KR102197712B1 - Cell and mobile terminal discovery method - Google Patents

Abstract

A cell and terminal discovery method is disclosed. The discovery method performed in the terminal includes transmitting a trigger signal, receiving a discovery signal from at least one cell that has received the trigger signal, measuring a discovery signal, and reporting a measurement result of the discovery signal to a serving cell. It includes the step of. Accordingly, it is possible to efficiently perform cell or terminal discovery in a cellular mobile communication system.

Description

Cell and terminal discovery method {CELL AND MOBILE TERMINAL DISCOVERY METHOD}

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

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

In many studies, it is predicted that the traffic usage of mobile users will increase rapidly in the future. As a representative solution to meet the requirements of such an explosive increase in traffic, the method of applying an advanced physical layer technology or allocating additional spectrum can be considered. However, the physical layer technology has reached a theoretical limit, and increasing the capacity of the cellular network through the allocation of additional spectrum cannot be a fundamental solution.

Accordingly, there is a growing demand for technologies for increasing the capacity of a wireless network by arranging small cells in multiple layers at locations where data demand is high and through close cooperation between a macro base station and a small cell base station.

At the 3GPP (3rd Generation Partnership Project)'s Long Term Evolution (LTE)-Advanced standardization meeting, technology for Small Cell Enhancement is being standardized in order to efficiently accommodate rapidly increasing data traffic demands. .

The technologies under consideration for small cell improvement include spectrum efficiency improvement technology, small cell activation/deactivation and cell discovery technology, interference control technology, wireless interface-based synchronization technology, and physical layer technology to support higher layer small cell enhancement technology. have. In particular, as a cell discovery technology, a discovery method, a discovery signal, and a discovery procedure are being discussed.

However, until now, only discussion for cell discovery has been made, and no specific and efficient method for cell discovery has been proposed.

An object of the present invention is to provide an efficient cell and terminal discovery method applicable to a cellular mobile communication system.

A cell and terminal discovery method according to an aspect of the present invention for achieving the object of the present invention described above includes receiving a discovery signal from at least one cell by a discovery method performed in the terminal, and measuring the discovery signal. And reporting a measurement result of the discovery signal to a serving cell.

Here, the discovery method may further include the step of transmitting, by the terminal, a trigger signal, and the terminal may receive the discovery signal from at least one cell receiving the trigger signal. Here, the trigger signal is received. The transmitting may include receiving setting information of the trigger signal from a serving cell of the terminal and transmitting the trigger signal based on the setting information of the trigger signal.

Here, the setting information of the trigger signal is at least one of signal information that the terminal uses for transmission of the trigger signal, time resource and frequency resource information that the terminal uses for transmission of the trigger signal, and transmission power information of the trigger signal. May contain information.

Here, the trigger signal may be composed of a sounding reference signal (SRS), and the setting information of the trigger signal includes physical layer cell identification information of the serving cell, and setting parameters for the at least one cell to receive the SRS. Information, timing advance (TA) information for transmission of the SRS, and transmission power information of the SRS may include at least one of information.

Here, the trigger signal may be composed of a PRACH (Physical Random Access Channel), and the setting information of the trigger signal may include at least one of the PRACH configuration information and the PRACH transmission power information.

Here, the PRACH may be configured using a PRACH sequence pre-allocated for discovery among the PRACH sequence set.

Herein, in the step of transmitting the trigger signal, the trigger signal is periodically transmitted according to a preset period.

Here, in the step of transmitting the trigger signal, the terminal may transmit the trigger signal by using a resource used by the serving cell of the terminal or using a resource different from the resource used by the serving cell.

Here, in the step of transmitting the trigger signal, the trigger signal may be transmitted using the TA (Timing Advance) set by the serving cell.

Here, in the step of receiving the discovery signal from at least one cell, the terminal may periodically receive the discovery signal from the at least one cell.

Here, the discovery signal may include at least one of a synchronization signal for the terminal to acquire synchronization and a measurement signal for the terminal to perform measurement.

Here, the discovery method may further include receiving at least one of information from the serving cell, configuration information of the discovery signal and combination information indicating connectivity between the synchronization signal and the measurement signal.

Here, the setting information of the synchronization signal includes at least one of a period and an offset of the synchronization signal, a frequency position of the synchronization signal, and sequence generation information of the synchronization signal, and setting information of the measurement signal May include at least one of the measurement signal identification information, the period and offset of the measurement signal, the frequency position of the measurement signal, the sequence generation information of the measurement signal, and the transmission power information of the measurement signal.

Here, the combination information is obtained by the terminal through RRC (Radio Resource Control) signaling of the serving cell, when the terminal receives a measurement signal and measures Radio Resource Management (RRM) based on the measurement signal, It may include identification information of a synchronization signal capable of deriving time and/or frequency synchronization for demodulation of the measurement signal.

Here, when the synchronization signal is PSS (Primary Synchronization Signal)/SSS (Secondary Synchronization Signal), and the measurement signal is set to CSI-RS (Channel State Information-Reference Signal) or CRS (Cell Specific Reference Signal), The combination information may include identification information of a synchronization signal for each measurement signal transmitted by at least one cell, and the identification information of the synchronization signal may include physical layer cell identification (PCI). The discovery method may further include receiving, by the terminal, TA (Timing Advance) information included in the synchronization signal or the measurement signal from the serving cell.

Here, the measuring of the discovery signal includes receiving the discovery signal based on setting information of the discovery signal, acquiring time synchronization based on the received discovery signal, and based on the combination information Thus, it may include receiving a measurement signal included in the discovery signal and performing measurement on the received measurement signal.

In addition, a cell and discovery method according to another aspect of the present invention for achieving the object of the present invention is a discovery method performed in a cell, and performing measurement on a trigger signal transmitted from a terminal, and based on a measurement result Estimating a proximity to the terminal, and when the proximity estimation result satisfies a preset criterion, transmitting a discovery signal to the terminal.

Here, the discovery method may further include receiving configuration information of the trigger signal from a serving cell of the terminal, and in the step of measuring the trigger signal transmitted from the terminal, the received trigger The trigger signal may be received based on the signal setting information, and the received trigger signal may be measured.

Here, in the step of measuring the trigger signal transmitted from the terminal, the trigger signal is received at a time earlier than the uplink subframe reception timing of the serving cell of the terminal by a transmission delay time between the serving cell and the terminal. It may further include the step of.

Here, the performing of measurement on the trigger signal transmitted from the terminal includes comparing the received signal strength of the received signal with a preset threshold, and determining whether to receive the trigger signal based on the comparison result and/or It may include the step of estimating the proximity to the terminal.

Here, in the step of performing measurement on the trigger signal transmitted from the terminal, when receiving a PRACH (Physical Random Access Channel) as the trigger signal, the sequence of the PRACH is checked, and the sequence of the PRACH is used for discovery. In the case of an assigned sequence, a random access response may not be transmitted.

Here, the discovery signal may include at least one of a synchronization signal for obtaining downlink synchronization of the terminal and a measurement signal for measurement of the terminal. In the step of transmitting the discovery signal to the terminal, the synchronization The signal and/or the measurement signal may be periodically transmitted, but the transmission period of the synchronization signal and the measurement signal may be the same or different from each other.

Here, the discovery method may further include receiving a Sounding Reference Signal (SRS) from the terminal in an active state or a Discontinuous Transmission (DTX) state.

Here, the discovery method may further include updating, by the cell, a Timing Advance (TA) of the terminal based on the SRS, and sharing the TA update information with other cells through a backhaul.

Here, the discovery method may further include performing cooperation for SRS transmission of the UE with a cell in which the cell is different.

According to the cell and discovery method as described above, it is a cell discovery procedure based on an uplink trigger signal and a downlink measurement signal, and a method in which a terminal transmits a trigger signal using resources of a serving cell, a resource not used by a serving cell It provides a method of setting a trigger signal, a method of setting a discovery signal and configuring combined information, and a method of transmitting a synchronization signal and a measurement signal using In addition, as a terminal discovery method based on an uplink trigger signal and an uplink discovery signal, a terminal discovery procedure and a method for designing a discovery signal are provided.

Accordingly, cell discovery or terminal discovery can be efficiently performed in a cellular mobile communication environment.

