KR101513569B1 - Apparatus and method for determining uplink schduling priority in a broadband wireless communication system - Google Patents

Abstract

The present invention relates to an uplink scheduling priority in a broadband wireless communication system, the base station comprising: a base priority determiner for calculating a base priority indicator of each terminal; and a base station controller for calculating transmission power per tone of each terminal, And a final priority determiner for determining an uplink scheduling priority by calculating a final priority index using the correction value, By determining the uplink scheduling priority in consideration of the influence of interference, the amount of interference to other cells is reduced, thereby increasing the average data transmission rate as the system coverage is expanded.

Uplink scheduling priority, headroom, PF (Prop Fair Fair), interference, RoT (Rise over Thermal)

Description

[0001] APPARATUS AND METHOD FOR DETERMINING UPLINK SCHEDULING PRIORITY IN A BROADBAND WIRELESS COMMUNICATION SYSTEM [0002] BACKGROUND OF THE INVENTION [0003]

The present invention relates to a broadband wireless communication system, and more particularly, to an apparatus and method for determining an uplink scheduling priority in a broadband wireless communication system.

In a cellular wireless communication system, each of a plurality of base stations located at geographically fixed locations has a cell in charge, and each terminal performs wireless communication with a base station that is responsible for a cell to which the terminal belongs do. At this time, the radio link from the base station to the terminal is referred to as a downlink and the radio link from the terminal to the base station is referred to as an uplink.

In the case of a code division multiple access (CDMA) based wireless communication system, uplink communication is performed by a circuit transmission method. Accordingly, the UE always transmits certain data, and the BS only controls the data transmission rate of each UE. In determining the data rate of each UE, the Node B calculates a data rate of cells in the cell according to a size of a Rise over Thermal (RoT) ratio to a sum of self-cell interference, other-cell interference, Up or down. Thus, since the RoT value of each cell is maintained at a certain level, the coverage of each cell is kept constant, and each terminal can have a data transmission rate higher than a certain level.

On the other hand, a wireless communication system based on Orthogonal Frequency Division Multiplexing (OFDM) / Orthogonal Frequency Division Multiple Access (OFDMA) In the case of a communication system, the uplink communication is performed by a packet transmission scheme. Therefore, each terminal temporarily transmits data, and the base station determines through which scheduling the terminal and which size of data to transmit. To this end, the BS calculates a data rate that each MS can transmit on the uplink using information reported from each MS, and then determines a priority among the MSs. For example, the BS calculates a headroom of a terminal based on a specific MCS using a Modulation and Coding Scheme (MCS) level of a transmission packet of the MS and a power value used for packet transmission, The scheduling priority is determined so as to be proportional to the data transmission rate when a specific MCS level is used.

In the OFDM / OFDMA based wireless communication system, since the terminals belonging to the same cell use different radio resources, the self-cell interference occurring in the CDMA-based wireless communication system does not occur and only the other-cell interference occurs . The method of maintaining the RoT of each cell constant can not be applied by controlling the self cell interference through the data rate control of the UE as in the CDMA based wireless communication system because the self cell interference does not occur. Therefore, in an OFDM / OFDMA based broadband wireless communication system, there is a need for an alternative to keep the RoT of each cell below a predetermined level.

Accordingly, it is an object of the present invention to provide an apparatus and method for maintaining a Rise over Thermal (RoT) of each cell below a reference value in a broadband wireless communication system.

It is another object of the present invention to provide an apparatus and method for reducing interference to other cells due to uplink communication in a broadband wireless communication system.

It is another object of the present invention to provide an apparatus and method for determining an uplink scheduling priority in consideration of the degree of interference from other cells in a broadband wireless communication system.

It is another object of the present invention to provide an apparatus and method for determining an uplink scheduling priority by using uplink transmission power in a broadband wireless communication system.

