WO2014116050A1 - Method for cell discovery - Google Patents

Abstract

Disclosed is a method for cell discovery. In a network in which a macro cell overlaps at least one small cell, when the carrier frequency used by the macro cell is different from the carrier frequency used by the small cell, the small cell transmits a discovery signal using the carrier frequency used by the macro cell, or the small cell transmits a discovery signal using a carrier frequency of the small cell that is different from the carrier frequency used by the macro cell.

Description

Cell Discovery Method

The present invention relates to mobile communication technology, and more particularly, to a cell discovery method.

Due to the widespread dissemination of portable mobile terminals and tablet PCs and the rapid expansion of mobile computing based on wireless Internet technology, a dramatic increase in wireless network capacity is required.

Many studies predict that the traffic usage of mobile users will increase rapidly in the future. Representative solutions to meet the requirements of this explosive increase in traffic may consider applying advanced physical layer techniques or allocating additional spectrum. However, physical layer technology is approaching theoretical limits, and increasing the capacity of cellular networks through the allocation of additional spectrum cannot be a fundamental solution.

Therefore, there is a growing demand for techniques for increasing the capacity of a wireless network by arranging small cells in multiple locations at high data demands and by cooperating closely with macro base stations and small cell base stations.

The Long Term Evolution (LTE) -Advanced standardization conference of the 3rd Generation Partnership Project (3GPP) is standardizing technology for small cell enhancement to efficiently accommodate the rapidly growing demand for data traffic. .

Technologies under consideration for small cell enhancement include spectral efficiency enhancement techniques, small cell activation / deactivation and cell discovery techniques, interference control techniques, air interface-based synchronization techniques, and physical layer techniques to support higher layer small cell enhancement techniques. have. In particular, as a cell discovery technology, a discovery method, a discovery signal, a discovery procedure, and the like are discussed.

However, only a discussion for cell discovery has been made so far, and no specific and efficient method for cell discovery has been proposed.

It is an object of the present invention to provide an efficient cell discovery method that can be applied to a cellular mobile communication system.

The cell discovery method according to an aspect of the present invention for achieving the above object of the present invention is a cell discovery method of a small cell in a network in which a macro cell and at least one small cell is overlapped, the macro cell is used If the carrier frequency is different from the carrier frequency used by the small cell, the small cell transmits a discovery signal using the carrier frequency used by the macro cell.

Here, the position of the frequency domain of the resource for transmitting the discovery signal may correspond to six or less resource blocks located in the middle of the transmission band of the macro cell. In addition, the position of the subframe in which the discovery signal is transmitted may be the same as the subframe in which the cell search signal is transmitted.

In this case, the resource to which the discovery signal is transmitted includes a Cell-specific Reference Signal (CRS), a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), and a Physical Broadcast Channel (PBCH) within a subframe in which the discovery signal is transmitted. Among the symbols that are not transmitted, it may consist of two neighboring symbols in time.

Here, the discovery signal may be composed of a primary discovery signal and a secondary discovery signal, and the primary discovery signal and the secondary discovery signal may be transmitted through different symbols. Here, the main discovery signal sequence may be generated using a Zadoff-Chu sequence in a frequency domain, and may be generated using a root index value different from the root index applied to the PSS. Here, the sequence of the sub-discovery signal is a scrambling sequence

,

And physical-layer identity

Can be generated by differently setting the relationship between the SSS sequence generation or by setting the relationship between the physical layer cell ID group and the parameters m ₀ and m ₁ differently from the SSS sequence generation.

In addition, the cell discovery method according to another aspect of the present invention for achieving the object of the present invention is a cell discovery method of a small cell in a network in which a macro cell and at least one small cell overlapping, the small cell is the The discovery signal is transmitted using a carrier frequency of the small cell that is different from the carrier frequency used by the macro cell.

In this case, when the small cell is in the dormant state, the small cell is a physical downlink control channel (PDCCH), a primary synchronization signal (PSS), and a secondary SSSS (SSS) used by neighboring small cells in a subframe in which the discovery signal is transmitted. The discovery signal may be transmitted by using two neighboring symbols in time among symbols in which a synchronization signal (PBCH) and a physical broadcast channel (PBCH) are not transmitted.

In this case, when the small cell is in an active state, the small cell may transmit the discovery signal by using symbols different from symbols used by other neighboring cells to transmit the discovery signal.

In addition, the cell discovery method according to another aspect of the present invention for achieving the object of the present invention is a cell discovery method that is applied to a network in which cells of different sizes overlap each other, at least one cell of a predetermined number And constructing a discovery signal using a channel state information reference signal (CSI-RS) resource corresponding to an antenna port, and transmitting resource configuration information of the discovery signal to a terminal.

Here, in the configuring of the discovery signal, one cell configures a discovery signal using one antenna port in one subframe, but the one antenna port corresponds to CSI-RS resources for four antenna ports. can do.

The transmitting of the resource setting information of the discovery signal to the terminal may include at least one of sequence setting information of the discovery signal, subframe setting information, and resource information of transmitting the discovery signal within a subframe. Can be.

Here, the resource of the discovery signal may be set differently for each discovery signal, all discovery signals may be set identically, or may be set differently for each divided discovery signal group.

In addition, the cell discovery method according to another aspect of the present invention for achieving the object of the present invention is a cell discovery method applied to a network in which cells of different sizes overlap each other, having a predefined subframe interval Configuring a discovery hopping process comprised of subframes and determining resources in the time and frequency domain to which a discovery signal is to be transmitted in the configured discovery hopping process.

The determining of the resource in the time and frequency domain may include determining that only one discovery signal is transmitted at one unit transmission time, or use a plurality of discovery signals with different frequency resources at one unit transmission time. To be sent.

The determining of the resources of the time and frequency domain may include: mapping a predetermined row of the latin vibration matrix to a time domain resource of the discovery signal, and converting a predetermined latin vibration matrix of the plurality of different latin vibration matrices into the discovery signal. The time and frequency domain resources of the discovery signal may be determined in correspondence with the frequency domain resources.

The determining of the resources in the time and frequency domains may include distributing a plurality of resources constituting the discovery signal in a frequency domain.

In addition, the cell discovery method according to another aspect of the present invention for achieving the object of the present invention, the cell discovery method performed in the terminal, receiving the resource and sequence information of the discovery signal from the base station, and the received information Measuring a discovery signal corresponding to a discovery target resource and a sequence based on the measurement result; and reporting the measurement result to the base station.

The measuring of the discovery signal may include receiving signal strength indicator (RSSI) of the discovery signal, reference signal received power (RSRP) of the discovery signal, and receiving a reference signal of the discovery signal. It may include at least one of Quality Reference Signal Received Quality (RSRQ).

According to the cell discovery method described above, a cell discovery signal design method based on a synchronization signal, a cell discovery signal design method based on a CSI-RS (Channel State Information Reference Signal), a cell discovery signal transmission and reception resource setting method, a cell discovery signal A resource and sequence allocation method, a cell discovery signal reception, measurement, and reporting method, and a terminal discovery method by a cell in detail.

Accordingly, cell discovery can be efficiently performed in a cellular mobile communication system.

1 illustrates a state of a cell and whether a discovery signal is transmitted from a cell discovery perspective.

2 is a conceptual diagram illustrating a case in which small cells are disposed within coverage of a macro cell.

3 shows an example of a method of transmitting a discovery signal using subframe 0 in a subframe structure having a general CP.

4 shows an example of a method of transmitting a discovery signal using subframe 5 in a subframe structure having a general CP.

5 shows an example of a method of transmitting a discovery signal using subframe # 0 or # 5 in a subframe structure having an extended CP.

6 shows another example of a method for transmitting a discovery signal using subframe 0 in a subframe structure having a general CP.

7 illustrates a method of transmitting a discovery signal using subframe 5 in a subframe structure having a general CP.

8 illustrates a method of transmitting a discovery signal using subframe 0 in a subframe structure having an extended CP.

9 shows a method of transmitting a discovery signal using subframe 5 in a subframe structure having an extended CP.

10 shows the root sequence index for the main discovery signal.

11 shows the location of CSI-RS resources when there are four CSI-RS antenna ports.

12 is a conceptual diagram illustrating a subframe allocation method for discovery signal transmission.

13 is a conceptual diagram illustrating a frequency domain resource mapping method of a discovery signal.

14 shows an example of a 4x4 Latin square matrix.

15 is a conceptual diagram illustrating a configuration of a time domain for mapping of a discovery signal.

16 is a conceptual diagram illustrating a cell discovery method by a terminal.

17 is a conceptual diagram illustrating a time domain allocation method of discovery resources using a Latin square matrix.

18 is a conceptual diagram illustrating a method of multiplexing resources for a discovery signal.

