Patent Description:
In both the fourth Generation (<NUM>) and the fifth Generation (<NUM>) new radio (NR) mobile networks, before a user equipment (UE) sends data to a base station (BS), the UE needs to obtain uplink synchronization and downlink synchronization with the BS. The uplink timing synchronization may be achieved by performing a random access procedure.

An exemplary four-step random access procedure <NUM> is shown in <FIG>. As shown in <FIG>, a UE <NUM> transmits a preamble in Message (Msg) <NUM> to a BS <NUM> at operation <NUM>. Once the preamble is received successfully by the BS <NUM>, the BS <NUM> will send at operation <NUM> a Msg <NUM> back to the UE <NUM>, in which a medium access control (MAC) random access response (RAR) is included as a response to the preamble. The MAC RAR may include an uplink (UL) grant and a temporary cell radio network temporary identifier (TC-RNTI). After the MAC RAR is received, the UE <NUM> transmits Msg <NUM> at operation <NUM> to the BS <NUM> with the physical uplink shared channel (PUSCH) grant carried in the MAC RAR. After the Msg <NUM> is received, the BS <NUM> will send the Msg <NUM> back at operation <NUM> to the UE <NUM>, in which some kind of contention resolution identity (ID) will be included for the purpose of contention resolution. A communication system merely relying on an initial access procedure as mentioned above will induce latency and cannot meet the needs of faster and newer communications in future network developments.

Thus, existing systems and methods for performing a random access procedure in a wireless communication are not entirely satisfactory. 3GPP Draft R1-<NUM> is a related prior art document.

The exemplary embodiments disclosed herein are directed to solving the issues relating to one or more of the problems presented in the prior art, as well as providing additional features that will become readily apparent by reference to the following detailed description when taken in conjunction with the accompany drawings. In accordance with various embodiments, exemplary systems, methods, devices and computer program products are disclosed herein.

<FIG>, <FIG>, <FIG>, <FIG> and <FIG> represent unclaimed aspects.

Various exemplary embodiments of the present disclosure are described below with reference to the accompanying figures to enable a person of ordinary skill in the art to make and use the present disclosure.

A typical wireless communication network includes one or more base stations (typically known as a "BS") that each provides geographical radio coverage, and one or more wireless user equipment devices (typically known as a "UE") that can transmit and receive data within the radio coverage. In the wireless communication network, a BS and a UE can communicate with each other via a communication link, e.g., via a downlink radio frame from the BS to the UE or via an uplink radio frame from the UE to the BS.

The present disclosure provides methods for a terminal or a UE to complete access to a BS by a two-step random access channel (RACH) procedure, to accelerate the entire initial access procedure and significantly reduce the overall initial access latency of the communication network. A two-step RACH procedure will complete the random access in two steps. In one embodiment, the UE transmits a first message (referred as Msg A) including both a preamble and a payload to the BS in a first step. The BS will then transmit a second message (referred as Msg B) in response to the first message to the UE to complete the access. In other words, Msg A of two-step RACH merges the equivalent content of Msg <NUM> and Msg <NUM> of four-step RACH, and Msg B of two-step RACH merges the equivalent content of Msg <NUM> and Msg <NUM> of four-step RACH.

In some embodiments, after the UE transmits the Msg A to the network, the UE receives the response in Msg B which includes an indication for a type or function of each MAC RAR in Msg B. The indication may be carried in the downlink control information (DCI), or in the MAC RAR, or a MAC subheader. In case the indication for the type of MAC RAR is carried in the MAC RAR, the indication bit may be placed before the ordinary RAR content.

The type of MAC RAR in Msg B may be selected from at least one of the following options: a response for normal contention resolution, a response for fall back mode, a response for NACK indication, and a response for Msg <NUM> of a four-step RACH. The MAC RAR for contention resolution may contain a contention resolution ID carried in the payload of Msg A. The MAC RAR for fall back mode may contain a Msg <NUM> scheduling message.

