channel state factor and the signal reception strength is multiplied by a predetermined gain. Setting to a control value; And iv) transmitting the packet after setting the reference power plus the power control value as a transmission power; Open power control method comprising a. The method of claim 11, In step iii), If the difference value is less than zero, the difference value is multiplied by the first gain value, and the power control value is set. If the difference value is 0 or more, the difference value is greater than the second gain value greater than the first gain value. To set the multiplied value to the power control value Open power control method. The method of claim 6, In step iii), The power gain factor is set to 1 when the mobility factor is less than or equal to the reference value, and the value obtained by dividing the reference value by the mobility factor is set to the power gain factor when the mobility factor is greater than or equal to the reference value. The difference value is multiplied by the power gain factor and a third gain, wherein the third gain is a gain set according to a symbol measuring a channel state factor of a current frame and a symbol position where data to be transmitted is located. Set to the power control value Open power control method. The method of claim 1, The channel state factor is an average value of the received signal strength of the base station signal during the first time. Open power control method.

Images