WO2017188536A1

WO2017188536A1 - Method and apparatus for receiving synchronization signal in wireless communication system

Info

Publication number: WO2017188536A1
Application number: PCT/KR2016/013140
Authority: WO
Inventors: 안민기; 이길봄; 김기준; 김규석; 정재훈; 김봉회; 안준기
Original assignee: 엘지전자 주식회사
Priority date: 2016-04-27
Filing date: 2016-11-15
Publication date: 2017-11-02
Also published as: WO2017188545A1

Abstract

Provided are a method and a device for receiving a synchronization signal in a wireless communication system. Specifically, a terminal receives, from a base station, an ESS which is multiplexed, using an FDM method, and transmitted for each symbol in a synchronization subframe. The ESS comprises a ZC sequence. The terminal acquires transmission period information of the synchronization subframe on the basis of a root value of the ZC sequence. The terminal acquires symbol location information of the synchronization subframe on the basis of a cyclic shift value of the ZC sequence.

Description

Method and apparatus for receiving synchronization signal in wireless communication system

The present disclosure relates to wireless communication, and more particularly, to a method for receiving a synchronization signal in a wireless communication system and a device using the same.

Wireless communication systems have been studied to support higher data rates in order to meet the increasing demand for wireless data traffic. One such method is to use a beamforming-based base station that utilizes a wide frequency band in the millimeter wave (mmWave) band can be expected to dramatically increase the capacity of the cellular system.

On the other hand, in order to transmit a plurality of information to a single user or multiple users, multiple digital path (RF) or RF in a multiple input multiple output (MIMO) system that is considered in the existing standard such as Long Term Evolution (LTE) -Advanced It has a (Radio Frequency) chain. When performing MIMO communication using such a plurality of digital paths, performance gains such as diversity gain or multiplexing gain can be obtained. Nevertheless, increasing the number of digital paths to achieve greater gains can lead to problems such as synchronization, cost, and operational complexity between the digital paths.

In millimeter-wave band systems, the disadvantages of path attenuation can be offset by beamforming gains using a large number of physical antennas. However, the digital beamforming technique in the existing MIMO system requires a large number of RF chains because one RF chain is required for one physical antenna. This causes problems such as cost and operational complexity. Therefore, a hybrid beamforming system using digital beamforming and analog beamforming may be considered for efficient communication in the millimeter wave band. Analog beamforming connects multiple physical antennas to an RF chain in an array and uses a phase shifter to form a narrow beam. Compared to digital beamforming, analog beamforming has a low implementation cost and complexity because it does not increase the number of digital paths, although the beam sharpness and flexibility of the beam control are reduced. In order to efficiently obtain high communication capacity in the millimeter wave band, a hybrid beamforming system may be considered in which the advantages and disadvantages of the digital beamforming and the analog beamforming are appropriately combined.

The present disclosure provides a method and apparatus for receiving a synchronization signal in a wireless communication system.

The present specification proposes a method for receiving a synchronization signal in a wireless communication system.

First, the UE receives an Extended Synchronization Signal (ESS) which is multiplexed and transmitted by a frequency division multiplex (FDM) method for each symbol in a synchronization subframe from a base station. The ESS consists of a Zadoff-Chu (ZC) sequence.

In addition, the UE may receive a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS), which are multiplexed with the ESS by the FDM scheme for each symbol in the synchronization subframe from the base station.

PSS and SSS are used as in the existing LTE system. That is, the terminal may estimate the cell ID group through the PSS and may estimate the cell ID through the SSS. However, in the New RAT millimeter wave band system, unlike the existing LTE system, symbol position ambiguity may occur due to beam sweeping for each symbol. In order to solve this problem, the next-generation communication system may use the ESS to transmit symbol position information.

In addition, the UE may receive a PBCH (Physical Broadcast Channel) multiplexed with the ESS in the FDM scheme for each symbol in the synchronization subframe from the base station. However, in the millimeter wave band, when the transmission period information of the synchronization subframe is transmitted through the PBCH, the complexity of the terminal is increased because the terminal must decode the PBCH when the UE searches for a neighboring base station (adjacent cell). In order to solve this problem, the UE transmits transmission period information through the ESS using the ZC sequence. As a result, the terminal may not decode the PBCH used to search for the neighbor base station.

The terminal obtains transmission period information of the synchronization subframe based on a root value of the ZC sequence.

The UE obtains symbol position information of the synchronization subframe based on a cyclic shift value of the ZC sequence.

The terminal may receive a signal from reception beams indicating different directions. When the signal is received through the optimum beam of the terminal at this time, the beam gain (beam gain) is the largest to generate a peak (peak). If the cyclic shift values are the same, the autocorrelation of the ZC sequence does not become zero, indicating that a peak has occurred.