19 is a conceptual diagram illustrating a region overlap problem of a cell discovery signal.

20 is a conceptual diagram illustrating a method for setting a resource for CSI-RS-based discovery signal transmission and an RSSI measurement resource.

21 is a conceptual diagram illustrating a distance estimation method between a terminal and a small cell.

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description.

However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

The term "terminal" used in the present application is a mobile station (MS), a mobile terminal (MT), a user terminal, a user equipment (UE), a user terminal (UT: User Terminal), a wireless terminal, Access Terminal (AT), Subscriber Unit, Subscriber Station (SS), Wireless Device, Wireless Communication Device, Wireless Transmit / Receive Unit (WTRU), Mobile Node, Mobile Or other terms.

In addition, the 'base station' used in the present application generally refers to a fixed point for communicating with a terminal, and includes a base station, a Node-B, an eNode-B, and a BTS. It may be called other terms such as (Base Transceiver System), Access Point.

In addition, the 'transmission point' used in the present application is provided with at least one transmitting and receiving antenna, and a transmission and reception device capable of transmitting and receiving information with the base station connected to the base station and the optical fiber, microwave (Microwave), etc. And a remote radio head (RRH), a remote radio unit (RRU), a distributed antenna, and the like. The base station may also be included in the transmission point.

Further, embodiments of the present invention described below are standard documents disclosed in at least one of the Institute of Electrical and Electronics Engineers (IEEE) 802 system, the 3rd Generation Partnership Project (3GPP) system, the 3GPP LTE system, and the 3GPP2 system, which are wireless access systems. Can be supported by them. That is, steps or parts which are not described to clearly reveal the technical spirit of the present invention among the embodiments of the present invention may be supported by the above standard documents. In addition, all terms used in the present invention can be described by the above standard documents.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. In the following description of the present invention, the same reference numerals are used for the same elements in the drawings and redundant descriptions of the same elements will be omitted.

■ Cell Discovery

▣ Discovery signal

Cell discovery refers to a process in which a UE receives a discovery signal transmitted by a cell and discovers the existence of a cell. Here, the cell discovery signal refers to a physical channel or a physical signal transmitted by a cell for cell discovery. The cell discovery signal is used to transmit information including cell ID or cell index information, cell state information, and the like.

UE discovery refers to a process in which a base station receives a terminal discovery signal transmitted by a terminal and discovers the existence of the terminal. Here, the terminal discovery signal means a physical channel or a physical signal transmitted by the terminal for discovery. The base station may obtain information including the serving cell of the terminal, the terminal scheduling ID, etc. from the terminal discovery signal and estimate the proximity of the terminal.

1 illustrates a state of a cell and whether a discovery signal is transmitted from a cell discovery perspective.

Referring to FIG. 1, a cell in a Dormant_0 state transmits no signal. A cell in a Dormant_1 state periodically transmits its cell discovery signal and no other signal. A cell in the Active_0 state transmits various physical signals and channels necessary to operate as a cell, but does not transmit its own cell discovery signal. The cell in the Active_1 state transmits various physical signals and channels necessary to operate as a cell, and periodically transmits its own cell discovery signal.

▣ Method of transmitting discovery signal according to discovery signal transmission frequency

2 is a conceptual diagram illustrating a case in which small cells are disposed within coverage of a macro cell.

In FIG. 2, it is assumed that a carrier frequency used by the macro cell 110 is F1 and a carrier frequency used by the small cells 120 is F2. Ideal backhaul or non-ideal backhaul is formed between the macro cell 110 and the small cells 120 and between the small cell 120 and the small cell 120.

The discovery signal can be designed according to the following two scenarios according to whether the macro cell 110 and the small cell 120 use the same carrier frequency.

[Scenario 1] Macro cell 110 and small cell 120 use different carrier frequencies (F1 ≠ F2).

[Scenario 2] Macro cell 110 and small cell 120 use the same carrier frequency (F1 = F2).

The small cell 120 may transmit a discovery signal in a dormant state. Meanwhile, when the small cell 120 is in an active state, two discovery signal transmission methods may be considered as follows according to whether a discovery signal is transmitted.

[Method 1] The discovery signal is not transmitted when the small cell 120 is active.

[Method 2] The discovery signal is transmitted even when the small cell 120 is in an active state.

In addition, the following two discovery signal transmission methods may be considered according to the carrier frequency used by the small cell 120 to transmit the discovery signal.

[Method 1] The small cell 120 transmits a discovery signal using the carrier frequency F1 used by the macro cell 110.

[Method 2] The small cell 120 transmits a discovery signal using the carrier frequency F2 assigned to it.

■ Cell Discovery Signal Design Method Based on Synchronization Signal

▣ Macro cell and small cell use different carrier frequency (F1 ≠ F2)

As shown in FIG. 2, when the macro cell and the small cells are arranged, the cell discovery method may be classified into a case in which the macro cell operates in FDD and a case in which TDD operates.

First, the case in which the macro cell operates in FDD will be described.

The following two methods may be considered depending on the carrier frequency used by the small cell to transmit the discovery signal.

[Method 1] A small cell transmits a discovery signal using F1, which is a carrier frequency used by a macro cell.

[Method 2] The small cell transmits a discovery signal using F2, which is a carrier frequency assigned to the small cell.

□ When the small cell transmits a discovery signal using the carrier frequency (F1) of the macro cell

In order for a small cell to transmit a discovery signal using the carrier frequency of the macro cell, the position in the frequency domain and the time domain in the radio resource to which the discovery signal is transmitted must be determined.

Location in the frequency domain of the radio resource over which the discovery signal is transmitted

The resource to be used for discovery signal transmission preferably belongs to six or less resource blocks (RBs) located in the middle of a transmission bandwidth of a cell. In this case, the same resource allocation can be used for the discovery signal regardless of the transmission band of the cell. Since the UE can detect the discovery signal assuming the same resource allocation regardless of the transmission band of the cell, the complexity of the discovery signal detection of the UE can be reduced.

As specified in Release 8/9/10/11 of the 3GPP LTE specification, a Cell Search Signal (Primary Synchronization Signal) and PSS (Secondary Synchronization Signal) are the six resource blocks in the middle of a cell transmission band. Is sent using (RB). In this case, the discovery signal may be used for cell search instead of cell search signals. When the discovery signal is used in the same frequency region as the cell search signals, the UE may easily detect the discovery signal and the cell search signal together. That is, the positions of the resource blocks (RBs) through which the discovery signal is transmitted may be transmitted using six middle RBs in the transmission band, similarly to the transmission of the PSS and SSS. The location of the frequency domain where the discovery signal is transmitted may be determined in advance in a standard or a method in which the macro cell base station informs the terminal through RRC signaling.

Location of the subframe in which the discovery signal is sent

The position of the subframe in which the discovery signal is transmitted, the time position in the subframe, the subframe number, and the like should be determined. In consideration of the efficient DRX (Discontinuous Reception) operation of the terminal, it is possible to perform all the cell discovery, cell search, measurement, etc. in a constant and short time interval after waking from the DRX state in terms of power consumption of the terminal desirable. Therefore, it is preferable to transmit the discovery signal using a part of subframes in which the PSS / SSS is transmitted so that the UE can discover the discovery signal and the cell discovery signal in the same subframe as possible. That is, as defined in the LTE standard, one radio frame is composed of 10 subframes, and when 10 subframes are assigned numbers from 0 to 9, the PSS / SSS is subframe 0 of every frame. Frame and subframe # 5. Therefore, the discovery signal can also be designed to transmit using some of the subframes 0 and 5.

At this time, the discovery signal is periodically transmitted, the information on the transmission period and the offset may be informed to the terminal by the macro base station through the RRC signaling.

The time position at which the discovery signal is transmitted within the subframe

Since the physical downlink control channel (PDCCH) can be transmitted for up to four OFDM symbols according to the bandwidth of the system, the discovery signal can be designed to be transmitted to the remaining symbols except for the first four OFDM symbols in a subframe. In addition, the UE may be designed to estimate the cell index and synchronization for the cell using the discovery signal. The discovery signal may be configured to be transmitted in two neighboring OFDM symbols, as in the conventional PSS and SSS, respectively, in one OFDM symbol.

Discovery signal design method

It is preferable that the UE estimates time and frequency synchronization with respect to the small cell signal using the discovery signal and obtains a cell ID of the small cell. In addition, in consideration of the complexity of the base station and the terminal, it is preferable to reuse the structure of the existing PSS / SSS used in LTE.

The present invention provides a discovery signal design method as described below in consideration of the frequency domain position, the time position in a subframe, the subframe number, etc., to which the discovery signal is transmitted.

3 to 5 are conceptual views illustrating a discovery signal design method according to an exemplary embodiment of the present invention, which illustrates a discovery signal design method when a small cell uses a carrier frequency of a macro cell.

