KR102218925B1 - Milimeter wave communication estimating channel based on expectation-maximization apparatus and method - Google Patents

Abstract

According to embodiments, an apparatus for estimating a channel based on the maximization of a millimeter wave communication expectation value includes: a time varying signal function calculation part calculating a time varying signal function from a millimeter wave channel connected between a host vehicle and another vehicle through V2X; an expectation value maximization calculation part calculating an expectation value of log likelihood with an estimated value about at least one unknown parameter extracted based on the time varying signal function; and a channel estimation part calculating a time varying signal value by applying the calculated unknown parameter estimated value to the time varying signal function, and then, estimating a millimeter wave channel based on the calculated time varying signal value. The present invention is capable of improving a processing speed by estimating an optimal channel.

Description

An apparatus and method for estimating a channel based on the maximization of the expected value of millimeter wave communication {MILIMETER WAVE COMMUNICATION ESTIMATING CHANNEL BASED ON EXPECTATION-MAXIMIZATION APPARATUS AND METHOD}

The present disclosure relates to an apparatus and method for estimating a channel based on an expected value maximization of millimeter wave communication using an EM algorithm.

The fifth generation mobile communication system must support a data rate of up to 20 Gbps for a terminal, and must be able to maintain a data transmission rate of 100 Mbps to 1 Gbps no matter where the terminal is in the cell. In addition, it must support latency within 1ms and simultaneous access of a large number of terminals. In order to achieve this technical goal, the recent adoption of the millimeter wave band in mobile communication systems is in the spotlight.

In millimeter wave communications, a massive multiple input multiple output (MIMO) system is designed to provide the throughput improvements needed to meet the expected requirements for mobile data in a 5th generation mobile communication system (5G NR: new radio). Is one of the main candidates. The millimeter region is a higher frequency region than the conventional communication of 30 GHz or higher, and thus, a more serious predicted path loss is a big issue.

Millimeter wave communication can be utilized in a variety of mobile applications such as cellular systems, vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communication. In this situation, continuous beam alignment is essential to maintain the communication link, and for this, research on real-time beam tracking is being conducted.

An object of the present embodiment is to provide an apparatus and method for estimating a channel based on maximization of expected millimeter-wave communication by applying an EM algorithm to an unknown parameter that changes a time-varying signal in a millimeter-wave channel.

An embodiment devised to solve the above-described problem is a time-varying signal function calculating unit for calculating a time-varying signal function in a millimeter wave channel connected by V2X between another vehicle and an own vehicle, and at least one extracted based on the time-varying signal function. Time-varying by applying an expected value of log likelihood as an estimated value for an unknown parameter, an expected value maximization calculator that calculates the unknown parameter estimates that maximize the expected value, and applying the calculated unknown parameter estimate to a time-varying signal function It provides a channel estimation apparatus based on maximization of expected millimeter wave communication, including a channel estimator for calculating a signal value and estimating a millimeter wave channel based on the calculated time-varying signal value.

In another embodiment, a time-varying signal function calculation step of calculating a time-varying signal function in a millimeter wave channel connected by V2X between the other vehicle and the own vehicle, at least extracted based on the time-varying signal function determining a time-varying signal from the time-varying signal function The expected value of log likelihood is calculated as an estimated value for one unknown parameter, the expected value maximization calculation step of calculating the estimated values of the unknown parameter that maximizes the expected value, and the calculated unknown parameter estimate is applied to a time-varying signal function Thus, it provides a channel estimation method based on maximization of expected millimeter-wave communication, including a channel estimation step of calculating a time-varying signal value and estimating a millimeter-wave channel based on the calculated time-varying signal.

Through the present invention, the unknown parameter applied to the time-varying signal undergoes an expected value maximization step, so that all the transmission and reception beams are not sequentially transmitted, so that overhead is not generated, and the processing speed is improved by estimating the optimal channel. It is possible to provide a maximized-based channel estimation apparatus and method.

1 is a diagram schematically showing a structure of an NR wireless communication system to which this embodiment can be applied.
2 is a diagram for explaining a frame structure in an NR system to which the present embodiment can be applied.
3 is a diagram illustrating a resource grid supported by a radio access technology to which the present embodiment can be applied.
4 is a diagram for explaining a bandwidth part supported by a wireless access technology to which the present embodiment can be applied.
5 is a diagram illustrating a synchronization signal block in a wireless access technology to which the present embodiment can be applied.
6 is a diagram for explaining a random access procedure in a radio access technology to which the present embodiment can be applied.
7 is a diagram for explaining CORESET.
FIG. 8 is a diagram illustrating an exemplary millimeter wave communication expected value maximization-based channel estimation apparatus according to the present embodiment to estimate a millimeter wave channel by communicating with another vehicle.
9 is a block diagram illustrating an apparatus for estimating a channel based on an expected value maximization of millimeter wave communication according to the present embodiment.
10 is a flowchart illustrating a method of estimating a channel based on maximization of an expected millimeter wave communication value according to the present embodiment.
11 is a flowchart illustrating a method of maximizing an expected value of an unknown parameter according to an exemplary embodiment.

Hereinafter, some embodiments of the present technical idea will be described in detail with reference to exemplary drawings. In adding reference numerals to elements of each drawing, the same elements may have the same numerals as possible even if they are indicated on different drawings. In addition, in describing the technical idea, when it is determined that a detailed description of a related known configuration or function may obscure the gist of the technical idea, the detailed description may be omitted.

In addition, terms such as first, second, A, B, (a), and (b) may be used in describing the components of the present embodiments. These terms are only for distinguishing the component from other components, and the nature, order, order, or number of the component is not limited by the term. When a component is described as being "connected", "coupled" or "connected" to another component, the component may be directly connected or connected to that other component, but other components between each component It is to be understood that is "interposed", or that each component may be "connected", "coupled" or "connected" through other components.

