Patent Description:
In recent communication networks, a random access channel (RACH) is shared by terminal devices to request access to networks for call set-up and burst data transmission. Since the RACH is shared, it is possible that two or more terminal devices transmit at the same time and their transmissions collide. This is known as contention. If the user equipment does not get response, it performs the random access request again. Such transmission collisions may incur undesirable failure of random access and unexpected delay in transmission. <CIT>, which is an earlier application under Article <NUM>(<NUM>) EPC, describes a technique involving a user equipment in RRC idle mode directly transmitting uplink data via the RACH procedure. <CIT> describes a technique involving a UE transmitting a RA preamble and UE identifier to a base station, and receiving a sequence index of the RA preamble from the base station. 3GPP TSG-RAN WG2 R2-<NUM> includes proposals for the content of Msg2 in2-step RACH. <CIT> describes a technique involving a UE determining whether a UE identifier in a random access response is consistent with the UE identifier in the random access request sent by the UE. 3GPP TSG RAN WG1 R1-<NUM> and R1-<NUM> include proposals for <NUM>-step RACH.

Generally, embodiments of the present disclosure relate to a method for contention resolution in a random access procedure and the corresponding communication devices. According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims.

In a first aspect, there is provided an apparatus for communications according to claim <NUM>. The apparatus may comprise at least one processor; and at least one memory including computer program codes; the at least one memory and the computer program codes are configured to, with the at least one processor, cause the apparatus to perform the recited operations.

In a second aspect, there is provided an apparatus for communications according to claim <NUM>. The apparatus may comprise at least one processor; and at least one memory including computer program codes; the at least one memory and the computer program codes are configured to, with the at least one processor, cause the apparatus to perform the recited operations.

In a third aspect, there is provided a method implemented at a user equipment according to claim <NUM>.

In a fourth aspect, there is provided a method implemented at a network device according to claim <NUM>.

In another aspect, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method according to any one of the above third and fourth aspects.

As used herein, the term "communication network" refers to a network following any suitable communication standards, such as Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a user equipment and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (<NUM>), the second generation (<NUM>), <NUM>, <NUM>, the third generation (<NUM>), the fourth generation (<NUM>), <NUM>, the future fifth generation (<NUM>) communication protocols, and/or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

As used herein, the term "network device" refers to a node in a communication network via which a user equipment 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), an evolved NodeB (eNodeB or eNB), a NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, a low power node such as a femto, a pico, and so forth, depending on the applied terminology and technology.

As mentioned above, several mechanisms for RACH have been proposed. For example, four-step RACH procedure has been proposed. As shown in <FIG>, for four-step RACH procedure, a RACH transmission occasion is defined as the time-frequency resource on which a PRACH message <NUM> is transmitted using the configured PRACH preamble format. The user equipment (UE) <NUM> may transmit <NUM> the RACH preamble on a PRACH resource which is mapped to a RA-RNTI and the network device may decode the preamble and obtain the RA-RNTI depending on the PRACH resource where the preamble is received. The gNB <NUM> may transmit <NUM> message <NUM> which may indicate the transmission resource of message <NUM>. In particular, the gNB <NUM> may transmit RA response scheduled with PDCCH addressed the RA-RNTI which is calculated from the PRACH resource (for example, time and/or frequency allocation). The UE <NUM> may decode the RA response and obtain the transmission resource for message3. The UE <NUM> may transmit <NUM> a radio resource control (RRC) connection request as message3 scrambled by T-CRNTI obtained from the RA response (message2). The gNB <NUM> may response <NUM> a contention resolution ID (containing the UL CCCH SDU in msg3) in message4 scrambled by T-CRNTI obtained from the RA response (message2) and T-CRNTI is considered as C-RNTI by the UE upon reception of the message <NUM>.

