WO2011017953A1

WO2011017953A1 - Method and device for determining position of cell reference signal

Info

Publication number: WO2011017953A1
Application number: PCT/CN2010/072802
Authority: WO
Inventors: 戴博; 郁光辉; 张峻峰
Original assignee: 中兴通讯股份有限公司
Priority date: 2009-08-14
Filing date: 2010-05-14
Publication date: 2011-02-17
Also published as: CN101635950B; CN101635950A

Abstract

The present invention provides a method and a device for determining the position of a cell reference signal. The position used to transmit a Reference Signal of Channel Status Information (CSI-RS) of every coordinated cell is selected from the positions available to transmit the CSI-RSes of the different cells, and the position of the CSI-RS of every coordinated cell is determined according to the identifier of every coordinated cell. Through the method of the present invention, a target user equipment (UE) determines the positions for transmitting CSI-RSes in multiple cells, therefore achieving the aim that the UE measures the CSI of multiple cells and reports it to a base station (BS) so that the BS can use it to transmit data, thus ensuring the application of Coordinated Multiple Point (CoMP) transmission and reception and achieving the target of enhancing the overall system performance.

Description

Method and device for determining location of cell reference signal

The present invention relates to Long Term Evolution (LTE) technology, and more particularly to a method and apparatus for determining the location of a cell reference signal. Background technique

Orthogonal Frequency Division Multiplexing (OFDM) technology is essentially a multi-carrier modulation communication technology, and OFDM technology is one of the core technologies in the fourth generation of mobile communication. In the frequency domain, the multipath channel of OFDM exhibits frequency selective fading characteristics. To overcome this fading, the channel is divided into multiple subchannels in the frequency domain, and the spectral characteristics of each subchannel are approximately flat, and each OFDM sub-sub-channel The channels are orthogonal to each other. Therefore, the spectrums of the subchannels are allowed to overlap each other, so that the spectrum resources can be utilized to a large extent.

Multi-input and multi-output (ΜΙΜΟ) technology can increase system capacity, improve transmission performance, and integrate well with other physical layer technologies. Therefore, ΜΙΜΟ technology has become a key technology for B3G and 4G mobile communication systems. However, when the channel correlation is strong, the diversity gain and multiplexing gain brought by the multipath channel are greatly reduced, resulting in a significant drop in the performance of the system. In order to eliminate the influence of channel correlation, the ΜΙΜΟ precoding method is an efficient ΜΙΜΟ multiplexing method, which uses the precoding process of the transceiver to convert the ΜΙΜΟ channel into multiple independent virtual channels, thus ensuring the ΜΙΜΟ system in various environments. The stability of the energy.

The LTE system is an important program for third-generation partner organizations. FIG. 1 is a schematic diagram of a frame structure of a frequency division duplex (FDD) mode and a time division duplex (TDD) mode of an LTE system. As shown in FIG. 1, a frame structure of an FDD mode is 10 ms ( That is, Ί]= 10 ms, where 7} denotes a radio frame length. The radio frame consists of twenty slots (lengths) of length 0.5 to 0 and 19 (ie, T _sl . _t =0.5 ms, its In T _sl . _t represents the length of a time slot), time slots 2i and 2i+l form a subframe (frame) i of length 1 ms; in a frame structure of TDD mode, a 10 ms radio frame (length of 5 frames) is 5 ms long A half frame consists of five subframes (frames) of length 1 ms. The subframe i is defined as two slots 2i and 2i+1 that are 0.5 ms long. When the system adopts the regular cyclic prefix, one time slot contains 7 uplink/downlink symbols; when the system adopts the extended cyclic prefix, one time slot contains 6 uplink/downlink symbols. 2 is a schematic structural diagram of a physical resource block when the system bandwidth of the LTE system is 5 MHz. As shown in FIG. 2, one resource element (RE, Resource Element) is one subcarrier in one OFDM symbol, and one downlink resource block ( RB , Resource Block ) consists of 12 consecutive subcarriers and 7 consecutive OFDM symbols (6 in extended cyclic prefix), 180 kHz in the frequency domain, and the length of time in a time slot is a general time slot. When the resource block is used as the basic unit for allocation.

