WO2016122120A1 - Method and apparatus for performing random access by using multi-qos preambles in wireless communication system - Google Patents

Abstract

Provided are a method and an apparatus for performing random access by using multi-quality of service (QoS) preambles in a wireless communication system. An evolved NodeB (eNB) receives, from a first user equipment (UE), a first random access channel (RACH) preamble generated using a plurality of sequence combinations, and also receives a second RACH preamble from a second UE. The eNB transmits a random access response only to the first UE. The first RACH preamble can be a re-transmitted RACH preamble or an RACH preamble for a low delay request or an emergency service connection.

Description

Method and apparatus for performing random access using multi QOS preamble in wireless communication system

The present invention relates to wireless communications, and more particularly, to a method and apparatus for performing random access using a multi-QoS preamble in a wireless communication system.

3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology that enables high-speed packet communication. Many schemes have been proposed for the purposes of LTE, including reduced costs for users and suppliers, improved quality of service, and increased coverage and system capacity. 3GPP LTE is a higher layer requirement that requires reduced cost per bit, increased service availability, flexible frequency usage, simple structure, open interface and proper power consumption of the terminal.

A random access procedure may be performed in 3GPP LTE. The main uses of the random access procedure are uplink initial access and short message transmission. In WCDMA (Wideband Code Division Multiple Access), initial network access and short message transmission are achieved through a random access procedure. However, in 3GPP LTE, a short message is not transmitted through a random access procedure. In addition, in 3GPP LTE, a random access channel (RACH) for a random access procedure is transmitted separately from an uplink data transmission channel. More specifically, the random access procedure in 3GPP LTE may be performed in the following cases.

(1) When a user equipment (UE) in a radio resource control (RRC) connected state (RRC_CONNECTED) that is not uplink (UL) synchronized needs to transmit new UL data or control information (for example, For example, to report the event-triggered measurement

(2) When the UE of RRC_CONNECTED that is not UL synchronized receives new downlink (DL) data and needs to transmit corresponding ACK / NACK (acknowledgement / non-acknowledgement) accordingly in UL.

(3) When UE of RRC_CONNECTED hands over from the current serving cell to the target cell

(4) When timing advance is needed for UE positioning for positioning purposes in RRC_CONNECTED.

(5) When transitioning from RRC idle state (RRC_IDLE) to RRC_CONNECTED (e.g., initial connection or tracking area update)

(6) When recovering from a radio link failure

In general, a UE that fails to obtain UL synchronization or does not maintain UL synchronization acquires UL time synchronization using a random access procedure. When UL synchronization of the UE is obtained, the eNB (evolved NodeB) may schedule transmission resources maintained orthogonality. The UL transmission of the UE is possible only if the UL synchronization between the UE and the UE is established, and scheduling for data transmission may be received from the eNB. That is, through a random access procedure, the unsynchronized UE may perform radio access through a transmission scheme that is orthogonal or does not overlap as much as possible.

In general, the RACH preamble transmitted in the random access procedure to obtain UL synchronization is operated based on non-coherent detection. Accordingly, the eNB may recognize the RACH preamble transmitted simultaneously from a plurality of UEs at a specific time point as a collision. Meanwhile, a RACH preamble transmitted by a specific UE is detected by the eNB without collision according to a service type or emergency connection of the UE, and thus a random access procedure of the specific UE needs to be successfully performed. That is, an improvement of the random access procedure to prevent the collision of the RACH preamble is required.

An object of the present invention is to provide a method and apparatus for performing random access using a multiple quality of service (QoS) preamble in a wireless communication system. The present invention improves the structure of a random access channel (RAC) preamble of the existing random access procedure, and provides a method and apparatus for providing priority connection support in consideration of service type and emergency of a user equipment (UE). do. The present invention provides a method and apparatus for receiving a RACH preamble generated by using a combination of a plurality of sequences and preferentially transmitting a random access response to a UE that has transmitted the RACH preamble.

In one aspect, a method is provided for performing a random access procedure by an evolved NodeB (eNB) in a wireless communication system. The method receives a first random access channel (RACH) preamble generated from a combination of a plurality of sequences from a first user equipment (UE), receives a second RACH preamble from a second UE, and the first Sending a random access response only to the UE.

In another aspect, a method of performing a random access procedure by a user equipment (UE) in a wireless communication system is provided. The method includes transmitting a random access channel (RACH) preamble generated using a combination of a plurality of sequences to an eNB, and receiving a random access response from the eNB.

It is possible to give a random access response preferentially to a specific UE without redesigning the existing random access procedure.

1 illustrates a cellular system.

2 shows a structure of a radio frame in 3GPP LTE.

3 shows a resource grid for one DL slot.

4 shows a structure of a DL subframe.

5 shows a structure of an UL subframe.

6 illustrates a contention based random access procedure.

7 shows an example of a structure of a RACH preamble.

8 shows an example of a CAZAC sequence set.

9 shows another example of a CAZAC sequence set.

10 shows an example of an output of a receiver that receives a sequence in a CAZAC sequence set.

11 shows an example of an asymmetric CAZAC sequence set.

12 shows another example of an asymmetric CAZAC sequence set.

13 shows an example in which a RACH preamble collides in a contention based random access procedure.

14 shows a time-frequency resource at which a UE transmits a RACH preamble.

15 shows an example of collision of a RACH preamble.

16 shows an example of detecting a plurality of RACH preambles transmitted by a plurality of UEs in the same PRACH resource.

17 shows an example of transmitting a random access response when a plurality of RACH preambles are detected in the same PRACH resource.

18 shows an example of transmitting a random access response when a plurality of RACH preambles are detected in a TDD frame.

19 illustrates an example of a RACH preamble sequence using characteristics of a multi-QoS sequence according to an embodiment of the present invention.

20 illustrates detection of a RACH preamble sequence using characteristics of a multi-QoS sequence according to an embodiment of the present invention.

21 shows an example of a random access procedure using a RACH preamble generated based on a combination sequence according to an embodiment of the present invention.

22 shows an example of detection of a RACH preamble according to an embodiment of the present invention.

23 illustrates a method of performing a random access procedure by an eNB according to an embodiment of the present invention.

24 illustrates a method of performing a random access procedure by a UE according to an embodiment of the present invention.

25 is a block diagram of a wireless communication system in which an embodiment of the present invention is implemented.