In recent studies, two-step RACH has also been proposed, which is shown in <FIG>. The UE <NUM> transmits <NUM> messageA or msgA to the gNB <NUM> and the gNB <NUM> transmits <NUM> messageB or msgB to the UE <NUM>. Compared to the traditional four-step RACH with preamble, RAR, message3 and contention resolution message, two-step RACH combines the transmission of preamble and the message3 payload into messageA, and combines RAR and contention resolution message into messageB. For two-step RACH, the messageA is a signal to detect the UE while the second message is for contention resolution for CBRA with a possible payload. The messageA will at least include the equivalent information which is transmitted in message3 for four-step RACH.

As a baseline, all the triggers for <NUM>-step RACH are also applicable to <NUM>-step RACH; however further analysis is needed on request and BFR as well as how timing advance and grants can be obtained for messageA.

The contention resolution in <NUM>-step RACH may be performed by including a UE identifier in the first message which is echoed in the second message. Fall-back from <NUM>-step RACH to <NUM>-step RACH may be supported. The fallback after messageA transmission is feasible only if detection of the UE without the decoding of the payload is possible and thus relies on such support at the physical layer. If <NUM>-step RACH is used for initial access, the parameters for <NUM>-step RACH procedure including resources for messageA will be broadcasted.

Fall back operation has been discussed, which proposed to use the RAR for <NUM> step RACH scheduled by PDCCH addressed to RA-RNTI to indicate fall back. <FIG> illustrates a schematic diagram of MAC PDU <NUM>. The MAC PDU may comprise MAC sub PDU <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>,. , <NUM>-M (where M is an integer number). As shown in <FIG>, the MAC sub PDU <NUM>-<NUM> has a E/T/R/BI subheader <NUM>, the MAC sub PDU <NUM>-<NUM> has a E/T/R/RAPID subheader <NUM>-<NUM> the MAC sub PDU <NUM>-<NUM> has a E/T/R/RAPID subheader <NUM>-<NUM> and a MAC RAR <NUM>. As shown in <FIG>, this requires the UE to monitor both RAR from <NUM>-step RACH and messageB addressed to CR-RNTI (Contention Resolution RNTI) from <NUM>-step RACH at the same time. In some embodiments, it is possible to reuse the RA-RNTI design as for <NUM> step RACH as well for CR-RNTI, just a different terminology as short for "RA-RNTI for msgB for <NUM>-step RACH" to distinguish it from RA-RNTI for RAR for <NUM>-step RACH. Not only this increases monitoring efforts but another issue is that the windows are different. If the legacy starting point and window length for RAR was kept, it would be too late to schedule RAR after the gNB decodes PUSCH since the gNB is able to decide contention resolution or fall back only after decoding the PUSCH payload.

According to the present disclosure, the fallback to second random access mode is indicated in messageB and the user equipment only needs to monitor the messageB for the quick mode on the downlink control signal which is addressed to an identifier. The user equipment does not need to monitor the downlink control channel for the second random access mode. In this way, the user equipment is allowed to fall back to the second random access mode without further retry of the quick mode, thereby reducing overload and latency.

<FIG> illustrates a schematic diagram of a communication system <NUM> in which embodiments of the present disclosure can be implemented. The communication system <NUM>, which is a part of a communication network, comprises terminal devices <NUM>-<NUM>, <NUM>-<NUM>,. , <NUM>-N (collectively referred to as "terminal device(s) <NUM>" where N is an integer number). The communication system <NUM> comprises one or more network devices, for example, a network device <NUM>. It should be understood that the communication system <NUM> may also comprise other elements which are omitted for the purpose of clarity. It is to be understood that the numbers of terminal devices and network devices shown in <FIG> are given for the purpose of illustration without suggesting any limitations. The network device <NUM> may communicate with the terminal devices <NUM>.

It is to be understood that the number of network devices and terminal devices is only for the purpose of illustration without suggesting any limitations. The system <NUM> may include any suitable number of network devices and terminal devices adapted for implementing embodiments of the present disclosure.

Communications in the communication system <NUM> may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (<NUM>), the second generation (<NUM>), the third generation (<NUM>), the fourth generation (<NUM>) and the fifth generation (<NUM>) and on the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) <NUM> 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.