It is another object of the present invention to provide an apparatus and method for determining an uplink scheduling priority so that a priority of a UE having a large uplink transmission power is lowered in a broadband wireless communication system.

According to a first aspect of the present invention, in a broadband wireless communication system, a base station apparatus includes: a base priority determiner for calculating base priority indicators of respective terminals; A calculator for calculating a correction value for reflecting the degree of occurrence of interference in the base priority indicator using the per-tone transmission power, and a calculator for calculating a final priority indicator using the correction value, thereby determining an uplink scheduling priority And a priority determiner.

According to a second aspect of the present invention, there is provided a method of operating a base station in a broadband wireless communication system, comprising: calculating a base priority index of each terminal; calculating a transmission power per tone of each terminal; Calculating a correction value for reflecting the degree of occurrence of interference in the base priority indicator using the per-tone transmission power; and calculating a final priority indicator using the correction value to determine an uplink scheduling priority The method comprising the steps of:

In the broadband wireless communication system, by determining the uplink scheduling priority in consideration of the influence of the interference, the amount of interference to other cells decreases, thereby increasing the average data rate as the system coverage is expanded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Hereinafter, the present invention will be described with reference to a technique for reducing interference to other cells due to uplink communication in a broadband wireless communication system. Hereinafter, the present invention will be described by taking an example of a wireless communication system of Orthogonal Frequency Division Multiplexing (OFDM) / Orthogonal Frequency Division Multiple Access (OFDMA) , And can be similarly applied to other types of wireless communication systems.

First, the technical basis of the present invention for reducing interference to other cells will be described as follows.

In the broadband wireless communication system according to the present invention, in order to reduce interference to other cells, the base station assigns lower priority UL scheduling priority to terminals that cause large interference to other cells. Accordingly, interference with other cells is reduced by relatively reducing the chance of data transmission by a terminal that gives a large interference to another cell.

A priority determination method for allowing a UE that gives a large interference to the other cell to receive a low-order UL scheduling priority will be briefly described as follows. First, the base station calculates a base priority index of each terminal that does not reflect interference. For example, the base priority index can be calculated according to a PF (Propotional Pair) technique using a headroom. Here, the headroom is a parameter indicating the ratio of the currently used transmission power to the maximum transmission power of the terminal, and is generally used as a normalized value for a certain Modulation and Coding Scheme (MCS) level. For example, the base priority index according to the PF technique is calculated as Equation (1) below.

는 기초 우선순위 지표, 상기

는 단말의 평준화된 헤드룸, 상기

는 평준화된 헤드룸을 해당 MCS 레벨 사용 시의 데이터 전송률로 변환하는 값, 상기

는 단말의 평균 데이터 전송률, 상기

는 평균 데이터 전송률의 기여 정도를 조절하는 가중치, 상기

는 해당 MCS 레벨의 최소 요구 SINR(Signal to Interference and Noise Ratio), 상기

는 해당 MCS 레벨의 심벌당 정보 비트 수를 의미한다.In Equation (1) above,

Is a base priority index,

A normalized headroom of the terminal,

A value for converting the leveled headroom into a data rate at the time of using the corresponding MCS level,

Is the average data rate of the terminal,

Is a weight for adjusting the contribution of the average data rate,

A minimum required SINR (Signal to Interference and Noise Ratio) of the corresponding MCS level,

Denotes the number of information bits per symbol of the corresponding MCS level.

The headroom is a value depending on the channel quality between the terminal and the base station, and the worse the channel quality, the smaller the size of the headroom. For example, if the distance between the terminal and the base station is long, the loss of the signal is large, and the power required to transmit the signal using the reference MCS level increases, resulting in a low headroom and low base priority. Conversely, if the distance between the terminal and the base station is close to each other, the signal loss is small, the power required to transmit the signal using the reference MCS level is reduced, and as a result, the headroom is increased.

If the uplink scheduling priority is determined using only the base priority indicator, the average transmission rate has the following Equation (2).