In various embodiments, a BS may be referred to as a network side node and can include, or be implemented as, a next Generation Node B (gNB), an E-UTRAN Node B (eNB), a Transmission Reception Point (TRP), an Access Point (AP), a donor node (DN), a relay node, a core network (CN) node, a RAN node, a master node, a secondary node, a distributed unit (DU), a centralized unit (CU), etc. A UE in the present disclosure can be referred to as a terminal and can include, or be implemented as, a mobile station (MS), a station (STA), etc. A BS and a UE may be described herein as non-limiting examples of "wireless communication nodes;" and a UE may be described herein as non-limiting examples of "wireless communication devices. " The BS and UE can practice the methods disclosed herein and may be capable of wireless and/or wired communications, in accordance with various embodiments of the present disclosure.

<FIG> illustrates an exemplary two-step random access procedure <NUM>, in accordance with some embodiments of the present disclosure. A two-step RACH procedure will complete the <NUM> steps in <FIG> in <NUM> messages or <NUM> steps. In other words, at least some content of Msg <NUM> and Msg <NUM> in the four-step RACH are included in Msg A of the two-step RACH; and at least some content of Msg <NUM> and Msg <NUM> are included in Msg B of the two-step RACH. As shown in <FIG>, a UE <NUM> transmits, at operation <NUM>, Msg A that includes both a preamble and a payload to a BS <NUM> for access to the BS <NUM>. Then at operation <NUM>, the BS <NUM> transmits to the UE <NUM> Msg B in response to the Msg A.

In one embodiment, the channel structure of Msg A includes preamble and PUSCH carrying payload which includes at least the content of Msg <NUM> in the traditional <NUM>-step RACH. The Msg B may include the content equivalent to contents of Msg <NUM> and Msg <NUM> of <NUM>-step RACH and handle the contention resolution function for <NUM>-step RACH.

When the UE sends the Msg A, the BS needs to distinguish the random access (RA) types to determine whether the UE initiates from a two-step CBRA (contention based RACH) or a four-step CBRA. Otherwise, the BS will always try to decode the payload in each payload occasion and the RAR window will be significantly impacted when the preamble is successfully detected, which is not reasonable in terms of latency and energy efficiency. The RACH type may be indicated based on the used preamble time or frequency resource. The system allocates different available time/frequency resource occasions (ROs) for two-step CBRA and four-step CBRA individually, which can help the BS to distinguish the types of RACH. There may be two sets of parameters of PRACH (physical random access channel) configuration, one set for <NUM>-step RACH and the other set for <NUM>-step RACH. Msg B will be sent from the BS to the UE if the preamble in Msg A has been detected. Depending on whether the payload in Msg A is successfully decoded, the content of Msg B may be different. More details will be described later referring to <FIG>.

<FIG> illustrates a block diagram of a base station (BS) <NUM>, in accordance with some embodiments of the present disclosure. The BS <NUM> is an example of a node that can be configured to implement the various methods described herein. As shown in <FIG>, the BS <NUM> includes a housing <NUM> containing a system clock <NUM>, a processor <NUM>, a memory <NUM>, a transceiver <NUM> including a transmitter <NUM> and receiver <NUM>, a power module <NUM>, a random access message analyzer <NUM>, a random access message generator <NUM>, a response type configurator <NUM>, and a failure and fallback operator <NUM>.

In this embodiment, the system clock <NUM> provides the timing signals to the processor <NUM> for controlling the timing of all operations of the BS <NUM>. The processor <NUM> controls the general operation of the BS <NUM> and can include one or more processing circuits or modules such as a central processing unit (CPU) and/or any combination of general-purpose microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate array (FPGAs), programmable logic devices (PLDs), controllers, state machines, gated logic, discrete hardware components, dedicated hardware finite state machines, or any other suitable circuits, devices and/or structures that can perform calculations or other manipulations of data.