In addition, terms and technical names used in the present specification are for describing specific embodiments, and the technical idea is not limited thereto. The terms described below may be interpreted as meanings generally understood by those of ordinary skill in the technical field to which the present technical idea belongs unless otherwise defined. When the corresponding term is an incorrect technical term that does not accurately express the present technical idea, it will be replaced with a technical term that can be correctly understood by those skilled in the art to be understood. In addition, general terms used in the present specification should be interpreted as defined in the dictionary or according to the context before and after, and should not be interpreted as an excessively reduced meaning.

The wireless communication system in the present specification refers to a system for providing various communication services such as voice and data packets using radio resources, and may include a terminal, a base station, and a core network.

The embodiments disclosed below can be applied to a wireless communication system using various wireless access technologies. For example, the present embodiments are CDMA (code division multiple access), FDMA (frequency division multiple access), TDMA (timedivision multiple access), OFDMA (orthogonal frequency division multiple access), SC-FDMA (singlecarrier frequency division multiple access) It can be applied to various wireless access technologies such as. CDMA may be implemented with a radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. TDMA may be implemented using a radio technology such as global system for mobile communications (GSM)/general packet radio service (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA may be implemented with a wireless technology such as IEEE (institute of electrical and electronics engineers) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, E-UTRA (evolved UTRA), and the like. IEEE 802.16m is an evolution of IEEE 802.16e and provides backward compatibility with a system based on IEEE 802.16e. UTRA is part of a universal mobile telecommunications system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA), and employs OFDMA in downlink and SC- in uplink. Adopt FDMA. As described above, the present embodiments may be applied to a wireless access technology currently disclosed or commercialized, and may be applied to a wireless access technology currently being developed or to be developed in the future.

Meanwhile, a terminal in the present specification is a generic concept that refers to a device including a wireless communication module that performs communication with a base station in a wireless communication system, and is a UE in WCDMA, LTE, HSPA, and IMT-2020 (5G or New Radio). In addition to (User Equipment), it should be interpreted as a concept that includes all of MS (Mobile Station), UT (User Terminal), SS (Subscriber Station), and wireless device in GSM. In addition, the terminal may be a user's portable device such as a smart phone according to the usage type, and in the V2X communication system, it may mean a vehicle, a device including a wireless communication module in the vehicle, and the like. In addition, in the case of a machine type communication system, it may mean an MTC terminal or an M2M terminal equipped with a communication module so that machine type communication is performed.

The base station or cell of the present specification refers to the end of communication with the terminal in terms of the network, and Node-B (Node-B), eNB (evolved Node-B), gNB (gNode-B), LPN (Low Power Node), Sector, Site, various types of antennas, BTS (Base Transceiver System), Access Point, Point (e.g., Transmit Point, Receiving Point, Transmitting Point), Relay Node ), a mega cell, a macro cell, a micro cell, a pico cell, a femto cell, a remote radio head (RRH), a radio unit (RU), and a small cell.

In the various cells listed above, since there is a base station controlling each cell, the base station can be interpreted in two meanings. 1) In relation to the radio area, the device itself may provide a mega cell, a macro cell, a micro cell, a pico cell, a femto cell, and a small cell, or 2) the radio area itself may be indicated. In 1), all devices that are controlled by the same entity that provide a predetermined wireless area are controlled by the same entity, or all devices that interact to form a wireless area in collaboration are instructed to the base station. A point, a transmission/reception point, a transmission point, a reception point, etc. may be an embodiment of a base station according to the configuration method of the wireless area. In 2), it is possible to instruct the base station to the radio region itself that receives or transmits a signal from the viewpoint of the user terminal or the viewpoint of a neighboring base station.

In the present specification, a cell refers to a component carrier having coverage of a signal transmitted from a transmission/reception point or a coverage of a signal transmitted from a transmission/reception point, and the transmission/reception point itself. I can.

Uplink (Uplink, UL, or uplink) refers to a method of transmitting and receiving data to a base station by a UE, and downlink (Downlink, DL, or downlink) refers to a method of transmitting and receiving data to a UE by a base station. The downlink may refer to a communication or communication path from multiple transmission/reception points to the terminal, and the uplink may refer to a communication or communication path from the terminal to multiple transmission/reception points. In this case, in the downlink, the transmitter may be a part of the multiple transmission/reception points, and the receiver may be a part of the terminal. In addition, in the uplink, the transmitter may be a part of the terminal, and the receiver may be a part of the multiple transmission/reception points.

Uplink and downlink transmit and receive control information through a control channel such as Physical Downlink Control CHannel (PDCCH), Physical Uplink Control CHannel (PUCCH), and the like, and The same data channel is configured to transmit and receive data. Hereinafter, a situation in which signals are transmitted and received through channels such as PUCCH, PUSCH, PDCCH, and PDSCH is expressed in the form of'transmitting and receiving PUCCH, PUSCH, PDCCH and PDSCH'. do.

In order to clarify the description, hereinafter, the present technical idea is mainly described with respect to a 3GPP LTE/LTE-A/NR (New RAT) communication system, but the present technical feature is not limited thereto.

After research on 4G (4th-Generation) communication technology, 3GPP is conducting research on 5G (5th-Generation) communication technology to meet the requirements of ITU-R's next-generation wireless access technology. Specifically, 3GPP is conducting research on LTE-A pro, which has improved LTE-Advanced technology as a 5G communication technology in accordance with the requirements of ITU-R, and a new NR communication technology separate from 4G communication technology. It is expected that both LTE-A pro and NR will be submitted as 5G communication technology, but in the following, for convenience of explanation, these embodiments will be described focusing on NR.

The operation scenario in NR defined various operation scenarios by adding considerations to satellites, automobiles, and new verticals from the existing 4G LTE scenario.In terms of service, eMBB (Enhanced Mobile Broadband) scenario, high terminal density, but wide It is deployed in the range and supports the mMTC (Massive Machine Communication) scenario that requires a low data rate and asynchronous connection, and the URLLC (Ultra Reliability and Low Latency) scenario that requires high responsiveness and reliability and supports high-speed mobility. .

