KR100924964B1 - Apparatus and Method for Controlling of Uplink Power in Wireless Communication System - Google Patents

Abstract

Disclosed are an uplink power control apparatus and method using an open loop power control (OLPC) scheme in a wireless communication system. An example of an uplink power control method for this purpose includes determining a first base station offset for compensating a packet error rate (PER) for at least one uplink burst and applying the uplink burst. For a repetition of a specific MCS level, determining a second base station offset to compensate for arithmetic errors occurring in calculating a transmit power level per subcarrier, and using link adaptation using the first and second base station offsets. Determining a third base station offset for the mobile station and constructing an uplink map including a power control IE configured based on the first to third base station offsets and transmitting the uplink map to the subscriber station. Uplink channel environment can be maintained.

Description

Apparatus and Method for Controlling of Uplink Power in Wireless Communication System}

The present invention relates to uplink power control in a wireless communication system, and more particularly, to an apparatus and method for controlling uplink power using an open loop power control (OLPC) scheme in a wireless communication system.

In the wireless communication system, the resource is a frequency band, and a methodology for efficiently allocating and using a finite frequency band among users is multiple access, and connecting uplink and downlink in bidirectional communication. The concatenation methodology for classifying is multiplexing. Wireless multiple access and multiplexing is a platform technology that is the most basic technology of wireless transmission technology for efficiently using limited frequency resources, and is determined according to allocated frequency band, number of users, transmission rate, mobility, cell structure, and wireless environment.

Orthogonal Frequency Division Multiplexing (OFDM), which is one of the wireless transmission schemes, is a type of multi-carrier transmission / modulation (MCM) scheme using multiple carriers and parallelizes input data by the number of carriers used. The data is transmitted on each carrier. It can be divided into OFDM-FDMA, OFDM-TDMA, and OFDM-CDMA according to a user's multiple access scheme.

Among them, OFDM-FDMA (OFDMA) is suitable for 4G macro / micro cellular infrastructure, has no intra-cell interference, high frequency reuse efficiency, and excellent adaptive modulation. In addition, in order to make up for the shortcomings of OFDMA, distributed frequency hopping, multiple antenna techniques, and powerful coding techniques can be used to increase diversity and reduce the effects of inter-cell interference. In particular, the OFDMA scheme is suitable for a large number of subcarriers, and thus is effectively applied to a wireless communication system having a large area cell with a large time delay spread.

On the other hand, in general, adaptive modulation and coding (AMC) in a wireless communication system means changing a transmission rate to a wireless channel environment in order to more efficiently and adaptively use a poor radio link, and in an OFDMA-based wireless communication system, It is designed to select an appropriate Modulation and Coding Scheme (MCS) level to meet a Target Packet Error Rate (PER) at a particular link quality. The AMC subchannel is composed of bands by physically contiguous subcarriers for the selected MCS level subcarriers. This AMC subchannel is used to maximize bandwidth efficiency by selectively allocating only bands having good channel conditions. do.

The AMC structure effectively increases channel efficiency compared to fixed modulation and coding, and is a particularly useful method in a slowly changing channel environment. However, in a rapidly changing channel environment, the MCS level chosen by the AMC structure will produce more errors than the target PER. For example, as the fast channel environment changes, the carrier to interference and noise ratio (CINR) changes rapidly, thereby increasing the PER. However, since the CINR is fixed at the MCS level, if the transmit power is increased to compensate for the target PER in accordance with the above-mentioned PER increase, this increase in power does not apply in the direction of decreasing the PER, but causes a change in the MCS level. As a result, the PER was further increased. Therefore, a power control scheme that can maintain a stable channel state without affecting the MCS level at the MCS level selected by the AMC structure is very important.

Therefore, there is a need for an appropriate algorithm for performing uplink power control to maintain a constant CINR at a selected MCS level for stabilization of uplink power.

The present invention was devised to meet the above requirements, and an object of the present invention is to control uplink power to maintain a constant CINR for an MCS level allocated to an uplink burst in an OFDMA-based wireless communication system. To provide a method and apparatus.

For this purpose, a method of controlling uplink power in an OFDMA-based wireless communication system of one embodiment of the present invention includes (a) compensating a packet error rate (PER) for at least one uplink burst; Determining a first base station offset to perform; (b) for a repetition of a specific MCS level applied to the uplink burst, determining a second base station offset to compensate for arithmetic errors occurring in calculating a transmit power level per subcarrier; (c) determining a third base station offset for link adaptation using the first and second base station offsets; And (d) constructing an uplink map including base station offsets configured based on the first to third base station offsets and transmitting the uplink map to the subscriber station.

In addition, a method of controlling uplink power in an OFDMA-based wireless communication system according to another aspect of the present invention includes (a) a method for compensating a packet error rate (PER) for at least one uplink burst; Determining a base station offset; (b) determining a maximum available packet size for the uplink burst, a third base station offset for link adaptation, and an MCS level in view of the first base station offset; And (c) a subscriber station by configuring an uplink map including a base station offset calculated based on the first base station offset and the third base station offset, the number of subchannels corresponding to the maximum available packet size, and the MCS level. Characterized in that it comprises the step of transmitting to.