The LTE system supports 4-antenna MIMO applications. The corresponding antenna port #0, antenna port #1, antenna port #2, and antenna port #3 all use full-bandwidth cell-specific reference signals (CRS). . 3a is a schematic diagram of the location of a cell-specific reference signal in a physical resource block when the cyclic prefix is a regular cyclic prefix in an LTE system, and the locations of the dedicated reference signals in the physical resource block are as shown in FIG. 3a; 3b is a schematic diagram of the location of the cell-specific reference signal in the physical resource block when the cyclic prefix is the extended cyclic prefix in the LTE system, and the location of the dedicated reference signal in the physical resource block is as shown in FIG. 3b. In 3a and 3b, the abscissa represents the time domain and the ordinate represents the frequency domain. In addition, there is a user-specific reference signal (UE-specific reference signals), which is transmitted only in the time-frequency domain location where the user-specific Physical downlink shared channel (PDSCH) is located. The cell-specific reference signal function includes downlink channel quality measurement and downlink channel estimation (demodulation).

LTE-Advanced, Further Advancements for E-UTRA is an evolved version of LTE Release-8. In addition to meeting or exceeding 3GPP TR 25.913: "Requirements for In addition to all relevant requirements of Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN), it also meets or exceeds the requirements of IMT-Advanced proposed by ITU-R. Among them, the requirements for backward compatibility with LTE Release-8 Means: LTE Release-8 terminals can work in LTE-Advanced networks; LTE-Advanced terminals can work in LTE Release-8 networks.

In addition, LTE-Advanced should be able to operate in different spectrum configurations, including a wider spectrum configuration than LTE Release-8 (eg 100 MHz continuous spectrum resources) to achieve higher performance and target peak rates. Since the LTE-Advanced network needs to be able to access LTE users, its operating band needs to cover the current LTE band, and there is no available 100 MHz of spectrum bandwidth that can be allocated in this band. Therefore, a direct technology that LTE-Advanced needs to solve is to aggregate several consecutive component carrier carriers (spectrals) distributed in different frequency bands to form a 100MHz bandwidth that LTE-Advanced can use. That is, for the aggregated spectrum, it is divided into n component carrier frequencies, and the spectrum in each component carrier frequency is continuous.

LTE-Advanced downlink can support up to 8 antenna applications; and LTE-Advanced is used as an 8-antenna application and CoMP, Coordinated multiple point transmission and reception, and Beamforming technologies. The basic design framework of the LTE-Advanced downlink reference signal (Way forward) defines the downlink reference signal for LTE-Advanced operation as two types of reference signals: reference signal for PDSCH demodulation and channel-oriented status information (CSI, Channel) Status Information ) The generated reference signal.

The CoMP technology is essentially an extension of the multi-antenna technology. The base stations of multiple cells cooperate to transmit data to the target user terminal (UE). Therefore, the target UE needs to know the location of the CSI reference signal (CSI-RS) sent by multiple cells, so that The UE can measure channel state information of multiple cells and report it to the base station, so that the base station can be used for data transmission, thereby implementing CoMP technology. Currently, there is no solution for determining the CSI-RS locations of multiple cells. Summary of the invention

In view of this, the main object of the present invention is to provide a method and apparatus for determining the location of a cell reference signal, which can ensure the application of CoMP technology and improve the overall performance goal of the system.

In order to achieve the above object, the technical solution of the present invention is achieved as follows:

A method of determining a location of a cell reference signal, the method comprising:

Determining the location of the reference signal CSI-RS of the channel state information of the cell, the user equipment UE measures the channel state information of the plurality of cells according to the location of the CSI-RS and reports it to the base station.

The cell is a coordinated cell; the location of the reference signal CSI-RS that determines the channel state information of the cell includes:

Selecting a location for transmitting each coordinated cell CSI-RS from a location of a reference signal CSI-RS that can be used to transmit channel state information of a different cell;

The location of each coordinated cell CSI-RS is determined according to the identity of each coordinated cell.

The location sequence number of the CSI-RS that can be used to transmit the different cells is HL, k _n , and the location for selecting the CSI-RS of each coordinated cell includes:

The m positions of the m cells of the CSI-RS are transmitted as H ^L , ^k ; the _m locations are consecutive;

Where m is the number of coordinated cells or the multiplexing factor of the coordinated cell CSI-RS, where h is a fixed value or is preset.

When the h is a fixed value, it takes a value of 0, or (n-m);

Where n represents the number of locations that can currently be used to transmit CSI-RSs of different cells.