는 단말의 평준화된 헤드룸, 상기

는 평준화된 헤드룸을 해당 MCS 레벨 사용 시의 데이터 전송률로 변환하는 값, 상기

는 단말의 평균 데이터 전송률의

제곱을 의미한다.In Equation (2) above,

A normalized headroom of the terminal,

A value for converting the leveled headroom into a data rate at the time of using the corresponding MCS level,

Of the average data rate of the terminal

.

As shown in Equation (2), when only the basic priority index is used, the average data rate varies depending on the headroom and the MCS level and changes regardless of the degree of interference occurrence. Therefore, the base station according to the present invention calculates the final priority index reflecting the interference by correcting the base priority index according to the degree of interference of each terminal.

The degree of interference occurrence is estimated using the transmission power per tone of the terminal. Generally, the larger the transmission power of the terminal, the greater the amount of interference to other cells. In other words, the transmission power per tone is directly related to the amount of interference to other cells. Therefore, the base station must estimate the transmission power per tone of each terminal. The transmit power per tone may be predicted through the MCS level. This is because, if a high MCS level is used, the number of complex symbols to be separated per tone becomes large, so that the transmission power per tone becomes large. Therefore, the base station calculates the final priority indicator so that the terminal using the high MCS level has a low priority. To this end, the transmission power per tone is calculated using the MCS level. For example, the transmission power per tone is calculated by Equation (3) below.

는 해당 MCS 레벨 사용 시 톤당 송신 전력, 상기

는 해당 MCS 레벨의 최소 요구 SINR을 의미한다.In Equation (3) above,

Is the transmit power per tone when using the corresponding MCS level,

Denotes the minimum required SINR of the corresponding MCS level.

A correction value for converting the base priority indicator to the final priority indicator is calculated using the per-tone transmission power. For example, the correction value is calculated as shown in Equation (4) below.

는 간섭 정도를 반영하기 위한 보정치, 상기

는 톤당 송신 전력의 기여 정도를 조절하는 가중치, 상기

는 해당 MCS 레벨 사용 시 톤당 송신 전력, 상기

는 플로어 함수(floor function)을 의미한다.In Equation (4) above,

A correction value for reflecting the degree of interference,

Is a weight for adjusting the degree of contribution of the transmission power per tone,

Is the transmit power per tone when using the corresponding MCS level,

Denotes a floor function.

가 클수록 톤당 송신 전력이 큰 단말의 보정치는 작아진다.As shown in Equation (3), the correction value is calculated by an exponentiation multiplication of 10, which is a product of a maximum integer smaller than the transmission power per tone and a specific weight. Therefore, the larger the transmission power per tone is, the lower the correction value is. In other words, if the transmission power per tone is large, the correction value becomes small. On the other hand, if the transmission power per tone is small, the correction value becomes large. At this time,

The larger the transmission power per tone is, the smaller the correction value of the terminal.

When the uplink scheduling priority is determined using the final priority index, the average transmission rate has the following Equation (5).

는 단말의 평준화된 헤드룸, 상기

는 평준화된 헤드룸을 해당 MCS 레벨 사용 시의 데이터 전송률로 변환하는 값, 상기

는 단말의 평균 데이터 전송률의

지수 곱, 상기

는 톤당 송신 전력의 기여 정도를 조절하는 가중치, 상기

는 해당 MCS 레벨 사용 시 톤당 송 신 전력을 의미한다.In Equation (5) above,

A normalized headroom of the terminal,

A value for converting the leveled headroom into a data rate at the time of using the corresponding MCS level,

Of the average data rate of the terminal

Exponent product,

Is a weight for adjusting the degree of contribution of the transmission power per tone,

Means the transmission power per ton when using the corresponding MCS level.

