KR20100087589A - Apparatus and method for uplink scheduling in a broadband wireless communication system - Google Patents

Abstract

PURPOSE: An apparatus and a method for uplink scheduling in a broadband wireless communication system are provided to prevent the occurrence of an uplink burst error by enabling the transmission power of a terminal to be proximate to the maximum transmission power. CONSTITUTION: A calculation unit(118) predicts the entire transmission power of a terminal. If the entire transmission power is equal to or larger than a reference value, a margin determiner(110) adjusts transmission power margin for a setup period to be larger than a default value. A wireless resource determination unit(114) determines the number of slots allocated to the terminal by using the determined transmission power margin. A management unit(116) updates a parameter based on the uplink transmission power information by checking whether or not an error exists in an uplink burst.

Description

Device and method for uplink scheduling in broadband wireless communication system {APPARATUS AND METHOD FOR UPLINK SCHEDULING IN A BROADBAND WIRELESS COMMUNICATION SYSTEM}

The present invention relates to an apparatus and method for uplink scheduling in a wireless communication system, and more particularly, to an apparatus and method for estimating total transmission power of a terminal and performing uplink scheduling in consideration of the total transmission power in a broadband wireless communication system. will be.

In the 4th Generation communication system, which is the next generation communication system, active research is being conducted to provide users with services having various service qualities having a transmission rate of about 100 Mbps. In particular, 4G communication systems are actively researched to support high-speed services in the form of ensuring mobility and quality of service in a broadband wireless access (BWA) communication system. This is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system.

The IEEE 802.16 communication system uses orthogonal frequency division multiplexing (OFDM) / orthogonal frequency division multiple access (OFDMA) for a physical channel. The OFDM or OFDMA scheme has an advantage of obtaining optimal transmission efficiency in high-speed data transmission by maintaining orthogonality among a plurality of subcarriers.

  In the IEEE 802.16 based broadband wireless communication system, data transmission is performed in units of frames, and each frame can transmit an area for transmitting downlink (DL) data and uplink (UL) data. It is divided into areas. Here, the region for transmitting the uplink data is composed of a two-dimensional array of frequency and time axes, and each basic allocation unit is a slot. Each slot is assigned to only one terminal among terminals existing in a sector, and a set of slots allocated to each terminal may be defined as a burst.

Hereinafter, a method of allocating an uplink resource to a terminal in a broadband wireless communication system according to the prior art will be described.

First, the base station demodulates the received signal and extracts UL Tx power information (UL Tx Power per subcarrier) transmitted by the terminal. The base station determines radio resources (number of slots) that can be used with uplink modulation and coding scheme (MCS) using uplink transmission power information. According to the standard, the case of transmitting UL Tx power is as follows. Lastly, the setup period (Tx_Power_Report_Interval frame) has passed from the frame transmitting the UL Tx power, or the uplink channel larger than the setup value (Tx_Power_Report_Threshold dB) is detected. As such, since the terminal does not send the UL Tx Power every time, between the time when the terminal transmits the UL Tx Power and the time when the actual terminal transmits the uplink burst after the base station schedules the UL Tx Power from the terminal. Delay occurs. Therefore, in consideration of the channel variation of the delay time scheme, when determining the number of uplink slots, the number of slots smaller than the number of slots that can be actually allocated in consideration of the margin (Tx margin) is allocated. That is, by applying a margin to the recently transmitted UL Tx Power, the number of slots that can be allocated is reduced.

In general, an uplink burst will cause an error if the uplink channel situation worsens. In this case, a set point, which is the SINR reference value of the received burst, is increased by an outer-loop power control algorithm, and thus, the transmit power (Tx power) of the terminal is increased. When the terminal transmits the increased UL Tx Power information to the base station, the corresponding UL MCS level and the number of slots are determined again.