First, when the number of the subframe in which the discovery signal is transmitted is subframe number 0 or 5, and the position of the frequency domain is the middle N resource blocks (RBs) of the macro cell system bandwidth, as shown in FIGS. 3 to 5. The discovery signal can be transmitted in the same manner.

FIG. 3 illustrates a resource location for transmission of a discovery signal when a discovery signal is transmitted using subframe 0 in a subframe structure having a normal Cyclic Prefix (CP).

In FIG. 3, since cell-specific reference signals (CRSs) may be transmitted to OFDM symbols 0, 1, 4, 7, 8, and 11, in order to avoid collision with CRS. It is preferable not to transmit a discovery signal to the symbols. In addition, since PSS and SSS are transmitted to OFDM symbols 5 and 6, and a physical broadcast channel (PBCH) is transmitted to OFDM symbols 7 to 10, it is preferable not to transmit a discovery signal to these symbols. . Accordingly, the positions of the OFDM symbols capable of transmitting the discovery signal are symbols 2, 3, 12, and 13.

In case of transmitting a discovery signal using two OFDM symbols, as shown in FIG. 3, the symbols capable of transmitting the discovery signal are symbols 2 and 3 (Candidate 1), 12 and 13 symbols (Candidate 2).

FIG. 4 illustrates a resource location for transmission of a discovery signal when a discovery signal is transmitted using subframe 5 in a subframe structure having a normal CP.

Referring to FIG. 4, unlike subframe # 0, the PBCH is not transmitted in subframe # 5. In consideration of this, if a condition similar to a symbol determination method for transmitting a discovery signal in subframe 0 shown in FIG. 3 is applied, the discovery signal is transmitted to OFDM symbols 2 and 3 (Candidate 1) or 9 times. 10 and OFDM symbols (Candidate 2) or 12 and 13 OFDM symbols (Candidate 3).

FIG. 5 shows a resource location for discovery signal transmission when a discovery signal is transmitted using subframe # 0 or # 5 in a subframe structure having an extended CP.

In FIG. 5, CRS may be transmitted in OFDM symbols 0, 1, 3, 6, 7, and 9, and PSS / SSS may be transmitted in OFDM symbols 4 and 5, and thus, CRS and PSS. In order to avoid collision with / SSS, it is preferable not to transmit a discovery signal in the OFDM symbol period. Accordingly, the positions of the OFDM symbols to which the discovery signal can be transmitted are 10 and 11 symbols.

The terminal performs an operation of searching for a discovery signal in the OFDM symbols.

□ When the small cell transmits a discovery signal using the carrier frequency (F2) assigned to it (F1 ≠ F2)

The small cell may transmit a discovery signal in a dormant state.

Meanwhile, when the small cell is in an active state, the following two methods may be considered depending on whether a discovery signal is transmitted.

(Method 1) The discovery signal is not transmitted when the small cell is active.

(Method 2) The discovery signal is transmitted even when the small cell is active.

Hereinafter, each of the two methods will be described in detail.

(Method 1) Method of not transmitting discovery signal when small cell is active

This method allows a discovery signal to be transmitted only when the small cell is in the dormant state. When the small cell is in a dormant state and transmits a discovery signal using a carrier frequency assigned thereto, the small cell transmits a discovery signal in subframe 0 and a discovery signal in subframe 5 as described above. This may be considered.

6 illustrates a method of transmitting a discovery signal using subframe 0 in a subframe structure having a general CP.

In FIG. 6, neighboring small cells may transmit the PDCCH in OFDM symbols 0, 1, 2, and 3. Therefore, in order not to affect the PDCCH detection performance of the UEs present in neighboring small cells, it is preferable not to transmit a discovery signal in the 0 to 3 OFDM symbol intervals. In addition, since the neighboring small cells can transmit the PSS / SSS in OFDM symbols # 5 and # 6, the discovery signals are also applied to these symbols in order not to affect the PSS / SSS detection performance of terminals existing in the neighboring small cells. It is preferable not to transmit it. In addition, since the PBCHs of other cells are transmitted in OFDM symbols # 7 to # 10, it is preferable not to transmit a discovery signal even in periods 7 through 10. Meanwhile, as described above, since the discovery signal is preferably transmitted over two OFDM symbols, candidates for transmitting the discovery signal are two OFDM symbols adjacent to one of OFDM symbols 11 to 13 as shown in FIG. 6. do. In FIG. 6, 12 and 13 (Candidate 1) are illustrated as candidate symbols. The small cell may be configured to transmit a discovery signal in candidate OFDM symbols.

When the UE searches for a discovery signal in the subframe illustrated in FIG. 6 (that is, subframe 0), the UE may search for the candidate OFDM symbols.

7 illustrates a method of transmitting a discovery signal using subframe 5 in a subframe structure having a general CP.

The difference between the subframe # 5 of FIG. 7 and the subframe # 0 of FIG. 6 is that the PBCH is not transmitted in OFDM symbols # 7 to # 10. Therefore, the discovery signal may be additionally transmitted in the seventh to tenth OFDM symbol intervals. According to this condition, candidates for transmitting a discovery signal are OFDM symbols 8 and 9 (Candidate 1), 10 and 11 (Candidate 2), and 12 and 13 (Candidate) as shown in FIG. 3) becomes. The small cell may transmit a discovery signal in OFDM symbols corresponding to one of the three candidates.

When the UE searches for a discovery signal in the subframe illustrated in FIG. 7 (that is, subframe # 5), the UE may search among the candidates.

8 illustrates a method of transmitting a discovery signal using subframe 0 in a subframe structure having an extended CP.

In FIG. 8, neighboring small cells may transmit a PDCCH in OFDM symbols 0, 1, 2, and 3, and neighboring small cells may transmit PSS / SSS in OFDM symbols 4 and 5, Since small cells can transmit PBCH in OFDM symbols 6 to 9, in order to avoid affecting PDCCH, PSS / SSS, and PBCH detection performance of terminals existing in neighboring small cells, OFDM symbol intervals 0 to 9 are used. It is preferable not to transmit a discovery signal. As described above, since the discovery signal is preferably transmitted over two OFDM symbols, candidates for transmitting the discovery signal are OFDM symbols 10 and 11 (Candidate 1) as shown in FIG. 8. The small cell may transmit a discovery signal using the candidate OFDM symbols.

When the UE searches for a discovery signal in subframe 0 having an extended CP, the UE may search for the candidate.

9 shows a method of transmitting a discovery signal using subframe 5 in a subframe structure having an extended CP.

In FIG. 9, neighboring small cells can transmit a PDCCH in OFDM symbols 0, 1, 2, and 3, and neighboring small cells can transmit PSS / SSS in OFDM symbols 4 and 5, In order not to affect the PDCCH and PSS / SSS detection performance of terminals existing in the small cell, it is preferable not to transmit a discovery signal in the OFDM symbol period. In addition, as described above, since the discovery signal is preferably transmitted over two OFDM symbols, candidates for transmitting the discovery signal are OFDM symbols 6 and 7 (Candidate 1) and 8 as shown in FIG. And No. 9 (Candidate 2) and No. 10 and No. 11 (Candidate 3). The small cell may transmit a discovery signal using OFDM symbols corresponding to one candidate among the three candidates.

When the UE searches for a discovery signal in subframe 5 having an extended CP, the UE may search among the candidates.

(Method 2) Method of Transmitting Discovery Signal Even When Small Cell Is Active

This method is a method of transmitting a discovery signal when the small cell is not only dormant but also active. The reason why the discovery signal is transmitted even when the small cell is active is to improve cell index detection performance of terminals belonging to the small cell. When the neighboring cells coincide with the subframe and the symbol synchronization, the neighboring cells may transmit the PSS / SSS at the same OFDM symbol position. As a result, when a cell having a greater signal strength than other cells exists among neighboring cells, the PSS / SSS detection performance of the UE with respect to other cells is deteriorated.

In the discovery signal design method according to an embodiment of the present invention, the discovery signal is designed such that neighboring cells transmit the discovery signal at different OFDM symbol positions. If necessary, specific cells may perform neighboring cells transmitting nothing with respect to a resource for transmitting a discovery signal. This improves the detection performance of the discovery signal of the terminal.

The position of the OFDM symbol in which the discovery signal is transmitted may be configured as shown in FIGS. 6 to 9.

▣ Macro cell and small cell use same carrier frequency (F1 = F2)

In the case where the macro cell and the small cell use the same carrier frequency, the discovery signal is applied by the same method as in the case of "the small cell transmits the discovery signal using the carrier cell F1 of the macro cell" among the aforementioned methods. Can be designed and transmitted.