Through the determination of the uplink scheduling priority as described above, the UEs adjacent to other cells are assigned a low scheduling priority, thereby lowering the data rate of the UE and consequently reducing interference to other cells. For example, when there are two terminals having the same basic priority index, a terminal having a high transmission power per tone causes large interference to other cells, so the base station decreases the average data rate by lowering the priority of the terminal I will. Since a small terminal having a large transmission power per tone gives small interference to other cells, the base station increases the priority of the terminal and increases the average data transmission rate. As a result, interference to other cells is reduced.

Hereinafter, the present invention will be described in detail with reference to the drawings as to the configuration and operation procedure of a base station for determining an uplink scheduling priority as described above.

1A and 1B are block diagrams of a base station in a broadband wireless communication system according to an embodiment of the present invention.

1A, the base station includes an RF (Radio Frequency) receiver 102, an OFDM demodulator 104, a subcarrier demapper 106, a symbol demodulator 108, a decoder 110, The MAP generator 112, the MAP generator 114, the encoder 116, the symbol modulator 118, the subcarrier mapper 120, the OFDM modulator 122, the RF transmitter 124, the feedback information interpreter 126, An estimator 128, an average rate calculator 130, and an uplink scheduler 132.

The RF receiver 102 downconverts the RF band signal received through the antenna to a baseband signal. The OFDM demodulator 104 separates a signal provided from the RF receiver 102 on a per OFDM symbol basis and then removes a CP (Cyclic Prefix) and restores frequency-domain signals through an FFT (Fast Fourier Transform) do. The sub-carrier demapper 106 divides the frequency-domain signals according to a processing unit. For example, the sub-carrier demapper 106 provides a signal received via a feedback channel to the feedback information interpreter 126 and provides data signals to the symbol demodulator 108. The symbol demodulator 108 demodulates the data signals to convert them into bit streams. The decoder 110 decodes the information bit stream by channel decoding the bit stream.

The data buffer 112 temporarily stores data to be transmitted to and received from the terminals. The MAP generator 114 generates an uplink MAP message for informing uplink resource allocation result by the uplink scheduler 132. The encoder 116 channel-codes an information bit stream provided from the map generator 132 and the data buffer 112. The symbol modulator 118 demodulates the channel-encoded bit stream and converts it into complex symbols. The subcarrier mapper 120 maps the complex symbols to a frequency domain. The OFDM modulator 122 converts the complex symbols mapped in the frequency domain into a time domain signal through an Inverse Fast Fourier Transform (IFFT) operation, and constructs an OFDM symbol by inserting a CP. The RF transmitter 124 upconverts the baseband signal to an RF band signal and transmits it through an antenna.

The feedback information analyzer 126 interprets the signal received through the feedback channel, thereby confirming information fed back from the UEs. In particular, the feedback information interpreter 126 checks the downlink CINR information of the UE and the uplink transmission power information of the UE, and then provides the downlink CINR information to the uplink scheduler 132, And provides the information to the headroom calculator 128.

The headroom calculator 128 calculates the headroom of each terminal. In other words, the headroom calculator 128 calculates the difference value between the maximum transmission power and the used transmission power of each terminal, and then normalizes the difference value with respect to the reference MCS level. Here, the maximum transmission power of each of the terminals is a parameter controlled by the base station, and the used transmission power is confirmed by the feedback information analyzer 126.

The average transmission rate calculator 130 calculates an uplink average transmission rate of each terminal. Here, the uplink average transmission rate is calculated for only the data that is successfully received, or is calculated for the transmitted data. If only successful data is received, the average transmission rate calculator 130 calculates an average transmission rate for the received data successfully decoded by the decoder 110. [ On the other hand, when the transmitted data are targeted, the average transmission rate calculator 130 calculates the average transmission rate using the resources and the MCS level allocated to each terminal by the uplink scheduler 132. The average transmission rate calculator 130 provides the uplink average transmission rate of each terminal to the uplink scheduler 132.