When the h is preset, the value of the h is notified to the target UE by the base station. The location selected for transmitting the coordinated CSI-RS includes:

Numbering a combination of m positions for all n positions, the arbitrary m positions uniquely corresponding to a number index r, and each number index r uniquely corresponds to m positions; The base station selects a number index to send to the target UE according to the location of the m CSI-RSs; the target UE obtains m location information according to the received number index r and the correspondence between the number index r and the location;

Where n represents the number of locations currently available for transmitting CSI-RSs of different cells; m represents the number of coordinated cells.

The position sequence numbers of the CSI-RSs currently available for transmitting different cells are HL, k _n , and the selected m positions are, ^L , , where 1 ≤ ≤ ", <₊₁;

= I - -1丄

Numbered index

) , where the expansion of the binomial coefficient

A number indicating a combination of y values of X different values _χ a number index r of m positions of the m cell CSI-RSs is transmitted by the base station to the target UE by signaling.

The m locations of the m cells CSI-RS are transmitted by m signaling, and each signaling represents a CSI-RS location of one cell.

Determining the location of the CSI-RS of each coordinated cell includes: determining a location of the CSI-RS of the cell according to the order of the m cell identifiers sent by the base station;

Or, sorting the m cells according to the size of the cell identifier, and determining the location of the cell CSI-RS according to the sorted position.

Determining the location of the CSI-RS of the cell according to the order of the m cell identifiers sent by the base station includes:

When the order in which the cell ID is sent in the m cell identifiers is g, the corresponding cell

The position of the CSI-RS is the gth position among the m positions.

The m cells are sorted according to the size of the cell identifier, and determining the location of the CSI-RS according to the sorted location includes: When the location of the certain cell ID in the sorting is g, the location of the CSI-RS corresponding to the cell is the gth location of the m locations.

Determining, the location of each coordinated cell CSI-RS is

Wherein C - ID is a cell identifier, m represents a number of coordinated cells or a multiplexing factor of a coordinated cell CSI-RS; mod is a remainder operator;

X is a fixed value, or the value of X is signaled by the base station to the target UE.

The method further includes: the base station transmitting, according to the CSI-RS locations of the coordinated cells, the identifiers of the coordinated cells in a corresponding order.

An apparatus for determining a location of a cell reference signal, comprising: a selecting module and a determining module, wherein: a selecting module, configured to select, from a location of a CSI-RS that can be used to transmit a different cell, a CSI-RS for transmitting each coordinated cell Location

And a determining module, configured to determine a location of each coordinated cell CSI-RS according to an identifier of each coordinated cell.

For each cell in the cell, all CSI-RSs in the cell are located on one or two orthogonal frequency division multiplexing OFDM symbols in one subframe;

The cell is a single cell or a coordinated cell.

When the subframe adopts a regular cyclic prefix, the OFDM symbol is one or two OFDM symbols of a second, third, fourth OFDM symbol of a second slot in a subframe; When the subframe adopts an extended cyclic prefix, the OFDM symbol is one or two OFDM symbols in the second and third OFDM symbols of the second slot in the subframe.

When the CSI-RS and the reference signal of the antenna port #5 are sent on the same physical subcarrier, only the CSI-RS is sent;

When the CSI-RS is transmitted on the same physical subcarrier as the data carried by the physical shared channel sent to the R8 version terminal, only the CSI-RS is sent;

The physical shared channel transmitted to the terminal above the R8 version is not in the subcarrier where the CSI-RS is located. Map on.

It can be seen from the foregoing technical solution provided by the present invention that the location of the CSI-RS of the cell is determined, and the UE measures the channel state information of the multiple cells according to the location of the CSI-RS and reports the information to the base station. When the cell is a coordinated cell, the location for transmitting the CSI-RS of each coordinated cell is selected from the locations of the CSI-RSs that can be used to transmit the different cells; and the CSI-RS of each coordinated cell is determined according to the identifier of each coordinated cell. position. With the method of the present invention, the target UE clarifies the location of the CSI reference signal sent by multiple cells, so that the UE measures the channel state information of multiple cells and reports it to the base station, so that the base station can be used for data transmission, thereby ensuring CoMP. The application of technology has reached the goal of improving the overall performance of the system. DRAWINGS

FIG. 1 is a schematic diagram of a frame structure of an FDD mode and a TDD mode of an LTE system;

2 is a schematic structural diagram of a physical resource block when a system bandwidth of the LTE system is 5 MHz; FIG. 3a is a schematic diagram of a location of a cell public reference signal in a physical resource block when a cyclic prefix is a regular cyclic prefix in an LTE system;

FIG. 3b is a schematic diagram of a location of a cell public reference signal in a physical resource block when a cyclic prefix is an extended cyclic prefix in an LTE system; FIG.