However, if the channel suddenly worsens, a problem may occur even if uplink scheduling is performed in consideration of a margin (Tx margin). In general, the maximum transmission power of the terminal is limited. If the terminal is transmitting the uplink signal at the maximum transmission power, even if the channel becomes worse, the UL Tx Power per subcarrier does not increase any more. In this case, when determining the uplink channel state by using the UL Tx Power information transmitted by the terminal, the base station may determine that it is better than the actual uplink channel state. As such, when the base station incorrectly determines the uplink channel, an error may occur continuously in the uplink burst.

Accordingly, an object of the present invention is to provide an apparatus and method for detecting whether a transmission power of a terminal is close to a maximum transmission power in a wireless communication system.

Another object of the present invention is to provide an apparatus and method for reducing the number of slots allocated to a terminal when the transmission power of the terminal approaches a maximum transmission power in a wireless communication system.

Another object of the present invention is to provide an apparatus and a method for increasing a margin applied to an uplink transmission power during a set period when a transmission power of a terminal approaches a maximum transmission power in a wireless communication system.

Another object of the present invention is to provide an apparatus and method for estimating the total transmission power of a terminal in a wireless communication system and performing uplink scheduling in consideration of the total transmission power.

According to an aspect of the present invention for achieving the above object, in the base station apparatus in the wireless communication system, a calculation unit for estimating the total transmission power (P _N ) of the terminal, and the total transmission power (P _N ) of the terminal If greater than or equal to the reference value P _TH , a margin determination unit adjusts a transmission power margin T _MARIN greater than a default value for a set period, and allocates it to the terminal using a transmission power margin determined by the margin determination unit. It characterized in that it comprises a radio resource determination unit for determining the number of slots to be.

According to another aspect of the present invention, in a method of operating a base station in a wireless communication system, the process of estimating the total transmit power (P _N ) of the terminal, the total transmit power (P _N ) of the terminal is a reference value (P _TH ) If greater than or equal to, a step of adjusting the transmission power margin (T _MARIN ) greater than the default value during the set period, and increasing the transmit power margin during the set period to reduce the number of slots to be allocated to the terminal Characterized in that.

As described above, the present invention can determine the uplink channel situation quickly and accurately. In addition, the present invention can detect whether the transmission power of the terminal is close to the maximum transmission power. If the transmission power of the terminal is close to the maximum transmission power, the transmission power margin of the terminal is reduced by increasing the transmission power margin (Tx margin) for a certain period of time, thereby reducing the number of slots allocated to the terminal. The uplink burst error can be prevented.

Hereinafter, the operating principle of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, if 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. The following terms are defined in consideration of the functions of the present invention, and may be changed according to the intentions or customs of the user, the operator, and the like. Therefore, the definition should be made based on the contents throughout the specification.

Hereinafter, a technique for estimating total transmission power of a terminal in a broadband wireless communication system and performing uplink scheduling in consideration of the total transmission power will be described. In particular, the present invention is to reduce the number of slots allocated to the terminal during the set time by increasing the margin applied to the uplink transmit power during the set period, when the total transmit power of the terminal is close to the maximum transmit power.

Hereinafter, the present invention will be described with an OFDM / OFDMA-based broadband wireless communication system by way of example, but the present invention can be easily applied to a wireless communication system of another connection.

First, a method for calculating the total transmission power of the terminal will be described.

The present invention calculates the total transmit power of the terminal using the latest UL Tx power information received from the terminal and the number of UL burst slots of the n-th frame received most recently. After the terminal transmits the UL Tx Power information, in order to consider a situation in which the transmission power of the terminal is changed by outer-loop power control, the parameter C _SET will be used. The initial value of the C _SET is '0', and when UL Tx power is received, since the outer loop power control is already reflected in the UL Tx power, it is initialized to '0'. When an uplink burst error occurs in an n-th frame, the C _SET is increased by T _p , and when the uplink burst error does not occur, the C _SET is decreased by one. Here, T _P is a parameter related to the outer loop power control, and may be set according to Equation 1 according to a target bit error rate (BER).