The following techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and the like. It can be used in various wireless communication systems. CDMA may be implemented by a radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as global system for mobile communications (GSM) / general packet radio service (GPRS) / enhanced data rates for GSM evolution (EDGE). OFDMA may be implemented by wireless technologies such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), and the like. IEEE 802.16m is an evolution of IEEE 802.16e and provides backward compatibility with systems based on IEEE 802.16e. UTRA is part of a universal mobile telecommunications system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is part of evolved UMTS (E-UMTS) using evolved-UMTS terrestrial radio access (E-UTRA), which employs OFDMA in downlink and SC in uplink -FDMA is adopted. LTE-A (advanced) is the evolution of 3GPP LTE.

For clarity, the following description focuses on LTE-A, but the technical features of the present invention are not limited thereto.

1 illustrates a cellular system. Referring to FIG. 1, cellular system 10 includes at least one base station (BS) 11. BS 11 provides communication services for specific geographic regions (generally called cells) 15a, 15b, 15c. The cell can in turn be divided into a number of regions (called sectors). A user equipment (UE 12) may be fixed or mobile, and may have a mobile station (MS), a mobile terminal (MS), a user terminal (UT), a subscriber station (SS), a wireless device, a PDA, and the like. (personal digital assistant), wireless modem (wireless modem), a handheld device (handheld device) may be called other terms. BS 11 generally refers to a fixed point of communication with UE 12 and may be referred to in other terms, such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, and the like.

The UE typically belongs to one cell, and the cell to which the UE belongs is called a serving cell. An eNB that provides a communication service for a serving cell is called a serving eNB. The cellular system includes another cell adjacent to the serving cell. Another cell adjacent to the serving cell is called a neighbor cell. An eNB that provides a communication service for a neighbor cell is called a neighbor eNB. The serving cell and the neighbor cell are determined relatively based on the UE.

This technique can be used for downlink (DL) or uplink (UL). In general, DL means communication from eNB 11 to UE 12, and UL means communication from UE 12 to eNB 11. In the DL, the transmitter may be part of the eNB 11 and the receiver may be part of the UE 12. In the UL, the transmitter may be part of the UE 12 and the receiver may be part of the eNB 11.

The wireless communication system may be any one of a multiple-input multiple-output (MIMO) system, a multiple-input single-output (MIS) system, a single-input single-output (SISO) system, and a single-input multiple-output (SIMO) system. Can be. The MIMO system uses multiple transmit antennas and multiple receive antennas. The MISO system uses multiple transmit antennas and one receive antenna. The SISO system uses one transmit antenna and one receive antenna. The SIMO system uses one transmit antenna and multiple receive antennas. Hereinafter, the transmit antenna means a physical or logical antenna used to transmit one signal or stream, and the receive antenna means a physical or logical antenna used to receive one signal or stream.

2 shows a structure of a radio frame in 3GPP LTE. 2, a radio frame includes 10 subframes. The subframe includes two slots in the time domain. The time taken to transmit one subframe is defined as a transmission time interval (TTI). For example, the length of one subframe may be 1 ms, and the length of one slot may be 0.5 ms. One slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in the time domain. Since 3GPP LTE uses OFDMA in the DL, the OFDM symbol is for representing one symbol period. The OFDM symbol may be called another name according to the multiple access scheme. For example, when SC-FDMA is used as a UL multiple access scheme, it may be referred to as an SC-FDMA symbol. A resource block (RB) includes a plurality of consecutive subcarriers in one slot in resource allocation units. The structure of the radio frame is merely an example. Accordingly, the number of subframes included in the radio frame, the number of slots included in the subframe, or the number of OFDM symbols included in the slot may be variously changed.

Wireless communication systems can be largely divided into frequency division duplex (FDD) and time division duplex (TDD). According to the FDD scheme, UL transmission and DL transmission are performed while occupying different frequency bands. According to the TDD scheme, the UL transmission and the DL transmission are performed at different times while occupying the same frequency band. The channel response of the TDD scheme is substantially reciprocal. This means that the DL channel response and the UL channel response are almost the same in a given frequency domain. Therefore, in a TDD based wireless communication system, the DL channel response has an advantage that can be obtained from the UL channel response. In the TDD scheme, since the UL transmission and the DL transmission are time-divided over the entire frequency band, the DL transmission by the eNB and the UL transmission by the UE cannot be performed at the same time. In a TDD system in which UL transmission and DL transmission are divided in subframe units, UL transmission and DL transmission are performed in different subframes.

3 shows a resource grid for one DL slot. Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols in the time domain. Here, one DL slot includes 7 OFDM symbols and one RB includes 12 subcarriers in the frequency domain, but is not limited thereto. Each element on the resource grid is called a resource element. One RB contains 7x12 resource elements. The number N ^DL of resource blocks included in the DL slot depends on the DL transmission bandwidth. The structure of the UL slot may also be the same as the structure of the DL slot. The number of OFDM symbols and the number of subcarriers can be variously changed according to the length of the cyclic prefix (CP), the frequency interval, and the like. For example, the number of OFDM symbols is 7 for a normal CP and the number of OFDM symbols is 6 for an extended CP. The number of subcarriers in one OFDM symbol may be selected and used among 128, 256, 512, 1024, 1536 and 2048.

4 shows a structure of a DL subframe. Referring to FIG. 4, a maximum of 3 OFDM symbols of a first slot in a subframe is a control region to which a control channel is allocated. The remaining OFDM symbols correspond to data regions to which a physical downlink shared channel (PDSCH) is allocated. Examples of DL control channels used in 3GPP LTE may include a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), a physical HARQ indicator channel (PHICH), and the like. The PCFICH is transmitted in the first OFDM symbol of a subframe and carries information related to the number of OFDM symbols used for transmission of a control channel in the subframe. The PHICH is a response to the UL transmission and carries a hybrid automatic repeat request (HARQ) acknowledgment / non-acknowledgement (ACK) signal. Control information transmitted through the PDCCH is downlink control information (DCI). The DCI includes UL or DL scheduling information or a UL transmit power control (TPC) command for any UE group.

The PDCCH includes a resource allocation and transmission format of a downlink-shared channel (DL-SCH), resource allocation information of an uplink shared channel (UL-SCH), paging information on a paging channel, system information on a DL-SCH, and a random transmission on a PDSCH. Resource allocation of higher layer control messages such as access responses, aggregation of TPC commands for individual UEs in any UE group, activation of voice over internet protocol (VoIP), and the like. A plurality of PDCCHs may be transmitted in the control region. The UE may monitor the plurality of PDCCHs. The PDCCH is transmitted on an aggregation of one or several consecutive control channel elements (CCEs). CCE is a logical allocation unit used to provide a PDCCH having a coding rate according to a state of a radio channel. The CCE corresponds to a plurality of resource element groups (REGs).