1A, 1B, and 1C are conceptual diagrams illustrating a cell arrangement environment of a mobile communication system.
2 shows an example of subframe transmission/reception timing between a terminal and a cell.
3 shows another example of subframe transmission/reception timing between a terminal and a cell.
4A and 4B are conceptual diagrams illustrating a cell discovery process based on an uplink trigger signal and a downlink discovery signal.
5 shows an example of transmission of an uplink trigger signal and a downlink discovery signal.
6A and 6B show a discovery procedure based on an uplink trigger signal and an uplink discovery signal.
7 shows a procedure for a UE to transmit a trigger signal using a serving cell resource and a discovery signal using a resource not using a serving cell.
8 shows a procedure for a UE to transmit a discovery signal using only a serving cell resource.
9 shows a procedure for a UE to transmit a discovery signal using a resource not used by a serving cell.
10 shows a procedure for a UE to transmit a synchronization signal and a measurement signal as different signals using resources not used by a serving cell.
11 shows the reception timing of a subframe in a serving cell of a terminal.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail.

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

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

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

The'terminal' used in the present application is a mobile station (MS: Mobile Station), a mobile terminal (MT: Mobile Terminal), 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 may be referred to by other terms.

In addition, the'base station' used in the present application generally refers to a fixed point communicating with the terminal, and the base station, node-B, eNode-B, BTS (Base Transceiver System), access point (Access Point), etc. may be called other terms. In addition, the term'cell' may be regarded as a base station and/or a service area of the base station according to the context in which the term is used.

In addition, embodiments of the present invention described below are at least one of wireless access systems, the Institute of Electrical and Electronics Engineers (IEEE) 802 system, 3rd Generation Partnership Project (3GPP) system, 3GPP LTE and LTE-Advanced system, and 3GPP2 system. It can be supported by the standard documents disclosed in. That is, among the embodiments of the present invention, steps or parts not described in order to clearly reveal the technical idea 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 standard document.

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

■ Cell and terminal discovery

Discovery technologies for mobile communication systems can be broadly classified into cell discovery and terminal discovery.

Cell discovery by the terminal may include a process of estimating parameters by which the terminal can check cell identification information, and a measurement process of estimating a radio link quality between the cell and the terminal. Here, the cell identification information may include, for example, a physical cell identity (PCI), a virtual cell ID, and the like.

The terminal discovery by the cell may include a process of estimating parameters by which the cell can check the terminal identification information, and a measurement process of estimating a radio link quality between the terminal and the cell. Here, the terminal identification information may include, for example, a Cell Radio Network Temporary Identifier (C-RNTI) of the terminal.

■ Cell placement environment

1A, 1B, and 1C are conceptual diagrams illustrating a cell arrangement environment of a mobile communication system.

The mobile communication network may be configured in a form in which small cell clusters 121, 122, 123 are disposed in a wireless network in which macro cells 111 and 112 are disposed. The small cell clusters 121, 122 and 123 include a plurality of small cells, and the small cells may be connected to each other through a backhaul. The small cells in each small cell cluster 121, 122, 123 may be time-synchronized and frequency-synchronized through a backhaul. On the other hand, time and frequency synchronization between the large cells 111 and 112 and the small cell clusters 121, 122 and 123 is not necessarily required.

Assuming that the large cells 111 and 112 use the first frequency F1 and the small cell clusters 121, 122 and 123 use the second frequency F2, the first frequency F1 and the second frequency The frequency F2 may be the same or may be different from each other.

As in the cell arrangement environment illustrated in FIGS. 1A, 1B and 1C, the terminal may have three types of connection states. Here, connection means that the terminal is in an RRC connection (RRC_Connected) state by establishing a radio resource control (RRC) connection with a cell.

That is, as illustrated in FIG. 1A, the terminal 131 may have a connected state with all of the large cells 111 and any small cells included in the small cell cluster 121.

Alternatively, as illustrated in FIG. 1B, the terminal 132 may have a connected state only to the large cell 112.

Alternatively, as illustrated in FIG. 1C, the terminal 133 may have a connection state only to any small cells among small cells included in the small cell cluster 123.

■ Cell status

Hereinafter, the state of the cell will be described.

Table 1 shows the state of the cell by dividing the transmitting side and the receiving side.

The state of the cell may correspond to any one of the states shown in Table 1. Also, the cell state can be changed from one state to another.

A cell in a transmission active (Tx_active) state can transmit all signals and all channels using all resources.

A cell in a Discontinuous Transmission (DTX) state may transmit a discovery signal using some time and frequency resources according to a set dormant period. For example, a cell in a transmission dormant state transmits only a synchronization signal and a cell-specific reference signal (CRS) within one subframe at a period of 5 ms (millisecond), and Other signals may not be transmitted.

A cell in a transmission inactive (Tx_off) state does not transmit any signal.

A cell in a receiving active (Rx_active) state can receive all signals and all channels in all resources.

A cell in a DRX: Discontinuous Reception (DRX) state may receive a signal using some time and frequency resources according to a set dormant period. For example, a cell in a reception dormant state may receive a signal by selecting a specific resource block (RB) pair in units of 10 ms.

A cell in the Rx_off state does not receive any signal.

The small cell may change the state according to the signaling received through the backhaul from the large cell base station, or the small cell may change the state by itself. When the small cell base station manages a plurality of cells operating at a plurality of frequencies, the small cell base station may define a cell state for each cell.

■ Classification of discovery methods

Hereinafter, a discovery method will be described.

Table 2 shows the discovery methods classified according to the use of a trigger signal and a discovery signal.

Cell and terminal discovery schemes can be classified as shown in Table 2.

The trigger signal is transmitted by the terminal, and the cells may measure the trigger signal to check the approximate proximity between the terminal and the cells.

The discovery signal may be transmitted by the terminal or cells according to the discovery scheme. The discovery signal is used for more accurate proximity measurement, and includes information for discriminating a terminal or cell transmitting the discovery signal.

Discovery method 1 is a method in which the terminal transmits both a trigger signal and a discovery signal.

In discovery scheme 2, a trigger signal is transmitted by a terminal and a discovery signal is transmitted by a cell.

In discovery scheme 3, a trigger signal is not used, and a discovery signal is transmitted by the terminal.

In discovery scheme 4, a trigger signal is not used, and a discovery signal is transmitted by a cell.

The discovery signal may include a synchronization signal for obtaining synchronization, and may include a measurement signal for measurement.

Considering scheme 4 of the discovery schemes shown in Table 2, the serving cell of the terminal may transmit a discovery signal regardless of the cell state.

Depending on the time it takes for the serving cell to change state, the cell discovery method can be classified into a method that takes a long time, a method that takes a slow time, and a method that takes a very short time. Here, the state of the serving cell may be converted according to signaling of an adjacent small cell or a large cell, or may be converted according to the serving cell's own determination.

A method that takes a long time is a method in which the serving cell of the terminal notifies the neighboring cell of its state change and performs state change, and may take several seconds.

The slow time-consuming method is a method in which the UE performs Radio Resource Management (RRM) measurement on the discovery signal and then reports the measurement result to the serving cell of the UE, and the serving cell converts the cell state according to the RRM measurement result. , It may take tens of ms.

In a method that takes a very short time, the cell in the DTX state does not transmit data transmission and control information associated therewith, but transmits a discovery signal. The UE may perform RRM measurement and Channel State Information (CSI) measurement using the discovery signal, and report the measurement result to the serving cell according to a preset method. This method may take several ms, and the state of the cell may be defined differently as shown in Table 1.

■ How to set the cell's subframe transmission/reception timing

Hereinafter, a method of setting a subframe transmission/reception timing of a cell will be described.

In UE discovery and cell discovery, when a cell transmits a discovery signal through a downlink, it is preferable that the cell transmits a discovery signal according to its downlink subframe transmission timing. In addition, when the terminal transmits a trigger signal or a discovery signal through uplink, the terminal transmits a trigger signal and/or a discovery signal according to a transmission timing determined based on an uplink transmission timing used in a serving cell to which the terminal belongs. It is desirable.

Hereinafter, transmission/reception timing when large cells and small cells use the same frequency (ie, F1 = F2) will be described.

First, downlink transmission/reception timing will be described.

If the physical locations of the cells are different, since the propagation delay of the same terminal and each cell is different, the timing at which each cell receives a signal transmitted from the same terminal is different.

