DETERMINATION OF CONTENTION RESOLUTION TIMER

Example embodiments of the present disclosure relate to a solution for determining a contention resolution timer. In an aspect, a first device receives, from a second device, an indication to perform Msg3 transmission. The first device transmits, to the second device, information of the first device for contention resolution. In case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device, the first device determines a duration for monitoring a contention resolution message based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part. Example embodiments of the present disclosure can improve the performance of a random access procedure.

FIELD

Example embodiments of the present disclosure generally relate to the field of communication, and in particular to devices, methods, apparatuses and a computer readable medium for determining a contention resolution timer.

BACKGROUND

In wireless communications, a terminal device can perform a random access procedure with a network device to obtain access to a wireless network. The random access procedure may be triggered by a number of events, for example, an initial access from RRC_IDLE, an radio resource control (RRC) Connection Re-establishment procedure, downlink (DL) or uplink (UL) data arrival during RRC_CONNECTED when UL synchronisation status is “non-synchronised,” UL data arrival during RRC_CONNECTED when there are no physical uplink control channel (PUCCH) resources for scheduling request (SR) available, an SR failure, a request by RRC upon synchronous reconfiguration (such as handover), a transition from RRC_INACTIVE, to establish time alignment for a secondary Timing Advance Group (TAG), a request for other system information (SI), a beam failure recovery, and so on.

Currently, two types of random access procedure are supported: 4-step RA type and 2-step RA type. Both types of RA procedure support contention-based random access (CBRA) and contention-free random access (CFRA). CFRA with 2-step RA type is only supported for handover. However, various details of some aspects of the 2-step RA type have not been specified and need to be clarified.

SUMMARY

In general, example embodiments of the present disclosure provide a solution for determining a contention resolution timer.

In a first aspect, there is provided a first device. The first device comprises at least one processor and at least one memory storing computer program codes. The at least one memory and the computer program codes are configured, with the at least one processor, to cause the first device to receive, from a second device, an indication to perform Msg3 transmission. The at least one memory and the computer program codes are also configured, with the at least one processor, to cause the first device to transmit, to the second device, information of the first device for contention resolution. The at least one memory and the computer program codes are further configured, with the at least one processor, to cause the first device to, in case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device, determine a duration for monitoring a contention resolution message based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part.

In a second aspect, there is provided a second device. The second device comprises at least one processor and at least one memory storing computer program codes. The at least one memory and the computer program codes are configured, with the at least one processor, to cause the second device to transmit, to a first device, an indication to perform Msg3 transmission. The at least one memory and the computer program codes are also configured, with the at least one processor, to cause the second device to, in case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device, determine a duration for transmitting a contention resolution message to the first device based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part. The at least one memory and the computer program codes are further configured, with the at least one processor, to cause the second device to in accordance with a determination that information of the first device for contention resolution is received from the first device, transmit the contention resolution message to the first device within the duration.

In a third aspect, there is provided a method. The method comprises receiving, at a first device from a second device, an indication to perform Msg3 transmission. The method also comprises transmitting, to the second device, information of the first device for contention resolution. The method further comprises in case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device, determining a duration for monitoring a contention resolution message based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part.

In a fourth aspect, there is provided a method. The method comprises transmitting, at a second device to a first device, an indication to perform Msg3 transmission. The method also comprises in case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device, determining a duration for transmitting a contention resolution message to the first device based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part. The method further comprises in accordance with a determination that information of the first device for contention resolution is received from the first device, transmitting the contention resolution message to the first device within the duration.

In a fifth aspect, there is provided an apparatus. The apparatus comprises means for receiving, at a first device from a second device, an indication to perform Msg3 transmission. The apparatus also comprises means for transmitting, to the second device, information of the first device for contention resolution. The apparatus further comprises means for in case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device, determining a duration for monitoring a contention resolution message based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part.

In an sixth aspect, there is provided an apparatus. The apparatus comprises means for transmitting, at a second device to a first device, an indication to perform Msg3 transmission. The apparatus also comprises means for in case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device, determining a duration for transmitting a contention resolution message to the first device based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part. The apparatus further comprises means for in accordance with a determination that information of the first device for contention resolution is received from the first device, transmitting the contention resolution message to the first device within the duration.

In a seventh aspect, there is provided a non-transitory computer readable medium storing program instructions for causing an apparatus to perform at least the method according to the third or fourth aspect.

DETAILED DESCRIPTION

As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), a radio access network (RAN) node, an evolved NodeB (eNodeB or eNB), a NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), an infrastructure device for a V2X (vehicle-to-everything) communication, a Transmission/Reception Point (TRP), a Reception Point (RP), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, and so forth, depending on the applied terminology and technology.

As used herein, the term “resource,” “transmission resource,” “resource block,” “physical resource block,” “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other resource enabling a communication, and the like. In the following, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

As mentioned, two types of random access procedure are supported: 4-step RA type and 2-step RA type. The first message in the 4-step RA type may be Msg1 and first message in the 2-step RA type may be MSGA. There may be two possible cases where a UE needs to receive contention resolution with Msg4 when performing a 2-step RA procedure. The first case may be when the network receives only a random access preamble of a MSGA in the 2-step RA procedure, but does not correctly decode the physical uplink shared channel (PUSCH) payload of the MSGA, it may send a fallbackRAR to the UE to perform Msg3 transmission for the PUSCH payload of the MSGA and contention resolution with Msg4 for the UE may follow. The second case may be that after a predefined or configured number N of MSGA attempts over 2-step RACH without receiving a response from the network, the UE can switch to using a 4-step RA procedure over 4-step RACH, start with preamble transmission, then random access response (RAR) reception, then Msg3 transmission, and contention resolution reception with Msg4.