The uplink scheduler 132 allocates uplink resources to each UE. To this end, the uplink scheduler 132 determines an uplink scheduling priority among the UEs, and then allocates uplink resources according to the priority. In particular, in determining the uplink scheduling priority, the uplink scheduler 132 determines the uplink scheduling priority by reflecting the degree of indirectness to other cells. In other words, the uplink scheduler 132 calculates the priority index of each terminal so that the terminal having a low downlink CINR has a low priority.

1B, the uplink scheduler 132 includes an MCS determiner 150, a base priority determiner 152, a correction value calculator 154, a final priority determiner 156, And a resource allocation unit 158. [

The MCS determiner 150 is configured to determine the average transmission rate calculated by the average transmission rate calculator 130, the headroom calculated by the headroom calculator 128, And the link CINR to determine the MCS level to be used for the uplink communication by each terminal.

The base priority determiner 152 calculates the base priority indicator of each terminal using the average transmission rate calculated by the average transmission rate calculator 130 and the headroom calculated by the headroom calculator 128 do. Here, the base priority indicator is an uplink scheduling priority indicator that does not reflect the degree of interference occurrence. For example, the base priority determiner 152 calculates a base priority index according to the PF technique as shown in Equation (1). In other words, as shown in Equation (1), the base priority determiner 152 calculates the base priority indicator as a ratio of the data transmission rate allocable using the headroom of each terminal and the average data transmission rate to the present do.

The correction value calculator 154 calculates a correction value for the base priority indicator of each terminal using the headroom calculated by the headroom calculator 128 and the MCS level determined by the MCS determiner 150 . In more detail, the correction value calculator 154 calculates the transmission power per tone using the MCS level, and calculates the correction value using the transmission power per tone. For example, the correction value calculator 154 calculates the transmission power per tone as in Equation (3) and calculates the correction value as shown in Equation (4). In other words, as shown in Equation (3) and Equation (4), the correction value calculator 154 calculates the transmission power per tone for the reference MCS level and determines the transmission power per tone By performing the exponentiation multiplication of 10 by calculating the transmission power per tone by summing the difference between the required SINR of the MCS level and the required SINR of the reference MCS level and then multiplying the product of the maximum integer and the specific weight smaller than the transmission power per tone The correction value is calculated. Here, the required SINR of the MCS level is a predetermined value.

The final priority determiner 156 calculates a priority index reflecting each terminal's final priority index, i.e., the degree of interference generation, using the base priority index and the correction value. That is, the final priority determiner 156 calculates the final priority index of each terminal by multiplying the base priority index and the correction value. The resource assignment unit 158 determines the size and location of a resource to be used by each UE according to an uplink scheduling priority and an MCS level of each UE. That is, the resource assignment unit 158 determines how many slots each of the terminals uses and which physical location slot is used.

FIG. 2 illustrates a procedure of prioritizing uplink scheduling of a base station in a broadband wireless communication system according to an embodiment of the present invention.

Referring to FIG. 2, in step 201, the BS calculates a base priority indicator of each MS using an uplink average data rate and a headroom. Here, the base priority indicator is an uplink scheduling priority indicator that does not reflect the degree of interference occurrence. That is, the base station calculates the base priority indicator as a ratio of the data transmission rate that can be allocated using the headroom of each terminal and the average data transmission rate to the present. For example, the base station calculates a base priority index according to the PF technique as shown in Equation (1).

After calculating the basic priority index, the BS proceeds to step 203 and calculates a correction value for reflecting the interference occurrence information using the MCS level of each terminal. That is, the base station calculates the transmission power per tone using the MCS level, and calculates the correction value using the transmission power per tone. In detail, the base station calculates transmit power per tone by calculating the transmit power per tone for the reference MCS level, summing the difference between the required SINR of the MCS level and the required SINR of the reference MCS level determined on the per- Power is calculated. Then, the base station calculates the correction value by performing an exponentiation multiplication of 10 by multiplying a product of a maximum integer smaller than the transmission power per tone and a specific weight. Here, the required SINR of the MCS level is a predetermined value. For example, the base station calculates the transmission power per tone as in Equation (3), and calculates the correction value as shown in Equation (4).