As a result, the terminal can determine the transmission period information of the synchronization subframe as the root value through the ESS. Therefore, the root value of the ZC sequence is set identically in one synchronization subframe. In addition, the UE may determine the number of symbols in the synchronization subframe through the ESS as a cyclic shift value. Accordingly, the cyclic shift value of the ZC sequence is set differently for each symbol in one synchronization subframe.

In addition, the root value of the ZC sequence and the cyclic shift value of the ZC sequence are sequentially decoded. Since the root value and the cyclic shift value can be detected sequentially, the estimation complexity at the terminal can be greatly reduced.

In addition, the UE may obtain the number of antenna ports of a BRS (Beam Reference Signal) based on the root value of the ZC sequence. The BRS may be multiplexed and received in the FDM scheme together with the ESS for each symbol in the synchronization subframe from the base station.

In addition, the transmission period information of the synchronization subframe or the number of antenna ports of the BRS may be obtained by using conjugate pairs of the ZC sequence. That is, by using a mapping method using conjugate complex pairs of ZC sequences, the decoding process can be implemented with fewer correlators, thereby reducing the decoding process by half.

In addition, the present specification proposes an apparatus for receiving a synchronization signal in a wireless communication system.

The device may be a terminal. The apparatus includes a radio frequency (RF) unit for transmitting and receiving radio signals and a processor coupled to the RF unit. The processor first receives an Extended Synchronization Signal (ESS) which is multiplexed and transmitted by a frequency division multiplex (FDM) method for each symbol in a synchronization subframe from a base station. The ESS consists of a Zadoff-Chu (ZC) sequence.

The processor obtains transmission period information of the synchronization subframe based on a root value of the ZC sequence.

The processor obtains symbol position information of the synchronization subframe based on a cyclic shift value of the ZC sequence.

This specification proposes an ESS structure to perform synchronization of downlink initial access in a next-generation communication system. The base station may transmit not only symbol position information but also transmission period information and antenna port information of the BRS through the proposed ESS. Thus, the UE can greatly reduce the complexity of the UE by omitting the PBCH estimation process when searching for neighbor cells.

1 shows a structure of a radio frame in 3GPP LTE.

FIG. 2 is an exemplary diagram illustrating a resource grid for one uplink slot in 3GPP LTE.

3 shows an example of a structure of a downlink subframe in 3GPP LTE.

4 shows an example of an antenna array based antenna structure and a single beam.

5 shows an example of an antenna array based antenna structure and a multi beam.

6 is a configuration diagram of a hybrid beamforming based system to which an embodiment of the present specification can be applied.

7 shows an example of a structure of a synchronization subframe including a synchronization signal and a BRS according to an embodiment of the present specification.

8 is a flowchart illustrating a sequence allocation method according to an embodiment of the present invention.

9 illustrates an example of receiving a synchronization signal according to an embodiment of the present specification.

10 is a flowchart illustrating a procedure for receiving a synchronization signal according to an embodiment of the present specification.

11 is a block diagram illustrating a device in which an embodiment of the present specification is implemented.

The following technologies include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier-frequency division multiple access (SC-FDMA), and the like. Such as various wireless communication systems. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) long term evolution (LTE) is part of an Evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink.

For clarity, the following description focuses on 3GPP LTE / LTE-A, but the technical spirit of the present invention is not limited thereto.

1 shows a structure of a radio frame in 3GPP LTE.

Referring to FIG. 1, a radio frame consists of 10 subframes, and one subframe consists of two slots. Slots in a radio frame are numbered from 0 to 19 slots. The time taken for one subframe to be transmitted is called a transmission time interval (TTI). TTI may be referred to as a scheduling unit for data transmission. For example, one radio frame may have a length of 10 ms, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms.

The structure of the radio frame is merely an example, and the number of subframes included in the radio frame or the number of slots included in the subframe may be variously changed.

Referring to FIG. 2, an uplink slot includes a plurality of SC-FDMA symbols in a time domain and includes a _Nul resource block (RB) in a frequency domain. The SC-FDMA symbol is used to represent one symbol period and may be called an OFDMA symbol or a symbol period according to a system. The RB includes a plurality of subcarriers in the frequency domain in resource allocation units. The number _Nul of resource blocks included in the uplink slot depends on the uplink transmission bandwidth set in the cell. The uplink transmission bandwidth is system information. The terminal may know N _ul by acquiring system information.

Each element on the resource grid is called a resource element. Resource elements on the resource grid may be identified by an index pair (k, l) in the slot. Where k (k = 0, ..., _Nul × 12-1) is the subcarrier index in the frequency domain, and l (l = 0, ..., 6) is the SC-FDMA symbol index in the time domain.

Here, an exemplary resource block includes 7 SC-FDMA symbols in the time domain and 7 × 12 resource elements including 12 subcarriers in the frequency domain, but the number of subcarriers in the resource block and the SC-FDMA symbol are exemplarily described. The number of is not limited thereto. The number of SC-FDMA symbols or the number of subcarriers included in the RB may be variously changed. The number of SC-FDMA symbols may be changed according to the length of a cyclic prefix (CP). For example, the number of SC-FDMA symbols is 7 for a normal CP and the number of SC-FDMA symbols is 6 for an extended CP.