In RAN2#107bis, it was agreed to not allow switching to 4-step RACH when only 2-step RACH is configured to a bandwidth part (BWP) (for instance, uplink BWP) by not configuring 4-step RA resources or 4-step RACH in that BWP or by not configuring the number of N. In particular, a configuration where a switching from 2-step RA to 4-step RA is not allowed can be supported. The 2-step RACH resources can be configured on a BWP where 4-step RACH resources are not configured. In that case, switching to 4-step RA after N MSGA attempts may not be supported.

However, after receiving a fallbackRAR in a MSGB after MSGA transmission, a UE may need to continue with Msg3 transmission and perform contention resolution. How to determine the contention resolution window (or timer) to use after a fallback from 2-step RACH to Msg3 transmission or after switching from 2-step RACH to 4-step RACH is still not clear and indefinite, and thus needs to be studied and clarified.

For example, in one scenario, when a 4-step RACH configuration is not available for an active BWP of a UE where the RA procedure is performed, the UE behavior is unclear related to the timer for handling when the contention resolution is performed. One option would be to disallow using the fallbackRAR from the network in case 2-step RACH only BWP exists and the UE would always go back to MSGA reattempt even if preamble is correctly received. However, this will make the usage of such BWP for random access impractical, since there is much higher probability for the network being able to decode the preamble than the PUSCH part of a MSGA. Hence, the fallback as part of the 2-step RA procedure may need to be allowed in all BWPs even if the BWPs are configured only with 2-step RACH.

In view of the above problems and other potential problems in the traditional solutions, example embodiments of the present disclosure provide a solution for determining a contention resolution timer. In particular, in example embodiments of the present disclosure, duration for a terminal device to monitor a contention resolution message (or Msg4) transmitted by a network device in response to a Msg3 can be determined based on one or more of several factors in various scenarios including, for example, a fallback from the 2-step RA procedure to the Msg3 transmission, and a switching from the 2-step RA procedure to the 4-step RA procedure.

A plurality of advantages can be achieved through example embodiments of the present disclosure. For example, a fallback from the 2-step RA via a fallbackRAR is currently broken if the 4-step RA is not configured for the active BWP. Example embodiments can enable the fallback to Msg3 transmission and Msg4 reception, even if the 4-step RACH is not configured within the given BWP. In addition, example embodiments can also allow the network to prioritize, in the 4-step RACH, the UEs that have failed a plurality of times through the 2-step RACH. In general, example embodiments of the present disclosure can improve the performance of a random access procedure. Principles and implementations of example embodiments of the present disclosure will be described in detail below with reference to the figures.

FIG. 1illustrates a schematic diagram of a communication environment100in which some example embodiments of the present disclosure can be implemented. As shown inFIG. 1, the communication environment (also referred to as a communication network)100includes a first device110and a second device120which can communicate with each other via a communication link115.

In general, the first device110and the second device120can be any two suitable devices that can perform communications between them. In some example embodiments, the first device110may be a terminal device, and the second device120may be a network device. For example, the second device120can be a serving device of the first device110located in a cell105of the second device120. For transmissions from the second device120to the first device110, the communication link115may be referred to as a downlink channel, whereas for transmissions from the first device110to the second device120, the communication link115may alternatively be referred to as an uplink channel.

In order to communicate with the second device120and the communication network100, the first device110may need to first perform a random access procedure to obtain access to the second device120and the communication network100. Two types of random access procedure are supported: 4-step RA type and 2-step RA type. Both types of RA procedure support contention-based random access (CBRA) and contention-free random access (CFRA). The first device110can select the type of random access at initiation of the random access procedure based on network configuration.

In the CBRA with 4-step RA type performed on a 4-step random access channel, the first device110can first transmit a random access preamble (also referred to as a Msg1) to the second device120. Then, the second device120can transmit a random access response (also referred to as a Msg2) to the first device110. Based on the received random access response, the first device110may transmit a first scheduled transmission (also referred to as a Msg3) to the second device120, which may include information of the first device110for contention resolution, also termed as a PUSCH payload or payload for short. In response to the scheduled transmission from the first device110, the second device120can transmit a contention resolution message (also referred to as Msg4) to the first device110. The contention resolution message can indicate whether the contention resolution is successful for the first device110.

In some examples, the contention resolution may be considered as successful based on a contention resolution message if notification of a reception of a PDCCH transmission of the Special Cell (SpCell) is received from lower layers and if the Cell-Radio Network Temporary Identifier (C-RNTI) medium access control (MAC) control element (CE) was included in Msg3 and if the Random Access procedure was initiated for beam failure recovery (as specified in clause 5.17) and the PDCCH transmission is addressed to the C-RNTI.

In some examples, the contention resolution may be considered as successful based on a contention resolution message if notification of a reception of a PDCCH transmission of the SpCell is received from lower layers and if the C-RNTI MAC CE was included in Msg3 and if the Random Access procedure was initiated by a PDCCH order and the PDCCH transmission is addressed to the C-RNTI.

In some examples, the contention resolution may be considered as successful based on a contention resolution message if notification of a reception of a PDCCH transmission of the SpCell is received from lower layers and if the C-RNTI MAC CE was included in Msg3 and if the Random Access procedure was initiated by the MAC sublayer itself or by the RRC sublayer and the PDCCH transmission is addressed to the C-RNTI and contains a UL grant for a new transmission.

In some examples, the contention resolution may be considered as successful based on a contention resolution message if the common control channel (CCCH) service data unit (SDU) was included in Msg3 and the PDCCH transmission is addressed to its TEMPORARY_C-RNTI and if the MAC PDU is successfully decoded and if the MAC PDU contains a UE Contention Resolution Identity MAC CE and if the UE Contention Resolution Identity in the MAC CE matches the CCCH SDU transmitted in Msg3.

Otherwise, contention resolution may be considered as unsuccessful, for instance, when parts of the above conditions are fulfilled but not all.