In order to satisfy this scenario, NR discloses a wireless communication system to which a new waveform and frame structure technology, a low latency technology, a mmWave support technology, and a forward compatible provision technology are applied. In particular, in the NR system, various technical changes are proposed in terms of flexibility to provide forward compatibility. Main technical features will be described below with reference to the drawings.

<NR system general>

1 is a diagram schematically showing a structure of an NR system to which this embodiment can be applied.

1, the NR system is divided into 5GC (5G Core Network) and NR-RAN parts, and NG-RAN controls user plane (SDAP/PDCP/RLC/MAC/PHY) and UE (User Equipment). It is composed of gNB and ng-eNB that provide plane (RRC) protocol termination. The gNB or gNB and ng-eNB are interconnected through an Xn interface. The gNB and ng-eNB are each connected to 5GC through the NG interface. The 5GC may include an Access and Mobility Management Function (AMF) in charge of a control plane such as a terminal access and mobility control function, and a User Plane Function (UPF) in charge of a control function for user data. NR includes support for both frequency bands below 6GHz (FR1, Frequency Range 1) and frequencies above 6GHz (FR2, Frequency Range 2).

gNB means a base station that provides NR user plane and control plane protocol termination to a terminal, and ng-eNB means a base station that provides E-UTRA user plane and control plane protocol termination to a terminal. The base station described in the present specification should be understood in a sense encompassing gNB and ng-eNB, and may be used as a means to distinguish between gNB or ng-eNB as necessary.

<NR wave form, numer roller and frame structure>

In NR, a CP-OFDM waveform using a cyclic prefix is used for downlink transmission, and CP-OFDM or DFT-s-OFDM is used for uplink transmission. OFDM technology is easy to combine with MIMO (Multiple Input Multiple Output), and has the advantage of being able to use a low complexity receiver with high frequency efficiency.

On the other hand, in NR, since the requirements for data rate, delay rate, and coverage are different for each of the three scenarios described above, it is necessary to efficiently satisfy the requirements for each scenario through a frequency band constituting an arbitrary NR system. . To this end, a technique for efficiently multiplexing a plurality of different numerology-based radio resources has been proposed.

값이 2의 지수 값으로 사용되어 지수적으로 변경된다.Specifically, the NR transmission neuron is determined based on sub-carrier spacing and CP (Cyclic prefix), and is based on 15khz as shown in Table 1 below.

The value is used as an exponential value of 2 and changes exponentially.

Subcarrier spacing Cyclic prefix Supported for data Supported for synch 0 15 Normal Yes Yes One 30 Normal Yes Yes 2 60 Normal, Extended Yes No 3 120 Normal Yes Yes 4 240 Normal No Yes

As shown in Table 1 above, the NR numer rollers can be classified into 5 types according to the subcarrier interval. This is different from the fixed subcarrier spacing of 15khz of LTE, one of the 4G communication technologies. Specifically, subcarrier intervals used for data transmission in NR are 15, 30, 60, and 120khz, and subcarrier intervals used for synchronization signal transmission are 15, 30, 12, and 240khz. In addition, the extended CP is applied only to the 60khz subcarrier interval. Meanwhile, a frame structure in NR is defined as a frame having a length of 10 ms consisting of 10 subframes having the same length of 1 ms. One frame can be divided into 5 ms half frames, and each half frame includes 5 subframes. In the case of the 15khz subcarrier interval, one subframe consists of 1 slot, and each slot consists of 14 OFDM symbols. 2 is a diagram for explaining a frame structure in an NR system to which this embodiment can be applied.

Referring to FIG. 2, in the case of a normal CP, a slot is fixedly composed of 14 OFDM symbols, but the length of the slot may vary according to the subcarrier interval. For example, in the case of a newer roller having a 15khz subcarrier interval, a slot is 1ms long and has the same length as the subframe. In contrast, in the case of a newer roller with a 30khz subcarrier spacing, a slot consists of 14 OFDM symbols, but two slots may be included in one subframe with a length of 0.5ms. That is, the subframe and the frame are defined with a fixed time length, and the slot is defined by the number of symbols, and the time length may vary according to the subcarrier interval.

Meanwhile, NR defines a basic unit of scheduling as a slot, and introduces a mini-slot (or sub-slot or non-slot based schedule) in order to reduce the transmission delay of the radio section. If a wide subcarrier spacing is used, the length of one slot is shortened in inverse proportion, so that transmission delay in the radio section can be reduced. The mini-slot (or sub-slot) is for efficient support for the URLLC scenario, and scheduling is possible in units of 2, 4, or 7 symbols.

In addition, unlike LTE, NR defines uplink and downlink resource allocation as a symbol level within one slot. In order to reduce HARQ delay, a slot structure capable of transmitting HARQ ACK/NACK directly within a transmission slot has been defined, and this slot structure is named and described as a self-contained structure.

NR is designed to support a total of 256 slot formats, of which 62 slot formats are used in Rel-15. In addition, a common frame structure constituting an FDD or TDD frame is supported through a combination of various slots. For example, a slot structure in which all symbols of a slot are set to downlink, a slot structure in which all symbols are set to uplink, and a slot structure in which a downlink symbol and an uplink symbol are combined are supported. In addition, NR supports that data transmission is distributed and scheduled in one or more slots. Accordingly, the base station may inform the UE of whether the slot is a downlink slot, an uplink slot, or a flexible slot using a slot format indicator (SFI). The base station can indicate the slot format by indicating the index of the table configured through RRC signaling specifically through the UE, using SFI, and dynamically indicate through Downlink Control Information (DCI) or statically or semi-statically through RRC. May be.

<NR physical resource>

Regarding the physical resource in NR, the antenna port, resource grid, resource element, resource block, bandwidth part, etc. are considered. Can be.

