KR100801289B1 - Scheduling method and apparatus for uplink resource allocation in ofdma system - Google Patents

Abstract

A method and an apparatus for scheduling uplink resource allocation in an OFDMA(Orthogonal Frequency Division Multiple Access) system are provided to decrease a hardware complexity by determining a wireless resource allocated to a user terminal by using a distance between a base station and the terminal. An LUT(Look-Up Table)(160) stores wireless resource allocation values classified by corresponding to a distance between a base station and a user terminal, a maximum transmission power of the user terminal, and an interference level of the base station. A terminal position measuring unit(120) calculates the distance value from a ranging signal received from the user terminal. An interference level measuring unit(130) measures an interference level value. A scheduler(140) receives the distance and interference values, provides the values as address values to the LUT, and reads the wireless resource allocation values from the LUT. A wireless resource allocator(150) receives the allocation values and allocates the wireless resources to the user terminal corresponding to the wireless resource allocation value.

Description

Scheduling method and apparatus for uplink resource allocation in orthogonal frequency division multiple access system

1 is a diagram illustrating an MCS level and a number of subchannels that can be allocated to a subscriber station calculated based on a path loss estimation value according to an embodiment of the present invention.

2 is a diagram illustrating an uplink scheduling apparatus in an orthogonal frequency division multiple access system according to an embodiment of the present invention.

3 is a flowchart illustrating an uplink scheduling method in an orthogonal frequency division multiple access system according to an embodiment of the present invention.

The present invention relates to an uplink scheduling method and an apparatus in an Orthogonal Frequency Division Multiplexing Access (OFDMA) communication system, and more particularly to a modulation and coding scheme (hereinafter referred to as "modulation and coding scheme"). MCS ") and uplink scheduling method for allocating bandwidth, and an apparatus thereof.

In the 4th Generation ("4G") communication system, which is the next generation communication system, an active research for providing users with services having various Quality of Service (QoS) with a transmission rate of about 100 Mbps Is going on.

Meanwhile, wireless local area network ("LAN") systems and wireless metropolitan area network ("MAN") systems generally support transmission rates of 20 Mbps to 50 Mbps. Therefore, the current 4G communication system supports the high-speed service to be provided to the 4G communication system by developing a new communication system in the form of guaranteeing mobility and QoS in the wireless LAN system and the wireless MAN system that guarantee a relatively high transmission speed. There is a lot of research going on.

In order to solve this problem, the 4G communication system actively researches an orthogonal frequency division multiplex (OFDM) scheme as a method useful for high-speed data transmission in a wired or wireless channel, and the OFDM scheme is a multi-carrier ( A method of transmitting data using a multi-carrier, wherein a plurality of subcarriers, that is, a plurality of subcarriers having mutually orthogonality, are converted into a parallel sequence of symbol strings input in parallel. It is a kind of Multi Carrier Modulation (MCM) scheme that modulates and transmits sub-carrier channels.

The OFDMA scheme is a multiplexing scheme combining a frequency division scheme using a plurality of orthogonal frequency subcarriers as a plurality of subchannels and a time division (TDM) scheme. The OFDMA scheme is inherently resistant to fading occurring in a multipath and has a high data rate.

Meanwhile, in the OFDMA communication system, in order to support high-speed data transmission through a wireless channel, an adaptive modulation and coding (AMC) scheme is particularly used. The AMC scheme refers to a data transmission scheme in which different modulation schemes and coding schemes are determined according to a cell state, that is, a channel state between a base station and a subscriber station, thereby improving use efficiency in the entire cell.

The AMC scheme has a plurality of modulation schemes and a plurality of coding schemes, and modulates and codes a channel signal by combining the modulation schemes and the coding schemes. Typically, each of these combinations of modulation schemes and coding schemes is called a modulation and coding scheme (MCS), and a plurality of MCSs are defined from level 1 to level N according to the number of such MCSs. One of the levels of the MCS is adaptively determined according to the channel state between the subscriber station and the base station that is currently wirelessly connected.

In addition, in the OFDMA communication system, it is possible to vary the bandwidth (number of subchannels) allocated for uplink data transmission of the subscriber station according to the channel environment. That is, the subscriber station near the base station may allocate a high MCS level and use the entire subchannels because the path loss is small during data transmission, and the subscriber station in the cell boundary region has a low MCS level because the path loss is large during data transmission. And only one or two subchannels can be used.

