KR20210058663A - Method and apparatus for channel estimation in orthogonal frequency division multiplexing system based on time division duplex - Google Patents

Abstract

A channel estimation technique in a TDD scheme based OFDM system is disclosed. An operating method performed in a first communication node of a communication system comprises the following steps of: determining whether consecutive slots have been set; determining whether transmission methods of consecutively received slots are identical to each other if consecutive slots are set; and performing channel estimation of an extrapolation section of a corresponding slot by using a reference signal of a next slot if the transmission methods are identical to each other.

Description

Channel estimation method and apparatus in TDD based OFDM system {METHOD AND APPARATUS FOR CHANNEL ESTIMATION IN ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING SYSTEM BASED ON TIME DIVISION DUPLEX}

The present invention relates to a channel estimation technique, and more particularly, when a time-continuous slot is set in a frequency division duplex (TDD) system, if the transmission method of a slot that is continuously received is identical, the next slot in the demodulation process of the current slot It relates to a channel estimation technique that enables a channel to be estimated using a demodulated reference signal of.

For cellular mobile communication, the 3rd Generation Partnership Project (3GPP) may develop technologies such as Long Term Evolution System (LTE), LTE Advanced, and LTE Advanced Pro. Thereafter, 3GPP may be developing a new radio access technology for the 5G mobile communication (5th Generation Mobile Telecommunication) standard, which may be referred to as a new radio (NR).

The LTE series technology and its subsequent standard, NR, can transmit a signal using an orthogonal frequency domain multiplexing (OFDM) technology, and can use orthogonal frequency domain multiple access (OFDMA) as a multiple access method of a terminal.

OFDM technology can transmit various physical layer channels and physical layer signals on time-frequency resources. Taking LTE as an example, a physical downlink shared channel (PDSCH), a physical downlink control channel (PDCCH), a physical broadcast channel (PBCH), a physical uplink shared channel (PUSCH), and a physical uplink control channel (PUCCH) are a physical layer for data transmission. It can be a channel. The physical layer signal can be divided into a reference signal and a synchronization signal, and the reference signal can be a cell-specific reference signal (CRS), a demodulation reference signal (DMRS), and a sound reference signal (SRS). In addition, the synchronization signal may be a primary synchronization signal (PSS) or a secondary synchronization signal (SSS).

PDSCH and PUSCH may be channels for transmitting downlink and uplink data, respectively, and PDCCH is information for demodulating the PDSCH (frequency resource size and location, modulation method, Hybrid-ARQ (automatic repeat request) information, modulation method, etc.) ) Can be transmitted. PUCCH may transmit ACK/NACK feedback and channel state information.

The cell reference signal and the demodulation reference signal may be used for demodulation of a physical layer channel. The cell reference signal may be used for channel information acquisition and data demodulation, and the demodulated reference signal may be used for data demodulation. The receiving device may estimate a radio channel using this reference signal.

There may be two methods for multiplexing uplink and downlink in mobile communication, and may be divided into frequency division duplex (FDD) and time division duplex (TDD). Here, FDD may use different frequency bands for uplink and downlink, and TDD may be used by dividing the same frequency resource by time. LTE and NR can support both modes, and in particular, NR can use a wider variety of TDD formats. Both FDD and TDD can generally allocate a large number of resources to the downlink. In the case of TDD, since downlink resources are consecutively arranged, in this case, the receiver may continuously estimate a channel for consecutive time resources.

When estimating a channel, the receiving device may estimate a channel using a channel estimation algorithm for an OFDM resource including a reference signal. In addition, the receiving device may interpolate the remaining resources without the reference signal using the surrounding reference signal. In the case of LTE and NR, the receiving device may perform 2-D interpolation on the frequency axis and the time axis. However, the reception device cannot estimate a channel of a corresponding resource using interpolation because a neighboring reference signal is insufficient at a boundary of a slot or a boundary of a frequency band. The receiving device may need to estimate a channel by extrapolation at this time.

When the receiving device estimates a channel using extrapolation, a high algorithmic complexity may be required, but channel estimation performance may be inferior to that of the interpolation method. In particular, in the case of a mobile communication for a vehicle in which the terminal moves very fast, the channel estimation performance may be more deteriorated in the case of channel estimation using extrapolation because the receiving device may have a large channel change over time.