<FIG> illustrates a schematic diagram of interactions <NUM> in accordance with the present disclosure. The interactions <NUM> may be implemented at any suitable devices. Only for the purpose of illustrations, the interactions <NUM> are described to be implemented at the user equipment <NUM>-<NUM> and the network device <NUM>. Only for the purpose of illustrations, embodiments of the present disclosure are described with reference to the two-step RACH as the first random access mode and the four-step RACH as the second random access mode. It should be noted that embodiments of the present disclosure can be applied to any suitable types of RACH.

The user equipment <NUM>-<NUM> transmits <NUM> the first request (also referred to as "message A") to access the random access channel in the first random access mode to the network device <NUM>. The first request comprises a first preamble for a first random access mode. The first preamble is transmitted on a random access channel, for example, physical random accesses channel (PRACH). In some embodiments, the user equipment <NUM>-<NUM> may determine the PRACH and preamble based on predetermined configurations. For example, the user equipment <NUM>-<NUM> may be configured with information indicating PRACHs and/or preambles used for first random access mode.

In addition, the first request comprises identity information. The identity information may be transmitted on a physical uplink shared channel (PUSCH). In other embodiments, if the user equipment <NUM>-<NUM> has a cell radio network temporary identifier (C-RNTI), for example, the user equipment <NUM>-<NUM> may be in a connected mode, the identity information may be the C-RNTI. The request may comprise C-RNTI medium access control (MAC) control element (CE).

The network device <NUM> may be configured with information indicating a set of predetermined preambles used for first random access mode. If the preambles belong to the set of predetermined preambles, the network device <NUM> may determine that the first requests are used for first random access mode.

The network device <NUM> may obtain <NUM> the identity information and the first preamble from the first request. The identity information may be used to scramble the physical downlink control channel. The first preamble indicates that the random access is in the first random access mode. The network device <NUM> determines <NUM> whether the random access procedure in the first random access mode is successful based on the capacity of the random access channel. For example, if the random access channel is overloaded, the network device <NUM> determines to back off the UEs before trying next attempt.

The network device <NUM> generate <NUM> the response (messageB) to the first request. In some embodiments, the response to multiple terminal devices may be multiplexed into the same data unit. For example, the network device <NUM> may receive another request to the random access procedure in the first random access mode. The network device may also generate another response to the other request and transmit the other response together with the response in the same PDU.

The random access response may indicate whether the random access procedure in the first random access mode is successful or not. In this way, it avoids the user equipment monitoring both CR-RNTI for first random access mode and RA-RNTI for second random access mode. The response may comprise a field to indicate whether the first random access mode is successful. The response may comprise one of: an indication of back-off (Back-off Indicator), an indication of fall back response or an indication of contention resolution, and padding. Table <NUM> below shows an example of the response (messageB). It should be noted that the values and numbers shown in Table <NUM> are only examples, not limitations.

As shown in Table <NUM>, the "<NUM>" in the field indicates that back-off value follows <NUM> bits BI. The "<NUM>" in the field indicates contention resolution for the user equipment without C-RNTI follows: <NUM> bits TA, <NUM> bits Contention resolution ID (CCCH), and <NUM> bits allocated C-RNTI.

The " <NUM>" in the field indicates fall back format follows: Random Access Preamble Identity (RAPID) for the first random access mode, RACH Occasion (RO) (if not unique via RNTI) for the first random access mode, and Random Access Response (RAR) payload for the second random access mode. If the RO is not uniquely indicated via the CR-RNTI, the RO is indicated in the response for the fall back. In some embodiments, the RO may be indicated for the BI if the response comprises multiple BIs. The number of bits needed for RO depends on the CR-RNTI designed to indicate the part of information not implied by the CR-RNTI. For example, if with current RA-RNTI and other information indicated in DCI or RAR/messageB, RO field indicates the missing information. If with one common CR-RNTI for the first random access mode, RO field indicates which RO the preamble was transmitted. If with CR-RNTI uniquely indicates time domain information, RO only needs to indicate frequency domain information. The "<NUM>" in the field may be reserved for contention resolution for the terminal devices with C-RNTI or indicate padding. Alternatively, padding can be indicated with "<NUM>" in the field with another bit following it indicating padding or BI.