The antenna port is defined so that a channel carrying a symbol on an antenna port can be inferred from a channel carrying another symbol on the same antenna port. When the large-scale property of a channel carrying a symbol on one antenna port can be inferred from a channel carrying a symbol on another antenna port, the two antenna ports are QC/QCL (quasi co-located or quasi co-location) relationship. Here, the wide-range characteristic includes one or more of delay spread, Doppler spread, frequency shift, average received power, and received timing.

3 is a diagram illustrating a resource grid supported by a radio access technology to which the present embodiment can be applied.

Referring to FIG. 3, since the NR supports a plurality of neurons in the same carrier, a resource grid may exist according to each neuron in the resource grid. In addition, the resource grid may exist according to an antenna port, a subcarrier interval, and a transmission direction.

A resource block consists of 12 subcarriers, and is defined only in the frequency domain. In addition, a resource element consists of one OFDM symbol and one subcarrier. Accordingly, as shown in FIG. 3, the size of one resource block may vary according to the subcarrier interval. In addition, NR defines “Point A” that serves as a common reference point for the resource block grid, a common resource block, and a virtual resource block.

4 is a diagram for explaining a bandwidth part supported by a wireless access technology to which the present embodiment can be applied.

In NR, unlike LTE where the carrier bandwidth is fixed at 20Mhz, the maximum carrier bandwidth is set from 50Mhz to 400Mhz for each subcarrier interval. Therefore, it is not assumed that all terminals use all of these carrier bandwidths. Accordingly, in the NR, as shown in FIG. 4, the terminal can use the bandwidth part by designating the bandwidth part within the carrier bandwidth. In addition, the bandwidth part is associated with one neurology and is composed of a subset of consecutive common resource blocks, and can be dynamically activated over time. The UE is configured with up to four bandwidth parts, respectively, in uplink and downlink, and data is transmitted and received using the active bandwidth part at a given time.

In the case of a paired spectrum, uplink and downlink bandwidth parts are independently set, and in the case of an unpaired spectrum, unnecessary frequency re-tuning between downlink and uplink operations is prevented. For this purpose, the downlink and uplink bandwidth parts are set in pairs to share a center frequency.

<NR initial connection>

In NR, the terminal accesses the base station and performs cell search and random access procedures to perform communication.

Cell search is a procedure in which a terminal synchronizes with a cell of a corresponding base station, obtains a physical layer cell ID, and obtains system information by using a synchronization signal block (SSB) transmitted by a base station.

5 is a diagram illustrating a synchronization signal block in a wireless access technology to which the present embodiment can be applied.

Referring to FIG. 5, an SSB consists of a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) occupying 1 symbol and 127 subcarriers, respectively, and a PBCH spanning 3 OFDM symbols and 240 subcarriers.

The terminal receives the SSB by monitoring the SSB in the time and frequency domain.

SSB can be transmitted up to 64 times in 5ms. A plurality of SSBs are transmitted in different transmission beams within 5 ms time, and the UE performs detection on the assumption that SSBs are transmitted every 20 ms period based on one specific beam used for transmission. The number of beams that can be used for SSB transmission within 5 ms time may increase as the frequency band increases. For example, under 3GHz, up to 4 SSB beams can be transmitted, in a frequency band of 3 to 6GHz, up to 8, and in a frequency band of 6GHz or higher, SSBs can be transmitted using up to 64 different beams.

Two SSBs are included in one slot, and the start symbol and the number of repetitions in the slot are determined according to the subcarrier interval as follows.

Meanwhile, the SSB is not transmitted at the center frequency of the carrier bandwidth, unlike the conventional LTE SS. That is, the SSB may be transmitted even in a place other than the center of the system band, and a plurality of SSBs may be transmitted in the frequency domain when broadband operation is supported. Accordingly, the UE monitors the SSB by using a synchronization raster, which is a candidate frequency location for monitoring the SSB. The carrier raster and synchronization raster, which are information on the center frequency of the channel for initial access, have been newly defined in NR, and the synchronization raster has a wider frequency interval than the carrier raster to support fast SSB search of the terminal. I can.

The UE can acquire the MIB through the PBCH of the SSB. The MIB (Master Information Block) includes minimum information for the terminal to receive remaining system information (RMSI, Remaining Minimum System Information) broadcast by the network. In addition, PBCH is information about the location of the first DM-RS symbol in the time domain, information for the UE to monitor SIB1 (e.g., SIB1 neurology information, information related to SIB1 CORESET, search space information, PDCCH Related parameter information, etc.), offset information between the common resource block and the SSB (the position of the absolute SSB in the carrier is transmitted through SIB1), and the like. Here, the SIB1 neurology information is equally applied to messages 2 and 4 of the random access procedure for accessing the base station after the terminal completes the cell search procedure.

The aforementioned RMSI means SIB1 (System Information Block 1), and SIB1 is broadcast periodically (ex, 160 ms) in a cell. SIB1 includes information necessary for the UE to perform an initial random access procedure, and is periodically transmitted through the PDSCH. In order for the UE to receive SIB1, it is necessary to receive newer roller information used for SIB1 transmission and CORESET (Control Resource Set) information used for SIB1 scheduling through the PBCH. The UE checks scheduling information for SIB1 using SI-RNTI in CORESET, and acquires SIB1 on the PDSCH according to the scheduling information. SIBs other than SIB1 may be periodically transmitted or may be transmitted according to the request of the terminal.

6 is a diagram for explaining a random access procedure in a radio access technology to which the present embodiment can be applied.

Referring to FIG. 6, when the cell search is completed, the UE transmits a random access preamble for random access to the base station. The random access preamble is transmitted through the PRACH. Specifically, the random access preamble is transmitted to the base station through a PRACH consisting of consecutive radio resources in a specific slot that is periodically repeated. In general, when a terminal initially accesses a cell, a contention-based random access procedure is performed, and when a random access is performed for beam failure recovery (BFR), a contention-free random access procedure is performed.

