Patent Description:
To meet the demand for wireless data traffic having increased since deployment of fourth generation (<NUM>) communication systems, efforts have been made to develop an improved fifth generation (<NUM>) or pre-<NUM> communication system. Therefore, the <NUM> or pre-<NUM> communication system is also called a "beyond <NUM> network' or a 'post long term evolution (LTE) system'. To decrease propagation loss of the radio waves and increase the transmission distance, beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beam forming, and large scale antenna techniques are discussed in <NUM> communication systems. In the <NUM> system, hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

In the recent years several broadband wireless technologies have been developed to meet the growing number of broadband subscribers and to provide more and better applications and services. The second generation (<NUM>) wireless communication system has been developed to provide voice services while ensuring the mobility of users. The third generation (<NUM>) wireless communication system supports not only the voice service but also data service. The <NUM> wireless communication system has been developed to provide high-speed data service. However, the <NUM> wireless communication system currently suffers from lack of resources to meet the growing demand for high speed data services. Therefore, the <NUM> wireless communication system is being developed to meet the growing demand of various services with diverse requirements, e.g., high speed data services, ultra-reliability and low latency applications and massive machine type communication.

In existing wireless communication system, such as LTE, random access (RA) procedure is used to achieve uplink (UL) time synchronization. RA procedure is used in LTE during initial access, handover, radio resource control (RRC) connection re-establishment procedure, positioning purpose, scheduling request transmission, secondary cell group (SCG) addition/modification and data or control information transmission in UL by non?synchronized user equipment (UE) in RRC_CONNECTED state. In LTE two types of RA procedure are defined: contention-based and contention-free.

A procedure for idle to connected state transition using contention-based RA (CBRA) procedure leads to a total delay of <NUM> transmit time intervals (TTIs). However, for the next generation radio access technology the idle to connected transition delay requirement is <NUM>. Therefore, a need exits for enhancing the CBRA procedure.

Document <CIT> discloses that in a random access procedure, a preamble transmitter in UE sends a preamble, and gets a random access response with a sequence index from BS.

Aspects of the present disclosure are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present disclosure is to provide a communication method and system for converging a fifth generation (<NUM>) communication system for supporting higher data rates beyond a fourth generation (<NUM>) system. The solution is provided by the independent claims appended hereto with implementation aspects defined in the dependent claims.

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents.

Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

It is known to those skilled in the art that blocks of a flowchart (or sequence diagram) and a combination of flowcharts may be represented and executed by computer program instructions. These computer program instructions may be loaded on a processor of a general purpose computer, special purpose computer, or programmable data processing equipment. When the loaded program instructions are executed by the processor, they create a means for carrying out functions described in the flowchart. Because the computer program instructions may be stored in a computer readable memory that is usable in a specialized computer or a programmable data processing equipment, it is also possible to create articles of manufacture that carry out functions described in the flowchart. Because the computer program instructions may be loaded on a computer or a programmable data processing equipment, when executed as processes, they may carry out steps of functions described in the flowchart.

A block of a flowchart may correspond to a module, a segment, or a code containing one or more executable instructions implementing one or more logical functions, or may correspond to a part thereof. In some cases, functions described by blocks may be executed in an order different from the listed order. For example, two blocks listed in sequence may be executed at the same time or executed in reverse order.

In this description, the words "unit", "module" or the like may refer to a software component or hardware component, such as, for example, a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC) capable of carrying out a function or an operation. However, a "unit", or the like, is not limited to hardware or software. A unit, or the like, may be configured so as to reside in an addressable storage medium or to drive one or more processors. Units, or the like, may refer to software components, object-oriented software components, class components, task components, processes, functions, attributes, procedures, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays or variables. A function provided by a component and unit may be a combination of smaller components and units, and may be combined with others to compose larger components and units. Components and units may be configured to drive a device or one or more processors in a secure multimedia card.

<FIG> illustrates a contention-based random access (CBRA) procedure.

Referring to <FIG>, a user equipment (UE) transmits a random access (RA) preamble to evolved node B (eNB) at operation <NUM>.

The UE selects one of the available <NUM>-Ncf contention based RA preambles. Ncf is the number of RA preambles reserved for contention free access. The contention based RA preambles can be optionally partitioned into two groups. If two groups are configured, the UE selects the group based on size of a message (i.e., MSG3) that the UE can transmit at operation <NUM>. The initial RA preamble transmission power is set based on open loop estimation after compensating for path loss.