The network device <NUM> transmits <NUM> the random access response (also referred to as "message B") to the user equipment <NUM><NUM>-<NUM>. In some embodiments, the network device <NUM> may determine a physical downlink control channel for transmitting the random access response. The downlink control channel is scrambled with identity information.

The identity information may be common to requests received on different random access channels. Alternatively, the identity information may also be common to all requests received on the random access channels. In an example embodiment, one common specific RNTI, contention resolution RNTI (CR-RNTI) may be configured for transmitting the random access responses, instead of linking the response to the PRACH occasion where the preamble for first request is sent.

In some embodiments, the downlink control channel is scrambled with the CR-RNTI. In other embodiments, if the network device <NUM> knows the C-RNTI of the user equipment <NUM><NUM><NUM>-<NUM>, the downlink control channel is scrambled with the C-RNTI.

The user equipment <NUM>-<NUM> monitors <NUM> the response to the first request on the downlink control channel which is scrambled with the identity information. The user equipment <NUM>-<NUM> may monitor the downlink control channel during a configured window time (for example, the contention resolution window).

The user equipment <NUM>-<NUM> determines <NUM> the random access mode for the random access procedure if the request indicates that the random access in the first random access mode fails. As mentioned above, the response may comprise a field to indicate whether the first random access mode is successful.

In some embodiments, the response may comprise the back-off indication, which means that the user equipment which does not successfully complete the random access to apply back off before next attempt. In this way, enabling/disabling of falling back to the second random access mode can be dynamically indicated in the response. The user equipment <NUM><NUM>-<NUM> may derive a random value between <NUM> and the back-off indication as its back-off value and compare the back-off value with a threshold value. The threshold value may be configurable via Radio Resource Control (RRC) signaling. If the back-off value is greater than the threshold value, it means that the resources for first random access mode are overloaded and longer delay will be introduced. The user equipment <NUM><NUM>-<NUM> may determine the second random access mode for accessing the random access.

Alternatively, if the back-off value is less than the threshold value, the user equipment <NUM><NUM>-<NUM> may select the first random access mode for the random access. In other embodiments, the response may comprise one back-off indication for the first random access mode and one back-off indication for the second random access mode. If the back-off value for the first random access mode is greater than the back-off for the second random access mode, the user equipment <NUM><NUM>-<NUM> may determine the second random access mode. If the derived back-off value for the first random access mode is smaller than the derived back-off for the slow mode, the user equipment <NUM><NUM>-<NUM> may determine the first random access mode.

In some embodiments, the response may indicate that the falling back to the second random access mode is needed. For example, if the field in the response shows "<NUM>," it means the falling back to the second random access mode is needed. The user equipment <NUM><NUM>-<NUM> may continue with msg3 transmission using the uplink grant indicated in the RAR and start contention resolution timer in the second random access mode.

In some embodiments, if the user equipment <NUM>-<NUM> determines that the response comprises a random access preamble identity for the first request and a random access channel occasion for the first request, the user equipment <NUM>-<NUM> determines that it needs to fall back to the second random access mode. The user equipment <NUM>-<NUM> may also obtain random access response payload for the second random access mode from the response.

The user equipment <NUM>-<NUM> transmits <NUM> the second request for the random access. The second request comprises a preamble for the selected mode. In this way, the user equipment is allowed to fall back to the second random access mode without further retry of the quick mode, thereby reducing overload and latency.

<FIG> illustrates a flow chart of a method <NUM> in accordance with the present disclosure. The method <NUM> may be implemented at any suitable devices. Only for the purpose of illustrations, the method <NUM> is described to be implemented at the user equipment <NUM>-<NUM>.

At block <NUM>, the user equipment <NUM>-<NUM> transmits the first request (also referred to as "message A") for the random access procedure in the first random access mode to the network device <NUM>. The first request comprises a first preamble for a first random access mode. The preamble is transmitted on a random access channel, for example, physical random access channel (PRACH). In some embodiments, the user equipment <NUM>-<NUM> may determine the PRACH and preamble based on predetermined configurations. For example, the user equipment <NUM>-<NUM> may be configured with information indicating PRACHs and/or preambles used for first random access mode.

