WO2013109049A1

WO2013109049A1 - Apparatus and method of transmitting uplink signal in wireless communication system

Info

Publication number: WO2013109049A1
Application number: PCT/KR2013/000335
Authority: WO
Inventors: Ki Bum Kwon; Jae Hyun Ahn; Myung Cheul Jung
Original assignee: Pantech Co., Ltd.
Priority date: 2012-01-16
Filing date: 2013-01-16
Publication date: 2013-07-25
Also published as: KR20130084176A

Abstract

The present invention provides an apparatus for transmitting an uplink signal and a method using the apparatus in a wireless communication system. The discription discloses a method for transmitting an uplink signal by a user equipment, comprising receiving configuration information about a sounding reference signal (SRS) from a base station; receiving from the base station configuration information about a physical random access channel (PRACH) to which a random access preamble is mapped; transmitting an SRS to the base station during a first time interval in a first subframe of a first serving cell designated by the SRS configuration information; and transmitting the PRACH to the base station during a second time interval in a second subframe of a second serving cell designated by the PRACH configuration information.

Description

APPARATUS AND METHOD OF TRANSMITTING UPLINK SIGNAL IN WIRELESS COMMUNICATION SYSTEM

The present invention relates to wireless communication and more particularly, an apparatus for transmitting an uplink signal and a method using the apparatus in a wireless communication system.

A user equipment carries out a random access procedure to access a network. The random access procedure can be classified into a contention based random access procedure and a non-contention based random access procedure. The random access procedure can also be applied for the case where the user equipment establishes a new connection to a network through a handover process. Similarly, the random access procedure can be employed for the case where the user equipment changes synchronization or radio resource control (RRC) state from idle mode to connected mode after the user equipment is connected to the network or for the case where the user equipment requires uplink synchronization to carry out data transmission to and reception from a base station.

A wireless communication system usually employs one frequency band for data transmission. For example, the 2nd generation wireless communication system uses a frequency band ranging from 200 KHz to 1.25 MHz while the 3rd generation wireless communication system uses a frequency band ranging from 5 MHz to 10 MHz. To accommodate the transmission capacity increased, the recent 3GPP LTE or 802.16m is continuously expanding its bandwidth up to 20 MHz or more. It might be said that increasing the bandwidth is essential for increasing transmission capacity; however, allowing large bandwidth even when quality of service required is low may bring about large power consumption.

In this respect, a multiple component carrier system is now emerging, where a carrier wave is defined to have a central frequency with a single frequency band and broadband data transmission and/or reception is carried out through a plurality of carrier waves. By using one or more carrier waves, the multiple component carrier system supports narrow band and broadband data communication at the same time. For example, if one carrier wave corresponds to bandwidth of 5 MHz, a maximum of 20 MHz of bandwidth can be supported by using four carrier waves.

A user equipment can transmit various uplink control signals such as a random access preamble and a sounding reference signal (SRS) through a plurality of component carrier waves. Moreover, a multiple component carrier system allows different kinds of uplink control signals to be transmitted through component carrier waves different from each other. However, it has not been determined yet about whether parallel transmission is allowed, where the user equipment transmits different kinds of uplink control signals through component carrier waves different from each other but in the same subframe.

One technical objective of the present invention is to provide an apparatus for transmitting an uplink signal and a method using the apparatus in a wireless communication system.

Another technical objective of the present invention is to provide an apparatus for transmitting an uplink signal selectively according to a priority order at the time of parallel transmission and a method using the apparatus.

Yet another technical objective of the present invention is to provide an apparatus for determining whether to allow parallel transmission among a plurality of uplink signals and a method using the apparatus.

Yet another technical objective of the present invention is to provide an apparatus and method for transmitting one of SRS and PRACH based on priority when the SRS and the PRACH are expected to be transmitted simultaneously in a different serving cell.

Yet another technical objective of the present invention is to provide an apparatus and method for transmitting selectively any one of SRS and PRACH or both of them under the limitation of uplink maximum transmission power.

According to one aspect of the present invention, a method for transmitting an uplink signal by a user equipment comprises receiving configuration information about a sounding reference signal (SRS) from a base station, receiving from the base station configuration information about a physical random access channel (PRACH) to which a random access preamble is mapped, transmitting an SRS to the base station during a first time interval in a first subframe of a first serving cell designated by the SRS configuration information, and transmitting the PRACH to the base station during a second time interval in a second subframe of a second serving cell designated by the PRACH configuration information.

In the above, the first and the second subframe are a subframe of the same index; and the first and the second time interval do not overlap with each other because of a difference of uplink propagation delays in the first and the second serving cell.

According to another aspect of the present invention, a user equipment comprises a receiving unit receiving configuration information about a sounding reference signal (SRS) and configuration information about a physical random access channel (PRACH) to which a random access preamble is mapped; a transmission unit transmitting the SRS to the base station during a first time interval in a first subframe of a first servicing cell designated by the SRS configuration information or transmitting the PRACH to the base station during a second time interval in a second subframe of a second serving cell designated by the PRACH configuration information; and an uplink controller determining whether the first and the second subframe are a subframe of the same index and whether the first and the second time interval overlap with each other because of a difference of uplink propagation delays in the first and the second serving cell.

In case preamble transmission required for a random access procedure in a secondary serving cell and parallel transmission of SRSs in a primary serving cell of a wireless communication system utilizing a plurality of component carrier waves are carried out, prevented is excluding a particular uplink signal from transmission because parallel transmission is involved for the signal although in fact it is not simultaneous transmission. Also, a plurality of uplink signals for a plurality of serving cells designated by a base station can be transmitted without additional power consumption of a user equipment.

Furthermore, by clearly defining the priority between SRS and PRACH when transmitted simultaneously, a selected one of the SRS and the PRACH may be transmitted when the simultaneous transmission of the SRS and the PRACH exceeds an uplink maximum transmission power.

FIG. 1 is one example of a wireless communication system to which the present invention is applied;

FIG. 2 is one example of timing alignment during a synchronization procedure to which the present invention is applied;

FIG. 3 is one example of an uplink subframe structure transmitting a sounding reference signal to which the present invention is applied;

FIG. 4 illustrates the structure of a PRACH to which the present invention is applied;

FIG. 5 illustrates an example where the number of subframes occupied by a PRACH varies according to a preamble format;

FIG. 6 illustrates a transmission timing of serving cells according to one embodiment of the present invention;

FIG. 7 is a flow diagram illustrating a transmission procedure of an uplink signal of a user equipment according to one example of the present invention;

FIG. 8 is a flow diagram illustrating a transmission procedure of an uplink signal of a base station according to one example of the present invention; and

FIG. 9 is a block diagram illustrating a user equipment and a base station according to one example of the present invention.

In what follows, several embodiments according to the present invention will be described in detail with reference to illustrative drawings. In assigning reference symbols to constituting elements of each drawing, the same symbols will be assigned to the same constituting elements wherever possible, even though the elements may appear in different drawings. Also, in describing an embodiment of the present invention, if it is determined that specific description about a related well-known structure or function may mislead the technical principles of the present invention, the corresponding description will be omitted.

The present invention is intended for a wireless communication network; tasks carried out in a wireless communication network may be carried out while a procedure of controlling the network or transmitting data is carried out in a system managing the corresponding wireless communication network (for example, a base station) or may be carried out in a user equipment connected to the corresponding wireless network.