[Equation 1]

T _P = (1- Target BER) / Target BER

For example, if the target BER is 1%, T _P becomes (1-0.01) / (0.01) = 99. When there are two or more uplink bursts of a corresponding UE in an n-th frame, if an error occurs in any one of the bursts, it is assumed that an error has occurred and the C _SET value is increased. If a hybrid-automatic repeat request (H-ARQ) is operated, the C _SET value may be changed only for the initial transmission (or initial transmission) burst.

Therefore, the total transmit power P _N of the terminal may be calculated as in Equation 2 below.

[Equation 2]

Here, P _{Tx, REF} is UL TX power [dBm] per subcarrier transmitted by the UE, SINR [MCS] is a value [dB] to ensure the required BER is predetermined for each MCS level. The MCS _REF is the MCS level at the time when the UE transmits P _{Tx, REF} , and the MCS _N is the MCS level at the time of the n-th frame. N _SubCh is the number of frequency axis slots allocated to the UE in the n-th frame, and N _SubCr is the number of subcarriers included in one slot. P _D is a parameter related to the outer loop power control and is a step size [dB] used when increasing a set point when an uplink burst error occurs.

In the present invention, when the total transmit power P _N of the terminal calculated as in Equation 2 is greater than or equal to the threshold value P _TH , the Tx margin is increased by the set value for the set period. According to the present invention, since the C _SET increases to a relatively larger value when an uplink burst error occurs than when an uplink burst error does not occur, an uplink channel deterioration may be detected even if the uplink burst error does not occur continuously. Can be. In addition, even if the uplink burst error does not occur continuously, if several uplink burst errors occur, the total transmit power P _N of the terminal may exceed the reference value. In addition, if the uplink burst error occurs again after increasing the Tx margin for a set time, the total transmit power P _N may exceed the reference value, thereby immediately correcting the Tx margin.

Hereinafter, a specific embodiment of the present invention based on the above description will be described.

1 shows a configuration of a base station in a broadband wireless communication system according to an embodiment of the present invention.

As shown, the base station includes a radio frequency (RF) processor 100, a modem 102, a message processor 104, a traffic processor 106, a scheduler 108, a C _SET management unit 116, a P _N calculation unit. 118, a timer 120 is configured. Here, the scheduler 108 may include a margin determiner 110, an MCS level determiner 112, and a radio resource determiner 114.

Referring to FIG. 1, first, the RF processor 100 converts a signal of an RF band received through at least one antenna into a baseband signal, and converts the baseband signal into digital sample data to provide to the modem 102. do. In addition, the RF processor 100 converts the baseband sample data from the modem 102 into a baseband analog signal, converts the baseband signal into an RF band signal, and transmits the signal through at least one antenna.

The modem 102 demodulates the signal from the RF processor 100 into information data (receive packet) by physical layer demodulation, and provides the message processor 104 when the information data is a signaling message. If the data is traffic data, then provide it to the traffic handler 106. In the OFDM / OFDMA-based system, the modem 102 performs OFDM demodulation (FFT operation) on the sample data from the RF processor 100 and converts the data in the frequency domain into channel data and demodulates the data in the frequency domain. And channel decoding to restore the original information data. In addition, the modem 102 physically modulates transmission packets (transmission messages) from the message processor 104 and the traffic processor 106 and provides them to the RF processor 100. In an OFDM / OFDMA-based system, the modem 102 performs channel coding and channel modulation on the transmission packet, and converts the channel modulated data into sample data in the time domain by OFDM modulation.

Meanwhile, the modem 106 performs an error check (eg CRC) after channel coding an uplink burst received from the terminal and provides the result to the scheduler 108. The error check result for the uplink burst is used for parameter C _SET update. In addition, the modem 102 demodulates a channel signal (eg, a CQI channel) received from the terminal to obtain downlink carrier to interference and noise ratio (CINR) information, and obtains the downlink CINR information from the scheduler ( 108).

The message processor 104 protocolizes a reception signaling message (control message or MAC management message) from the modem 102 in case of reception, and generates and provides a transmission signaling message to the modem 102 in case of transmission. Meanwhile, the message processor 104 extracts UL Tx power information of the terminal from the burst received from the terminal and provides the information to the scheduler 108.