Meanwhile, a method of controlling uplink power in an OFDMA-based wireless communication system according to one embodiment of the present invention includes: (a) decoding uplink map information of a received frame; (b) measuring a path loss value L using the preamble of the frame and determining an offset specific to the subscriber station; And (c) determining transmission power using the uplink map information and the path loss value.

On the other hand, the apparatus for controlling uplink power in an OFDMA-based wireless communication system of one embodiment of the present invention includes: a packet scheduler for determining a packet size allocated to at least one uplink burst; A base station offset calculator configured to determine a base station offset for the uplink burst; A burst scheduler for selecting the number of subchannels and the MCS level corresponding to the packet size determined by the packet scheduler; And a map constructing unit constituting an uplink map including the base station offset, the determined number of subchannels, and the MCS level.

According to the present invention, the base station delivers the number of sub-channels, MCS level, and base station-specific offset corresponding to the maximum available packet size for the uplink burst for the limited subscriber station power so that the subscriber station is selected by the base station. By controlling the uplink power to maintain the target CINR for the MCS level, there is an effect that can maintain a stable uplink channel environment.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments. For reference, in the following description, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention are omitted.

In IEEE 802.16d / e, OFDMA-based uplink power control is defined in two modes. One is Closed Loop Power Control (CLPC) mode, and the other is Open Loop Power Control (OLPC) mode.

In the CLPC mode, the base station determines the power level to be used by the subscriber station with reference to the power level (ie, CINR) sent by the subscriber station to the base station and sends power control information directly to the subscriber station. This CLPC mode is advantageous in a slowly changing channel environment, but since power control information for one subscriber station is distributed and transmitted in several frames, it is difficult to control power as desired due to feedback loss in a fast changing channel environment.

Meanwhile, in the OLPC mode according to the present invention, if the base station sets power control information necessary for initial power control, the subscriber station performs power control in the remaining frames. That is, the base station does not directly inform the subscriber station of the CINR, but when the base station checks the information on the signal strength and the received CINR transmitted from the terminal and transmits the information to the user equipment, the terminal considers the burst size and the like and transmit power based on this. To control.

)과, 기지국에 의해 제어되는 기지국 특유의 전력 오프셋(

)을 보상한다.Specifically, Equation 1 below is an equation for OLPC and represents a power level to be transmitted in the next frame. That is, the power level estimates the forward path loss L and compensates for it, and if there is noise and interference NI, power compensation (power increase) corresponding to this value is performed. In addition, power compensation (power increase) is made to satisfy the signal-to-noise ratio (C / N) to provide the MCS level currently required. In addition, if repetition (R) is used, the transmit power is determined so as to compensate for lowering the power corresponding to the set number of repetitions. And, the power offset specific to the terminal controlled by the terminal (

) And a power offset specific to the base station controlled by the base station (

) To compensate.

[Equation 1]

는 가입자 단말에 의해 조절되는 가입자 단말 특유의 전력 오프셋을,

은 기지국에 의해 조절되는 기지국 특유의 전력 오프셋을 나타낸다. Where P is the transmit power level in dBm per subcarrier, L is the currently estimated uplink path loss, C / N is the normalized C / N corresponding to the current MCS level, NI is dBm per subcarrier Average power level estimate of noise and interference in units,

Is a power offset unique to the subscriber station controlled by the subscriber station,

Denotes a power offset peculiar to the base station controlled by the base station.

Hereinafter, uplink power control of such an OLPC structure will be described in more detail.

1 is a diagram illustrating a method of controlling uplink power of an OLPC structure according to the present invention.

Referring to FIG. 1, a base station configures a normalized C / N table, measures noise and interference amount, determines a base station specific offset (hereinafter, referred to as a base station offset), and acquires uplink power control parameters including a base station offset. When transmitting to the terminal (S100-S400), the transmission power level in dBm per subcarrier based on the measured value of the subscriber station measuring the path loss value, the subscriber terminal specific offset (hereinafter referred to as subscriber terminal offset) and the uplink parameters. Determine (S500-S700). In addition, the subscriber station determines whether the determined transmission power level satisfies a specific condition and transmits an uplink burst to the base station at the determined transmission power level (S800-S900). Thereafter, the base station tracks the transmission power of each subscriber station so that the subscriber station updates the transmission power level every frame or every predetermined frame (S1000).

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

First, in step S100, the base station configures a normalized C / N table. That is, the base station configures a normalized first C / N table based on the Forward Error Correction (FEC) block error rate (BLER) for the measured CINR. The subscriber station controls the uplink power based on this table. Hereinafter, this will be referred to as a C / N threshold table for power control. Further, the base station averages the measured CINRs for a predetermined frame period, and then constructs a normalized C / N table based on the packet error rate (PER) for this average CINR. The base station determines the MCS level for the uplink burst using the normalized second C / N table. Hereinafter, this will be called a C / N threshold table for AMC.

As described above, the C / N threshold table for power control configured based on the FEC block error rate for the measured CINR includes target CINR values for various MCS levels, and the C / N table for power control thus created is UCD ( Uplink Channel Descript) message is transmitted to the subscriber station, it may be modified for each frame. Meanwhile, the C / N threshold table for AMC is prepared based on the probability of packet error in the corresponding CINR by averaging the measured CINR.