In addition, the first request comprises identity information of the user equipment <NUM><NUM>-<NUM>. The identity information may be transmitted on a physical uplink shared channel (PUSCH). In other embodiments, if the user equipment <NUM>-<NUM> has a cell radio network temporary identifier (C-RNTI), for example, the user equipment <NUM>-<NUM> may be in a connected mode, the identity information may be the C-RNTI. The request may comprise C-RNTI medium access control (MAC) control element (CE).

At block <NUM>, the user equipment <NUM>-<NUM> monitors the response to the first request on the downlink control channel. The downlink control channel is scrambled with identity information. The identity information may be common to requests received on different random access channels. Alternatively, the identity information may also be common to all requests received on the random access channels. In an example embodiment, one common specific RNTI, contention resolution RNTI (CR-RNTI) may be configured for transmitting the random access responses, instead of linking the response to the PRACH occasion where the preamble for first request is sent.

In some embodiments, the downlink control channel is scrambled with the CR-RNTI. In other embodiments, if the network device <NUM> knows the C-RNTI of the user equipment <NUM><NUM>-<NUM>, the downlink control channel is scrambled with the C-RNTI.

At block <NUM>, the user equipment <NUM>-<NUM> determines the RA mode for the random access procedure if the request indicates that first request fails. In some embodiments, the response may comprise the back-off indication, which means that the user equipment does not successfully complete the random access in the first random access mode and needs to apply back off for its next attempt. In this way, enabling/disabling of falling back to the second random access mode can be dynamically indicated in the response. The user equipment <NUM><NUM>-<NUM> may derive a random value between <NUM> and the back-off indication as its back-off value and compare the back-off value with a threshold value. The threshold value may be configurable via Radio Resource Control (RRC) signaling. If the back-off value is greater than the threshold value, it means that the resources for first random access mode are overloaded and longer delay will be introduced. The user equipment <NUM><NUM>-<NUM> may determine the second random access mode for the random access.

Alternatively, if the back-off value is less than the threshold value, the user equipment <NUM><NUM>-<NUM> may determine the first random access mode for the random access procedure. In other embodiments, the response may comprise one back-off indication for the first random access mode and one back-off indication for the second random access mode. If the derived back-off value for the first random access mode is greater than the derived back-off for the second random access mode, the user equipment <NUM><NUM>-<NUM> may determine the second random access mode. If the back-off value for the first random access mode is smaller than the back-off for the slow mode, the user equipment <NUM><NUM>-<NUM> may determine the first random access mode.

At block <NUM>, the user equipment <NUM>-<NUM> transmits the second request to the network device <NUM> for the random access procedure in the determined random access mode. The second request comprises a preamble for the selected mode. In this way, the user equipment is allowed to fall back to the second random access mode without further retry of the quick mode, thereby reducing overload and latency.

<FIG> illustrates a flow chart of a method <NUM> in accordance with the present disclosure. The method <NUM> may be implemented at any suitable devices. Only for the purpose of illustrations, the method <NUM> is described to be implemented at the network device <NUM>.

At block <NUM>, the network device <NUM> receives the request for the random access procedure in the first random access mode. The request may comprise a first preamble for the first random access mode. The preamble is transmitted on a random access channel, for example, physical random access channel (PRACH). In some embodiments, the user equipment <NUM>-<NUM> may determine the PRACH and preamble based on predetermined configurations. For example, the user equipment <NUM>-<NUM> may be configured with information indicating PRACHs and/or preambles used for first random access mode.

In addition, the first request comprises identity information of the user equipment <NUM>-<NUM>. The identity information may be transmitted on a physical uplink shared channel (PUSCH). In other embodiments, if the user equipment <NUM>-<NUM> has a cell radio network temporary identifier (C-RNTI), for example, the user equipment <NUM>-<NUM> may be in a connected mode, the identity information may be the C-RNTI. The request may comprise C-RNTI medium access control (MAC) control element (CE).