The terminal receives a random access response to the transmitted random access preamble. The random access response may include a random access preamble identifier (ID), a UL Grant (uplink radio resource), a temporary C-RNTI (Temporary Cell-Radio Network Temporary Identifier), and a TAC (Time Alignment Command). Since one random access response may include random access response information for one or more terminals, the random access preamble identifier may be included to inform which terminal the included UL Grant, temporary C-RNTI, and TAC are valid. The random access preamble identifier may be an identifier for the random access preamble received by the base station. TAC may be included as information for the UE to adjust uplink synchronization. The random access response may be indicated by a random access identifier on the PDCCH, that is, a Random Access-Radio Network Temporary Identifier (RA-RNTI).

Upon receiving a valid random access response, the terminal processes information included in the random access response and performs scheduled transmission to the base station. For example, the UE applies TAC and stores a temporary C-RNTI. Also, by using UL Grant, data stored in the buffer of the terminal or newly generated data is transmitted to the base station. In this case, information for identifying the terminal should be included.

Finally, the terminal receives a downlink message for resolving contention.

<NR CORESET>

The downlink control channel in NR is transmitted in CORESET (Control Resource Set) having a length of 1 to 3 symbols, and transmits uplink/downlink scheduling information, SFI (Slot Format Index), and TPC (Transmit Power Control) information. .

In this way, NR introduced the concept of CORESET to secure system flexibility. CORESET (Control Resource Set) means a time-frequency resource for a downlink control signal. The terminal may decode the control channel candidate using one or more search spaces in the CORESET time-frequency resource. A QCL (Quasi CoLocation) assumption for each CORESET is set, and this is used to inform the characteristics of the analog beam direction in addition to the delay spread, Doppler spread, Doppler shift, and average delay, which are characteristics assumed by conventional QCL.

7 is a diagram for explaining CORESET.

Referring to FIG. 7, CORESET may exist in various forms within a carrier bandwidth within one slot, and CORESET may consist of up to 3 OFDM symbols in the time domain. In addition, CORESET is defined as a multiple of 6 resource blocks up to the carrier bandwidth in the frequency domain.

The first CORESET is indicated through the MIB as part of the initial bandwidth part configuration so that additional configuration information and system information can be received from the network. After establishing the connection with the base station, the terminal may receive and configure one or more CORESET information through RRC signaling.

In this specification, frequencies, frames, subframes, resources, resource blocks, regions, bands, subbands, control channels, data channels, synchronization signals, various reference signals, various signals, and various messages related to NR (New Radio) Can be interpreted as a meaning used in the past or present, or in various meanings used in the future.

<NR MIMO and Beam operation>

In NR, a technology related to beam management, which is an analog beamforming evolution technology, has been added, and the MIMO codebook/feedback technology, which is a conventional digital beamforming technology, has been developed.

In the case of analog beamforming, a technology related to beam operation that forms an optimal beam pair between the base station and the terminal through beam sweeping transmission of the base station/terminal and beam repetition transmission, etc. It can be broadly classified into a beam failure recovery technique to form.

Initial beam establishment

The procedure of forming an optimal beam pair between the initial base station and the terminal, that is, initial beam establishment, is performed in the initial access procedure. During the initial cell search, the UE may acquire some of the plurality of SSBs each composed of different downlink beams transmitted from the base station in time order.

The terminal selects an optimal beam based on the acquired SSBs, and transmits a random access preamble associated with the optimal beam to the base station. Specifically, different SSB time indices are associated with different random access channel time/frequency occasions and/or different preamble sequences.

In the case where one SSB is associated with two or more random access time/frequency occasions, the frequency is the highest priority, the time is the next in one slot, and the time is the priority between the two slots. do.

Accordingly, the base station can identify the optimal beam through the random access preamble associated with the optimal beam. As a result, the base station and the terminal initially form an optimal beam pair.

Beam adjustment

Since relatively wide beams were used in initial beam formation, the base station and the terminal perform beam adaptation with a relatively narrow beam after initial beam formation. In addition, beam adaptation is performed even when movement or rotation of the terminal occurs.

Beam adaptation can be divided into downlink beam adaptation and uplink beam adaptation.

The downlink beam adaptation can be divided into downlink transmitter-side beam adjustment and downlink receiver-side beam adjustment.

For example, the downlink transmission side beam adaptation will be described as an example. When the base station transmits two or more downlink signals (eg, CSI-RS or SSB), the terminal performs measurements on them and reports the result to the base station. The base station determines an optimal beam according to the report result from the terminal, and the base station and the terminal form a beam pair based on the optimal beam.

When the base station and the terminal form a beam pair using the CSI-RS, the base station sequentially transmits two or more and up to four CSI-RSs each composed of different beams to the terminal. The UE measures each CSI-RS measurement, for example, L1-RSRP, and reports the result to the base station.

The report result is the indication information of up to four CSI-RSs, the measured L1-RSRP for the strong beam, the difference between the L1-RSRP of the remaining beams and the L1-RSRP of the strongest beam. May contain values.

Beam Directive and TCI

NR supports a beam indication function. For example, the base station informs the UE of beams used in the PDSCH and PDCCH using configuration information and a Transmission Configuration Indicator (TCI).

For example, the UE may be configured with up to 64 candidate TCI states. For PDCCH beam indication, a subset of M configured candidate TCI states is allocated by higher layer signaling, for example, RRC signaling, and the base station dynamically informs the specific TCI state by MAC signaling.

For PDSCH beam indication, when the PDCCH-PDSCH timing offset (scheduling offset) included in the PDCCH is greater than N symbols, the scheduling assignment DCI (eg, 3 bits) explicitly indicates the TCI state for PDSCH transmission. When the PDCCH-PDSCH timing offset (scheduling offset) included in the PDCCH is equal to or smaller than the N symbol, the UE assumes that the TCI state of the PDCCH indicated by MAC signaling and the TCI state for PDSCH transmission are the same as described above. .