The format of the PDCCH and the number of possible bits of the PDCCH are determined by the correlation between the number of CCEs and the coding rate provided by the CCEs. The eNB determines the PDCCH format according to the DCI to be transmitted to the UE, and attaches a cyclic redundancy check (CRC) to the control information. The CRC is scrambled with a radio network temporary identifier (RNTI) according to the owner or purpose of the PDCCH. If the PDCCH is for a specific UE, a unique identifier of the UE, for example, a cell-RNTI (C-RNTI) may be scrambled in the CRC. Alternatively, if the PDCCH is for a paging message, a paging indication identifier, eg, p-RNTI (P-RNTI), may be scrambled in the CRC. If the PDCCH is for system information, the system information-RNTI (SI-RNTI) may be scrambled in the CRC. A random access-RNTI (RA-RNTI) may be scrambled in the CRC to indicate a random access response that is a response to the transmission of the random access preamble of the UE.

5 shows a structure of an UL subframe. Referring to FIG. 5, a UL subframe may be divided into a control region and a data region in the frequency domain. The control region is allocated a physical uplink control channel (PUCCH) for transmitting UL control information. The data area is allocated a physical uplink shared channel (PUSCH) for transmitting user data. If indicated in the higher layer, the UE may support simultaneous transmission of PUSCH and PUCCH. PUCCH for one UE is allocated to an RB pair in a subframe. Resource blocks belonging to the RB pair occupy different subcarriers in each of the first slot and the second slot. This is called that the RB pair allocated to the PUCCH is frequency-hopped at the slot boundary. The UE may obtain a frequency diversity gain by transmitting UL control information through different subcarriers over time.

The UL control information transmitted on the PUCCH may include HARQ ACK / NACK, a channel quality indicator (CQI) indicating a DL channel state, a scheduling request (SR) that is a UL radio resource allocation request, and the like. PUSCH is mapped to UL-SCH, which is a transport channel. The UL data transmitted on the PUSCH may be a transport block that is a data block for the UL-SCH transmitted during TTI. The transport block may be user information. Alternatively, the UL data may be multiplexed data. The multiplexed data may be data obtained by multiplexing a transport block for UL-SCH and control information. For example, the control information multiplexed on the data may include a CQI, a precoding matrix indicator (PMI), a HARQ, a rank indicator (RI), and the like. Alternatively, the UL data may be composed of control information only.

The random access procedure may be divided into a contention-based random access procedure and a contention-free random access procedure. First, in the contention-based random access procedure, different UEs are allowed to simultaneously access the eNB using the same RACH preamble. Thus, competition may occur. To handle this competition, additional competition resolution steps are needed.

6 illustrates a contention based random access procedure.

In step S60, the UE sends a RACH preamble to the eNB. The RACH preamble may be referred to as "message 1". The RACH preamble may include a RA-RNTI. RA-RNTI may be determined as (1 + t_id + 10 * f_id). t _{_id} is the index of the first subframe of a specific PRACH (physical random access channel) ( 0≤t_id <10), f_id is an index of a specific PRACH in the, the sub-frame according to the ascending order in the frequency domain (0 ≦ f_id <6). The eNB can obtain the RA-RNTI by decoding the RACH preamble.

In step S61, the eNB sends a random access response to the UE. The random access response may be called "message 2". The random access response may include RA-RNTI, TA, temporary C-RNTI and resource block allocation (ie, UL grant for L2 / L3 message) obtained by the eNB decoding the RACH preamble. The UE may decode the random access response to obtain resource block allocation and a modulation and coding scheme (MCS) configuration. The eNB may be configured to receive the RRC connection request message via DCI format 0.

In step S62, the UE sends an L2 / L3 message, that is, an RRC connection request message to the eNB. The RRC connection request message may be called "message 3". The UE may send the RRC Connection Request message using the temporary C-RNTI obtained from the random access response.

In step S63, when the eNB successfully decoded the RRC connection request message sent by the UE, and transmits the HARQ ACK to the UE. The UE can know that the random access procedure is successful. This process is called competitive resolution. In more detail, the eNB sends an RRC connection setup message to the UE using the temporary C-RNTI in response to the RRC connection request message. The RRC connection establishment message may be called "message 4". The RRC connection establishment message may include a C-RNTI. From this time, the UE and the eNB may exchange messages using the C-RNTI.

If the UE has not received the HARQ ACK, it may return to step S60 again to transmit the RACH preamble to the eNB.

In the non-competition based random access procedure, contention is not allowed for timing limitation. The eNB may indicate which RACH preamble each UE will transmit. For this purpose, the UE must be in the connected state (RRC_CONNECTED) before the random access procedure. For example, a non-competition based random access procedure may be performed during handover. In a contention free random access procedure, the eNB first sends a RACH preamble assignment to the UE. The UE transmits to the eNB a RACH preamble including an indication of the RA-RNTI and L2 / L3 message size according to the received RACH preamble allocation. Receiving the RACH preamble, the eNB sends a random access response to the UE that includes a timing advance (TA), C-RNTI, and UL grant for L2 / L3 messages. Accordingly, the non-competition based random access procedure may be completed.

7 shows an example of a structure of a RACH preamble. Referring to FIG. 7, the RACH preamble includes a CP, a sequence, and a guard time (GT). CP absorbs maximum channel delay spread and round trip time (RTT), while GT absorbs RTT. The CP is generated by inserting the second half of the existing OFDM symbol into the CP section of the RACH preamble. Through this, periodic correlation may be possible in the eNB receiving the RACH preamble. The UE may transmit the RACH preamble on the assumption that it is synchronized with the eNB (ie, TA = 0 ms). Therefore, the RACH preamble transmitted by the UE close to the eNB is received without delay at the eNB, and the RACH preamble transmitted by the UE far away from the eNB is received later with a propagation delay at the eNB. In this case, since the eNB knows the sequence transmitted by each UE, the random access procedure may proceed according to the detection position of the RACH preamble transmitted by each UE through periodic correlation.

Multiple sequences may be used for the RACH preamble. Typically, auto-correlation based ZC (Zadoff-Chu) sequence and cross-correlation based Pseudo-random sequence may be used for the RACH preamble. In general, an autocorrelation-based sequence may be used in a situation where intracellular interference is small, and a cross correlation sequence may be used in a situation where intracellular interference is large. In 3GPP LTE, a ZC sequence of length 839 may be used for the RACH preamble. The ZC sequence used for the RACH preamble may satisfy the following condition.