In some embodiments, at block <NUM>, the network device <NUM> may obtain the identity information and the preamble from the request. The identity information may be used to scramble the physical downlink control channel. The preamble indicates that the random access is in the first random access mode.

The network device <NUM> may determine whether the request is successful based on the capacity of the random access channel. For example, if the random access channel is overloaded, the network device <NUM> may determine that the first random access mode fails.

At block <NUM>, if the network device <NUM> determines that the request fails, the network device <NUM> generates the response indicating the failure. In some embodiments, the response to multiple terminal devices may be multiplexed into the same data unit. In this way, it avoids the user equipment monitoring both CR-RNTI for first random access mode and RA-RNTI for second random access mode. The response may comprise a field to indicate whether the first random access mode is successful. The response may comprise one of: an indication of back-off (Back-off Indicator), an indication of fall back response or an indication of contention resolution, or padding.

In some embodiments, the "<NUM>" in the field indicates that back-off indication follows <NUM> bits BI. The "<NUM>" in the field indicates contention resolution for UEs without C-RNTI follows: <NUM> bits timing advance (TA), <NUM> bits Contention resolution ID (common control channel, CCCH) and <NUM> bits allocated C-RNTI.

In some embodiments, the "<NUM>" in the field indicates fall back format follows: a random access preamble identity (RAPID) for the request, RACH Occasion (RO) (if not unique via RNTI) for the request, and random access response (RAR) payload for the second random access mode. If the RO is not uniquely indicated via the CR-RNTI, the RO is indicated in the response for the fall back. In some embodiments, the RO may be indicated for the BI if the response comprises multiple BIs. The number of bits needed for RO depends on the CR-RNTI designed to indicate the part of information not implied by the CR-RNTI. For example, if with current RA-RNTI and other inform indicated in DCI or RAR/messageB, RO field indicates the missing information. If with one common CR-RNTI for the first random access mode, RO field indicates which RO the preamble was transmitted. If with CR-RNTI uniquely indicates time domain information, RO only needs to indicate frequency domain information. The "<NUM>" in the field may be reserved or for contention resolution for the terminal devices with C-RNTI.

In some embodiments, network device <NUM> may indicate fall back indication for a certain Random Access Preamble Identity (RAPID) transmitted by the user equipment <NUM>-<NUM> as well as the contention resolution identity of the user equipment <NUM>-<NUM>. Such case may happen, for instance, when two random access preambles map to the same data resource when terminal devices transmit the messageA/msgA and network device <NUM> is only able to decode one of the data resources transmitted by the terminal devices. Hence, in some embodiments, the contention resolution identities of the terminal devices are multiplexed before the fall back indications in the messageB/msgB by the network device <NUM>. When the user equipment <NUM>-<NUM> decodes the received messageB/msgB, it will first find its contention resolution identity and can determine the first random access to be successful. In some embodiments, for example, if there is no fixed order of the contention resolution and fall back indication, the terminal devices ignores fall back indication if it finds its contention resolution identity.

At block <NUM>, the network device <NUM> transmits the response to the first request. In some embodiments, the network device <NUM> may determine a physical downlink control channel for transmitting the random access response. The downlink control channel is scrambled with identity information.

In some embodiments, an apparatus for performing the method <NUM> (for example, the user equipment <NUM>-<NUM>) may comprise respective means for performing the corresponding steps in the method <NUM>. These means may be implemented in any suitable manners. For example, it can be implemented by circuitry or software modules.

In some embodiments, the apparatus comprises: means for transmitting, at a user equipment, a first request to a network device for a random access procedure in a first random access mode; means for monitoring a response to the first request on a downlink control channel; and means for n response to receiving the response indicating that the first request fails, determining the first random access mode or a second random access mode for the random access procedure; and means for transmitting a second request to the network for the random access procedure in the determined random access mode.

In some embodiments, the means for determining the first random access mode or a second random access mode for the random access channel comprises: means for in response to the response comprising an back-off indication, determining a back-off value for the first random access mode based on the back-off indication; means for comparing the back-off value with a threshold value; and means for in response to the back-off value exceeding the threshold value, determining the second random access mode for the random access procedure.