The subscriber station controls the transmission power level as follows with reference to the C / N threshold table for power control. That is, since the purpose of uplink power control is to maintain the channel state at any MCS level, the CINR threshold for power control is set between the CINR threshold of the target MCS level and the CINR threshold of the higher MCS level. For better link quality, the CINR threshold for the power control may be higher than the CINR threshold for AMC. This means that a link with power control has a lower PER than a link without power control at the same MCS level. However, if the CINR threshold for power control is too high, the MCS level selection is not uniform, and a problem may occur that causes a higher MCS level to be selected. Accordingly, the base station configures the C / N threshold table for power control based on the median of the C / N threshold table for the AMC, and transmits the configured table to the subscriber station. In step S700 described later, the subscriber station controls the uplink power to have a median value between two CINR thresholds based on the C / N threshold table for power control.

In step S200, the base station estimates an interference and noise power (NI) value applied to each subscriber station based on the signals received from each subscriber station. The NI value may be estimated by using a data burst or a method of estimating using a preamble. For example, differences between adjacent subcarriers may be obtained from signals received from each subscriber station, and the difference may be averaged to estimate an NI value. The estimated NI value is transmitted to the subscriber station through a "Noise and Interference IE" or UCD (Uplink Channel Descript) message.

In step S300, the base station determines the base station offset. In IEEE 802.16d / e, this offset value can be modified using a PMC_RSP (Power Control Mode Change Response) message, RNG_RSP (Ranging Response) message, FPC (Fast Power Control) message, `` Power Control IE '', `` UL MAP Fast ''. Tracking IE ”can be adjusted using only the specifics of this offset. In the present invention, this offset is used for three purposes: packet error rate (PER) compensation, repetition of bursts, and link adaptation. In this process, the maximum available packet size and MCS level for at least one uplink burst are determined. This will be described later.

In step S400, the uplink power control parameter configured as described above is transmitted to the subscriber terminal. To this end, the base station configures a frame for transmitting the uplink power control parameter, the downlink map of the frame includes the UCD information recorded the C / N threshold table for the power control, the uplink map "Power Control IE" configured based on the NI value and the determined base station offset is included, and includes uplink burst allocation information in which the number of subchannels and the MCS level for the at least one uplink burst determined in step S300 are recorded.

In step S500 to step S700, after the subscriber station measures the path loss value L through the preamble (S500), determines the subscriber station offset (S600), the uplink power control parameter, the path loss value, and the subscriber described above. The transmission power is determined based on the terminal offset (S700).

In step S800, the subscriber station determines whether the condition for transmission power transmission is satisfied. That is, as described above, in order to design the uplink power control algorithm according to the present invention, the base station must know the power margin value (ie, headroom) of each subscriber station. The base station may know the power margin value due to the transmission power through the maximum transmission power in the SBC-REQ message, through the bandwidth request and the UL Tx Power Report header. However, the bandwidth request and UL Tx Power Report header are not transmitted every frame. In IEEE 802.16d / e, two conditions such as Equation 2 and Equation 3 below are presented in order for a subscriber station to transmit a transmission power (P in Equation 1).

[Equation 2]

, 또는

, or

[Equation 3]

을 만족해야 한다.

Must be satisfied.

이고, here,

ego,

이다. 또한,

는 가입자 단말의 마지막 송신 전력 보고가 보내질 때의 시간 인덱스를 나타내고, 단위는 프레임이다. Tx_Power_Report_Threshold, Tx_Power_Report_Interval, 및

는 UCD에서 지정된다.

to be. Also,

Denotes a time index when the last transmission power report of the subscriber station is sent, and the unit is a frame. Tx_Power_Report_Threshold, Tx_Power_Report_Interval, and

Is specified in UCD.

In step S900, the subscriber station transmits an uplink burst to which the transmission power determined as described above is allocated to the base station.

In step S1000, the base station tracks to update the transmission power of the subscriber station every frame. For this tracking, the IEEE 802.16d / e starts OLPC after receiving the transmit power report from the base station and resets the transmit power of the subscriber station when a new transmit power is received. In addition, it is specified to update the transmit power of the subscriber station when the offset is changed, the MCS level is changed, or the NI is changed. However, since it is inefficient for the base station to transmit "Power Control IE" containing these parameters every frame, it is proposed to transmit "Power Control IE" only when the following condition (4) is satisfied.

[Equation 4]

는 n번째 프레임에서 기지국 오프셋을,

은 「Power Control IE」가 전송되어야 하거나 그렇지 않을 경우를 결정하기 위한 오프셋 임계치를 나타낸다. 만일, 수학식 4와 같은 조건에 위배되면, 현재 프레임에서의 기지국 오프셋이 이전 프레임에서의 기지국 오프셋이 동일하며, 「Power Control IE」가 전송되지 않을 것이다.here,

Is the base station offset in the nth frame,

Denotes an offset threshold for determining if a "Power Control IE" should be transmitted or not. If the condition of Equation 4 is violated, the base station offset in the current frame is the same as the base station offset in the previous frame, and the "Power Control IE" will not be transmitted.

Meanwhile, in step 300, a base station offset used for three purposes of PER compensation, repetition of bursts, and link adaptation will be described in more detail with reference to the accompanying drawings.

2 is a flowchart illustrating a method of determining a base station offset according to an embodiment of the present invention.