However, in order to support inter-cell interference coordination (ICIC), coordinated multipoint (CoMP), dual connectivity, etc., from the viewpoint of reception of the terminal, the subframe of the serving cell and the cells neighboring the terminal It is preferable that the subframes are received by the terminal at the same or almost the same time. For example, when the terminal is connected to a large cell (that is, when the large cell is the serving cell of the terminal) and there are small cells around the terminal, the subframes transmitted by the large cell and the small cells around the terminal are the same or almost It is preferable to be received by the terminal at the same time.

Accordingly, considering the transmission delay time from the transmission point of the cell to the terminal, the transmission timing of the downlink subframe of the large cell and the small cell may be set differently. That is, the transmission timing of the subframe may be set differently between the large cells and the small cells.

Next, uplink transmission/reception timing will be described.

Consider a case where a terminal is served by a large cell and a small cell, and the distance between the terminal and the reception point of the large cell is relatively long compared to the distance between the terminal and the small cell reception point.

From the viewpoint of transmission of the terminal, if the transmission timing of the uplink subframe transmitted by the terminal to the serving cells does not coincide with each other, a region overlapping with each other in time occurs between the subframes, and thus uplink power control is performed on a subframe basis. You may not be able to lose.

Accordingly, it is preferable that the transmission timings of the uplink subframes for the serving cells of the terminal are the same or substantially the same.

Even when the terminal is served by either a large cell or a small cell, considering the uplink interference control and CoMP operation, the uplink subframes transmitted to the large cell to which the terminal belongs and the small cells around the terminal are the same. Or, it is desirable to have almost the same transmission timing.

2 shows an example of subframe transmission/reception timing between a terminal and a cell.

As illustrated in FIG. 2, when the terminal transmits the n-th subframe to the small cell and the large cell using the same uplink subframe timing, transmission between each cell and the terminal when the locations of the small cell and the large cell are different. Since the delay times are different, the timing of receiving the n-th subframe in the small cell and the large cell is different.

That is, when the distance between the large cell and the terminal is relatively long compared to the distance between the small cell and the terminal, the small cell receives the n-th subframe transmitted from the terminal after the transmission delay time 201 has passed, and The cell receives the n-th subframe transmitted from the terminal after the low transmission delay time 202 has elapsed.

As described above, in order to set the time point at which the terminal receives the downlink subframe transmitted from the large cell and the small cell located around the terminal is the same, the downlink subframe transmission time of the small cell is set to the downlink of the large cell. Compared to the subframe transmission time point, the transmission delay time between the terminal and the transmission point of the large cell can be delayed.

In addition, when the UE applies the same UL subframe transmission timing to small cells and large cells around the UE, the UL subframe reception timing of the small cell and the large cell is different. Here, as illustrated in FIG. 2, when the large cell sets the transmission time t1 of the downlink subframe and the reception time t1 of the uplink subframe to be the same, the small cell sets the transmission time of the downlink subframe to the large size. Compared to the transmission time of the downlink subframe of the cell, the transmission delay time between the terminal and the large cell transmission point (i.e., downlink timing offset, 203) is delayed, and the reception time of the uplink subframe is the transmission delay time (i.e., uplink Timing offset, 204) should be advanced.

When the large cell knows the transmission delay time for the link between the terminal and the large cell through the PRACH (Physical Random Access Channel) transmitted by the terminal, the large cell delays the transmission of the terminal through a backhaul to the small cells near the terminal. You can pass time. The small cell can determine the downlink transmission timing and the uplink reception timing of its own cell by using the transmission delay time transmitted from the large cell.

Hereinafter, transmission/reception timing when large cells and small cells use different frequencies (ie, F1 ≠ F2) will be described.

From a downlink perspective, it may not be necessary to have a specific relationship between the downlink subframe transmission times of cells using different frequencies.

However, considering a case in which cells using different frequencies and located in different locations are bundled in the form of inter-site carrier aggregation to serve a terminal, a plurality of TAGs ( Timing Advance Group).

Considering from the transmission point of view of the terminal, if the transmission timings of the uplink subframes sent by the terminal to the serving cells do not coincide with each other, a temporally overlapping region between subframes occurs, and thus uplink power control is performed on a subframe basis. There may be a problem that cannot be achieved. Accordingly, it is preferable that the transmission timings of the uplink subframes for the serving cells of the terminal are the same or substantially the same.

In order to acquire downlink synchronization, the small cell may receive a signal transmitted from the large cell and determine the transmission synchronization of the downlink subframe based on the received signal. In this case, the downlink subframe transmission timing of the small cell may be delayed by a transmission delay time between the transmission/reception points of the small cell and the large cell compared to the downlink subframe transmission timing of the large cell.

In addition, when considering the reception point of the terminal, if the reception timing of the downlink subframes of the large cell and the small cell is the same or almost the same, when the terminal needs to change the frequency between the frequencies used by the large cell and the small cell, the subframe Since frequency change can be performed in units, radio resources can be used more efficiently. Here, when the large cell sets the transmission time of the downlink subframe and the reception time of the uplink subframe to be the same, the reception time of the uplink subframe of the small cell is compared to the transmission time of the downlink subframe of the large cell. When the transmission delay time between the transmission and reception points of the large cell and the large cell is advanced, the UL subframe transmission timing of the terminal for the small cell and the large cell around the terminal is the same or almost the same.

When the serving cell of the terminal is a large cell, the terminal transmits a subframe for a large cell using frequency F1 and a subframe for small cell using frequency F2 around the small cell using the same subframe timing. In this case, the timing at which the large cell and the small cell receive the corresponding subframe is as shown in FIG. 3. In FIG. 3, the timing advance (TA) of the terminal with respect to the small cell is set based on the TA of the large cell, and compared with the transmission timing of the downlink subframe of the large cell, the small cell transmits the downlink subframe by the transmission delay time. The transmission is delayed and the uplink subframe of the terminal is transmitted by the transmission delay time.

3 shows another example of subframe transmission/reception timing between a terminal and a cell.

In FIG. 3, the serving cell of the terminal is a large cell, and the terminal uses the same subframe transmission timing for a large cell using a frequency F1 and a subframe for a small cell using a frequency F2 around the small cell. Thus, the transmission and reception timing in the case of transmission is illustrated.

Referring to FIG. 3, a timing advance (TA) of a terminal for a small cell may be set based on a TA of a large cell. The small cell compares the downlink subframe with the downlink subframe transmission timing of the large cell and transmits it by delaying the downlink timing offset 302 corresponding to the transmission delay time 301, and the uplink subframe of the terminal is It is received at a time point advanced by the uplink timing offset 303 corresponding to the transmission delay time 301.

When a terminal transmits a trigger signal and/or a discovery signal using a frequency that the serving cell does not use as a resource, other cells except the serving cell of the terminal do not know exactly the transmission timing of the terminal, so the trigger signal or It is necessary to estimate the approximate reception time of the discovery signal. The transmission timing of the trigger signal and the discovery signal of the terminal is the transmission timing of the uplink subframe of the terminal set by the serving cell of the terminal so that cells other than the serving cell can predict the timing of reception of the trigger signal or discovery signal with low complexity. It can be set the same as

[Discovery signal transmission and discovery method based on uplink trigger signal and downlink discovery signal]

Hereinafter, a discovery method based on an uplink trigger signal and a downlink discovery signal will be described.

■ Cell discovery procedure based on uplink trigger signal and downlink measurement signal

FIG. 4A is a conceptual diagram illustrating a cell discovery procedure based on an uplink trigger signal and a downlink discovery signal, and FIG. 4B is a flowchart illustrating a cell discovery procedure based on an uplink trigger signal and a downlink discovery signal.

4A and 4B, the terminal 430 transmits a trigger signal to the cells 430 (S401). Here, the terminal 430 may receive configuration information for configuring a trigger signal from the serving cell 420. In addition, the trigger signal may be configured using a frequency resource of the serving cell 410 of the terminal 430 or a frequency resource different from that of the serving cell 410. For example, when the terminal 430 is being served by a large cell, the terminal 430 may transmit a trigger signal using a frequency resource used by the large cell. Alternatively, when the terminal 430 is served by a large cell, and the large cell and the small cell use different frequencies, the terminal 430 may transmit a trigger signal using the frequency resource used by the small cell. .

The cells 420 perform measurement on the trigger signal and estimate the proximity to the terminal 430 based on the measurement result (S402).

Cells 420 around the terminal 430 transmit a discovery signal to the terminal 430 (S403). Here, each cell 420 may determine whether to transmit the discovery signal based on a result of estimating the proximity to the terminal 430 through measurement of a trigger signal. The discovery signal may include a synchronization signal and a measurement signal for obtaining synchronization. In addition, the serving cell 410 of the terminal 430 may transmit association information indicating information on each synchronization signal and measurement signals corresponding to each synchronization signal to the terminal 430.