An object of the present invention for solving the above problems is to change the channel estimation of the extrapolation period to the interpolation method when the transmission method of the continuously received slots is matched when the timely consecutive slots are set in the TDD system. It is to provide a channel estimation technique that can be performed.

The channel estimation method in the OFDM system based on the TDD scheme according to the first embodiment of the present invention for achieving the above object is an operation method performed in the first communication node of the communication system, and determines whether consecutive slots are set. Judging; If consecutive slots are set, determining whether the transmission method of the consecutively received slots matches; And if the transmission methods match, performing channel estimation of the extrapolation period of the corresponding slot by using the reference signal of the next slot.

According to the present invention, if a transmission method of consecutively received slots is identical when a temporally continuous slot is set in a TDD system, channel estimation performance of an extrapolation period may be changed to an interpolation method to increase channel estimation performance. .

That is, in order to calculate the channel estimation value of the symbol corresponding to the extrapolation period, the present invention estimates the channel using the reference signal transmitted to the reference signal symbol of the next slot when it is available. We can propose a method to improve the channel estimation performance.

As described above, according to the present invention, when a temporally continuous slot is set in a TDD system, the channel estimation performance can be improved by using the reference signal of the next slot in the demodulation process of the current slot.

1 is a conceptual diagram showing a first embodiment of a communication system.
2 is a block diagram showing a first embodiment of a communication node constituting a communication system.
3 is a conceptual diagram showing a physical layer resource grid of LTE.
4 is a conceptual diagram illustrating an embodiment of mapping a downlink control channel, a downlink data channel, and a cell reference signal allocated to a resource block pair of LTE.
5 is a conceptual diagram illustrating a frame format when transmitted in the TDD scheme.
6A is a block diagram of a transmitting device, and FIG. 6B is a block diagram of a receiving device.
7 is a conceptual diagram illustrating an embodiment of downlink resource mapping in the NR standard.
8 is a conceptual diagram illustrating an operation of a receiving device according to time.
9A and 9B are flowcharts of a channel estimation method in an OFDM system based on a TDD scheme according to an embodiment of the present invention.
10 is a conceptual diagram illustrating an operation of a reception device according to time according to an embodiment of the present invention.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms such as first and second may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another component. For example, without departing from the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. The term and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being "connected" or "connected" to another component, it is understood that it may be directly connected or connected to the other component, but other components may exist in the middle. It should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof does not preclude in advance.

Unless otherwise defined, all terms used herein including technical or scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in this application. Does not.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In describing the present invention, in order to facilitate an overall understanding, the same reference numerals are used for the same elements in the drawings, and duplicate descriptions for the same elements are omitted.

A communication system to which embodiments according to the present invention are applied will be described. The communication system to which the embodiments according to the present invention are applied is not limited to the contents described below, and the embodiments according to the present invention can be applied to various communication systems. Here, the communication system may have the same meaning as a communication network.

1 is a conceptual diagram showing a first embodiment of a communication system.

Referring to FIG. 1, the communication system 100 includes a plurality of communication nodes 110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6). The plurality of communication nodes are 4G communication (e.g., long term evolution (LTE), LTE-A (advanced)), 5G communication (e.g., new radio) specified in the 3rd generation partnership project (3GPP) standard. ), etc. 4G communication may be performed in a frequency band of 6 GHz or less, and 5G communication may be performed in a frequency band of 6 GHz or more as well as a frequency band of 6 GHz or less.

For example, for 4G communication and 5G communication, a plurality of communication nodes may include a code division multiple access (CDMA)-based communication protocol, a wideband CDMA (WCDMA)-based communication protocol, a time division multiple access (TDMA)-based communication protocol, Frequency division multiple access (FDMA)-based communication protocol, OFDM (orthogonal frequency division multiplexing)-based communication protocol, Filtered OFDM-based communication protocol, CP (cyclic prefix)-OFDM-based communication protocol, DFT-s-OFDM (discrete) Fourier transform-spread-OFDM)-based communication protocol, OFDMA (orthogonal frequency division multiple access)-based communication protocol, SC (single carrier)-FDMA-based communication protocol, NOMA (Non-orthogonal Multiple Access), GFDM (generalized frequency) Division multiplexing) based communication protocol, FBMC (filter bank multi-carrier) based communication protocol, UFMC (universal filtered multi-carrier) based communication protocol, SDMA (Space Division Multiple Access) based communication protocol, etc. can be supported. .