According to embodiments of the present invention, ‘transmission of a channel’ can be interpreted such that information is transmitted through the channel or information mapped to the channel is transmitted. At this point, the channel may include a physical downlink control channel (PDCCH), physical downlink shared channel (PDSCH), physical uplink shared channel (PUSCH), or physical uplink shared channel (PUSCH). Also, ‘transmission of a component carrier wave’ can be interpreted such that information is transmitted through the component carrier wave or information mapped to the component carrier wave is transmitted.

FIG. 1 is one example of a wireless communication system to which the present invention is applied.

With reference to FIG. 1, the wireless communication system 10 is widely deployed to provide various kinds of communication services such as voice and packet data.

The wireless communication system 10 includes at least one base station (BS) 11. Each base station 11 provides a communication service for a particular geographic or frequency region (which is generally called a cell) 15a, 15b, 15c. A cell can be further divided into a plurality of regions (which are called sectors).

A user equipment (UE) 12 may be fixed or mobile, being called alternatively a mobile station (MS), mobile terminal (MT), user terminal (UT), subscriber station (SS), wireless device, personal digital assistant (PDA), wireless modem, or handheld device.

A base station 11 generally refers to a station performing communication with the UE 12, being called alternatively evolved-NodeB (eNB), base transceiver system (BTS), access point, relay, remote radio head (RRH), or home eNB (HeNB). The cell should be interpreted comprehensively to represent a partial region covered by the base station 11, including various types of coverage region such as a mega cell, macro cell, micro cell, pico cell, and femto cell.

In what follows, downlink transmission refers to communication from the base station 11 to the UE 12 whereas uplink transmission refers to communication from the UE 12 to the base station 11. In the downlink transmission, a transmitter may be part of the base station 11 and a receiver may be part of the UE 12. In the uplink transmission, a transmitter may be part of the UE 12 while a receiver may be part of the base station 11.

There is no limit on the types for implementing multiple access technique; various multiple access techniques can be employed, including CDMA (Code Division Multiple Access), TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access), OFDMA (Orthogonal Frequency Division Multiple Access) SC-FDMA (Single Carrier-FDMA), OFDM-FDMA, OFDM-TDMA, and OFDM-CDMA. For uplink and downlink transmission, time division duplex (TDD) technique can be applied, where transmission is carried out at different time intervals. Similarly, frequency division duplex (FDD) technique can be applied, where transmission is carried out by using different frequencies.

Radio interface protocol layers between the UE and a network employs lower three layers defined in the OSI (Open System Interconnection) model well known for communication systems, comprising L1 (first layer), L2 (second layer), and L3 (third layer).

The first layer (physical layer) is connected to its upper layer (Medium Access Control (MAC) layer) through a transport channel and data moves back and forth between the MAC and physical layer through the transport channel. Data moves between different physical layers, namely between physical layers of a transmitter and a receiver, through a physical channel. A couple of physical control channels and uplink control channels are defined to be used for the physical layer.

A physical downlink control channel (PDCCH), which transmits physical control information, informs the UE about resource allocation of a paging channel (PCH) and a downlink shared channel (DL-SCH) and information of a hybrid automatic repeat request (HARQ) related to the DL-SCH. The PDCCH is capable of carrying an uplink grant informing the UE about resource allocation for uplink transmission. A physical control format indicator channel (PCFICH) informs the UE about the number of OFDM symbols used by PDCCHs and is transmitted at each subframe. A physical hybrid ARQ indicator channel (PHICH) carries a HARQ ACK/NAK signal in response to uplink transmission.

A physical uplink control channel (PUCCH) carries uplink control information such as a HARQ ACK/NAK signal in response to downlink transmission, a scheduling request, and channel quality information (CQI). A physical random access channel (PRACH) is used for the UE to transmit a random access preamble. A sounding reference signal (SRS) is an uplink signal, which is used as a reference signal for uplink scheduling. If the UE sends an SRS to an uplink channel, the base station checks the uplink channel state and carries out uplink scheduling for the UE.

The second layer (radio datalink layer) consists of an MAC layer, RLC layer, and PDCH layer. The MAC layer, which carries out mapping between a local channel and a transmission channel, selects an appropriate transmission channel to transmit data delivered from the RLC layer and adds required control information to the header of an MAC protocol data unit (PDU). The RLC layer, located above the MAC layer, supports data transmission to be carried out reliably. Also, the RLC layer, to configure the data to have a relevant size appropriate for radio channel carries out segmentation of RLC service data units (SDUs) delivered from its upper layer and concatenation of the segmented RLC SDUs. The RLC layer of a receiver provides a function of reassembling data to reconstruct the original RLC SDUs from the received RLC PDUs. The PDCP layer is used only in a packet exchange region; to improve transmission efficiency of packet data through a radio channel, the PDCP layer can transmit IP packet headers after compression thereof.

The third layer (Radio Resource Control (RRC) layer) performs exchanging radio resource control information between the UE and a network as well as controlling its lower layer. Depending on communication conditions of the UE, various states can be defined for the RRC layer, including idle mode, RRC connected mode, and so on and depending on the needs, transition between the RRC states can be performed. The RRL layer defines various procedures related to radio resource management such as system information broadcasting, RRC connection management, multiple component carrier wave configuration, radio bearer control, security, measurement, mobility management (handover) procedure, and so on.

Carrier aggregation (CA) is intended for supporting a plurality of component carrier waves and alternatively called spectrum aggregation or bandwidth aggregation. A unit carrier wave grouped together in terms of carrier aggregation is called a component carrier (in what follows, it is denoted as CC). Each CC is defined by its bandwidth and central frequency. Carrier aggregation is introduced to support an increased throughput, prevent increase of costs due to introduction of broadband RF (Radio Frequency) devices, and ensure compatibility with the existing systems. For example, if five CCs are allocated to form granularity consisting of carriers each with 5 MHz bandwidth, maximum bandwidth of 25 MHz can be supported.

Component carriers (CCs) can be divided into primary CCs (in what follows, they are called PCCs) and secondary CCs (in what follows, they are called SCCs) depending on their activation state. The PCC is a kind of carrier which is always activated while the SCC is a kind of carrier which is activated or deactivated depending on particular conditions. Activation refers to the conditions where transmission or reception of traffic data is in progress or in a standby state. Deactivation refers to the conditions where transmission or reception of traffic data is not possible but only measurement or transmission/reception of a minimal amount of data is carried out. The UE may use only one PCC or one or more SCCs along with the PCC. The PCC or SCC can be assigned to the UE by the base station.

A multiple component carrier system refers to a system which supports carrier aggregation. A multiple component carrier system can employ adjacent carrier aggregation or non-adjacent carrier aggregation and can also employ symmetric aggregation or non-symmetric aggregation.

A primary serving cell refers to a serving cell providing a security input and NAS mobility information while RRC is established or re-established. Depending on the UE’s capabilities, at least one cell is allowed to form a set of serving cells together with the primary serving cell, where the at least one cell is called a secondary serving cell.

Therefore, the set of serving cells configured for one UE may comprise only one primary serving cell or one primary serving cell and at least one secondary serving cell.