Referring to FIG. 2, the method of determining the offset may include determining a first base station offset for PER compensation (S310), determining a second base station offset for burst repetition (S320), and a third for link adaptation. After determining the base station offset (S330), the final base station offset is determined using the first to third base station offsets (S340). In this case, when the determined MCS level does not include a repetition term, step S320 may be omitted and step S340 may determine a final base station offset using the first and third base station offsets. Hereinafter, the above-described process will be described in more detail.

First, in step S310, a first base station offset for PER compensation is determined. This first base station offset is to solve the problem of increasing the PER in response to a sudden change in the instant CINR (CINR).

3 is a diagram illustrating MCS levels and CINRs in a fading channel. As shown in FIG. 3, the MCS level is selected based on the average CINR in the AMC. Do not. In FIG. 3, when the state of some instantaneous CINRs changes drastically, and the PER increases according to the change to increase the power to compensate for this PER increase, a problem may occur in the AMC in which the MCS level itself changes. . Therefore, the embodiment according to the present invention proposes a power control structure for solving this problem. That is, when the PER in FIG. 3 exceeds a preset threshold, power control is performed to increase the uplink signal strength, but the subscriber station has a predetermined amount of power (that is, the first base station offset) as shown in Equation 5 below. To increase.

[Equation 5]

Where n is the frame number, PER (i) is the average PER up to the current state, Threshod _HighPER is the PER threshold for power demand rise, Threshod _LowPER is the PER threshold for power reduction, and P _increment is high PER. P _decrement represents power reduction for high PER, and P _decrement represents power reduction for low PER.

According to Equation 5, in condition 1, if the difference between the average PER for the current frame and the average PER for the previous frame is equal to or greater than Threshod _HighPER (PER threshold for power demand increase), the first base station offset is Set to increase by P _increment more than the first base station offset of the frame. In condition 2, if the difference between the average PER for the current frame and the average PER for the previous frame is less than or equal to Threshod _LowPER , the first base station offset is P _decrement greater than the first base station offset of the previous frame. Set it to decrease further. In condition 3, in other cases, the first base station offset is set equal to the first base station offset of the previous frame.

In step S320, the burst repetition is not described in the C / N threshold table for power control transmitted to the subscriber station through the aforementioned UCD, and the result of the repetition term calculated through Equation 1 is C for AMC. Since a difference occurs with a result calculated through the / N threshold table, a second base station offset is determined to compensate for the difference.

Specifically, in Equation 1, the 10log ₁₀ R term is used to calculate the uplink transmit power when the MCS level with repetition (eg, QPSK 1/2 repetition 6) is selected. This term is appropriate in the case of the CINR threshold for power control described above, which meets the target block error rate (BLER). However, since the CINR threshold for AMC uses BLER on average over a rather long period, the repetition causes a problem that the required CINR decreases smaller than the 10log ₁₀ R term of Equation 1. The second base station offset is used to compensate for this gap.

For example, in an OFDMA-based wireless communication system, the repetitive MCS level corresponds to QPSK 1/2, and subtracting 10log ₁₀ R from the CINR threshold for power control of QPSK 1/2 yields an operation value for that R. The difference between the CINR threshold for power control of the MCS level including R and the derived calculation value corresponds to the second base station offset for each repetition term. A method of calculating the second base station offset will be described with reference to Table 1 below.

TABLE 1

In Table 1 above, an example of CINR thresholds for AMC and CINR thresholds for power control is shown for each MCS level, and as described above, each of the CINR thresholds for power control is a value of each MCS level of CINR thresholds for AMC. It is the median. In this case, the MCS level including the repetition term and requiring compensation is QPSK 1/2 repetition 6, QPSK 1/2 repetition 4, and QPSK 1/2 repetition 2. Among the parameters of Equation 1, the terms related to the MCS level are two terms of the C / N term and the 10log ₁₀ R term, which are [9.75-10log ₁₀ 6, 9.75-10log ₁₀ 4, 9.75-10log ₁₀ 2 ] = [1.97, 3.73, 6.74]. Therefore, the second base station offset is determined as [0.53, 0.62, -0.4].

In step S330, a third base station offset for link adaptation is determined. At this time, the current transmission power of each subscriber station is reported to the base station, and the base station can calculate a power headroom using this current transmission power.

The base station determines the MCS level to achieve the maximum available packet size, the third base station offset and the 1% FEC block error rate to transmit to each subscriber station through uplink power control for this link adaptation. In this case, in order to optimally use the limited power of the subscriber station, a reference table such as Table 2, which is made up of the expected CINR, the expected MCS level, the expected packet size, and the third base station offset per subcarrier, is configured for each subchannel number. do. That is, unlike the base station, each subscriber station uses limited power due to its mobility, and therefore, the strength of the uplink signal transmitted by each subscriber station is limited by the maximum value of the number of subchannels allocated to each symbol period. . For example, assuming that the UE transmits an uplink burst using the maximum power available during the unit symbol period, the power spectral density (PSD) is 2 than when using one subchannel in the same symbol period. This is because it becomes weaker when using 2 subchannels. Accordingly, the base station determines the MCS level through this reference table, but determines the third base station offset such that the PER remains constant and has the maximum available packet size no matter which MCS level is selected.

The base station configures a table as shown in Table 2 below, and repeats the steps S332 to S334 described later by the maximum number of available subchannels (for example, 35 in Table 2) to form a table as described below.