In addition, the communication system 100 may further include a core network. When the communication system 100 supports 4G communication, the core network may include a serving-gateway (S-GW), a packet data network (PDN)-gateway (P-GW), a mobility management entity (MME), and the like. have. When the communication system 100 supports 5G communication, the core network may include a user plane function (UPF), a session management function (SMF), an access and mobility management function (AMF), and the like.

Meanwhile, a plurality of communication nodes 110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130- constituting the communication system 100 4, 130-5, 130-6) Each may have the following structure.

2 is a block diagram showing a first embodiment of a communication node constituting a communication system.

Referring to FIG. 2, the communication node 200 may include at least one processor 210, a memory 220, and a transmission/reception device 230 connected to a network to perform communication. In addition, the communication node 200 may further include an input interface device 240, an output interface device 250, and a storage device 260. Each of the components included in the communication node 200 may be connected by a bus 270 to communicate with each other.

However, each of the components included in the communication node 200 may be connected through an individual interface or an individual bus based on the processor 210 instead of the common bus 270. For example, the processor 210 may be connected to at least one of the memory 220, the transmitting/receiving device 230, the input interface device 240, the output interface device 250, and the storage device 260 through a dedicated interface. .

The processor 210 may execute a program command stored in at least one of the memory 220 and the storage device 260. The processor 210 may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor in which methods according to embodiments of the present invention are performed. Each of the memory 220 and the storage device 260 may be configured with at least one of a volatile storage medium and a nonvolatile storage medium. For example, the memory 220 may be composed of at least one of read only memory (ROM) and random access memory (RAM).

Referring back to FIG. 1, the communication system 100 includes a plurality of base stations 110-1, 110-2, 110-3, 120-1, 120-2, and a plurality of terminals 130- 1, 130-2, 130-3, 130-4, 130-5, 130-6). Base stations (110-1, 110-2, 110-3, 120-1, 120-2) and terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) The containing communication system 100 may be referred to as an “access network”. Each of the first base station 110-1, the second base station 110-2, and the third base station 110-3 may form a macro cell. Each of the fourth base station 120-1 and the fifth base station 120-2 may form a small cell. The fourth base station 120-1, the third terminal 130-3, and the fourth terminal 130-4 may belong to the cell coverage of the first base station 110-1. The second terminal 130-2, the fourth terminal 130-4, and the fifth terminal 130-5 may belong to the cell coverage of the second base station 110-2. The fifth base station 120-2, the fourth terminal 130-4, the fifth terminal 130-5, and the sixth terminal 130-6 may belong within the cell coverage of the third base station 110-3. have. The first terminal 130-1 may belong to the cell coverage of the fourth base station 120-1. The sixth terminal 130-6 may belong to the cell coverage of the fifth base station 120-2.

Here, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 is a NodeB, an evolved NodeB, gNB, and a base transceiver station (BTS). ), a radio base station, a radio transceiver, an access point, an access node, and the like. Each of the plurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5, and 130-6 is a user equipment (UE), a terminal, an access terminal, and a mobile device. It may be referred to as a mobile terminal, a station, a subscriber station, a mobile station, a portable subscriber station, a node, a device, and the like.

Meanwhile, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may operate in different frequency bands or may operate in the same frequency band. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to each other through an ideal backhaul link or a non-ideal backhaul link, , Information can be exchanged with each other through an ideal backhaul link or a non-ideal backhaul link. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to the core network through an ideal backhaul link or a non-ideal backhaul link. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits a signal received from the core network to the corresponding terminal 130-1, 130-2, 130-3, 130 -4, 130-5, 130-6), and the signal received from the corresponding terminal (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) is transmitted to the core network. Can be transferred to.