Intracell interference between different RACH preambles using the same frequency-time RACH resources is relatively small.

Intracell interference can be optimized according to cell size. That is, making smaller orthogonal preambles may improve the detection performance of the eNB.

-The greater the number of orthogonal preambles, the better the detection performance. (64 signatures for 3GPP LTE, 16 signatures for WCDMA)

the detection complexity of the eNB is relatively small.

Can support a high speed mobile terminal.

When intra-cell interference between signatures is large, a pseudo-noise (PN) sequence may be used for the RACH preamble.

Hereinafter, a constant amplitude zero auto-correlation (CAZAC) sequence will be described.

8 shows an example of a CAZAC sequence set. Referring to FIG. 8, each sequence in the CAZAC sequence set has different cyclic shifting (cyclic shifting) (0, 1, 2, and 3). In addition, each sequence in the CAZAC sequence set is mapped to a specific bit. At this time, each sequence becomes one signature having specific information. Referring to FIG. 8, [0 0] is set for a sequence with cyclic shifting 0, [0 1] is set for a sequence with cyclic shifting 1, [1 0] is set for a sequence with cyclic shifting 2, and cyclic shifting is 3 [1 1] is mapped to each sequence. That is, in FIG. 8, the transmitter may transmit two bits of information.

When the transmitter transmits one sequence in the CAZAC sequence set, the receiver can identify it and determine the information mapped to that sequence. For example, if the receiver identifies a sequence where cyclic shifting is zero, the receiver may know that the transmitter has transmitted information of [0 0]. Assuming an additive white Gaussian noise (AWGN) channel and an environment free of noise, the receiver can identify the transmitted sequence by looking for the output with the largest magnitude.

Meanwhile, the CAZAC sequence set defined in FIG. 8 may significantly degrade performance in a multipath environment. In order to solve this problem, in a commercialized system such as 3GPP LTE, a CAZAC sequence set may be defined in consideration of a zero-correlation zone (ZAC) which is an effective delay period.

9 shows another example of a CAZAC sequence set. 9, each sequence in the CAZAC sequence set has different cyclic shifts (0, 4, 8, and 12). That is, compared to the CAZAC sequence set of FIG. 8, each sequence in the CAZAC sequence set of FIG. 9 is generated with a cyclic shifting interval of four. In this case, the interval may be determined by the channel effective delay period L (the position of the last tap of the channel on the time axis).

10 shows an example of an output of a receiver that receives a sequence in a CAZAC sequence set. FIG. 10 corresponds to an output of a receiver that receives a sequence having a cyclic shift of 0 in FIG. 9 under the assumption that there is no receiver noise. Referring to FIG. 10, the size W of ZCZ may be determined as the maximum cyclic shifting (= L) of a sequence. The receiver first selects one of the largest y- _i in each ZCZ and compares them to select the ZCZ having the largest value. That is, the receiver can select the first ZCZ. In the first ZCZ, unlike the other ZCZ, there are four large output values {y ₀ , y ₁ , y ₂ , y ₃ }, which are caused by the delay spread. However, by setting the size W of ZCZ to be greater than the channel effective delay period L, the receiver can identify the sequence sent by the transmitter.

On the other hand, the smaller the interval of cyclic shifting between sequences, the more signatures can be defined. For example, when the interval of cyclic shifting is set to 1 in FIG. 9, a total of 16 signatures may be defined.

The following describes a multiple quality of service (QoS) sequence. The multi-QoS sequences may be generated based on an asymmetric CAZAC sequence set. An asymmetric CAZAC sequence set refers to a CAZAC sequence set having different intervals of cyclic shifting between sequences in the time domain. On the other hand, the CAZAC sequence set described with reference to FIGS. 8 and 9 may be referred to as a symmetric CAZAC sequence set since the intervals of cyclic shifting between sequences are equal to 1 and 4. In the asymmetric CAZAC sequence set, bits may be mapped to each sequence so that sequences having a small difference in cyclic shifting share a specific bit. In addition, information of high importance may be mapped to shared bits.

11 shows an example of an asymmetric CAZAC sequence set. Referring to FIG. 11, each sequence in the CAZAC sequence set has different cyclic shifts (0, 3, 8, and 11), and the intervals of the cyclic shifts between the sequences are not the same (3 and 5). In this case, sequences having a small difference in cyclic shifting may be grouped into one group. That is, in FIG. 11, a sequence with cyclic shifting of 0 and 3 is grouped into group A, and a sequence with cyclic shifting of 8 and 11 is grouped into group B. The bits may be mapped to each sequence such that the first bit is the same in each group and the second bit is different from each other. In FIG. 11, [0] is mapped to the first bit in the sequence of group A, and [1] is mapped to the first bit in the sequence of group B. In FIG. As a result, in FIG. 11, [0 0] is shown for a sequence having cyclic shifting of 0, [0 1] for a sequence having cyclic shifting of 3, [1 1] for a sequence having cyclic shifting of 8, and 11 for cyclic shifting. [1 0] is mapped to each sequence.

When the asymmetric CAZAC sequence set is configured as above, the interval of cyclic shifting between sequences in each group is 3, while the interval of cyclic shifting between groups is 5. In this case, the probability that the sequence with cyclic shifting is 3 is mistaken for the sequence with cyclic shifting is 0 is higher than the probability that the sequence with cyclic shifting is mistaken as the sequence with 8. In other words, the first bit shared in the group is less likely to cause an error than the second bit shared in the group. Therefore, information of high importance may be mapped to the first bit, and information of relatively low importance may be mapped to the second bit.

As a result, the asymmetric CAZAC sequence set is generated by different cyclic shifting intervals between the sequences, and thus the probability of false in a group and the probability of false in a group may vary. As information having different importance, that is, different QoS, is mapped according to a probability of being mistaken in and between groups, a multi-QoS sequence may be finally transmitted.

The following information is an example of high importance information.

Packet identifier (ID): The UE reads the packet ID to determine whether the currently received packet is its own. If it's not yours, you can do power saving by discarding the received packet without any further decoding. That is, if the packet ID is incorrectly determined, the system yield can be greatly reduced by losing the packet itself. Therefore, the packet ID may be considered as high importance information.