In the CBRA with 2-step RA type performed on a 2-step random access channel, the first device110can first transmit a MSGA to the second device110, which MSGA may include random access preamble and payload (also referred to as PUSCH payload) transmissions of the random access procedure for 2-step RA type. In other words, the MSGA in the CBRA with 2-step RA type can include both the contents of the Msg1 and Msg3 in the CBRA with 4-step RA type. In response to the MSGA, the second device120can transmit a MSGB to the first device110. For example, the MSGB may consist of response(s) for contention resolution, fallback indication(s), and backoff indication.

In the random access procedure of the 2-step RA type, after MSGA transmission, the first device110can monitor for a response (namely, the MSGB) from the second device120within a configured time window, for instance, a MSGB reception window. In particular, for CBRA, if contention resolution is successful upon receiving the network response, the first device110can end the random access procedure; while if an fallback indication is received in the MSGB (for example, in case that the second device120successfully receives the random access preamble in the MSGA, but unsuccessfully receives the PUSCH payload in the MSGA), first device110can perform Msg3 transmission and monitors a contention resolution message (a Msg4) from the second device120. If contention resolution is not successful after Msg3 (re)transmission(s), first device110may go back to MSGA transmission, for example, if the contention resolution timer (or window) expires. In addition, if the 2-step random access procedure is not completed after a predefined or configured number of MSGA transmissions, first device110can be configured to switch to the 4-step CBRA procedure.

In some scenarios, the first device110may be configured, for example by the second device120, with a number of bandwidth parts, which may have different bandwidths and configurations. For example, the bandwidth parts may be uplink bandwidth parts. For example, the configurations of the 2-step random access channel and the 4-step random access channel may be different in different bandwidth parts of the first device110. In addition, one of the 2-step random access channel and the 4-step random access channel may be unavailable for one or more bandwidth parts of the first device110. For instance, the 4-step random access channel may be unavailable in an active bandwidth part for the first device110, which is the bandwidth part in which the first device110is currently operating, for example, the active bandwidth part.

In addition to the active bandwidth part, the first device110may be configured with other bandwidth parts for various functions. For example, the first device110may have an initial bandwidth part, in which the 4-step random access channel is available for the first device110to obtain access to network through the random access procedure. More specifically, a UE configured for operation in bandwidth parts (BWPs) of a serving cell, is configured by higher layers for the serving cell a set of bandwidth parts (BWPs) for receptions by the UE (DL BWP set) in a DL bandwidth by parameter BWP-Downlink or by parameter initialDownlinkBWP with a set of parameters configured by BWP-DownlinkCommon and BWP-DownlinkDedicated, and a set of BWPs for transmissions by the UE (UL BWP set) in an UL bandwidth by parameter BWP-Uplink or by parameter initialUplinkBWP with a set of parameters configured by BWP-UplinkCommon and BWP-UplinkDedicated.

As another example, the first device110may have a first active bandwidth part for the handover scenario, in which the first device110can first operate after a handover. More specifically, the UE can be provided by firstActiveDownlinkBWP-Id a first active DL BWP for receptions and by firstActiveUplinkBWP-Id a first active UL BWP for transmissions on a carrier of a serving cell, for example, primary cell or primary secondary cell or secondary cell. If a UE is provided by firstActiveDownlinkBWP-Id a first active DL BWP and by firstActiveUplinkBWP-Id a first active UL BWP on a carrier of a secondary cell, the UE uses the indicated DL BWP and the indicated UL BWP as the respective first active DL BWP on the secondary cell and first active UL BWP on the carrier of the secondary cell when it is activated from deactivated state or upon configuration.

As a further example, the first device110may have a default bandwidth part for saving power, where default bandwidth part may be relatively narrower than other bandwidth parts. More specifically, for a serving cell, a UE can be provided by defaultDownlinkBWP-Id a default DL BWP among the configured DL BWPs. If a UE is not provided a default DL BWP by defaultDownlinkBWP-Id, the default DL BWP is the initial DL BWP.

Although the first device110and the second device120are described in the communication environment100ofFIG. 1, example embodiments of the present disclosure may be equally applicable to any other suitable communication devices in communication with one another. That is, example embodiments of the present disclosure are not limited to the example scenario ofFIG. 1. In this regard, it is noted that although the first device110and the second device120are schematically depicted as a mobile phone and a base station inFIG. 1, it is understood that this depiction is only for example without suggesting any limitation. In other example embodiments, the first device110and the second device120may be any other communication devices, for example, wireless communication devices.

It is to be understood that the number of communication devices, the number of communication links, and the number of other elements as shown inFIG. 1are only for the purpose of illustration without suggesting any limitations. The communication environment100may include any suitable number of communication devices, any suitable number of communication links, and any suitable number of other elements adapted for implementing example embodiments of the present disclosure. In addition, it would be appreciated that there may be various wireless communications as well as wireline communications (if needed) among all the communication devices.

Communications in the communication environment100may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1G), the second generation (2G), the third generation (3G), the fourth generation (4G) and the fifth generation (5G) and on the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and/or any other technologies currently known or to be developed in the future.

Reference is now made toFIG. 2, which illustrates an example communication process200between the first device110and the second device120in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the communication process200will be described with reference toFIG. 1. However, it would be appreciated that the communication process200may be equally applicable to other communication scenarios where two devices communicate with each other.

As shown inFIG. 2, the second device120transmits210an indication205to the first device110, and the indication205may cause the first device110to perform Msg3 transmission. For example, before the second device120transmits210the indication205, the first device110may have transmitted a MSGA to the second device120to initiate a 2-step random access procedure. However, the second device120may have successfully received the random access preamble in the MSGA, but have failed to receive the PUSCH payload in the MSGA.