The traffic processor 106 protocolizes the received traffic from the modem 102 in case of reception, and protocolizes the transmitted traffic to the modem 102 in case of transmission.

The scheduler 108 determines scheduling priorities for service flows (SFs), and determines an MCS level and a radio resource (radio resource amount) for each service flow (or terminal) according to the determined priorities. do. When the resource allocation for the terminals to be serviced (service flows) is completed, the scheduler 108 provides a scheduling result (resource allocation result) to the message processor 104. Then, the message processor 104 generates a resource allocation message (eg, a MAP message) using the scheduling result and provides it to the modem 102.

The C _SET management unit 116 manages the parameter C _SET for each terminal under the control of the scheduler 108. Here, when UL Tx power information is received from the corresponding UE, the C _SET is initialized to '0', and if an error occurs in an uplink burst received from the UE, the C _SET is increased by a set value T _P and received from the UE. If no error occurs in the uplink burst is reduced by '1'. The set value T _P is a parameter related to the outer loop power control and may be determined according to the target BER as shown in Equation 1 above.

The P _N calculator 118 calculates the total transmit power P _N of the UE, which is an uplink scheduling target, and provides the calculated power to the scheduler 108. Here, the total transmission power P _N may be calculated as in Equation 2.

The margin determiner 110 in the scheduler 108 compares the total transmit power P _N and the set value P _TH of the terminal from the P _N calculator 118, and the total transmit power P _N. If T) is greater than or equal to the set value P _TH , the Tx margin to be used for scheduling is increased by the set value T _D , otherwise the Tx margin is kept at the default value (or default value). In addition, when the Tx margin is increased by T _D , the scheduler 108 drives the timer 120 to set a period for which the increased Tx margin is used. Here, it is assumed that the timer 120 is driven during the F _M frame.

The MCS level determiner 112 determines a modulation and coding scheme (MCS) level for each service flow (or terminal) according to scheduling priority. In this case, the MCS level determination unit 112 may determine the MCS level by using a Tx margin for the corresponding terminal, UL Tx power information received from the terminal, and the like.

For example, as shown in FIG. 3, the base station normalizes uplink transmission power of the terminal based on a specific uplink MCS level (for example, QPSK, 1/2) and a specific resource unit (one slot). The transmission power margin may be added to the normalized transmission power, and the added value may be compared with a preset UL MCS threshold to determine the MCS level.

The radio resource determining unit 114 determines the amount of radio resources (number of slots) to be serviced at the MCS level using the transmission power margin, the uplink transmission power information, and the like. For example, the radio resource determination unit 114 limits (or determines) the maximum data size by the corresponding uplink MCS level. The radio resource determining unit 114 allocates radio resources (number of slots) to the terminal by using available UL Tx headroom and available data size of the corresponding terminal.

For example, as shown in FIG. 4, the radio resource determining unit 114 may apply a normalized uplink transmission power 403 to which a transmission power margin is applied at a maximum uplink transmission power 401 that can be used by a corresponding terminal. By subtracting, the uplink transmission headroom 407 can be calculated. The radio resource determination unit 114 may determine the number of slots to be allocated to the terminal based on the calculated uplink transmission headroom 407. At this time, if the increased transmission margin (Tx margin + T _D ) for the corresponding terminal is applied, the number of slots allocated to the terminal is reduced than when the transmission margin is the default. That is, the present invention estimates the total transmission power (PN) of the terminal, and if it is determined that the estimated total transmission power has reached the maximum value that the terminal can support, by increasing the transmission power margin (Tx margin) to the corresponding terminal This is to reduce the number of slots allocated.

The MCS level and radio resource amount (slot number) for each service flow determined as described above are provided to the message processor 104, and the message processor 104 allocates resources based on information provided from the scheduler 108. Create and send a message (MAP message).