The terminal 430 acquires time synchronization by receiving a synchronization signal based on the combination information. In addition, the terminal 430 performs measurement by receiving a measurement signal related to a synchronization signal based on time synchronization based on the combination information (S404), and reports the measurement result to the serving cell 410 (S405). Meanwhile, the discovery signal may not include a synchronization signal and may include only a measurement signal. In this case, the terminal 430 may receive a measurement signal using reference time information provided by the serving cell 410 and perform measurement on the received measurement signal.

Thereafter, a specific cell 420 to be newly connected to the terminal 430 is determined based on the measurement result of the discovery signal (S406). Here, the serving cell 410 may determine a specific cell 420 to which the terminal 430 connects among a plurality of cells based on a measurement result of the discovery signal received from the terminal 430. In addition, the serving cell 410 may transmit information on the determined specific cell 420 to the terminal 430 and the specific cell 420.

The terminal 430 establishes a connection with the specific cell 420 and transmits and receives data with the connected specific cell 420 (S407). Here, the terminal 430 may receive information on a specific cell 420 to establish a connection from the serving cell 410, and establish a connection with the specific cell 420 based on the received information.

■ Method for UE to transmit trigger signal using serving cell resource

Hereinafter, a method of transmitting a trigger signal by using its own serving cell resource will be described in detail.

The serving cell uses RRC signaling, or transmits configuration information of a trigger signal to the terminal using RRC signaling and downlink control information (DCI). The trigger signal configuration information may include signal information to be used by the terminal for transmission, time resource and frequency resource information of the corresponding signal, transmission power information, and the like.

In addition, the serving cell base station transmits trigger signal configuration information to other cells so that at least one cell can receive the trigger signal.

The trigger signal may use a sounding reference signal (SRS) or a physical random access channel (PRACH) for backward-compatibility.

Cells that provide a service to the terminal using a different frequency from the serving cell must also be able to receive a trigger signal transmitted using the serving cell frequency resource of the terminal and measure the proximity of the terminal.

When the terminal transmits a trigger signal using the resources of the serving cell, the trigger signal may be transmitted using the TA set by the serving cell. Cells located around the terminal may receive the trigger signal at a time earlier than the reception timing of the uplink subframe of the serving cell by the transmission delay time between the serving cell and the terminal.

How to use SRS as trigger signal

The UE transmits the SRS as a trigger signal, and the cells may measure the reception strength (eg, RSRP: Reference Signal Received Power) of the SRS transmitted by the UE.

The configuration information necessary for the UE to transmit the SRS using the resources of the serving cell and for the cells to receive the SRS to estimate the proximity to the UE is the physical layer cell identification information of the serving cell of the UE and for receiving the corresponding SRS. It may include configuration information of all parameters, TA information used when the terminal transmits the SRS to the serving cell, and transmission power information of the SRS.

In addition, the setting information of all parameters for receiving the corresponding SRS may include the following information according to a trigger type of the SRS.

Trigger type 0 (Trigger type 0) parameter setting information of the SRS includes a transmission comb, a starting position of a physical RB assignment, a duration, a period and a subframe offset, and a bandwidth. , A frequency hopping bandwidth, a cyclic shift, and the number of antenna ports used for SRS transmission.

The trigger type 1 parameter setting information of the SRS may include period and subframe offset, transmission comb, starting position of a physical resource block, bandwidth, information on the number of antenna ports used for SRS transmission, and the like.

The serving cell of the terminal may transmit the value of the parameter determined when triggering the SRS to the terminal through RRC signaling or RRC signaling and DCI. In addition, the serving cell may transmit corresponding parameter information to a cell that will receive a trigger signal transmitted from the terminal through a backhaul.

In order for cells not serving the terminal to receive a trigger signal transmitted by the terminal, a procedure for obtaining the reception timing of the trigger signal is required.

If the distance between the terminal and the cell is not close enough, the transmission delay time between the terminal and the cell cannot be known, and thus the reception procedure must be performed without deriving the reception time of the SRS. At this time, since the reception procedure needs to estimate the reception timing of the SRS, processing complexity increases.

In general, if the distance between the terminal and the cell is not close enough, it can be assumed that the radio distance is also not close. In this case, the cell may set an observation window for receiving the SRS, and detect only SRSs reaching within the set measurement window. If the cell does not detect the SRS within the measurement window, it can be assumed that the terminal is far away.

In addition, when the cell knows the transmission delay time between the terminal and the serving cell and the uplink reception timing of the serving cell, the cell is triggered using the transmission delay time under the assumption that the distance between the terminal and the cell is sufficiently close. You can estimate when you need to receive a signal. That is, assuming that the distance between the terminal and the cell is sufficiently close, the transmission delay time between the terminal and the cell can be approximated to 0, so that the cell is equal to the transmission delay time between the terminal and the serving cell at the uplink subframe reception timing of the serving cell It is possible to attempt to receive the SRS from an early point in time.

The cell receives the SRS transmitted by the UE and can know the received power strength (eg, RSRP) of the SRS, and can more accurately estimate the reception timing of the SRS from the received SRS.

In order to improve the proximity measurement accuracy, the UE may periodically transmit the SRS and the cell may periodically receive the SRS.

When the SRS transmission of the terminal and other signal or channel transmission overlap in time, the SRS transmission may be dropped. For example, when PUCCH (Physical Uplink Control Channel) format 2a/2b and SRS are configured in the same subframe, the UE may transmit only the PUCCH without transmitting the SRS.

In order not to exceed the transmission power limit even when a plurality of timing advance groups (TAGs) are configured, the terminal may give up SRS transmission when other signals or channel transmissions overlap in time.

Even if the serving cell communicates whether or not the UE is giving up transmission of the SRS to another cell through the backhaul, other cells may be measuring the SRS unnecessarily due to the backhaul delay time. Accordingly, cells need to determine whether the SRS is actually transmitted by measuring the average reception power of the corresponding resource element in which the SRS is set. To this end, as shown in Table 3, two thresholds (T1, T2) can be introduced and used to measure whether the SRS is not transmitted and the distance between the terminal and the cell.

If the cell determines that the SRS has not been transmitted, the cell may not determine the proximity between the UE and the cell.

How to use PRACH as trigger signal

The cell may estimate the proximity between the cell and the terminal by receiving the PRACH transmitted by the terminal. The configuration information necessary for the UE to transmit the PRACH using the resources of the serving cell and the cells to receive the PRACH to estimate the UE proximity may include PRACH configuration information and PRACH transmission power value information.

The PRACH configuration information includes information such as a transmission subframe or period and a subframe offset, a frequency position, a transmission set type required to generate a RACH sequence, a RACH root sequence, a cyclic shift value, etc. It may include.

The serving cell of the terminal provides PRACH configuration information to the terminal, and the terminal transmits the PRACH according to the PRACH configuration information provided from the serving cell. The serving cell of the UE transmits PRACH configuration information to other cells so that each cell can receive the PRACH transmitted from the UE.

The cell may receive the PRACH and measure the received power strength (eg, RSRP) of the PRACH.

The cell receiving the PRACH must transmit a random access response in downlink.However, when the UE transmits the PRACH for discovery purposes, a random access (RA) procedure so that the cell does not perform a random access response. Need to be modified.

In addition, a specific sequence from among the PRACH sequence set may be pre-allocated for cell discovery purposes. In this case, the cell may detect the PRACH sequence to distinguish the transmission purpose (ie, random access or discovery) of the PRACH.

Therefore, when the serving cell instructs the UE to transmit a PRACH for discovery purposes, when the serving cell and other cells receive the corresponding sequence in the form of a PRACH, the discovery procedure can be performed without transmitting a random access response to the UE.

In the case of using the PRACH as a trigger signal, since the cells know the sequence information and configuration information of the PRACH in advance, as shown in Table 4, by comparing the received signal strength (RSRP) of the received PRACH with a preset threshold value (T2). The proximity to the terminal can be measured, and it can also be used to obtain uplink synchronization between the terminal and the cell.

■ Method for the terminal to transmit the trigger signal using a frequency not used by the serving cell

When the terminal transmits a trigger signal using resources of a non-serving cell (meaning a cell not serving the terminal), and the frequency used by the serving cell and the frequency used by the non-serving cell are different, the non-serving cell is There is an advantage that it is not necessary to perform inter-frequency measurement.