In addition, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits multiple antenna technology (MIMO) (e.g., single user (SU)). )-MIMO, MU (multi user)-MIMO, massive MIMO, etc.), coordinated multipoint (CoMP) transmission, carrier aggregation (CA) transmission, transmission in an unlicensed band, direct communication between terminals (device to Device communication, D2D) (or ProSe (proximity services)), etc. may be supported. Here, each of the plurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5, and 130-6 is the base station 110-1, 110-2, 110-3, 120-1 , 120-2) and operations supported by the base stations 110-1, 110-2, 110-3, 120-1, and 120-2. For example, the second base station 110-2 may transmit a signal to the fourth terminal 130-4 based on the SU-MIMO scheme, and the fourth terminal 130-4 can transmit a signal to the fourth terminal 130-4 by the SU-MIMO scheme. A signal may be received from the second base station 110-2. Alternatively, the second base station 110-2 may transmit a signal to the fourth terminal 130-4 and the fifth terminal 130-5 based on the MU-MIMO method, and the fourth terminal 130-4 And each of the fifth terminal 130-5 may receive a signal from the second base station 110-2 by the MU-MIMO method.

Each of the first base station 110-1, the second base station 110-2, and the third base station 110-3 may transmit a signal to the fourth terminal 130-4 based on the CoMP scheme, and The terminal 130-4 may receive signals from the first base station 110-1, the second base station 110-2, and the third base station 110-3 by the CoMP method. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 has terminals 130-1, 130-2, 130-3, and 130-4 belonging to their cell coverage. , 130-5, 130-6) and CA schemes to transmit and receive signals. Each of the first base station 110-1, the second base station 110-2, and the third base station 110-3 can control D2D between the fourth terminal 130-4 and the fifth terminal 130-5. And each of the fourth terminal 130-4 and the fifth terminal 130-5 may perform D2D under the control of each of the second base station 110-2 and the third base station 110-3. .

3 is a conceptual diagram showing a physical layer resource grid of LTE.

,

)로 매핑 될 수 있으며,

는 부채널의 번호일 수 있고,

은 슬롯 내부 OFDM 심볼 번호일 수 있다. 물리 계층 자원은 리소스 블록(resource block: RB) 단위로나누어질 수 있다. 리소스 블록은 주파수 도메인으로 연속적인

개의 부채널과 시간적으로 연속적인

개의 OFDM 심볼로 구성될 수 있다. LTE는 일반적으로

=12,

=7의 값을 가질 수 있다. LTE는 한 서브 프레임을 구성하는 2슬롯에 걸친 리소스 블록 쌍을 기준으로 물리 채널을 할당할 수 있다.Referring to FIG. 3, the physical layer resource grid of LTE may divide a transmission frequency band into subchannels, and may allocate and transmit data to each subchannel. In LTE, several OFDM symbols can be bundled and transmitted in units of slots. LTE's physical layer resources are (

,

) Can be mapped to,

Can be the number of the subchannel,

May be an intra-slot OFDM symbol number. Physical layer resources may be divided into resource block (RB) units. Resource blocks are contiguous in the frequency domain

Subchannels and temporally continuous

It may consist of four OFDM symbols. LTE is generally

=12,

It can have a value of =7. LTE can allocate physical channels based on a pair of resource blocks spanning two slots constituting one subframe.

In the physical layer resource indicated by frequency-time mapping, various physical layer channels and physical layer signals may be mapped and transmitted according to standards. Taking LTE as an example, the physical layer resources indicated by frequency-time mapping are physical layer channels for data transmission such as PDSCH, PDCCH, PBCH, PUSCH, PUCCH, reference signals such as CRS, DMRS, SRS, and synchronization such as PSS and SSS. There may be a physical layer signal that is divided into signals.

Reference signals may be classified into two types according to their purpose, and there may be a cell reference signal for obtaining channel information and a demodulation reference signal used for data demodulation. The cell reference signal (CRS) used by the UE to obtain downlink channel information may have to be transmitted over a wideband, and even a UE that does not receive downlink data in a specific subframe needs to receive a cell reference signal. I can. In addition, the cell reference signal can be used in situations such as handover. A demodulation reference signal (DMRS) for data demodulation is a reference signal that is transmitted to a corresponding resource when a base station transmits data in downlink and uplink, and the terminal can demodulate data by measuring a channel by receiving the corresponding demodulation reference signal. Can be.