2 illustrates a procedure for setting a transmit power margin (Tx margin) used for uplink scheduling in a base station according to an embodiment of the present invention.

Referring to FIG. 2, in step 201, the base station initializes the parameter C _SET value to '0' and initializes the transmission power margin (Tx margin) to the default value (T _FIXED ). In other words, various parameters required for algorithm execution are initialized.

In step 203, the base station determines whether uplink transmission power (UL Tx power) information is received from the corresponding terminal. When the uplink transmission power information is received, the base station proceeds to step 205 and sets the C _SET value to '0'. That is, when uplink transmission power information is received, the setpoint value is initialized to '0' by considering that the outer loop power control information is already reflected in the uplink transmission power.

In step 207, the base station determines whether an uplink burst is received from the terminal. When the uplink burst is received, the base station determines whether an error occurs in the uplink burst. If an error occurs in the uplink burst, the base station proceeds to step 209 and increases the C _SET value by a set value T _P and then proceeds to step 213. On the other hand, if no error occurs in the uplink burst, the base station proceeds to step 211 and decreases the C _SET value by '1' and proceeds to step 223.

After increasing the C _SET value, the base station checks whether a timer for setting a period for adjusting a current transmission power margin is running in step 213. If the timer is running, the base station proceeds to step 223 because the scheduling is performed with the transmission power margin increased by the current T _D. On the other hand, if the timer is not running, the base station proceeds to step 215 to calculate the total transmit power (P _N ) of the terminal. In this case, the base station may calculate the total transmit power (P _N ) of the terminal as shown in Equation 2.

After calculating the total transmit power P _N of the terminal, the base station compares the total transmit power P _N value of the terminal with a reference value PTH in step 217. If the total transmit power (P _N ) value of the terminal is smaller than the reference value, the base station proceeds to step 223. On the other hand, if the total transmit power (P _N ) value of the terminal is greater than or equal to the reference value, the base station proceeds to step 218 and the transmit power margin (T _MARGIN ) of the terminal to the value of [T _FIXED + T _D ] Set it. That is, when it is determined that the maximum value that can be supported by the total transmission power of the terminal is reached, the transmission power margin is set to a value increased by T _D from the default value T _FIXED . As such, the reason for increasing the transmission power margin is to reduce the number of slots to be allocated to the terminal.

As such, when the transmission power margin is adjusted, the base station drives the timer for setting a period during which the transmission power margin is adjusted in step 221. For example, the timer may be driven for a set number of frame periods (FM).

Meanwhile, the base station checks whether the timer expires in step 223. If the timer expires, the base station proceeds to step 225 and sets the transmission power margin T _MARGIN to a default value T _FIXED and returns to step 203. On the other hand, if the timer is running, the base station returns to step 203 to continue receiving the uplink signal from the terminal.

The present invention sets a transmission power margin (Tx margin: T _MARGIN ) used for uplink scheduling as shown in FIG. The transmission power margin set through FIG. 2 may be used to determine the MCS level and the number of slots to be allocated to the uplink of the 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.

1 is a diagram illustrating a configuration of a base station in a wireless communication system according to an embodiment of the present invention.

2 is a diagram illustrating a procedure for setting a transmit power margin (Tx margin) used for uplink scheduling in a base station according to an embodiment of the present invention.

3 is a diagram illustrating an MCS level determination method according to a transmission power of a terminal according to an embodiment of the present invention.

4 is a diagram illustrating a radio resource allocation method using available uplink headroom of a terminal according to an embodiment of the present invention.

