KR20100037888A - Apparatus and method for determining uplink schduling priority in a broadband wireless communication system - Google Patents

Abstract

PURPOSE: An apparatus and a method for determining uplink scheduling priority in a broadband wireless communication system are provided to increase the average data transmission rate by determining uplink scheduling priority in consideration of the influence of interference. CONSTITUTION: An uplink scheduler(130) includes an MCS(Modulation and Coding Scheme) determiner(150), a base priority determined(152), a correction value calculator(154) and a final priority determiner(156). The MSC determiner determines the MSC level for uplink communication, and the base priority determiner calculates a base priority index for each terminal. The correction calculator calculates the correction value for the base priority index, and the final priority determiner calculates the final priority index for each terminal.

Description

Apparatus and method for determining priority of uplink scheduling in broadband wireless communication system {APPARATUS AND METHOD FOR DETERMINING UPLINK SCHDULING PRIORITY IN A BROADBAND WIRELESS COMMUNICATION SYSTEM}

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

In a cellular wireless communication system, each of a plurality of base stations arranged at a geographically fixed location has a cell in charge, and each terminal performs wireless communication with a base station in charge of a cell to which it belongs. do. In this case, the radio link from the base station to the terminal is downlink, and the radio link from the terminal to the base station is uplink.

In a wireless communication system based on Code Division Multiple Access (hereinafter referred to as 'CDMA'), uplink communication is performed by a circuit transmission method. Accordingly, the terminal always transmits constant data, and the base station controls only the data transmission rate of each terminal. In determining the data rate of each terminal, the base station determines the data rate of the terminals in the cell according to the magnitude of the Rise over Thermal (RoT) to the sum of the self-cell interference, other cell interference, thermal noise Up or down at a time. As a result, since the RoT value of each cell is maintained at a certain level, the coverage of each cell is kept constant, and each terminal may have a data transmission rate of a predetermined level or more.

In contrast, Orthogonal Frequency Division Multiplexing (OFDM) / Orthogonal Frequency Division Multiple Access (OFDMA) based wireless, which is considered as a next generation mobile communication system. In the case of a communication system, uplink communication is performed in a packet transmission scheme. Therefore, each terminal temporarily transmits data, and the base station determines which terminal should transmit which size and at what size through scheduling. To this end, the base station calculates a data rate that each terminal can transmit in the uplink using information reported from each terminal, and then determines the priority among the terminals. For example, the base station calculates a headroom of a terminal based on a specific MCS by using a modulation and coding scheme (MCS) level for a transmission packet of the terminal and a power value used for packet transmission, and the head Using the room, scheduling priority is determined to be proportional to the data rate when a specific MCS level is used.

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

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

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

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

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

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

According to a first aspect of the present invention for achieving the above object, in a broadband wireless communication system, a base station apparatus, a basic priority determiner for calculating the basic priority indicator of each terminal, and calculates the transmission power per tone of each terminal and A calculator for calculating a correction value for reflecting the degree of interference in the basic priority indicator using the transmission power per tone, and a final priority indicator for calculating an uplink scheduling priority by calculating a final priority indicator using the correction value. And a priority determiner.

According to a second aspect of the present invention for achieving the above object, a method of operating a base station in a broadband wireless communication system, the process of calculating the basic priority indicator of each terminal, the process of calculating the transmission power per tone of each terminal Calculating a correction value for reflecting the degree of interference in the basic priority indicator by using the transmission power per tone, and calculating a final priority indicator using the correction value to determine uplink scheduling priority. It characterized in that it comprises a process.

By determining the uplink scheduling priority in consideration of the influence of the interference in the broadband wireless communication system, the amount of interference to other cells is reduced, thereby increasing the system coverage and increasing the average data rate.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, the present invention describes 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 using an Orthogonal Frequency Division Multiplexing (OFDM) / Orthogonal Frequency Division Multiple Access (OFDMA) scheme as an example. The same applies to other wireless communication systems.

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

In order to reduce the interference to other cells in the broadband wireless communication system according to the present invention, the base station assigns a low priority uplink scheduling priority to the terminal having a large interference to other cells. As a result, the data transmission opportunity of the terminal which gives a large interference to another cell is relatively small, thereby reducing interference to other cells.

A prioritization scheme for briefly giving a low priority uplink scheduling priority to a terminal which has a large interference to another cell will be described below. First, the base station calculates the basic priority index of each terminal that does not reflect the interference. For example, the basic priority indicator may be calculated according to a Proportional Pair (PF) technique using headroom. Here, the headroom is a parameter representing the ratio of the transmission power currently used to the maximum transmission power of the terminal, and is generally used as a normalized value for a specific modulation and coding scheme (MCS) level. For example, the basic priority indicator according to the PF technique is calculated as in 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,

Is the basis priority indicator,

Is the leveled headroom of the terminal, the

Is a value that converts the leveled headroom to the data rate when using the corresponding MCS level,

Is the average data rate of the terminal, the

Is a weight to adjust the degree of contribution of the average data rate,

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

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

The headroom is a value that depends on the channel quality between the terminal and the base station. The worse the channel quality, the smaller the headroom size. For example, if the distance between the terminal and the base station is far, the loss of the signal is large, the power required to transmit a signal using the reference MCS level is increased, and as a result, the headroom is reduced, the basic priority is lowered. On the contrary, when the distance between the terminal and the base station is close, the loss of the signal is small, the power required to transmit the signal using the reference MCS level is reduced, and as a result, the headroom is increased, thereby increasing the basic priority.