TABLE 2

Table 2 consists of the expected CINR per subcarrier, the expected MCS level, the expected packet size, and the third base station offset for each subchannel, and is used to determine the number of subchannels and the MCS level for the maximum available packet size.

4 is a flowchart for determining a third base station offset for link adaptation according to an embodiment of the present invention.

Referring to FIG. 4, first, a headroom of each subscriber station is determined (S331), an expected CINR per subcarrier for each subchannel number is determined (S332), and an expected MCS level and the corresponding A third base station offset for the expected MCS level is determined (S333). Subsequently, the expected packet size is determined at the determined expected MCS level (S334).

Thereafter, steps S331 to S334 are repeated as many as the number of available subchannels (S335), and the number of subchannels having the maximum available packet size is selected based on the configured table 2 (S336). The corresponding expected MCS level and the third base station offset are determined with reference to Table 2 above (S337). Hereinafter, the above-described process will be described in more detail.

In step S331, a power margin of each subscriber station is determined. The base station determines the power margin for each subscriber station using the maximum transmission power, the current transmission power, and the preset first or second base station offset. This may be expressed as in Equation 6 below.

[Equation 6]

Where P _{max , QPSK} is the maximum transmit power for QPSK, P _tx is the current transmit power, N _offset is the number of preset base station offsets, and BS_offset [i] is the i-th power control algorithm (e.g., N _subcarrier indicates the number of subcarriers applied in the previous uplink burst.

×4 = 12.65이다. 전력 여유값은 하나의 서브캐리어에 대한 CINR을 구할 수 있으며, 그 값은

×4 +

= 15.81이다. 다음으로, 3개의 서브채널(12개의 서브캐리어)에 대한 CINR이 서브 캐리어당 15.81/12 = 1.32 이고, [dB] 스케일로 1.2dB를 가질 것이다. In step S332, when the available power margin value is applied, the expected CINR per subcarrier for the number of individual subchannels is determined. In this case, the sum of the power calculated in Equation 1 and the available power margin is referred to as available power. For example, assume that the power margin determined in step S331 is 5 dB, the reported CINR is 5 dB, the number of subcarriers for the transmission power message is four, and the number of subchannels allocated is three. First reported CINR will be concentrated on one subcarrier, and its value is equal to the current transmit power (P _tx ).

4 = 12.65. The power margin can be used to find the CINR for one subcarrier.

× 4 +

= 15.81. Next, the CINRs for the three subchannels (12 subcarriers) will be 15.81 / 12 = 1.32 per subcarrier and will have 1.2 dB on the [dB] scale.

In step S333, the MCS level is determined. In other words, an MCS level suitable for achieving a preset FEC block error rate BLER is determined based on the expected CINR determined in step S332. This will be described in more detail with reference to FIG. 5.

5 is a flowchart illustrating a method of determining an MCS level according to an embodiment of the present invention.

Referring to FIG. 5, first, an MCS level is selected based on an AMC rule (S333a).

Subsequently, when the selected MCS level is allocated to the burst, the expected transmission power applied to the subscriber station is calculated (S333b). That is, the base station can estimate the transmission power using Equation 1 in which the updated NI is used. At this time, if the selected MCS level includes repetition, a second base station offset should be added. As described above, if L is constant, the expected transmission power can be estimated as shown in Equation 7 below.

[Equation 7]

는 n 번째 프레임에서 기대 송신 전력을,

는 제2 기지국 오프셋을 나타낸다. here,

Is the expected transmit power in the nth frame,

Denotes a second base station offset.

In Equation 7, the log operation may be implemented through a lookup table as shown in Table 3 below.

TABLE 3

Thereafter, it is checked whether the expected transmission power calculated in step S333b is greater than the available power calculated in step S332 (S333c). If greater, select an MCS level one step below the current MCS level and repeat steps S333b and S333c (S333d). However, if it is small, the selected MCS level is fixed (S333e).

Then, the third base station offset is calculated as shown in Equation 8 (S333f).

[Equation 8]

은 n번째 프레임에서 제3 기지국 오프셋을,

는 가용 전력과 기대 전력간의 차이값을 나타낸다. 이

는 다음 수학식 9과 같이 연산된다.here,

Is the third base station offset in the nth frame,

Represents the difference between the available power and the expected power. this

Is calculated as in Equation 9 below.

[Equation 9]

는 단계 S332에서 dB 스케일로 연산된 가용 전력을 나타낸다.here,

Denotes the available power calculated on the dB scale in step S332.

Meanwhile, in step S334 of FIG. 4, the expected packet size is determined based on the number of subchannels and the expected MCS level. Thereafter, in step S335, the above-described steps S331 to S334 are repeated to configure a table as shown in Table 2 above.

Then, in step S336, the number of subchannels having the maximum available packet size is determined with reference to the configured table of Table 2, and in step S337, the expected MCS level and the third base station offset according to the determined number of subchannels are determined. do.

In operation S340 of FIG. 2, the first base station offset is added to calculate the final base station offset. In this case, the second base station offset is omitted when the MCS level does not apply repetition. In addition, if the last base station offset is different from the previous base station offset, "Power Control IE" for power control is configured and transmitted to the subscriber station in the next frame.

Hereinafter, a configuration of a base station for uplink power control of the OLPC structure described above will be described. Since detailed operation principles for each component are described in detail in the method for determining the base station offset of FIGS. 1 to 5 described above, redundant descriptions thereof will be omitted.