In such an event, the second device120may then inform the first device110to transmit a Msg3 as a retransmission of the PUSCH payload of the MSGA (or generally the MAC PDU stored in the MSGA buffer), and the indication205can be a fallbackRAR in a MSGB in response to MSGA transmission. It should be understood that example embodiments of the present disclosure are not limited to this specific scenario, but are equally applicable to any other scenarios in which the second device120transmit an indication to the first device110to perform Msg3 transmission.

After receiving220the indication205from the second device120, the first device110transmits240information215of the first device110for contention resolution to the second device120, and the second device120receives250the same from the first device110. In some example embodiments, the information215may include C-RNTI MAC CE or CCCH SDU, submitted from upper layer and associated with the UE Contention Resolution Identity, as part of a Random Access procedure. More generally, the information215may include any information of the first device110that can be used for contention resolution in a random access procedure. In some example embodiments, the information215may be transmitted240via a Msg3 of a random access procedure and the second device120may thus receive250the information215via the Msg3. In the following, the information215may also be referred to as the Msg3215for ease of discussion. However, it is to be understood that the first device110can alternatively transmit240the information215via any other existing or future messages.

As mentioned above, subsequent to transmitting240the Msg3215, the first device110may expect a contention resolution message (also referred to as Msg4)235from the second device120. In particular, the first device110can monitor the contention resolution message or potential retransmission grant for Msg3 re-transmission235from the second device120for duration225, which may be determined in a same way at both sides of the first device110and the second device120. If the Msg3 is not correctly decoded by the second device120, it may schedule retransmission within the contention resolution timer. The first device220restarts the timer upon retransmission of Msg3.

If the contention resolution message235is received within the duration225, then the first device110may determine whether the contention resolution is successful for itself based on the content of the contention resolution message235. If the contention resolution is successful, the first device110can end the random access procedure. Otherwise, if the contention resolution message235is not received within the duration225but Msg3 retransmission grant is received, the first device110may retransmit the Msg3215based on the scheduled retransmission grant. If the first device110still fails to receive the contention resolution message and Msg3 retransmission grant235within the duration225, the first device110can start another attempt of the random access procedure. Similarly, if the content of the contention resolution message235indicates that the contention resolution is unsuccessful for the first device110, the first device110can also start another attempt of the random access procedure, with either MSGA or Msg1 transmission depending on whether it has performed maximum number of MSGA re-attempts.

Therefore, in order to allow the first device110to complete the random access procedure, the second device120may need to know the duration225for the first device110to monitor the contention resolution message or Msg3 retransmission grant235, and may need to transmit270the contention resolution message or Msg3 retransmission grant235to the first device110within the duration225. Accordingly, before transmitting270the contention resolution message or Msg3 retransmission grant235to the first device110, the second device120can determine230the duration225during which the first device110monitors the contention resolution message or Msg3 retransmission grant235. In other words, the second device120determines230the duration225for transmitting the contention resolution message or Msg3 retransmission grant235to the first device110. Although the determining operation230is depicted after the transmitting operation210and before the receiving operation250, it should be noted that the second device120can determine the duration225at any suitable time point prior to the transmission of the contention resolution message or Msg3 retransmission grant235. Similarly, the first device110needs to determine the duration225.

With different configurations of the 2-step random access channel and the 4-step random access channel, the first device110and/or the second device120may determine230the duration225in different ways. For example, it may be assumed that the first device110is operating in its active bandwidth part, and the 4-step random access channel is available in the active bandwidth part. Then, the configuration of the 4-step random access channel for the active bandwidth part may indicate a contention resolution timer, which may be used by the first device110for monitoring a Msg4 in a 4-step random access procedure. In this event, the first device110can determine the duration225as the time length of the contention resolution timer as indicated in the configuration of the 4-step random access channel. Accordingly, if the 4-step random access channel is available in a bandwidth part for the first device110, the network (for example, the second device120) may not need to configure a contention resolution timer in the configuration of the 2-step random access channel in the bandwidth part.

However, as discussed above, the 4-step random access channel may sometimes be unavailable in the active bandwidth part for the first device110. In other words, there is not a configured contention resolution timer for the active bandwidth part that can be used by the first device110to monitor the contention resolution message235. In this event, as an explicit rule for determining the duration225, the first device110and/or the second device120may determine230the duration225based on a configuration of the 2-step random access channel in the active bandwidth part, which configuration may also be referred to as a first configuration hereinafter. More specifically, if the 4-step random access channel is unavailable for the active bandwidth part and the first configuration indicates a contention resolution timer, the first device110and/or the second device120can determine230the duration225as the time length of the contention resolution timer as indicated in the first configuration. With such an explicit rule, the efficiency of the determination of the duration225by the first device110(and also the second device120) can be improved.

Alternatively, as an implicit rule for determining the duration225, the first device110and/or the second device120may determine230the duration225based on a configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part, which configuration may also be referred to as a second configuration hereinafter. In other words, although the 4-step random access channel is unavailable for the active bandwidth part, it may be available in other bandwidth parts of the first device110. Thus, in case the 4-step random access channel is unavailable for the active bandwidth part, the first device110and/or the second device120can determine230the duration225as the time length of a contention resolution timer indicated in the second configuration of the 4-step random access channel in another bandwidth part. With such an implicit rule, there is no need to use extra signaling for indicating the duration225, and thus the signaling overhead can be reduced. In some example embodiments, the implicit rule may be applied only if the explicit rule is not applied. In other words, if the first configuration does not indicate a contention resolution timer, then the second device120can determine230the duration225based on the second configuration.