In 3GPP LTE of FIG. 2, a resource grid for one uplink slot may be applied to a resource grid for a downlink slot. However, the downlink slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in the time domain.

3 shows an example of a structure of a downlink subframe in 3GPP LTE.

Referring to FIG. 3, the downlink subframe includes two contiguous slots. Up to three OFDM symbols of the first slot in the downlink subframe are control regions to which a physical downlink control channel (PDCCH) is allocated, and the remaining OFDM symbols are data regions to which a physical downlink shared channel (PDSCH) is allocated. data region). In addition to the PDCCH, the control region may be allocated a control channel such as a physical control format indicator channel (PCFICH) and a physical hybrid-ARQ indicator channel (PHICH). Here, it is merely an example that the control region includes 3 OFDM symbols. The number of OFDM symbols included in the control region in the subframe can be known through the PCFICH. The PHICH carries hybrid automatic repeat request (HARQ) acknowledgment (ACK) / not-acknowledgement (NACK) information in response to uplink data transmission.

The PDCCH may carry a downlink grant informing of resource allocation of downlink transmission on the PDSCH. The UE may read downlink user data transmitted through the PDSCH by decoding control information transmitted through the PDCCH. In addition, the PDCCH may carry control information used for physical uplink shared channel (PUSCH) scheduling to the UE. The control information used for PUSCH scheduling is an uplink grant informing of resource allocation of uplink transmission.

The control region consists of a set of a plurality of control channel elements (CCE). The PDCCH is transmitted on an aggregation of one or several consecutive CCEs. The CCE corresponds to a plurality of resource element groups. Resource element groups are used to define control channel mappings to resource elements. If the total number of CCEs in the downlink subframe is N _cce , the CCE is _indexed from 0 to N _cce , k-1. Since the number of OFDM symbols included in the control region in the subframe may change for each subframe, the total number of CCEs in the subframe may also change for each subframe.

Hereinafter, a beamforming technique will be described.

Beamforming may be classified into transmit beamforming performed by a transmitting end and receive beamforming performed by a receiving end. The transmission beamforming generally uses multiple antennas to increase the directivity by concentrating the area of arrival of radio waves in a specific direction. In this case, a form in which a plurality of antennas are collected may be referred to as an antenna array, and each antenna included in the antenna array may be referred to as an array element. The antenna array may be configured in various forms such as a linear array and a planar array. In addition, using the transmission beamforming increases the directivity of the signal, thereby increasing the transmission distance of the signal. In addition, since a signal is hardly transmitted in a direction other than the direction to which the signal is directed, signal interference with respect to other receivers is greatly reduced at the receiver.

The receiving end may perform beamforming on the received signal using the receiving antenna array. The reception beamforming concentrates the reception of radio waves in a specific direction to increase the sensitivity of the reception signal received in the specific direction, and blocks the interference signal by excluding signals from directions other than the specific direction from the reception signal. to provide.

Referring to FIG. 4, one radio frequency (RF) beam (single beam) is defined using one antenna array including two sub-arrays. At this time, one sub array is composed of 8 (H) * 8 (V) * 2 (P) antennas (P denotes Xpol) and has two RF chains. In addition, the width of the one RF beam is 15 '(H) * 15' (V).

Referring to FIG. 5, RF beams having different directions for each RF chain are defined. In this case, four beams according to each RF chain may cover different areas.

When beam scanning using the single beam or the multi-beam, there are advantages and disadvantages as shown in Table 1 below.

Table 1

	Single beam	Multi beam
Advantages	High beam gain	Fast beam scanning
Disadvantages	Slow beam scanning	Lower beam gain

Hereinafter, a method and apparatus for a terminal to feed back more accurate channel related information on an effective channel to a base station in an environment in which multiple signals are transmitted to a single user or multiple users.

Referring to FIG. 6, the hybrid beamforming based system 600 includes, for example, a transmitter 610 and a receiver 620. The transmitters 610 each have a predetermined number of antenna arrays 616 to form a MIMO channel. For convenience of description, it is assumed that a total of n antenna arrays 616-1, 616-2,..., 616-n are provided. Each of the antenna arrays 616-1, 616-2, ..., 616-n consists of a predetermined number of antenna elements. Here, the case of the same number of antenna elements constituting each antenna array is illustrated, but may be composed of a different number of antenna elements for each antenna array. The receiver 620 may also include antenna arrays 622-1, 622-2,..., 622-m configured in the same manner as the antenna array of the transmitter 610. Here, as an example, it is assumed that the total number of antenna array 622 of the receiver 620 is m. M and n are each one or more natural numbers, and may be set to the same value or different values according to embodiments.