Beam failure recovery

The UE may detect a beam failure based on whether the error probability for the PDCCH exceeds a specific set value or a measurement result of the quality of a specific RS.

When detecting a beam failure, the terminal selects an optimal candidate beam according to, for example, measurement of CSI-RSs or SSBs, for example, L1-RSRP measurement, and makes a beam-recovery request to the base station. send.

The beam recovery request is performed through a contention-free random access channel. First, the UE transmits a random access preamble associated with an optimal beam in the same manner as initial beam formation. And the base station transmits a response to this request.

The terminal monitors the response, and upon receiving the response, beam recovery is completed.

Since a 5G mobile communication system requires a transmission speed of 1,000 times or more compared to the current LTE, a millimeter wave transmission system is drawing attention as part of a technology to meet these requirements. The millimeter wave band refers to a 30 to 300 GHz band whose wavelength is in mm units that are distinguished from the less than 6 GHz band used in conventional mobile communication. Millimeter wave has shortcomings such as signal attenuation and transmission distance reduction due to its short wavelength due to high frequency, but it is suitable for large-scale MIMO (Multiple-Input Multiple-Output) systems because it can integrate multiple antennas into a small space. Based on these characteristics, many studies are being conducted to overcome large path loss in the millimeter wave band by applying a high-directional beamforming technology.

For beamforming using many antennas, a channel must be accurately estimated. A simple and effective method for estimating the millimeter wave channel is the beam training method. In the beam training method, it is possible to estimate a beam channel in the analog domain using only a phase shifter. This method is used in IEEE standards 802.11ad and 802.15.3c as a method in which a transmitter and a receiver sequentially replace directional analog beams and find a transmission/reception beam pair that maximizes the signal-to-noise ratio of the link. However, this method has a disadvantage in that a large overhead is generated in order to sequentially transmit all transmit/receive beams. In addition, the existing studies do not take into account large overhead and time-varying channels, so they are difficult to apply in large-scale MIMO systems and environments that move at high speeds.

FIG. 8 is an exemplary diagram illustrating that the millimeter wave communication expected value maximization-based channel estimation apparatus 10 according to the present embodiment communicates with other vehicles 12, 12-1, 12-2, and 12-3 to estimate a millimeter wave channel. It is a drawing shown as.

8, the millimeter wave communication expected value maximization-based channel estimation apparatus 10 is a millimeter wave connected between another vehicle 12, 12-1, 12-2, 12-3 and an own vehicle 11 through V2X communication. The estimated value of at least one unknown parameter received from other vehicles (12, 12-1, 12-2, 12-3) in the channel and extracted based on the time-varying signal function is calculated through the EM algorithm. Can be calculated. In addition, the channel estimating apparatus 10 based on maximization of the expected millimeter wave communication may estimate the millimeter wave channel based on the calculated time-varying signal by applying the calculated expected value to a time-varying signal function.

Here, the host vehicle 11 may be equipped with a plurality of antennas, may perform V2X communication with other vehicles 12 nearby, and V2I communication with a base station that manages the cell on which the host vehicle 11 is traveling. Can be done. In addition, the host vehicle 11 may perform beamforming between vehicles (between the host vehicle and another vehicle) for the aforementioned V2X communication.

The own vehicle 11 may be an autonomous vehicle according to an example. Here, an autonomous vehicle refers to a vehicle that has a function of detecting and processing external information during driving, recognizing the surrounding environment, determining a driving route by itself, and running independently using its own power. The own vehicle 11 may be provided with a channel estimation device based on the maximization of the expected millimeter wave communication, and receive a control signal for the own vehicle 11 through this. However, this is only an example, and the description below may be applied to a vehicle equipped with a driver assistance system other than an autonomous vehicle.

The other vehicle 12 can perform V2X communication with the own vehicle 11 by mounting a plurality of antennas, and can also perform V2I communication with a base station that manages a cell in which the other vehicle 12 is running. In addition, beamforming may be performed for V2X communication with the own vehicle 11.

9 is a block diagram illustrating an apparatus 10 for estimating a channel based on an expected value maximization of millimeter wave communication according to the present embodiment.

Referring to FIG. 9, the channel estimation apparatus 10 based on the millimeter wave communication expected value maximization may include a time-varying signal function calculation unit 910, an expected value maximization calculation unit 920, a channel estimation unit 930, and the like.

The time-varying signal function calculation unit 910 is a time-varying signal received from the k-th other vehicle 12 in a millimeter wave channel connected by V2X communication between the k-th other vehicle 12 and the own vehicle 11 in the n-th time slot. You can calculate a function.

Specifically, a millimeter-wave channel between the own vehicle and the k-th connected vehicle in the n-th time slot may be calculated as shown in [Equation 1] below.

는 경로손실,

는 복소 채널 이득일 수 있다.

와

는 각각 도래각 (Angle of Arrival, AoA)와 발사각(Angle of Departure, AoD)이고

와

는 각각 자차량(11) 및 타차량(12)의 조향 벡터일 수 있다.here

Is the path loss,

May be a complex channel gain.

Wow

Is the Angle of Arrival (AoA) and Angle of Departure (AoD) respectively

Wow

May be steering vectors of the own vehicle 11 and the other vehicle 12, respectively.

In addition, the time-varying signal function received from the k-th other vehicle 12 is as shown in [Equation 2] below.

와

는 각각 송수신단의 빔포밍 벡터,

은 가우시안 잡음,

는 각 블록마다 시간 프레임일 수 있다.

는 송신 신호로 관찰되지 않는 잠재 변수(latent variable),

은 전파 지연일 수 있다.here

Wow

Is a beamforming vector of each transmitting and receiving end,

Silver Gaussian noise,

May be a time frame for each block.

Is a latent variable that is not observed as a transmitted signal,

May be the propagation delay.

