WO2013042982A1

WO2013042982A1 - Method and apparatus for transmitting and receiving reference signal

Info

Publication number: WO2013042982A1
Application number: PCT/KR2012/007587
Authority: WO
Inventors: Jian Jun Li; Kyoung Min Park
Original assignee: Pantech Co., Ltd.
Priority date: 2011-09-23
Filing date: 2012-09-21
Publication date: 2013-03-28
Also published as: KR20130032707A

Abstract

The present invention relates to a method and apparatus of transmitting and receiving an uplink reference signal, such as an SRS (Sounding Reference Signal). A reference signal transmitting method according to the present invention includes the steps of receiving an SRS (Sounding Reference Signal) request over a downlink control channel and transmitting SRS according to the SRS request, wherein antenna ports that perform uplink transmission are divided into a first group and a second group. The SRSs may be transmitted through antenna ports included in one of the first group and the second group. According to the present invention, transmission resources may be effectively used, and interference that may occur between different user equipment devices may be reduced.

Description

METHOD AND APPARATUS FOR TRANSMITTING AND RECEIVING REFERENCE SIGNAL

The present invention concerns wireless communication systems using multi-antennas, and more specifically to methods and apparatuses of transmitting and receiving reference signals in uplink multi-antenna systems using a plurality of antenna ports.

High-speed transmission of high-capacity data is recently achieved by using a multi-antenna system to raise data transmission efficiency.

For this purpose, in the 3GPP-based, next generation communication systems, technologies of supporting 4 Tx as the uplink and 8 Tx as the downlink, which uses 8 antenna ports, are in discussion. The uplink peak rate is enhanced by spatial multiplexing using four layers through the uplink, 4 Tx.

Besides the multi-antennas, scenarios for guaranteeing high mobility together with enhanced channel quality and wireless backhaul are also the issues of the talk. Channel-independent multi-antenna systems may be useful in such cases.

Meanwhile, user equipment transmits a reference signal, e.g., sounding reference signal, to the base station so that the base station can grasp the state of the uplink channel. In the multi-antenna system, the base station may determine the channel state of each antenna port on the uplink from the user equipment through the sounding reference signal transmitted per antenna port.

Considering this communication environment, there is a need for a method of more efficiently transmitting the reference signal.

An object of the present invention is to provide an apparatus and method of transmitting an uplink reference signal in a multi-antenna system.

An object of the present invention is to provide an apparatus and method of dividing antenna ports that transmit an uplink reference signal into predetermined groups and transmitting the reference signal in each group in a multi-antenna system.

An object of the present invention is to provide an apparatus and method of transmitting a downlink control signal for dividing antenna ports that transmit an uplink reference signal into predetermined groups and using the groups in a multi-antenna system.

An object of the present invention is to provide an apparatus and method of configuring a parameter set regarding transmitting a reference signal for dividing antenna ports that transmit an uplink reference signal into predetermined groups and using the groups in a multi-antenna system.

(1) An aspect of the present invention relates to a reference signal receiving method comprising the steps of transmitting an SRS (Sounding Reference Signal) request over a downlink control channel and receiving SRSs transmitted according to the SRS request, wherein antenna ports that perform uplink transmission are divided into a first group and a second group, and wherein the SRSs may be transmitted through antenna ports included in one of the first group and the second group.

(2) In (1), in the step of receiving the SRS, first SRS transmission performed through the first group of antenna ports may be received, and in a predetermined time determined by an upper layer, second SRS transmission performed through the second group of antenna ports may be received.

(3) In (1), the SRS request may indicate one of the first group and the second group, wherein the SRSs may be transmitted using antenna ports of the group indicated by the SRS request.

(4) In (1), the SRS request may indicate a parameter set for SRS transmission, and the SRSs may be transmitted using antenna ports configured in the parameter set.

(5) In (4), the antenna ports configured in the parameter set may be included in one of the first group and the second group.

(6) Another aspect of the present invention relates to a reference signal transmitting method comprising the steps of receiving an SRS (Sounding Reference Signal) request over a downlink control channel and transmitting SRS according to the SRS request, wherein antenna ports that perform uplink transmission may be divided into a first group and a second group, and wherein the SRSs may be transmitted through antenna ports included in one of the first group and the second group.

(7) In (6), the number of antenna ports that perform the uplink transmission may be N, and the first group and the second group respectively may include N/2 antenna ports and N/2 antenna ports, wherein the antenna ports included in the first group are different from the antenna ports included in the second group.

(8) In (6), in the step of transmitting the SRSs, first SRS transmission may be performed using the first group of antenna ports, and in a predetermined time, second SRS transmission may be performed using the second group of antenna ports.

(9) In (8), the predetermined time may be determined by an upper layer of a base station and transmitted through upper layer signaling.

(10) In (6), the SRS request may indicate one of the first group and the second group, and in the step of transmitting the SRSs, the SRSs may be transmitted using antenna ports included in the group indicated by the SRS request.

(11) In (10), the SRS request may indicate a parameter set for SRS transmission, and in the step of transmitting the SRSs, the SRSs may be transmitted using antenna ports configured in the parameter set.

(12) In (11), the antenna ports configured in the parameter set may be included in one of the first group and the second group.

(13) A still another aspect of the present invention relates to a reference signal receiving apparatus comprising an RF unit transmitting an SRS request over a downlink control channel and receiving SRSs transmitted according to the SRS request and a processor configuring a parameter set necessary for SRS transmission and estimating a state of an antenna port channel over which an SRS is transmitted based on the received SRSs, wherein antenna ports used for uplink transmission may be divided into a first antenna port group and a second antenna port group, and wherein the processor may enable the SRSs to be transmitted through an antenna port in one antenna port group at a time through the SRS request or a configuration of the parameter set.

(14) A yet still another aspect of the present invention relates to a reference signal transmitting apparatus comprising an RF unit including a plurality of antenna ports divided into a first antenna port group and a second antenna port group, a memory storing information of a parameter set necessary for SRS transmission, and a processor configuring an SRS based on the SRS request and the parameter set, wherein the processor may transmit SRSs using antenna ports in one antenna port group at a time.