The transmitter 610 includes a MIMO encoder 612 and a baseband precoder 614 for encoding and precoding a signal to be transmitted, and the receiver 620 is configured to provide the antenna array 622. A case where a baseband combiner 624 and a MIMO decoder 626 for combining and decoding a signal received through the apparatus is illustrated. Each of the transmitter 610 and the receiver 620 is illustrated in a form that includes schematic configurations for convenience of description, and may be embodied in more detailed configurations according to an embodiment of the present specification.

In the hybrid beamforming-based communication system as described above, when a transmitter transmits a plurality of signals to multiple users or a single user (hereinafter, referred to as 'multiplex transmission'), channel related information fed back through the corresponding receiver Can be used for various purposes. As a representative example, when the transmitter adopts a precoding scheme based on the channel-related information in the multiplexing transmission, the transmitter reduces system transmission capacity by reducing interference between signals of a single user or interference among multiple users with multiple antennas. Can be increased.

It is assumed that frequency division duplexing (FDD) is used in the hybrid beamforming based communication system. In this case, when the receiver receives a reference signal from the transmitter, the receiver may estimate channel information between the transmitter and the receiver using the received reference signal. The estimated channel information is fed back to the transmitter. For example, in the LTE-Advanced system, the feedback of the estimated channel information is referred to as PMI (Precoding Matrix Indicator) feedback. The PMI fed back from the receiver is used when the transmitter forms a precoding matrix for the receiver. Specifically, the transmitter and the receiver prestore the precoding matrix, and the PMI indicates one of the precoding matrices.

In addition, the receiver may further transmit a channel quality indicator (CQI) to the transmitter, and based on this, the transmitter may be used for scheduling, selection of a modulation and coding scheme (MCS), and the like.

When the hybrid beamforming based system 600 operates in the millimeter wave band, it has a very small antenna form factor due to the high frequency band. Therefore, the configuration of the beamforming system using a plurality of array antennas becomes very easy. The beamforming in the millimeter wave band can be transmitted by changing the beam direction in a desired direction by applying different phase shift values to each array antenna element. In addition, each antenna element may be arranged to have a narrow beam width in order to compensate for high pathloss in the millimeter wave band.

Accordingly, the hybrid beamforming-based communication system 600 as shown in FIG. 6 has a difference from the conventional MIMO system in that a beam is formed using an antenna array.

Specifically, in the case of configuring the hybrid beamforming-based communication system for multiple users, as the number of antenna arrays is increased, the sharper the beam of each antenna array, the effective channel gain for the antenna. The difference between the gains is large. For example, assuming a beam division multiple access (BDMA) type communication in which a single beam transmits a signal for only one user, a gain value of an effective channel for an antenna corresponding to the single beam is higher than that of the other antennas. It has a very high value, the gain value of the effective channel for each of the remaining antennas may have a value close to '0'.

Meanwhile, as one example of existing wireless communication standards, LTE-Advanced uses a code book based on a unitary matrix for PMI feedback. The unitary matrix is uniform in that the variation in channel gain is not large.

In addition, in the hybrid beamforming-based communication system 600, the terminal selects an analog beam corresponding to a beam formed by a physical antenna using a beam reference signal (BRS), and uses a codebook to obtain the best digital signal. Select a digital beam. The digital beam may correspond to a digital precoder. The terminal may feed back the selected analog beam and digital beam to the base station, and the base station may perform beamforming to the terminal using the analog beam and the digital beam. Analog beams are rough, beam wide and slow variation. Digital beams are accurate, narrow in beam width, and fast in variation. Therefore, in the hybrid beamforming based communication system 600, a sharp final beam can be obtained.

In an existing LTE system, a primary synchronization channel (P-SCH) is located in the last OFDM symbol of the 0 th slot and the 10 th slot of a radio frame. Two P-SCHs use the same primary synchronization signal (PSS). P-SCH is used to obtain OFDM symbol synchronization or slot synchronization. The PSS may use a ZCoff (Zadoff-Chu) sequence, and each PSS may indicate a cell identity according to the root value of the ZC sequence. If there are three PSSs, the base station selects one of the three PSSs and sends the last OFDM symbol in the 0 th slot and the 10 th slot.

The Secondary Synchronization Channel (S-SCH) is located in the last OFDM symbol in the last OFDM symbol of the 0 th slot and the 10 th slot of a radio frame. The S-SCH and the P-SCH may be located in contiguous OFDM symbols. S-SCH is used to obtain frame synchronization. One S-SCH uses two secondary synchronization signals (SSS). One S-SCH includes two PN sequences, namely m-sequences. For example, when one S-SCH includes 64 subcarriers, two PN sequences of length 31 are mapped to one S-SCH.

The number and location of OFDM symbols in which P-SCHs and S-SCHs are arranged on a slot is merely an example, and may be variously changed according to a system.