That is, the channel estimating apparatus 10 based on maximization of the expected millimeter wave communication may estimate the millimeter wave channel based on the variable value of the time-varying signal function described above.

The expected value maximization calculation unit 920 may extract an unknown parameter for determining a time-varying signal from a time-varying signal function, calculate an expected value of log likelihood as an estimated value for the extracted unknown parameter, and maximize the expected value. It is possible to calculate the unknown parameter estimates.

Specifically, the expected value maximization calculator 920 may find a transmission/reception beam pair that maximizes a signal-to-noise ratio by maximizing an unknown parameter that determines a time-varying signal in a time-varying signal function. To this end, the expected value maximization calculator 920 may set an unknown parameter for EM-based channel estimation as shown in [Equation 3] below.

)에 관한 추정값으로 로그 가능도(log likelihood)의 기댓값을 산출하는 기댓값 (E)단계와 이 기댓값을 최대화하는 언노운 파라미터 추정값들을 산출하는 최대화 (M)단계로 설정할 수 있다. The expected value maximization calculation unit 920 is an unknown parameter (

) Can be set as an expected value (E) step, which calculates an expected value of log likelihood, and a maximization (M) step, which calculates unknown parameter estimates that maximize the expected value.

The detailed formula for each step is as shown in [Equation 4] below.

가 주어지고 새로운

를 사용할 때 가능도의 기댓값 Q를 정의할 수 있다. 이 때 기댓값을 취하는 확률 분포는

와

가 주어졌을 때 s의 조건부 분포일 수 있다.In the expected value (E) step

Is given and new

When using, we can define the expected value Q of likelihood. In this case, the probability distribution taking the expected value is

Wow

Given is, it can be a conditional distribution of s.

In the maximization (M) step, an unknown parameter for maximizing Q can be calculated as shown in [Equation 5] below.

The channel estimating unit 930 may calculate a time-varying signal from the calculated unknown parameter estimate values, and estimate a millimeter wave channel based on the calculated time-varying signal. Specifically, the above-described expected value (E) and maximization (M) steps are performed to calculate an unknown parameter that maximizes the Q value, and a time-varying signal is calculated by applying the calculated unknown parameter value to a time-varying signal function. The millimeter wave channel can be estimated based on the time-varying signal.

의 l은 반복 횟수일 수 있다.When the maximized expected value is less than a preset value, the channel estimating unit 930 may recalculate the expected value of the log likelihood and calculate an unknown parameter estimate value for maximizing the recalculated expected value. When the above-described Q value is less than a preset value, the channel estimator may repeat steps (E) and (M) of maximizing the Q value until the Q value is greater than or equal to the preset value. In [Equation 5]

L of may be the number of repetitions.

As described above, the channel estimating apparatus 10 based on maximizing the expected value of millimeter-wave communication may quickly estimate a millimeter-wave channel in which the signal-to-noise ratio is maximized by maximizing the expected value of the unknown parameter value.

In the above, the method of estimating the millimeter wave channel through the EM algorithm has been described, but this is an example and is not limited thereto. In addition, as long as the millimeter wave channel is estimated, a known technique can be applied.

In an embodiment, the channel estimation apparatus 10 based on the expected millimeter wave communication maximization calculates beamforming vectors of the own vehicle 11 and the other vehicle 12 through the estimated millimeter wave channel, and the accuracy of millimeter wave channel estimation It may further include a channel estimation accuracy determiner for calculating the error and.

The channel estimation accuracy determination unit may calculate beamforming vectors of the own vehicle 11 and the other vehicle 12 through the estimated channel through [Equation 6] below. Also, the channel estimation accuracy determination unit may determine the accuracy and error of channel estimation through [Equation 6].

Hereinafter, a method for estimating a channel based on maximization of an expected millimeter-wave communication using the channel estimation apparatus 10 based on an expected millimeter-wave communication maximization capable of performing all of the above-described present disclosure will be described.

10 is a flowchart illustrating a method of estimating a channel based on maximization of an expected millimeter wave communication value according to the present embodiment.

Referring to FIG. 10, in the method for estimating a channel based on an expected value of millimeter wave communication according to the present disclosure, a time-varying signal function is calculated for calculating a time-varying signal function in a millimeter-wave channel connected by V2X between the other vehicle 12 and the own vehicle 11 Step S1010 and an expected value maximization calculation step of calculating an expected value of log likelihood as an estimate of an unknown parameter that determines a time-varying signal in a time-varying signal function, and calculating estimates of an unknown parameter that maximizes the expected value (S1020) ) And calculating a time-varying signal value by applying the calculated unknown parameter estimation value to a time-varying signal function, and estimating a millimeter-wave channel based on the calculated time-varying signal (S1030). Here, the unknown parameter may include at least one of a propagation delay, an angle of arrival, an emission angle, and a complex channel gain.

In addition, the channel estimation method based on the expected millimeter wave communication value maximization according to the present disclosure calculates beamforming vectors of the own vehicle 11 and the other vehicle 12 through the estimated millimeter wave channel, and calculates the accuracy of millimeter wave channel estimation. It may further include determining the accuracy of the channel estimation.

In the expected value maximization calculation step S1020, the unknown parameter may include at least one of a propagation delay, an angle of arrival, an angle of emission, and a complex channel gain.

In the expected value maximization calculation step S1020, when the maximized expected value is less than a preset value, an expected value of the log likelihood may be recalculated and an unknown parameter estimate value for maximizing the recalculated expected value may be calculated.

11 is a flowchart illustrating a method of maximizing an expected value of an unknown parameter according to an exemplary embodiment.

Referring to FIG. 11, an apparatus for estimating a channel based on an expected value for millimeter wave communication may calculate an expected value of a log likelihood as an estimated value for an unknown parameter (S1110). The channel estimation apparatus 10 based on the millimeter wave communication expected value maximization may extract an unknown parameter capable of determining the time-varying signal function from the time-varying signal function.