A downlink CC (DL CC) corresponding to the primary serving cell is called a downlink primary CC (DL PCC) while an uplink CC (UP CC) corresponding to the primary serving cell is called an uplink primary CC (UL PCC). One serving cell may relate to DL CCs only or both of DL CCs and UL CCs. Therefore, communication between the UE and the base station through DL CC or UL CC in a carrier system can be regarded conceptually the same as communication between the UE and the base station through a serving cell. For example, in a random access method according to the present invention, the UE’s transmission of a preamble by using a UL CC can be regarded the same as the primary or secondary serving cell’s transmitting the preamble. Similarly, the UE’s receiving downlink information by using the DL CC can be regarded the same as the primary or secondary serving cell’s receiving downlink information.

Technical principles of the present invention related to the characteristics of the primary and secondary serving cell are not necessarily limited to the description above, which is just an example and more examples can be devised to illustrate the technical principles of the present invention.

A plurality of serving cells can be configured for the UE. For example, the primary serving cell and one secondary serving cell can be configured for the UE; similarly, the primary serving cell and a plurality of secondary serving cells can be configured for the UE. An uplink channel or uplink signal can be transmitted simultaneously or in a parallel fashion from a plurality of serving cells configured for the UE. At this point, the uplink channel includes the PUCCH, PUSCH, and PRACH. A random access channel (RACH), which is a transport channel, is mapped to the PRACH.

In a wireless communication environment, a radio signal experiences a propagation delay (PD) while the signal is transmitted from a transmitter to a receiver. Therefore, even if the receiver knows exactly the time at which a signal is transmitted from the transmitter, the time at which the signal arrives at the receiver is influenced by various factors such as the distance between the transmitter and receiver, ambient radio environment, movement of the receiver, and so on. In case the receiver does not know exactly the time at which the signal transmitted from the transmitter arrives at the receiver, the receiver may receive a distorted signal.

Therefore, in a wireless communication system, synchronization between the base station and the UE has to be established before a signal is received regardless of downlink/uplink transmission. Various types of synchronization are used for this purpose: frame synchronization, information symbol synchronization, sampling period synchronization, and so on. The sampling period synchronization is the most basic type of synchronization to be secured for distinguishing physical signals.

Acquisition of downlink synchronization is carried out in the UE based on a signal of the base station. The base station transmits a mutually agreed synchronization signal to the UE to support easy acquisition of downlink synchronization. The UE must be able to detect the exact time at which a synchronization signal is transmitted from the base station. In the case of downlink transmission, since one base station transmits the same synchronization signal to a plurality of UEs at the same time, the UEs can acquire synchronization independently of each other.

In the case of uplink transmission, the base station receives a signal from a plurality of UEs. In case distances from the plurality of UEs to the base station differ from each other, signals received by the base station have different propagation delays from each other. In case a plurality of UEs transmit uplink signals with respect to downlink synchronization signals acquired individually, the signal from each UE arrives at the base station at different time point from each other. In this case, the base station cannot acquire synchronization with respect to any of the UEs. Therefore, acquisition of uplink synchronization requires a different procedure from downlink transmission.

A random access procedure is carried out for uplink synchronization acquisition; during the random access procedure, the UE acquires uplink synchronization based on a timing alignment value transmitted from the base station. In case the timing alignment value is always greater than zero, in other words, uplink synchronization timing always precedes a current downlink subframe synchronization timing, the timing alignment value can be defined as a timing advanced value.

After uplink synchronization is acquired, the UE starts a time alignment timer. While the time alignment timer is in operation, the UE and the base station is in synchronization with each other. If the time alignment timer expires or does not operate, it is determined that the UE and the base station are not synchronized with each other and the UE does not carry out uplink transmission except for the transmission of a random access preamble.

FIG. 2 is one example of timing alignment during a synchronization procedure to which the present invention is applied.

With reference to FIG. 2, the UE, taking into account the time difference caused by a propagation delay, has to transmit an uplink radio frame 520 to the base station at a time point 530 prior to the time point at which the UE receives a downlink radio frame 510. By doing so, the base station can receive the uplink radio frame 520 from the UE at the time the base station transmits the downlink radio frame 510. The uplink transmission timing T, 530 aligned by the UE can be obtained by using Math Figure 1 as follows.

MathFigure 1

where N_TA is a timing alignment value and is controlled in a various manner according to a timing advance command (TAC) of the base station and N_{TA offset} is a value fixed by a frame structure. T_S is a sampling period. It should be noted that if the timing alignment value (N_TA) is positive, uplink timing is made to advance whereas if the timing alignment value (N_TA) is negative, the uplink timing is made to be delayed.

For uplink synchronization, the UE receives N_TA value provided by the base station and applies the N_TA value to timing alignment so that the UE acquires synchronization needed for wireless communication with the base station.

In a multiple component carrier system, one UE carries out transmission with a base station through a plurality of CCs or a plurality of serving cells. A plurality of serving cells configured for the UE may have different propagation delays from each other; in this case, the UE has to apply an uplink transmission timing T different for each serving cell. The above scheme is called multiple timing alignment (MTA). In case each of the multiple timing alignment values is always greater than zero, in other words, an uplink synchronization timing always precedes a current downlink subframe synchronization timing in a plurality of serving cells, the multiple timing alignment values can be defined as multiple timing advanced values. If the UE carries out a random access procedure for each serving cell to obtain multiple timing alignment values, overhead is imposed on the limited uplink resources and complexity of random access may be increased.

Therefore, the same timing alignment value is used for the base station and the UE and complexity is reduced by using a timing alignment group (TAG) which uses the same timing reference and includes at least one serving cell. For example, if a first and a second serving cell belong to the same timing alignment group TAG1, the same timing alignment value NTA1 is applied to the first and the second serving cell. The UE can obtain a timing alignment value for two serving cells from a single random access procedure. A timing alignment group can include a primary serving cell. In this case, the timing alignment group is called a secondary TAG (sTAG). The timing alignment group can include the primary serving cell and at least one secondary serving cell, which in this case is called a pTAG. The initial setting of the timing alignment group and re-organization thereof are determined by the base station and the timing alignment group is transmitted to the UE through RRC signaling.

The primary serving cell does not change a TAG. Also, the UE has to be able to support at least two TAGs when a multiple timing advanced value is needed. As one example, the UE has to be capable of supporting a TAG comprising a pTAG (primary TAG) including the primary serving cell and an sTAG (secondary TAG) not including the primary serving cell. Here, there always exists only one pTAG whereas at least one or more sTAGs can exist if it is the case that a multiple timing advanced value is needed.

FIG. 3 is one example of an uplink subframe structure transmitting a sounding reference signal to which the present invention is applied.

With reference to FIG. 3, an uplink subframe includes two slots on the time axis and each slot includes seven SC-FDMA (Single Carrier-Frequency Division Multiple Access) symbols. The uplink subframe includes a PUCCH and a PUSCH on the frequency axis. The PUCCH for one UE uses one resource block occupying different frequency bands at each of the two slots of the subframe. The two slots use different resource blocks (or sub-carriers) within the subframe. In this case, the two resource blocks allocated for the PUCCH are said to perform frequency hopping at slot boundaries.