4 is a flowchart of a method for determining a location of a reference signal of a coordinated cell according to the present invention;

FIG. 5 is a schematic structural diagram of a device for determining a location of a reference signal of a coordinated cell according to the present invention. DETAILED DESCRIPTION OF THE INVENTION The location of a reference signal (CSI-RS) of channel state information of a cell is determined, and the UE measures a plurality of cell channel state information according to the location of the CSI-RS and uplinks it to the base station. The cell is a coordinated cell, and may be a coordinated cell including a primary cell and a primary cell, or may be a coordinated cell that does not include a primary cell but only a primary cell.

4 is a flowchart of a method for determining a location of a reference signal of a coordinated cell according to the present invention, as shown in FIG. Show, including:

Step 400: Select a location for transmitting each coordinated cell CSI-RS from a location that can be used as a CSI-RS for transmitting different cells.

It is assumed that the location order numbers of the CSI-RSs currently available for transmitting different cells are kl, k2, ···, kn, and the cell IDs associated with the CoMP set are ID1, ID2, ···, IDm, where m, n Is an integer. m represents the number of coordinated cells or the multiplexing factor of the coordinated cell CSI-RS. In this step, the location for selecting the CSI-RS of each coordinated cell is specifically as follows: One implementation method is: transmitting m locations of the C cells of the m cells as ' ^L , d, and the m locations are consecutive m Location. Wherein, h is a fixed value, such as 0 or (nm), etc.; or, h is preset, and the value is notified by the base station to the target UE by signaling.

Another implementation method is: numbering a combination of m locations for all n locations, ensuring that any m locations are uniquely corresponding to a number index, and the base station selects a number index according to the location of the m cells CSI-RS. Sending to the target UE; the target UE obtains m pieces of position information according to the received number index and the correspondence between the number index and the position. Assume that the selected m positions are , , ^L , , 1 ≤ ≤ ", < ₊₁ , then, the number index r is as shown in equation (1):

r = 0, L

Thus, the numbered index m , where the extended binomial coefficient is defined as a formula

(2) shown:

A combination number G representing y values among X different values The number index of m positions of the m cell CSI-RSs transmitted by the base station is signaled to the UE by the base station. m positions of m cells CSI-RS are transmitted by m signaling, and each signaling represents one The CSI-RS location of the cell.

Step 401: Determine, according to the identifier of each coordinated cell, the location of each coordinated cell CSI-RS. There are two ways to implement this step:

The first method determines the location of the cell CSI-RS according to the order of the m cell identifiers sent by the base station, that is, the order of the m cell identifiers received by the UE. For example, the order in which the cell IDi is transmitted in the m cell identifiers is g, and the location of the corresponding CSI-RS is the gth position in the m locations.

The base station (eNB) needs to send m cell identifiers according to the CSI-RS locations of the m cells according to the corresponding order;

In the second method, the m cells are sorted according to the size of the cell identifier, and the location of the cell CSI-RS is determined according to the sorted position. For example, the location of the cell IDi in the above sorting is g, and then the location of the corresponding CSI-RS is the gth position among the m locations.

In addition to the method illustrated in FIG. 3, the present invention also provides a method of determining a cell reference signal. First, from among the locations that can be used to transmit CSI-RSs of different cells, the location for transmitting each of the cooperative cell CSI-RSs is selected.

Then, 位置, the current location of the CSI-RS that can be used to transmit different cells is kl, k2, ··., kn, and the cell IDs associated with the CoMP set are IDI, ID2, ··. , IDm, where m, n It is an integer; the cell identifier is ^CeZZ - ⁾ , and its corresponding CSI-RS position is - ° , where mod is the remainder operator; X is a fixed value, such as 0; or, the value of X is passed by the base station. Let the target UE be notified.