The transceiver <NUM>, which includes the transmitter <NUM> and receiver <NUM>, allows the BS <NUM> to transmit and receive data to and from a remote device (e.g., another BS or a UE). An antenna <NUM> is typically attached to the housing <NUM> and electrically coupled to the transceiver <NUM>. In various embodiments, the BS <NUM> includes (not shown) multiple transmitters, multiple receivers, and multiple transceivers. In one embodiment, the antenna <NUM> is replaced with a multi-antenna array <NUM> that can form a plurality of beams each of which points in a distinct direction. The transmitter <NUM> can be configured to wirelessly transmit packets having different packet types or functions, such packets being generated by the processor <NUM>. Similarly, the receiver <NUM> is configured to receive packets having different packet types or functions, and the processor <NUM> is configured to process packets of a plurality of different packet types. For example, the processor <NUM> can be configured to determine the type of packet and to process the packet and/or fields of the packet accordingly.

In a communication system including the BS <NUM> that can serve one or more UEs, the BS <NUM> may receive a random access request from a UE for access to the BS <NUM>. In one embodiment, the random access message analyzer <NUM> may receive, via the receiver <NUM> from the UE, a first message including a preamble and a payload for an access to the BS <NUM>. The random access message analyzer <NUM> may analyze the first message and inform the random access message generator <NUM> about the first message for generating a response.

In one embodiment, the random access message generator <NUM> may generate a second message including a response to the first message. The random access message generator <NUM> may transmit the second message via the transmitter <NUM> to the UE. In one embodiment, the second message includes an indication indicating a type of the response selected from a plurality of types.

In one embodiment, the indication is carried in downlink control information (DCI). In another embodiment, the indication is carried in a subheader in a header of the second message. The header includes at least one subheader. In one example, the indication is carried by at least one additional bit added into the subheader. In another example, the indication is carried by at least one reserved bit in the subheader.

In another embodiment, the indication is carried in a random access response (RAR) in the second message. For example, the indication is located before ordinary RAR content in the RAR. The ordinary RAR content may include a contention resolution identity (ID) and/or scheduling information for a third message of a <NUM>-step random access. In one example, the indication is carried by at least one additional bit added into the RAR. In another example, the indication is carried by at least one reserved bit in the RAR.

In one embodiment, the second message indicates whether the second message is for a <NUM>-step random access or a <NUM>-step random access based on at least one selected from the group of: a radio network temporary identifier (RNTI) used for scrambling a downlink control channel of the second message; and a random access preamble (RAP) ID in a subheader in the second message.

The response type configurator <NUM> in this example may configure the response for a contention resolution for the access to the BS <NUM>; and determine the type of the response based on the configuring. In this case, the response may include a contention resolution identity (ID) carried in the payload of the first message.

In another embodiment, the response type configurator <NUM> may configure the response for a fallback to a <NUM>-step random access and for a UE that supports a <NUM>-step random access; and determine the type of the response based on the configuring. In this case, the response may include scheduling information for a third message of the <NUM>-step random access.

In another embodiment, the response type configurator <NUM> may configure the response for a negative acknowledgement (NACK) indication for a retransmission of the payload of the first message. In another embodiment, one of the plurality of types corresponds to a response that is configured for a UE that supports a <NUM>-step random access.

The failure and fallback operator <NUM> in this example may perform one or more operations in response to a determination of failure or fallback. In one embodiment, the failure and fallback operator <NUM> may generate a negative acknowledgement (NACK) indicator for a retransmission of the payload of the first message in response to a decoding error of the payload. The failure and fallback operator <NUM> may inform the random access message generator <NUM> to generate the second message based on the NACK indicator. Then, the failure and fallback operator <NUM> may receive the exact payload transmitted again from the UE. The MAC layer entity in this case is still for a <NUM>-step random access.

In another embodiment, the failure and fallback operator <NUM> generate an indication for a fallback to a <NUM>-step random access in response to a decoding error of the payload, and inform the random access message generator <NUM> to generate the second message based on the fallback indication. Then, the failure and fallback operator <NUM> may receive a second payload transmitted from the UE. The second payload may or may not be the same as the original payload transmitted in the first message Msg A. The MAC layer entity in this case switches to fit a <NUM>-step random access.

The power module <NUM> can include a power source such as one or more batteries, and a power regulator, to provide regulated power to each of the above-described modules in <FIG>. In some embodiments, if the BS <NUM> is coupled to a dedicated external power source (e.g., a wall electrical outlet), the power module <NUM> can include a transformer and a power regulator.