The ENB transmits a RA response (RAR) on physical downlink shared channel (PDSCH) addressed to RA-radio network temporary identifier (RA-RNTI) to the UE at operation <NUM>.

The RA-RNTI identifies the time-frequency slot in which RA preamble was detected by eNB. RAR conveys RA preamble identifier (ID), timing alignment information, temporary cell-radio network temporary identifier (C-RNTI) and uplink (UL) grant for a message (i.e., MSG3) to be transmitted at operation <NUM>. RAR may also include back off indicator to instruct the UE to back off for period of time before retrying RA attempt. RAR is transmitted in RAR window. RAR window starts at subframe 'x+<NUM>' for RA preamble transmitted in subframe 'x'. RAR window size is configurable.

The UE performs scheduled UL transmission on UL shared channel (UL SCH) at operation <NUM>.

A message, such as RRC Connection Request, RRC Connection Re-establishment request, RRC handover confirm, scheduling request, and the like, may be transmitted at operation <NUM>. The message transmitted at operation <NUM> is commonly referred as MSG3. The message transmitted at operation <NUM> may include the UE identity, such as C-RNTI or system architecture evolution (SAE)-temporary mobile subscriber identity (S-TMSI) or a random number. Hybrid automatic repeat request (HARQ) is used for the scheduled UL transmission.

The ENB transmits a contention resolution message at operation <NUM>.

HARQ is used for transmission of a contention resolution message. A contention resolution message is addressed to C-RNTI (if C-RNTI is included in MSG3) or temporary C-RNTI (if the UE identity is included in MSG3). On successful decoding of the contention resolution message, HARQ feedback is only sent by the UE which detects its own UE ID (or C-RNTI).

<FIG> illustrates a contention-free RA (CFRA) procedure.

Referring to <FIG>, contention free RA procedure is used for scenarios, such as handover where low latency is required, timing advance establishment for secondary cell (Scell), and the like.

The ENB assigns to the UE non-contention RA preamble in dedicated signaling at operation <NUM>.

The UE transmits the assigned non-contention RA preamble at operation <NUM>.

The ENB transmits the RAR on PDSCH addressed to RA-RNTI at operation <NUM>. RAR conveys RA preamble ID and timing alignment information. RAR may also include UL grant. RAR is transmitted in RAR window similar to contention based RA procedure. Contention free RA procedure terminates after receiving the RAR.

<FIG> illustrates a procedure for idle to connected state transition using a CBRA procedure.

Referring to <FIG>, the UE transmits an RA preamble to the eNB at operation <NUM>, the eNB transmits a RAR on PDSCH addressed to RA-RNTI to the UE at operation <NUM>, and the UE performs scheduled UL transmission on UL SCH at operation <NUM>, similar to the CBRA procedure illustrated <FIG>. The scheduled transmission in operation <NUM>, i.e., MSG3 may refer to a connection request or a connection resume request.

The ENB transmits a contention resolution message at operation <NUM>. The contention resolution message in operation <NUM> of <FIG> may refer to a connection setup (if a connection request is received at operation <NUM>) or a connection resume (if a connection resume request is received at operation <NUM>).

The UE performs scheduled transmission at operation <NUM>. The scheduled transmission in operation <NUM> may refer to a connection setup complete (if a connection setup is received at operation <NUM>) or a connection resume complete (if a connection resume is received at operation <NUM>).

Meanwhile, the CBRA procedure leads to a total delay of <NUM> transmit time intervals (TTIs) as shown in Table <NUM> below.

For the next generation radio access technology the idle to connected transition delay requirement is <NUM>. So there is need to enhance the CBRA procedure.

<FIG> illustrates a two-step contention based RA procedure according to an embodiment of the present disclosure. In the procedure illustrated in <FIG>, contention resolution is performed in two steps.