As some examples, the above bandwidth part different from the active bandwidth part may be an initial bandwidth part, a default bandwidth part, a first active bandwidth part, or other defined bandwidth parts of the first device110. For example, the 4-step random access channel may be always available in an initial bandwidth part for the first device110, and thus the contention resolution timer advertised in the system information block (SIB) for the initial UL BWP or configured by dedicated radio resource control (RRC) signaling for the UE for the initial UL BWP may be used for contention resolution reception by the first device110. Further, which one of the various bandwidth parts is to be used for the above purpose may be configurable by the network, for example, the second device120.

In this way, the contention resolution timer as indicated in the configuration of the 4-step random access channel in an already defined bandwidth part for the first device110can be used for the active bandwidth part without a configuration of the 4-step random access channel, and thus the signaling overhead for indicating a particular bandwidth part for such a function can be saved.

Alternatively, the above bandwidth part different from the active bandwidth part may be a predetermined bandwidth part indicated by the second device120. In other words, the second device120can indicate a specific bandwidth part, and the contention resolution timer as indicated in the configuration of the 4-step random access channel in this indicated bandwidth part can be used by the first device110and/or the second device120(also the first device110) to determine the duration225. In this way, the flexibility of selection of the bandwidth part whose configuration of the 4-step random access channel is to be used for the active bandwidth part can be improved.

In some example embodiments, as another implicit rule for determining the duration225, the first device110and/or the second device120may determine230the duration225based on a time length during which the first device110monitors a MSGB from the second device120. The MSGB monitored by the first device110is transmitted by the second device120in response to a MSGA transmitted by the first device110over the 2-step random access channel. For example, such a timer length during which the first device110monitors a MSGB from the second device120may be referred to as MSGB response window or msgB-ResponseWindow. Such example embodiments will be described later in more details with reference toFIG. 3.

In some example embodiments, for determining the duration225, the first device110and/or the second device120may determine230the duration225based on a partial configuration of a 4-step random access channel in the active bandwidth part, which configuration may also be referred to as a second configuration hereinafter. In other words, although the 4-step random access channel is unavailable for the active bandwidth part, part of the configuration may be provided for the active bandwidth part as well, for instance, the part of the configuration consisting of the contention resolution timer configuration. In some embodiments, any other parameters (in addition to the contention resolution timer configuration) of the 4-step random access channel configuration may be ignored by the first device110.

The above discussions are based on the assumption that the 4-step random access channel is unavailable in the active bandwidth part for the first device110. However, as an example embodiment of the explicit rule for determining the duration225, the first configuration of the 2-step random access channel in the active bandwidth part may always indicate a contention resolution timer, regardless of whether the 4-step random access channel is unavailable in the active bandwidth part. In another example embodiment, the first configuration of 2-step random access channel with contention resolution timer in the active bandwidth part may be only present or configured by the second device120if the 4-step random access channel is not configured or is unavailable in the active bandwidth part as explained above.

In other words, there is a possibility that both the configuration of the 2-step random access channel and the configuration of the 4-step random access channel are present for the active bandwidth part, and the two configurations indicate two contention resolution timers with different time lengths. For ease of discussion, the contention resolution timer indicated in the configuration of the 2-step random access channel may be referred to as a first contention resolution timer, and the contention resolution timer indicated in the configuration of the 4-step random access channel may be referred to as a second contention resolution timer.

In the case that both the first and second contention resolution timers are present in the active bandwidth part for the first device110, the second device120(also the first device110) may always determine the duration225as the time length of the first contention resolution timer, since it is indicated for the 2-step random access procedure as currently being performed by the first device110. However, for the scenario in which the first device110switches from a 2-step random access procedure to a 4-step random access procedure after a predefined or configured number of unsuccessful random access attempts, there are two options for selecting the contention resolution timer to be used by the first device110in the 4-step random access procedure.

As the first option, the first contention resolution timer may be selected as the contention resolution timer to be used in the 4-step random access procedure. If the first contention resolution timer has a shorter time length than the second contention resolution timer, this allows the network (for example, the second device120) to prioritize, in the 4-step RACH, UEs whose random access procedures lasted already over a number of MSGA attempts through the 2-step RACH.

Alternatively, as the second option, the second contention resolution timer may be selected as the contention resolution timer to be used in the 4-step random access procedure. This may be a more intuitive option, since a 4-step random access procedure is currently performed by the first device110anyway. On the other hand, if the 4-step random access channel is not configured, namely, there is only the first contention resolution timer but no second contention resolution timer, then the first contention resolution timer may be used for a fallback case and the first device110cannot switch to a 4-step random access procedure after a number of MSGA attempts in a 2-step random access procedure.

Continuing with reference toFIG. 2, after transmitting240the Msg3215to the second device120, the first device110may determine260the duration225in a same way as that used by the second device120for determining230the duration225, so that the first device110and the second device120can obtain identical duration225. For example, if the configuration of the 4-step random access channel is unavailable in the active bandwidth part for the first device110, the first device110can determine260the duration225based on the first configuration of the 2-step random access channel in the active bandwidth part, or the second configuration of the 4-step random access channel in a bandwidth part different from the active bandwidth part. Further details of the determining operation260may be understood with reference to the description of the determining operation230, and thus will not be repeated herein. Although the determining operation260is depicted after the transmitting operation240, it is appreciated that the first device110can determine the duration225at any suitable time point prior to receiving280the contention resolution message235.

In general, the first configuration and the second configuration for determining the duration225can be obtained by the first device110and the second device120in any suitable manner. For example, the two configurations may be predefined or predetermined by the higher layer, so that there is no need to use extra signaling for indicating the first and second configurations. In some other example embodiments, the second device120can determine the first and second configurations for the first device110, and then inform the first device110of the two configurations. In this way, the first and second configurations can be determined by the network in a flexible manner. Such example embodiments will be detailed later with reference toFIG. 4.