In addition, when the frequency used by the serving cell and the frequency used by the non-serving cell are significantly different, the proximity measured at the frequency used by the serving cell may not mean the proximity at the frequency used by the non-serving cell. Therefore, in such a case, it is preferable that the terminal transmits a trigger signal using a non-serving cell resource. For example, when the terminal is connected to a large cell and the frequencies used by the large cell and the small cell are different, it is preferable that the terminal transmits a trigger signal using the small cell frequency resource.

The serving cell may use RRC signaling or transmit configuration information of a trigger signal to the terminal using RRC signaling and DCI. The setting information of the trigger signal may include a signal to be used by the terminal for transmission, time resources and frequency resources of the corresponding signal, and transmission power.

The serving cell base station must transmit the trigger signal configuration information to other cells so that at least one cell can receive the trigger signal.

The trigger signal may use SRS or PRACH.

When the SRS is used as a trigger signal, the setting information of the trigger signal may include the transmission power of the SRS and the setting information of a parameter according to the trigger method of the SRS below.

Trigger type 0 (Trigger type 0) SRS parameter setting information includes transmission comb, starting position of physical resource block, transmission period, period and subframe offset, bandwidth, frequency hopping bandwidth, cyclic shift, and antenna used for SRS transmission. It may include the number of ports, etc.

The trigger type 1 parameter setting information of the SRS may include period and subframe offset, transmission comb, starting position of a physical resource block, bandwidth, information on the number of antenna ports used for SRS transmission, and the like.

The serving cell of the terminal may transmit the value of the parameter determined when triggering the SRS to the terminal through RRC signaling or RRC signaling and DCI. In addition, the serving cell may transmit corresponding parameter information to a cell that will receive a trigger signal transmitted from the terminal through a backhaul.

When the PRACH is used as a trigger signal, the setting information of the trigger signal may include setting information of the PRACH and a transmission power value of the PRACH.

The PRACH configuration information includes information such as a transmission subframe or period and a subframe offset, a frequency position, a transmission set type required to generate a RACH sequence, a RACH root sequence, a cyclic shift value, etc. It may include.

The serving cell of the terminal provides PRACH configuration information to the terminal, and the terminal transmits the PRACH according to the PRACH configuration information provided from the serving cell. The serving cell of the UE transmits PRACH configuration information to other cells so that each cell can receive the PRACH transmitted from the UE.

When the terminal transmits a trigger signal using resources not used by the serving cell, the trigger signal may be transmitted using a TA set by the serving cell. Cells located around the terminal may perform reception of the trigger signal at a time earlier than the reception timing of the uplink subframe of the serving cell by a transmission delay time between the serving cell and the terminal.

■ How to configure discovery signal settings and combination information

The discovery signal may include a synchronization signal for obtaining synchronization, and may include a measurement signal for measurement. Hereinafter, a method in which the discovery signal includes both a synchronization signal and a measurement signal will be described.

The combination information of the discovery signal is information defining connectivity between a downlink synchronization signal transmitted by a cell and a downlink measurement signal, and may be transmitted by a serving cell to a terminal through RRC signaling. Cells that transmit the discovery signal may transmit only one of a synchronization signal and a measurement signal or both of a synchronization signal and a measurement signal according to configuration information and combination information of the discovery signal.

5 shows an example of transmission of an uplink trigger signal and a downlink discovery signal.

FIG. 5 illustrates a process in which a UE transmits a trigger signal using a frequency (F1) resource used by a serving cell and a downlink discovery signal transmitted using a frequency (F2) resource used by another cell. .

Referring to FIG. 5, the terminal receives the setting information 501 of the trigger signal through the downlink from the serving cell, and transmits the trigger signal 502 in the uplink based on the received setting information 501 of the trigger signal. do. Here, the serving cell may transmit trigger signal configuration information 501 to the terminal through RRC signaling.

In addition, the serving cell transmits the discovery signal configuration information and the combination information 503 to the terminal and neighboring cells through downlink. Here, the serving cell may transmit configuration information and combination information 503 of the discovery signal to the terminal through RRC signaling, and may transmit it to neighboring cells through a backhaul. The discovery signal includes a synchronization signal and a measurement signal.

Cells around the terminal transmit the synchronization signal 504 and the measurement signal 505 through downlink based on the discovery signal configuration information and the combination information 503 received from the serving cell.

If each cell transmits the combined information of the system information and the discovery signal to the terminal, the power consumption of each cell increases because the cells must be converted to the TX_active state and operate. In particular, in the case of a large number of cells, the method of transmitting the setting and combination information by the serving cell of the terminal to the terminal as illustrated in FIG. 5 is more effective in terms of power consumption than the method in which all cells transmit each configuration and combination information. It is efficient, and the latency it takes to deliver configuration and binding information will be shorter.

In the present invention, since the serving cell transmits the configuration and combination information 503 of the discovery signal to the terminal using RRC signaling, the serving cell detects the discovery signal by receiving the configuration and combination information 503 normally. I don't know exactly when to start. In addition, in order to accurately acquire time and frequency synchronization of discovery signals and improve measurement quality, it is preferable that the terminal receives the synchronization signal 504 and the measurement signal 505 several times for a predetermined time. Therefore, it is preferable that the cells transmit the synchronization signal 504 and the measurement signal 505 periodically rather than transmitting only once. Here, the period of the synchronization signal 504 and the period of the measurement signal 505 may be set independently, or may always be set to the same period.

The synchronization signal setting information for each synchronization signal may include a period and an offset of the synchronization signal, a frequency position of the synchronization signal, information on sequence generation of the synchronization signal, and the like.

Measurement signal setting information for each measurement signal may include measurement signal identification information, period and offset of measurement signal, frequency position of measurement signal, sequence generation information of measurement signal, transmission power information of downlink measurement signal, and the like.

The combination information may include identification information of measurement signals corresponding to each synchronization signal.

The terminal may receive measurement signals related to the synchronization signal indicated by the combination information based on the time and frequency synchronization obtained from the received synchronization signal, and may perform measurement on the measurement signals.

On the other hand, it is possible to transmit only the measurement signal without including the synchronization signal in the discovery signal. In this case, the terminal may obtain the reception timing of the measurement signal from the serving cell of the terminal. For example, the terminal may receive a measurement signal using a primary synchronization signal (PSS)/secondary synchronization signal (SSS) of a serving cell and a timing of a serving cell obtained from a CRS.

■ Transmission method of synchronization signal

The terminal first receives the synchronization signal before receiving the measurement signal transmitted from the small cell. The synchronization signal may use a main synchronization signal (PSS) and an immobile signal (SSS) defined in the LTE standard.

Small cells may transmit a synchronization signal at a time delayed by a transmission delay time between a transmission/reception point of a large cell and a small cell than a transmission timing of a downlink subframe of the large cell.

Synchronization signal transmission method when small cells form a cell cluster

When a plurality of small cells are arranged in close proximity to each other to form a cell cluster, and the downlink transmission synchronization of small cells belonging to the cell cluster is the same, even if only one or a few cells transmit the synchronization signal, the terminal It can be assumed that the acquired synchronization is the same as the downlink synchronization of other cells included in the cell cluster.

If each of the cells belonging to the cell cluster transmits a synchronization signal, the synchronization acquisition performance of the terminal may decrease due to an inter-cell interference problem, and the number of synchronization signals that the terminal can detect may decrease.

In order to improve the synchronization signal reception quality of the terminal, the following three methods can be considered.

-Interference cancellation method of the receiver: When the receiver of the terminal has an interference cancellation function, the synchronization signal reception performance of the terminal can be improved through interference cancellation of the synchronization signal through the receiver.

-Method of transmitting synchronization signals only in a small number of small cells: By transmitting synchronization signals only in a small number of small cells among a plurality of small cells constituting a cell cluster, interference of synchronization signals can be avoided and synchronization performance can be guaranteed.

When the serving cell and small cells are connected through a non-ideal backhaul with delay, since the serving cell cannot dynamically change the state of the small cells, each cell independently determines whether to transmit a synchronization signal. It is desirable to do. For example, each cell may determine whether to transmit a synchronization signal based on a result of observing a transmission state of a neighboring cell using a Network Listen Mode (NLM).