A sounding reference signal can be transmitted in the last SC-FDMA symbol interval of the subframe; the PUCCH of the last SC-FDMA symbol is punctured. At this time, the UE transmits data by using 13 SC-FDMA symbols and applies preprocessing such as rate matching to the remaining one SC-FDMA symbol, thereby transmitting the sounding reference signal. Although it is assumed that the 14-th SC-FDMA symbol transmits the sounding reference signal, the assumption is just an illustration and thus, the positions and the number of SC-FDMA symbols can be changed as needed. The sounding reference signal can be transmitted from the whole PUSCH or from part of the PUSCH. Since one SC-FDMA symbol is punctured in the uplink subframe to which the sounding reference signal is transmitted, the uplink subframe can be called a subframe of shortened format. The sounding reference signal is not transmitted in a special subframe.

The sounding reference signal can be transmitted periodically or aperiodically. For an aperiodic sounding reference signal, the UE transmits the sounding reference signal aperiodically; therefore, radio resources can be utilized efficiently compared with the case where the sounding reference signal is transmitted periodically. Related to the transmission of an aperiodic sounding reference signal, the base station has to either make the UE transmit the sounding reference signal or inform the UE of information related to the transmission of the sounding reference signal.

The subframe which transmits a sounding reference signal satisfies the following equation.

MathFigure 2

With reference to Math Figure 2, ns is a slot number within a radio frame; TSFC is a cell-specific subframe configuration period; and ΔSFC is a cell-specific subframe offset. In the case of a frame structure defined for TDD, the sounding reference signal is transmitted only to uplink subframes configured or UpPTS. T_SFC and Δ_SFC are parameters related to the transmission of the sounding reference signal and can be defined by srs-SubframeConfig, which is a message transmitted from an upper layer such as the RRC layer. Table 1 describes a sounding reference signal subframe structure used in a frame structure defined for FDD while Table 2 describes a sounding reference signal subframe structure used in a frame structure defined for TDD.

Table 1

srs-SubframeConfig	Bit information	T_SFC (subframes)	Δ_SFC (subframes)
0	0000	1	{0}
1	0001	2	{0}
2	0010	2	{1}
3	0011	5	{0}
4	0100	5	{1}
5	0101	5	{2}
6	0110	5	{3}
7	0111	5	{0,1}
8	1000	5	{2,3}
9	1001	10	{0}
10	1010	10	{1}
11	1011	10	{2}
12	1100	10	{3}
13	1101	10	{0,1,2,3,4,6,8}
14	1110	10	{0,1,2,3,4,5,6,8}
15	1111	reserved	reserved

Table 2

srs-SubframeConfig	Bit information	T_SFC (subframes)	Δ_SFC (subframes)
0	0000	5	{1}
1	0001	5	{1, 2}
2	0010	5	{1, 3}
3	0011	5	{1, 4}
4	0100	5	{1, 2, 3}
5	0101	5	{1, 2, 4}
6	0110	5	{1, 3, 4}
7	0111	5	{1, 2, 3, 4}
8	1000	10	{1, 2, 6}
9	1001	10	{1, 3, 6}
10	1010	10	{1, 6, 7}
11	1011	10	{1, 2, 6, 8}
12	1100	10	{1, 3, 6, 9}
13	1101	10	{1, 4, 6, 7}
14	1110	reserved	reserved
15	1111	reserved	reserved

With reference to Tables 1 and 2, if srs-SubframeConfig is 13 (bit information = 1101), T_SFC is 10 in the frame structure defined for FDD and a related transmission offset group is 0, 1, 2, 3, 4, 6, 8. On the other hand, in the frame structure defined for TDD, T_SFC is 10 and a related transmission offset group is 1, 4, 6, 7. As stated above, even if the same srs-SubframeConfig is used, cell-specific parameters can be varied according to the frame structure employed.

If the UE transmits a signal to a first and a second secondary serving cell at the same time, the base station receives the signal of the first secondary serving cell later than the signal of the second secondary serving cell by T_d due to a timing difference. Therefore, the UE has to transmit the signal of the first secondary serving cell earlier by T_d to compensate the timing difference. As stated above, advancing or backing the uplink transmission is called timing alignment (TA).

Since frequency characteristics or transmission paths actually do not change in one frequency band, a timing difference is small even if aggregation within the band is carried out. However, since frequency characteristics and transmission paths vary for individual frequency bands, a timing difference may be developed if aggregation among the bands is carried out.

For example, in case carrier aggregation is carried out between the first and the second secondary serving cell (namely, aggregation among bands), the SRS in the first secondary serving cell is transmitted at a timing different from that for the SRS of the second secondary serving cell. In other words, the SRS of the first secondary serving cell can be transmitted simultaneously with the PUSCH or PUCCH of the second secondary serving cell; and the PUSCH or PUCCH of the first secondary serving cell can be transmitted simultaneously with the SRS of the second secondary serving cell.

Meanwhile, the timing advance command (TAC) field of an MAC message indicates the timing alignment value for each timing alignment group. The TAC field indicates a timing alignment value intended for adjusting an uplink timing to be the same for the whole serving cells within a timing alignment group. The MAC message may correspond to a random access response message used for a random access procedure.

For example, to obtain a timing alignment value about a secondary serving cell, the UE receives a PDCCH order from the base station and starts a random access procedure in response to the order. The UE can obtain a timing alignment value about a secondary serving cell by using the random access procedure. While carrying out the random access procedure, the UE generates a random access preamble. And the UE maps the generated random access preamble to the PRACH and transmits the mapped preamble to the base station.

FIG. 4 illustrates the structure of a PRACH to which the present invention is applied.

With reference to FIG. 4, the PRACH 800 is defined by one SC-FDMA symbol structure. The bandwidth of a subcarrier constituting the PRACH is 12 times larger than that of a subcarrier in a subframe structure. Therefore, the PRACH symbol except for the cyclic prefix (CP) 810 occupies a time interval 12 times larger than that occupied by SC-FDMA symbol except for the CP 810 in a general subframe structure.

T_CP, a parameter representing an interval of CP 810 of the PRACH symbol and T_SEQ, a parameter representing a sequence interval 820 can be configured differently according to individual formats as shown in Table 3. In Table 3, T_S represents a sampling time.

Table 3

Preamble format	T_CP	T_SEQ
0	3168·T_S	24576·T _S
1	21024·T_S	24576·T _S
2	6240·T _S	2·24576·T _S
3	21024·T _S	2·24576·T_S
4	448·T_S	4096·T_S

With reference to Table 3, the number of subframes occupied by the PRACH according to each preamble format can be defined variably as shown in FIG. 5. For example, in the case of preamble format 0, the sum of the CP and the sequence is smaller than a subframe and provides the smallest maximum cell size (two times the radius) for which a propagation delay can be taken into account. On the other hand, in the case of

preamble format

1, 2, 3, the sum of the CP and the sequence is larger than a subframe and preamble format 3 is defined for three subframes and provides the largest maximum cell size for which a propagation delay can be taken into account, amounting to a radius of 100 km.

Meanwhile, Table 4 illustrates a random access configuration for the preamble formats 0 to 3 of Table 3 from a frame structure defined for the FDD.

Table 4

PRACH Configuration Index	Preamble Format	System Frame No.	Subframe No.	PRACH Configuration Index	Preamble Format	System Frame No.	Subframe No.
0	0	Even	1	32	2	Even	1
1	0	Even	4	33	2	Even	4
2	0	Even	7	34	2	Even	7
3	0	Any	1	35	2	Any	1
4	0	Any	4	36	2	Any	4
5	0	Any	7	37	2	Any	7
6	0	Any	1, 6	38	2	Any	1, 6
7	0	Any	2 ,7	39	2	Any	2 ,7
8	0	Any	3, 8	40	2	Any	3, 8
9	0	Any	1, 4, 7	41	2	Any	1, 4, 7
10	0	Any	2, 5, 8	42	2	Any	2, 5, 8
11	0	Any	3, 6, 9	43	2	Any	3, 6, 9
12	0	Any	0, 2, 4, 6, 8	44	2	Any	0, 2, 4, 6, 8
13	0	Any	1, 3, 5, 7, 9	45	2	Any	1, 3, 5, 7, 9
14	0	Any	0, 1, 2, 3, 4, 5, 6, 7, 8, 9	46	N/A	N/A	N/A
15	0	Even	9	47	2	Even	9
16	1	Even	1	48	3	Even	1
17	1	Even	4	49	3	Even	4
18	1	Even	7	50	3	Even	7
19	1	Any	1	51	3	Any	1
20	1	Any	4	52	3	Any	4
21	1	Any	7	53	3	Any	7
22	1	Any	1, 6	54	3	Any	1, 6
23	1	Any	2 ,7	55	3	Any	2 ,7
24	1	Any	3, 8	56	3	Any	3, 8
25	1	Any	1, 4, 7	57	3	Any	1, 4, 7
26	1	Any	2, 5, 8	58	3	Any	2, 5, 8
27	1	Any	3, 6, 9	59	3	Any	3, 6, 9
28	1	Any	0, 2, 4, 6, 8	60	N/A	N/A	N/A
29	1	Any	1, 3, 5, 7, 9	61	N/A	N/A	N/A
30	N/A	N/A	N/A	62	N/A	N/A	N/A
31	1	Even	9	63	3	Even	9

In the time domain, the unit for uplink or downlink transmission is called a transmission time interval (TTI), which may correspond to the subframe. Therefore, parallel transmission of various signals indicates transmission of the signals to serving cells different from each other within the same subframe. For example, if a first uplink signal is transmitted to a first serving cell in a first subframe and a second uplink signal is transmitted to a second serving cell in the first subframe, it is said that the first and the second uplink signal are transmitted in a parallel fashion.

In what follows, described is an example where a plurality of uplink channels or uplink signals are transmitted to a plurality of serving cells in a parallel fashion. In one example, the PUCCH is transmitted to a first serving cell and the PRACH is transmitted to a second serving cell in a parallel fashion within the same subframe. In another example, the PUSCH can be transmitted to the first serving cell and the PRACH can be transmitted to the second serving cell in a parallel fashion within the same subframe. In a yet another example, the SRS can be transmitted to the first serving cell and the PRACH can be transmitted to the second serving cell within the same subframe.

Depending on communication systems, such parallel transmission can be either prohibited or allowed. In case parallel transmission is allowed, it suffices to apply power scaling to uplink signals of individual serving cells and transmit the scaled uplink signals. In case parallel transmission is not allowed, however, only the uplink signals selected are transmitted. Prohibition of parallel transmission does not necessarily imply the prohibition of simultaneous transmission. Simultaneous transmission is different from parallel transmission in that different uplink signals are transmitted at physically the same time. In other words, parallel transmission does not necessarily imply simultaneous transmission. For example, even if a plurality of uplink signals are transmitted in a parallel fashion within the same uplink subframe, propagation delays for the respective uplink signals can differ from each other, which in fact makes a plurality of uplink signals transmitted at different timings from each other. Prohibiting parallel transmission even for such a situation is a waste of resources and may lead to degradation of system performance.

FIG. 6 illustrates a transmission timing of serving cells according to one embodiment of the present invention. FIG. 6 is one example of parallel transmission of the SRS and PRACH.

With reference to FIG. 6, the UE transmits the SRS 1010 through an uplink subframe 1005 of a primary serving cell. The SRS 1010 can be transmitted through ratio aggregation in the last SC-FDMA symbol of the uplink subframe 1005 of the primary serving cell. And the UE transmits the PRACH 1022 through the uplink subframe 1020 of a secondary serving cell. The SRS 1010 and the PRACH 1022 are transmitted through the uplink subframe of the same index, which corresponds to parallel transmission. SRSs can be divided into two types: aperiodic SRSs and periodic SRSs. In particular, if an aperiodic SRS and the PRACH are to be transmitted in a parallel fashion, conditions should be met before, where the UE triggers aperiodic SRS transmission for a primary serving cell and receives a PDCCH order about a secondary serving cell from the base station.

Meanwhile, a downlink subframe 1000 of a primary serving cell, a uplink subframe 1010 of the primary serving cell, a downlink subframe 1015 of a secondary serving cell, and an uplink subframe 1020 of the secondary serving cell have transmission or reception timings different from each other. This is because the primary and the secondary serving cell generate a propagation delay (PD) with respect to the base station due to frequency characteristics or a transmission path. Due to the propagation delay, from the UE’s standpoint, the downlink subframe 1000 of the primary serving cell is delayed from a reference time by PD1. Therefore, the UE has to transmit the uplink subframe 1005 of the primary serving cell to the base station early by a timing alignment value NTA1 than the time point at which the downlink subframe 1000 of the primary serving cell begins. By doing so, the base station can receive the uplink subframe 1005 of the primary serving cell at the reference time.

The downlink subframe 1015 of a secondary serving cell for the UE is delayed by PD2 with respect to the reference time. Therefore, the UE has to transmit the uplink subframe 1020 of the secondary serving cell to the base station early by a timing alignment value NTA2 than the time point at which the downlink subframe 1015 of the secondary serving cell begins. By doing so, the base station can receive the uplink subframe 1020 of the secondary serving cell at the uplink reference time required. Here, the reference time can be determined differently by the base station for downlink and uplink transmission in each serving cell. The reference time of FIG. 6 corresponds to the case where a transmission reference time of the downlink signal transmitted by the base station is the same as a reference time of receiving the uplink signal anticipated by the base station. In general, the downlink transmission reference time of each serving cell may show a deviation ranging from 0 to 1.3μs.

The uplink subframe 1020 for transmitting the PRACH of a secondary serving cell further includes a blank interval 1021 and a guard time (GT) 1023 in addition to the PRACH interval 1022 consisting of the CP and a sequence. The blank interval 1021 is generated by the downlink propagation delay PD2 of the secondary serving cell. The start time of the blank interval 1021 is the same as the time at which the uplink transmission begins when the secondary serving cell obtains the NTA2 value while the end time of the blank interval 1021 corresponds to the time where NTA = 0, namely, the start time of the downlink subframe 1015 of the secondary serving cell. Therefore, if the transmission reference time of the downlink signal transmitted by the base station is the same as the reference time of receiving the uplink signal anticipated by the base station, the blank interval 1021 has twice the downlink propagation delay value of the corresponding secondary serving cell. The interval including the blank interval 1021 and the GT 1023 is defined as the GT interval for each format as shown in the following table.

Table 5

Format	GT time length (μs unit)
0(SFN=1)	96.88
1(SFN=2)	515.63
2(SFN=2)	196.88
3(SFN=3)	715.63

With reference to Table 5, since one SC-FDMA symbol interval (with respect to a normal CP) is approximately 71.44μs, the SC-FDMA symbol interval may overlap with the GT interval for each format.