6 is a diagram illustrating a configuration of a base station supporting OFDMA according to an embodiment of the present invention.

As shown in FIG. 6, the base station includes an interface 100, a band signal processing module 200, a transmission module 300, a reception module 600, a scheduler 500, and an antenna 400. Include. The base station supports TDD and may be divided into a reception path and a transmission path.

In the reception path, the reception module 600 receives one or more radio signals transmitted by the terminals through the antenna 400 and converts the signal into a baseband signal. For example, the reception module 600 removes and amplifies noise from the above-described signal for data reception of the base station, down-converts the amplified signal to a baseband signal, and digitizes the down-converted baseband signal. The band signal processing module 200 extracts information or data bits from the digitized signal to perform demodulation, decoding, and error correction processes. The received information is transmitted to the adjacent wired / wireless network via the interface 100, or is transmitted to other terminals serviced by the base station through the transmission path again.

In the transmission path, the interface 100 receives voice, data, or control information from a control station or a wireless network, and the band signal processing module 200 encodes voice, data, or control information, and then transmits the transmission module 300. Will output The transmission module 300 modulates the encoded voice, data, or control information into a carrier signal having a desired transmission frequency or frequencies, amplifies the modulated carrier signal to a level suitable for transmission, and propagates to the air through the antenna 400. do.

On the other hand, the scheduler 500 controls the operation of the reception path and the transmission path and each component. In particular, in accordance with the present invention, the scheduler 500 configures a frame to be transmitted to each subscriber station in the transmission path, maps the corresponding burst, and then calculates parameters for uplink power control for each burst for the uplink burst. The parameters are included in the downlink map and transmitted to the subscriber station. The scheduler will be described in more detail with reference to the accompanying drawings.

7 is a diagram illustrating a configuration of a scheduler according to an embodiment of the present invention, and calculates parameters for uplink power control for each burst for an uplink burst, and includes the parameters in a downlink map to a subscriber station. Is to be sent to.

As shown in FIG. 7, the scheduler 500 includes a packet scheduler 510, a burst scheduler 520, a base station offset calculator 530, and a map constructer 540.

The packet scheduler 510 determines the packet size allocated to the uplink burst based on the QoS information. In addition, the base station offset calculator 530 configures Table 2 as described above, and transfers the table 2 and the final base station offset to the burst scheduler 520 and the map component 540.

The burst scheduler 520 allocates the burst to the packet size required by the packet scheduler 510 using various packet scheduling algorithms based on the burst allocation information and Table 2 above. In this case, the burst scheduler 520 determines the number of subchannels and the MCS level suitable for the required packet size of the packet scheduler 510 with reference to Table 2 above.

The map configuration unit 540 identifies the final base station offset corresponding to the number of subchannels with reference to Table 2 based on the number of subchannels determined by the burst scheduler 520. In addition, the map configuration unit 540 configures a downlink map for the UCD message in which the C / N threshold table for the MCS level is recorded. In addition, the map configuration unit 540 configures an uplink map including "Power Control IE" configured based on the NI information and the last base station offset and uplink burst allocation information in which the determined number of subchannels and the MCS level are recorded. do.

Hereinafter, the base station offset calculator of FIG. 7 will be described in more detail with reference to FIG. 8.

8 is a diagram illustrating a base station offset calculator according to an embodiment of the present invention. As shown in FIG. 8, the base station offset calculator 530 includes a PER compensation module 531 and an iterative check module 532. And a link adaptation module 533 and an addition module 534. Here, the PER compensation module 531 and the repeat checking module 532 are independent of the base station offset, and the link adaptation module 534 is dependent on the PER compensation module 531 and / or the repeat checking module 532. . In addition, all offsets are reset each time the OLPC operates.

The PER compensation module 531 outputs a first base station offset for compensating a PER increased according to an instantaneous CINR sudden change. For example, if the difference between the average PER for the current frame and the average PER for the previous frame is greater than or equal to Threshod _HighPER , the first base station offset is increased by P _increment more than the first base station offset of the previous frame. If the difference between the average PER for the current frame and the average PER for the previous frame is less than or equal to Threshod _LowPER , the first base station offset is P _decrement greater than the first base station offset of the previous frame. The first base station offset is set equal to the first base station offset of the previous frame.

To this end, the PER compensation module 531 includes an average PER comparator 531a and a first base station offset controller 532b.

The average PER comparator 531a compares the difference between the average PER for the current frame and the average PER for the previous frame, and compares the _{Threshod HighPER} (PER threshold for power demand rise), or compares the average PER for the current frame to the previous frame. Compare the difference between the average PERs for the two and the Threshod _LowPER .

The first base station offset controller 531b reduces the first base station offset by P _decrement (power reduction for low PER) or P _increment only (power for high PER) according to the comparison result. Increments).

The repetition check module 532 does not describe burst repetition in the C / N threshold table for power control transmitted to the subscriber station through UCD, and the result of the repetition term calculated through Equation 1 is determined for AMC. Since a difference occurs with a result calculated through the C / N threshold table, a second base station offset is determined to compensate for the difference. For example, the iteration checking module 532 assigns the CINR threshold for power control of this QPSK 1/2 and 10log ₁₀ R to Equation 1 for the MCS level with repetition, that is, QPSK 1/2, and the threshold for that R. Derived by calculating the difference between the CINR threshold for power control of QPSK 1/2 including R and the derived threshold value and outputs a second base station offset. At this time, wherein associated with the MCS level from the equation (1) C / N because 10log and wherein R _10, wherein R is a threshold for the difference between the CINR threshold and 10log ₁₀ R for power control.