Basic service set ID (BSSID) of the Wi-Fi system: In a next-generation Wi-Fi system, a dense environment in which a large number of BSSs exist can be supported. At this time, if the UE reads the BSSID and recognizes that packet transmission is occurring in its BSS, the UE may delay its packet transmission even when it is determined that the channel is idle. This is because when the packet is sent by the receiver, the receiver AP needs to receive a large number of packets, so that decoding may be difficult due to a collision problem. Therefore, the BSSID may be considered as high importance information.

Bandwidth information: For example, if bit information is mapped to each sequence in the CAZAC sequence set as described above, bandwidth information of 20 MHz, 40 MHz, 80 MHz, and 160 MHz may be mapped.

Examples of information of low importance include the number of transmit antennas or the enhanced PDCCH (EPDCCH) location. In general, the information is detected by blind decoding. However, blind decoding must be performed several times, which can increase the delay and complexity of the system. If the information is transmitted through a signaling scheme, the disadvantages can be reduced or eliminated. And, if the information transmitted through the signaling scheme is not correct, it can be detected again by the existing blind decoding scheme. That is, since the error can be repaired, the effect due to the failure of information transmission is relatively small. As a result, recoverable information can be classified into less important information.

12 shows another example of an asymmetric CAZAC sequence set. Referring to FIG. 12, four sequences A, B, C, and D having a length of N = 6W constitute an asymmetric CAZAC sequence set. Sequence A / B constitutes one group, and sequence C / D constitutes another group. The interval of cyclic shifting in each group is W, and the interval of cyclic shifting between groups is 2W. At this time, it can be seen that the probability that the sequence is mistaken as one of two adjacent sequences is different. For example, the probability that sequence B is mistaken for sequence A is greater than the probability that it is mistaken for sequence C. Accordingly, a bit can be mapped to each sequence so that sequences in a group with a small interval of cyclic shifting share a particular bit. In FIG. 12, the first bit mapped to the sequence is a bit shared in each group, and the second bit is a bit not shared in each group. [0] is mapped to the first bit in sequence A / B and [1] is mapped to the first bit in sequence C / D. In addition, information of high importance may be mapped to bits shared in the group, and information of low importance may be mapped to bits not shared in the group. For example, a cell ID having high importance may be mapped to bits shared within a group, and control channel information having low importance may be mapped to bits not shared within a group.

A collision of the RACH preamble in the random access procedure will be described.

13 shows an example in which a RACH preamble collides in a contention based random access procedure. All UEs use the contention-based random access procedure described in FIG. 6 above for UL synchronization acquisition and can transmit their RACH preamble using a specific time-frequency resource. In this case, if two or more RACH preambles are transmitted from the plurality of UEs through the same time-frequency resource, a collision may occur when the eNB detects the RACH preambles, and the random access procedure of each UE may be restarted. That is, in FIG. 13, when the RACH preamble of UE # 0 and the RACH preamble of UE # 1 are transmitted through the same time-frequency resource, collision of the RACH preamble occurs.

If the eNB cannot recognize the collision upon detecting the RACH preamble, the actual collision occurs but the eNB cannot know it. In this case, all of the UEs with which the RACH preamble collides may receive a random access response, and all of the UEs with which the collision has occurred may transmit an RRC connection request message to the eNB. The eNB that receives the RRC connection request message from the collision-prone UE may recognize the collision of the RACH preamble and may restart the random access procedure. If the eNB can recognize the collision upon detecting the RACH preamble, the UE cannot receive a random access response for the RACH preamble.

Meanwhile, the eNB receiving the RACH preamble may transmit a random access response after 3ms. However, the size of ra-ResponseWindowSize of RACH - ConfigCommon information element (IE) is set to 2 ~ 10ms. Therefore, a difference of up to 12 ms may occur between the reception of the RACH preamble and the transmission of the random access response. As a result, the UE may recognize whether the RACH preamble collides after 12 ms at maximum, and retransmits the RACH preamble after waiting for reception of the random access response for up to 12 ms. If UE # 0 and UE # 1 retransmitting the RACH preamble by the collision of the RACH preamble use the same RACH preamble again, the collision may occur again.

14 shows a time-frequency resource at which a UE transmits a RACH preamble. In FIG. 14, it is assumed that a PRACH resource according to a PRACH configuration index 6 is configured in a frame structure type 1, that is, an FDD frame. The region checked in FIG. 14 is a PRACH resource region, that is, an area in which the UE maps and transmits a sequence for the RACH preamble. If UE # 0 and UE # 1 select the same preamble sequence and select the same PRACH resource region to transmit the RACH preamble, collision of the RACH preamble occurs.

15 shows an example of collision of a RACH preamble. Referring to FIG. 15, two correlation peaks are detected in one ZCZ. Thus, the eNB assumes two or more UEs have selected the same RACH preamble and recognizes the collision.

Next, a case in which a random access response is transmitted when a plurality of RACH preambles are detected in a specific PRACH resource will be described. In general, although the resources of the RACH preamble can be allocated in multiple numbers, since eNBs should detect correlation peaks for multiple resources when detecting the RACH preamble, resource scheduling is generally performed through the PRACH configuration in the time domain as described above with reference to FIG. 14. Do this.

16 shows an example of detecting a plurality of RACH preambles transmitted by a plurality of UEs in the same PRACH resource. Referring to FIG. 16, RACH preambles transmitted by three UEs of UE # 0, UE # 1, and UE # 2 are simultaneously detected. In this case, since it is assumed that the PRACH resources transmitting the RACH preamble are the same, it may be assumed that the RA-RNTI is also the same (in case of FDD).

Meanwhile, the random access response is scheduled by DCI format 1A scrambled with 16 bits of RA-RNTI and transmitted through PDCCH, and then transmitted through PDSCH. The PDCCH is divided into a common search space (CSS) searched by all UEs in a cell and a UE-specific search space (USS) for finding a DCI corresponding to each UE. The RA-RNTI is Passed through CSS However, since CSS is not very large and must be used for various cell common information such as P-RNTI, SI-RNTI, TPC-PUCCH-RNTI, TPC-PUSCH-RNTI, etc., in addition to RA-RNTI, transmission of a random access response is always performed. Cannot be used for

Therefore, when the PDCCH capacity of the eNB CSS is limited to N _CSS and a RACH preamble transmitted by N _RA UEs larger than N _CSS is detected in a specific PRACH resource, the eNB sequentially processes the N _CSS UEs having the largest peak power. The random access response may be selected and transmitted, or the random access response may be distributed to subframes within the random access response window to schedule the random access response.