All CSI-RSs of a cell are located on one or two OFDM symbols in one subframe. Here, a cell refers to a single cell or a coordinated cell.

When the subframe adopts a regular cyclic prefix, the OFDM symbol is one or two OFDM symbols of the second, third, and fourth OFDM symbols of the second slot in the subframe;

When the subframe adopts an extended cyclic prefix, the OFDM symbol is the second time slot in the subframe. One or two OFDM symbols in the second, third OFDM symbol.

When the CSI-RS and the reference signal of the antenna port #5 are transmitted on the same physical subcarrier, only the CSI-RS is transmitted, and the reference signal of the antenna port #5 is not transmitted, that is, the antenna on the subcarrier is dropped. Reference signal for port #5.

When the data carried by the physical shared channel of the R8 version terminal is transmitted on the same physical subcarrier as the CSI-RS, only the CSI-RS is sent, and the data carried by the physical shared channel is not transmitted;

The physical shared channel transmitted to the terminal above the R8 version is not mapped on the subcarrier where the CSI-RS is located.

Through the method of the invention, the location of the cell reference signal is clarified, thereby ensuring the application of the CoMP technology and achieving the goal of improving the overall performance of the system.

For the method of the present invention, a device for determining a location of a cell reference signal is provided. FIG. 5 is a schematic structural diagram of a device for determining a reference signal of a coordinated cell according to the present invention. As shown in FIG. 5, the method includes a selection module and a determining module, where

And a selection module, configured to select a location for transmitting each coordinated cell CSI-RS from a location that can be used to transmit CSI-RSs of different cells.

The method of the present invention will be described below by way of examples.

In the first embodiment, the CSI-RS locations currently available for transmitting different cells are k1, k2, ···, kn, and the cell identifiers associated with the CoMP set are ID1, ID2, ···, IDm, (m <n, and, ID1<ID2< -.. <IDm), then, the CSI-RS position of the cell IDi is k (h+i), where

1 < i < m, h, m, n is an integer.

That is to say, all CoMP centralized cells are sorted according to the size of the cell identifier, and then mapped to the corresponding available CSI-RS locations in the sorted order. Wherein, h is a fixed value, such as 0 or nm, etc.; or, the value of h is notified to the target UE by the base station by signaling.

In the second embodiment, it is assumed that the cell identifiers associated with the CoMP set are ID1, ID2, . . . , IDm, and the CSI-RS locations currently available for transmitting different cells are kl, k2, ··· ·, kn, then, the CSI-RS position of the cell IDi is k (h+i), where Ki < m, h, m, n are integers.

Where, h is a fixed value, such as 0 or n-m, etc.; or, the value of h is notified by the base station to the target UE through a signaling.

The base station (eNB) needs to transmit m cell identifiers according to the CSI-RS locations of the m cells in the corresponding order. In the third embodiment, the extended binomial coefficient is defined as. Hypothesis, selected

m positions are, fc , L , , l<s _k <n, s _k <s _k+1 , then, number index r = Z

Π

r = 0, L 1

The number index m is decoded as follows:

The input parameter is r, and the output parameter after decoding is k _Si , L , k _Sm ; Step 1: Set ^n ^{= 1} ; k=0; Step 2:

Step 3: Determine if p ^>r is true, if it is established, = +ι,

Return to the third step; if not, perform the fourth step; Step 4: Set ^=JC , ^=^ ⁺¹ , r = rp . Step 5: Determine whether k is equal to m-1, if it is established, output, ,L , , knot Beam decoding process; if not, set k = k + l, return to the second step.

First, the combination of m positions is selected for all n positions to ensure that any m positions are uniquely corresponding to a number index r. According to the positions of the m cells CSI-RS, the base station selects a number index r to send to the target UE. The target UE obtains m pieces of position information according to the received number index r and the correspondence between the number index r and the position.

Then, the UE determines the location of the cell CSI-RS according to the order of the received m cell identifiers. That is, if the cell IDi is transmitted in the order of m cell identifiers, then the location of the corresponding CSI-RS is the g-th position of the m locations.

Or,

Sorting the m cells according to the size of the cell identifier, and determining the location of the cell CSI-RS according to the sorted position; that is, the location of the cell IDi in the above sorting is g, then the location of the corresponding CSI-RS is The gth position of the m positions.