Hereinafter, a subframe structure in which a synchronization signal is transmitted in a millimeter wave band system will be described.

Reference signals such as Channel State Indicator (CSI) -Reference Signal (RS) include Time Division Multiplexing (TDM), Frequency Division Multiplexing (TDM) for a plurality of beams supported by a base station; FDM) or Code Division Multiplexing (CDM) scheme is transmitted. The CSI-RS has a wide radiation angle of 120 degrees for each antenna port. However, a BRS (Beam Reference Signal) that may be applied in an embodiment of the present specification is a reference signal for feeding back beam state information about a plurality of beams. The BRS can be applied to a sharp beam because the beam radiation angle is smaller than that of the CSI-RS. In addition, the BRS may be multiplexed by FDM for each antenna port in one symbol and transmitted during at least one subframe. In this case, one antenna port may correspond to one beam of the plurality of beams for each symbol of the at least one subframe. That is, as illustrated in FIG. 7, the BRS may be transmitted only at different resource elements RE for each antenna port.

The subframe transmitting the BRS may be referred to as a synchronization subframe. The synchronization subframe has 12 or 14 symbols and may be transmitted according to a transmission period in which one synchronization subframe is transmitted every 5 ms. Here, it is assumed that the synchronization subframe has 14 symbols (two slots) in consideration of the case of a normal CP. The symbol may correspond to an OFDM symbol.

The terminal acquires downlink synchronization using a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and / or an extended synchronization signal (ESS), and then selects an optimal beam using a BRS. Referring to FIG. 7, synchronization signals such as PSS, SSS and / or ESS occupy a relatively small band based on the center frequency. On the other hand, since BRS occupies the entire system band of the base station, the BRS has an advantage of searching for an optimal beam based on a wideband channel.

In addition, PSS, SSS and / or ESS are multiplexed by FDM in one symbol. In addition, the BRS is also multiplexed by the FDM scheme in one symbol and a synchronization signal such as the PSS, SSS and / or ESS. In the case of the millimeter wave band, since the sharp beam is used, the synchronization subframe shown in FIG. 7 may be used to cover the area where the beam emission angle is 120 degrees. The synchronization subframe consists of 14 PSSs, and 14 PSSs point in different directions. The UE is time synchronized with the PSS having the strongest received power among the 14 PSSs.

In the New Radio Access Technology (RAT) millimeter wave band system, it may be assumed that PSS / SSS in an existing LTE system is reused. That is, in the millimeter wave band system, the OFDM symbol timing and the cell ID group can be estimated using the PSS. In addition, it is possible to estimate the cell ID using the SSS. However, in the millimeter wave band system, symbol location ambiguity may occur due to beam sweeping for each symbol unlike the existing LTE system. In order to solve this problem, in the New RAT millimeter wave band system, a new synchronization signal, that is, an ESS, may be considered as shown in FIG. 7 to transmit symbol position information. Therefore, the present specification proposes a method for configuring an ESS assuming a synchronization subframe structure as shown in FIG.

Hereinafter, a sequence used in the wireless communication system will be described.

In wireless communication systems, sequences are widely used for signal detection, channel estimation, and multiplexing. Orthogonal sequences with good correlation characteristics are used to easily detect sequences at the receiver. An example of an orthogonal sequence is a constant amplitude zero auto-correlation (CAZAC) sequence.

The Zadoff-Chu sequence, which is one of the CAZAC sequences, is called a Chu sequence or a ZC sequence. In the following, it is referred to collectively as a ZC sequence. The n th element of the ZC sequence may be expressed as the following equation.

Equation 1

Where N is the length of the ZC sequence and r is the root value. The ZC sequence has three important features.

(1) All elements of the ZC sequence have the same size. (Constant Amplitude)

The Discrete Fourier Transform (DFT) result of the ZC sequence also has the same size of all elements.

(2) The correlation between the ZC sequence and the sequence in which the ZC sequence is cyclically shifted (autocorrelation of the ZC sequence) can be expressed as follows.

Equation 2

In the above equation

Defines Xr as a sequence of i cycles. The above equation indicates that the auto-correlation of the ZC sequence is 0 except when i = j (Zero Auto-Correlation). The ZC sequence is also called a CAZAC sequence because all elements have the same magnitude (Constant Amplitude) and Zero Auto-Correlation.

(3) The correlation (correlation of the ZC sequence) of the ZC sequence having a length N and a root value that is mutually prime can be expressed as follows.

Equation 3

Unlike the autocorrelation of Equation 2, the cross-correlation of the ZC sequence of Equation 3 is not completely zero.

Referring to FIG. 8, the length L of the mapping section to which the sequence is mapped is determined (S810). The mapping section may be a data channel for transmitting user data or a control channel for transmitting a control signal. In another form, the mapping section may be a radio resource carrying data. The mapping interval may be a constant interval including a plurality of subcarriers.