Referring to <FIG>, the UE transmits a RA channel (RACH) preamble and a UE ID to a base station (BS) (e.g., node B (NB), eNB, or gNB) at operation <NUM>. RACH preamble and UE ID can be transmitted in a single physical layer protocol data unit (PDU) or separate physical layer PDUs. The RACH preamble and the UE ID at operation <NUM> can be sent by UE in an unclaimed embodiment i in same time slot or in a claimed embodiment in different time slots. The operation <NUM> of transmitting RACH preamble and UE ID can be referred as MSG1 transmission. The UE ID can be at least one of Random ID, S-TMSI, C-RNTI, Resume ID, IMSI, idle mode ID, Inactive Mode ID, and the like. The UE ID can be different in different scenarios in which the UE performs the RA procedure. When the UE performs RA after power on (i.e., before the UE is attached to the network), the UE ID can be a random ID. Meanwhile, the UE may have a previously assigned or predetermined UE ID. For example, when the UE perform RA in IDLE state after the UE is attached the network the UE can use a previously assigned S-TMSI as the UE ID. If UE has an assigned C-RNTI (e.g., in connected state) the UE can use the C-RNTI as the UE ID. In case the UE is in INACTIVE state, the UE can use a resume ID as the UE ID.

NB determines whether NB has received the RACH preamble and the UE ID at operation <NUM>.

If the NB has received both the RACH preamble and the UE ID, NB sends a RAR (also referred as MSG2) to the UE at operation <NUM>. The RAR include at least one of timing advanced (TA), RACH preamble ID (RAPID) or the UE ID. The RAPID may refer to information on the received RACH preamble, e.g., a sequence index of the received RACH preamble. UE ID included in RAR is the UE ID received from UE. C-RNTI (or temporary C-RNTI) can be additionally included in RAR if the UE ID received from UE is not C-RNTI. Grant for UL transmission may also be included.

If physical downlink control channel (PDCCH) scheduling RAR is addressed to RA-RNTI corresponding to UE's RACH preamble transmitted at operation <NUM>, RAPID received in RAR at operation <NUM> corresponds to UE's RACH preamble transmitted in operation <NUM>, and the UE ID included in RAR is the UE ID transmitted by UE at operation <NUM>, then the UE considers contention resolution as successful. Note that RA-RNTI is used to mask cyclic redundancy check (CRC) of PDCCH which schedules the RAR message. The RA-RNTI is specific to time and/or frequency resource in which RACH preamble is transmitted. The RAR message may include a RAPID.

<FIG> illustrates an alternative two-step contention based RA procedure according to an embodiment of the present disclosure.

Referring to <FIG>, the two-step contention based RA procedure illustrated in <FIG> is similar to that illustrated in <FIG> except that in addition to the UE ID some additional control information can be sent in operation <NUM>. In other words, the UE transmits a RACH preamble, a UE ID, and control information to NB at operation <NUM>. RACH preamble, UE ID and control information can be transmitted in a single physical layer PDU or separate physical layer PDUs. The RACH preamble, the UE ID and the control information at operation <NUM> can be sent by UE in same time slot or different time slots. The operation <NUM> of transmitting RACH preamble, UE ID and control information can also be referred as MSG1 transmission. The control information may include one or more of connection request indication, connection resume request indication, system information (SI) request indication, bitmap wherein each bit is mapped to SI message or system information block (SIB) requested by UE, buffer status indication, beam information (e.g., one or more DL TX beam ID(s)), data indicator, cell/BS/transmission reception point (TRP) switching indication, or connection re-establishment indication, and the like. Note that any other control information is not precluded.

NB determines whether NB has received the RACH preamble, the UE ID and control information at operation <NUM>.

If RACH preamble, UE ID and control information is received, NB sends a RAR to the UE at operation <NUM>. In addition, NB may transmit a control message based on the control information received at operation <NUM>. In other words, NB may respond with a control message in addition to RAR message at operation <NUM>. The control message may depend on control information received at operation <NUM>. The RAR at operation <NUM> and the control message at operation <NUM> can be sent by NB in same time slot or different time slot.

Network can signal in dedicated or broadcast signaling the events or services for which UE should use two-step contention based random access procedure.

<FIG> and <FIG> illustrate enhanced PRACH slot/resource formats for performing a two-step RA procedure according to various embodiments of the present disclosure.