(15) In (14), the processor may perform first SRS transmission using antenna ports in the first antenna port group according to the SRS request, and in a predetermined time, may perform second SRS transmission using antenna ports in the second antenna port group.

(16) In (14), the processor may transmit SRSs using antenna ports in an antenna port group indicated by the SRS request or using antenna ports in an antenna port group configured in a parameter set indicated by the SRS request.

According to the present invention, antenna ports for transmitting an uplink reference signal in the multi-antenna system may be effectively operated.

According to the present invention, antenna ports for transmitting an uplink reference signal in the multi-antenna system may be divided into predetermined groups, and the reference signal may be transmitted per group, so that transmission resources used for transmitting the reference signal may be effectively distributed and used.

According to the present invention, interference between user equipment devices that transmit uplink reference signals in the multi-antenna system may be greatly reduced.

According to the present invention, although antenna ports of transmitting an uplink reference signal are used while divided into predetermined groups in the multi-antenna system, overhead while transferring information necessary for signal transmission may be prevented from increasing.

Fig. 1 schematically illustrates a structure of a radio frame.

Fig. 2 schematically illustrates an exemplary structure of an uplink subframe that transmits SRS.

Fig. 3 is a concept view schematically illustrating hopping of antenna port group when aperiodic SRS is subject to multi-transmission in a system according to the present invention.

Fig. 4 is a flowchart schematically illustrating the operation of eNB when multi-transmission of SRS is performed with transmission antenna ports divided into two groups in a system according to the present invention.

Fig. 5 is a flowchart schematically illustrating the operation of UE when multi-transmission of SRS is performed with transmission antenna ports divided into two groups in a system according to the present invention.

Fig. 6 is a flowchart schematically illustrating the operation of eNB when all the antenna ports are divided into two groups, one of which is used to perform single transmission of SRS in a system according to the present invention.

Fig. 7 is a flowchart schematically illustrating the operation of UE when all the antenna ports are divided into two groups, one of which is used to perform single transmission of SRS in a system according to the present invention.

Fig. 8 is a flowchart schematically illustrating the operation of eNB in an example of newly defining an SRS parameter set and performing single transmission using one antenna port group in a system according to the present invention.

Fig. 9 is a flowchart schematically illustrating the operation of UE in an example of newly defining an SRS parameter set and performing single transmission using one antenna port group in a system according to the present invention.

Fig. 10 schematically illustrates the configuration of UE according to the present invention.

Fig. 11 schematically illustrates the configuration of eNB according to the present invention.

Hereinafter, some embodiments will be described in greater detail with reference to the accompanying drawings. The same denotations are used to denote the same elements throughout the drawings. When determined to make the gist of the invention unclear, the specific description on the known configurations or functions will be omitted.

Hereinafter, a wireless communication network is described. Tasks may be done in the wireless communication network when the network is controlled by a system (e.g., base station) that is in charge of the wireless communication network or when data transmission is in progress. Or, such tasks may also be done by user equipment in the wireless network.

User equipment (hereinafter, “UE”) may be stationary or mobile and may be referred to by other names, such as MS (Mobile Station), MT(Mobile Terminal), UT(User Terminal), SS(Subscriber Station), wireless device, PDA(Personal Digital Assistant), wireless modem, or handheld device.

Base station generally refers to a station that communicates with UE, and may be also called by other names, such as eNB (evolved-NodeB), BTS (Base Transceiver System), or access point. Hereinafter, for convenience of description, the base station is referred to as ‘eNB’.

Each eNB provides a communication service in a specific geographical area (generally referred to as “cell”). The cell may be divided into a plurality of regions (referred to as “sectors”). A plurality of transmission terminals may constitute one cell.

Fig. 1 schematically illustrates a structure of a radio frame. The radio frame includes 20 (#0 to #19) slots. One subframe consists of two slots. Time (length) taken to transmit one subframe is referred to as TTI (transmission time interval). Referring to Fig. 1, for example, the length of one subframe may be 1ms, and the length of one slot may be 0.5ms.

One slot may include a plurality of symbols in the time domain. For example, in case of downlink (DL) using OFDMA (Orthogonal Frequency Division Multiple Access), the symbol may be OFDM symbol, and in case of uplink (UL) using SC (Single Carrier)-FDMA (Frequency Division Multiple Access), the symbol may be SC-FDMA symbol. Hereinafter, for convenience of description, OFDM symbol is referred to as symbol in the downlink (in the time domain), and SC-FDMA symbol is referred to as symbol in the uplink (in the time domain).

The number of symbols included in one slot may vary depending on the length of CP (Cyclic Prefix). For example, in case of normal CP, one slot may include 7 OFDM symbols, and in case of extended CP, one slot may include 6 OFDM symbols.

The downlink subframe may be divided into a control region and a data region in the time domain. The control region may include up to four first symbols in the first slot in the subframe. The number of symbols included in the control region may change. The control region is assigned with a control channel, such as PDCCH, and the data region is assigned with a data transmission channel, such as PDSCH.

Control information transmitted through PDCCH is referred to as downlink control information (DCI). DCI may include information on resource allocation of PDSCH (which is referred to as DL (downlink) grant), resource allocation of PUSCH (which is referred to as UL (uplink) grant), a set of transmission power control commands for individual UEs in any UE group, and/or activation of VoIP (Voice over Internet Protocol).

Meanwhile, DCI may have different uses depending on its format and may have different fields that are defined therein. Table 1 schematically shows examples of DCI formats.

Table 1

DCI format	Description
0	used for scheduling of PUSCH in one uplink cell
1	used for scheduling of one PDSCH codeword in one cell
1A	used for random access procedure initiated by PDCCH order and for scheduling of one PDSCH in one cell
1B	used for compact scheduling of one PDSCH codeword in one cell together with precoding information
1C	used to transmitting very compact scheduling information of one PDSCH codeword or for notifying change in MCCH (Multicast Control Channel)
1D	used for compact scheduling of one PDSCH codeword in one cell together with precoding information
2	used for resource assignment for PDSCH for closed-loop MIMO operation
2A	used for resource assignment for PDSCH for open-loop MIMO (Multi-Input Multi-Output) operation
2B	support transmission mode 8
2C	support transmission mode 9
3	used for transmitting TPC command for PUCCH and PUSCH with 2 bit power adjustment
3A	used for transmitting TPC (Transmission Power Control) command for PUSCH and PUCCH with one bit power adjustment
4	used for scheduling of PUSCH in one uplink cell in multi-antenna port transmission mode

Among the DCI formats, DCI formats 0, 1A, 2B, 2C, and 4 may include an SRS (Sounding Reference Signal) request.

SRS is one of uplink reference signals. In the wireless communication system, uplink channel or downlink channel needs to be estimated for data transmission/reception, obtaining system synchronization, or channel information feedback. For channel estimation or channel state measurement, a reference signal (RS) known to the transmitter and receiver may be used.

Because of being aware of information on the reference signal, the receiver (e.g., eNB) may precisely obtain data transmitted from the transmitter (e.g., UE) by estimating the channel based on the received reference signal and by compensating for the channel value.

The reference signal may be generally configured as a sequence. The reference signal sequence may use any sequence without any limitation. The reference signal sequence may use PSK(Phase Shift Keying)-based computer generated sequence, CAZAC (Constant Amplitude Zero Auto-Correlation) sequence, such as ZC (Zadoff-Chu)-based sequence or ZC sequence with cyclic extension, PN (Pseudo-random) sequence, such as gold sequence, or cyclically shifted sequence.

Among the reference signals, the sounding reference signal (hereinafter, “SRS”), as an uplink reference signal, is a reference signal transmitted through the uplink so that eNB may estimate quality of the uplink channel. If UE transmits SRS signal on the uplink channel, eNB grasps channel state based on the SRS and then performs scheduling for uplink transmission.

Meanwhile the reference signal may be configured as a sequence, and SRS may be also generated by UE as ZC-based sequence. The SRS sequence

may be defined with cyclic shift (phase shift) α and base sequence

as in Equation 1:

MathFigure 1

In Equation 1,

refers to the length of the reference sequence, u a sequence group number, and v a base sequence number.

Referring to Fig. 2, the uplink subframe includes two slots on a time axis, and each slot includes 7 SC-FDMA (Single Carrier-Frequency Division Multiple Access) symbols. The uplink subframe includes PUCCH (Physical Uplink Control Channel) and PUSCH (Physical Uplink Shared Channel).

In the SC-FDMA symbol section during which SRS is transmitted, UE transmits data using 13 SC-FDMA symbols and performs pre-treatment, such as rate matching, on the last one SC-FDMA symbol, thereby transmitting SRS. Although the 14th SC-FDMA symbol transmits SRS, this is merely an example, and positions or number of SF-FDMA symbols may readily vary. The SRS may be transmitted on the whole or part of PUSCH.

As methods of transmitting SRS, there are periodic SRS that periodically transmits SRS and aperiodic SRS that aperiodically transmits SRS. Compared with when SRS is periodically transmitted, when SRS is aperiodically transmitted, transmission resources may be efficiently used, and UE may transmit SRS when eNB requests. In case of aperiodic SRS, UE may receive a request from eNB, and a predetermined time after aperiodic SRS is triggered, may transmit SRS. For example, it may be set that SRS is transmitted at the first transmission chance, four subframes after aperiodic SRS is triggered. Further, in case of aperiodic SRS, eNB may inform UE of time to transmit SRS and information on transmission resource together with the transmission request.

UE may transmit SRS over SRS resource per serving cell. SRS may have two triggering types as follows:

In triggering type 0, SRS is triggered by upper layer signaling. For example, in case of periodic SRS, triggering may be done by the first triggering type.

In triggering type 1, SRS is triggered through DCI. For example, in case that DCI formats 0/4/1A are FDD (Frequency Division Duplex) and TDD (Time Division Duplex), they may be used for triggering aperiodic SRS, and in case that DCI formats 2B/2C are TDD, they may be used for triggering aperiodic SRS.

Meanwhile, SRS parameter information necessary for UE to transmit SRS may be transferred from eNB to UE through RRC message. UE transmits SRS according to the SRS parameter received from eNB. For example, UE may generate SRS sequence based on SRS sequence information included in the SRS parameter.

The SRS parameters may represent information on subframe through which SRS is transmitted, SRS bandwidth, position where SRS transmission begins, subcarrier to transmit SRS, CS (Cyclic Shift) applying to SRS, transmission period and offset of SRS, whether to be periodic transmission or one-time transmission, sequence to generate SRS, and frequency hopping of SRS transmission.

UE may be configured with SRS parameter for triggering type 0 and SRS parameter for triggering type 1 per serving cell. Further, in the two cases, triggering type 0 and triggering type 1, SRS transmission may occur in the same subframe, in which case it may be set that SRS of triggering type 1 may be transmitted by UE.

In case that DCI format 4 is used in triggering type 1, two bits of SRS request field may be included in DCI format 4 when transmitted to UE. Three sets of SRS parameters which may be indicated by the two bits of SRS request field may be configured through upper layer signaling, such as RRC. The two bits of SRS request field may trigger SRS and may indicate the SRS parameter set that is to be used when SRS is triggered.

Table 2 schematically shows what is indicated by the SRS request field for triggering type 1, which is transmitted through DCI format 4.

Table 2

SRS request field value	Description
00	No type 1 SRS triggering
01	First SRS parameter set configured by upper layer
10	Second SRS parameter set configured by upper layer
11	Third SRS parameter set configured by upper layer

In Table 2, each SRS parameter set may be configured by upper layer, such as RRC.

Table 3 schematically shows an example of SRS parameter set.

Table 3

Referring to Table 3, srs-AntennaPortAp refers to the number of antenna ports to be used for aperiodic SRS transmission.

srs-BandwidthAp refers to bandwidth of aperiodic SRS, freqDomainPositionAp frequency position of aperiodic SRS, transmissionCombAp what subcarrier is to be used to transmit SRS when comb mode applies. cyclicShiftAp refers to a cyclic shift value that applies to SRS.

In case that in triggering type 1 DCI other than DCI format 4-for example, DCI formats 0/1A/2B/2C-are used, one bit of SRS request field is included in DCI when transmitted. In such case, a single SRS parameter set may be configured by upper layer signaling for each of DCI formats 0/1A/2B/2C. In case that the value of the one bit SRS request field is, e.g., 1, SRS may be triggered.

Meanwhile, the MIMO (Multi-Input Multi-Output) system also called “multi-antenna system” enhances transmit/receive data transmission efficiency by using a multi-transmit antenna and a multi-receive antenna.

MIMO technologies include transmit diversity, spatial multiplexing, and beamforming.

Transmit diversity is a technology that enhances transmission reliability by transmitting the same data through antennas that constitute the multi-transmit antenna. Spatial multiplexing transmits different data through a multi-transmit antenna at the same time so that high-speed data may be transmitted without increasing system bandwidth. Beamforming adds a weight to each of antennas constituting a multi-antenna according to the channel state to thereby increase signal SINR (Signal to Interference plus Noise Ratio). At this time, the weight may be represented as weight vector or weight matrix, which is referred to as precoding vector or precoding matrix, respectively.

Spatial multiplexing includes spatial multiplexing for a single user and spatial multiplexing for multiple users. The spatial multiplexing for a single user is referred to as SU-MIMO (Single User MIMO), and the spatial multiplexing for multiple users is referred to as SDMA (Spatial Division Multiple Access) or MU-MIMO (Multi User MIMO). The capacity of MIMO channel increases in proportion to the number of antennas.

In case that SRS signal is transmitted by using all the antenna ports in the MIMO system, SRS in which different CSs (Cyclic Shifts) apply for the antenna ports, respectively, should be transmitted. Accordingly, many resources are used once for SRS transmission, and difficulty ensues when a plurality of UEs transmit SRS.

The present invention provides a method of performing periodic SRS transmission, with N transmission (Tx) antenna ports divided into two groups. For example, eight transmission antenna ports are divided into two groups each consisting of four antenna ports, so that SRS may be transmitted through one group at a time.

As methods of doing so, with N transmission antenna ports divided into two groups, (1) a method of performing multi-transmission in response to one SRS request, and (2) while performing single transmission in response to one-time SRS request, ① a method of designating a transmission antenna port group to be used for SRS transmission using two bits of SRS request field to be transmitted in DCI format 4 and ② a method of designating a transmission antenna port group to be used for SRS transmission by newly defining an SRS parameter set.

Since SRSs are transmitted using one antenna port group at a time, for N antenna port channels all to be used to transmit the SRSs on the uplink, when SRSs are transmitted, hopping needs to be done between the antenna port groups. In case that rather than multi-transmission, single transmission is conducted, for N antenna port channels all to be used to transmit SRSs on the uplink, aperiodic SRS should be triggered at least two or more times. At this time, the antenna port group used for each SRS transmission is subjected to hopping to thereby use a different antenna port group so that all of the N antenna port channels may be used to transmit the SRSs.

Both the multi-transmission and single transmission perform transmission of a plurality of SRSs by using two antenna port groups, and thus, receiving the SRSs, eNB may estimate the channel states of all of the N antenna port channels.

Hereinafter, the method of using N transmission antenna ports with the antenna ports divided into two groups will be described in detail with reference to the drawings.

Aperiodic SRS is triggered by the SRS request included in DCI transmitted over the downlink control channel. UE receives the DCI and transmits SRS through each antenna port according to the SRS request, and eNB may estimate the uplink channel state through the received SRS.

At this time, rather than the SRSs being transmitted once through all of the N antenna ports, the antenna ports are divided into two groups, and the SRSs are transmitted per group, so that transmission resources may be efficiently used while simultaneously reducing interference that may occur between transmission sessions of different UEs.

In response to the SRS request, multi-transmission may be performed which transmits SRS at least once for each antenna port group, or in response to the SRS request, single transmission may be performed which transmits SRS once by using one of he antenna port groups.

First, the multi-transmission is described.

Fig. 3 is a concept view schematically illustrating hopping of antenna port group when aperiodic SRS is subject to multi-transmission in a system according to the present invention. If aperiodic SRS is triggered by the SRS request transmitted through DCI, UE performs first SRS transmission using a first antenna port group. At this time, the SRS transmission request may be transmitted through DCI format 4 and DCI formats 0/1A/2B/2C.

The first SRS transmission may be preset so that transmission is conducted a predetermined time after UE receives the SRS request. For example, four subframes after UE receives the SRS request, at the first transmission chance, transmission may be performed by using the last SC-FDMA symbol in the corresponding subframe.

At this time, the SRSs transmitted through the antenna ports in the antenna port groups may be constituted of different sequences to which different CSs (Cyclic Shifts) apply.

Since SRSs are transmitted in one antenna port group at a time, the antenna port group is subjected to hopping, thereby performing multi-transmission. Two subframes are used. In one subframe, SRSs are transmitted by using one antenna port group (first SRS transmission) and in the other subframe SRSs are transmitted by using another antenna port group (second SRS transmission), so that SRSs may be transmitted by using all of the antenna ports. Accordingly, the states of all the antenna port channels may be estimated through SRSs.

At this time, a predetermined time (Δt) after the first SRS transmission is performed, the second SRS transmission is performed by using the second antenna port group. At this time, Δt, which is a time interval between the first SRS transmission and the second SRS transmission, may be configured UE-specifically or cell-specifically through upper layer signaling, such as RRC message.

At this time, the first antenna port group used for the first SRS transmission consists of antenna ports #N0 to Nn, and the second antenna port group used for the second SRS transmission consists of #Nn+1 to NN-1. At this time, antenna port #Nn refers to nth antenna port among all N antenna ports.

How many antenna ports each antenna port group to be used by UE to transmit SRS consists of may be set through upper layer signaling, such as RRC message.

Multi-transmission of SRS may be configured so that SRS transmission is performed once for each of the first antenna port group and the second antenna port group, or so that SRS transmission may be performed more often by using each antenna port group at least once.

Fig. 4 is a flowchart schematically illustrating the operation of eNB when multi-transmission of SRS is performed with transmission antenna ports divided into two groups in a system according to the present invention. Fig. 5 is a flowchart schematically illustrating the operation of UE.

In Figs. 4 and 5, as an example, the number of antenna ports used for uplink transmission is N (N Tx), and the first antenna port group consists of antenna ports #N0 to #Nn (n is N/2-1), and the second antenna port group consists of antenna ports #Nm to #NN-1 (m is N+1).

Referring to Fig. 4, eNB configures SRS parameter set and transmits the SRS parameter set to UE (S410). The SRS parameter set is configured by the upper layer, such as RRC, and may be transmitted to UE through upper layer signaling, such as RRC message. While configuring the SRS parameter, eNB allows SRS transmission to be done with the antenna ports divided into two groups, such as the first antenna port group and the second antenna port group.

eNB transmits an SRS request to UE through DCI transmitted over PDCCH (S420). SRS of UE may be triggered by the SRS request included in DCI formats 0/1A/2B/2C/4.

eNB receives SRSs transmitted from UE (S430). At this time, SRSs transmitted from UE are transmitted at least twice by using each antenna port group as described above. The interval between SRS transmission sessions using the antenna port groups may be configured through upper layer signaling, such as RRC message.

Referring to Fig. 5 regarding the operation of UE, first, UE receives the SRS parameter set from eNB (S510). The SRS parameter set may be transmitted through the upper layer signaling, such as RRC message. The SRS parameter set may include information regarding the antenna port groups grouping all the antenna ports. For example, all the antenna ports may be configured into the first antenna port group and the second antenna port group.

UE receives the SRS request transmitted through DCI (S520). Aperiodic SRS multi-transmitting SRS is triggered by the received SRS request. The SRS request, as described above, may be transmitted over the PDDCH, included in DCI formats 0/1A/2B/2C/4.

UE performs the first SRS transmission among multi-transmission types for SRS (S530). UE transmits SRSs using the first antenna port group (antenna ports #N0 to #Nn). At this time, the SRSs are transmitted using the first antenna port group over the first aperiodic SRS transmission subframe.

UE performs the second SRS transmission among the multi-transmission types for SRS (S540). UE performs hopping on the antenna port group to be able to transmit the SRSs using the second antenna port group (antenna ports #Nm to #NN-1). At this time, the SRSs are transmitted using the second antenna port group over the second aperiodic SRS transmission subframe.

The time interval, Δt, between the first SRS transmission and the second SRS transmission may be configured by the upper layer signaling.

At this time, the number of times of multi-transmission and the number of times of use of each antenna port group may be also configured through upper layer signaling. However, it may be configured that SRS may be transmitted through all the antenna ports by using each antenna port group for SRS transmission at least once.

In case that the number of antenna ports used for uplink transmission is 8 (8 Tx), each antenna port group may include four antenna ports. For example, the first antenna port group may include antenna ports #80 to #83, and the second antenna port group may include antenna ports #84 to #87.

In case that the number of antenna ports used for uplink transmission is 4 (4 Tx), each antenna port group may include two antenna ports. For example, the first antenna port group may include antenna ports #40 and #41, and the second antenna port group may include antenna ports #42 and #43.

When SRS is triggered, UE may perform SRS transmission using the first antenna port group, and in a predetermined time, may perform SRS transmission using the second antenna port group.

Although aperiodic SRS transmission (triggering type 1) has been described herein, the present invention may also apply to periodic SRS transmission (triggering type 0).

In case of periodic SRS transmission, SRS is triggered by RRC message and SRS is periodically transmitted. In such case, UE performs hopping on the antenna port group while performing SRS transmission using the first antenna port group and performing SRS transmission using the second antenna port group at the next period of transmission time.

Unless multi-transmission for SRS is supported, with all the antenna ports divided into two groups, SRSs are transmitted once. Here, it may be indicated which antenna ports are to be used to transmit the SRSs.

In such case, if SRS is requested through DCI, and thus, SRS is triggered, UE transmits SRSs using one antenna port group.

If the SRS request field value transmitted through DCI format 4 is newly defined and used, eNB then may indicate to UE which antenna port group is to be used to transmit SRSs. As shown in Table 1, dedicated SRS request fields are used, so that no additional overhead is created nor does the SRS parameter set need to be additionally transmitted.

Table 4 is to newly define the SRS request field values included in DCI format 4 for SRS single transmission in the system according to the present invention. The SRS request field values may indicate whether SRS triggering type 1 applies so SRS is triggered, and if triggered, which antenna port group is to be used to transmit SRS.

Table 4

SRS request field value	Description
00	No type 1 SRS triggering
01	First antenna port group
10	Second antenna port group
11	Reserved

Referring to Table 4, in case that two-bit SRS request field value transmitted through DCI format 4 is 00, there is no type 1 triggering. Accordingly, aperiodic SRS is not triggered.

In case that SRS request field value is 01, aperiodic SRS transmission is performed using the first antenna port group. For example, in case of 8 Tx using eight antenna ports, the first antenna port group may consist of antenna ports #80 to #83.

In case that SRS request field value is 10, aperiodic SRS transmission is performed using the second antenna port group. For example, in case of 8 Tx using eight antenna ports, the second antenna port group may consist of antenna ports #84 to #87.

At this time, parameters regarding the antenna port groups, i.e., information on the first and second antenna port groups (for example, specific information about the antenna ports constituting each group) may be transmitted together with other aperiodic SRS parameters to UE through upper layer signaling, such as RRC message.

Fig. 6 is a flowchart schematically illustrating the operation of eNB when all the antenna ports are divided into two groups, one of which is used to perform single transmission of SRS in a system according to the present invention. Fig. 7 is a flowchart schematically illustrating the operation of UE.

In Figs. 6 and 7, as an example, the number of transmission antenna ports used for uplink transmission is N (N Tx, where N is a multiple of two), and the first antenna port group consists of antenna ports #N0 to #Nn (n is N/2-1) and the second antenna port group consists of antenna ports #Nm to #NN-1 (m is n+1).