Although it is parallel transmission, because of the propagation delay, transmission of the SRS 1010 and the PRACH 1022 is not simultaneous transmission performed at the same time. This is because if transmission of the PRACH 1022 and the SRS 1010 is described with respect to a break point, transmission of the PRACH 1022 is completed before the break point whereas transmission of the SRS 1010 is carried out after the break point. Rather, the SRS 1010 of the primary serving cell overlaps with the GT 1023 of the secondary serving cell instead of the PRACH 1022 of the secondary serving cell; in this case, transmission of the SRS 1010 does not run into a problem. Instead of prohibiting transmission of the SRS 1010 because the UE carries out parallel transmission, if it is checked whether the UE is capable of simultaneous transmission and thus a choice can be made afterwards to carry out transmission of the SRS 1010, system performance can be improved.

As one example, to remove a timing gap between parallel transmission and simultaneous transmission of the SRS and PRACH, the base station may carry out parallel transmission or simultaneous transmission by using its own scheduling. However, since there can be a variety of operating scenarios for transmission of the SRS and PRACH, scheduling complexity of the base station may increase. For example, a situation where the base station has to receive an aperiodic SRS may include the following cases: i) a case where uplink frequency channel gain for each antenna or for the whole antennas has to be measured, ii) a case where a reference value for tracking uplink synchronization of each serving cell (for example, the primary serving cell) needs to be obtained, and iii) a case where it is determined that an SRS operation is needed for the UE incapable of periodic SRS resource assignment.

Meanwhile, a situation where the base station has to receive the PRACH includes the following cases: i) a case where the base station tries to use resources of an uplink secondary serving cell and ii) a case where the base station tries to obtain or update the timing alignment value of an sTAG to which a secondary serving cell defining (comprising) the PUCCH belongs.

As another example, to remove a timing gap between parallel transmission and simultaneous transmission of the SRS and PRACH, the UE may take the lead in parallel or simultaneous transmission. In other words, the UE can choose parallel transmission of the SRS and PRACH or transmission of either of the SRS and PRACH, which indicates that parallel transmission or simultaneous transmission can be changed depending on the implementation by the UE. For example, in case the UE receives a triggering indicator of an aperiodic SRS about the primary serving cell and a PDCCH order about the secondary serving cell simultaneously, the UE carries out a simultaneous transmission check operation based on the received indicator and order. And if it is determined that the PRACH transmission and the periodic SRS transmission in the secondary serving cell are not simultaneous transmission, the UE can transmit both of the SRS and PRACH.

FIG. 7 is a flow diagram illustrating a transmission procedure of an uplink signal of a user equipment according to one example of the present invention.

With reference to FIG. 7, the UE receives SRS configuration information and PRACH configuration information from the base station S1100. The SRS configuration information includes various fields required for transmission of the SRS as shown in Table 6.

Table 6

SRS information element	No. of Bits	Description
SRS activation
	1	Interpretation of DCI format
Transmission bandwidth
	2	4 SRS bands for each operating bandwidth
Frequency position
	3 or 5	Start position of bandwidth(3 bits for the bandwidth smaller than 5MHz)
Transmission comb	1	Two combs
SRS cyclic shift (CS)	3	8 CS
SRS configuration index I_SRS	9	Configuration of subframe assigned for SRS transmission
Duration
	0	Time for single transmission or duration equivalent thereto
SRS bandwidth configuration	0	Time for single transmission or already known by SIB
CRC (UE ID)	16	Masked by UE ID within CRC
Total sum	35 or 37

With reference to Table 6, the SRS activation field provides 1-bit information and indicates whether the corresponding DCI is a format related to transmission of an aperiodic SRS. The frequency position field is a parameter used for determining the start position of bandwidth for uplink transmission related to the aperiodic SRS. The transmission comb field is a parameter defining a UpPTS interval which belongs to a special subframe in a TDD system. The SRS configuration index field is a parameter used for determining the position and offset of a subframe through which the aperiodic SRS is transmitted. The cyclic shift field is a parameter used for generating a sequence for transmission of the aperiodic SRS. The amount of information of a new field is limited by the range expressible by a resource indicator value of a second indicator range.

Here, it is assumed that the SRS configuration information and the PRACH configuration information are received simultaneously but the assumption is only an example and it is still possible that either of the SRS and PRACH configuration information is received first and the other one is received afterwards.

The UE determines a subframe through which the SRS is transmitted in a first serving cell S1105. The first serving cell can be the primary serving cell. As one example, if the SRS is a periodic SRS, a subframe through which the periodic SRS is transmitted can be determined based on the SRS configuration information. As another example, if the SRS is an aperiodic SRS, a subframe through which the aperiodic SRS is transmitted can be determined when transmission of the SRS is triggered based on the SRS configuration information. This is because if transmission of the aperiodic SRS is triggered, the transmission of the aperiodic SRS is expected to be performed at the n-th subframe from the time point (subframe) at which the SRS transmission is triggered. An aperiodic SRS is triggered when the UE receives an aperiodic SRS triggering indicator from the base station. For this purpose, although not shown in the figure, a step for the UE to receive the aperiodic SRS triggering indicator from the base station can be further included.

The UE receives from the base station a PDCCH order related to the PRACH in a second serving cell S1110. In case the second serving cell is the secondary serving cell, the UE receives the PDCCH order from the base station. From the PDCCH order, the UE can figure out the PRACH parameter, for example, the parameter of the random access preamble and time/frequency resource information.

The PDCCH order is a physical layer signaling control information (for example, format 1A downlink control information (DCI)) and can be mapped to the PDCCH and thus transmitted to the UE. The format 1A DCI can be defined as shown in the following table.

Table 7

- Carrier indicator field (CIF) - 0 or 3 bits.

- Flag for identifying a format 0/1A - 1 bit (indicates format 0 in the case of 0 and format 1A in the case of 1)

In case the format 1A CRC is scrambled by C-RNTI and the remaining fields are configured as follows, the format 1A is used for carrying out a random access procedure initiated by the PDCCH order.

- The following -

- Localized/Distributed VRB assignment flag - 1 bit. Set to 0

- Resource block assignment -

bits. All the bits are set to 1

- Preamble Index - 6 bits

- PRACH Mask Index - 4 bits

- All the remaining bits of the format 1A used for simplified scheduling assignment of one PDSCH codeword are set to 0.

With reference to Table 7, according to the value of the preamble index, the random access procedure due to the order of the base station can be a contention based or non-contention based procedure. As one example, if 6 bits of the preamble index information are all set to ‘0’, the UE selects an arbitrary preamble and also sets the PRACH mask index value to ‘0’ and carries out a contention based random access procedure. The PDCCH order can be transmitted in the form of an MAC control element (CE) as well as physical signaling as shown in Table 7; the PDCCH order can also be transmitted together with the periodic SRS configuration information within an RRC reconfiguration message.

The UE determines whether the SRS transmission and the PRACH transmission are parallel transmission S1115. As one example, determination of parallel transmission can be made by checking whether the uplink subframe of the first serving cell through which the SRS is transmitted is the same with the uplink subframe of the second serving cell through which the PRACH is transmitted. As another example, if the length of the random access preamble occupies two or more subframes as in the

format

1, 2, or 3 of FIG. 5, determination of parallel transmission can be made by checking whether the position of a subframe of the last preamble is the same as the position of a subframe for which SRS transmission has been ordered. It is still possible, however that the SRS transmission overlaps with the PRACH transmission, namely, parallel transmission is carried out even though the position of the subframe through which the SRS is transmitted is not the same as the position of the last subframe for the PRACH transmission. This is because the number of subframes occupied by the PRACH can be 2 or 3 according to the PRACH format. At this time, the UE omits the simultaneous transmission determination step S1120 and directly carries out a competition resolving procedure S1130.

The UE determines whether the SRS transmission and the PRACH transmission are carried out simultaneously if the SRS transmission and the PRACH transmission are parallel transmission S1120.

As one example, with respect to FIG. 6, determination of simultaneous transmission can be implemented by checking whether the following mathematical equation is satisfied, which incorporates GT, SC-FDMA symbol length, propagation delay (PD), and timing alignment value N_TA as parameters.

MathFigure 3

With reference to Math Figure 3, GT_RE represents the remaining GT except for the blank interval from a GT defined for each format and L_SYM represents the length of 1 SC-FDMA (or OFDM) symbol including the CP required at the time of SRS transmission. N_TA1 is a timing alignment value of the first serving cell and PD1 is a downlink propagation delay value of the first serving cell, and PD2 is a downlink propagation delay value of the second serving cell. If Math Figure 3 is satisfied, the UE determines that it is not simultaneous transmission whereas if Math Figure 3 is not satisfied, the UE determines it as simultaneous transmission.

In case a current situation does not correspond to simultaneous transmission according to a determination result, the UE transmits the SRS to the first serving cell and the PRACH to the second serving cell in the same uplink subframe S1125. In other words, the UE carries out parallel transmission of the SRS and PRACH.

On the other hand, in case it corresponds to simultaneous transmission after the determination result, the UE carries out the competition resolving procedure S1130. The competition resolving procedure carries out the operation of selectively transmitting either of the SRS and the PRACH. Particularly, the competition resolving procedure may be carried out when the sum of transmission powers of SRS and PRACH exceeds an uplink maximum transmission power of the UE. As one example, the competition resolving procedure selects and transmits either the SRS or the PRACH according to a priority order. In one respect, the PRACH takes precedence over a periodic SRS. Therefore, if the SRS corresponds to a periodic SRS, the UE ignores the periodic SRS and transmits only the PRACH to the second serving cell. In another respect, an aperiodic SRS takes precedence over the PRACH. Therefore, if the SRS corresponds to an aperiodic SRS, the UE ignores the PRACH or defers it to the next subframe which is capable of PRACH transmission and transmits only a periodic SRS to the first serving cell. Deferring the PRACH transmission is possible because although resources for transmission of the aperiodic SRS are not reserved for the corresponding UE, in the case of the secondary serving cell’s PRACH transmission, the random access preamble is reserved for the corresponding UE and thus cannot be used by other UEs. Therefore, in case the UE receives a particular PRACH mask index, the secondary serving cell’s PRACH transmission can be deferred by the UE to the next subframe capable of PRACH transmission.

As another example, the competition resolving procedure can drop or give up transmission of part of the SRS. For example, if part of the CP interval of the SRS overlaps the PRACH, the UE can drop the overlapping part of the CP interval. At this time, the CP interval which can be dropped may be limited to 1/2, 1/3, or 1/5 of the entire CP interval.

Back in the S1115 step, if it is found that the SRS and PRACH transmission do not correspond to parallel transmission after a checking result against parallel transmission at S1115 step, the UE transmits the SRS and PRACH through different subframes from each other S1135. As stated above, if there are chances that the preamble transmission required for the random access procedure in the secondary serving cell and the SRS transmission in the primary serving cell are carried out by parallel transmission in a wireless communication system operating a plurality of CCs, uplink transmission orders given to a plurality of serving cells by the base station can be reflected as possibly as can be without additional power consumption of the UE by preventing transmission of a particular uplink signal from being ignored only because parallel transmission is employed although it does not correspond to simultaneous transmission.

FIG. 8 is a flow diagram illustrating a transmission procedure of an uplink signal of a base station according to one example of the present invention.

With reference to FIG. 8, the base station checks triggering conditions S1200. The SRS triggering conditions describe conditions to be met when the base station has to receive an aperiodic SRS, including the following cases: i) a case where uplink frequency channel gain for each antenna or for the whole antennas has to be measured, ii) a case where a reference value for tracking uplink synchronization of each serving cell (for example, the primary serving cell) needs to be obtained, and iii) a case where it is determined that an SRS operation is needed for the UE incapable of periodic SRS resource assignment.

The base station checks the conditions based on which the PDCCH order is transmitted S1200. The conditions for transmitting the PDCCH order describe conditions to be met when the base station receives the PRACH from the UE, including the following cases: i) a case where the base station tries to use resources of an uplink secondary serving cell and ii) a case where the base station tries to obtain or update the timing alignment value of an sTAG to which a secondary serving cell defining (comprising) the PUCCH belongs.

If either of the SRS triggering conditions and the transmission conditions for the PDCCH order is met, the base station transmits either of the indicator and the order satisfying the conditions to the UE (for example, SRS triggering indicator or PDCCH order). Similarly, if the SRS triggering conditions and the transmission conditions for the PDCCH order are both satisfied, the base station transmits the SRS triggering indicator and the PDCCH order to the UE S1210.

At this time, the PDCCH order can be transmitted to the secondary serving cell. Also, if the SRS triggering indicator and the PDCCH order are all transmitted to the UE, the base station is supposed to receive the SRS according to the SRS triggering indicator and the PRACH according to the PDCCH order through different serving cells of the same subframe. Therefore, the UE has to choose whether transmit the SRS and the PRACH simultaneously or transmit either of the SRS and the PRACH.

The base station may receive from the UE either of the SRS and the PRACH chosen by the UE or receives the SRS and the PRACH in a parallel fashion S1220.

With reference to FIG. 9, the UE 1300 comprises a receiving unit 1305, a UE processor 1310, and a transmission unit 1320. The UE processor 1310 further comprises an uplink controller 1311 and a signal generating unit 1312.

The receiving unit 1305 receives from the base station SRS configuration information, PRACH configuration information, SRS triggering indicator, PDCCH order, timing alignment value, and so on. The SRS configuration information and the PRACH configuration information are an RRC message and the SRS configuration information includes the parameters of Table 6. The SRS triggering indicator is an indicator used for triggering transmission of an aperiodic SRS and may correspond to an MAC message or physical layer signaling. The PDCCH order is physical layer signaling and may correspond to the format 1A DCI and may be received being mapped to the PDCCH. The format 1A DCI can be defined as shown in Table 7. The timing alignment value can be specified by the timing advance command (TAC) field. The TAC field indicates a timing alignment value intended for adjusting an uplink timing to be the same for the whole serving cells within a timing alignment group. The MAC message may correspond to a random access response message used for a random access procedure. The timing alignment value is applied the same for the whole serving cells within one timing alignment group.

The uplink controller 1311 controls periodic or aperiodic transmission of the SRS based on the SRS configuration information; generates a random access preamble and Msg3 required for carrying out the random access procedure; determines parallel transmission and simultaneous transmission. In other words, the uplink controller 1311 determines whether the timing of SRS transmission on a first serving cell based on the SRS configuration information and the timing of PRACH transmission on a second serving cell determined by the PDCCH order. And the uplink controller 1311 carries out a competition resolving procedure.