In the fourth embodiment, it is assumed that the cell identifiers associated with the CoMP set are IDI, ID2, ··., IDm, and the CSI-RS locations currently available for transmitting different cells are kl, k2, ··., kn, then, the cell IDi The CSI-RS position is _{i+; c} ) _m . _Dm ) (Ki<m), x, m, n are integers. Where x is a fixed value, such as 0 or nm, etc.; or, the value of X is signaled by the base station.

The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included. Within the scope of protection of the present invention.

Claims

Claim

A method for determining a location of a cell reference signal, the method comprising: determining a location of a reference signal CSI-RS of channel state information of a cell, and measuring, by the user equipment UE, a plurality of cell channel states according to a location of the CSI-RS The information is reported to the base station.

The method according to claim 1, wherein the cell is a coordinated cell, and the location of the reference signal CSI-RS for determining channel state information of the cell includes:

The method according to claim 2, wherein the location sequence number of the CSI-RS currently available for transmitting different cells is HL, k _n , and the selection is used to transmit each coordinated cell CSI-RS. The location includes:

The m positions of the M cells transmitting the CSI-RS are ^L , ^k ^; the _m positions are consecutive;

The method according to claim 3, wherein when the h is a fixed value, the value is 0, or (n-m);

The method according to claim 3, wherein when the h is preset, the value of the h is notified by the base station to the target UE.

The method according to claim 2, wherein the selecting, for transmitting, the location of each cooperative cell CSI-RS includes:

The method according to claim 6, wherein the position sequence number of the CSI-RS currently available for transmitting different cells is HL, and the selected m positions are k _Sl , k _Si , L , k _Sm , where l ≤ ≤ w, <_+1;

n

/" = 0,L ,| I - -1丄

, ^m J , where the expansion binomial coefficient

definition:

x < y represents the number of combinations of y values from x different values

The method according to claim 6, wherein the number index r of the m locations of the m cells of the CSI-RS is transmitted by the base station to the target UE by signaling.

The method according to claim 2, wherein the m locations of the m cells of the CSI-RS are transmitted by m signaling, and each signaling represents a CSI-RS location of one cell.

The method according to claim 2, wherein determining a location of each coordinated cell CSI-RS comprises: determining a location of a cell CSI-RS according to an order of m cell identifiers sent by the base station;

The method according to claim 10, wherein the determining the location of the CSI-RS of the cell according to the sequence of the m cell identifiers sent by the base station includes:

When the order in which the cell IDs are transmitted in the m cell identifiers is g, the location of the CSI-RS corresponding to the cell is the g-th position in the m locations.

The method according to claim 10, wherein the m cells are sorted according to the size of the cell identifier, and determining the location of the CSI-RS according to the sorted location specifically includes: when the cell ID is When the position in the sorting is g, the position of the CSI-RS corresponding to the cell is the gth position among the m positions.

13. The method according to claim 2, wherein the determining each coordinated cell

The location of the CSI-RS is ^„— _m . , where C / _ / ) is the cell identity, m represents the number of coordinated cells or the multiplexing factor of the coordinated cell CSI-RS; mod is the remainder operator;

The method according to claim 2, wherein the method further comprises: the base station transmitting, according to the CSI-RS location of each coordinated cell, the target of each coordinated cell according to the corresponding order.

A device for determining a location of a reference signal of a cell, comprising: a selecting module and a determining module, wherein

a selecting module, configured to select a location for transmitting each coordinated cell CSI-RS from a location that can be used as a CSI-RS for transmitting different cells;

16. The apparatus according to claim 15, wherein, for each cell in the cell, all CSI-RSs in the cell are located in one or two orthogonal frequency division multiplexing OFDM in one subframe. Symbolic

The cell is a single cell or a coordinated cell.

The apparatus according to claim 16, wherein when the subframe adopts a regular cyclic prefix, the OFDM symbol is the second, third, fourth of the second slot in the subframe. One or two OFDM symbols in one OFDM symbol;

When the subframe adopts an extended cyclic prefix, when the OFDM symbol is the second one of the subframes One or two OFDM symbols in the second, third OFDM symbol of the slot.

18. Apparatus according to claim 16 wherein:

When the CSI-RS and the reference signal of the antenna port #5 are transmitted on the same physical subcarrier, only the CSI-RS is transmitted.

19. Apparatus according to claim 16 wherein: