Method for performing random access between user equipment and network node in wireless communication network

Abstract

A method for performing a random access between a user equipment and a network node in a wireless communication network, the method comprising the steps of: transmitting (501) a random access preamble to said base station; receiving (502) a random access response; transmitting (503) a contention resolution message; configuring (504) at least one discontinuous monitoring period of the downlink channel to receive a response to the transmitted contention resolution message; and receiving (505) a contention resolution message during an active period of the discontinuous monitoring cycle. The disclosure also relates to an apparatus configured to implement the method.

Description

Technical Field

[0001] The present invention relates generally to wireless communications, and more particularly to a method for performing contention-based random access in a wireless communication system. Background Art

[0002] Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on.

[0003] A wireless multiple access communication system may include multiple base stations, each of which supports communication for multiple mobile devices simultaneously. A base station can communicate with UEs on both the downlink and uplink. Each base station has a coverage area, sometimes referred to as a cell coverage area.

[0004] Non-terrestrial networks (NTN) have become a general term for any network involving non-terrestrial flying objects, such as satellite communications networks or high altitude platform systems (HAPS), which include aircraft, balloons and airships.

[0005] Satellite communication networks rely on spaceborne platforms including low earth orbit (LEO) satellites, medium earth orbit (MEO) satellites and geosynchronous earth orbit (GEO) satellites.

[0006] Today, there is growing interest in broadband supported by LEO NTNs leveraging larger satellite constellations. The satellite industry is currently working on integrating satellite networks into the 5G ecosystem within the 3GPP process.

[0007] The integration of non-terrestrial networks (NTNs) within the 5G framework is being standardized and can bring multiple advantages, such as wide service coverage capabilities (5G services in underserved areas), reduced vulnerability of space / airborne vehicles to physical attacks and natural disasters, enhanced service reliability (service continuity, backup links for M2M / IoT devices or passengers on mobile platforms (e.g., aircraft or ships)), and efficient multicast / broadcasting when delivering data to the network edge or even user terminals.

[0008] However, NTN integration also brings challenges related to the application and adaptation of technologies originally designed for terrestrial networks to space networks.

[0009] In particular, compared to traditional terrestrial communications, UEs communicating with NTN base stations will experience high round trip times (RTTs), which results in increased power consumption.

[0010] Whenever a UE needs to access a wireless network, it usually performs a so-called random access procedure (RA). RA is used to achieve uplink (UL) synchronization and radio resource control (RRC) connection, for example, at initial network access, RRC connection reestablishment or handover.

[0011] Two types of random access procedures can be distinguished: a contention-based random access procedure and a contention-free based random access procedure.

[0012] Figure 2 An example of messages that can be exchanged between a UE and a base station (gNB) during a contention-based random access procedure is shown. When performing a RA, the UE transmits a random access preamble to the base station using a first message (MSG1). In the case of contention-based RA, the preamble is randomly selected by the UE from a predefined set of preambles shared with other UEs, while in contention-free RA, the preamble (dedicated preamble) is allocated to the UE by the base station.

[0013] After sending the preamble, the UE monitors the PDCCH and waits for the RA response (MSG2) within the response window (RARW).

[0014] Once the preamble is received, the base station transmits a RA response (MSG2) to the UE via PDSCH (Physical Downlink Shared Channel). The response contains the RA preamble identifier, timing alignment information, an uplink grant allowing the UE to send MSG3, and a temporary C-RNTI (Cell Radio Network Temporary Identifier).

[0015] When the UE receives a response including a preamble identifier corresponding to the preamble transmitted in MSG1, it transmits uplink (UL) scheduling information (MSG3). Otherwise, the RA fails and the UE may perform a new RA attempt.

[0016] After sending MSG3, the UE starts a contention resolution (CR) timer (CRT) and keeps monitoring on the PDCCH until the CR timer expires. Finally, when the UE receives a contention resolution message (MSG4) before the CR timer (CRT) expires, random access is successful.

[0017] In the case of NTN communication, a long round trip time (RTT) may be experienced between the UE and the base station. In order to avoid contention resolution failure in such a long RTT situation, the UE may need to extend the CR timer. However, this will also increase the power consumption of the UE because the PDCCH monitoring period will also increase.