4 is a conceptual diagram illustrating an embodiment of mapping a downlink control channel, a downlink data channel, and a cell reference signal allocated to a resource block pair of LTE.

Referring to FIG. 4, a downlink control channel allocated to a resource block pair of LTE may be transmitted in first to third OFDM symbols, and a downlink data channel may be transmitted in fourth to fourteenth OFDM symbols. , The cell reference signal may be transmitted at regular time and frequency intervals. The downlink control channel may include information necessary to receive the downlink data channel (frequency resource size and location, modulation method, Hybrid-ARQ information, modulation method, etc.), and thus may be transmitted to the front in time.

5 is a conceptual diagram illustrating a frame format when transmitted in the TDD scheme.

Referring to FIG. 5, in a frame format when transmitted in the TDD scheme, 7 downlink slots may be transmitted every 8 slots, and 1 uplink slot may be transmitted. In the case of transmission in the TDD scheme, the frame format may be set asymmetrically because there is a large amount of downlink data in general.

6A is a block diagram of a transmitting device, and FIG. 6B is a block diagram of a receiving device.

Referring to FIG. 6A, a transmitting device may include a channel code encoder 611, a modulation mapper 612, an OFDM modulator 613, a digital to analog converter 614, and an RF antenna 615. And, referring to FIG. 6B, the receiving device includes an RF antenna 621, an analog-to-digital converter 622, an OFDM demodulator 623, a channel equalizer 624, a channel estimator 625, a modulation demapper 626, and A channel code decoder 627 may be included.

Data may be converted into a modulation symbol represented by in-phase, quadrature (hereinafter, I, Q) through a channel code encoder 611 and a modulation mapper 612. The modulation symbol and the reference signal can be mapped to the frequency axis and converted into an OFDM signal through the OFDM modulator 613. The OFDM signal may be converted into an analog signal through a digital to analog converter (DAC) 614. The analog signal may be propagated into the atmosphere through the RF antenna 615.

On the other hand, the RF antenna 621 of the reception device can receive radio waves in the air, and can convert a signal of a carrier frequency band into a signal of a base band. The baseband signal may be converted into a digital signal through an analog to digital converter (ADC) 622. The OFDM demodulator 623 may receive a digital signal and perform a fast Fourier transform (FFT) operation to generate and output demodulated data and a demodulated reference signal in the frequency domain.

The channel equalizer 624 may calculate and output a demodulated symbol using demodulated data and a channel estimate. In addition, the channel estimator 625 may receive the demodulation reference signal, generate a channel estimation value, and output it to the channel equalizer 624. The modulation demapper 626 may receive demodulation symbols I and Q, convert it into a log likelihood ratio (LLR) for soft decision, and output it. The channel code decoder 627 may receive the LLR, decode it into information bits, and output it.

In mobile communication, a frequency shift may occur between the transmitting device and the receiving device according to the moving speed of the terminal, and the frequency shift may cause fading of a channel that changes with time. The fading of such a channel can be referred to as a Doppler spread, and the Doppler spread can be inversely proportional to the coherence time of the channel, and can be a measure of how quickly the channel changes over time. Therefore, in mobile communication, if the speed of the terminal is high, the channel may change rapidly. In such an environment, the mobile communication receiving device may estimate the channel and may have to compensate for this. In this case, the reference signal among the frame signals can be used to estimate a channel between the transmitting device and the receiving device.

The channel estimation can be calculated using the received reference signal and a reference signal that is previously promised. Algorithms for channel estimation may include least squares (LS) and minimum mean squared error (MMSE).

7 is a conceptual diagram illustrating an embodiment of downlink resource mapping in the NR standard.

Referring to FIG. 7, in the downlink resource mapping in the NR standard, OFDM symbols 0 to 1 may be allocated as a downlink control channel, and the remaining OFDM symbols may be allocated as a downlink data channel. In the NR standard, resource mapping of the downlink may allocate even subchannels (0, 2, 4, 6, 8, 10) of OFDM symbols 2, 7 and 11 to transmit a demodulation reference signal. The receiving apparatus may estimate a subchannel of an OFDM symbol to which a demodulation reference signal is allocated using a channel estimation algorithm of LS or MMSE. In contrast, the receiving device may interpolate the remaining OFDM symbols without a reference signal in the time and frequency axes by using the neighboring reference signal in the resource mapping of the downlink according to the NR standard.