For example, the uplink controller 1311 determines whether to carry out parallel transmission of the SRS and PRACH as in the S1115 step of FIG. 7 and if it is found from the determination result that parallel transmission of the SRS and PRACH is supposed to start, determines based on Math Figure 3 whether to start simultaneous transmission of the SRS and PRACH as in the S1120 step of FIG. 7. If Math Figure 3 is satisfied, the uplink controller 1311 determines that it is not simultaneous transmission and controls the transmission unit 1320 to transmit the SRS and PRACH in a parallel fashion. On the other hand, if Math Figure 3 is not satisfied, the uplink controller 1311 determines that it is simultaneous transmission. If it is found to be simultaneous transmission, the uplink controller 1311 carries out a competition resolving procedure such as the S1130 step of FIG. 7.

The competition resolving procedure is a procedure for carrying out operations of transmitting selectively one of the SRS and PRACH. As one example, the uplink controller 1311 can select the SRS or PRACH according to a priority order. In one respect, the PRACH takes precedence over a periodic SRS. Therefore, if the SRS corresponds to a periodic SRS, the uplink controller 1311 ignores the periodic SRS and selects only the PRACH. In another respect, an aperiodic SRS takes precedence over the PRACH. Therefore, if the SRS corresponds to an aperiodic SRS, the uplink controller 1311 either ignores the PRACH or defers it to the next subframe which is capable of PRACH transmission and selects only a periodic SRS.

As another example, the uplink controller 1311 can drop or give up transmission of part of the SRS. For example, if part of the CP interval of the SRS overlaps the PRACH, the uplink controller 1311 can drop the overlapping part of the CP interval. At this time, the CP interval which can be dropped may be limited to 1/2, 1/3, or 1/5 of the entire CP interval.

The signal generating unit 1312 can generate a periodic or an aperiodic SRS or PRACH.

The transmission unit 1320 either transmits the generated SRS or PRACH to the base station in a parallel fashion or transmits to the base station 1350 either of the SRS and PRACH selected by the uplink controller 1311. In the case of parallel transmission, the transmission unit 1320 transmits the SRS and PRACH through different serving cells of the same subframe.

The base station 1350 comprises a transmission unit 1355, a receiving unit 1360, and a base station processor 1370. Meanwhile, the base station processor 1370 comprises a control information generation unit 1371 and a scheduling unit 1372.

The transmission unit 1355 transmits to the UE SRS configuration information, PRACH configuration information, SRS triggering indicator, PDCCH order, timing alignment value, and so on.

The receiving unit 1360 may receive the SRS and PRACH from the UE 1300 in a parallel fashion or receive either one of the SRS and PRACH from the UE 1300.

The control information generation unit 1371 generates SRS configuration information, PRACH configuration information, SRS triggering indicator, PDCCH order, and timing alignment value.

The scheduling unit 1372 measures an uplink channel from the SRS received by the receiving unit 1360 and carries out scheduling about uplink transmission of a serving cell to which the SRS has been transmitted.

Various examples of logic blocks, modules, and circuits described in association with the embodiments of the present invention can be controlled by a general-purpose processor, digital signal processor (DSP), application-specific integrated circuit (ASIC), field programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or an arbitrary combination of things designed to carried out the functions described in this document. The methods or control steps of algorithms described in association with the embodiments of the present invention can be implemented directly in the form of hardware modules, in the form of software modules executed by a processor, or a combination thereof. In one or more embodiments of the present invention, the control functions described above can be implemented in the form of hardware, software, firmware modules, or an arbitrary combination of the above. If the functions are realized by software modules, the functions can be stored or transmitted in the form of one or more commands or program codes in a computer-readable medium.

Claims

A method for transmitting an uplink signal by a user equipment in a wireless communication system supporting multiple timing alignment (MTA), the method comprising:

receiving configuration information about a sounding reference signal (SRS) from a base station;

determining whether a transmission timing of a physical random access channel (PRACH) in a second serving cell is the same as transmission timing of the SRS configured according to the SRS configuration information in a first serving cell; and

in case transmission timing of the SRS is the same as transmission timing of the PRACH, transmitting to the base station only one of the SRS and the PRACH selected based on a priority.
The method of claim 1, wherein the priority is given to the PRACH over the SRS.
The method of claim 1, wherein transmission timing of the SRS in a first serving cell is aperiodic.
The method of claim 3, further comprising receiving from the base station an SRS triggering indicator which triggers transmission of the SRS.
The method of claim 1, wherein the first serving cell is a primary serving cell while the second serving cell is a secondary serving cell.
The method of claim 1, wherein transmission timing of the SRS in a first serving cell and transmission timing of the PRACH in a second serving cell are defined in units of sub-frame.
The method of claim 1, wherein whether transmission timing of the SRS in a first serving cell is the same as transmission timing of the PRACH in a second serving cell is determined based on guard period (GT) of the SRS; symbol length of SC-FDMA (single carrier-frequency division multiple access); and timing alignment values of the first and the second serving cell.
A user equipment transmitting an uplink signal in a wireless communication system supporting multiple timing alignment, the user equipment comprising:

a receiver receiving from the base station a PDCCH indicator indicating sounding reference signal (SRS) configuration information and a PDCCH indicator indicating the start of a random access procedure;

a controller determining whether transmission timing of the SRS based on the SRS configuration information is the same as transmission timing of a PRACH determined based on the PDCCH indicator in a second serving cell and if it is determined that transmission timing of the SRS is the same as transmission timing of the PRACH, selecting either of the SRS and the PRACH according to a priority order; and

a transmitter transmitting the selected signal to the base station.
The user equipment of claim 8, wherein the uplink controller selects the PRACH before the SRS.
The user equipment of claim 8, wherein transmission timing of the SRS in a first serving cell is aperiodic.
The user equipment of claim 10, wherein the receiver further comprises receiving from the base station an SRS triggering indicator which triggers transmission of the SRS.
The user equipment of claim 8, wherein the first serving cell is a primary serving cell while the second serving cell is a secondary serving cell.
The user equipment of claim 8, wherein transmission timing of the SRS in a first serving cell and transmission timing of the PRACH in a second serving cell are defined in units of sub-frame.
The user equipment of claim 8, wherein the uplink controller determines whether transmission timing of the SRS in a first serving cell is the same as transmission timing of the PRACH in a second serving cell based on guard period (GT) of the SRS; symbol length of SC-FDMA; and timing alignment values of the first and the second serving cell.
A method for receiving an uplink signal by a base station in a wireless communication system supporting multiple timing alignment, the method comprising:

transmitting a sounding reference signal (SRS) configuration information to a user equipment;

transmitting to the user equipment a PDCCH indicator indicating the start of a random access procedure; and

in case transmission timing of the SRS based on the SRS configuration information is the same as transmission timing of a PRACH determined based on the PDCCH indicator, transmitting to the user equipment only one of the SRS and the PRACH selected based on a priority.
The method of claim 15, wherein the priority is given to the PRACH over the SRS.
The method of claim 15, wherein transmission timing of the SRS in a first serving cell is aperiodic.
The method of claim 17, further comprising transmitting to the user equipment an SRS triggering indicator which triggers transmission of the SRS.
The method of claim 15, wherein the first serving cell is a primary serving cell while the second serving cell is a secondary serving cell.
The method of claim 15, wherein transmission timing of the SRS in a first serving cell and transmission timing of the PRACH in a second serving cell are defined in units of sub-frame.