[0018] like Figure 3 As shown above, 3GPP proposes to delay the start of the CR timer based on the RTT value. Figure 31 shows a contention resolution message exchange between a UE and an NTN base station, where the start of the CR timer is delayed based on the RTT value. More specifically, the UE starts the RTT timer at the time of Msg3 transmission, and starts the CR timer only after the RTT timer expires. In this way, the UE can save power and start monitoring on the DL channel only after the RTT period expires (given by Figure 2 ” box on the top).

[0019] Even though such an approach avoids useless monitoring on the DL channel during a message round trip period while no message is expected to be received, and thus avoids wasting power, problems may arise when blind message retransmissions are implemented.

[0020] To improve coverage under such long RTT conditions, 3GPP envisions blind retransmission of Msg3, which enables the base station to blindly schedule the retransmission of Msg3 during the UE base station round trip time. As used herein, "blind retransmission" may generally refer to a retransmission scheme in which the transmitting device blindly performs one or more retransmissions for transmission without receiving any feedback from the receiving device.

[0021] Figure 4 is a partial message flow showing contention resolution messages that may be exchanged during a random access procedure performed by a UE accessing an NTN base station, the random access procedure involving blind Msg3 retransmissions. Under such conditions, the CR timer will expire upon receipt of a PDCCH indicating an Msg3 retransmission, and the UE will consider contention resolution unsuccessful, even though Msg4 will arrive later. In fact, at the time of Msg3 retransmission (MSG3 RTX), the CR timer will be restarted only after the RTT-based delay expires.

[0022] To avoid contention resolution failure, the UE may need to extend the CR timer, which will increase the power consumption of the IoT UE.

[0023] Therefore, there is a need for a method that will allow blind retransmissions during a random access procedure between a UE and an NTN base station, thereby preventing power waste. Summary of the invention

[0024] Therefore, an object of the present disclosure is to provide a method and apparatus for performing a random access procedure that reduces power consumption of a UE during contention resolution.

[0025] One aspect of the present disclosure relates to a method, performed by a user equipment, for a random access procedure between the user equipment and a network node in a wireless network, the method comprising:

[0026] - transmitting a random access preamble to the network node,

[0027] - receiving a random access response,

[0028] - transmit a contention resolution message,

[0029] - configuring at least one discontinuous monitoring period of the downlink channel to receive a response to the transmitted contention resolution message, and

[0030] - receiving a contention resolution message during an active period of said discontinuous monitoring cycle.

[0031] Discontinuous reception allows the UE to periodically switch from a dormant state to an active state according to a predefined or dynamically configured timing pattern. By discontinuously monitoring the PDCCH, this method makes it possible to extend the contention resolution timer duration (and associated PDCCH monitoring) without increasing power consumption. In this way, the UE can appropriately handle blind Msg3 retransmissions in an energy-saving manner.

[0032] According to an embodiment, discontinuous monitoring is configured based on a configuration received from said network node.

[0033] The scheduling of the on / off periods is configured by a network node (eg, base station).Thus, the base station can know when PDCCH monitoring is active on the UE side and schedule the transmission of contention resolution messages accordingly.

[0034] According to an embodiment, the discontinuous monitoring configuration is received in a system information message.

[0035] The base station can transmit the on / off scheduling and other configuration parameters in the system information block (SIB). Because the system information is cell-specific, all UEs in the cell can read the same information through one signaling. Therefore, the signaling overhead is reduced.

[0036] According to an embodiment, the discontinuous monitoring configuration is received in a random access response including a Msg3 retransmission uplink grant.

[0037] Thus, the discontinuous monitoring configuration may be transmitted by the base station together with the Msg3 retransmission uplink (UL) grant, for example in a Msg2 or random access response (RAR) message. Thus, the base station may dynamically adjust the discontinuous monitoring timing based on network conditions experienced during previous message exchanges, which is particularly advantageous because NTN base stations are moving at high speeds, resulting in frequent changes in signal propagation delays.

[0038] According to an embodiment, the discontinuous monitoring configuration is received in both the random access response including the Msg3 retransmission grant and the system information message.

[0039] It is also envisaged that the discontinuous monitoring configuration may be transmitted in both the SIB and the RAR.Thus, the default configuration transmitted in the system information may be updated later to better correspond to the network conditions experienced by the UE and the network nodes.