Here, the interpolation method may include piecewise linear interpolation, linear interpolation, spline interpolation, and the like. The partial linear interpolation may be to determine a sample value with data closest to the sample value, and the linear interpolation may be to infer between a given data and data by making a one-dimensional straight line. In addition, spline interpolation may represent a third-order polynomial between data and data, and may be inferring a value between the data. Linear interpolation may have better performance than partial linear interpolation, and spline interpolation may have the best performance but the greatest complexity.

Meanwhile, the receiving device may interpolate symbols 2, 7 and 11 through which the reference signal is transmitted on the frequency axis, and may determine channel estimation values for all of the frequency axis subchannels 0 to 11.

In addition, the receiving apparatus may interpolate channel estimates of symbols 2 and 7 interpolated along the frequency axis with respect to OFDM symbols 3 to 6 on the time axis to calculate channel estimates of all subcarriers of each symbol. Likewise, the receiving device may calculate a channel estimation value through time-axis interpolation using Nos. 7 and 11 interpolated on the frequency axis for OFDM symbols 8 to 10.

However, since the signal of the next slot is received immediately after symbols 12 to 13, the receiving device cannot determine a channel estimate using interpolation, and may have to perform extrapolation. In order to use extrapolation, the receiving device may need channel prediction for a slot without a training signal. Such channel prediction may require algorithmic complexity beyond channel estimation, but it may be known that channel estimation performance is inferior to the interpolation method.

8 is a conceptual diagram illustrating an operation of a receiving device according to time.

Referring to FIG. 8, the operation according to time of the receiving device may be a case in which three slots (slot 1, slot 2, and slot 3) are continuously configured for downlink in a TDD environment, and OFDM resources are allocated according to FIG. Can be assumed. Here, the reception slot 1, the reception slot 2, and the reception slot 3 may refer to input signals that have passed through an RF antenna and an analog-to-digital converter at the time of slot 1, slot 2, and slot 3 in the reception device.

The receiving device may perform FFT on the received OFDM signal and convert it into the frequency domain. Here, FFT1, FFT2, and FFT3 may be FFT outputs of each receiving slot. Referring back to FIG. 7, the first two OFDM symbols of the FFT output may be set as a control channel (PDCCH), and the receiving device may obtain information for demodulating the data channel (PDSCH) after demodulating the control channel. have. The information for demodulating the data channel (PDSCH) may include a frequency resource size and location, modulation information, retransmission information, and a modulation method.

Since the channel estimator of the receiving device knows the frequency resource information of the PDSCH after the control channel demodulation ends, it can perform channel estimation using the reference signal in the corresponding frequency resource. In the OFDM symbols s2, s7, and s11 inside the slot, a reference signal may be arranged at intervals of two subchannels along the frequency axis. The channel estimator performs interpolation on the frequency axis using such a reference signal, so that channel estimation values of all subchannels for a corresponding symbol can be calculated.

The channel estimator may calculate a channel estimate value for a corresponding symbol by performing time-axis interpolation on a symbol to which a reference signal is not mapped using channel estimate values of front and rear reference signals. However, the channel estimator can estimate the channel by extrapolation after s11.

The channel equalizer may compensate for distortion caused by the transmission channel by using the FFT output data and the previously determined channel estimate values (CHEST1, CHEST2, CHEST3). A demodulated symbol that has undergone a channel equalizer may be converted to an LLR for soft decision decoding. The channel code decoder may generate and output decoded data using LLR. The decoder can export data after a delay for internal operation.

Meanwhile, the present invention may propose a method for improving channel estimation performance in an OFDM communication system using a reference signal.

The channel estimation method according to the present invention changes the channel estimation of the extrapolation period (s12 to s13) to the interpolation method if the transmission method of the slots continuously received is the same when the timely continuous slot is set in the TDD system. It may be to increase the channel estimation performance.