After determining230the duration225and receiving250the information215of the first device110for contention resolution from the first device110, the second device120transmits270the contention resolution message or Msg3 re-transmission grant235to the first device110within the duration225. For example, if the contention resolution is successful for the first device110, the second device120can transmit the contention resolution message235indicating the success of the contention resolution for the first device110. Otherwise, if the contention resolution is unsuccessful for the first device110, the second device120can transmit the contention resolution message235indicating that the contention resolution is failed for the first device110.

Similarly, after transmitting240the Msg3215to the second device120and determining260the duration225, the first device110can monitor the contention resolution message235for the duration225. For example, the first device110can start a contention resolution timer with the duration225for monitoring the contention resolution message235. Upon receiving280the contention resolution message235from the second device120within the duration225, the first device110can determine whether the contention resolution is successful for itself based on the content of the contention resolution message235. If the contention resolution is successful for the first device110, the random access procedure is complete. Otherwise, if the first device110fails to receive the contention resolution message235within the duration225after a number of transmissions of the Msg321, or receives the contention resolution message235indicating the contention resolution is unsuccessful for itself, the first device110can make another attempt to perform the random access procedure.

As described above, in some example embodiments, the first device110and/or the second device120may determine230the duration225based on a time length during which the first device110monitors a MSGB from the second device120, for example MSGB response window. Such example embodiments will now be described with reference toFIG. 3, which illustrates another example communication process300between the first device110and the second device120in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the communication process300will be described with reference toFIG. 1. However, it would be appreciated that the communication process300may be equally applicable to other communication scenarios where two devices communicate with each other.

As shown inFIG. 3, in order to initiate a 2-step random access procedure, the first device110may transmit310a MSGA305to the second device120, for example, on the 2-step random access channel. After transmitting310the MSGA305, the first device110may expect a MSGB315to be transmitted330by the second device120in response to the MSGA305. Therefore, the first device110can monitor the MSGB315for a time length325, which may be indicated in the configuration of the 2-step random access channel for the active bandwidth part and may be referred to as an MSGB response window hereinafter. If the MSGB315is received340within the time length325, the first device110can proceed to perform a next operation based on the content of the MSGB315.

For example, if the second device120successfully receives320the random access preamble but not the payload in the MSGA305, then the MSGB315transmitted330by the second device120may contain a fallback indication to indicate the first device110to perform Msg3 transmission. Upon receiving340the MSGB315containing the fallback indication, the first device may transmit a Msg3 to the second device120, which Msg3 may be a retransmission of the payload in the MSGA305. In this event, the MSGB315containing the fallback indication may be an embodiment of the indication205as shown inFIG. 2.

As another example, if the second device120successfully receives both the random access preamble and the payload in the MSGA305, and the contention resolution is successful for the first device110, then the MSGB315transmitted330by the second device120can include contention resolution information indicating the success of the contention resolution for the first device110. Upon receiving340the MSGB315containing the contention resolution information, the first device110may determine that the contention resolution is successful for itself and the 2-step random access procedure is complete.

On the other hand, if the first device110fails to receive the MSGB315within the time length325, the first device110can retransmit the MSGA305to the second device120. If the first device110still fails to receive the MSGB315within the time length325after a predefined or configured number of (re)transmission of the MSGA305, the first device110may switch to a 4-step random access procedure in case the 4-step random access channel is available. Otherwise, the first device110may determine that the random access procedure fails.

At the network side, after receiving320the MSGA305from the first device110, the second device120can transmit330the MSGB315to the first device110within the time length325, which time length325is also known by the second device120. As discussed above, the content of the MSGB315may depend on whether the contention resolution is successful for the first device110and whether the content of the MSGA305is successfully received320by the second device120.

Referring to bothFIGS. 2 and 3, in the case that the MSGB315contains a fallback indication, the communication process200as shown inFIG. 2may be performed between the first device110and the second device120subsequently. In some example embodiments, when determining230the duration225, the first device110and/or the second device120can determine230the duration225as the time length325for the first device110monitoring the MSGB315from the second device120. In other words, the first device110and/or the second device120can determine230the duration225as the time length325for the second device120to transmit the MSGB315to the first device110. Analogously, when determining260the duration225, the first device110can determine260the duration225as the time length325for monitoring the MSGB315from the second device120.

In this way, the duration225and the time length325can be configured to be identical, and thus can be indicated using a common indication instead of separate indications, thereby reducing the signaling overhead. Alternatively, the duration225may be determined as the time length325regardless of whether the 4-step random access channel is configured for the active bandwidth part, since the MSGB response window is intended for monitoring a response to the PUSCH part of the MSGA, which is retransmitted in the Msg3 for the fallback case. Further, the network (for example, the second device120) can configure which one of the MSGB response window and the contention resolution timer indicated in the configuration of the 4-step random access channel is to be applied to determine the duration225if both are configured.

As mentioned above in describingFIG. 2, in some example embodiments, the second device120can determine the first configuration and the second configuration for the determining the duration225, and then inform the first device110of the first configuration and the second configuration. In this way, the first configuration and the second configuration can be determined by the network in a flexible manner. Such example embodiments will now be detailed with reference toFIG. 4.

FIG. 4illustrates a further example communication process400between the first device110and the second device120in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the communication process400will be described with reference toFIG. 1. However, it would be appreciated that the communication process400may be equally applicable to other communication scenarios where two devices communicate with each other.

As shown inFIG. 4, the second device120may determine410the first configuration405and the second configuration415for the first device110. In particular, the second device120can configure various parameters of the 2-step random access channel in the active bandwidth part for the first device110, and also configure various parameters of the second configuration of the 4-step random access channel in the bandwidth part different from the active bandwidth part. In addition, the second device120can configure whether the 2-step random access channel or the 4-step random access channel is available for a bandwidth part for the first terminal device110. For example, the second device120may configure the 4-step random access channel to be unavailable in a particular bandwidth part for the first device110.