▣ Sequence Design of Discovery Signal

□ Primary Discovery Signal (PDS) Sequence Design

Since the discovery signal performs a function similar to the synchronization signal defined in the 3GPP LTE standard, it can be designed in a structure similar to the existing PSS / SSS. That is, the discovery signal is composed of a primary discovery signal (PDS: Primary Discovery Signal, hereinafter abbreviated as 'PDS') and a secondary discovery signal (SDS: Secondary Discovery Signal, hereinafter abbreviated as 'SDS'), and the PDS and The SDS may be configured to be transmitted at different OFDM symbol positions. In addition, the PDS may be designed to perform a function similar to the PSS and to have the same structure as the PSS (ie, a sequence length, a resource element mapping method, and the like). SDS can be designed to have the same structure as SSS. Through this, the existing PSS / SSS detection algorithm can be similarly applied to PDS / SDS detection.

However, in order for the terminal to distinguish the existing PSS / SSS and the discovery signal (ie, PDS / SDS), the sequence of the PDS / SDS should be designed to be different from the sequence of the PSS / SSS.

PDS / SDS and Cell ID

The relationship may be set as in Equation 1 similarly to the relationship between the PSS / SSS and the cell ID.

Equation 1

In Equation 1,

Represents an integer value between 0 and 167,

Represents a value of any one of 0, 1, and 2.

The sequence d (n) for the PDS may use the frequency domain Zadoff-Chu sequence shown in Equation 2 like the PSS.

Equation 2

In Equation 2, the Zadoff-Chu root sequence index u may be given as shown in FIG. In FIG. 10, A1, A2, and A3 are integer values existing between 0 and 61, and values except 25, 29, and 34 are used. In this case, the reason for excluding 25, 29, and 34 is that the PSS uses these values.

□ SDS Sequence Design

The sequence d (n) for the existing SSS is generated as shown in Equation 3.

Equation 3

In Equation 3,

,

,

,

,

,

Are the sequences generated by the m-sequence, m ₀ and m ₁ are the physical-layer cell-identity group

Parameters derived from the scrambling sequence

Wow

Is the physical-layer identity

Related parameters. Therefore, the following three methods may be considered for generating the SDS sequence differently from the SSS sequence.

(Method 1) When an SDS Sequence Occurs

,

Wow

To set the relationship of SSS differently from SSS

(Method 2) m ₀ , m ₁ and SDS Sequence

To set the relationship of SSS differently from SSS

(Method 3) Method to Apply Both Method 1 and Method 2

First, when an SDS sequence occurs

,

Wow

As a method (method 1) to set the relationship of SSS differently from SSS,

and

When generated, a method of adding an offset K as shown in Equation 4 may be applied.

Equation 4

In Equation 4,

Can have a value of 0, 1, or 2, so {

,

+3} may have a value among 0, 1, 2, 3, 4, and 5. Therefore, in order to generate an SDS sequence different from the SSS sequence, K must use an integer value of 6 or more and 25 or less. If you set the K value like this,

,

} Has a value from 6 to 30. For example, K = 6 can be used.

When m SDS sequence occurs, m ₀ , m ₁ and

As a method (method 2) for setting the relation differently from that of SSS, a method of adding an offset L as in Equation 5 when m ₀ and m ₁ occurs may be applied.

Equation 5

In Equation 5, when L is less than 7, since the same pair as the (m ₀ , m ₁ ) pair existing when the existing SSS occurs, it is preferable to use an integer value of 7 or more and 29 or less.

The method of applying both Method 1 and Method 2 above is to generate an SDS sequence by applying both the offset K presented in Method 1 and the offset L presented in Method 2.

■ Discovery Signal Design Based on CSI-RS

Hereinafter, a method of designing a discovery signal based on a non-zero power (NZP) channel state information reference signal (CSI-RS) defined in the 3GPP LTE standard will be described.

According to the 3GPP LTE standard, the number of antenna ports supported by CSI-RS is 1, 2, 4, and 8. The CSI-RS resources occupied by each antenna port occupy two resource elements (REs) per one resource block (RB), but the two resource elements have the same position on the frequency axis.

11 shows the location of CSI-RS resources when there are four CSI-RS antenna ports.

In FIG. 11, resource elements (REs) in which numbers are written represent resources to which a CSI-RS can be transmitted, and one CSI-RS port is written with 0, 1 and 2, 3 among resource elements indicated by the same pattern. It is transmitted through four resource elements. Let four resource elements (REs) configured as shown in FIG. 11 be called CSI-RS resource groups.

Referring to FIG. 11, in the case of FDD, there are 10 resource setting methods for CSI-RS in one subframe, and there are 16 in TDD. However, in the case of both FDD and TDD, up to 10 different CSI-RS resource groups may be used for CSI-RS transmission in one subframe.

The discovery signal based on the CSI-RS can be designed as follows.

Discovery signals based on the CSI-RS can basically reuse the resource allocation and sequence generation methods of the CSI-RS.

The discovery signal of one cell may use CSI-RS resources corresponding to four antenna ports. That is, the discovery signal for one antenna port may be configured to occupy and use CSI-RS resources (four resource elements) corresponding to four antenna ports.

In the case of the CSI-RS corresponding to one or two antenna ports, the density on the frequency axis is only one resource element (RE) per one resource block (RB), which may cause a large measurement error for the discovery signal. In order to reduce the measurement error, the density on the frequency axis is preferably configured to be at least two resource elements per one resource block, as in the case of the CRS. In consideration of this, the discovery signal of one cell uses only one antenna port in one subframe, and the resources used by the one antenna port are CSI-RS resources (that is, four REs for four antenna ports). ) Can be configured to

On the other hand, since CSI-RS resources corresponding to eight antenna ports occupy four resource elements per one resource block, the discovery signal overhead when transmitting a discovery signal to CSI-RS resources corresponding to eight antenna ports Has the disadvantage of becoming too large. Therefore, it is preferable to transmit the discovery signal using CSI-RS resources corresponding to four antenna ports rather than eight antenna ports.

According to the 3GPP LTE specification, in case of four CSI-RS antenna ports, a total of 10 CSI-RS configuration methods for the location of CSI-RS resources in a subframe can be performed in the case of FDD, and in the case of TDD 16 kinds are possible. If the CSI-RS configuration method supported by the existing LTE standard is applied as it is, FDD can transmit a total of 10 discovery signals within the same subframe, and even TDD can detect up to 10 discovery signals according to CRS configuration. The signal may be transmitted in the same subframe.

Another CSI-RS-based discovery signal design method according to the present invention has an advantage of maintaining backward compatibility by designing not to affect legacy terminals supporting the existing standard. That is, by setting resources to which the discovery signal is transmitted as Zero Power CSI-RS resources to the existing LTE Release-10 / 11 terminals and applying PDSCH rate matching to the resources, the discovery signal is released in LTE Release-10 / 11. It may not affect the operation of the terminals supporting the standard.

The base station may inform the terminal of the resource configuration information for the discovery signal. Here, the base station should also inform the terminal of the sequence information used by each discovery signal. When reusing a CSI-RS sequence when generating a sequence of discovery signals, the UE may only notify initialization parameters necessary for sequence generation. In this case, the sequence information informed by the base station to the terminal is a physical cell ID or a virtual cell ID as an initialization parameter for generating a sequence.

It can consist of values.

[Method for generating sequence of discovery signals]

Sequence for discovery signal

May be defined as in Equation 6.

Equation 6

In Equation 6, n _s denotes a slot number in one frame, and l denotes an OFDM symbol number in a slot. The pseudo-random sequence c (i) is the same as defined in the 3GPP LTE specification. The pseudo random sequence is initialized by a c _init value for each OFDM symbol as shown in Equation (7).

Equation 7

In Equation 7, N _CP is 1 for a general CP and 0 for an extended CP.

And virtual cell ID

Is not provided with setting information from the upper layer.

Is the same as

[Discovery signal setting method]

The setting for the discovery signal may include a setting for a sequence and a resource setting (subframe number and resource position in a subframe).

First, a method of setting a sequence of discovery signals is as follows.

The setting information for the sequence of the discovery signal means an initialization parameter for the sequence. The base station informs the terminal of initialization parameters for each discovery signal configuration resource. In this case, the initialization parameter may be one of a total of 504 numbers from 0 to 503. If the base station does not inform the terminal of the initialization parameters, the terminal needs to perform blind detection on 504 initialization values, thereby greatly improving the complexity of the terminal. Therefore, it is preferable that the base station notifies the terminal of the initialization parameter.

The discovery signal resource setting method may consider three methods as follows.

Method (1): How to set resources per discovery signal

In this method, the base station informs the terminal of the subframe configuration information and the resource configuration information in the subframe for each discovery signal. Here, the position of the subframe in which the discovery signal is transmitted may be indicated by period information and offset information.