-Method of using the same identification information: This is a method in which a plurality of cells constituting a cell cluster do not transmit different synchronization signals, but a synchronization signal generated in the same sequence based on the same identification information used inside the cell cluster. . The UE can obtain rough downlink synchronization by using a common synchronization signal inside the cell cluster. Thereafter, the UE can obtain accurate synchronization from the downlink measurement signal received from the cell.

Synchronization signal transmission method when small cells are spaced apart

If the small cell does not belong to the cell cluster and thus it cannot be assumed that it shares the same synchronization as the cell cluster, the small cell must transmit its own synchronization signal. In this case, since the small cell does not belong to the cell cluster, interference by neighboring small cells may not be large, and accordingly, synchronization performance may not be reduced.

■ Transmission method of measurement signal

The cell may transmit a measurement signal based on a parameter set in the association information. The measurement signal may be, for example, a Channel State Information Reference Signal (CSI-RS). The terminal may receive the measurement signal based on the configuration parameter included in the association information.

■ Transmission method of discovery signal for cell opening/closing (On/Off) conversion

The faster the cell opening/closing speed, the greater the amount of transmission can be. Here, the opening/closing conversion of the cell means conversion of the state of the cell, and includes the conversion of the cell state from TX_active to DTX or from DTX to TX_active.

The UE measures the discovery signal transmitted from the small cell in the TX_active or DTX state. In order to improve the cell state conversion speed, the UE may perform channel measurement of the corresponding cell. In this case, the UE may perform both RRM measurement and CSI measurement using the discovery signal.

Considering the environment to which the frequency aggregation (CA: Carrier Aggregation) is applied, when a PCell (primary cell) and a SCell (secondary cell) belong to different Timing Advance Groups (TAGs), the terminal is a TA for transmission to the SCell (Timing Advance) value and transmit power value must be known. On the other hand, considering an environment in which dual connectivity (DC) is applied, when a primary serving cell (pSCell) and a secondary serving cell (sSCell) belong to different TAGs, the terminal transmits to a secondary serving cell (sSCell). You need to know the TA value and the transmit power value. To this end, the serving cell of the terminal may inform the terminal by adding TA information to configuration information or combination information of the discovery signal. Through this, it takes only 4ms for the UE to receive an UL grant and transmit a Physical Uplink Shared Channel (PUSCH).

To update the TA value, the UE may transmit an SRS to the small cell in the DTX state. It is assumed that the initial TA value can be known by performing a random access channel (RACH) procedure of the terminal and the small cell. In this case, when small cells that are geographically adjacent belong to the same TAG, they may have the same TA value. The terminal does not need to individually transmit the SRS to each cell, and transmits the SRS to only one small cell among small cells belonging to the same TAG, and the small cell receiving the SRS determines the TA value of the terminal based on the received SRS. After updating, TA update information can be shared with other small cells by transmitting the updated value of the TA value to other small cells through the backhaul. These small cells are effective when they belong to the same small cell cluster and share the same TAG with each other.

In addition, in an environment in which small cells are arranged very closely, it is inefficient for the UE to transmit the SRS for each cell in terms of power consumption of the UE, and the uplink transmission amount may be reduced. Therefore, SRS control between small cells is essential. For example, small cells can perform cooperation for SRS transmission of the terminal by exchanging control information for SRS transmission of the terminal through the backhaul.

If the terminal transmits the SRS, small cells receiving the SRS can estimate the uplink CSI and use it for uplink scheduling. Therefore, it is possible to improve the state conversion speed of the small cell.

Meanwhile, in order to determine the transmission power, the UE obtains CRS cell specific reference signal energy per resource element (EPRE) information through signaling from a serving cell, and estimates a downlink pathloss based on this. If the TX_active small cell transmits the CRS, the UE can estimate the downlink path attenuation based on the CRS, but in the case of the DTX small cell, only the discovery signal can be transmitted without transmitting the CRS, so downlink path attenuation is performed. Cannot be estimated. If carrier aggregation (CA) having different TAGs or dual connectivity (DC) in which the primary serving cell (pSCell) and the secondary serving cell (sSCell) have different TAGs are considered, the terminal uses only the discovery signal to perform the downlink path. The attenuation should be estimated.

To this end, the serving cell of the terminal must inform the terminal of the transmission power of the discovery signal transmitted by the small cells to be measured by the terminal. For example, when a small cell uses a CSI-RS as a discovery signal, the serving cell must transmit CSI-RS EPRE information of the small cell to the terminal. When the UE estimates the downlink path attenuation through the transmission power of the discovery signal, it is preferable to use the estimated information in a power headroom report (PHR).

[Discovery method based on uplink trigger signal and uplink discovery signal]

When the number of cells per unit area is large, the number of terminals in one cell area may be expected to be small. In this case, it is more efficient in terms of interference management that a plurality of cells do not transmit measurement signals and that the UE transmits measurement signals to cells. In addition, in this case, since both the trigger signal and the measurement signal are transmitted from the terminal, a discovery signal that satisfies both purposes of checking and measuring proximity can be defined.

■ Discovery procedure based on uplink trigger signal and uplink discovery signal

6A is a conceptual diagram illustrating a discovery procedure based on an uplink trigger signal and an uplink discovery signal, and FIG. 6B is a flowchart illustrating a discovery procedure based on an uplink trigger signal and an uplink discovery signal.

6A and 6B, the terminal 630 transmits a trigger signal and/or a discovery signal using a frequency used by the serving cell 610 or another frequency not used by the serving cell 610 (S601). . Here, the trigger signal may be configured according to the trigger signal setting information transmitted from the serving cell 610 to the terminal 630 through RRC signaling. In addition, the discovery signal may also be configured according to configuration information transmitted from the serving cell 610 to the terminal 630 through RRC signaling.

Cells 620 located around the terminal 630 measure the trigger signal and/or the discovery signal transmitted by the terminal 630, and estimate proximity to the terminal based on the measurement result (S602). Here, each cell may not perform a subsequent discovery procedure if it is determined that the distance to the terminal is far from the terminal according to the proximity estimation result, and may continue to perform the discovery procedure when it is determined that the distance to the terminal is close. That is, cells 620 having a close distance to the terminal 630 report the measurement result to the serving cell 610 of the terminal 630.

The serving cell 610 selects at least one cell 630 to be connected to the terminal 630 based on the measurement result report received from the neighboring cells 620 of the terminal (S604). Here, the cell selected by the serving cell 610 may be converted to the TX_active state according to control signaling of the serving cell 610. In addition, the serving cell 610 may provide information on the selected cell to the terminal 630.

After establishing a connection with at least one corresponding cell 630, the terminal 630 performs data transmission/reception with the cell in which the connection is established (S605).

Meanwhile, it is possible to use a method in which only a measurement signal is transmitted without a synchronization signal in the discovery signal. In this case, the cell may obtain the timing of the measurement signal from the serving cell of the terminal. For example, the serving cell of the terminal may provide a transmission delay time between the terminal and the transmission/reception point of the serving cell to cells receiving the discovery signal, and the cells receive a measurement signal transmitted from the terminal based on the transmission delay time. You can decide the timing.

Hereinafter, a case in which the UE transmits an uplink discovery signal will be described by dividing into four cases.

In the first case, the UE transmits a synchronization signal and a measurement signal using a frequency other than the frequency used by the serving cell, and transmits a trigger signal using resources of the serving cell. For example, when the terminal is connected to a large cell and the frequencies used by the large cell and the small cell are different, the terminal transmits a trigger signal using the frequency resource of the large cell and the synchronization signal and the synchronization signal are generated using the frequency resource of the small cell. This is the case of transmitting a measurement signal.

7 shows a procedure for a UE to transmit a trigger signal using a serving cell resource and a discovery signal using a resource not using a serving cell. In FIG. 7, it is assumed that the serving cell uses a first frequency F1 and adjacent cells use a second frequency F2.

The serving cell delivers configuration information 701 of a trigger signal to be transmitted by the terminal to the terminal through RRC signaling.

The terminal transmits the trigger signal 702 using the serving cell resource based on the setting information 701 of the trigger signal received from the serving cell.

Cells determine proximity by measuring the reception strength of the trigger signal 702 transmitted from the terminal. If the cell determines that the UE is sufficiently close to its own cell based on the proximity determination result, the cell reports the proximity measurement result to the serving cell.

The serving cell delivers the discovery signal (ie, synchronization signal and measurement signal) configuration and combination information 703 to the UE through RRC signaling. In addition, the serving cell transmits the information 703 to other cells measuring the discovery signal through a backhaul.