Referring to <FIG> and <FIG>, in a PRACH slot, the UE performs a PRACH transmission in a PRACH resource (e.g., R1 of <FIG>). In other words, the UE transmits a RA preamble in a PRACH resource on PRACH at first step of a two-step RA procedure (e.g., operation <NUM> of <FIG>, operation <NUM> of <FIG>). The PRACH format (i.e., RA preamble) for performing the PRACH transmission according to an embodiment of the present disclosure may include cyclic prefix (CP), PRACH preamble sequence, additional information (i.e., the UE ID, data, control information, CRC, and the like) and guard time (GT). In the system, there can be several PRACH formats wherein all PRACH format may not include additional information (i.e., the UE ID, data, control information, CRC, and the like) The PRACH format indicator in PRACH configuration may indicate the PRACH format to be used for PRACH configuration. In an embodiment of the present disclosure, NB may configure multiple PRACH configurations having PRACH formats which include additional information (i.e., the UE ID, data, control information, CRC, and the like) and which do not include additional information. The UE may choose PRACH configuration based on service/slice in which the UE is interested. For example, for ultra-reliable low latency (URLL) slice/service, the UE may use PRACH configuration which allows transmitting additional information. NB may also indicate which PRACH format to be used for which service/slice.

<FIG> illustrates an enhanced PRACH slot/resource format for performing a two-step RA procedure according to an embodiment of the present disclosure.

Referring to <FIG>, PRACH sequence and additional information (i.e., the UE ID, data, control information, CRC, and the like) are frequency division multiplexed in PRACH resources. PRACH format of <FIG> requires more resources because of additional CP and GT compared to PRACH format of <FIG>. However, duration of a slot of PRACH format of <FIG> is shorter, compared to that of <FIG>, which is beneficial in reducing latency.

Referring to <FIG>, PRACH sequence and additional information (i.e., the UE ID, data, control information, CRC, and the like) are frequency division multiplexed in PRACH resource, similar to a PRACH format illustrated <FIG>. Furthermore, resource R1 for a PRACH sequence and resource R3 for additional information are separated. The PRACH configuration indicates resources for a PRACH sequence (i.e., PRACH resources) as well as resources for additional information. Mapping between resources for a PRACH sequence and resources for additional information can be implicit (e.g., first resource for a PRACH sequence maps to first resource for additional information, and so on) or can be explicitly indicated. For example, first resource is for a PRACH preamble and then next N (N can be <NUM>) resource(s) is for additional information, and so on. Since all UEs performing RA may not have to transmit additional information, separating resources for a PRACH preamble and resources for additional information can reduce contention on the resources for the additional information. There can be one to one mapping or one to many mapping between resources for a PRACH preamble and resource for additional information. In an embodiment of the present disclosure, only resources for a PRACH preamble are indicated, and resources for additional information can be pre-defined.

Referring to <FIG>, PRACH sequence and additional information (i.e., the UE ID, data, control information, CRC, and the like) are time division multiplexed. In other words, a slot for PRACH sequence (i.e., PRACH slot) and a slot for additional information (i.e., data slot) are different. A PRACH slot and a data slot may or may not be consecutive.

Meanwhile, it is possible that NB can only receive PRACH preamble and cannot decode additional information (i.e., the UE ID, data, control information, and the like) successfully. In an embodiment of the present disclosure, NB may not send RAR if only PRACH preamble is received and additional information is not received. But this is not efficient as the UE will again send RA preamble which leads to more delay. Therefore, in case only PRACH preamble is received and additional information is not successfully decoded, a two-step RA procedure may fall back to a four-step RA procedure according to an embodiment of the present disclosure. In the two-step to four-step fall back method, if only PRACH preamble is received and additional information cannot be successfully decoded, NB sends RAR including TA and RAPID. Temporary C-RNTI may also be included in the RAR. In addition, the RAR may include an indication that additional information is not decoded. NB may indicate that additional information is not decoded implicitly. For example, NB may transmit RAR without the UE ID and the absence of the UE ID in RAR may implicitly indicate that NB has only received RACH preamble. Alternatively, NB may indicate that additional information is not decoded explicitly. For example, NB may transmit one bit indication in RAR to indicate that only RACH preamble is received and additional information (e.g. UE ID) is not received.

<FIG> illustrates a two-step to four-step fall back method for a RA according to an embodiment of the present disclosure.

If the UE ID transmitted by UE to NB in MSG1 is not included in RAR (i.e., implicitly indicated) or there is an explicit indication in RAR that additional information (i.e., the UE ID, data, control information, and the like) is not decoded by NB, the UE falls back to a four-step RA procedure as shown in <FIG>.