Referring to Fig. 6, eNB configures a SRS parameter set and transmits the SRS parameter set to UE (S610). The SRS parameter set is configured by the same upper layer and may be transferred through upper layer signaling, such as RRC message. While configuring the SRS parameter, eNB may perform SRS transmission with the antenna ports divided into two groups, such as the first antenna port group and the second antenna port group.

eNB transmits an SRS request to UE through DCI format 4 (S620). eNB selects an antenna port group to be used for SRS transmission and may inform UE of which antenna port group is to be used to perform SRS transmission. Specifically, the SRS request included in DCI format 4 is two bits which may indicate which antenna port group is to be used. For example, referring to Table 4, in case that the first antenna port group is used to perform SRS transmission, an SRS request field value to trigger SRS may be set as ‘01’. Further, in cae that the second antenna port group is used to perform SRS transmission, the SRS request field value to trigger SRS may be set as ‘10’.

eNB receives SRSs transmitted from UE (S630). At this time, the SRSs transmitted from UE are transmitted using the antenna port group indicated by eNB. In case SRS for all the antenna port channels is needed, eNB configures an SRS request field to indicate another antenna port group, and may trigger SRS again by transmitting the SRS request to eNB through DCI format 4.

Referring to Fig. 7 regarding the operation of UE, UE first receives an SRS parameter set (S710). The SRS parameter set may be transmitted through upper layer signaling, such as RRC message. The SRS parameter set may include information regarding antenna port groups obtained by dividing all the antenna ports. For example, all the antenna ports may be set as the first antenna port group and the second antenna port group.

UE receives an SRS request from eNB (S720). With respect to SRS single transmission, the SRS request consists of two bits which are included in DCI format 4 and transmitted from eNB. At this time, the two-bit SRS request may indicate an antenna port group designated by eNB. For example, in case that the SRS request field exemplified in Table 4 is used, the SRS request whose field value is ’00’ indicates no type 1 triggering, i.e., stop triggering aperiodic SRS. The SRS request whose field value is ‘01’ indicates to perform SRS transmission using the first antenna port group, and the SRS request whose field value is ‘10’ indicates to perform SRS transmission using the second antenna port group.

UE transmits SRS to eNB (S730). UE may perform SRS transmission through antenna ports of the antenna port group indicated by eNB. As described above, the SRSs are transmitted through the antenna ports at the first transmission chance four subframes after the SRS request is received. The SRSs may be transmitted through the last SC-FDMA symbol in the subframe or may be constituted of sequences having different CSs (Cyclic Shifits).

In the example illustrated in Fig. 7, SRS single transmission (one-time transmission) is performed, and in case that eNB intends to receive SRS using all the transmission antenna port channels, an SRS request may be transmitted again from eNB. Also in this case, UE performs SRS transmission using the antenna port group indicated by eNB in the order illustrated in Fig. 7.

In case that eight antenna ports are used for uplink transmission (8 Tx), the antenna ports may be divided into the first antenna port group consisting of antenna ports #80 to #83 and the second antenna port group consisting of antenna ports #84 to #87.

In case that four antenna ports are used for uplink transmission (4 Tx), the antenna ports may be divided into the first antenna port group consisting of antenna ports #40 and #41 and the second antenna port group consisting of antenna ports #42 and #43.

The antenna port group to be used for SRS transmission is indicated by eNB through the SRS request field as described above, and UE transmits SRSs through the antenna ports of the antenna port group indicated by the SRS request field. In case that the uplink transmission is 8 Tx, one-time SRS transmission may be performed through the antenna port group consisting of four antenna ports, and in case that the uplink transmission is 4 Tx, the one-time SRS transmission may be conducted through the antenna port group consisting of two antenna ports.

Meanwhile, in another embodiment which does not perform multi-transmission of SRS, in case that the SRS request field of DCI format 4 is not newly defined as described above, SRS configuration, for example, SRS parameter set may be newly defined.

In case that N antenna ports (N is a multiple of two) are used for uplink transmission (N Tx), as described above, all the antenna ports may be separated into the first antenna port group consisting of antenna ports #N0 to #Nn (n is N/2-1) and the second antenna port group consisting of antenna ports #Nm to #NN-1 (m is n+1). At this time, the newly defined SRS parameter set may indicate one of the first and second antenna port groups.

While configuring an aperiodic SRS parameter set through the upper layer, such as RRC, when the first antenna port group is used, eNB configures at least one parameter set regarding SRS transmission and may configure at least one parameter set regarding SRS transmission through the second antenna port group. The configured parameter sets may be transmitted to UE through upper layer signaling, such as RRC message.

At this time, while transmitting control information to UE using DCI format 4, eNB may indicate through a two-bit SRS request field which antenna port group is to be used to transmit SRS.

For example, assume that in Table 2 the first SRS parameter set includes parameters regarding transmission of SRS using the first antenna port group and the second SRS parameter set includes parameters regarding transmission of SRS using the second antenna port group. In case of indicating that the first antenna port group is used to perform SRS transmission, eNB may transmit to UE through DCI format 4 an SRS request field ‘01’ to indicate the first SRS parameter set. Further, in case of indicating that the second antenna port group is used to perform SRS transmission, eNB may transmit to UE through DCI format 4 an SRS request field ‘10’ to indicate the second SRS parameter set.

Also in such case, when needing SRS transmitted through all the antenna port channels, eNB may transmit an SRS request to UE again to indicate whether an antenna port group different from the previous one is to be used.

Table 5 schematically shows an example of an SRS parameter set that may indicate an antenna port group used for SRS transmission in the system according to the present invention.

Table 5

In the example shown in Table 5, parameter srs-AntennaPortAp indicates the antenna port used for SRS transmission. At this time, an1 indicates the antenna port for SRS transmission in case that SRS is transmitted through one antenna port (1 Tx). an2 may indicate the antenna port used for SRS transmission in case that two antenna ports are used for SRS transmission (2 Tx). an4_1 may indicate the antenna port used for SRS transmission in case that SRS transmission is performed through four antenna ports.

Further, in case that eight antenna ports are used for SRS transmission (8 Tx), an4_1 may indicate the first antenna port group consisting of four antenna ports (antenna ports #80 to #83) and an4_2 may indicate the second antenna port group consisting of other four antenna ports (antenna ports #84 to #87). As described above, assume in Table 2 that the first SRS parameter set includes parameters regarding transmitting SRS using the first antenna port group, and the second SRS parameter set includes parameters regarding transmitting SRS using the second antenna port group. eNB may instruct UE to perform SRS transmission using the first antenna port group (antenna ports #80 to #83) through an SRS request field ‘01’. Further, eNB may instruct UE to perform SRS transmission using the second antenna port group (antenna ports #84 to #87) through the SRS request field ‘10’.