If the uplink scheduling priority is determined using only the basic priority indicator, the average transmission rate has a characteristic as shown in Equation 2 below.

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,

Is the leveled headroom of the terminal, the

Is a value that converts the leveled headroom to the data rate when using the corresponding MCS level,

Is the average data rate of the terminal

Means squared.

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

The degree of interference is estimated using the transmission power per ton of the terminal. In general, the greater 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 ton of each terminal. The transmit power per tone can be predicted through the MCS level. This is because, when a high MCS level is used, the number of complex symbols to be distinguished per tone increases, so that the transmission power per tone increases. 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 transmit power per tone is calculated using the MCS level. For example, the transmission power per tone is calculated as in Equation 3 below.

는 해당 MCS 레벨 사용 시 톤당 송신 전력, 상기

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

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

Means minimum required SINR of the corresponding MCS level.

A correction value for converting the basic priority indicator into the final priority indicator is calculated using the transmission power per tone. For example, the correction value is calculated as 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,

Is a correction value for reflecting the degree of interference,

Is a weight to adjust the degree of contribution of transmit power per tone,

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

Means a floor function.

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

The larger is, the smaller the correction value of a terminal having a larger transmit power per tone is.

When the uplink scheduling priority is determined using the last priority indicator, the average transmission rate has a characteristic as shown in Equation 5 below.

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,

Is the leveled headroom of the terminal, the

Is a value that converts the leveled headroom to the data rate when using the corresponding MCS level,

Is the average data rate of the terminal

Exponential product, above

Is a weight to adjust the degree of contribution of transmit power per tone,

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

By determining the uplink scheduling priority as described above, a terminal adjacent to another cell is assigned a low scheduling priority, thereby lowering the data rate of the terminal, and as a result, interference to other cells is reduced. For example, when there are two terminals having the same basic priority indicator, since a terminal having a large transmission power per ton gives a large interference to another cell, the base station lowers the average data rate by lowering the priority of the terminal. Drop. In addition, since a small terminal having a large transmission power per ton gives small interference to another cell, the base station increases the average data rate by increasing the priority of the terminal. This reduces interference to other cells.

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

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

As shown in FIG. 1A, the base station includes a radio frequency (RF) receiver 102, an OFDM demodulator 104, a subcarrier demapper 106, a symbol demodulator 108, a decoder 110, and a data buffer. (112),, map generator 114, encoder 116, symbol modulator 118, subcarrier mapper 120, OFDM modulator 122, RF transmitter 124, feedback information interpreter 126, headroom The calculator 128, the average rate calculator 130, and the uplink scheduler 132 are configured.

The RF receiver 102 downconverts an RF band signal received through an antenna to a baseband signal. The OFDM demodulator 104 divides the signal provided from the RF receiver 102 in OFDM symbol units, removes a cyclic prefix (CP), and restores signals in a frequency domain through a fast fourier transform (FFT) operation. do. The subcarrier demapper 106 divides signals in a frequency domain according to processing units. For example, the subcarrier mapper 106 provides a signal received through a feedback channel to the feedback information interpreter 126 and provides data signals to the symbol demodulator 108. The symbol demodulator 108 converts the data signals into bit strings by demodulating the data signals. The decoder 110 restores the information bit stream by channel decoding the bit stream.

The data buffer 112 temporarily stores data transmitted and received with the terminals. The map generator 114 generates an uplink map message for notifying the uplink resource allocation result by the uplink scheduler 132. The encoder 116 channel codes the information bit stream provided from the map generator 132 and the data buffer 112. The symbol modulator 118 demodulates the channel-coded bit string and converts the complex code into complex symbols. The subcarrier mapper 120 maps the complex symbols to the frequency domain. The OFDM modulator 122 converts the complex symbols mapped to 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 up-converts the baseband signal into an RF band signal and transmits it through an antenna.

The feedback information interpreter 126 analyzes a signal received through a feedback channel, thereby confirming information fed back from the terminals. In particular, the feedback information parser 126 checks downlink CINR information of the terminal and uplink transmission power information of the terminal, and then provides the downlink CINR information to the uplink scheduler 132 and the uplink transmission power. Information is provided to the headroom calculator 128.

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

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

The uplink scheduler 132 allocates an uplink resource to each terminal. To this end, the uplink scheduler 132 determines an uplink scheduling priority among terminals, and then allocates uplink resources according to the priority. In particular, when determining the uplink scheduling priority, the uplink scheduler 132 determines the uplink scheduling priority by reflecting an indirect degree to another cell. In other words, the uplink scheduler 132 calculates a priority indicator of each terminal so that a terminal having a low downlink CINR has a low priority.