Referring to <FIG>, the UE transmits MSG1 including RA preamble and additional information (i.e., the UE ID) to NB at operation <NUM>. Additional information may also include data and control information.

If MSG1 is received, NB tries decoding additional information. If the additional information is successfully decoded, NB sends MSG2 (i.e., RAR) including the UE ID, as illustrated in <FIG> and <FIG>. If the additional information is not successfully decoded, NB sends RAR including UL grant. RAR also includes TA and RAPID. Temporary C-RNTI may also be included in the RAR.

If RAR corresponding to the UE's transmitted RA preamble is received, the UE determines whether RAR includes the UE ID at operation <NUM>. Alternatively, the UE may determine whether RAR includes an indication that additional information (e.g., the UE ID) is received by NB. If RAR includes the UE ID or indicates that additional information is received, contention resolution is successful at operation <NUM> (i.e., two-step RA procedure END). Otherwise, the UE falls back to four-step procedure, i.e., the UE transmits MSG3 including at least the UE ID using the allocated grant at operation <NUM>. Other information such as connection request or connection resume request or SI request and the like can also be transmitted in MSG3.

After transmitting MSG3, the UE waits for MSG4 for pre-defined time at operation <NUM>. If MSG4 is received, the UE determines whether MSG4 includes the UE ID transmitted in MSG3 at operation <NUM>. If MSG4 includes the UE ID, contention resolution is successful at operation <NUM> (i.e., four-step fall back RA procedure END). If MSG4 including UE ID transmitted in MSG3 is not received for pre-defined time UE retransmits MSG1.

Referring to <FIG>, similar to a two-step to four-step fall back method of <FIG>, if the UE ID is not included in RAR (i.e., implicitly indicated) or there is an explicit indication in RAR that additional information (i.e., the UE ID, data, control information, and the like) is not decoded by NB, the UE falls back to a four-step RA procedure as shown in <FIG>.

Specifically, similar to the method of <FIG>, the UE transmits MSG1 including RA preamble and additional information (i.e., the UE ID, data, control information, and the like) to NB at operation <NUM>. If MSG1 is received, NB tries decoding additional information. If the additional information is successfully decoded, NB sends MSG2 (i.e., RAR) including the UE ID, as illustrated in <FIG> and <FIG>. If the additional information is not successfully decoded, NB may determine whether to include grant in RAR. In other words, contrary to the method of <FIG>, grant is not always included in RAR. If NB wants the UE to fall back to four-step procedure, NB includes grant in MSG2, otherwise NB does not include grant in RAR. RAR also includes TA and RAPID. Temporary C-RNTI may also be included in the RAR.

If RAR corresponding to the UE's transmitted RA preamble is received, the UE determines whether RAR includes the UE ID at operation <NUM>. Alternatively, the UE may determine whether RAR includes an indication that additional information (e.g., the UE ID) is received by NB. If RAR includes the UE ID or indicates that additional information is received, contention resolution is successful at operation <NUM> (i.e., two-step RA procedure END).

If the UE ID is not included in RAR or there is an explicit indication in RAR that additional information (i.e., the UE ID, data, control information, and the like) is not decoded by NB, the UE determines whether grant is received in RAR at operation <NUM>. If grant is not received in RAR, the UE retransmits RA preamble and the UE ID. If grant is received in RAR, the UE falls back to four-step procedure i.e., the UE transmits MSG3 including the UE ID using the allocated grant at operation <NUM>. Other information such as connection request or connection resume request or SI request and the like can also be transmitted in MSG3.

<FIG> illustrates a two-step to four-step fall back method for an RA according to an embodiment of the present disclosure.

Referring to <FIG>, similar to a two-step to four-step fall back methods of <FIG> and <FIG>, if the UE ID is not included in RAR (i.e., implicitly indicated) or there is an explicit indication in RAR that additional information (i.e., the UE ID, data, control information, and the like) is not decoded by NB, the UE falls back to a four-step RA procedure as shown in <FIG>.