The various modules discussed above are coupled together by a bus system <NUM>. The bus system <NUM> can include a data bus and, for example, a power bus, a control signal bus, and/or a status signal bus in addition to the data bus. It is understood that the modules of the BS <NUM> can be operatively coupled to one another using any suitable techniques and mediums.

As used herein, the term "layer" refers to an abstraction layer of a layered model, e.g. the open systems interconnection (OSI) model, which partitions a communication system into abstraction layers. A layer serves the next higher layer above it, and is served by the next lower layer below it.

Although a number of separate modules or components are illustrated in <FIG>, persons of ordinary skill in the art will understand that one or more of the modules can be combined or commonly implemented. For example, the processor <NUM> can implement not only the functionality described above with respect to the processor <NUM>, but also implement the functionality described above with respect to the random access message analyzer <NUM>. Conversely, each of the modules illustrated in <FIG> can be implemented using a plurality of separate components or elements.

<FIG> illustrates a flow chart for a method <NUM> performed by a BS, e.g. the BS <NUM> in <FIG>, for performing a random access procedure, in accordance with some embodiments of the present disclosure. At operation <NUM>, the BS receives and analyzes a first message including a preamble and a payload from a UE for an access to the BS. At operation <NUM>, the BS generates a response to the first message and an indication indicating a type of the response. At operation <NUM>, the BS transmits, to the UE, a second message including the response and the indication. At operation <NUM>, the BS optionally performs operations in response to a determination of failure or fallback. According to various embodiments, the order of the above operations may be changed.

<FIG> illustrates a block diagram of a user equipment (UE) <NUM>, in accordance with some embodiments of the present disclosure. The UE <NUM> is an example of a device that can be configured to implement the various methods described herein. As shown in <FIG>, the UE <NUM> includes a housing <NUM> containing a system clock <NUM>, a processor <NUM>, a memory <NUM>, a transceiver <NUM> including a transmitter <NUM> and a receiver <NUM>, a power module <NUM>, a random access message generator <NUM>, a random access message analyzer <NUM>, a response type determiner <NUM>, and a failure and fallback operator <NUM>.

In this embodiment, the system clock <NUM>, the processor <NUM>, the memory <NUM>, the transceiver <NUM> and the power module <NUM> work similarly to the system clock <NUM>, the processor <NUM>, the memory <NUM>, the transceiver <NUM> and the power module <NUM> in the BS <NUM>. An antenna <NUM> or a multi-antenna array <NUM> is typically attached to the housing <NUM> and electrically coupled to the transceiver <NUM>.

In a communication system, the UE <NUM> may want to access a BS for data transfer. In one embodiment, the random access message generator <NUM> may generate a first message including a preamble and a payload for an access to the BS. The random access message generator <NUM> may transmit the first message via the transmitter <NUM> to the BS. The random access message generator <NUM> may inform the random access message analyzer <NUM> about the first message so that the random access message analyzer <NUM> will monitor a response from the BS.

The random access message analyzer <NUM> in this example may receive, via the receiver <NUM> from the BS, a second message including a response to the first message. The random access message analyzer <NUM> may analyze the second message to determine that the second message includes an indication indicating a type of the response selected from a plurality of types.

The response type determiner <NUM> in this example may determine, based on the type of the response, that the response is configured for a contention resolution for the access to the BS. In this case, the response may include a contention resolution identity (ID) carried in the payload of the first message.

In another embodiment, the response type determiner <NUM> may determine, based on the type of the response, that the response is configured for a fallback to a <NUM>-step random access, and is configured for a UE that supports a <NUM>-step random access. In this case, the response may include scheduling information for a third message of the <NUM>-step random access.

In another embodiment, the response type determiner <NUM> may determine, based on the type of the response, that the response is configured for a negative acknowledgement (NACK) indication for a retransmission of the payload of the first message. In another embodiment, one of the plurality of types corresponds to a response that is configured for a UE that supports a <NUM>-step random access.