In detail, as shown in FIG. 1B, the uplink scheduler 132 includes an MCS determiner 150, a basic priority determiner 152, a correction value calculator 154, a final priority determiner 156, The resource allocator 158 is configured.

The MCS determiner 150 determines the average rate calculated by the average rate calculator 130, the headroom calculated by the headroom calculator 128, and the downward identified by the feedback information checker 126. By using at least one information of the link CINR, each terminal determines the MCS level to use for uplink communication.

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

The correction value calculator 154 calculates a correction value for the basic priority index of each terminal by using the headroom calculated by the headroom calculator 128 and the MCS level determined by the MCS determiner 150. . In 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 in Equation 4. In other words, as shown in Equation 3 and Equation 4, the correction value calculator 154 calculates the transmit power per tone for the reference MCS level, and is determined in the transmit power per tone for the reference MCS level. Calculating the transmit 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 performing an exponential multiplication of 10 with the product of the maximum integer smaller than the transmit power per tone and a specific weight as an exponent. The correction value is calculated. Here, the required SINR of the MCS level is a predetermined value.

The final priority determiner 156 calculates a final priority index of each terminal, that is, a priority index reflecting the degree of interference using the basic priority index and the correction value. That is, the final priority determiner 156 calculates the final priority index of each terminal by multiplying the basic priority index and the correction value. The resource allocator 158 determines the size and location of resources to be used by each terminal according to the uplink scheduling priority of each terminal and the MCS level. That is, the resource allocator 158 determines how many slots each terminal uses, and which physical location slots to use.

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

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

After calculating the basic priority index, the base station proceeds to step 203 and calculates a correction value for reflecting interference occurrence information using the MCS level of each terminal. That is, the base station calculates 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 the transmission power per tone for the reference MCS level, and transmits the transmission per tone by adding up the difference between the required SINR of the determined MCS level and the required SINR of the reference MCS level to the transmission power per tone for the reference MCS level. Calculate the power. The base station calculates the correction value by performing an exponential multiplication of 10, which is an exponent of a product of a maximum integer smaller than the transmit 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 shown in Equation 3, and calculates the correction value as shown in Equation 4.

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

After calculating the last priority indicator, the base station proceeds to step 207 to allocate uplink resources according to the uplink scheduling priority and the MCS level of each terminal. In other words, the base station determines the physical size and location of resources to be used by each terminal according to the uplink scheduling priority and MCS level of each terminal.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

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

2 is a diagram illustrating an uplink scheduling priority determination procedure of a base station in a broadband wireless communication system according to an embodiment of the present invention.

Claims (16)

A base station apparatus in a broadband wireless communication system, A basic priority determiner for calculating basic priority indicators of respective terminals; A calculator for calculating transmission power per tone of each terminal and calculating a correction value for reflecting the degree of interference in the basic 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. The method of claim 1, And the basic priority determiner calculates the basic priority indicator according to a propagation fair (PF) technique. The method of claim 1, The calculator, characterized in that for calculating the transmission power per tone using the MCS level of each terminal. The method of claim 3, The calculator calculates the transmission power per tone for the reference MCS level, and calculates the transmission power per tone by summing the difference between the required SINR of the determined MCS level and the required SINR of the reference MCS level to the transmission power per tone for the reference MCS level. Device characterized in that. The method of claim 1, And the correction value is calculated to be lower as the transmission power per tone is larger. The method of claim 5, The calculator, characterized in that for calculating the correction value as shown in the following formula,

Where

Is a weight to adjust the degree of contribution of transmit power per tone,

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

Means floor function. The method of claim 1, And the final priority determiner calculates the final priority indicator by multiplying the basic priority indicator and the correction value. The method of claim 1, And an allocator for allocating uplink resources to the respective terminals according to the uplink scheduling priority. A method of operating a base station in a broadband wireless communication system, Calculating a basic priority indicator of each terminal; Calculating transmission power per ton of each terminal; Calculating a correction value for reflecting the degree of interference in the basic priority indicator by using the transmission power per tone; Determining an uplink scheduling priority by calculating a final priority indicator using the correction value. 10. The method of claim 9, The basic priority indicator is calculated according to the Proportional Fair (PF) technique. 10. The method of claim 9, The transmission power per tone is calculated using the MCS level of each terminal. The method of claim 11, The process of calculating the correction value, Calculating transmit power per ton for a reference MCS level; Summing the difference between the determined SINR of the determined MCS level and the required SINR of the reference MCS level to the transmit power per tone for the reference MCS level. 10. The method of claim 9, The correction value is calculated so that the lower the transmission power per tone is calculated. The method of claim 13, The correction value is calculated as in the following formula,

Where

Is a weight to adjust the degree of contribution of transmit power per tone,

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

Means floor function. 10. The method of claim 9, And the final priority indicator is calculated by multiplying the basic priority indicator and the correction value. 10. The method of claim 9, And allocating an uplink resource to each terminal according to the uplink scheduling priority.

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