That is, in the above example, in order to calculate the channel estimate value of the symbols (s12, s13) corresponding to the extrapolation interval, when the reference signal transmitted to the reference signal symbol s2 of the next slot is available, it is It may be to estimate the channel by using.

9A and 9B are flowcharts of a channel estimation method in an OFDM system based on a TDD scheme according to an embodiment of the present invention.

9A and 9B, in the TDD based OFDM system according to an embodiment of the present invention, a channel estimation method may perform channel estimation by dividing a received slot into two parts by a channel estimator of a receiving device. have. To this end, the channel estimator of the receiving device can define a portion of the reference signal of the corresponding slot and the channel estimation by the interpolation as a unique symbol period (or interpolation period), and the existing extrapolation as an OFDM symbol after the intrinsic symbol period. A portion for estimating the channel by the method may be defined as a standby symbol interval (or extrapolation interval) (S901). That is, the channel estimator of the receiving device may define intervals s0 to s11 as intrinsic symbol intervals in FIG. 7 and may define intervals s12 to s13 as standby symbol intervals.

In addition, the channel estimator of the receiving device determines whether the corresponding symbol is a symbol corresponding to the unique symbol interval (S902), and if the corresponding symbol is a symbol corresponding to the unique symbol interval, the channel is interpolated using a reference signal inside the slot. It can be estimated and demodulation can be performed (S903). Alternatively, as a result of determining whether the corresponding symbol corresponds to the unique symbol interval, the channel estimator of the receiving device may determine whether the next slot is allocated if the corresponding symbol does not correspond to the unique symbol interval and thus corresponds to the standby symbol interval (S904). ).

As a result of determining whether the next slot is allocated, the receiving device may estimate a channel for a corresponding symbol using an extrapolation method and perform demodulation if the next slot is not allocated (S905). However, as a result of determining whether the next slot is allocated, the receiving device may not perform channel estimation and demodulation on the corresponding symbol when the next slot is allocated, and may wait for the control channel demodulation result of the next slot.

Thereafter, the receiving device may determine whether the control channel demodulation of the next slot has ended (S906), and the control channel demodulation of the next slot has not been completed and may repeat the waiting process. In contrast, when the control channel demodulation of the next slot is finished, the receiving device may determine whether the data channel transmission information of the next slot matches the data channel transmission information of the current slot (S907).

As a result of determining whether the data channel transmission information of the next slot coincides with the data channel transmission information of the current slot, the receiving device may perform channel estimation on the corresponding symbol in the standby symbol section by an extrapolation method, and demodulation is performed. It can be performed (S905).

In contrast, if the data channel transmission information of the next slot matches the data channel transmission information of the current slot, the reception device may wait again until the channel estimate value of the first reference signal symbol of the next slot is determined.

Thereafter, the receiving device may determine whether the channel estimate value of the first reference signal symbol of the next slot is determined (S908), and if not determined, may wait again until the channel estimate value of the first reference signal symbol of the next slot is determined. . In contrast, if the channel estimation value of the first reference signal symbol of the next slot is determined, the receiving device can estimate the channel of the standby symbol interval using the determined channel estimation value by an interpolation method, and perform demodulation (S909). ). Here, the data channel transmission information that the receiving device compares with respect to the current slot and the next slot may include a frequency resource size, a frequency resource location, and a modulation method. Here, the modulation scheme may refer to a MIMO transmission method using multiple antennas, and there may be many cases that are not changed in consecutive slots. In this case, the modulation scheme may not be included in the information to be compared.

10 is a conceptual diagram illustrating an operation of a reception device according to time according to an embodiment of the present invention.

Referring to FIG. 10, it is assumed that the time-dependent operation of the reception device according to an embodiment of the present invention can use the TDD frame format of FIG. 7 and that three slots are allocated as a downlink channel as shown in FIG. This can be explained.

Since the receiving device already knows the TDD frame format, it is possible to define a symbol interval s0 to s11 among OFDM symbols inside a slot as a unique symbol interval, and may define a symbol interval s12 to s13 as a standby symbol interval. Each slot signal can be stored through the FFT stage. Here, the FFT processing result of the unique symbol interval for slot 1, slot 2, and slot 3 may be FFT1, FFT2, and FFT3, and the FFT processing result of the waiting symbol interval is referred to as FFT1-1, FFT2-1, FFT3-1. I can.