The period for the subframe that transmits the discovery signal may be indicated by one of values such as 20, 40, 80, 160, and the like. Here, the unit of the period is a subframe, and a period of 20 means that the discovery signal is transmitted every 20 subframes.

In addition, the unit of the offset for the transmission position of the discovery signal may be set to a subframe.

The method (1) has the advantage of freely setting the subframe period, offset, resource location within the subframe, etc. for each discovery signal, while having a large signaling overhead.

Method (2): how to set all discovery signals at once

In this method, the base station provides information on all discovery signals to the terminal using one configuration information. Here, the configuration information may include a subframe number where the discovery signals are transmitted and resource information within the subframe.

The setting information on the subframe number in which the discovery signal is transmitted may be composed of a period and an offset. Here, the subframe period may be expressed as one of values of 20, 40, 80, 160, etc. in subframe units. The offset information may also be configured in subframe units.

In method (2) all discovery signals have the same subframe period and offset.

The discovery resource configuration information in the subframe may utilize existing Zero Power CSI-RS resource configuration information. The configuration information of the existing ZP CSI-RS resource is composed of a 16-bit bitmap, and the base station informs the terminal of the ZP CSI-RS resource configuration information by transmitting the bitmap information to the terminal. In the same manner as described above, the discovery resource configuration information may be informed to the terminal through a 16-bit bitmap. Each bit in the bitmap may be configured to comply with the 3GPP LTE standard, and may indicate whether a discovery signal exists in a corresponding resource by setting each bit value to 0 or 1.

The method (2) has an advantage that the number of bits required for signaling is smaller than that of the method (1), but has a disadvantage in that flexible configuration is difficult.

 Method (3): a method in which a base station informs a user equipment of resource configuration information about discovery signals using a plurality of ZP CSI-RS configuration information

In this method, the discovery signals are divided into a plurality of groups, and for the discovery signals belonging to each group, the base station informs the user equipment of the resource configuration information on the discovery signal using one ZP CSI-RS resource configuration information. At this time, ZP CSI-RS resource configuration information as many as the number of groups is required.

Discovery signal transmission resources can be set to satisfy the following characteristics for backward compatibility.

The resources defined by one ZP CSI-RS configuration information are configured to include all discovery transmission resources.

In case of using a plurality of ZP CSI-RS configuration information, more discovery signals may be configured to the UE. In this case, subframes through which discovery signals to be monitored or measured are transmitted may be repeated with a certain period on the time axis.

■ Cell discovery signal transmission and reception resource

The cell discovery signal may be transmitted using a downlink frequency band in the case of a cell using the FDD scheme. In the case of a cell using the TDD scheme, a cell discovery signal may be transmitted using a downlink subframe or a special subframe.

The UE discovery signal may use an uplink frequency band when using FDD and transmit a discovery signal by using an uplink subframe or a special subframe when using TDD.

The resources allocated to the cell discovery signal transmission may be used in advance by defining a range of time-frequency resources commonly applied between cells. For this purpose, subframe synchronization between cells must be correct. When one cell transmits one cell discovery signal, the UE may receive discovery signals of several cells in a short time by multiplexing and transmitting a plurality of cell discovery signals within a predetermined range of the same time-frequency resource. Can be.

Hereinafter, a method for allocating a resource used for cell discovery signal transmission, that is, a discovery resource, will be described. Hereinafter, a subframe in which the cell discovery signal can be transmitted is referred to as a discovery subframe.

▣ Set period and offset of subframe for discovery signal transmission

12 is a conceptual diagram illustrating a subframe allocation method for discovery signal transmission.

As illustrated in FIG. 12, subframes having a constant subframe interval may be designated as a discovery subframe, and the designated discovery subframes may configure a discovery hopping process. In addition, as illustrated in FIG. 12, a plurality of independent discovery hopping processes may be configured. 12 illustrates discovery hopping process 0 and discovery hopping process 1 as examples of a discovery hopping process.

▣ Frequency domain resource mapping method of discovery signal

The time-frequency resource used for transmitting one discovery signal may be determined by the following discovery hopping process number and discovery resource index.

Discovery hopping process number NDC_hop_ID

-Discovery resource index NDC_ID

Given a discovery resource index for a given discovery hopping process, resources in the time-frequency domain are determined. One discovery signal may use one or a plurality of resource block (RB) ranges on the frequency axis, and one or a plurality of OFDM symbols on the time axis.

The sequence of discovery signals should be configured to correspond one-to-one with cell ID (or cell index) information. Accordingly, the terminal detects the received sequence of discovery signals and can know the cell ID (or cell index) information corresponding to the detected sequence. In addition, the UE may estimate the proximity of the corresponding cell by measuring the detected sequence.

Hereinafter, a method of mapping a frequency domain resource of a discovery signal will be described, and a matter to be considered when mapping a frequency domain resource of a discovery signal will be described.

First, the frequency domain resource mapping method of the discovery signal may be classified into the following two methods.

13 is a conceptual diagram illustrating a frequency domain resource mapping method of a discovery signal.

[Method A] As shown in Fig. 11A, only one discovery signal is transmitted in one unit transmission time interval. Here, discovery signals of other cells adjacent to one cell are allocated to different positions in time. However, if two cells are so far apart that their effects on each other are negligible, the same resource may be used to transmit a plurality of discovery signals.

[Method B] As shown in FIG. 11B, a plurality of discovery signals mapped to different frequency resources are simultaneously transmitted in one unit transmission time interval. At this time, the reception power of a cell close to a predetermined cell is so large that the discovery signal of another cell having a relatively low reception power may not be normally detected. That is, even when AGC (Automatic Gain Control) adaptation is properly performed in the terminal, the effective number of bits of the analog-to-digital converter (ADC) is reduced (that is, due to a resolution limit) to have a low reception power. The discovery signal may not be properly detected at the terminal. In order to solve the problem of de-sensing due to the near-far effect between the cells, it is preferable to apply time-base hopping to resources for discovery signal transmission. If the two cells are so far apart that their effects on each other are negligible, the discovery resource can be transmitted using the same resource.

▣ Time Domain Resource Mapping using Latin Dust Matrix

For more efficient resource utilization, the time base discovery resource may be allocated using the Latin square matrix for the above-described [Method A] and [Method B].

A Latin square matrix of size N × N has the following characteristics:

Each element of each row has a value of 1, 2, or N, and elements within the same row have different values. That is, each of the numbers 1, 2, and N in a row exists once.

-Each element constituting each column is 1, 2,... , N has one value and elements in the same column have different values. That is, in one column 1, 2,... Each number in N exists once.

Comparing any two rows in one Latin square matrix does not have the same number at the same element position.

Comparing two random columns in a Latin square matrix does not have the same number at the same element position.

N × N matrices can be made by performing a cyclic shift on the positions of the columns except for the first column of the symmetric N × N Latin square matrix with natural order. Since one matrix can be obtained for each cyclic shift, new (N-2) matrices can be generated through the cyclic shift, and each generated matrix becomes a Latin square matrix satisfying the above characteristics. Thus, the total number of Latin square matrices is (N-1) including natural ordered and symmetric Latin square matrices.

The (N-1) Latin square matrices further satisfy the following feature.

Comparing two randomly taken rows from different Latin square matrices produces the same number once at the same element position.

Comparing two randomly taken columns from different Latin square matrices, the same number occurs once at the same element position.

We can get a total of N × (N-1) rows from the (N-1) Latin square matrices and see that when we pick any two of them, the same number occurs at most once in the same element position. Can be.

The features of the Latin square matrix can be used for time domain resource mapping of a discovery signal. Rows of the Latin square matrix may correspond to a time base resource mapping pattern of the discovery signal. That is, when N rows belonging to one Latin square matrix are mapped to time-base resource mapping patterns of N discovery signals, the N discovery signals are mapped to resources that do not overlap each other on the time axis. Therefore, even if they are mapped to the same resource on the frequency axis, the N discovery signals do not overlap each other in the time-frequency resource space because they do not overlap each other on the time axis.

On the other hand, different Latin square matrices can correspond to different frequency resources. A total of (N-1) Latin square matrices can be obtained for order N, so allocate a total of (N-1) non-overlapping resources on the frequency axis and assign each resource to the (N-1) Latin square matrices. One-to-one correspondence with one.

FIG. 14 illustrates an example of a 4 × 4 Latin square matrix, and when N is 4, a total of three Latin square matrices generated by the cyclic shift method described above are illustrated.

15 is a conceptual diagram illustrating a configuration of a time domain for mapping of a discovery signal.

Referring to FIG. 15, one period of the discovery hopping process may include L discovery frames, and each discovery frame may again include L unit transmission intervals. One discovery signal may have a time range corresponding to a unit transmission interval, and a unit transmission interval may be

It may consist of OFDM symbols. That is, one discovery signal is a discovery signal unit transmission period.