17 shows an example of transmitting a random access response when a plurality of RACH preambles are detected in the same PRACH resource. In FIG. 17, it is assumed that a CSS can support only one UE for each subframe, and the size of the random access response window is 2ms (2 subframes). Referring to FIG. 17, since the RACH preamble having the largest peak power among the RACH preambles transmitted by UE # 0, UE # 1, and UE # 2 is a RACH preamble transmitted by UE # 0 and UE # 1, the eNB # UE # 0 and UE # 1 may be selected to transmit a random access response through the PDSHC. UE # 2 that is not selected may retransmit the RACH preamble.

In addition, in the case of TDD, the capacity of CSS that a plurality of UEs must transmit all random access responses may be absolutely insufficient according to the UL / DL configuration. Therefore, in this case, the eNB should transmit the random access response of a specific UE with a long delay or perform the RACH preamble retransmission procedure without transmitting the random access response.

18 shows an example of transmitting a random access response when a plurality of RACH preambles are detected in a TDD frame. In FIG. 18, it is assumed that the PRACH configuration index is 6 and the UL / DL configuration index is 0. When the UL / DL configuration index of the TDD frame is 0, the TDD frame is configured as [D S U U U D S U U U]. D denotes a DL subframe, S denotes a special subframe, and U denotes a UL subframe. That is, six UL subframes, two DL subframes, and two special subframes exist in one TDD frame. It can be seen that there is an absolute shortage of DL subframes capable of transmitting random access responses compared to UL subframes capable of transmitting RACH preambles. In addition, in FIG. 18, UE # 0, UE # 1, and UE # 2 transmit RACH preambles in subframe # 2, and UE # 3, UE # 4, and UE # 5 transmit RACH preambles in subframe # 3. It is assumed that the size of the random access response window is set to 6 ms. In this case, all random access responses for the corresponding UEs should be transmitted in the first DL subframe of the next radio frame. However, if the number of UEs that CSS can support is limited to two, UE # 0 and UE # 4 having the largest peak powers are selected and a random access response is transmitted only to the corresponding UE, and the remaining UEs perform the RACH preamble retransmission procedure. Will be performed.

As described above, when only a random access response for a specific UE is transmitted when a plurality of RACH preambles are detected, improvement of a random access procedure may be required in the following situations.

(1) Retransmitted RACH Preamble: Even by the above-described method, as long as there is another RACH preamble transmitted on basically the same PRACH resource, the retransmitted RACH preamble may continue to collide. That is, the detection of the retransmitted RACH preamble cannot be completely guaranteed. Therefore, the random access procedure needs to be improved in such a manner as to prioritize detection to the retransmitted RACH preamble. For example, the random access procedure may be improved such that the retransmission UE is preferentially selected to receive the random access response by sending additional information on the sequence of RACH preambles. That is, determination information to help the eNB select the UE to retransmit the corresponding RACH preamble may be added to the RACH preamble in the form of a signature. However, the determination information should not affect or minimize the existing RACH preamble detection.

(2) Low latency request UE or RACH of emergency connection: There may be a UE requesting emergency link establishment, which also needs to perform a random access procedure in order to obtain UL synchronization, and due to collision of the RACH preamble, the RACH preamble A situation in which retransmission may occur. Accordingly, the random access procedure needs to be improved in such a manner as to prioritize detection to the RACH preamble transmitted by the low latency request UE or the RACH preamble corresponding to the emergency connection. In this case, determination information to help the eNB select the low latency request UE may be added to the RACH preamble in the form of a signature. However, the determination information should not affect or minimize the existing RACH preamble detection.

As described above, when the RACH preambles transmitted by two or more UEs collide, it is necessary to improve the random access procedure so that the RACH preamble transmitted by a specific UE requiring fast UL synchronization is first detected. Accordingly, the present invention proposes a specific method of defining asymmetric CAZAC sequence set using a multi-QoS QoS sequence and using the same in the RACH preamble, so that the random access response can be preferentially transmitted for RAN preamble detection of a specific UE. The eNB may detect the sequence further transmitted in addition to the existing RACH preamble detection. Through this, UL synchronization acquisition of the UE retransmitting the RACH preamble or the low latency request UE may be supported first. For example, when a specific UE retransmits the RACH preamble, even if a collision occurs in the RACH preamble, the eNB may detect the retransmitted RACH preamble and transmit a random access response to the UE. Alternatively, when the low latency request UE transmits the RACH preamble, the eNB may preferentially detect the corresponding RACH preamble and transmit a random access response to the low latency request UE even if a collision occurs in the corresponding RACH preamble.

First, a method of generating a RACH preamble sequence using characteristics of a multi-QoS sequence according to an embodiment of the present invention will be described. According to an embodiment of the present invention, the RACH preamble sequence may be generated such that the cyclic shift N _CS between sequences in the same sequence group is the same, and that the cyclic shift offset between different sequence groups is different by a predetermined value. In detail, first, a first sequence group may be generated such that a cyclic shift between sequences becomes N _CS . In this case, the existing ZC sequence used for generating the RACH preamble sequence may be applied as it is. In addition, the cyclic shift offsets N _{off and g} between sequence groups may be set. g is a group index and g = 1,2,3, ..., N _G and N _G is the total number of sequence groups.

19 illustrates an example of a RACH preamble sequence using characteristics of a multi-QoS sequence according to an embodiment of the present invention. In FIG. 19, it is assumed that a sequence length N _ZC = 20 and the number of sequence groups are three. First, a first sequence group may be generated such that a cyclic shift between sequences becomes N _CS . At this time, it may be generated to have the same characteristics as the existing RACH preamble sequence. In FIG. 18, it is assumed that N _CS = 5. In the second sequence group, the cyclic shift between sequences in the group is equal to the first sequence group with N _CS = 5, but the cyclic shift offset N _{off, 2} may be set such that the sequence is further cyclically shifted. In FIG. 18, it is assumed that N _{off, 2} = 2. Similarly, in the third sequence group, the cyclic shift between sequences in the group is equal to the first sequence group with N _CS = 5, but the cyclic shift offset N _{off, 3} may be set such that the sequence is further cyclically shifted as a whole. In FIG. 18, it is assumed that N _{off, 3} = 3.

The cyclic shift offset N _{off, g} between sequence groups may be adaptively set or changed depending on the system. Also, it may be assumed that the cyclic shift offset N _{off, 1} = 0 of the first sequence group basically. Meanwhile, the video tube region refers to a region where the receiver output is observed in consideration of the channel delay of the RACH preamble transmitted by the UE. Therefore _, the relationship between max (N _{off, g} ) + W _D <N _CS is required between the cyclic shift offset between the sequence groups and the channel delay window W _D to prevent ambiguity of sequence detection. It is assumed that there is no round trip delay.