The failure and fallback operator <NUM> in this example may perform one or more operations in response to an indication of failure or fallback. In one embodiment, the failure and fallback operator <NUM> may determine that there is a negative acknowledgement (NACK) indicator in the second message for a retransmission of the payload of the first message in response to a decoding error of the payload. The failure and fallback operator <NUM> may inform the random access message generator <NUM> to retransmit, via the transmitter <NUM>, the exact payload again to the BS, in response to the NACK indicator in the second message. The MAC layer entity in this case is still for a <NUM>-step random access.

In another embodiment, the failure and fallback operator <NUM> may determine that there is an indication in the second message for a fallback to a <NUM>-step random access in response to a decoding error of the payload. The failure and fallback operator <NUM> may generate and transmit, via the transmitter <NUM>, a third message to the BS, in response to the fallback indication. The third message includes a second payload which may or may not be the same as the original payload transmitted in the first message. The MAC layer entity in this case switches to fit a <NUM>-step random access.

The various modules discussed above are coupled together by a bus system <NUM>. The bus system <NUM> can include a data bus and, for example, a power bus, a control signal bus, and/or a status signal bus in addition to the data bus. It is understood that the modules of the UE <NUM> can be operatively coupled to one another using any suitable techniques and mediums.

Although a number of separate modules or components are illustrated in <FIG>, persons of ordinary skill in the art will understand that one or more of the modules can be combined or commonly implemented. For example, the processor <NUM> can implement not only the functionality described above with respect to the processor <NUM>, but also implement the functionality described above with respect to the random access message generator <NUM>. Conversely, each of the modules illustrated in <FIG> can be implemented using a plurality of separate components or elements.

<FIG> illustrates a flow chart for a method <NUM> performed by a UE, e.g. the UE <NUM> in <FIG>, for performing a random access procedure, in accordance with some embodiments of the present disclosure. At operation <NUM>, the UE generates and transmits a first message including a preamble and a payload to the BS. At operation <NUM>, the UE receives and analyzes, from the BS, a second message including a response to the first message. At operation <NUM>, the UE determines a type of the response based on an indication in the second message. At operation <NUM>, the UE optionally performs operations in response to a failure or fallback indication. According to various embodiments, the order of the above operations may be changed.

<FIG> illustrates an exemplary method <NUM> for performing a random access procedure, in accordance with some embodiments of the present disclosure. As shown in <FIG>, a UE <NUM> transmits, at operation <NUM>, a Msg A that includes both a preamble and a payload to a BS <NUM> for access to the BS <NUM>. Then at operation <NUM>, the BS <NUM> determines that whether the payload is successfully detected. If so, the BS <NUM> transmits at operation <NUM> to the UE <NUM> Msg B including a contention resolution ID in response to the Msg A. That is, for the case both the preamble and payload of Msg A are successfully detected and decoded, the Msg B is for a two-step RACH contention resolution. A C-RNTI or TC-RNTI disclosed in the payload can well fulfill contention resolution purpose. The UL grant could be used to schedule the possible uplink data packets right after the RACH procedure if buffer state report (BSR) is reported in Msg A.

If the BS <NUM> determines that the payload is not successfully detected at operation <NUM>, the BS <NUM> transmits at operation <NUM> to the UE <NUM> Msg B which contains identical content as Msg <NUM> in a <NUM>-step RACH. Then the UE <NUM> transmits at operation <NUM> Msg <NUM> including the PUSCH grant to the BS <NUM>. In response, the BS <NUM> transmits at operation <NUM> Msg <NUM> including a contention resolution ID to the UE <NUM>. That is, for the case that the preamble is successfully detected but the payload is not successfully decoded, the RACH procedure will fall back to traditional four-step RACH. The Msg B sent in the second step could be identical to a legacy Msg <NUM>. The content of the Msg B may include a traditional RAR which includes the random access preamble identity (RAPID) as well as a TC-RNTI. The UL grant in fallback mode is for Msg <NUM> scheduling as in a legacy <NUM>-step RACH.