[0040] According to an embodiment, discontinuous monitoring on the downlink channel period is performed while the contention resolution timer is running.

[0041] The network reduces the UE's monitoring time by configuring the on-off period in the contention resolution timer.

[0042] According to an embodiment, discontinuous monitoring of the downlink channel is performed from the expiration of a first contention resolution timer associated with the transmission of a first Msg3 message and the initiation of a second contention resolution timer associated with the retransmission of the Msg3 message.

[0043] The CR timer is thus extended until the retransmission CR timer starts.By configuring discontinuous PDCCH monitoring, power consumption is reduced during the extended CR timer period.

[0044] According to another aspect of the present disclosure, an apparatus is contemplated for performing random access between the apparatus and a base station in a wireless communication network, the apparatus comprising a processor coupled to a memory, the memory comprising computer program instructions stored thereon, the instructions configured to implement the following steps:

[0045] - transmitting a random access preamble to the base station,

[0046] - receiving a random access response,

[0047] - transmit a contention resolution message,

[0048] - configuring at least one discontinuous monitoring period of a downlink channel to receive a response to said transmitted contention resolution message, and

[0049] - Receive contention resolution messages.

[0050] In some embodiments, the various steps of the method for performing random access by a user equipment are determined by computer program instructions.

[0051] Therefore, the present disclosure further contemplates a computer program on an information medium, the program being suitable for being implemented in a user equipment device, or more generally in a computer, the program comprising instructions adapted to implement the steps of the method disclosed herein for performing a random access procedure.

[0052] These programs may use any programming language and may be in the form of source code, object code, or an intermediate code between source code and object code, such as partially compiled form or any other desired form.

[0053] On the other hand, an information medium readable by a computer is envisaged, which information medium comprises instructions of a computer program such as mentioned above.

[0054] The information medium may be any entity or device capable of storing a program. For example, the medium may include a storage device such as a ROM (read-only memory) (e.g., a CD ROM or a microelectronic circuit ROM), an EEPROM (electrically erasable programmable read-only memory), a FLASH memory, or any magnetic recording device (e.g., a hard disk drive).

[0055] Furthermore, the information medium may be a transmissible medium such as an electric or optical signal that may be transmitted via an electrical or optical cable, by radio or by other means.

[0056] Alternatively, the information medium may be an integrated circuit in which the program is contained, the circuit being arranged to execute or for executing the method for performing random access.

[0057] The advantages of the apparatus, the user equipment, the computer program and the information medium are the same as those presented with respect to the method for performing random access according to any of the above-mentioned embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Other advantages and characteristics of the invention will become more apparent on reading the following description, given by way of simple illustrative and non-limiting examples, and the accompanying drawings, in which:

[0059] - Figure 1 is a schematic diagram of an NTN wireless communication system suitable for implementing the method for random access procedure disclosed herein according to an embodiment,

[0060] - Figure 2 is a sequence diagram showing messages exchanged for a contention-based random access procedure,

[0061] - Figure 3 is a sequence diagram showing contention resolution messages between a UE and an NTN base station,

[0062] - Figure 4 is a sequence diagram showing contention resolution message exchange between a UE and an NTN base station involving blind Msg3 retransmission,

[0063] - Figure 5 is a flowchart showing the main steps of the method for random access procedure disclosed herein according to an embodiment,

[0064] - Figure 6 is a sequence diagram showing contention resolution messages involving blind Msg3 retransmission between a UE and a base station according to a first embodiment,

[0065] - Figure 7 is a sequence diagram showing contention resolution messages involving blind Msg3 retransmission between a UE and a base station according to a second embodiment, and

[0066] - Figure 8 A schematic architecture of an apparatus for performing a random access procedure in a wireless network according to an embodiment is shown. DETAILED DESCRIPTION

[0067] The specific embodiments described below with reference to the accompanying drawings are intended as descriptions of various configurations and are not intended to represent the only configurations in which the concepts described herein may be practiced. The specific embodiments include specific details to provide a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In particular, although terminology from 3GPP 5G NR may be used in this disclosure to illustrate the embodiments herein, this should not be viewed as limiting the scope of the invention.