20 illustrates detection of a RACH preamble sequence using characteristics of a multi-QoS sequence according to an embodiment of the present invention. If the UE has transmitted all the sequences of the sequence groups 1, 2, and 3 described in FIG. 19, and assumes an ideal communication environment without channel delay, the eNB may obtain correlation based peak power as shown in FIG. 20.

The characteristics of the above-described multi-QoS sequences are applied to the RACH preamble sequence of 3GPP LTE / LTE-A as follows. In the existing LTE / LTE-A, the ZC sequence of the root index u may be defined by Equation 1.

<Equation 1>

In Equation 1, N _ZC is the length of the ZC sequence. In this case, the RACH preamble sequence having the image tube region N _CS may be represented by Equation 2.

<Equation 2>

In equation (2), the cyclic shift C _v can be given by equation (3).

<Equation 3>

When the characteristics of the multi-QoS sequences are applied to the cyclic shift C _v of the RACH preamble sequence of Equation 3 according to an embodiment of the present invention, they are as follows. As an example, the unrestricted sets in Equation 3 will be described. The cyclic shift of the first sequence group is equal to vN _CS as in Equation 3, but the cyclic shift of the second sequence group is represented by Equation 4. The cyclic shift of the third sequence group may be defined by Equation 5.

<Equation 4>

<Equation 5>

Referring to Equation 4, it can be seen that N _{off, 2, which} is a cyclic shift offset of the second sequence group _, is added to the cyclic shift of the second sequence group. In addition, referring to Equation 5, it can be seen that N _{off, 3, which} is a cyclic shift offset of the third sequence group _, is added to the cyclic shift of the third sequence group.

A method of transmitting a RACH preamble generated based on a multi-QoS sequence according to an embodiment of the present invention will be described. When a UL synchronization acquisition is required first, a UE, when transmitting the RACH preamble, may transmit a sequence composed of a specific combination of sequences belonging to different sequence groups, alone or in addition to an existing RACH preamble sequence. A sequence composed of a specific combination of sequences belonging to different sequence groups refers to the above-described multi QoS sequence, and may be referred to as a combination sequence hereinafter. The combination rule of the sequence may be predefined between the eNB and the UE. When three or more priorities of UL synchronization acquisition are set, different combination rules may be defined according to the priority. In addition, the UE may select the number of sequence groups used for generating the final RACH preamble sequence according to a specific pattern. In addition, the UE may perform power control of each sequence group according to the purpose.

A method of transmitting a RACH preamble generated based on a multi QoS sequence or a combination sequence will be described in detail. First, the sequence of each sequence group may be expressed as in Equation 6. In Equation 1 s _i (j) represents the i-th sequence (i = 0, 1, 2, ...) of the j-th group (j = 1, 2, 3, ...).

<Equation 6>

Based on the sequence of each sequence group represented by Equation 6, a multi-QoS sequence may be generated by Equation 7.

<Equation 7>

Referring to Equation 7, multi-QoS sequences are calculated by adding the weight i _j to the same i th sequence of each sequence group. For example, the first sequence of the first group is s ₀ ⁽¹⁾ = [s ₀ , s ₁ , s ₂ , s ₃ , ..., s ₁₉ ] ^T and the first sequence of the second sequence group is s ₀ ⁽²⁾ = [s ₁₈ , s ₁₉ , s ₀ , s ₁ , ..., s ₁₇ ] ^T , and assuming that the weight of each sequence α ₁ = α ₂ = 1, the UE finally transmits the multi The QoS sequence s may be generated as shown in Equation 8.

<Equation 8>

The following procedure may follow the existing RACH preamble transmission procedure as it is.

According to an embodiment of the present invention, a method of reducing collisions in a random access procedure by using a RACH preamble generated based on a multi-QoS sequence also a combination sequence will be described. In detail, the RACH preamble generated based on the multi-QoS sequences or combination sequences may be transmitted by a UE that preferentially acquires UL synchronization. That is, the multi-QoS sequence or the combination sequence itself may be used for the purpose of priority information of the random access response of the UE. The RACH preamble generated based on the multi-QoS sequences or combination sequences may indicate a combination of sequences having a cyclic shift offset N _{off, g} ≠ 0 between sequence groups as described above. In addition, a conventional RACH preamble that is not generated based on a multi-QoS sequence or a combination sequence may be transmitted by a general UE. That is, the multi-QoS sequence or the combination sequence itself may be used for the purpose of priority information of the random access response of the UE. The RACH preamble not generated based on the multi-QoS sequences or combination sequences may represent a combination of sequences having a cyclic shift offset N _{off, g} = 0 between the sequence groups.

21 shows an example of a random access procedure using a RACH preamble generated based on a combination sequence according to an embodiment of the present invention. In step S100, the first UE transmits a RACH preamble including the combined sequence or the multi QoS sequence to the eNB. The transmission of the RACH preamble including the combined sequence or the multi-QOS sequence by the first UE may be information implicitly indicating that the collision of the random access procedure has occurred and the retransmission procedure is being performed. In step S101, the second UE transmits a RACH preamble not including the combined sequence or the multi QoS sequence to the eNB. The RACH preamble transmitted by the first UE and the RACH preamble transmitted by the second UE are not the same. In step S110, the eNB selects the first UE that transmitted the RACH preamble including the combination sequence. In step S120, the eNB may transmit a random access response only to the selected first UE, and the first UE may perform a subsequent random access procedure. Through this, the random access response may be preferentially provided to the first UE retransmitting the RACH preamble, thereby reducing the UL synchronization acquisition delay through the RACH. Table 1 shows an example in which a UE uses a combination sequence or a multi-QOS sequence in transmitting a RACH preamble according to the purpose.

Sequence of first sequence group	Combination Sequence or Multi QoS Sequence	purpose
send	X	-General Upward Acquisition
send	send	Fast UL Sync Acquisition with RACH Preamble Retransmission Fast UL Sync Acquisition with Low Delay Request or Emergency Service Request

According to an embodiment of the present invention, when the UE transmits the RACH preamble generated based on the multi-QoS sequences or combination sequences, the eNB detects this. The eNB may detect the final received output according to equation (9). In Equation 4, N _ZC is a length of a signal or sequence, r is a reception vector on a time axis, s ⁽ⁱ⁾ is an i-th cyclically shifted sequence vector, and y _i is a final reception output.