In some embodiments, the means for determining the first random access mode or a second random access mode for the random access channel comprises: means for in response to the response comprising an back-off indication, determining a back-off value based on the back-off indication; means for comparing the back-off value with a threshold value; and means for in response to the back-off value being below the threshold value, determining the first random access mode for the random access procedure.

In some embodiments, the means for determining the first random access mode or a second random access mode for the random access channel comprises: means for in response to the response comprising an back-off indication, determining based on the response a first back-off value for the first random access mode and a second back-off value for the second random access mode; means for comparing the first back-off value with the second back-off value; and means for in response to the first back-off value exceeding the second back-off value, determining the second random access mode for the random access procedure.

In some embodiments, the means for determining the first random access mode or a second random access mode for the random access channel comprises: means for in response to the response indicating the falling back to the second random access mode is needed, determining the second random access mode for the random access channel.

In some embodiments, the apparatus further comprises: means for in response to determining that the response comprising at least one of: a random access preamble identity for the first request and a random access channel occasion for the first request, obtain random access response payload for the second random access mode from the response.

In some embodiments, the identity information comprises a preamble and identity information of the user equipment, and the apparatus further comprise: means for in response to failing to find the identity information and/or identification of the first preamble in the response, determining the first random access mode fails.

In some embodiments, an apparatus for performing the method <NUM> (for example, the network device <NUM>) may comprise respective means for performing the corresponding steps in the method <NUM>. These means may be implemented in any suitable manners. For example, it can be implemented by circuitry or software modules.

In some embodiments, the apparatus comprises: means for receiving a request from a user equipment for a random access procedure; means for in response to determining that the request fails, generating a response indicating the failure, the response further comprising information on determining the first random access mode or a second random access mode by the user equipment; and means for transmitting the response to the request on a downlink control channel.

In some embodiments, the request comprises ate least one of an back-off indication, an indication of contention resolution, or an indication of the second random access mode.

In some embodiments, if the response comprises the indication of back-off value, the response further comprises at least one of: a first back-off value for the first random access mode, or a second back-off value for the second random access mode.

In some embodiments, if the response comprises the indication of contention resolution, the response further comprises at least one of: a timing advance for the terminal device, a contention resolution identity for the user equipment, a cell radio network temporary identifier for the user equipment, or a contention resolution cell radio network temporary identifier medium access control (MAC) control element for the user equipment.

In some embodiments, if the response comprises the indication of the second random access mode, the response further comprises at least one of: a random access preamble identity for the request, a random access channel occasion for the request, or random access response payload for the second random access mode.

In some embodiments, the apparatus further comprise: means for receiving, from a further user equipment, a further request for the random access procedure; means for generating a further response to the further request; and means for transmitting the response and the further response on the downlink control channel.

<FIG> is a simplified block diagram of a device <NUM> that is suitable for implementing embodiments of the present disclosure. The device <NUM> may be provided to implement the communication device, for example the network device <NUM> or the user equipment <NUM> as shown in <FIG>. As shown, the device <NUM> includes one or more processors <NUM>, one or more memories <NUM> coupled to the processor <NUM>, and one or more communication module (for example, transmitters and/or receivers (TX/RX)) <NUM> coupled to the processor <NUM>.

In some embodiments, the program <NUM> may be tangibly contained in a computer readable medium which may be included in the device <NUM> (such as in the memory <NUM>) or other storage devices that are accessible by the device <NUM>.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the methods <NUM> and <NUM> as described above with reference to <FIG>. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Claim 1:
An apparatus (<NUM>) for communications comprising:
means for transmitting a first request to a network device (<NUM>) for a random access procedure in a first random access mode; and
means for monitoring a response to the first request on a downlink control channel; wherein the response comprises a first bit and a second bit, wherein the first bit indicates whether or not the apparatus is to switch to a second random access mode, and the second bit indicates, in the event that the first bit indicates not switching to the second random access mode, provision of a back-off value or the provision of contention resolution information;
wherein the first random access mode is a quick mode compared to the second random access mode.