The receiving device can calculate the channel estimate value (chest1) by the interpolation method using the reference signal for FFT1, which is the FFT processing result of the inherent symbol interval of the first slot (slot 1), and calculate the demodulation data (LLR1). have.

Since the receiving device already knows that the next slot (slot 2) exists immediately after the demodulation of the unique symbol period ends, it may not immediately demodulate the FFT1-1, which is the result of the FFT processing in the waiting symbol period, and the next slot (slot 2). It can wait until the control channel (PDCCH) is demodulated.

For example, the receiving device may wait for t1 time. If the data channel transmission information of the next slot (slot 2) coincides with the data channel transmission information of the current slot (slot 1), the receiving device is re-established until the channel estimate value of the first reference signal symbol of the next slot (slot 2) is determined. I can wait. For example, the receiving device may wait for t2 hours.

Thereafter, the receiving device may calculate a channel estimate value for the symbol of the standby symbol period of the first slot (slot 1) using the channel estimate value of the first reference signal symbol of the next slot (slot 2) by interpolation method, and demodulate Data (LLR1-1) can be calculated.

However, if the data channel transmission information of the next slot (slot 2) does not coincide with the data channel transmission information of the current slot (slot 1), for example, the receiving device adds an extra to the symbols included in the waiting symbol period without the waiting time of t2. The channel can be estimated by polling and demodulation can be performed.

On the other hand, the receiving device can calculate channel estimation and demodulation data (LLR2) immediately after demodulation of the waiting symbol period of the previous slot (slot 1) for FFT2, which is the result of FFT processing of the unique symbol period of the second slot (slot 2). have. The receiving device already knows that the next slot (slot 3) exists for FFT2-1, which is the result of FFT processing in the waiting symbol period of the second slot (slot 2), until the PDCCH of the next slot (slot 3) is demodulated. You can wait.

As a result of demodulating the control channel of the next slot (slot 3), the receiving device estimates the channel of the first reference signal symbol of the next slot (slot 3) if the data channel transmission information matches the data channel transmission information of the current slot (slot 2). Can wait again.

Thereafter, the receiving device calculates channel estimation and demodulation data (LLR2-1) for the standby symbol period of the current slot (slot 2) by interpolation method using the channel estimate value of the first reference signal symbol of the next slot (slot 3). can do.

However, if the data channel transmission information of the next slot (slot 3) does not match the data channel transmission information of the current slot (slot 2), the receiving device estimates the channel using the extrapolation method without waiting time for the symbol in the standby symbol period. Demodulation can be performed.

In an embodiment of the present invention, slot 3 may be the last slot of a continuous stream. The receiving apparatus may calculate channel estimation and demodulation data LLR3 using an interpolation method for FFT3, which is a result of FFT processing for the unique symbol period of slot 3, according to the channel estimation result. And since it is the last slot, the receiving device does not need to wait for the control channel demodulation result of the next slot, and calculates the channel estimation and demodulation data (LLR3-1) using the extrapolation method for FFT3-1, which is the FFT processing result of the waiting symbol period. can do.

The methods according to the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like alone or in combination. The program instructions recorded on the computer-readable medium may be specially designed and configured for the present invention, or may be known and usable to those skilled in computer software.

Examples of computer-readable media include hardware devices specially configured to store and execute program instructions, such as rom, ram, flash memory, and the like. Examples of program instructions include machine language codes such as those produced by a compiler, as well as high-level language codes that can be executed by a computer using an interpreter or the like. The above-described hardware device may be configured to operate as at least one software module to perform the operation of the present invention, and vice versa.

Although described with reference to the above embodiments, those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention described in the following claims. I will be able to.

Claims (1)

A method of operation performed in a first communication node of a communication system, comprising:
Determining whether consecutive slots are set;
If consecutive slots are set, determining whether the transmission method of the consecutively received slots matches; And
And performing channel estimation of an extrapolation interval of a corresponding slot using a reference signal of a next slot if the transmission methods match.

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