Without loss of generality, it is assumed that the particular bandwidth part is used by the first device110as the active bandwidth part. In this event, there is no available configuration of the 4-step random access channel for the first device110to perform a fallback from the 2-step random access procedure to Msg3 transmission. Accordingly, the second device120can configure a contention resolution timer in the first configuration405of the 2-step random access channel in the particular bandwidth part. In other words, if the configuration of the 4-step random access channel is unavailable in a bandwidth part, the second device120can determine410the first configuration405to indicate a contention resolution timer for the bandwidth part. In this way, an explicit indication of the contention solution timer is provided to the first device110to enable a fallback from the 2-step random access procedure to Msg3 transmission.

On the other hand, if the 4-step random access channel is available in a bandwidth part for the first device110, the second device120may not indicate a contention resolution timer in the first configuration405of the 2-step random access channel in the bandwidth part. In other words, if the configuration of the 4-step random access channel is available in a bandwidth part, the second device120may determine410the first configuration405to not indicate a contention resolution timer for the bandwidth part. In this way, the signaling overhead for indicating the contention resolution timer can be saved.

Alternatively, the second device120may determine the first configuration405to indicate a contention resolution timer for a bandwidth part, regardless of whether the 4-step random access channel is available in the bandwidth part. In other words, the second device120can always configure a contention resolution timer in the first configuration405of the 2-step random access channel in a bandwidth part for the first device110, no matter whether the 4-step random access channel is available in the bandwidth part or not. In this way, the operation of the second device120for configuring the contention resolution timer in the first configuration405can be simplified, because the second device120does not to determine whether the 4-step random access channel is available before configure the contention resolution timer in the first configuration405.

After determining410the first configuration405and the second configuration415, the second device120may transmit420them to the first device110. For example, the first configuration405and the second configuration415may be transmitted420via one message, such as a RRC message. Alternatively, the first configuration405and the second configuration415can be transmitted420in separate messages, such as two RRC messages. In addition, referring bothFIGS. 2 and 4, the first device110and/or the second device120can determine230the duration225based on the first configuration405and the second configuration415. In a similar way, after receiving430the first configuration405and the second configuration415from the second device120, the first device110may determine260the duration225based on the first configuration405and the second configuration415.

FIG. 5illustrates a flowchart of an example method500in accordance with some example embodiments of the present disclosure. In some example embodiments, the method500can be implemented at a device in a communication network, such as the first device110as shown inFIG. 1. Additionally or alternatively, the method500can also be implemented at other devices shown inFIG. 1. In some other example embodiments, the method500may be implemented at devices not shown inFIG. 1.

At block510, the first device110receives, from the second device120, an indication to perform Msg3 transmission. At block520, the first device110transmits, to the second device120, information of the first device for contention resolution. At block530, in case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device110, the first device110determines a duration for monitoring a contention resolution message based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part.

In some example embodiments, determining the duration comprises: in accordance with a determination that the first configuration indicates a contention resolution timer, determining the duration as a time length of the contention resolution timer.

In some example embodiments, determining the duration comprises: in case the first configuration does not indicate a contention resolution timer, determining the duration as a time length of a contention resolution timer indicated in the second configuration.

In some example embodiments, the bandwidth part comprises one of the following: an initial bandwidth part for the first device110, a default bandwidth part for the first device110, a first active bandwidth part for the first device110, or a predetermined bandwidth part indicated by the second device120.

In some example embodiments, the method500further comprises: in case the first configuration does not indicate a contention resolution timer, determining the duration as a time length for monitoring a MSGB from the second device120, the MSGB being transmitted by the second device120in response to a MSGA transmitted over the 2-step random access channel.

In some example embodiments, the time length for monitoring the MSGB is a time length of an MSGB response window.

In some example embodiments, the information of the first device for contention resolution is transmitted via a Msg3 of a random access procedure.

In some example embodiments, the method500further comprises: receiving the first configuration and the second configuration from the second device120.

In some example embodiments, the first device110comprises a terminal device, and the second device120comprises a network device.

FIG. 6illustrates a flowchart of another example method600in accordance with some example embodiments of the present disclosure. In some example embodiments, the method600can be implemented at a device in a communication network, such as the second device120as shown inFIG. 1. Additionally or alternatively, the method600can also be implemented at other devices shown inFIG. 1. In some other example embodiments, the method600may be implemented at devices not shown inFIG. 1.

At block610, the second device120transmits, to the first device110, an indication to perform Msg3 transmission. At block620, in case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device110, the second device120determines a duration for transmitting a contention resolution message to the first device110based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part. At block630, the second device120determines whether information of the first device for contention resolution is received from the first device110. At block640, in accordance with a determination that the information of the first device for contention resolution is received from the first device110, the second device120transmits the contention resolution message to the first device110within the duration.

In some example embodiments, determining the duration comprises: in accordance with a determination that the first configuration indicates a contention resolution timer, determining the duration as a time length of the contention resolution timer.

In some example embodiments, determining the duration comprises: in case the first configuration does not indicate a contention resolution timer, determining the duration as a time length of a contention resolution timer indicated in the second configuration.

In some example embodiments, the bandwidth part comprises one of the following: an initial bandwidth part for the first device110, a default bandwidth part for the first device110, a first active bandwidth part for the first device110, or a predetermined bandwidth part indicated by the second device120.

In some example embodiments, the method600further comprises: in case the first configuration does not indicate a contention resolution timer, determining the duration as a time length for the first device110to monitor a MSGB from the second device120, the MSGB being transmitted by the second device120in response to a MSGA transmitted over the 2-step random access channel.

In some example embodiments, the time length for monitoring the MSGB is a time length of an MSGB response window.

In some example embodiments, the information of the first device for contention resolution is received via a Msg3 of a random access procedure.