Specifically, similar to the methods of <FIG> and <FIG>, the UE transmits MSG1 including RA preamble and additional information (i.e., the UE ID, data, control information, and the like) to NB at operation <NUM>. If MSG1 is received, NB tries decoding additional information. If the additional information is successfully decoded, NB sends MSG2 (i.e., RAR) including the UE ID, as illustrated in <FIG> and <FIG>. If the additional information is not successfully decoded, NB may determine whether to include grant in RAR. In other words, contrary to the method of <FIG>, grant is not always included in RAR. Similar to the method of <FIG>, if NB wants the UE to fall back to four-step procedure, NB includes grant in MSG2, otherwise NB does not include grant in RAR. In addition, NB may determine whether to include an indication to transmit the UE ID in RAR.

If RAR corresponding to the UE's transmitted RA preamble is received, the UE determines whether RAR includes the UE ID at operation <NUM>. Alternatively, the UE may determine whether RAR includes an indication that additional information (e.g., the UE ID) is received by NB. If RAR includes the UE ID or indicates that additional information is received, contention resolution is successful at operation <NUM> (i.e., two-step RA procedure END). If the UE ID is not included in RAR or there is an explicit indication in RAR that additional information (i.e., the UE ID, data, control information, and the like) is not decoded by NB, the UE determines whether grant is received in RAR at operation <NUM>. If grant is received in RAR, the UE falls backs to <NUM> step procedure i.e., the UE transmits MSG3 including the UE ID using the allocated grant at operation <NUM>. Other information such as connection request or connection resume request or SI request and the like can also be transmitted in MSG3. After transmitting MSG3, the UE waits for MSG4 for pre-defined time at operation <NUM>. If MSG4 is received, the UE determines whether MSG4 includes the UE ID transmitted in MSG3 at operation <NUM>. If MSG4 includes the UE ID, contention resolution is successful at operation <NUM> (i.e., four-step fall back RA procedure END). If MSG4 including UE ID transmitted in MSG3 is not received for pre-defined time, the UE retransmits MSG1.

If grant is not received in RAR, the UE retransmits RA preamble. In addition, the UE may retransmit additional information (i.e., the UE ID, data, control information, and the like) while transmitting RA preamble based on indication from NB. Specifically, the UE may determine whether RAR includes indication to transmit additional information at operation <NUM>. If RAR includes the indication, the UE retransmits MSG1 including both RA preamble and additional information, otherwise the UE retransmits MSG1 only including RA preamble at operation <NUM>.

Referring to <FIG>, similar to a two-step to four-step fall back methods of <FIG>, <FIG> and <FIG>, if the UE ID is not included in RAR (i.e., implicitly indicated) or there is an explicit indication in RAR that additional information (i.e., the UE ID, data, control information, and the like) is not decoded by NB, the UE falls back to a four-step RA procedure as shown in <FIG>.

Specifically, similar to the methods of <FIG>, <FIG>, and <FIG>, the UE transmits MSG1 including RA preamble and additional information (i.e., the UE ID, data, control information, and the like) to NB at operation <NUM>. If MSG1 is received, the NB tries decoding additional information. If the additional information is successfully decoded, NB sends MSG2 (i.e., RAR) including the UE ID, as illustrated in <FIG> and <FIG>. If the additional information is not successfully decoded, the NB may determine whether to include grant in RAR. In other words, contrary to the method of <FIG>, grant is not always included in RAR. Similar to the methods of <FIG> and <FIG>, if NB wants the UE to fall back to four-step procedure, NB includes grant in MSG2, otherwise NB does not include grant in RAR.

If RAR corresponding to UE's transmitted PA preamble is received, the UE determines whether RAR includes the UE ID at operation <NUM>. Alternatively, the UE may determine whether RAR includes an indication that additional information (e.g., the UE ID) is received by NB. If RAR includes the UE ID or indicates that additional information is received, contention resolution is successful at operation <NUM> (i.e., two-step RA procedure END). If the UE ID is not included in RAR or there is an explicit indication in RAR that additional information (i.e., the UE ID, data, control information, and the like) is not decoded by NB, the UE determines whether grant is received in RAR at operation <NUM>. If grant is received in RAR, the UE falls backs to <NUM> step procedure i.e., the UE transmits MSG3 including the UE ID using the allocated grant at operation <NUM>. Other information such as connection request or connection resume request or SI request and the like can also be transmitted in MSG3. After transmitting MSG3, the UE waits for MSG4 for pre-defined time at operation <NUM>. If MSG4 is received, the UE determines whether MSG4 includes the UE ID transmitted in MSG3 at operation <NUM>. If MSG4 includes the UE ID, contention resolution is successful at operation <NUM> (i.e., four-step fall back RA procedure END). If MSG4 including UE ID transmitted in MSG3 is not received for pre-defined time UE retransmits MSG1.