Based on the discovery signal configuration and combination information 703 received from the serving cell, the UE uses a resource different from the resource used by the serving cell (e.g., a second frequency (F2)) with the synchronization signal 704 The measurement signal 705 is transmitted. Here, the terminal may periodically transmit the synchronization signal 704 and/or the measurement signal 705.

The cells receive the synchronization signal 704 and the measurement signal 705 transmitted from the terminal, perform measurement, and report the result to the serving cell of the terminal.

In the second case, the UE transmits the discovery signal using only the serving cell resource.

8 shows a procedure for a UE to transmit a discovery signal using only a serving cell resource. In FIG. 8, it is assumed that the serving cell uses the first frequency F1.

When the terminal transmits the synchronization signal and the measurement signal using only the resources of the serving cell, since it is not necessary to define a separate trigger signal, the terminal may transmit only the synchronization signal and the measurement signal as illustrated in FIG. 8.

The serving cell delivers the discovery signal (ie, synchronization signal and measurement signal) configuration and combination information 801 to the terminal through RRC signaling.

The terminal transmits the synchronization signal 802 and the measurement signal 803 using the resources of the serving cell based on the information 801 received from the serving cell. Here, the synchronization signal 802 and/or the measurement signal 803 may be periodically transmitted.

The cells acquire the transmission timing of the terminal based on the synchronization signal 802 received from the terminal, receive the measurement signal 803 based on the obtained transmission timing, and measure the reception strength of the measurement signal 803.

The cells report the measurement result to the serving cell.

In the third case, the UE transmits the discovery signal using a frequency other than the frequency used by the serving cell.

9 shows a procedure for a UE to transmit a discovery signal using a resource not used by a serving cell. In FIG. 9, it is assumed that the serving cell uses a first frequency F1 and adjacent cells use a second frequency F2.

When one signal is used as a trigger signal and a measurement signal, the UE provides a frequency that the serving cell does not use based on the discovery signal configuration information 901 delivered by the serving cell through RRC signaling. The discovery signal 902 is transmitted using frequency (F2). Here, the discovery signal 902 may be periodically transmitted.

The cells acquire uplink synchronization by receiving the discovery signal 902 transmitted by the terminal, and measure proximity between the terminal and the cell and the received power of the discovery signal 902 based on the obtained synchronization.

The cells report the measurement result to the serving cell of the terminal.

In the fourth case, two different signals are used as the synchronization signal and the measurement signal, respectively.

10 shows a procedure for a UE to transmit a synchronization signal and a measurement signal as different signals using resources not used by a serving cell. In FIG. 10, it is assumed that the serving cell uses a first frequency F1 and adjacent cells use a second frequency F2.

Even when two different signals are used as a synchronization signal and a measurement signal, respectively, as illustrated in FIG. 10, the UE according to the discovery signal configuration and combination information 1001 set by the serving cell to the UE through RRC signaling. The synchronization signal 1002 and the measurement signal 1003 are generated and transmitted.

The synchronization signal 1002 and the measurement signal 1003 may be transmitted at different periods to improve measurement quality of cells.

Cells use the synchronization signal 1002 transmitted by the terminal to obtain the transmission timing of the signal transmitted by the terminal, and measure the measurement signal 1003 transmitted by the terminal to estimate the proximity between the terminal and the cell.

If the cells determine that the distance to the terminal is sufficiently close based on the estimated proximity, they report the measurement result of the measurement signal to the serving cell of the terminal.

When the frequency used by the serving cell and the frequency used by other cells are not significantly different, the cells can measure the proximity between the cell and the terminal and the reception strength of the measurement signal transmitted by the terminal using the resources of the serving cell. . In this case, the terminal transmits the synchronization signal and the measurement signal using the resources of the serving cell, and the other cell measures the proximity between the terminal and the cell by measuring the synchronization signal and measurement signal of the terminal received through the resource of the serving cell. Can be done.

■ Discovery signal design method

Cells should measure the reception strength of the discovery signal based on the uplink transmission timing of the terminal acquired based on the discovery signal transmitted by the terminal. The discovery signal can be designed using PRACH and SRS defined in the LTE standard.

Depending on the method of using the PRACH and SRS, a case of transmitting the PRACH and the SRS in different subframes and a case of transmitting in the same subframe may be considered.

The UE determines an uplink transmission timing using a timing advance (TA) set by the serving cell, and transmits a discovery signal at the determined timing.

When using PRACH as synchronization signal and SRS as measurement signal

The cell receives the PRACH transmitted by the terminal to obtain the transmission timing of the terminal, and receives the SRS based on the obtained transmission timing to measure the proximity and the reception strength of the uplink signal.

The terminal identification information and the configuration and association information of the PRACH and SRS of the corresponding terminal may be provided by the serving cell of the terminal to neighboring cells. The combination information is information that defines the connectivity between the PRACH and the SRS transmitted by the terminal, and enables the receiving side to know the PRACH and the SRS transmitted by the same terminal. The serving cell of the terminal transmits the configuration information and association information of the PRACH and SRS to the terminal through RRC signaling, and transmits the configuration information and the association information to other cells adjacent to the terminal through a backhaul.

The serving cell configures PRACH and SRS configuration information and combination information for each UE as follows. That is, the serving cell configures PRACH and SRS configuration information and combination information for each terminal identification information.

The PRACH configuration information may include information such as a transmission subframe or period and a subframe offset, a frequency position, a transmission set type required for generating a RACH sequence, a RACH root sequence, a cyclic shift value, and a transmission power.

All parameter setting information for cells to receive the SRS may include the following information according to the trigger method of the SRS.

Trigger type 0 (Trigger type 0) SRS parameter setting information includes transmission comb, starting position of physical resource block, transmission period, period and subframe offset, bandwidth, frequency hopping bandwidth, cyclic shift, and antenna used for SRS transmission. It may include the number of ports, etc.

The trigger type 1 parameter setting information of the SRS may include period and subframe offset, transmission comb, starting position of a physical resource block, bandwidth, information on the number of antenna ports used for SRS transmission, and the like.

The serving cell of the terminal may transmit the value of the parameter determined when triggering the SRS to the terminal through RRC signaling or RRC signaling and DCI. In addition, the serving cell may transmit corresponding parameter information to a cell that will receive the SRS transmitted by the UE through a backhaul.

The cell may receive the PRACH transmitted by the UE, obtain a reception timing for the UE, and perform measurement on the SRS associated with the PRACH based on configuration and association information.

Here, the UE may periodically transmit the PRACH so that the cells can more accurately estimate the reception timing for each UE. If the terminal transmits the PRACH only once, the information of the subframe transmitting the PRACH is included in the configuration and combination information, and when the terminal periodically transmits the PRACH, the transmission period and the subframe offset are determined in the configuration and combination information. Can be included.

The serving cell does not need to transmit a random access response for the PRACH transmitted by the UE for discovery purposes. Therefore, it is desirable to manage the PRACH sequence for discovery separately from the PRACH sequences for random access purposes. When the PRACH sequence used when the UE transmits the PRACH for discovery is specified separately, or the serving cell indicates to the UE that the PRACH is transmitted for discovery purposes (indicate), the UE and the serving cell of the UE perform unnecessary random access procedures. I never do that.

When the SRS is used as a measurement signal, when the terminal transmits the SRS only once, the Type 1 SRS transmission method, which is an aperiodic SRS transmission method, is used, and when the terminal periodically transmits the SRS, periodic (periodic) Type 0 SRS transmission method, which is an SRS transmission method, can be used. Accordingly, the SRS configuration and combination information includes configuration information for Type 1 SRS transmission or configuration information for Type 0 SRS transmission according to the transmission method of the SRS.

PRACH and SRS can be used for both proximity measurement and reception strength measurement of a measurement signal. When the cells participating in the discovery know the transmission power of the PRACH and the SRS of the UE, more accurate proximity measurement can be performed. To this end, the serving cell of the terminal can inform neighboring cells of the transmission power of the PRACH and SRS, and the terminal can transmit the PRACH and the SRS using the transmission power of the PRACH and SRS set by the serving cell.

When allocating PRACH and SRS to the same subframe

Hereinafter, a method of allocating the PRACH and the SRS to the same subframe will be described.

When the UE transmits the PRACH for random access, the subframe for transmitting the PRACH consists of a cyclic shift period, a sequence period, and a guard time period. Among the periods, the cyclic shift period and the guard time period are defined in consideration of a propagation delay from a terminal to a cell and delay spread due to multipaths.

