KR20200005365A - Separable base station system for 5G fronthaul, uplink SRS compression method and compression rate control method using the same - Google Patents

Abstract

The present invention relates to a method of a separate base station system for compressing a sounding reference signal. According to the present invention, the method calculates a change amount of a value of a second sounding reference signal and a value of a first sounding reference signal transmitted and stored from a terminal at a second time point before a first time point when the first sounding reference signal transmitted from the terminal at the first time point is received. If the calculated change amount is less than a preset threshold, the method inserts the change amount into the first sounding reference signal and transmits the change amount to a central unit (CU) through an uplink channel.

Description

Separable base station system for 5G fronthaul, uplink SRS compression method and compression rate control method using the same}

The present invention relates to a separate base station system for 5G fronthaul, an uplink control signal compression method and a compression rate control method using the same.

Due to the explosion of data traffic required in the mobile network, a base station in which a digital unit (DU) and a radio unit (RU) are separated is operating in 4G. A common public radio interface (CPRI) is used between the DU and the RU.

CPRI in 4G, when using a 2 * 2 MIMO structure to transmit the LTE signal having a 20MHz bandwidth, CPRI transmission amount is about 2.5Gbps. Such a limitation of the transmission amount is continuously increased with the continuous increase of the system capacity, thus reaching the limit of signal transmission in terms of system capacity and cost. In particular, with the evolution from LTE to 5G, the system bandwidth can be increased by five times and the number of antennas increases, resulting in the required transmission rate of CPRI from tens of Gbps to hundreds of Gbps.

When calculating the bandwidth of the limited CPRI, it is calculated using the number of single carriers, the TTI, the Sounding Reference Signal (SRS) channel estimation value, and the like. In this case, although the uplink overhead due to SRS transmission occupies at least 21%, the SRS should be periodically transmitted for channel estimation even if the uplink signal is not transmitted.

SRS is transmitted every 20ms in LTE, and in 5G needs to be implemented to be transmitted more frequently, such as 5ms, for beamforming. Accordingly, the overhead due to SRS transmission is greater than that of LTE, and there is a demand for development of a technology to reduce the overhead. In addition, techniques for compressing data transmitted to the fronthaul interface to reduce the required transmission rate of the fronthaul interface have been studied.

Accordingly, the present invention provides a separate base station system for 5G fronthaul to reduce the SRS transmission overhead in 5G, and control the compression rate and the transmission rate of the fronthaul, an uplink control signal compression method and a compression rate control method using the same.

In a separate base station system including a plurality of distributed units, which are one feature of the present invention, and a central unit interoperating with the plurality of distributed units, each of the distributed units is sounded. A method of compressing a reference signal,

Receiving a first sounding reference signal transmitted from the terminal at a first point in time, and a value of the second sounding reference signal transmitted and stored from the terminal at a second point in time before the first point of view and the first sounding reference Calculating a change amount of the value of the signal, and if the change amount is smaller than a preset threshold, inserting the change amount into the first sounding reference signal and transmitting the change amount to the central unit through an uplink channel. .

The calculating of the change amount may be calculated as an absolute value of a difference value between the value of the first sounding reference signal and the value of the second sounding reference signal.

After calculating the amount of change, if the amount of change is greater than the threshold value, the method may include compressing the first sounding reference signal according to the compression rate determined by the central unit.

After calculating the amount of change, if the amount of change is greater than the threshold value, the method may include compressing the first sounding reference signal according to the compression rate determined by the central unit.

In a separate base station system including a plurality of distributed units, and a central unit interworking with the plurality of distributed units, which are another feature of the present invention for achieving the technical problem of the present invention, the distributed units refer to sounding, respectively. As a method of compressing a signal,

Receiving a signal consisting of a sounding reference signal and a signal channel transmitted from a terminal, identifying a vector in the sounding reference signal, and estimating a wireless channel in a time domain based on the identified vector, in the estimated wireless channel Estimating an impulse response, and inserting channel information for the sounding reference signal into the impulse response.