In some example embodiments, the method600further comprises: determining the first configuration and the second configuration; and transmitting the first configuration and the second configuration to the first device110.

In some example embodiments, determining the first configuration comprises: in accordance with a determination that the configuration of the 4-step random access channel is unavailable in the active bandwidth part, determining the first configuration to indicate a contention resolution timer for the active bandwidth part.

In some example embodiments, determining the first configuration comprises: determining the first configuration to indicate a contention resolution timer for the active bandwidth part, regardless of whether the 4-step random access channel is available in the active bandwidth part.

In some example embodiments, the first device110comprises a terminal device, and the second device120comprises a network device.

In some example embodiments, an apparatus capable of performing the method500(for example, the first device110) may comprise means for performing the respective steps of the method500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises means for receiving, at a first device from a second device, an indication to perform Msg3 transmission; means for transmitting, to the second device, information of the first device for contention resolution; and means for in case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device, determining a duration for monitoring a contention resolution message based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part.

In some example embodiments, the means for determining the duration comprises: means for in accordance with a determination that the first configuration indicates a contention resolution timer, determining the duration as a time length of the contention resolution timer.

In some example embodiments, the means for determining the duration comprises: means for in case the first configuration does not indicate a contention resolution timer, determining the duration as a time length of a contention resolution timer indicated in the second configuration.

In some example embodiments, the bandwidth part comprises one of the following: an initial bandwidth part for the first device, a default bandwidth part for the first device, a first active bandwidth part for the first device, or a predetermined bandwidth part indicated by the second device.

In some example embodiments, the apparatus further comprises: means for in case the first configuration does not indicate a contention resolution timer, determining the duration as a time length for monitoring a MSGB from the second device, the MSGB being transmitted by the second device in response to a MSGA transmitted over the 2-step random access channel.

In some example embodiments, the time length for monitoring the MSGB is a time length of an MSGB response window.

In some example embodiments, the apparatus further comprises: means for receiving the first configuration and the second configuration from the second device.

In some example embodiments, the first device comprises a terminal device, and the second device comprises a network device.

In some example embodiments, the apparatus further comprises means for performing other steps in some example embodiments of the method500. In some example embodiments, the means comprises at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

In some example embodiments, an apparatus capable of performing the method600(for example, the second device120) may comprise means for performing the respective steps of the method600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises means for transmitting, at a second device to a first device, an indication to perform Msg3 transmission; means for in case a configuration of a 4-step random access channel is unavailable in an active bandwidth part for the first device, determining a duration for transmitting a contention resolution message to the first device based on one of: a first configuration of a 2-step random access channel in the active bandwidth part, or a second configuration of a 4-step random access channel in a bandwidth part different from the active bandwidth part; and means for in accordance with a determination that information of the first device for contention resolution is received from the first device, transmitting the contention resolution message to the first device within the duration.

In some example embodiments, the means for determining the duration comprises: means for in accordance with a determination that the first configuration indicates a contention resolution timer, determining the duration as a time length of the contention resolution timer.

In some example embodiments, the means for determining the duration comprises: means for in case the first configuration does not indicate a contention resolution timer, determining the duration as a time length of a contention resolution timer indicated in the second configuration.

In some example embodiments, the bandwidth part comprises one of the following: an initial bandwidth part for the first device, a default bandwidth part for the first device, a first active bandwidth part for the first device, or a predetermined bandwidth part indicated by the second device.

In some example embodiments, the apparatus further comprises: means for in case the first configuration does not indicate a contention resolution timer, determining the duration as a time length for the first device to monitor a MSGB from the second device, the MSGB being transmitted by the second device in response to a MSGA transmitted over the 2-step random access channel.

In some example embodiments, the time length for monitoring the MSGB is a time length of an MSGB response window.

In some example embodiments, the apparatus further comprises: means for determining the first configuration and the second configuration; and means for transmitting the first configuration and the second configuration to the first device.

In some example embodiments, the means for determining the first configuration comprises: means for in accordance with a determination that the configuration of the 4-step random access channel is unavailable in the active bandwidth part, determining the first configuration to indicate a contention resolution timer for the active bandwidth part.

In some example embodiments, the means for determining the first configuration comprises: means for determining the first configuration to indicate a contention resolution timer for the active bandwidth part, regardless of whether the 4-step random access channel is available in the active bandwidth part.

In some example embodiments, the first device comprises a terminal device, and the second device comprises a network device.

In some example embodiments, the apparatus further comprises means for performing other steps in some example embodiments of the method600. In some example embodiments, the means comprises at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

FIG. 7illustrates a simplified block diagram of a device700that is suitable for implementing example embodiments of the present disclosure. The device700may be provided to implement a communication device, for example the first device110and the second device120as shown inFIG. 1. As shown, the device700includes one or more processors710, one or more memories720coupled to the processor710, and one or more communication modules740coupled to the processor710.

The communication module740is for bidirectional communications. The communication module740has at least one antenna to facilitate communications. The communication interface may represent any interface that is necessary for communications with other network elements.

A computer program730includes computer executable instructions that are executed by the associated processor710. The computer program730may be stored in the ROM724. The processor710may perform any suitable actions and processing by loading the computer program730into the RAM722.

The example embodiments of the present disclosure may be implemented by means of the computer program730so that the device700may perform any process of the disclosure as discussed with reference toFIG. 5 or 6. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some example embodiments, the computer program730may be tangibly contained in a computer readable medium which may be included in the device700(such as in the memory720) or other storage devices that are accessible by the device700. The device700may load the computer program730from the computer readable medium to the RAM722for execution. The computer readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like.

FIG. 8illustrates a block diagram of an example computer readable medium800in accordance with some example embodiments of the present disclosure. In the example ofFIG. 8, the computer readable medium800is in form of CD or DVD. The computer readable medium800has the computer program730stored thereon.