Since the time/frequency resources for Msg A and Msg <NUM> are different, the RNTI used for scrambling the physical downlink control channel (PDCCH) of the second step message are different. For a two-step RACH, the second step message is Msg B and its PDCCH is scrambled by the two-step-RA-RNTI. For a four-step RACH, the second step message is Msg <NUM> and its PDCCH is scrambled by the traditional RA-RNTI. The two-step-RA-RNTI is derived at least from the time/frequency resources of Msg A, while the RA-RNTI for <NUM>-step RACH is derived at least from the time/frequency resources of Msg <NUM>. As discussed before, the time/frequency resources of Msg A and the time/frequency resources of Msg <NUM> are different. As such, the two-step-RA-RNTI is different from the RA-RNTI. Although the content of the Msg B of a <NUM>-step RACH may be identical to the content of a legacy Msg <NUM>, Msg B is different from the real Msg <NUM> of a four-step RACH. The MAC layer entity for Msg B in this case is still for a two-step RACH.

Msg B is used for the <NUM>-step contention based RACH, while Msg <NUM> is used for the <NUM>-step RACH. UE could distinguish whether the second message is Msg B in response to Msg A or Msg <NUM> in response to Msg <NUM>, based on a determination that whether the PDCCH scramble code is two-step-RA-RNTI or RA-RNTI.

<FIG> illustrates a basic medium access control (MAC) protocol data unit (PDU) structure <NUM> for a message in a random access procedure. As shown in <FIG>, a MAC PDU <NUM> carried by the physical downlink shared channel (PDSCH) of Msg B may include a MAC header <NUM>, MAC RARs <NUM>, <NUM>, <NUM> (MAC payload), and a padding <NUM>. The PDSCH is scheduled by the DCI of Msg B. The MAC header <NUM> includes the RAPID subheaders which include in this example at least the detected RAPID k <NUM>, <NUM>, <NUM> corresponding to the MAC RAR k <NUM>, <NUM>, <NUM>, where k = <NUM>, <NUM>. That is, the Msg B includes one or multiple MAC RARs depending on the number of detected preamble index (RAPID) in the same Msg A time/frequency resource.

The network cannot guarantee that the payloads of all Msg A's are decoded. One possibility is that some UEs' preambles are detected but their payloads are not decoded, and some other UE's preambles and payloads are both successfully detected and decoded. If all the above mentioned UEs' Msg A responses need to be carried in a same Msg B, the cascaded MAC RARs corresponding to different RAPIDs may be different. Some are for a contention resolution, while the others are for a fall back mode.

As such, there are at least two options for the type or function of a MAC RAR. One option is for normal contention resolution as long as the payload is successfully decoded, where the contention resolution means the MAC RAR contains the contention resolution ID which is carried in the payload of Msg A. The other option is for a fall back mode when the preamble is successfully detected but the payload is not successfully decoded. The fall back mode means the MAC RAR contains a Msg <NUM> scheduling message.

The network can indicate UE in the Msg B which option the MAC RAR corresponds to, and indicate whether the payload is successfully decoded or the MAC RAR is for fall back mode or for the NACK indication of payload which will be described in detail referring to <FIG>. Without the indication, UE may no longer distinguish the type or function of MAC RAR and misunderstand the content of MAC RAR. The indication for type or function of MAC RAR can be carried in the DCI (downlink control information) of Msg B, or carried in the MAC header or MAC RAR content.

The indication carried in the DCI is commonly used for all the MAC RARs in Msg B. So when the Msg B includes only one MAC RAR, this kind of indication is suitable. While when multiple MAC RARs are included in the Msg B, it is preferable that the indication for the type or function of MAC RAR is carried in the MAC RAR itself or the MAC subheader which can individually indicate the type or function of each MAC RAR. If the indication bits are in the MAC subheader, the indication bits may use the reserved bits in a traditional MAC subheader or use some new bits added into a traditional MAC subheader. If the indication bits are carried in a MAC RAR, the indication bits may be placed before the ordinary RAR content which includes the details of contention resolution ID or Msg <NUM> scheduling message. The indication bits can reuse the reserved bits in MAC RAR or newly added bits in MAC RAR.