Claims (18)

A base station apparatus in a wireless communication system, A calculator for estimating the total transmit power (P _N ) of the terminal; A margin determining unit that adjusts a transmission power margin T _MARIN greater than a default value for a set period when the total transmission power P _N of the terminal is greater than or equal to the reference value P _TH ; And a radio resource determination unit for determining the number of slots to be allocated to the terminal using the transmission power margin determined by the margin determination unit. The method of claim 1, And a management unit for updating the parameter C _SET by using UL Tx power information received from the terminal and an error of an uplink burst received from the terminal. The method of claim 2, When the UL Tx power information is received, the management unit initializes the parameter C _SET to '0', and increases the set value T _P when an error occurs in the uplink burst. If the error does not occur in the uplink burst, characterized in that for reducing by '1'. The method of claim 3, The set value (TP) is characterized in that determined by the following formula. T _P = (1- Target BER) / Target BER The method of claim 3, And the management unit increases the parameter C _SET by T _P when an error occurs in any one burst when there is at least two bursts of the corresponding terminal in a frame. The method of claim 3, And the management unit updates the parameter C _SET with respect to an initial transmission burst for a HARQ connection. The method of claim 3, The total transmission power (P _N ) of the terminal is characterized in that calculated by the following equation.

Here, P _{Tx, REF} is a UL TX power [dBm] per subcarrier transmitted by the terminal, SINR [MCS] is a value [dB] to ensure the required BER is predetermined for each MCS level, MCS _REF is a terminal and P _Tx, MCS level at the time of transmitting the _REF, MCS _n is an MCS level of the n-th frame time, n _SubCh is a frequency axis slot number assigned to the terminal in the n-th frame, n _SubCr is the first slot The number of subcarriers included and P _D is the step size [dB] used to increase the set point when an uplink burst error occurs. The method of claim 1, And a determining unit to determine an MCS level to be allocated to the uplink of the terminal by using the uplink transmission power information received from the terminal and the transmission power margin. The method of claim 1, The radio resource determination unit calculates a headroom of the terminal using the transmission power margin (T _MARIN ), uplink transmission power (UL Tx power) information received from the terminal and the maximum transmission power of the terminal. And determining the number of slots to be allocated to the terminal based on the headroom. In the method of operation of a base station in a wireless communication system, Estimating the total transmit power (P _N ) of the terminal; If the total transmit power (P _N ) of the terminal is greater than or equal to the reference value (P _TH ), adjusting the transmit power margin (T _MARIN ) to a greater than the default value for a set period; And decreasing the number of slots to be allocated to the terminal by increasing the transmission power margin during the setting period. The method of claim 10, And updating the parameter C _SET by using UL Tx power information received from the terminal and an error of an uplink burst received from the terminal. The method of claim 11, wherein the updating process, Initializing the parameter C _SET to '0' when the UL Tx power information is received; When an error occurs in an uplink burst, increasing the parameter C _SET by a set value T _P ; If an error does not occur in an uplink burst, reducing the parameter C _SET by '1'. The method of claim 12, The set value (TP) is characterized by the following formula. T _P = (1- Target BER) / Target BER The method of claim 12, wherein increasing the parameter C _SET comprises: And at least two bursts of the corresponding terminal in a frame, if an error occurs in any one burst, increases the parameter C _SET by T _P. The method of claim 12, The parameter C _SET is updated for an initial transmission burst for a HARQ connection. The method of claim 12, The total transmission power (P _N ) of the terminal is characterized in that it is calculated by the following equation.

Here, P _{Tx, REF} is a UL TX power [dBm] per subcarrier transmitted by the terminal, SINR [MCS] is a value [dB] to ensure the required BER is predetermined for each MCS level, MCS _REF is a terminal and P _Tx, MCS level at the time of transmitting the _REF, MCS _n is an MCS level of the n-th frame time, n _SubCh is a frequency axis slot number assigned to the terminal in the n-th frame, n _SubCr is the first slot The number of subcarriers included and P _D is the step size [dB] used to increase the set point when an uplink burst error occurs. The method of claim 10, And determining the MCS level to be allocated to the uplink of the terminal by using the uplink transmission power information received from the terminal and the transmission power margin. The method of claim 10, wherein the determining of the number of slots comprises: Calculating a headroom of the terminal using the transmission power margin (T _MARIN ), uplink transmission power (UL Tx power) information received from the terminal, and maximum transmission power of the terminal; And determining the number of slots to be allocated to the terminal based on the headroom.

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