The length N of the sequence is determined (S820). The sequence length N may be smaller than the length L of the mapping interval or may be larger than the length L of the mapping interval. In an embodiment, when the length L of the mapping interval is even, the sequence length N may select the next odd number larger than the length L of the mapping interval. Alternatively, the sequence length N may select an immediately preceding odd number smaller than the length L of the mapping interval. This is because the correlation of the ZC sequence and the sequence itself characteristics are better generated from odd lengths than from even lengths. In another embodiment, the sequence length N may select the next even number greater than the length L of the mapping interval. Alternatively, the sequence length N may select an even number just before the length L of the mapping interval. If the length L of the mapping interval is odd, the sequence length N may be selected as an even number. In another embodiment, the sequence length N may be made larger than the length L of the mapping interval by one. Alternatively, the sequence length N may be made smaller than the length L of the mapping interval. By making the sequence length N differ by 1 from the length L of the mapping section, and assigning this sequence to the mapping section, the sequence characteristic (correlation characteristic) can be improved.

The sequence is adjusted to fit the length L of the mapping section (S830). If the sequence length N is smaller than the length L of the mapping interval, a null (for example, zero) is inserted, an arbitrary value, or a cyclic transposition in the interval exceeding the sequence length N. You can insert a prefix or a cyclic suffix. When the sequence length N is larger than the length L of the mapping interval, any element of the elements included in the sequence may be removed. For example, you can remove from the end of the sequence.

The sequence is mapped to the mapping section (S840). If there is a DC component in the interval, the DC component may be punctured. That is, the sequence is continuously mapped to the mapping interval, and the element corresponding to the DC component is replaced with null. As another example, the sequence may be mapped to the interval excluding the DC component. The DC component refers to the point where the center frequency or frequency offset is zero in the baseband.

Here, an example of mapping a sequence to a mapping section after adjusting the length of the sequence according to the length of the mapping section, but after mapping the sequence to the mapping section, may adjust the length of the sequence according to the length of the mapping section.

In an OFDM / OFDMA system, a sequence is mapped to a subcarrier in the frequency domain. If the transmission scheme is a single carrier, for example an SC-FDMA system, the sequence is mapped to a time domain sample. Control channels based on sequences or ZC sequences used as pilots can be mapped directly in the frequency domain.

In the New RAT millimeter wave band, the transmitter performs a beam sweep using an analog beam. Therefore, the transmitting end transmits the same PSS / SSS information on the time axis within the synchronization subframe. Since the PSS / SSS of the existing LTE system cannot synchronize the symbol position in this environment, the ESS is considered. Meanwhile, in the New RAT millimeter wave band, the transmission period of the synchronization subframe may be variously varied according to a system environment such as 5ms, 10ms, 20ms, and 40ms.

In this system environment, when transmission period information of a synchronization subframe is transmitted from a transmitter through a PBCH (Physical Broadcast Channel), the UE must decode the PBCH when searching for an adjacent cell. Therefore, a problem arises in that the complexity of the terminal increases.

In order to solve this problem, the present specification proposes a scheme for configuring an ESS for synchronization of downlink initial access in a next-generation communication system. Specifically, the UE may additionally detect the transmission period information of the synchronization subframe as well as the symbol position information using the characteristics of the ZC sequence.

ESS can be defined using ZC sequence. The base station may transmit transmission period information and symbol position information using a root value and a cyclic shift value of the ZC sequence. That is, the base station can transmit the transmission period information through the ESS using the ZC sequence. Specifically, the base station transmits transmission period information as a root value using a ZC sequence and transmits symbol position information as a cyclic shift value.

For example, referring to FIG. 7, PSS and SSS are used as in the existing LTE system. That is, the terminal may estimate the cell ID group through the PSS and may estimate the cell ID through the SSS. However, in the New RAT millimeter wave band system, unlike the existing LTE system, symbol position ambiguity may occur due to beam sweeping for each symbol.

As a result, the UE can determine the transmission period information of the synchronization subframe shown in FIG. 7 as the root value through the ESS. Thus, the root value has the same value in one synchronization subframe. In addition, the UE may determine the number of symbols in the synchronization subframe through the ESS as a cyclic shift value. Accordingly, the cyclic shift value has a different value for each symbol in the synchronization subframe.

However, this increases the number of hypothesis of the ZC sequence, which increases the complexity of ESS estimation. However, it is possible to minimize the increase in the complexity of the terminal by using Equation 4 below. Equation 4 is a metric for obtaining an estimated value of the root.

Equation 4

Where y _k is the received signal of the kth subcarrier, r is the root value,

Is the trial value of root,

Is an estimated value of root, q is a cyclic shift value, and N is the length of the sequence.

If the noise is ignored in Equation 4, it can be expressed as follows. Equation 5 is a metric for obtaining an estimated value of a root when ignoring noise.