<FIG> illustrates a detailed exemplary MAC PDU structure <NUM> for a message in a random access procedure, in accordance with some embodiments of the present disclosure. As shown in <FIG>, a MAC PDU <NUM> carried by the PDSCH of Msg B may include a MAC header <NUM>, MAC RARs <NUM>, <NUM>, <NUM> (MAC payload), and a padding <NUM>. The MAC header <NUM> includes the RAPID subheaders <NUM>, <NUM>, <NUM> each of which in this example may include a RAPID and a RAR type indication for a corresponding one of the MAC RARs <NUM>, <NUM>, <NUM>. According to various embodiments, one or more of the subheaders <NUM>, <NUM>, <NUM> include RAR type indications, while other subheaders do not. In addition, each of the MAC RARs <NUM>, <NUM>, <NUM> may include a RAR type indication for the RAR itself. According to various embodiments, one or more of the MAC RARs <NUM>, <NUM>, <NUM> include RAR type indications, while other MAC RARs do not.

In addition to the above two options for the type of a MAC RAR, a MAC RAR may also indicate a NACK to a UE when the preamble is successfully detected but the payload is not successfully decoded. When the UE gets the NACK indication, the UE will retransmit the exact payload again but without the preamble. <FIG> illustrates another exemplary method <NUM> for performing a random access procedure, in accordance with some embodiments of the present disclosure. As shown in <FIG>, a UE <NUM> transmits, at operation <NUM>, a Msg A that includes both a preamble and a payload to a BS <NUM> for access to the BS <NUM>. Then at operation <NUM>, the BS <NUM> transmits to the UE <NUM> Msg B including a NACK indicator in response to the Msg A, after the BS <NUM> determines that the preamble is successfully detected but the payload is not successfully decoded. At operation <NUM>, the UE <NUM> retransmits the same payload in Msg A to the BS <NUM>. Then at operation <NUM>, the BS <NUM> may transmit to the UE <NUM> a message for contention resolution.

As discussed above, when the time/frequency resources for Msg A and Msg <NUM> are different, then the RNTI used for scrambling the PDCCH of the second step message are different. The UE could distinguish whether the second message for response of Msg A or Msg <NUM> is a Msg B and a Msg <NUM>, based on the PDCCH scramble code. But in case the time/frequency resources for Msg A and Msg <NUM> are same, the RNTI used for scrambling the PDCCH of the second step message cannot be used to distinguish between the Msg B and the Msg <NUM>. In that case, the UE could distinguish between the Msg B and Msg <NUM> based on the different preamble indices used for Msg A and Msg <NUM>. For example, it may be pre-determined that one group of preamble indices are used for Msg A, Msg B, and <NUM>-step RACH, while another group of preamble indices are used for Msg <NUM>, Msg <NUM>, and <NUM>-step RACH.

In another embodiment, as the preamble index will be included in the Msg B MAC subheader, it means one of the MAC RARs in Msg B may be the MAC RAR for a traditional <NUM>-step RACH. That is, another option for the type or function of a MAC RAR in Msg B is that the MAC RAR in Msg B is a traditional MAC RAR of Msg <NUM>. This may be configured for a UE that can only support a <NUM>-step RACH. It is possible that a BS serves multiple UEs, where some of the UEs support a <NUM>-step RACH, while other UEs support a <NUM>-step UE. The traditional MAC RAR of Msg <NUM> contains time advance (TA), UL grant of Msg <NUM>, and TC-RNTI, etc..

Claim 1:
A method performed by a wireless communication device, the method comprising:
transmitting, to a wireless communication node, a first message comprising a preamble and a payload for an access to the wireless communication node;
receiving, from the wireless communication node, a second message comprising a response to the first message, wherein the second message comprises an indication indicating a type of the response from a plurality of types; and
determining, based on the type of the response, that the response is configured for a contention resolution for the access to the wireless communication node or is configured for a fallback to a <NUM>-step random access, wherein when the response is configured for the contention resolution, the response comprises a contention resolution identity, ID, carried in the payload of the first message,
characterized in that the response includes a sub-header and a medium access control, MAC, random access response, RAR, associated with the sub-header, the indication indicating either the MAC RAR is a fallback MAC RAR or a contention resolution RAR and being carried in the sub-header.