Estimating the impulse response,

Calculating a signal channel from the received signal, obtaining the calculated signal channel as a function of changing a signal channel over time, and determining a signal channel change function according to the obtained time as a wireless channel in a time domain, wherein the time domain Obtaining a frequency response of a discrete-time linear time-invariant system from a wireless channel of the signal, and inverse discrete fourier transform (IDFT) or IFFT (inverse) Estimating the time-domain impulse response by performing a Fast Fourier Transform.

As a separate base station system of a wireless communication network which is another feature of the present invention for achieving the technical problem of the present invention,

The separate base station system is composed of a plurality of distributed units, and a central unit for interworking with the plurality of distributed units, wherein the central unit monitors the traffic load of the fronthaul connected with the plurality of distributed units, respectively, Calculates the signal-to-noise ratios of the uplink channel and the downlink channel using signals transmitted from a terminal located in any one of the plurality of distributed units, and a fronthaul throughput calculation module for calculating the fronthaul data throughput from the load A channel signal-to-noise ratio calculation module, and a transmission rate at which the terminal transmits a signal through an uplink channel and a front to transmit a signal through a downlink channel based on the calculated fronthaul data throughput and the calculated signal-to-noise ratio. Transmission rate determining hole compression rate It includes a module.

The rate determining module may determine a modulation and coding scheme (MCS) level for uplink and downlink based on the signal-to-noise ratios of the uplink channel and the downlink channel, and determine the determined MCS as the transmission rate of the terminal.

The rate determining module calculates a wireless channel capacity calculated using the signal-to-noise ratio, and calculates a distortion level for further compression of a signal based on the margin of the signal-to-noise ratio calculated based on the wireless channel capacity and the transmission rate of the terminal. Can be.

In a separate base station system including a plurality of distributed units, and a central unit interworking with the plurality of distributed units, which is another feature of the present invention for achieving the technical problem of the present invention, the central unit controls the compression rate As a method,

Monitoring a traffic load of a fronthaul connected to the plurality of distributed units, calculating a fronthaul data throughput from the traffic load, a signal transmitted from any terminal located in any one of the plurality of distributed units Calculating signal-to-noise ratios of the uplink channel and the downlink channel for the terminal, and if the calculated fronthaul data throughput is greater than a preset threshold, an MCS (Modulation) determined corresponding to the signal-to-noise ratio and Coding Scheme) level is determined as the transmission rate of the terminal, and obtaining a compression rate of the front hole based on the determined transmission rate of the terminal.

The calculating of the compression ratio of the front hole may include calculating a wireless channel capacity calculated using the signal-to-noise ratio, and if the margin of the signal-to-noise ratio calculated based on the wireless channel capacity and the transmission rate of the terminal is greater than a preset threshold, The method may include calculating a distortion level for further compressing a signal to be transmitted through the hole, and obtaining a compression ratio of the front hole by reflecting the calculated distortion level.

According to the present invention, an additional compression effect can be obtained by using time correlation of SRS transmitted from a distributed unit (DU) to a central unit (CU) due to separation of lower layer functions in 5G, thereby effectively reducing transmission overhead. .

In addition, in the case of an SRS signal having sparse characteristics in the time domain, such as a millimeter wave signal, an additional compression effect can be obtained.

In addition, when applying link adaptation, the compression ratio of the fronthaul is calculated in consideration of not only the quality of the radio link but also the data signal and the SRS signal, thus enabling more efficient use of the radio resource and the fronthaul resource.

1 is a diagram illustrating an environment to which a separate base station system according to an embodiment of the present invention is applied.
2 is an exemplary diagram in which a physical layer is partitioned according to an embodiment of the present invention.
3 is an exemplary diagram of an SRS based channel estimation structure according to a first embodiment of the present invention.
4 is a structural diagram of a separate base station system according to a first embodiment of the present invention.
5 is a flowchart illustrating a method for compressing a content link control signal according to a first embodiment of the present invention.
6 is a flowchart illustrating another uplink control signal compression method according to the first embodiment of the present invention.
7 is a structural diagram of a separate base station system according to a second embodiment of the present invention.
8 is a flowchart illustrating a transmission rate determining method according to a second embodiment of the present invention.

DETAILED DESCRIPTION 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.

Throughout the specification, when a part is said to "include" a certain component, it means that it may further include other components, except to exclude other components unless specifically stated otherwise.