In order to change radio resources such as MCS level or bandwidth allocated to the subscriber station, information that can know channel information is required, and the MCS level or bandwidth is changed based on this information. On the other hand, the selection of the optimal MCS level and bandwidth to be used for uplink data transmission may be performed at the subscriber station or the base station. However, when the subscriber station selects the network, traffic control or real-time support in the network is difficult, so it is preferable to control the base station. .

To this end, the base station uses a signal loss-to-noise ratio (Signal-to-) depending on the path loss, which means power loss according to the distance between the base station and the terminal, the interference level (hereinafter referred to as "NI"), and the MCS level. Optimum MCS level and bandwidth should be allocated for uplink data transmission by considering Interference-and Noise Ratio (SINR).

The IEEE 802.16 standard stipulates that only the combination of MCS level and bandwidth satisfying the condition of Equation 1 described below is allocated to each subscriber station in consideration of the transmission power limit of the subscriber station for uplink resource allocation.

: Scheduling 하고자 하는 burst의 최대 점유 반송파수. Burst가 여러 심볼에 걸쳐있을 경우 각 심볼의 점유 반송파 중 가장 많은 반송파수를 의미.

: Maximum occupied carrier of burst to be scheduled. When burst is spread over several symbols, it means the largest number of carriers occupied by each symbol.

: 전송하고자 하는 상향 burst의 MCS 레벨이 요구하는 수신 SINR값.

: Receive SINR value required by MCS level of uplink burst to be transmitted.

: 기지국 수신단에서의 반송파당 간섭 및 잡음수준(dBm) 추정치

: Estimated per-carrier interference and noise level (dBm) at base station receiver

: UL(UpLink) burst의 반복 횟수

: Number of repetitions of UL (UpLink) burst

: 가입자 단말의 최대 전송전력

: Maximum transmission power of subscriber station

: 상향링크 경로손실

Uplink Path Loss

: 가장 최근에 보고된 상향전송에 사용된 전력

: Most recently reported power used for uplink transmission

: 상향 전송전력에 대한 가장 최근보고 이후 이 값에 대한 보정값

: Correction value for this value since the most recent report on uplink transmission power.

: 상향 전송전력을 보고한 burst의 수신전력

: Burst received power reporting uplink transmission power

As shown in Equation 1, the base station uses the maximum transmission power ( P _ULMAX ), the uplink path loss ( L _UL ), and the interference level ( NI _UL ) value to repeat the uplink burst to the subscriber station. Radio resources such as (R), MCS level and bandwidth (number of subchannels) can be allocated. Meanwhile, the SINR _req , NI _UL, and P _{ULMAX shown in} Equation 1 The value is a value already known by the measurement at the base station.

That is, when the smaller the path loss (L _UL) as shown in equation (1), but to keep the subscriber terminal and also part-per-channel received power assigned to the subchannel all to a certain level, the path loss (L _UL) this time is greater With limited transmit power, it is difficult to maintain the received power per subchannel above a certain level. Therefore, the number of subchannels is reduced and the transmit power per subchannel is increased to maintain the receive power per subchannel at a constant level.

As described above, if the base station knows only an uplink path loss ( L _UL ) value, it is possible to allocate an optimal MCS level and bandwidth to the subscriber station according to the radio channel environment. However, in order to obtain the uplink path loss L _UL as shown in Equation 2, the subscriber station should report the transmit power ( P _UL ) of the subscriber station used for uplink data transmission to the base station, and the base station transmits the uplink transmitted. The reception power ( P _{UL _ BS} ) of the link data should be measured.

This causes the subscriber station to report the transmission power to the base station whenever the uplink data is transmitted. In addition, the algorithm for measuring the base station reception power of the signal transmitted by a specific terminal in the base station is very complicated and there is a problem that the complexity of hardware to implement this increases. In addition, even if the base station measures the base station reception power of a signal transmitted by a specific terminal, it is difficult to accurately measure the reception power due to the characteristics of a mobile wireless environment, and a standard deviation of about 8 to 12 dB is usually generated.

An object of the present invention is to provide an uplink scheduling method and apparatus for improving accuracy and reducing hardware complexity when performing uplink scheduling in an orthogonal frequency division multiple access system.

In an orthogonal frequency division multiple access communication system according to a feature of the present invention for achieving the above object, an uplink scheduling apparatus for allocating radio resources to a subscriber station by a base station includes:

A lookup table for storing radio resource allocation values classified according to distance values between the base station and the subscriber station, a maximum transmit power value of the subscriber station, and an interference level value of the base station; A terminal position estimator for calculating and outputting the distance value from the ranging signal received from the subscriber station; An interference level measuring unit measuring and outputting the interference level value; A scheduler for receiving the distance value and the interference level value, inputting the address value of the lookup table together with the maximum transmit power value of the subscriber station, and reading and outputting the radio resource allocation value from the lookup table; And a radio resource allocator configured to receive the radio resource allocation value and allocate radio resources to the subscriber station in response to the radio resource allocation value.

Meanwhile, in an orthogonal frequency division multiple access communication system according to another aspect of the present invention, an uplink scheduling method in which a base station allocates radio resources to a subscriber station,

a) receiving a ranging signal from the subscriber station and calculating a distance value between the base station and the subscriber station from the ranging signal; b) a distance value calculated in step a) from a lookup table storing distance values between the base station and the subscriber station, radio resource allocation values classified according to the base station's maximum transmit power value and the base station's interference level value; Reading a radio resource allocation value corresponding to the radio resource allocation value; And c) allocating a radio resource to the terminal in response to the radio resource allocation value.

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

Next, a method of obtaining a path loss estimation value from a distance between a base station and a subscriber station, that is, a location of a subscriber station, calculated through ranging in an OFDMA communication system according to an embodiment of the present invention will be described.

In an OFDMA communication system, a base station receiver demodulates a transmission signal of each terminal after performing a fast fourier transform (FFT) on an uplink signal received at an antenna. In this case, if the signals transmitted by the respective terminals do not reach the base station receiver within the CP (Cyclic Prefix) period from the demodulation reference time, demodulation is impossible, and the performance of the channel estimator decreases as the signal is received away from the demodulation reference time. Therefore, it is necessary to control the transmission time so that the transmission signals of the subscriber stations reach the reference time. To this end, in the OFDMA communication system, a range for adjusting the power level and adjusting the power level is precisely adjusted between the base station and the subscriber station. ranging) is required.

Four ranging modes are defined in the physical layer of the OFDMA communication system. The ranging modes include Initial Ranging, Maintenance Ranging (ie, Periodic Ranging, Bandwidth Request ranging, and Handoff Ranging). In this mode, bandwidth request ranging is used for the purpose of the terminal requesting bandwidth from the base station, and all other modes are used for obtaining uplink synchronization and power control between the terminal and the base station.

The ranging signal is allowed to send a ranging signal from a plurality of terminals at the same time, each subscriber station is used to distinguish the ranging mode according to the above-described use. For modulation of the ranging signal, the UE randomly selects one of the available ranging codes (PN (Pseudo-random Noise) codes) and modulates and transmits BPSK (Binary Phase Shift Keying). At this time, since the subscriber station attempts ranging with a randomly selected ranging code, the subscriber station may collide with the ranging channel.

Accordingly, when the subscriber station transmits the PN code through the allocated ranging channel by BPSK modulation, the base station measures the distance d between the base station and the terminal through PN correlation and then transmits each terminal based on this. Control the timing. After the initial transmission timing of the subscriber station is determined through initial ranging, the transmission timing of the subscriber station is controlled at a predetermined time ( TPR ) through periodic ranging.

The transmission timing control unit (Δ) of the subscriber station through ranging is determined by the system clock and the maximum error of the distance measurement ( d _{max _)} obtained through the ranging when the moving speed of the terminal is v (km / h). _error ) is shown in Equation 3 below.

For example, when a 10 MHz bandwidth is used in an OFDMA communication system, the transmission timing control unit (Δ) of the terminal is 0.1 us, the periodic ranging is performed at 1 second intervals, and the movement speed of the terminal is 60 km / h. In this case, the maximum error of the distance measured during the ranging process is about 47m. If the standard deviation of the received power measured in the mobile wireless environment is about 8-12 dB, it is about 200m to 300m when converted into the path loss distance using the path loss model, and thus the path calculated based on the received power of the base station. It can be seen that the accuracy of the path loss estimate calculated from the distance between the base station and the terminal is higher than the loss estimate.

In this case, the path loss refers to a power loss occurring while a signal is transmitted from a transmitter to a receiver, that is, a power loss occurring when a signal is transmitted and received between the base station and the terminal. The path loss model corresponds to the distance between the base station and the terminal according to this characteristic. This means a simulation model for estimating path loss.

There may be various path loss models for estimating the path loss value between the base station and the terminal. An optimal path loss model may be used depending on the type of obstacle between the base station and the terminal and whether the base station and the terminal are located in the city center. have.

In the following, an example of estimating a path loss value using a Standford University interim (SUI) model among path loss models and calculating a radio resource to be allocated to the terminal will be described as an example.

FIG. 1 is a diagram illustrating an MCS level and a number of subchannels that can be allocated to a subscriber station calculated based on a path loss estimation value estimated using a path loss model according to an embodiment of the present invention. The MCS level and the number of subchannels according to the distance between the base station and the terminal calculated using the Standford university interim-type A (SUI-A), SUI-B, and SUI-C path loss models when the transmission power is 23 dBm are shown. .

As shown in FIG. 1, when the distance between the base station and the terminal is less than 500 m in the case of using the QPSK modulation scheme, the terminal may use all of the subchannels. However, when the location of the terminal is a cell boundary region 1000 m away from the base station. A maximum of three subchannels can be used by a terminal. On the other hand, in the case of using the 16QAM modulation scheme, if the distance between the base station and the terminal is within 350m, the terminal can use all the subchannels, but if the distance between the base station and the terminal exceeds 800m, it can be seen that the 16QAM modulation scheme cannot be used. have.

Hereinafter, an apparatus and a method for allocating a radio resource to a subscriber station in an OFDMA communication system according to an embodiment of the present invention will be described with reference to the drawings.

2 is a block diagram illustrating an uplink scheduling apparatus 10 for allocating radio resources to a subscriber station in an OFDMA communication system according to an exemplary embodiment of the present invention.

As shown in FIG. 2, the uplink scheduling apparatus 10 according to an embodiment of the present invention may include a maximum transmit power receiver 110, a terminal position estimator 120, an NI (interference level) measurer 130, The scheduler 140 includes a radio resource allocator 150 and a lookup table 160.

The maximum transmission power receiver 110 receives and outputs the maximum transmission power P _ULMAX from the subscriber station. Meanwhile, the uplink scheduling apparatus 10 may use a fixed maximum transmit power ( P _ULMAX ) value. In this case, the uplink scheduling apparatus 10 may not include the maximum transmit power receiver 110.

The terminal position estimator 120 calculates and outputs a distance d between the subscriber station and the base station from the ranging signal input from the subscriber station during the ranging process.

The interference level measuring unit 130 measures the interference and noise level (dBm) estimate per carrier received from the base station and outputs the interference level NI _UL accordingly.

The scheduler 140 receives the maximum transmission power, the distance d between the subscriber station and the base station, and the interference level value, inputs the address value of the lookup table 160, and the lookup table 160 outputs the corresponding value. The resource allocation value (MCS level and number of subchannels) is read and transmitted to the radio resource allocation unit 150.

The radio resource allocator 150 allocates a radio resource allocation value (MCS level and number of subchannels) received from the scheduler 150 to the corresponding subscriber station.

The lookup table 160 is a memory in which radio resource allocation values (MCS level and number of subchannels) classified according to the maximum power, the distance d between the subscriber station and the base station, and the interference level value are stored.

3 is a flowchart illustrating an uplink scheduling method in which the uplink scheduling apparatus 10 allocates radio resources to a subscriber station in an OFDMA communication system according to an embodiment of the present invention.

As shown in FIG. 3, a base station first receives a distance (d), a maximum transmit power ( P _ULMAX ), and an interference level ( NI _UL ) between a base station and a terminal as an address value, and assigns a corresponding radio address to a corresponding subscriber station. A lookup table 160 for outputting resource (MCS level and number of subchannels) values is generated and stored in a memory (S10).

To this end, the base station estimates the path loss according to the distance value d inputted to the path loss model while changing the distance value d between the base station and the terminal. At this time, the path loss model used may be selected and used by those skilled in the art in consideration of the wireless environment to which the subscriber station belongs.

Meanwhile, the path loss value ( L _UL ) versus the distance between the base station and the terminal estimated by the simulation using the path loss model as described above is allocated to the subscriber station together with the maximum transmission power ( P _ULMAX ) and the interference level ( NI _UL ). Used to construct a lookup table that classifies resources. In this case, a method of measuring the maximum transmit power ( P _ULMAX ) and the interference level ( NI _UL ) value used is generally well known and thus can be executed by those skilled in the art without detailed description.

That is, the base station calculates a path loss value ( L _UL ) by performing a simulation through a path loss model while changing the distance between the base station and the terminal, and calculates a path loss value ( L _UL ) and a maximum transmission power ( P _ULMAX ) using Equation 1 ) And the radio resources (MCS level and the number of subchannels) allocated to the subscriber station according to the NI _UL ) value and the interference level ( NI _UL ) value to obtain the lookup table 160.

At this time, as described above, the variable used as the address value of the lookup table uses the distance value d between the base station and the subscriber station, not the path loss value L _UL . This has already included the process of calculating the path loss value L _UL corresponding to the distance value d between the base station and the subscriber station in the process of creating a lookup table. It is to omit the complicated hardware addition corresponding to the complicated algorithm for obtaining L _UL ).