Table 6 schematically shows other examples of aperiodic SRS parameter set that may indicate an antenna port group used for SRS transmission in the system according to the present invention.

Table 6

In the example shown in Table 6, parameter srs-AntennaPortAp refers to an antenna port used for SRS transmission. At this time, an1 is an antenna port used for SRS transmission when SRS is transmitted through one antenna port (1 Tx). an2_1 may refer to an antenna port used for SRS transmission when two antenna ports are used for SRS transmission (2 Tx). an4 may refer to an antenna port used for SRS transmission when four antenna ports are used for SRS transmission (S Tx).

Further, as an example where SRS is transmitted through four antenna ports (8 Tx), the four antenna ports are divided into two groups, and SRS transmission is performed through one of the two groups, an2_1 may refer to a first antenna port group consisting of two antenna ports (antenna ports #40 and #41), and an2_2 may refer to a second antenna port group consisting of two other antenna ports (antenna ports #42 and #43). As described above, in Table 2, assume that the first SRS parameter set includes parameters regarding transmitting SRS using the first antenna port group, and the second SRS parameter set includes parameters regarding transmitting SRS using the second antenna port group. eNB may inform UE that SRS transmission is performed by the first antenna port group (antenna ports #40 and #41) through the SRS request field ‘01’. Further, eNB may inform UE that SRS transmission is performed using the second antenna port group (antenna ports #42 and #43) through the SRS request field ‘10’.

Referring to Fig. 8, eNB configures an SRS parameter set and transmits the configured SRS parameter set to UE (S810). The SRS parameter set is configured by the upper layer, such as RRC, and may be transmitted to UE through upper layer signaling, such as RRC message. At this time, eNB may divide all the antenna ports used for uplink transmission into two groups, so that the SRS parameter set may include parameters regarding SRS transmission using the antenna port group. For example, the first SRS parameter set may include parameters regarding SRS transmission using the first antenna port group, and the second SRS parameter set may include parameters regarding SRS transmission using the second antenna port group.

eNB transmits an SRS request to UE (S820). The SRS request may be included in DCI and transmitted over PDCCH to UE. Using the two-bit SRS request transmitted through DCI format 4, eNB may inform UE of which antenna port group is to be used to perform SRS transmission. For example, as a situation of using what is disclosed in Table 2, assume that the first SRS parameter set includes parameters regarding transmitting SRS using the first antenna port group, and the second SRS parameter set includes parameters regarding transmitting SRS using the second antenna port group. In such case, the SRS request whose field value is ‘01’ is transmitted to indicate that the first antenna port group is used for SRS transmission, and the SRS request whose field value is ‘10’ is transmitted to indicate that the second antenna port group is used for SRS transmission.

eNB receives SRS from UE (S830). The SRS received from UE is transmitted through the antenna ports of the antenna port group indicated through the SRS request. Accordingly, eNB may estimate the state of the corresponding antenna port channel. In case of further needing information regarding the state of another antenna port channel, eNB may transmit an SRS request to UE again to indicate that the other antenna port group is used to perform SRS transmission.

Referring to Fig. 9, UE receives an SRS parameter set from eNB (S910). The SRS parameter set may be transmitted through the upper layer signaling, such as RRC message. The SRS parameter set may include information regarding antenna port groups obtained by dividing all the antenna ports. For example, all the antenna ports may be configured into a first antenna port group and a second antenna port group.

UE receives the SRS parameter set from eNB (S920). The SRS parameter set may be transmitted to UE through the upper layer signaling, such as RRC message. All the uplink antenna ports may be divided into two groups. The SRS parameter set may include parameters for performing SRS transmission using a specific antenna port group. For example, the first SRS parameter set includes parameters to perform SRS transmission using the first antenna port group, and the second SRS parameter set includes parameters for performing SRS transmission using the second antenna port group.

UE receives an SRS request from eNB (S930). The SRS request may be included in DCI and transmitted over PDCCH. By the SRS request, aperiodic SRS may be triggered. The two-bit SRS request received through DCI format 4 may indicate which antenna port group is to be used to perform SRS transmission. For example, as a situation to use what is disclosed in Table 2, assume that the first SRS parameter set includes parameters regarding transmitting SRS using the first antenna port group, and the second SRS parameter set includes parameters regarding transmitting SRS using the second antenna port group. In such case, the SRS request field value ‘01’ indicates that the first antenna port group is used for SRS transmission, and the SRS request field value ‘10’ indicates that the second antenna port group is to be used for SRS transmission.

UE generates SRS and transmits the SRS to eNB (S940). At this time, UE performs SRS transmission using an antenna port group designated by the SRS parameter set indicated by the received SRS request field.

Referring to Fig. 10, the UE 1000 includes an RF unit 1010, a memory 1020, and a processor 1030.

The UE 1000 transmits and receives information through the RF unit 1010. The RF unit 1010 may include a plurality of antennas. The RF unit 1010 may transmit and receive information using at least one antenna port.

The memory 1020 may store information necessary for the UE 1000 to perform communication. For example, the memory 1020 may store various types of communication configuration information received from eNB. The parameter set necessary for SRS transmission may be received through the RF unit 1010 and may be stored in the memory 1020.

The processor 1030 implements the functions, procedures, and/or methods suggested herein. For example, the processor 1030 may configure SRSs according to the SRS parameter set as described above and may transmit SRSs using a designated antenna port group.

The processor 1030 includes an SRS setting unit 1040 and an SRS configuration unit 1050. The SRS setting unit 1040 performs setting for SRS transmission according to the SRS parameter set received through the upper layer signaling, such as RRC message. The SRS configuration unit 1050 configures SRS according to the SRS request included in DCI and transmitted over PDCCH and transmits the SRS. The method of selecting an antenna port according to the SRS request and performing single transmission or multi-transmission has been described above.

Fig. 11 schematically illustrates the configuration of eNB according to the present invention. Referring to Fig. 11, eNB 1100 includes an RF unit 1110, a memory 1120, and a processor 1130.