In the present specification, a terminal is a mobile station (MS), a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), a user device (User). It may also refer to an Equipment (UE), an Access Terminal (AT), or the like, and may include all or some functions of a mobile terminal, a subscriber station, a portable subscriber station, a user device, and the like.

In the present specification, a base station (BS) is an access point (AP), a radio access station (Radio Access Station, RAS), a Node B (Node B), a base transceiver station (Base Transceiver Station, BTS), MMR ( Mobile Multihop Relay) -BS and the like, and may include all or part of functions such as an access point, a radio access station, a Node B, a base transceiver station, and an MMR-BS.

Hereinafter, a separate base station system for a 5G fronthaul, an uplink control signal compression method, and a compression rate control method using the same will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating an environment to which a separate base station system according to an embodiment of the present invention is applied.

As shown in FIG. 1, a 5G Radio Access Network (RAN) is mainly a central unit 100 installed in a central office and a distributed unit 200 installed in a cell site. It is constructed separately. One CU 100 is connected to a plurality of DUs 200 and configured as a separate base station system. The CU 100 and each DU 200 are connected via a fronthaul interface.

Signals transmitted and received between the CU 100 and the DU 200 through the fronthaul are transmitted and received in the form of digital I / Q data. The digital I / Q data may include general data to be transmitted, and a sounding reference signal used by the CU 100 to estimate an uplink channel with the terminal 300 located in the DU 200. Also included.

Although the terminal 300 does not transmit the uplink data to the CU 100, the terminal 300 should periodically transmit the SRS to the CU 100 for channel estimation. The SRS has a structure for estimating a channel in the frequency domain, but has a sparse characteristic in which the signal distribution is rare in the time domain in a millimeter wave (mmWave) environment.

Therefore, in the embodiment of the present invention, unlike the uplink data transmitted in a large amount of capacity, by using sparse characteristics in the time domain of the sounding reference signal, the sounding reference signal information may be compressed on the time axis to reduce overhead of the uplink. An uplink control signal compression method is proposed. In the embodiment of the present invention, the uplink control signal compression system 400 configured in the DU 200 among the detachable base station systems will be described as an example.

In addition, the CU 100 is equipped with a rate determining system 500. Due to the increase in the bandwidth and the number of antennas in the 5G environment shown in FIG. 1, the required transmission rate of the interface connecting the CU 100 and the DU 200 is increasing. As an alternative to this, the newly standardized 5G fronthaul interface (eCPRI) divides the split boundary between the CU 100 and the DU 200 into upper and lower blocks of the physical layer as shown in FIG. I suggest by dividing.

In addition, data such as I / Q signals and bit streams transmitted through the 5G fronthaul interface are compressed to lower the eCPRI transmission rate. Accordingly, in the embodiment of the present invention, the uplink control signal compression system 400 compresses an uplink signal from the DU 200 and transmits the uplink signal to the CU 100, and a rate determining system located in the CU 100 ( Also, a technique for determining a terminal transmission rate and a fronthaul compression rate in order to reduce a fronthaul rate by compressing a signal transmitted through an interface using 500) is also proposed.

First, prior to describing the uplink control signal compression system 400, physical division of the boundary between the CU 100 and the DU 200 considered in the eCRRI according to an embodiment of the present invention is divided into upper and lower blocks of the physical layer. An example of division of a layer will be described first with reference to FIG. 2.

2 is an exemplary diagram in which a physical layer is partitioned according to an embodiment of the present invention.

FIG. 2A illustrates an example in which the physical layer processing the downlink signal is divided into upper blocks and lower blocks and implemented in the CU 100 and the DU 200. In addition, FIG. 2B illustrates an example in which the physical layer of the network processing the uplink signal is divided into upper blocks and lower blocks in the CU 100 and the DU 200.

As shown in (a) of FIG. 2, in the embodiment of the present invention, a physical layer for processing a downlink signal is cyclic prefix insertion block for inserting a guard interval into the downlink signal to a modulation block for modulating the signal. Is placed in the DU 200 as a lower block, and is located in the CU 100 up to a coding module encrypted from the scrambling block as an upper block. The lower block and the upper block interlock with the interface I _D.

In an embodiment of the present invention, the DU is configured by using a physical layer for processing a downlink signal as a lower block from a cyclic prefix insertion block for inserting a guard interval into the downlink signal to a block for mapping a resource element. It may be located in the (200), it may be located in the CU (100) from the coding module for encrypting the downlink signal to the module for confirming the precoding transmission power as an upper block. The lower block and the upper block also interwork with the interface II _D.

On the other hand, the physical layer processing the uplink signal is located in the DU (200) with a lower block from the block to remove the cyclic prefix from the uplink signal to the block to unmap resource resources, and from the block for estimating the channel Positioning up to the decoding block as the upper block in the CU 100 is shown as an example. The lower block and the upper block interwork with the interface I _U.

Since the first embodiment of the present invention describes a signal compression system for uplink signal processing, as shown in (b) of FIG. 2, the upper blocks and lower layers of the physical layer are assigned to the CU 100 and the DU 200. Each block is implemented, and it demonstrates to an example which interlocks with the interface I _U. In the second embodiment of the present invention, since both uplink and downlink signal processing are considered, the upper block and the lower block are not separately described in any one form.

Next, the sounding reference signal value is confirmed in the uplink signal transmitted from the terminal 300, and based on this, the control information section is compressed among the uplink signals in various forms, and the uplink due to the sounding reference signal transmission is performed. A system and method for reducing the overhead of a link channel is described with reference to FIGS. First, a sounding reference signal based channel estimation structure will be described with reference to FIG. 3.

3 is an exemplary diagram of a sounding reference signal based channel estimation structure according to a first embodiment of the present invention.

As shown in FIG. 3, the terminal 300 having M antenna arrays measures a change value of the received signal strength received for a predetermined time, and sounds the measured value in a specific frame of the uplink signal. It is inserted as a reference signal and transmitted to the DU 200 according to a preset period. In LTE, the terminal 300 is generally transmitted in a cycle of 20 ms or more, but in 5G, the terminal 300 transmits to the DU 200 in a 5 ms cycle that is more frequent than a cycle transmitted in LTE for beamforming.

Here, a subframe in which the sounding reference signal is transmitted will be described together with reference to FIG. 4.

4 is an exemplary diagram of a subframe in which a sounding reference signal is transmitted.

As shown in FIG. 4, the sounding reference signal is transmitted to the DU 200 through one SC-FDMA symbol in a subframe. Although the sounding reference signal is transmitted to the last symbol among the plurality of symbols constituting the subframe, the position and the number are not necessarily limited.

The sounding reference signal has a structure that allows the DU 200 to estimate the terminal channel in the frequency domain. However, in a millimeter wave (mmWave) environment, the sounding reference signal is sparse in the time domain.

Therefore, unlike normal uplink data, a time existing between two adjacent sounding reference signal values based on a sparse characteristic in the time domain of the sounding reference signal or according to a transmission period in which the sounding reference signal value is transmitted. Time correlation may be used to compress the sounding reference signal. A method of compressing a sounding reference signal in the DU 200 of the separate base station system will be described with reference to FIGS. 5 and 6.

5 is a flowchart illustrating a method for compressing a uplink control signal according to a first embodiment of the present invention, and FIG. 6 is a flowchart illustrating another uplink control signal compression method according to a first embodiment of the present invention.

First, as shown in FIG. 5, the DU 200 receives a first sounding reference signal transmitted in an arbitrary antenna array from the terminal 300 having a plurality of antenna arrays (S100). The DU 200 checks the value of the second sounding reference signal stored in the DU 200 by the terminal 300 transmitting the first sounding reference signal transmitted from another antenna array in a previous sounding reference signal transmission period. (S110).

The DU 200 has a time correlation in the sounding reference signal using the first sounding reference signal received in step S100 and the second sounding reference signal received from the terminal 300 according to a transmission period before step S100. Check whether or not (S120).

In an embodiment of the present invention, Equation 1 is used to determine whether a time correlation exists in a sounding reference signal.

That is, the time difference is correlated with the sounding reference signal by checking whether a difference between the value of the second sounding reference signal as the previous sounding reference signal and the value of the first sounding reference signal as the current sounding reference signal is smaller than a preset threshold. It is determined whether there exists (S130). According to an embodiment of the present invention, whether the time correlation exists by using the difference between two sounding reference signal values may be checked, or the time correlation may be determined by comparing the movement speed of the terminal and the transmission period of the sounding reference signal. .

If the absolute value is smaller than the threshold as a result of checking in step S130, it is confirmed that time correlation exists in the sounding reference signal, and the DU 200 only changes the amount between the first sounding reference signal and the second sounding reference signal. The sounding reference signal is changed to be transmitted (S140). At this time, compression information indicating that the sounding reference signal includes only the change amount is also included.

The DU 200 transmits an uplink signal including the sounding reference signal changed in step S140 to the CU 100 (S150). Using this scheme, since the sounding reference signal in the uplink signal transmitted to the CU 100 includes only the variation information, it is more effective than the conventional sounding reference signal including the value of the sounding reference signal. .

On the other hand, if it is determined in step S130 that no time correlation exists in the sounding reference signal, the DU 200 compresses the sounding reference signal according to the compression rate determined by the CU 100 (S160). The uplink signal including the compressed sounding reference signal is transmitted to the CU 100 (S170).

In FIG. 5, an example in which only a change amount of the sounding reference signal changed with time when the time correlation exists in the sounding reference signal has been described. Next, a method of compressing and transmitting a sounding reference signal by estimating a time domain radio channel using a vector of the sounding reference signal will be described with reference to FIG. 6.

As shown in FIG. 6, when the DU 200 receives a sounding reference signal transmitted from the terminal 300 (S200), the DU 200 checks a vector in the sounding reference signal (S210). Basically, the sounding reference signal is composed of several symbols in the frequency domain, and several symbols may be mathematically represented as a vector. In this case, the expressed vector corresponds to the vector checked in step S210.

For example, assuming that a sounding reference signal is transmitted on a total of 1024 OFDM subcarriers, 1024 symbols constitute one vector, and thus, the frequency domain channel characteristics of the entire frequency band can be determined through the vector. Specifically, through the sounding reference signal transmission, the channel may be estimated with the change of the reception vector (phase and amplitude) relative to a known transmission vector (phase and amplitude).

The DU 200 estimates the radio channel in the time domain instead of the channel estimation value in the frequency domain using the vector of the sounding reference signal identified in step S210 (S220). In order to estimate the radio channel in the time domain, the DU 200 estimates an impulse response of the radio channel (S230).

In general, the received signal y, which receives the signal transmitted from the UE by the DU 200, is composed of a convolution of the signal channel h and the transmitted signal x (y = h * x). When the DU 200 receives the received signal, the signal channel h may be obtained. If the DU 200 is repeatedly performed according to time, the DU 200 may obtain a function h (t) or h [n] according to a change in time t. Here, h (t) means a radio channel value of the time domain to be estimated according to an embodiment of the present invention.

When the DU 200 estimates the frequency domain channel using the sounding reference signal, it is equivalent to obtaining H (k), which is a frequency response of a discrete-time linear time-invariant system. When H (k) is obtained, the DU 200 may obtain h [n], which is a time domain impulse response, through an Inverse Discrete Fourier Transform (IDFT) or an Inverse Fast Fourier Transform (IFFT).

For radio channels with sparse characteristics in the time domain, such as the channel characteristics of millimeter waves (mmWave), the impulse response in the time domain has a value of 0 for most n. In this case, transmitting n with a nonzero value and h [n] at that time as data has the effect of delivering a much smaller amount of data than delivering both the entire frequency response H (k).

When the DU 200 checks the impulse response h (n) of the radio channel in the time domain in which the sounding reference signal is inserted, the DU 200 inserts channel information in the impulse response (S240).

Through the above procedure, the DU 200 may compress uplink sounding reference signal data to reduce transmission overhead caused by transmitting the sounding reference signal. Next, a method of lowering a transmission rate of a fronthaul by compressing data transmitted through an interface in a separate base station system according to an embodiment of the present invention is proposed. In the embodiment of the present invention, for the convenience of description, the function of determining the transmission rate and the compression rate in the CU 100 will be described as an example by the transmission rate determination system 400.

7 is a structural diagram of a separate base station system according to a second embodiment of the present invention.

As shown in FIG. 7, the rate determination system 400 located in the CU 100 includes a fronthaul throughput calculation module 410, a channel signal-to-noise ratio calculation module 420, a data rate determination module 430, and rate information. Providing module 440.

The fronthaul throughput calculation module 410 monitors the fronthaul traffic load to calculate data throughput of the fronthaul. The fronthaul throughput calculation module 410 may monitor the fronthaul traffic load and the method of calculating the data throughput of the current fronthaul based on the monitored fronthaul traffic load in various ways. Therefore, the embodiment of the present invention is not limited to any one method.

The channel signal to noise ratio calculation module 420 estimates the signal to noise ratio of the uplink channel based on the uplink signal transmitted from the terminal 300. In addition, the channel signal-to-noise ratio calculation module 420 estimates the signal-to-noise ratio of the downlink channel using channel information or channel reciprocity fed back from the terminal 300 through the downlink. Since the channel signal-to-noise ratio calculation module 420 may estimate the signal-to-noise ratio of the uplink channel and the signal-to-noise ratio of the downlink channel in various ways, embodiments of the present invention are not limited to any one method.

In general, when the compression ratio of the signal is increased to decrease the transmission rate of the interface of the fronthaul, the distortion generated when the compressed signal is restored is increased. For example, when transmitting an uplink signal, it is assumed that the DU 200 compresses a signal received from the terminal 300 and transmits the compressed signal to the CU 100 through the fronthaul. When the DU 200 lowers the front rate by increasing the signal compression rate, the signal received by the CU 100 has much distortion, and the signal to distortion plus noise ratio (SDNR) is lowered.

In addition, when the CU 100 transmits a downlink signal, link adaptation that adapts a modulation scheme or a coding rate of error correction according to the quality of a radio channel in consideration of the transmission rate and the signal compression ratio of the fronthaul is applied. This is possible. Conversely, the compression ratio of the fronthaul may be determined by using the link adaptation result and the signal-to-noise ratio information of the terminal.

Accordingly, the data rate determining module 430 is a data rate that the terminal transmits a signal through an uplink channel and a front to transmit a signal through the downlink channel according to the throughput of the front hole calculated by the front hole throughput calculation module 410. Determine the compressibility of the hole. This will be described later in detail.

The data rate providing module 440 transmits the compression rate of the fronthaul or the data rate of the terminal 300 determined by the data rate determining module 430 to the CU 100 or the DU 200.

A method of determining the compression rate of the front hole and the transmission rate of the terminal by the rate determining system 400 described above will be described with reference to FIG. 8.

8 is a flowchart illustrating a transmission rate determining method according to a second embodiment of the present invention.

As shown in FIG. 8, the rate determining system 400 monitors the fronthaul traffic load and calculates data throughput of the fronthaul (S300). The rate determining system 400 calculates a signal-to-noise ratio for each of the uplink channel and the downlink channel (S310).

Here, when the rate determining system 400 receives the channel information fed back from the terminal 300, the rate determining system 400 may estimate the signal-to-noise ratio of the downlink channel using channel reciprocity. In addition, the signal-to-noise ratio of the uplink channel may be estimated based on the uplink signal transmitted from the terminal 300. A method of estimating a signal-to-noise ratio of a downlink channel using channel reversibility, or a method of estimating a signal-to-noise ratio of an uplink channel based on an uplink signal is already known. In one embodiment of the present invention, It does not limit to description.

When the fronthaul throughput, the signal-to-noise ratio of the uplink channel, and the signal-to-noise ratio of the downlink channel are calculated, the rate determining system 400 checks whether the fronthaul throughput determined in step S300 is greater than or equal to a preset threshold (S320). This is to maximize the transmission rate of the terminal when the throughput is sufficient to process the signal in the fronthaul, and to increase the compression rate of the fronthaul and lower the transmission rate of the terminal when the throughput is not sufficient.

First, if it is determined in step S320 that the fronthaul throughput is greater than or equal to the threshold value, the rate determining system 500 first calculates the rate of the terminal (S330). To calculate the terminal rate, the rate determining system 400 adjusts the modulation and coding scheme (MCS) levels for the uplink and the downlink based on the signal-to-noise ratio of the uplink channel and the signal-to-noise ratio of the downlink channel calculated in step S310. Decide

The terminal 300 determines a transmission rate, which is a transmission rate at which data is transmitted through a channel, based on the determined MCS level. In this case, the rate determining system 400 determines a rate using reference information previously stored in the data rate determining module 430. The reference information refers to an MCS level corresponding to a signal-to-noise ratio of a terminal. Reference information stored in the data rate determining module 430 is as shown in Table 1 below.

MCS level Signal to noise ratio of the terminal One 1 dB to 3 dB 2 3 dB to 5 dB 3 5 dB to 7 dB 4 7dB ~ 9dB … …

An example of determining the data rate by the data rate determining module 430 will be described with reference to Table 1, if the uplink signal-to-noise ratio calculated by the channel signal-to-noise ratio calculating module 420 is 2 dB, the data rate determining module 430 Determines the MCS level to be 1. In the embodiment of the present invention, the mapping between the MCS level and the transmission rate will be described as an example. In this case, the data rate determination module 430 determines the transmission rate as 1 dB.

The transmission rate determination system 400 calculates an uplink signal-to-noise ratio (R_margin) when calculating the transmission rate of the terminal in operation S330 (S331). The rate determining system 400 calculates a margin of the signal-to-noise ratio using Equation 2 below.

Here, C is calculated as 'log (1 + S / N)' as the radio channel capacity, and R_ue means the transmission rate of the terminal calculated in step S230.

The rate determining system 400 checks whether the SNR margin calculated in step S331 is greater than a preset threshold. If the SNR margin is smaller than the threshold, the transmission rate calculated in step S330 is determined as the transmission rate of the terminal (S335).

However, if the SNR margin is greater than the threshold, it means that the signal can be further compressed by the SNR margin. Accordingly, the rate determining system 400 calculates the distortion level D using the following equation (3) (S333).

Where S is the signal strength where the signal-to-noise ratio is calculated and N is the noise strength where the signal-to-noise ratio is calculated.

The transmission rate determination system 400 having calculated the distortion level in operation S333 calculates the compression ratio of the front hole to compress the signal at a transmission rate corresponding to the calculated distortion level and transmit the signal through the front hole (S334). Here, the compression rate R_frthl of the front hole is calculated by using Equation 4 below.

Here, sigma ² means dispersion.

The rate determining system 400 calculates the compression rate of the front hole in step S334, and then transmits the terminal rate calculated in step S330 to the terminal (S335). In addition, even if the SNR margin is less than the threshold in step S332, step S335 is performed.

On the other hand, as a result of checking in step S320, when the fronthaul throughput is less than the threshold, the rate determination system 400 determines to increase the compression rate of the fronthaul and lower the transmission rate of the terminal.

Accordingly, the rate determining system 400 calculates the compression rate R_frthl of the front hole based on the front hole throughput (S340). Here, the compression ratio of the front hole is determined by the limit of the front hole capacity, so that the compression ratio of the front hole is arbitrarily determined to meet the limit. The distortion level corresponding to the compression ratio of the front hole calculated in step S340 is calculated using Equation 5 (S350).

After calculating the distortion level, the rate determining system 400 calculates the channel capacity C using Equation 6 (S342).

Where S is the signal strength used when calculating the signal-to-noise ratio, and N is the noise strength.

When the channel capacity is calculated according to the step S342, the rate determining system 400 determines the largest value among the available MCS levels smaller than the channel capacity calculated in the step S342 as the terminal transmission rate (S343). The determined terminal transmission rate is transmitted to the terminal 300 (S344).

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.

Claims (11)

In a separate base station system composed of a plurality of distributed units and a central unit interoperating with the plurality of distributed units, each of the distributed units compresses a sounding reference signal,
Receiving a first sounding reference signal transmitted from a terminal at a first time point,
Calculating a change amount of the value of the second sounding reference signal and the value of the first sounding reference signal transmitted and stored from the terminal at a second time point before the first time point,
If the change amount is smaller than a preset threshold, inserting the change amount into the first sounding reference signal and transmitting the change amount to the central unit through an uplink channel.
Sounding reference signal compression method comprising a. The method of claim 1,
Calculating the amount of change,
And calculating the absolute value of the difference between the value of the first sounding reference signal and the value of the second sounding reference signal. The method of claim 2,
After calculating the amount of change,
If the amount of change is greater than the threshold, compressing the first sounding reference signal according to a compression ratio determined by the central unit
Sounding reference signal compression method comprising a. In a separate base station system composed of a plurality of distributed units and a central unit that cooperates with the plurality of distributed units, the distributed units each compress a sounding reference signal,
Receiving a signal consisting of a sounding reference signal and a signal channel transmitted from a terminal,
Identifying a vector from the sounding reference signal and estimating a wireless channel in a time domain based on the identified vector;
Estimating an impulse response in the estimated wireless channel, and
Inserting channel information for the sounding reference signal into the impulse response
Sounding reference signal compression method comprising a. The method of claim 4, wherein
Estimating the impulse response,
Calculating a signal channel from the received signal;
Obtaining the calculated signal channel as a function of changing a signal channel over time, and determining the obtained signal channel change function as a wireless channel in a time domain;
Obtaining a frequency response of a discrete-time linear time-invariant system from the wireless channel in the time domain, and
Estimating the time-domain impulse response by performing an Inverse Discrete Fourier Transform (IDFT) or an Inverse Fast Fourier Transform (IFFT) on the frequency response of the time-dependent modified time-invariant system.
Sounding reference signal compression method comprising a. A separate base station system in a wireless communication network,
The separate base station system is composed of a plurality of distributed units, and a central unit for interworking with the plurality of distributed units, the central unit,
A fronthaul throughput calculation module for monitoring a traffic load of a fronthaul connected to each of the plurality of distributed units and calculating a fronthaul data throughput from the traffic load,
A channel signal-to-noise ratio calculation module for calculating signal-to-noise ratios of the uplink channel and the downlink channel using signals transmitted from a terminal located in any one of the plurality of distributed units, and
A rate determining module for determining a transmission rate at which the terminal transmits a signal through an uplink channel and a compression rate of a fronthaul at which the terminal transmits a signal through a downlink channel based on the calculated fronthaul data throughput and the calculated signal-to-noise ratio
Detachable base station system comprising a. The method of claim 6,
The rate determining module,
Separate base station system for determining the modulation and coding scheme (MCS) level for the uplink and downlink based on the signal-to-noise ratio of the uplink channel and the downlink channel, and determines the determined MCS as the transmission rate of the terminal. The method of claim 7, wherein
The rate determining module,
The base station system of claim 1, wherein the calculated radio channel capacity is calculated using the signal-to-noise ratio, and the distortion level for further compression of the signal is calculated based on the margin of the signal-to-noise ratio calculated based on the radio channel capacity and the transmission rate of the terminal. The method of claim 8,
The rate determining module,
The base station system of claim 1, wherein the compression rate of the front hole is determined using the calculated distortion level. In a separate base station system composed of a plurality of distributed units and a central unit that cooperates with the plurality of distributed units, the central unit controls the compression ratio,
Monitoring a traffic load of a fronthaul connected with the plurality of distributed units and calculating a fronthaul data throughput from the traffic load,
Calculating signal-to-noise ratios of the uplink channel and the downlink channel for the terminal using signals transmitted from any terminal located in any one of the plurality of distributed units;
If the calculated fronthaul data throughput is greater than a preset threshold, determining a modulation and coding scheme (MCS) level determined according to the signal-to-noise ratio as the transmission rate of the terminal; and
Obtaining a compression rate of the fronthaul based on the determined transmission rate of the terminal
Compression ratio control method comprising a. The method of claim 10,
Obtaining the compression rate of the front hole,
Calculating a wireless channel capacity calculated using the signal-to-noise ratio;
Calculating a distortion level for further compressing a signal to be transmitted through a fronthaul if a margin of a signal-to-noise ratio calculated based on the radio channel capacity and the transmission rate of the terminal is greater than a preset threshold; and
Obtaining the compression ratio of the front hole by reflecting the calculated distortion level
Compression ratio control method comprising a.

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