The link adaptation module 533 may include the expected CINR, the expected MCS level, the expected packet size, and the third base station offset for each subchannel in order to optimally use the limited power of the subscriber station. The same reference table is configured to output the MCS level and the third base station offset value according to the requested packet size or the maximum available packet size based on the QoS information. This will be described in more detail with reference to FIG. 9.

9 is a diagram illustrating a configuration of the link adaptation module of FIG. 8.

9, the link adaptation module 533 includes a power margin value determiner 533a, a CINR determiner 533b, an MCS level determiner 533c, a packet size determiner 533d, and a subchannel number determiner. (533e).

The power margin determiner 533a determines the power margin for each subscriber station using the maximum transmission power, the current transmission power, and the preset first or second base station offset, which is calculated through Equation 6 above. .

The CINR determiner 533b determines the expected CINR per subcarrier for the number of subchannels when the calculated power margin value is applied. The number of subchannels depends on the subchannel allocation scheme (PUSC, FRF-1, FRF-3, etc.), and the expected CINR per subcarrier is determined for each subchannel number. Exemplary operations are described in detail in step S332 of FIG. 4 described above, and will be omitted to avoid repetition.

MCS level determiner 533c determines an MCS level suitable for achieving a preset FEC block error rate (BLER) based on the expected CINR determined in CINR determiner 533b. At this time, the MCS level determiner 533c calculates the expected transmit power applied to the subscriber station when the selected MCS level is assigned to the burst, and the calculated expected transmit power is equal to the available power calculated by the CINR determiner 533b. In comparison, if the calculated expected transmission power is larger, an MCS level one level below the current MCS level is selected, but if it is smaller, the selected MCS level is output. In addition, the MCS level determiner 533c calculates as shown in Equation 8 to output the third base station offset.

The packet size determiner 533d determines the packet size according to the number of subchannels based on the number of each subchannel in Table 2 and the determined MCS level.

Subchannel Number Determiner 533e Determines the number of subchannels having the maximum available packet size by referring to the table of Table 2 above, and determines and outputs the MCS level and the third base station offset according to the determined number of subchannels.

Meanwhile, in FIG. 8, the adding module 534 adds the first base station offset to the third base station offset and outputs the final base station offset. At this time, if there is no repetition at the selected MCS level, the final base station offset is determined only by the first base station offset and the third base station offset without the second base station offset.

By configuring the uplink power control device in the base station as described above, the number of subchannels for the uplink burst, the MCS level, and the base station-specific offset are transmitted so that the subscriber station maintains the target CINR for the MCS level selected by the base station. Uplink power can be controlled to be

Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art to which the present invention pertains can implement the present invention in other specific forms without changing the technical spirit or essential features, The examples are to be understood in all respects as illustrative and not restrictive.

In addition, the scope of the present invention is specified by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts are included in the scope of the present invention. Should be interpreted as

1 is a view for explaining the uplink power control method of the OLPC structure according to the present invention.

2 is a flowchart illustrating a method of determining a base station offset according to an embodiment of the present invention.

3 illustrates MCS levels and CINRs in a fading channel.

4 is a flowchart for determining a third base station offset for link adaptation according to an embodiment of the present invention.

5 is a flowchart illustrating a method of determining an MCS level according to an embodiment of the present invention.

6 is a diagram illustrating a configuration of a base station supporting OFDMA according to an embodiment of the present invention.

7 is a diagram illustrating a configuration of a scheduler according to an embodiment of the present invention.

8 is a block diagram illustrating a base station offset calculator according to an embodiment of the present invention.

FIG. 9 is a diagram illustrating a configuration of the link adaptation module of FIG. 8. FIG.

Explanation of symbols on the main parts of the drawings

510: packet scheduler 520: burst scheduler

530: base station offset calculator 540: map component

Claims (25)