It can be transmitted over OFDM symbols.

An index of i = 0, 1, 2, 3, and (L-1) is assigned in time order to L discovery frames included in one discovery hopping process period. In addition, an index of i = 0, 1, 2, 3, and (L-1) is assigned to the L discovery signal transmission intervals in each discovery frame in chronological order.

As described above, in the case of Latin square matrices of size L × L, a total of (L−1) Latin square matrices may be generated, and a total of L × (L−1) rows may be obtained from the matrix. An index value q (q = 0, ..., L-2) is assigned to each of the (L-1) Latin square matrices. For a total of L × (L-1) rows, index values m are assigned in turn, and T (m) [m = 0,1, 2... , L × (L-1) -1] represents one row. Assume that T (m) [i] means the value of element i (i = 0, 1, ..., L-1) in row m.

If a discovery resource index NDC_ID = m in a given discovery hopping process, the location on the time axis of the discovery resource may be determined by T (m). That is, the discovery signal transmission resource corresponding to the discovery resource index m is located in the unit transmission section corresponding to the discovery signal transmission section index T (m) [i] value in the discovery frame i.

In the case of [Method A], a plurality of discovery signals may be transmitted using the same frequency resource in one unit transmission section. In this case, even though the Latin square matrix indices q are different, the frequency domain resources used for discovery signal transmission are the same. If q is used to map discovery signal resources using two random rows belonging to different Latin square matrices, the same unit transmission interval used by the same two discovery signals may occur once during the discovery hopping process. If q is used to map discovery signal resources using two arbitrary rows belonging to the same latin square matrix, the unit transmission intervals used by the two discovery signals do not overlap each other.

In Method B, the frequency resource may be determined according to the index q value of the Latin square matrix. In other words, if q is different, different frequency resources are used. If q is used to map discovery signal resources using two random rows belonging to different Latin square matrices, the same unit transmission interval used by the two discovery signals may occur once during the discovery hopping process. If q is used to map discovery signal resources using two arbitrary rows belonging to the same latin square matrix, the unit transmission intervals used by the two discovery signals do not overlap each other.

[Method A] will be described below in more detail.

16 is a conceptual diagram illustrating a cell discovery method by a terminal.

As shown in FIG. 16, it is assumed that the terminal A 130 is located at the cell center of the small cell SO 120. The terminal A 130 may receive the discovery signal transmitted by the small cell S0 120 at a very large signal level. If neighboring small cells transmit the discovery signal using the same resource as the discovery resource used by the small cell S0 120, the terminal A 130 detects the remaining discovery signals except for the discovery signal of the small cell S0 120. You may not be able to. In order to solve such a problem, it is preferable that small cells adjacent to each other transmit discovery signals using resources that do not overlap each other in time.

On the other hand, if all of the small cells all use different time resources, so many radio resources can be used to transmit the discovery signal, small cells separated from each other can be configured to reuse the discovery resources. Here, efficient reuse of discovery resources is needed. For example, when the small cell S4 124 reuses the discovery resource used by the small cell S0 120, the terminal A 130 may be small due to interference from the discovery signal transmitted from the small cell S0 120. The discovery signal transmitted by cell S4 124 may not be detected. In order to solve such a problem, it is not preferable that the time axis resources used by the small cell S4 124 overlap with the small cell SO 120 in all transmission intervals.

In the resource mapping method of the discovery signal described in the present invention, a region in which a discovery resource of one small cell and a discovery resource of another small cell overlap in time is minimized by using a Latin square matrix. Through this method, a section in which discovery resources used by two small cells for transmission in time overlaps at most once during the discovery hopping process period.

17 is a conceptual diagram illustrating a time domain allocation method of discovery resources using a Latin square matrix.

Hereinafter, a method of allocating a discovery resource using a Latin square matrix in the time domain will be described in detail with reference to FIGS. 14, 16, and 17.

In the three latin square matrices shown in FIG. 14, when the small cell S0 120 uses the time base resource determined using the A row, the discovery of the small cell S0 120 is performed in discovery frames 0, 1, 2, and 3, respectively. The unit transmission intervals through which signals are transmitted are 1, 2, 3 and 4, respectively. When the small cell S4 124 uses the F row, the unit transmission intervals used by the discovery signal of the small cell S4 124 are 2, 4, 3, and 4 in the discovery frames 0, 1, 2, and 3, respectively. It becomes 1. That is, the discovery resources used by the two small cells 120 and 124 overlap only in one unit transmission section of the four unit transmission sections (the discovery frame 2 to the third unit transmission section). When the discovery signal is allocated to the time domain resource through the above method, the terminal A 130 may detect this signal in three unit transmission intervals among four unit transmission intervals in which the discovery signal of the small cell S4 14 is transmitted. Can be. When mapping the discovery signals of a plurality of cells to resources in the time domain, when different rows of one Latin square matrix are used, transmission intervals do not overlap each other on the time axis. For example, when the small cells S0 120, S1 121, S2 122, and S3 123 map resources using rows A, B, C, and D of the Latin square matrix of FIG. 14, respectively. In this case, the transmission sections of the discovery signals do not overlap each other on the time axis.

In generalizing the resource allocation method of the discovery signal described above, small cells are grouped by region, and small cells belonging to the same group determine time base resources using rows belonging to the same Latin square matrix, and small cells belonging to different groups Different Latin square matrices can be used to determine time base resources.

For example, in FIG. 16, when the small cells 120, 121, 122, and 123 belonging to the same macro cell 110 are grouped to belong to the same group, the small cells 120, 121, 122, and 123 within the macro cell 110 are included. ) May determine the time base resource using the same Latin square matrix, and thus may transmit discovery signals at different time locations. That is, the discovery resource may be determined as follows.

Small cells in the same macro cell use different rows of the Latin square matrix with the same q value to allow discovery resources to be mapped.

Adjacent macro cells allow the small cells in the cell to use a Latin square matrix with different q values. That is, if the small cells belong to different neighboring macro cells, the Latin square matrix having different q values is used.

One macro cell can be divided into sections so that other sections use different Latin square matrices.

The terminal may receive latin vibration matrix information used by neighboring cells of the terminal from the base station, and detect the discovery signal using the base station. Alternatively, even if the base station does not transmit the latin dust matrix information to the terminal, if the terminal knows the frequency and temporal range of the discovery resource, the cell discovery signal may be detected through blind detection.

□ Frequency hopping

The discovery resource may be frequency division multiplexed (FDM) with the cellular mobile communication resource in the subframe.

18 is a conceptual diagram illustrating a multiplexing method of resources for a discovery signal, and illustrates a multiplexing method of discovery resources and cellular resources in a discovery subframe in which a discovery signal may be transmitted. Meanwhile, the entire uplink band may be allocated as a resource for transmission of a discovery signal.

In FIG. 18, a D-REG is a discovery resource group and one discovery signal may occupy one or a plurality of discovery resource groups. Frequency hopping may be applied to resource mapping of the discovery signal to obtain a frequency diversity effect. Frequency hopping may be performed in units of D-REG. That is, the frequency diversity effect can be obtained by evenly distributing the positions on the frequency axis of the plurality of D-REGs constituting one discovery signal. For example, as shown in FIG. 16B, a frequency diversity effect can be obtained by dropping a position on a frequency between two D-REGs belonging to the same discovery signal.

■ Resource and sequence allocation for discovery signals

Discovery signal area overlap problem

Discovery signal resources are preferably spatially reused to increase frequency utilization efficiency. However, when cells transmitting using the same discovery signal resources are located close to each other, a problem may occur in that transmission regions of discovery signals transmitted by each cell overlap.

19 is a conceptual diagram illustrating a region overlap problem of a cell discovery signal.

As shown in FIG. 19, when cells A 210 and B 220 are located outside the discovery signal detection area of each other and cooperation for discovery resources used by each cell is not performed, two cells 210 and 220 are not provided. ) May allocate the same transmission resource for transmitting the discovery signal. As a result, there may exist a portion where the discovery signal arrival regions of the two cells overlap.

In FIG. 19, the terminal is located in the discovery signal arrival regions of the cell A 210 and the cell B 220. If the discovery signal sequences used by the cell A 210 and the cell B 220 are the same, the terminal 230 receives a signal that is the sum of two discovery signals transmitted by the cell A 210 and the cell B 220. Since the discovery signal is detected using this, ambiguity occurs in the identification of a cell ID or an index according to the discovery signal detection.