Equation 5

If in Equation 5

When the estimated value of the root can be maximized as follows.

Equation 6

As a result, it can be seen that the optimal route value can be found using Equation 4 irrespective of the cyclic shift value.

However, in Equation 5

, The estimated value of the route can be approximated as follows.

Equation 7

To keep it simple

Assume that the estimated value of the root can be expressed as follows.

Equation 8

In Equation 8

It can be seen that when the estimated value of the root of about 1 / N. Thus, it can be seen that the proposed metric for finding the root value can work efficiently.

As an example, a method of transmitting transmission period information using a ZC sequence of length 71 is as follows.

TABLE 2

Root value	Beam period (transmission period of synchronization subframe)
25	5 ms
29	10 ms
33	20 ms
37	40 ms

The proposed method can omit the process of estimating PBCH for neighboring cell search by additionally transmitting transmission period information through the ESS. In addition, the proposed scheme can detect the root value and the cyclic shift value sequentially, thereby greatly reducing the decoding complexity in the terminal. For example, when cyclic shift (CS) = 16 and root = 4, there are a total of 64 hypothesis. However, in case of using the proposed method, by detecting root = 4 first and cyclic shift (CS) = 16, only 20 hypothesis can be considered. Therefore, the estimated complexity of the terminal can be lowered from 64 to 20.

As another example, a method of mapping a transmission period to a root value using conjugate pairs of ZC sequences is as follows.

TABLE 3

Root value	Beam period (transmission period of synchronization subframe)
25	5 ms
29	10 ms
42	20 ms
46	40 ms

By using a mapping method using conjugate complex pairs of the ZC sequence, fewer correlators may be implemented in the decoding process. In Table 2, the root value must be decoded using four correlators to obtain transmission period information according to the root value. However, in Table 3, one correlator can be used to decode the root value, which is a complex pair, and two correlators can be used to decode the root value. If the length of the sequence is 71, complex conjugate pairs can be configured such that the sum of the root values is 71. In Table 3, the root values and 25 and 46 are one conjugate pair, and the root values 29 and 42 are one conjugate pair. As a result, the decoding performance can be reduced by half than before, thereby minimizing hardware cost and power consumption.

As another example, a method of transmitting transmission period information and the number of BRS antenna ports by using a root value of a ZC sequence is as follows.

Table 4

Root value	Beam cycle	Number of BRS Ports
25	5 ms	2
29	5 ms	4
33	10 ms	2
37	10 ms	4

Table 5

Root value	Beam cycle	Number of BRS Ports
25	5 ms	2
29	10 ms	2
42	10 ms	4
46	5 ms	4

The proposed scheme can transmit not only the transmission period information but also the number of BRS antenna ports using the root value of the ZC sequence. In the proposed method, the transmission period information and the number of BRS antenna ports can be obtained simply by using a root value as shown in Table 4, and the transmission period information and the number of BRS antenna ports using a conjugate pair of ZC sequences as shown in Table 5 below. Can be obtained. That is, in Table 4, to obtain the transmission period information and the number of BRS antenna ports, the root value must be decoded using four correlators. In Table 5, the root value must be decoded using two correlators to obtain transmission period information and the number of BRS antenna ports.

9, in order to perform synchronization of downlink initial access in a next-generation communication system, the base station transmits PSS / SSS / ESS to the terminal (S910). The synchronization subframe for the downlink initial access is shown in FIG. In order to perform synchronization as in the existing LTE system, the base station may transmit the PSS / SSS. However, since the next generation communication system supports a communication environment using beam scanning, symbol position ambiguity may occur due to beam sweeping for each symbol unlike the existing LTE system. In order to overcome this, the base station may transmit a new synchronization signal, that is, an ESS, for transmitting symbol position information to the terminal. The ESS is defined using a ZC sequence and transmits transmission period information and symbol position information using a root value and a cyclic shift value of the ZC sequence.

The terminal obtains transmission period information based on the root value of the ZC sequence (S920). In addition, the terminal obtains symbol position information based on the cyclic shift value of the ZC sequence (S930). At this time, since the terminal decodes the root value and the cyclic shift value sequentially, the complexity of the entire decoding process can be greatly reduced.

The terminal may perform synchronization with the base station using the obtained information (S940).

First, in step S1010, the terminal receives an Extended Synchronization Signal (ESS) that is multiplexed and transmitted in a frequency division multiplex (FDM) scheme for each symbol in a synchronization subframe from a base station. The ESS consists of a Zadoff-Chu (ZC) sequence.

In step S1020, the terminal obtains transmission period information of the synchronization subframe based on a root value of the ZC sequence.

In step S1030, the UE obtains symbol position information of the synchronization subframe based on a cyclic shift value of the ZC sequence.

The wireless device 1100 may include a processor 1110, a memory 1120, and a radio frequency (RF) unit 1130.