A method of controlling uplink power in an OFDMA-based wireless communication system, (a) determining a first base station offset to compensate for a Packet Error Rate (PER) for at least one uplink burst; (b) for a repetition of a specific MCS level applied to the uplink burst, determining a second base station offset to compensate for arithmetic errors occurring in calculating a transmit power level per subcarrier; (c) determining a third base station offset for link adaptation using the first and second base station offsets; And and (d) constructing an uplink map including base station offsets configured based on the first to third base station offsets, and transmitting the uplink map to a subscriber station. The method of claim 1, wherein step (a) comprises: If the difference between the average PER for the current frame and the average PER for the previous frame is greater than or equal to the PER threshold required for power up, determining the first base station offset to increase by a predetermined power more than the first base station offset of the previous frame. Uplink power control method. The method of claim 1 or 2, wherein step (a) comprises: When the difference between the average PER for the current frame and the average PER for the previous frame is less than or equal to the PER threshold required for power reduction, determining the first base station offset to decrease the power more than the first base station offset of the previous frame by a predetermined power. Uplink power control method. The method of claim 1 or 2, wherein in step (b), And the second base station offset is determined based on the C / N threshold for power control and the C / N threshold for AMC. The method of claim 1 or 2, wherein step (c) comprises: And determining the maximum available packet size and MCS level for the uplink burst. The method of claim 5, wherein step (c) comprises: (c-1) determining expected MCS levels, the third base station offsets, and expected packet sizes, respectively, in consideration of the first and second base station offsets by the number of available subchannels for the uplink burst; And (c-2) selecting the number of subchannels having the maximum available packet size among the determined expected packet sizes, and determining an MCS level and a third base station offset corresponding to the number of subchannels. Uplink power control method. The method of claim 5, wherein the MCS level is, And determined to be suitable to achieve a preset Forward Error Correction (FEC) block error rate (BLER) based on expected Carrier to Interference and Noise Ratio (CINR) per subcarrier. The method of claim 5, wherein the MCS level is, The expected transmit power applied to the subscriber station when the expected MCS level is assigned to the burst is compared with the available power, the power of the expected transmit power level plus the power margin value, and if the expected transmit power is greater than the MCS level, The uplink power control method of claim 1, characterized in that determined by the MCS level below one level. The method of claim 5, wherein the MCS level is, When the expected MCS level is assigned to the burst, the expected transmit power applied to the subscriber station and the available power, the power plus the expected transmit power level and the power margin value, are compared. Uplink power control method characterized in that the. The method of claim 5, wherein in step (d), The uplink map further includes uplink burst allocation information in which the number of subchannels corresponding to the maximum available packet size and the determined MCS level are recorded. A method of controlling uplink power in an OFDMA-based wireless communication system, (a) determining a first base station offset to compensate for a Packet Error Rate (PER) for at least one uplink burst; (b) determining a maximum available packet size for the uplink burst, a third base station offset for link adaptation, and an MCS level in view of the first base station offset; And (c) an uplink map including a base station offset calculated based on the first base station offset and the third base station offset, the number of subchannels corresponding to the maximum available packet size, and the MCS level, to the subscriber station; Uplink power control method comprising the step of transmitting. The method of claim 11, wherein after step (a), Determining a second base station offset to compensate for an error in a transmission power level calculation per subcarrier upon repetition (R) of a specific MCS level applied to the uplink burst, And determining the third base station offset based on the first base station offset and the second base station offset. The method of claim 12, wherein the base station offset, And configuring the second base station offset further. A method of controlling uplink power in an OFDMA-based wireless communication system, (a) decoding uplink map information of a received frame; (b) measuring a path loss value L using the preamble of the frame and determining an offset specific to the subscriber station; And and (c) determining a transmission power using the uplink map information and the path loss value. The method of claim 14, wherein the uplink map information, An uplink comprising a base station offset calculated based on a first base station offset for compensating a packet error rate (PER) for at least one uplink burst and a third base station offset for link adaptation Power control method. The method of claim 15, wherein the base station offset, For the repetition of a specific MCS level applied to the uplink burst, an operation error generated in calculating a transmit power level per subcarrier is calculated based on the C / N threshold for power control and the C / N threshold for AMC. And calculating a second base station offset to compensate. The method of claim 16, wherein the uplink map information, And uplink burst allocation information including the maximum available packet size and MCS level for at least one uplink burst recorded in the uplink map of the received frame. The method according to any one of claims 14 to 17, wherein the uplink map information is And a normalized C / N value corresponding to the MCS level of the uplink burst. The method according to any one of claims 14 to 17, wherein the uplink map information is And further comprising an average power level estimate (NI) of noise and interference per subcarrier. An apparatus for controlling uplink power in an OFDMA-based wireless communication system, A packet scheduler for determining a packet size allocated to at least one uplink burst; A base station offset calculator configured to determine a base station offset for the uplink burst; A burst scheduler for selecting the number of subchannels and the MCS level corresponding to the packet size determined by the packet scheduler; And And a map constructing unit configured to construct an uplink map including the base station offset, the determined number of subchannels, and the MCS level. The method of claim 20, wherein the base station offset calculation unit, A PER compensation module for determining a first base station offset for compensating for a packet error rate (PER) for at least one uplink burst; A repetition acknowledgment module for determining a second base station offset to compensate for an error in a transmission power level calculation per subcarrier upon repetition of a specific MCS level applied to the uplink burst; And And a link adaptation module for determining a third base station offset for link adaptation using the first and second base station offsets. The method of claim 21, wherein the PER compensation module, Compare the difference between the average PER for the current frame and the average PER for the previous frame with a PER threshold for power up or a PER threshold for power reduction, and adjust the first base station offset to increase or decrease by a predetermined power according to the comparison result. Uplink power control apparatus, characterized in that for determining. The method of claim 21 or 22, wherein the repetition check module, Compensation for arithmetic errors that occur when calculating the transmit power level per subcarrier based on the C / N threshold for power control and the C / N threshold for AMC for repetition of a specific MCS level applied to the uplink burst. Uplink power control apparatus for determining a second base station offset so as to determine. 23. The apparatus of claim 21 or 22, wherein the link adaptation module comprises: And further determining a maximum available packet size and MCS level for the uplink burst. The method of claim 20 or 22, wherein the burst scheduler, And selecting the number of subchannels and the MCS level corresponding to the packet size determined by the packet scheduler or the maximum available packet size determined by the base station offset calculator.

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