The eNB 1100 transmits and receives necessary information through the RF unit 1110. The RF unit 1110 may include a plurality of antennas. The RF unit 1110 may transmit and receive information using at least one antenna port.

The memory 1120 may store information necessary for the eNB 1100 to perform communication or to manage the network. For example, the memory 1120 may store an SRS parameter set configured by the upper layer and may store channel information received from UE.

The processor 1130 implements the functions, procedures, and/or methods suggested herein. For example, the processor 1130 may configure an SRS parameter set as described above and may transmit the SRS parameter set through the RF unit 1110 to UE. The SRS parameter set may include information for dividing antenna ports available for UE to transmit SRS and to transmit SRS using a specific group. Further, in case of needing aperiodic SRS, the processor 1130 may configure DCI including SRS. DCI is transmitted to UE over PDCCH through the RF unit 1110. At this time, the processor 1130 may designate an antenna port group over which SRS is to be transmitted through the SRS request.

The processor 1130 may include an SRS setting unit 1140 and a channel state estimating unit 1150. The SRS setting unit 1140 may configure an SRS parameter set necessary for SRS transmission. The channel state estimating unit 1150 may estimate the state of an antenna port channel that has transmitted the corresponding SRS through the SRS received from UE.

Meanwhile, what has been described regarding UE may also apply to a relay in the same way.

Further, the invention is characterized by further including a method of applying a 4Tx SRS transmission control scheme so as to control SRS transmission of UE or relay having eight transmission antennas. In connection, as a first method, a method of adding an SRS transmission antenna port indicator to the SRS parameter set, and as a second method, a method of transmitting twice control information that has the same type as in the method of transferring SRS control information to UE having four transmission antennas upon transferring control information regarding SRS transmission to UE having eight transmission antennas are considered. According to the second method, UE having the eight transmission antennas receives independent two control information for SRS transmission, and the control information applies to each SRS antenna port group consisting of four transmission antennas. This is advantageous in that the first method is implemented to fit aperiodic SRS transmission while the second method may apply to periodic SRS transmission.

Although the embodiments of the present invention have been described, it will be understood by those skilled in the art that various modifications or variations may be made to the present invention without departing from the technical spirit or scope of the invention. Accordingly, the present invention is not limited to the embodiments and includes all the embodiments within the appended claims.

Claims

A reference signal receiving method comprising the steps of:

transmitting an SRS (Sounding Reference Signal) request over a downlink control channel; and

receiving SRSs transmitted according to the SRS request, wherein antenna ports that perform uplink transmission are divided into a first group and a second group, and wherein the SRSs are transmitted through antenna ports included in one of the first group and the second group.
The reference signal receiving method of claim 1, wherein in the step of receiving the SRS, first SRS transmission performed through the first group of antenna ports is received, and in a predetermined time determined by an upper layer, second SRS transmission performed through the second group of antenna ports is received.
The reference signal receiving method of claim 1, wherein the SRS request indicates one of the first group and the second group, wherein the SRSs are transmitted using antenna ports of the group indicated by the SRS request.
The reference signal receiving method of claim 1, wherein the SRS request indicates a parameter set for SRS transmission, and wherein the SRSs are transmitted using antenna ports configured in the parameter set.
The reference signal receiving method of claim 4, wherein the antenna ports configured in the parameter set are included in one of the first group and the second group.
A reference signal transmitting method comprising the steps of:

receiving an SRS (Sounding Reference Signal) request over a downlink control channel; and

transmitting SRS according to the SRS request, wherein antenna ports that perform uplink transmission are divided into a first group and a second group, and wherein the SRSs are transmitted through antenna ports included in one of the first group and the second group.
The reference signal transmitting method of claim 6, wherein the number of antenna ports that perform the uplink transmission is N, and wherein the first group and the second group respectively include N/2 antenna ports and N/2 antenna ports, wherein the antenna ports included in the first group are different from the antenna ports included in the second group.
The reference signal transmitting method of claim 6, wherein in the step of transmitting the SRSs, first SRS transmission is performed using the first group of antenna ports, and in a predetermined time, second SRS transmission is performed using the second group of antenna ports.
The reference signal transmitting method of claim 8, wherein the predetermined time is determined by an upper layer of a base station and transmitted through upper layer signaling.
The reference signal transmitting method of claim 6, wherein the SRS request indicates one of the first group and the second group, and wherein in the step of transmitting the SRSs, the SRSs are transmitted using antenna ports included in the group indicated by the SRS request.
The reference signal transmitting method of claim 10, wherein the SRS request indicates a parameter set for SRS transmission, and wherein in the step of transmitting the SRSs, the SRSs are transmitted using antenna ports configured in the parameter set.
The reference signal transmitting method of claim 11, wherein the antenna ports configured in the parameter set are included in one of the first group and the second group.
A reference signal receiving apparatus comprising:

an RF unit transmitting an SRS request over a downlink control channel and receiving SRSs transmitted according to the SRS request; and

a processor configuring a parameter set necessary for SRS transmission and estimating a state of an antenna port channel over which an SRS is transmitted based on the received SRSs, wherein antenna ports used for uplink transmission are divided into a first antenna port group and a second antenna port group, and wherein the processor enables the SRSs to be transmitted through an antenna port in one antenna port group at a time through the SRS request or a configuration of the parameter set.
A reference signal transmitting apparatus comprising:

an RF unit including a plurality of antenna ports divided into a first antenna port group and a second antenna port group;

a memory storing information of a parameter set necessary for SRS transmission; and

a processor configuring an SRS based on the SRS request and the parameter set, wherein the processor transmits SRSs using antenna ports in one antenna port group at a time.
The reference signal transmitting apparatus of claim 14, wherein the processor performs first SRS transmission using antenna ports in the first antenna port group according to the SRS request, and in a predetermined time, performs second SRS transmission using antenna ports in the second antenna port group.
The reference signal transmitting apparatus of claim 14, wherein the processor transmits SRSs using antenna ports in an antenna port group indicated by the SRS request or using antenna ports in an antenna port group configured in a parameter set indicated by the SRS request.