After the configuration of the lookup table as described above, the base station calculates the distance (d) with the subscriber station through the terminal position estimation unit 120 in the ranging process (S20). Accordingly, the scheduler 140 of the uplink scheduling apparatus 10 transmits the calculated distance value d to the maximum transmit power P _ULMAX and the interference level measurer of the subscriber station measured from the maximum transmit power measurer 110. 130) reads the number of the MCS level and the sub-channel output from the look-up table 160 inputs the address of the look-up table 160 is stored, and thus the memory in conjunction with the interference level (NI _UL) value measured by the (S30 ).

As described above, the radio resource allocator 150 receives the MCS level and the number of subchannels read from the lookup table from the scheduler 140 and assigns them to the corresponding subscriber station (S40).

As described above, in the radio resource allocation method according to an embodiment of the present invention, the radio resource to be allocated to the subscriber station is determined by using the distance between the base station and the terminal calculated in the ranging process without measuring or calculating a path loss value. As a result, hardware for measuring path loss can be omitted. In addition, since only an error less than an error occurring in the path loss measurement process, an uplink scheduling method capable of reducing hardware complexity and increasing accuracy is provided.

In addition, the present invention provides an uplink scheduling method in which hardware complexity is reduced and control is simplified by using a lookup table, which is complicatedly calculated as in Equation 1 and thus the optimal MCS level and the number of subchannels are determined.

 Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

According to an embodiment of the present invention, the radio resource allocation method may determine the radio resource to be allocated to the subscriber station using the distance between the base station and the terminal calculated in the ranging process, without having to separately measure or calculate the path loss value. It is possible to omit the hardware for measuring. In addition, the present invention provides an uplink scheduling method and apparatus capable of reducing hardware complexity and increasing accuracy since only a smaller error than an error occurring in a path loss measurement process occurs.

In addition, the present invention provides a uplink scheduling method and apparatus for reducing hardware complexity and simplifying control by using a lookup table, which is complex and has been determined to determine an optimal MCS level and the number of subchannels.

Claims (8)

An uplink scheduling apparatus in which a base station allocates radio resources to a subscriber station in an orthogonal frequency division multiple access communication system, A lookup table for storing radio resource allocation values classified according to distance values between the base station and the subscriber station, a maximum transmit power value of the subscriber station, and an interference level value of the base station; A terminal position estimator for calculating and outputting the distance value from the ranging signal received from the subscriber station; An interference level measuring unit measuring and outputting the interference level value; A scheduler for receiving the distance value and the interference level value, inputting the address value of the lookup table together with the maximum transmit power value of the subscriber station, and reading and outputting the radio resource allocation value from the lookup table; And A radio resource allocator configured to receive the radio resource allocation value and allocate radio resources to the subscriber station in response to the radio resource allocation value Uplink scheduling apparatus comprising a. The method of claim 1, Maximum transmission power receiver for receiving and outputting the maximum transmission power value from the subscriber station The uplink scheduling apparatus further comprises a. The method according to claim 1 or 2, The radio resource allocation value comprises a modulation and coding scheme level and the number of subchannels. The method of claim 1, The lookup table obtains a path loss value calculated from a distance value using a path loss model, a radio resource allocation value corresponding to the maximum transmission power value and the interference level value, and then assigns the radio resource allocation value to the distance value. Uplink scheduling apparatus characterized in that configured to correspond to the classification. An uplink scheduling method in which a base station allocates radio resources to a subscriber station in an orthogonal frequency division multiple access communication system, a) receiving a ranging signal from the subscriber station and calculating a distance value between the base station and the subscriber station from the ranging signal; b) a distance value calculated in step a) from a lookup table storing distance values between the base station and the subscriber station, radio resource allocation values classified according to the base station's maximum transmit power value and the base station's interference level value; Reading a radio resource allocation value corresponding to the radio resource allocation value; And c) allocating radio resources to the terminal in response to the radio resource allocation value; Uplink scheduling method comprising a. The method of claim 5, Before step a), A lookup table constructing step of constructing the lookup table The uplink scheduling method further comprises. The method of claim 6, The lookup table configuration step, Obtaining a path loss value for each distance value while gradually changing the distance value using the path loss model; Constructing a lookup table by obtaining a radio resource allocation value corresponding to the path loss value and classifying the radio resource allocation value according to the distance value; Uplink scheduling method comprising a. The method of claim 7, wherein The path loss model is a model for estimating a path loss corresponding to the distance between the base station and the subscriber station.

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