If the transmission delay time between the terminal and the serving cell can be known in advance, the terminal transmits the PRACH at a time earlier as the transmission delay time, and in the case of PRACH format 0, the PRACH sequence is all in the serving cell. The arrival time may be set to be faster than the start time of the next subframe by the guard time period. In this case, it can be used for measurement signal transmission by transmitting an additional signal during the guard time period.

In a general random access procedure, a UE transmits a PRACH at a reception time of a downlink subframe boundary. This corresponds to considering TA as 0.

However, in the method of allocating the PRACH and the SRS to the same subframe, when the UE transmits the PRACH for discovery purposes, the PRACH may be transmitted based on the uplink transmission timing for the serving cell of the UE. That is, PRACH transmission is started at the time when transmission of the corresponding uplink subframe starts.

11 shows the reception timing of a subframe in a serving cell of a terminal.

Referring to FIG. 11, PRACH format 0 and SRS, which are discovery signals transmitted by the UE, are allocated to the same subframe. When the UE transmits PRACH format 0 in advance of the uplink subframe by TA, the serving cell performs the PRACH format 0 sequence before the guard time by about 1.4 OFDM symbols from the next uplink subframe. Can receive. Therefore, even if the SRS is transmitted in the last symbol of the subframe transmitting the discovery signal, the PRACH format 0 sequence transmission is not affected. That is, the PRACH format 0 and the SRS can be allocated to the same subframe without overlapping each other. Format 1, format 2, and format 3 of PRACH can be used as discovery signals in the same way.

In the case of transmitting the discovery signal using the serving cell resource of the terminal, if the subframe transmitting the discovery signal and the subframe transmitting a different channel (e.g., PUSCH, PUCCH, PRACH) are set identically, the discovery signal and the Another channel may cause interference, and the reception quality of the serving cell may decrease. In this case, in order to improve reception quality, it is preferable that the serving cell does not receive other signals and channels transmitted from other terminals by setting separate subframes and resources for one terminal to transmit the discovery signal.

When the UE transmits the discovery signal using a frequency that the serving cell does not use as a resource, interference does not occur unless the UE in the TX_active state exists in the region of the cell participating in the discovery. However, when a cell participating in discovery is in a Tx_active state and there is a serving terminal, in order to improve the reception quality of the cell, one terminal sets a separate subframe and resource for transmitting the discovery signal and transmits it from another terminal. It is desirable to avoid interference with signals and channels.

How to set up the discovery signal

The UE transmits the PRACH and SRS according to the configuration information of the PRACH and SRS provided from the serving cell. Even in this case, the serving cell of the terminal transmits PRACH and SRS configuration information and combination information to the terminal through RRC signaling, and transmits the same configuration information to related cells through the backhaul.

The serving cell of the terminal may configure a transmission subframe or period, a subframe offset, PRACH configuration information, and SRS configuration information for each terminal (ie, for terminal identification information).

The PRACH configuration information includes information such as a transmission subframe or period, a subframe offset, a frequency position, a transmission set type required to generate a RACH sequence, a RACH root sequence, a cyclic shift value, and a transmission power. Can include.

The setting information of all parameters for receiving the corresponding SRS may include the following parameter setting information according to a trigger type of the SRS.

Trigger type 0 (Trigger type 0) SRS parameter setting information includes transmission comb, starting position of physical resource block, transmission period, period and subframe offset, bandwidth, frequency hopping bandwidth, cyclic shift, and antenna used for SRS transmission. It may include the number of ports, etc.

The trigger type 1 parameter setting information of the SRS may include period and subframe offset, transmission comb, starting position of a physical resource block, bandwidth, information on the number of antenna ports used for SRS transmission, and the like.

The serving cell of the terminal may transmit the value of the parameter determined when triggering the SRS to the terminal through RRC signaling or RRC signaling and DCI, and the corresponding information to the cell that will receive the trigger signal transmitted by the terminal through the backhaul. .

In order to allocate the PRACH and SRS to the same subframe, in the case of periodically transmitting the PRACH and the SRS, the same period and offset are set, and in the case of aperiodic transmission, the transmission subframe must be specified.

If the discovery signal is transmitted using a serving cell resource, if the SRS uses resources other than the subframe and resource block (RB) occupied by the PRACH sequence, interference with the PUSCH transmitted from another terminal may occur. Therefore, in order to avoid interference, the discovery signal can be configured using separate resources.

According to the existing LTE standard, the bandwidth of the SRS can be set as a multiple of 4 RBs, but since the PRACH uses 6 RBs, the SRS sequence is also set to use 4 RBs so that the entire discovery signal uses 6 RBs. It is desirable. Therefore, it is desirable to set the center frequency of the SRS according to the center frequency of the PRACH so that the RB used by the SRS is included within 6 RBs used by the PRACH.

If the discovery signal is transmitted using a frequency that the serving cell does not use as a resource, it is preferable that the SRS is transmitted within RBs occupied by the PRACH in a subframe in which the PRACH is transmitted. At this time, the SRS can be adjusted such as a position and a bandwidth on the frequency axis, and may be set to be transmitted within RBs occupied by the PRACH.

Since PRACH transmission for uplink synchronization acquisition of a terminal for discovery purposes does not require a random access response by a serving cell, the PRACH sequence for uplink synchronization acquisition of a discovery terminal is random access. It is desirable to manage separately from target sequences. When the PRACH sequence used when the UE transmits the PRACH for discovery is specified separately or the serving cell indicates to the UE that the PRACH is transmitted for discovery purposes (indicate), the UE and the serving cell of the UE do not perform unnecessary random access procedures. It is desirable.

PRACH and SRS can be used for both proximity measurement and reception strength measurement of a measurement signal. In order for the cells participating in the discovery to more accurately measure the proximity of the terminal, the cells must know in advance the transmission power of the PRACH and the SRS transmitted by the terminal. The terminal may set the transmission power of the PRACH and SRS according to the configuration information of the serving cell.

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

111, 112: large cell
121, 122, 123: small cell cluster
131, 132, 133: terminal
410: serving cell
420: terminal
430: cell(s)
610: serving cell
620: terminal
630: cell(s)

Claims (27)

As a small cell discovery method performed in a terminal,
Receiving association information for discovery of a small cell from a serving cell through radio resource control (RRC) signaling-the association information corresponds to identification information of the synchronization signal of the small cell and the synchronization signal Consisting of a pair of sequence generation information of the channel state information referece signal (CSI-RS) of the small cell;
Synchronizing with the small cell using the synchronization signal indicated by the identification information;
Determining a CSI-RS to be measured based on the sequence generation information;
Performing channel measurement on the determined CSI-RS;
Reporting a result of the channel measurement to the serving cell; And
When the serving cell determines the small cell as a cell to be connected to the terminal, receiving information on the small cell from the serving cell,
The association information is received from the serving cell other than the small cell prior to the step of synchronizing with the small cell,
Small cell discovery method. The method according to claim 1,
The synchronization signal is composed of a first synchronization signal (primary synchronization signal (PSS)) and a second synchronization signal (secondary synchronization signal (SSS)),
Small cell discovery method. The method according to claim 1,
The identification information of the synchronization signal is a physical cell identification (PCI) of the small cell,
Small cell discovery method. As a small cell discovery method performed in a serving cell,
Transmitting association information for discovery of a small cell to a terminal through radio resource control (RRC) signaling-The association information is the identification information of the synchronization signal of the small cell and the synchronization signal. Consisting of a pair of sequence generation information of a channel state information referece signal (CSI-RS) of a small cell;
Transmitting the synchronization signal and the CSI-RS based on the association information;
Receiving a result of channel measurement performed on the CSI-RS from the terminal; And
When the serving cell determines the small cell as a cell to be connected to the terminal, transmitting information on the small cell to the terminal,
Synchronization between the terminal and the small cell is obtained using the synchronization signal indicated by the identification information,
The association information is transmitted to the terminal before synchronization between the terminal and the small cell is acquired,
Small cell discovery method. The method of claim 4,
The synchronization signal is composed of a first synchronization signal (primary synchronization signal (PSS)) and a second synchronization signal (secondary synchronization signal (SSS)),
Small cell discovery method. The method of claim 4,
The identification information of the synchronization signal is a physical cell identification (PCI) of the small cell,
Small cell discovery method. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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