<Equation 9>

Unlike conventional RACH preambles, RACH preambles based on multi-QoS sequences have multiple peaks detected pair-wise when no channel delay occurs. For example, suppose that the sequence length N _ZC = 839, the cyclic shift N _CS = 119, N _{off, 2} = 20, N _{off, 3} = 30, and the UE is the fourth sequence of the first 1,2,3 sequence groups Suppose we sum to produce the final RACH preamble. The final RACH preamble transmitted by the UE may be represented by Equation 10.

<Equation 10>

In this case, it is assumed that the ratio of transmit power of each sequence is set to 3: 1: 2. Therefore, when the total transmission power is P, the weights α1, α2, and α3 for each sequence may be set as in Equation (11).

<Equation 11>

22 shows an example of detection of a RACH preamble according to an embodiment of the present invention. 22 illustrates detection of a RACH preamble based on the above-described multi QoS. Referring to FIG. 22, three preambles are simultaneously detected in a size N _CS = 119 of a fourth picture tube region of a fourth sequence of a first, second, and third sequence group transmitted by a UE. As such, the RACH preamble based on the multi-QoS sequence is distinguished from the existing RACH preamble. Therefore, the eNB may preferentially transmit a random access response to a UE that transmits the RACH preamble based on the multi-QoS sequence. If the cyclic shift offsets N _{off, g} between the sequence groups cannot be distinguished due to channel delay, correlation peaks cannot be distinguished. Therefore, one correlation peak may be assumed and the same procedure as in the conventional random access procedure may be followed.

23 illustrates a method of performing a random access procedure by an eNB according to an embodiment of the present invention.

In step S200, the eNB receives from the first UE a first RACH preamble generated using a combination of a plurality of sequences. In step S210, the eNB receives a second RACH preamble from the second UE. The combination of the plurality of sequences may be the above-described multi QoS sequence or combination sequence. That is, each of the plurality of sequences may belong to a different sequence group. The different sequence groups may have different cyclic shift offsets. The combination of the plurality of sequences may correspond to the sum of the plurality of sequences. Alternatively, the combination of the plurality of sequences may correspond to the sum of the plurality of sequences in consideration of weights for each of the plurality of sequences. The first RACH preamble may be a retransmitted RACH preamble or a RACH preamble for low latency request or emergency service connection. In step S220, the eNB transmits a random access response only to the first UE. The eNB may receive an RRC connection request message from the first UE.

24 illustrates a method of performing a random access procedure by a UE according to an embodiment of the present invention.

In step S300, the UE transmits the generated RACH preamble to the eNB using a combination of a plurality of sequences. In step S310, the UE receives a random access response from the eNB. The combination of the plurality of sequences may be the above-described multi QoS sequence or combination sequence. That is, each of the plurality of sequences may belong to a different sequence group. The different sequence groups may have different cyclic shift offsets. The combination of the plurality of sequences may correspond to the sum of the plurality of sequences. Alternatively, the combination of the plurality of sequences may correspond to the sum of the plurality of sequences in consideration of weights for each of the plurality of sequences. The first RACH preamble may be a retransmitted RACH preamble or a RACH preamble for low latency request or emergency service connection.

25 is a block diagram of a wireless communication system in which an embodiment of the present invention is implemented.

The eNB 800 may include a processor 810, a memory 820, and a transceiver 830. Processor 810 may be configured to implement the functions, processes, and / or methods described herein. Layers of the air interface protocol may be implemented by the processor 810. The memory 820 is connected to the processor 810 and stores various information for driving the processor 810. The transceiver 830 is connected to the processor 810 to transmit and / or receive a radio signal.

The UE 900 may include a processor 910, a memory 920, and a transceiver 930. Processor 910 may be configured to implement the functions, processes, and / or methods described herein. Layers of the air interface protocol may be implemented by the processor 910. The memory 920 is connected to the processor 910 and stores various information for driving the processor 910. The transceiver 930 is connected to the processor 910 to transmit and / or receive a radio signal.

Processors 810 and 910 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processing devices. The memory 820, 920 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium, and / or other storage device. The transceivers 830 and 930 may include a baseband circuit for processing radio frequency signals. When the embodiment is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in the memory 820, 920 and executed by the processor 810, 910. The memories 820 and 920 may be inside or outside the processors 810 and 910, and may be connected to the processors 810 and 910 by various well-known means.

In the exemplary system described above, methods that may be implemented in accordance with the above-described features of the present invention have been described based on a flowchart. For convenience, the methods have been described as a series of steps or blocks, but the claimed features of the present invention are not limited to the order of steps or blocks, and certain steps may occur in the same order as other steps and in a different order than described above. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

Claims (15)

1. In the method for performing a random access procedure by an evolved NodeB (eNB) in a wireless communication system,

   Receive, from a first user equipment (UE), a first random access channel (RACH) preamble generated using a combination of a plurality of sequences;

   Receive a second RACH preamble from a second UE; And

   Transmitting a random access response only to the first UE.
2. The method of claim 1,

   Wherein each of the plurality of sequences belongs to a different sequence group.
3. The method of claim 2,

   Wherein the different sequence groups each have a different cyclic shift offset.
4. The method of claim 1,

   The combination of the plurality of sequences corresponds to the sum of the plurality of sequences.
5. The method of claim 1,

   And the combination of the plurality of sequences corresponds to the sum of the plurality of sequences taking into account weights for each of the plurality of sequences.
6. The method of claim 1,

   Wherein the first RACH preamble is a RACH preamble retransmitted.
7. The method of claim 1,

   Wherein the first RACH preamble is a RACH preamble for low latency request or emergency service connection.
8. The method of claim 1,

   And receiving a radio resource control (RRC) connection request message from the first UE.
9. The method of claim 1,

   Generating a combination of the plurality of sequences.
10. A method of performing a random access procedure by a user equipment (UE) in a wireless communication system,

    Transmit a random access channel (RACH) preamble generated using the combination of the plurality of sequences to the eNB; And

    Receiving a random access response from the eNB.
11. The method of claim 10,

    Wherein each of the plurality of sequences belongs to a different sequence group.
12. The method of claim 11,

    Wherein the different sequence groups each have a different cyclic shift offset.
13. The method of claim 10,

    The combination of the plurality of sequences corresponds to the sum of the plurality of sequences.
14. The method of claim 10,

    And the combination of the plurality of sequences corresponds to the sum of the plurality of sequences taking into account weights for each of the plurality of sequences.
15. The method of claim 10,

    Wherein the RACH preamble is a retransmitted RACH preamble or a RACH preamble for low latency request or emergency service connection.

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