As a method for solving the channel estimation error of the terminal due to the overlap of the discovery signal transmission region as described above, the base stations managing the cell A 210 and the cell B 220 cooperate with each other to orthogonal discovery signal resources in each cell By using the above, it is possible to prevent the above problem from occurring. Here, when cell A 210 and cell B 220 are managed by different base stations, it may be difficult for immediate cooperation between base stations. Accordingly, if the sequence of discovery signals used by the two cells is set differently in advance, the terminal located in the overlapped area can alleviate the problem caused by the overlap of the signal arrival areas when the UE located in the overlapped area receives the discovery signal. That is, the sequence detected by the terminal may have a one-to-one correspondence with a cell ID or a cell index. When the sequence is set as described above, ambiguity does not occur in checking the cell ID or the cell index of each cell acquired through the sequence detected by the terminal.

The base station delivers discovery sequence information necessary for the terminal to receive the discovery signal to the terminal. This information may include a base sequence for which a discovery signal is available and information for determining a cyclic shift. The terminal may attempt to detect the discovery signal based on the discovery sequence information received from the base station.

■ How to send and receive discovery signals

▣ Search and Detection Method of Discovery Signal

Cell discovery signal discovery and reception performed by the UE may be classified into discovery and reception for blind discovery and discovery and reception for assisted discovery.

[Search and Receive for Blind Discovery]

A terminal performing blind discovery searches for and receives a discovery signal based only on information on a discovery resource range for blind discovery. The discovery resource range for blind discovery should inform the terminal by the base station.

[Search and Receive for Support-based Discovery]

A terminal performing support-based discovery searches for and receives a discovery signal only for specific discovery resources designated by a base station. For support-based discovery, the base station may inform the discovery hopping process number, resource indexes, and sequence information for the terminal to perform discovery and reception for each terminal.

Types of Discovery Signal Measurements

The measurement of the discovery signal includes received signal strength indicator (RSSI: Received Signal Strength Indicator) of the discovery signal, reference signal received power (RSRP) of the discovery signal, and reference signal received quality (RSRQ) of the discovery signal. ) May be included.

The RSSI (D-RSSI) of the discovery signal is measured for resource elements (REs) for transmission of discovery signals corresponding to discovery resources (discovery hopping process number and discovery resource index) designated by a higher layer. Received power per resource element, including contributions from all signal sources such as serving cell, adjacent channel interference, thermal noise, and the like.

The RSRP of the discovery signal (D-RSRP) refers to a reception power per resource element of a discovery signal corresponding to a discovery resource (discovery hopping process number and discovery resource index) and a discovery signal sequence designated by an upper layer.

The RSRQ (D-RSRQ) of the discovery signal may be defined as (N × RSRP) / D-RSSI. Here, N means the number of resource blocks (RBs) in the bandwidth in which D-RSSI measurement is performed. D-RSRP and D-RSSI measurement is preferably performed to target the same resource block sets.

Measures for Specific Discovery Resources and Sequences

The terminal performs RSRP (D-RSRP) measurement on a discovery signal corresponding to a specific discovery resource and a sequence indicated by the base station. The base station informs the terminal of discovery resources and sequence information to perform measurement. The UE performs RSRP (D-RSRP) measurement of discovery signals corresponding to each discovery resource and sequence and reports the result to the base station. The base station can be used for cell selection, inter-cell interference control, etc. using the measurement results.

When comparing the radio link quality of cells using different carriers, RSRQ, which considers interference amount, is more useful than RSRP considering only the signal component of each cell. As specified in the LTE standard, the RSRQ value can be obtained from the RSSI value and the RSRP value. The CRS-based RSRQ defined in the existing LTE standard measures and receives a reference signal corresponding to antenna port 0 or antenna ports 0 and 1 among CRSs transmitted by a cell that is a target of RSRP measurement. RSSI is obtained by measuring the total received power received in OFDM symbols corresponding to antenna port 0 in the CRS.

When the CSI-RS based discovery signal is applied, RSRP may be measured by receiving the CSI-RS based discovery signal. That is, the RSRP may be calculated by receiving a CSI-RS signal used for discovery and measurement instead of the CRS. In order to ensure reception quality of the CSI-RS, resources used for CSI-RS signal transmission used for discovery and measurement purposes are preferably not used by neighboring cells for transmission. Therefore, similar to the case of the CRS, accurate RSSI measurement may be difficult if the RSSI measurement is performed using the total reception power received in the OFDM symbols to which the CSI-RS configured for discovery and measurement purposes are transmitted. In consideration of this, it is desirable to set resources for RSSI measurement separately. That is, the terminal may be configured to measure the RSSI only from the resources set by the base station for RSSI measurement. The resource setting for RSSI measurement may simply use an existing non-zero power (NZP) CSI-RS resource setting method or a ZP (zero power) CSI-RS resource setting method. In this case, the terminal can obtain the RSSI by measuring the total received power received from the configured resource elements (REs). CSI-RS resources used for RSRP measurement of each cell are resources that a real cell uses CSI-RS for transmission. On the other hand, in order to measure the actual resource usage of each cell, it is preferable that the resources used for RSSI measurement correspond to the resources used by the cells for data transmission.

20 is a conceptual diagram illustrating a method for setting a resource for CSI-RS-based discovery signal transmission and an RSSI measurement resource. FIG. 20 illustrates an example of a CSI-RS-based discovery signal resource and an RSSI measurement resource used by two neighboring transmission points. It is shown. As shown in FIG. 18, the transmission point A and the transmission point B transmit NZP CSI-RS, which is a CSI-RS based discovery signal, using different resources, and the transmission point A transmits the CSI-RS based discovery signal of the transmission point B. Muting the corresponding resource (muting), and the transmission point B mutes the resource corresponding to the CSI-RS-based discovery signal of the transmission point A. In addition, the RSSI measurement resource is used by allocating the same resource regardless of the transmission point. The terminal measures the RSRP for the transmission point A using the discovery signal resources of the transmission point A. The terminal measures the RSRP for the transmission point B using the discovery signal resources of the transmission point B. The terminal measures the RSSI using the resources for the RSSI measurement.

▣ Discovery and measurement report for discovery signal transmission channel selection

To help the cell select a resource to use for discovery signal transmission, the terminal performs discovery signal RSSI (D-RSSI) measurement on discovery signals belonging to a range of discovery resources specified and the lowest discovery signal RSSI (D-). Transmit a discovery signal corresponding to the RSSI) value, or report using the discovery hopping process number and resource index for several discovery resources corresponding to the lowest discovery signal RSSI (D-RSSI) value, or along with the corresponding discovery signal The RSSI (D-RSSI) measurement result may be reported to the base station in charge of controlling the cell. The base station may determine the discovery resource to be used for cell discovery signal transmission based on the reported discovery and measurement results.

▣ Capability

□ Discovery Reference Signal Received Power (D-RSRP)

The discovery reference signal received power (D-RSRP) for the discovery signal may be defined as follows.

D-RSRP is defined as the linear average of the power distribution (unit [W]) of the resource elements carrying the discovery signal, corresponding to the discovery sequence. DS resources for which the UE performs D-RSRP measurement are DS resource elements corresponding to a discovery hopping process number and discovery resource index designated in an upper layer. The DS sequence in which the UE performs D-RSRP measurement may also be configured by a higher layer.

□ Discovery Received Signal Strength Indicator (D-RSSI)

The RSSI (Discovery Received Signal Strength Indicator) for the discovery signal may be defined as follows.

D-RSSI is the total received power (in [units of unit [s]) of the resource elements carrying the discovery signal, including contributions from all signal sources including serving and non-serving cells, adjacent channel interference, thermal noise, and the like. W]) is defined as the linear mean.

The discovery signal resource for which the UE performs D-RSSI measurement is a discovery resource element corresponding to a discovery hopping process number and discovery resource index designated by a higher layer.

The reference point for the D-RSSI may be an antenna connector of the terminal.

■ Receive, measure, and report on cell discovery signals

The macro base station may provide configuration information on discovery signals to the terminals. The configuration information may include at least one of a period and offset of a discovery signal for a discovery signal, OFDM symbol position information in a subframe, and frequency information (resource block number). The macro base station may inform the terminal of the configuration information by using RRC signaling.

The terminal receives the discovery signal according to the configuration information provided from the macro base station and detects or measures necessary information. In this case, the information detected or measured by the terminal may include at least one of the following information.

Cell index (ID) information

State information of the cell (determining whether the cell is active or dormant)

RSRP (Reference Signal Received Power)

* Signal strength measured using discovery signal

Reference Signal Received Quality (RSRQ)

* The quality of the received signal measured using the discovery signal, which is similar to the signal-to-interference plus noise (SINR). In this case, the discovery signal is considered a desired signal, not an interference signal.

-Amount of interference by discovery signal

* The quality of the received signal obtained when the discovery signal acts as an interference signal, similar to SINR. Here, the discovery signal is considered an interference signal. One method of measuring the amount of interference by the discovery signal is to obtain a modified RSSI value by adding the discovery signal strength to the previously measured RSSI, and calculate the modified RSRQ using the modified RSSI value.