The processor 1110 may be configured to implement the above-described functions, procedures, and methods. Layers of a radio interface protocol may be implemented in a processor. The processor 1110 may perform a procedure for driving the above-described operation. The memory 1120 is operatively connected to the processor 1110, and the RF unit 1130 is operatively connected to the processor 1110.

The processor 1110 may include an application-specific integrated circuit (ASIC), another chipset, a logic circuit, and / or a data processing device. The memory 1120 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium, and / or other storage device. The RF unit 1130 may include a baseband circuit for processing a radio signal. When the embodiment is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in the memory 1120 and executed by the processor 1110. The memory 1120 may be inside or outside the processor 1110 and may be connected to the processor 1110 through various well-known means.

Based on the examples described above, various techniques in accordance with the present disclosure have been described with reference to the drawings and reference numerals. For convenience of description, each technique described a number of steps or blocks in a specific order, but the specific order of these steps or blocks does not limit the invention described in the claims, and each step or block may be implemented in a different order, or In other words, it is possible to be performed simultaneously with other steps or blocks. In addition, it will be apparent to those skilled in the art that the steps or blocks have not been described in detail, and that at least one other step may be added or deleted without departing from the scope of the invention.

The above-described embodiments include various examples. Those skilled in the art will appreciate that not all possible combinations of examples of the inventions can be described, and that various combinations can be derived from the description herein. Therefore, the protection scope of the invention should be judged by combining various examples described in the detailed description within the scope not departing from the scope of the claims.

Claims

In a method for receiving a synchronization signal from a terminal in a wireless communication system,

Receive an Extended Synchronization Signal (ESS) which is multiplexed and transmitted in a Frequency Division Multiplex (FDM) scheme for each symbol in a synchronization subframe from the base station, wherein the ESS is configured of a Zoffoff-Chu (ZC) sequence. step;

Acquiring transmission period information of the synchronization subframe based on a root value of the ZC sequence; And

Acquiring symbol position information of the synchronization subframe based on a cyclic shift value of the ZC sequence.

Way.
The method of claim 1,

The root value of the ZC sequence and the cyclic shift value of the ZC sequence are sequentially decoded.

Way.
The method of claim 1,

The terminal does not decode a physical broadcast channel (PBCH) used for searching for an adjacent base station.

Way.
The method of claim 1,

The root value of the ZC sequence is equally set in one synchronization subframe,

The cyclic shift value of the ZC sequence is set differently for each symbol in one synchronization subframe.

Way.
According to claim 1,

Acquiring an antenna port number of a beam reference signal (BRS) based on a root value of the ZC sequence;

The BRS is received from the base station multiplexed with the ESS by FDM for each symbol in the synchronization subframe.

Way.
The method of claim 5,

Transmit period information of the synchronization subframe or the number of antenna ports of the BRS is obtained by using conjugate pairs of the ZC sequence.

Way.
The method of claim 1,

Receiving a primary synchronization signal (PSS) and a secondary synchronization signal (SSS), which are multiplexed and transmitted in an FDM scheme with the ESS for each symbol in the synchronization subframe from the base station;

Way.
In a wireless device for receiving a synchronization signal in a wireless communication system,

RF (radio frequency) unit for transmitting and receiving a radio signal; And

And a processor operatively connected to the RF unit, wherein the processor

Receive an Extended Synchronization Signal (ESS) which is multiplexed and transmitted by a Frequency Division Multiplex (FDM) scheme for each symbol in a synchronization subframe from the base station, wherein the ESS consists of a Zadoff-Chu (ZC) sequence,

Obtaining transmission period information of the synchronization subframe based on a root value of the ZC sequence, and

Symbol position information of the synchronization subframe is obtained based on a cyclic shift value of the ZC sequence

Wireless device.
The method of claim 8,

The root value of the ZC sequence and the cyclic shift value of the ZC sequence are sequentially decoded.

Wireless device.
The system of claim 8, wherein the processor is

Characterized in that it does not decode the Physical Broadcast Channel (PBCH) used to search for neighboring base stations.

Wireless device.
The method of claim 8,

The root value of the ZC sequence is equally set in one synchronization subframe,

The cyclic shift value of the ZC sequence is set differently for each symbol in one synchronization subframe.

Wireless device.
The method of claim 8,

Acquiring an antenna port number of a beam reference signal (BRS) based on a root value of the ZC sequence;

The BRS is received from the base station multiplexed with the ESS by FDM for each symbol in the synchronization subframe.

Wireless device.
The method of claim 12,

Transmit period information of the synchronization subframe or the number of antenna ports of the BRS is obtained by using conjugate pairs of the ZC sequence.

Wireless device.
The system of claim 8, wherein the processor is

Receiving a primary synchronization signal (PSS) and a secondary synchronization signal (SSS), which are multiplexed with the ESS in the FDM scheme and transmitted to each symbol in the synchronization subframe from the base station;

Wireless device.