After calculating the correction value, the BS proceeds to step 205 and calculates a priority index reflecting the final priority index of each terminal, that is, the degree of occurrence of interference, using the correction value. In other words, the base station calculates the final priority indicator of each terminal by multiplying the base priority indicator and the correction value. That is, the BS determines an uplink scheduling priority.

After calculating the final priority index, the BS proceeds to step 207 and allocates uplink resources according to the uplink scheduling priority and the MCS level of each MS. In other words, the BS determines a physical size and a location of a resource to be used by each MS according to an uplink scheduling priority and an MCS level of each MS.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but is capable of various modifications within the scope of the invention. Therefore, the scope of the present invention should not be limited by the illustrated embodiments, but should be determined by the scope of the appended claims and equivalents thereof.

1A and 1B are block diagrams of a base station in a broadband wireless communication system according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a method and apparatus for scheduling uplink scheduling of a base station in a broadband wireless communication system.

Claims (16)

A base station apparatus in a broadband wireless communication system, A base priority determiner for calculating a base priority indicator of each terminal; A calculator for calculating a transmission power per tone of each terminal and calculating a correction value for reflecting the degree of occurrence of interference in the base priority indicator using the transmission power per tone; And a final priority determiner for determining an uplink scheduling priority by calculating a final priority indicator using the correction value, Wherein the calculator calculates the transmission power per tone using the MCS level of each terminal. The method according to claim 1, Wherein the base priority determiner calculates the base priority index according to a PF (Propotional Fair) technique. delete The method according to claim 1, The calculator calculates the transmit power per tone by calculating the transmit power per ton for the reference MCS level and summing the difference between the required SINR of the MCS level determined at the transmit power per tone for the reference MCS level and the required SINR at the reference MCS level Lt; / RTI > The method according to claim 1, Wherein the correction value is calculated such that the larger the transmission power per tone is, the lower the correction value is. 6. The method of claim 5, Wherein the calculator calculates the correction value according to the following equation:

Here,

Is a weight for adjusting the degree of contribution of the transmission power per tone,

Is the transmit power per tone when using the corresponding MCS level,

Refers to a floor function. The method according to claim 1, Wherein the final priority determiner calculates the final priority indicator by multiplying the base priority indicator and the correction value. The method according to claim 1, Further comprising an allocator for allocating uplink resources to the UEs according to the UL scheduling priority. A method of operating a base station in a broadband wireless communication system, Calculating a base priority index of each terminal; Calculating transmission power per tone of each terminal; Calculating a correction value for reflecting the degree of interference generation in the base priority indicator using the transmission power per tone; And calculating a final priority indicator using the correction value to determine an uplink scheduling priority, Wherein the per-tone transmission power is calculated using the MCS level of each terminal. 10. The method of claim 9, Wherein the base priority indicator is calculated according to a PF (Propotional Fair) technique. delete 10. The method of claim 9, Wherein the step of calculating the correction value comprises: Calculating a transmission power per tone for the reference MCS level, And summing the difference between the required SINR of the MCS level and the required SINR of the reference MCS level determined in the per-tone transmission power for the reference MCS level. 10. The method of claim 9, Wherein the correction value is calculated such that the larger the transmission power per tone is, the lower the correction value is. 14. The method of claim 13, Wherein the correction value is calculated according to the following equation:

Here,

Is a weight for adjusting the degree of contribution of the transmission power per tone,

Is the transmit power per tone when using the corresponding MCS level,

Refers to a floor function. 10. The method of claim 9, Wherein the final priority indicator is calculated by multiplying the base priority indicator and the correction value. 10. The method of claim 9, And allocating an uplink resource to each of the MSs according to the UL scheduling priority.

Images