Receive Timing Offset

* Receive timing offset of discovery signal based on signal to macro base station

The terminal reports the detected or measured information using the discovery signal to the macro base station according to the configuration information provided from the macro base station.

■ UE discovery method by cell

In the UE discovery method by a cell, the UE transmits a preamble using a physical random access channel (PRACH), and the cells monitor and detect the preamble to determine whether the UE exists in the vicinity.

Even if the UE detects a discovery signal and discovers a cell, if the cell found by the UE is in a dormant state, the UE cannot know a random access preamble transmission resource that can be used to access the found cell. In this case, the terminal may attempt random access to a neighbor cell (small cell or macro cell) in an active state.

The small cells in the dormant state can confirm the presence of the terminal close to the self by monitoring the random access channel transmitted by the terminal to the cells in the active state. However, in this random access scheme, since the UE adjusts the preamble transmission power through an open-loop power control for the serving cell, the small cells are separated from the UE based on the preamble received signal. There is a disadvantage that can not be determined.

In order to solve the above problem, the terminal may transmit the fixed power to a specific size without using power control when transmitting the preamble. That is, in order to enable the small cells to determine the distance from the terminal, the terminal transmits the random access preamble at a predetermined transmission power of a predetermined size according to the configuration information of the base station. In this case, the preamble sequence used for transmission may be one of sequences used by the serving cell of the terminal, and the preamble index may be set by the base station or use a predetermined preamble index. If the small cells around the preamble index information are known, the small cells can be used to estimate the distance to the terminal.

A PRACH resource for allowing cells to discover a terminal may be separately configured and operated. That is, the preamble transmission for the purpose of discovery is to use a PRACH resource configured separately.

After detecting the PRACH transmitted by the UE, the small cells may perform the following measurement and transfer the measurement results to the macro cell or the small cells.

The magnitude of the received power of the detected PRACH

Receive timing of the detected PRACH (for example, when a downlink subframe transmission timing of a small cell or a macro cell is set as the origin, a point when the detected PRACH is first received)

Assuming that the terminal uses a predetermined transmission power or a transmission power determined by the macro cell command, the macro cell knows the strength of the radio link between the terminal and the small cell from the PRACH reception power of the terminal measured by the small cell. Can be. In addition, the macro cell may instruct the terminal to transmit the PRACH and may receive a PRACH transmitted by the terminal to estimate a propagation delay for the macro cell of the terminal. The macro cell may estimate the approximate distance between the terminal and the small cell using the propagation delay value of the macro cell of the terminal and the PRACH reception timing measurement result of the small cell, and also estimate the approximate location of the terminal. .

21 is a conceptual diagram illustrating a distance estimation method between a terminal and a small cell.

Referring to Fig. 21, due to propagation delay,

Signal arrives at the terminal at the last time and PRACH transmitted by the terminal is delayed due to the propagation delay.

As long as you arrive at the small cell. If the downlink subframe transmission timings of the small cell and the macro cell match, the macro cell

Value

It can be estimated by the value. Even when the downlink subframe transmission timings of the small cell and the macro cell do not match, when the timing difference is known, the macro cell

The value can be estimated. Macro cells are

The approximate distance between the terminal and the small cell can be estimated from the.

Another method for discovering a terminal in which a small cell is located is to use an aperiodic sounding reference signal (SRS) or a periodic SRS. In this case, similarly to the method using the PRACH, the UE uses a constant transmission power without applying the open circuit power control during SRS transmission. The terminal transmits the SRS using the SRS sequence or the predetermined SRS sequence set by the base station.

The SRS resource may be an aperiodic or periodic SRS resource defined in the existing LTE standard.

SRS resources for UE discovery may be separately set and operated. That is, SRS transmission for the purpose of discovery is to use SRS resources set separately for discovery.

If the cell in the dormant state recognizes that the terminal exists around the monitoring, it can change from the dormant state to the active state using this information.

When the cell in the active state is recognized through the monitoring that the terminal does not exist in the surrounding state may be a state transition from the active state to the dormant state.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

Claims (20)

1. A cell discovery method of a small cell in a network in which a macro cell and at least one small cell are overlapped with each other,

   And when the carrier frequency used by the macro cell is different from the carrier frequency used by the small cell, the small cell transmits a discovery signal using the carrier frequency used by the macro cell.
2. In claim 1,

   The location of the frequency domain of the resource to which the discovery signal is transmitted corresponds to 6 or less resource blocks located in the middle of the transmission band of the macro cell.
3. In claim 1,

   The location of the subframe in which the discovery signal is transmitted is the same as the subframe in which the cell discovery signal is transmitted.
4. In claim 1,

   In the resource in which the discovery signal is transmitted, a Cell-specific Reference Signal (CRS), a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), and a Physical Broadcast Channel (PBCH) are not transmitted in a subframe in which the discovery signal is transmitted. Cell discovery method, characterized in that the two neighboring symbols in time.
5. In claim 1,

   The discovery signal is composed of a primary discovery signal and a secondary discovery signal, wherein the primary discovery signal and the secondary discovery signal is transmitted through different symbols.
6. In claim 5,

   The main discovery signal sequence is generated using a Zadoff-Chu sequence in a frequency domain, and is generated using a root index value different from the root index applied to the PSS.
7. In claim 5,

   The secondary discovery signal sequence is a scrambling sequence

   

   ,

   

   And physical-layer identity

   

   And generating a relationship different from the SSS sequence generation or setting the relationship between the physical layer cell ID group and the parameters m ₀ and m ₁ differently from the SSS sequence generation.
8. A cell discovery method of a small cell in a network in which a macro cell and at least one small cell are overlapped with each other,

   And wherein the small cell transmits a discovery signal using a carrier frequency of the small cell that is different from a carrier frequency used by the macro cell.
9. In claim 8,

   When the small cell is in the dormant state, the small cell is a physical downlink control channel (PDCCH), a primary synchronization signal (PSS), and a secondary synchronization signal (SSS) used by neighboring small cells in a subframe in which the discovery signal is transmitted. And a discovery signal is transmitted using two temporally neighboring symbols among symbols for which no PBCH (Physical Broadcast Channel) is transmitted.
10. In claim 8,

    And when the small cell is active, the small cell transmits a discovery signal using symbols different from symbols used by other neighboring cells to transmit the discovery signal.
11. In the cell discovery method applied to a network in which cells of different sizes overlap each other,

    Constructing a discovery signal using at least one cell using channel state information reference signal (CSI-RS) resources corresponding to a preset number of antenna ports; And

    And transmitting resource configuration information of the discovery signal to a terminal.
12. In claim 11,

    Comprising the discovery signal,

    One cell configures a discovery signal using one antenna port in one subframe, wherein the one antenna port corresponds to CSI-RS resources for four antenna ports.
13. In claim 11,

    The step of transmitting the resource setting information of the discovery signal to the terminal,

    And at least one of sequence configuration information of the discovery signal, subframe configuration information, and resource information through which the discovery signal is transmitted within a subframe.
14. In claim 13,

    The resource of the discovery signal may be set differently for each discovery signal, or all discovery signals may be set identically, or may be set differently for each divided discovery signal group.
15. In the cell discovery method applied to a network in which cells of different sizes overlap each other,

    Configuring a discovery hopping process consisting of subframes having a predefined subframe interval; And

    Determining a resource in a time and frequency domain in which a discovery signal is to be transmitted in a configured discovery hopping process.
16. In claim 15,

    Determining a resource in the time and frequency domain,

    And determining that only one discovery signal is transmitted at one unit transmission time, or determining that a plurality of discovery signals are transmitted using different frequency resources at one unit transmission time.
17. The method according to claim 15,

    Determining a resource in the time and frequency domain,

    The time and frequency domain resources of the discovery signal are mapped by matching a predetermined row of a latin vibration matrix with a time domain resource of the discovery signal and by mapping a predetermined latin vibration matrix among a plurality of different latin vibration matrices with a frequency domain resource of the discovery signal. Cell discovery method, characterized in that for determining.
18. In claim 15,

    Determining a resource in the time and frequency domain,

    And a plurality of resources constituting the discovery signal are distributed in a frequency domain.
19. In the cell discovery method performed in the terminal,

    Receiving resource and sequence information of a discovery signal from a base station;

    Measuring a discovery signal corresponding to a measurement target discovery resource and a sequence based on the received information; And

    Reporting the measurement result to the base station.
20. In claim 19,

    Measuring the discovery signal

    Received Signal Strength Indicator (RSSI) of the discovery signal, Reference Signal Received Power (RSRP) of the discovery signal, Reference Signal Received Quality (RSRQ) of the discovery signal Cell discovery method comprising at least one.

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