를 사용할 때 가능도의 기댓값 Q를 최대화하는 언노운 파라미터를 산출할 수 있다.The channel estimation apparatus 10 based on millimeter wave communication expected value maximization may maximize the expected value calculated by applying the above-described [Equation 4] (S1120). The millimeter-wave communication expected value maximization-based channel estimation apparatus 10 performs the step of maximizing the expected value, thereby in [Equation 4]

When using, we can calculate an unknown parameter that maximizes the expected value Q of likelihood.

The channel estimation apparatus 10 based on the millimeter wave communication expected value maximization may determine whether the calculated Q value is equal to or greater than a preset value (S1130). If the calculated Q value is greater than or equal to a preset value, the millimeter wave communication expected value maximization-based channel estimation apparatus 10 may terminate the expected value maximization step and apply the calculated unknown parameter to the time-varying signal function (Yes in S1130). In addition, when the calculated Q value is less than a preset value, the millimeter wave communication expected value maximization-based channel estimation apparatus may re-perform the expected value calculation step of maximizing the Q value and the expected value maximization step (No in S1130).

According to the foregoing, the apparatus and method for estimating a channel based on an expected value maximization of millimeter wave communication undergoes a step of maximizing an expected value of an unknown parameter applied to a time-varying signal, so that all transmission and reception beams are not sequentially transmitted, so that overhead is not generated, and is optimal. The processing speed can be improved by estimating the channel.

The above-described embodiments may be supported by standard documents disclosed in at least one of IEEE 802, 3GPP, and 3GPP2 wireless access systems. That is, steps, configurations, and parts not described in order to clearly reveal the present technical idea among the embodiments may be supported by the aforementioned standard documents. In addition, all terms disclosed in this specification may be described by the standard documents disclosed above.

The above-described embodiments can be implemented through various means. For example, the present embodiments may be implemented by hardware, firmware, software, or a combination thereof.

In the case of implementation by hardware, the method according to the embodiments includes one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), and FPGAs. (Field Programmable Gate Arrays), can be implemented by a processor, a controller, a microcontroller, a microprocessor.

In the case of implementation by firmware or software, the method according to the embodiments may be implemented in the form of an apparatus, procedure, or function that performs the functions or operations described above. The software code may be stored in a memory unit and driven by a processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor through various known means.

In addition, terms such as "system", "processor", "controller", "component", "module", "interface", "model", and "unit" described above are generally used for computer-related entity hardware, hardware and software. It can mean a combination, software, or running software. For example, the above-described components may be, but are not limited to, a process driven by a processor, a processor, a controller, a control processor, an object, an execution thread, a program, and/or a computer. For example, components can be both a controller or processor and an application running on a controller or processor. One or more components can reside within a process and/or thread of execution, and components can reside on one machine or be deployed on more than one machine.

The description above and the accompanying drawings are merely illustrative of the spirit of the present technology, and those of ordinary skill in the art can combine, separate, replace, and configure configurations within the range not departing from the essential characteristics of the present technology. Various modifications and variations such as changes will be possible. Accordingly, the embodiments disclosed in the present specification are not intended to limit the present technical idea, but to describe it, and the scope of the present technical idea is not limited by these embodiments. The scope of protection of the present technical idea should be interpreted by the claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present specification.

10: millimeter wave communication expected value maximization based channel estimation device
910: time-varying signal function calculation unit 920: expected value maximization calculation unit
930: channel estimation unit

Claims (8)

A time-varying signal function calculating unit for calculating a time-varying signal function in a millimeter wave channel connected by V2X between the other vehicle and the own vehicle;
An expected value maximization calculation unit that calculates an expected value of log likelihood as an estimate value for at least one unknown parameter extracted based on the time-varying signal function, and calculates estimated values of unknown parameters that maximize the expected value; And
A channel estimating unit for calculating a time-varying signal value by applying the calculated unknown parameter estimate value to a time-varying signal function, and estimating a millimeter wave channel based on the calculated time-varying signal value,
The expected value maximization calculation unit,
When the maximized expected value is less than a preset value, the expected value of the log likelihood is recalculated and an estimated unknown parameter for maximizing the recalculated expected value is calculated.
The method of claim 1,
The unknown parameter is,
A millimeter wave communication expected value maximization-based channel estimation apparatus comprising at least one of a propagation delay, an angle of arrival, an emission angle, and a complex channel gain.
delete The method of claim 1,
A channel estimation apparatus based on an expected millimeter wave communication, further comprising a channel estimation accuracy determination unit that calculates beamforming vectors of the own vehicle and the other vehicle through the estimated millimeter wave channel, and calculates the accuracy of the millimeter wave channel estimation.
A time-varying signal function calculating step of calculating a time-varying signal function in a millimeter-wave channel connected by V2X between the other vehicle and the own vehicle;
An expected value maximization calculation step of calculating an expected value of log likelihood as an estimate value for at least one unknown parameter extracted based on the time-varying signal function, and calculating unknown parameter estimate values that maximize the expected value; And
Comprising a channel estimation step of calculating a time-varying signal value by applying the calculated unknown parameter estimate value to a time-varying signal function, and estimating a millimeter wave channel based on the calculated time-varying signal,
The expected value maximization calculation step,
When the maximized expected value is less than a preset value, the expected value of the log likelihood is recalculated and an unknown parameter estimation value for maximizing the recalculated expected value is calculated.
The method of claim 5,
The unknown parameter is,
A method of estimating a channel based on an expected value maximization of millimeter-wave communication including at least one of a propagation delay, an angle of arrival, an emission angle, and a complex channel gain.
delete The method of claim 5,
A channel estimation method based on the maximization of an expected millimeter wave communication, further comprising: calculating a beamforming vector of the own vehicle and the other vehicle through the estimated millimeter wave channel, and calculating the accuracy of the millimeter wave channel estimation.

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