If grant is not received in RAR, the UE retransmits RA preamble. In addition, the UE may retransmit additional information (i.e., the UE ID, data, control information, and the like) while transmitting RA preamble based on parameter 'N,' where parameter 'N' indicates the number of times the UE can retransmit additional information (i.e., the UE ID, data, control information, and the like) along with RA preamble. Specifically, the UE may determine whether the UE has transmitted RA preamble with the UE ID 'N' times at operation <NUM>. If the UE has transmitted RA preamble with the UE ID more than 'N' times, the UE retransmits MSG1 only including RA preamble at operation <NUM>. Parameter 'N' can be pre-defined or indicated by network in broadcast or dedicated signaling. Alternatively, parameter 'N' can be signaled along with PRACH configuration.

<FIG> illustrates an RA procedure when a UE does not receive a RAR after transmitting an RA preamble and additional information according to an embodiment of the present disclosure.

Referring to <FIG>, if the UE does not receive RAR after transmitting MSG1 including RA preamble and additional information (i.e., the UE ID, data, control information, and the like), then in an embodiment of the present disclosure, the UE may retransmit MSG1 including RA preamble and additional information. In an alternate embodiment of the present disclosure, the UE may determine whether to retransmit additional information along with RA preamble or not. The UE can determine whether to retransmit additional information along with RA preamble based on parameter 'N,' where parameter 'N' indicates the number of times the UE can retransmit additional information along with RACH preamble. Parameter 'N' can be pre-defined or indicated by network in broadcast or dedicated signaling. Alternatively, parameter 'N' can be signaled along with PRACH configuration.

Referring to <FIG>, the UE transmits MSG1 including RA preamble and additional information (i.e., the UE ID, data, control information, and the like) to NB at operation <NUM>. If nothing is received by NB, the NB does not transmit RAR to UE, and the UE cannot receive RAR. Therefore, the UE retransmits MSG1 including RA preamble and additional information to NB at operation <NUM>. Meanwhile, if the UE retransmits MSG1 including RA preamble and additional information several times but RAR is not received, the UE may determine whether to retransmit additional information along with RA preamble to NB at operation <NUM>. For example, the UE may determine whether to retransmit additional information along with RA preamble based on parameter 'N,' where parameter 'N' indicates the number of times the UE can retransmit additional information. Based on the determination, the UE may retransmit only RACH preamble, or both RACH preamble and additional information to the NB at operation <NUM>.

<FIG> is a block diagram of a UE for performing an RA procedure according to an embodiment of the present disclosure.

Referring to <FIG>, the UE include a transceiver (<NUM>), a controller (<NUM>) and a memory (<NUM>). The controller (<NUM>) may refer to a circuitry, an application-specific integrated circuit (ASIC), or at least one processor. The transceiver (<NUM>), the controller (<NUM>) and the memory (<NUM>) are configured to perform the operations of the UE in the RA procedure illustrated in <FIG>, <FIG>, and <FIG> or described above. For example, the transceiver (<NUM>) is configured to receive signals from a BS and transmit signals to the BS. The controller (<NUM>) may be configured to control the transceiver (<NUM>) to transmit a first message including a RA preamble and a UE ID to the BS, and control the transceiver (<NUM>) to receive a second message including a sequence index of the RA preamble from the BS.

<FIG> is a block diagram of a BS for performing an RA procedure according to an embodiment of the present disclosure.

Claim 1:
A method performed by a user equipment, UE, in a wireless communication system, the method comprising:
transmitting, to a base station, a random access preamble for a <NUM>-step random access and a UE identifier, ID, wherein the random access preamble is transmitted on a first resource and the UE ID is transmitted on a second resource separated with the first resource;
receiving, from the base station, a random access response; characterized in that:
in case that the random access response does not include the UE ID and includes an uplink grant, transmitting, to the base station, a message <NUM> of a <NUM>-step random access, the message <NUM> including the UE ID; and
in case that the random access response does not include the UE ID and does not include the uplink grant, transmitting, to the base station, the random access preamble and the UE ID.