[0068] Figure 1 An exemplary 5G New Radio (NR) wireless communication system 100 including user equipment 101 and base station 102 in which aspects of the present disclosure may be practiced is shown. Wireless network 100 may be an LTE network or some other wireless network, such as an LTE, 5G, or NR network. Wireless network 100 may include one or more base stations 102. Depending on the wireless standard implemented, base station 102 may be referred to as a BS, NB, eNodeB (or eNB), gNodeB (or gNB), access point, etc. Base station 102 provides radio communication coverage for a specific geographic area called a "cell".

[0069] The user device 101 may be referred to as a mobile station, a wireless terminal, etc. In some examples, the user device 101 may be a cellular phone, a wireless modem, a wireless communication device, a handheld device, a laptop computer, etc. The user device 101 may also be an IoT (Internet of Things) device like a wireless camera, a smart sensor or smart meter, a vehicle, a global positioning system device, or any other device configured to communicate over a wireless network.

[0070] Now, refer to Figure 5 and Figure 6 A first embodiment of a method for performing energy-efficient random access in a wireless NTN network is described.

[0071] Figure 5 is a flow chart showing main steps of a method for performing random access according to an embodiment.

[0072] During a first step 500, Figure 1 The user equipment 101 shown above can receive a system information block (SIB) periodically broadcast by the base station 102. According to an embodiment, the system information may include parameters for configuring discontinuous monitoring of the PDCCH. In some embodiments, the parameters may include the duration of the discontinuous reception cycle (i.e., the duration of the sleep state + the duration of the active monitoring state), and / or the duration of the active state ("on"), and / or the duration of the inactive state ("off"), and / or the duration of the discontinuous monitoring period.

[0073] The present disclosure contemplates that the parameters included in the system information may further include an indication (e.g., a single bit) for indicating whether the discontinuous on / off monitoring period first starts with the "on" period or the "off" period. In some examples, the bit is set to indicate that the discontinuous reception cycle should start with an active reception period.

[0074] At step 501, in order to establish downlink synchronization with the base station 102, the UE 101 initiates a contention-based random access procedure by sending a Msg1 message including a RACH preamble code randomly selected by the UE.

[0075] At step 502, the user equipment 101 receives a random access response (RAR or Msg2) transmitted by the base station 102 within the time window. The UE 101 may then decode the RAR message and initiate a radio resource control (RRC) procedure by first self-configuring and replying to an RRC connection request (Msg3) for uplink scheduled transmission. The RAR message received in response to the random access preamble sent in step 501 may include a temporary C-RNTI, a timing advance (TA), and an uplink grant for an L2 / L3 message.

[0076] According to an embodiment, the RAR message (Msg2) received in step 502 may further include parameters for configuring discontinuous monitoring of the PDCCH. According to an embodiment, the parameters received in the RAR message may include parameters for configuring discontinuous monitoring of the PDCCH. In some embodiments, the parameters may include the duration of the off+on period (i.e., the duration of the sleep state+the duration of the active state), and / or the duration of the active state, and / or the duration of the inactive state, and / or the duration of the discontinuous monitoring period.

[0077] The present disclosure contemplates that the parameters included in the system information may further include an indication (eg, a single bit) for indicating whether the discontinuous on / off monitoring period starts first with an “on” period or first with an “off” period.

[0078] Because multiple UEs may select the same preamble, a collision may occur when sending the RACH preamble (Msg1). In this case, the UE cannot receive the expected RAR message within its time window, and the UE retransmits the PRACH preamble after the backoff timer expires.

[0079] The method for performing random access may further include step 503, during which the UE transmits uplink scheduling information (Msg3) to the base station through PUSCH (Physical Uplink Shared Channel).

[0080] After sending the uplink scheduling information (Msg3), the UE may perform step 504, during which the UE configures discontinuous monitoring of the physical downlink channel (i.e., PCDDH) based on the parameters received in the SIB and / or RAR message. In some embodiments, the step of configuring discontinuous monitoring may include delaying the start of a contention resolution timer until a delay based on the UE-base station RTT value expires, and starting the contention resolution timer after the delay based on the RTT value expires. For example, a user equipment with pre-compensation capability may obtain a UE-specific UE-gNB RTT based on its GNSS (Global Navigation Satellite System) position in LEO / GEO.

[0081] According to an embodiment, discontinuous monitoring begins when the contention resolution timer starts, and discontinuous monitoring stops when the contention resolution timer expires.

[0082] According to an embodiment, the UE continuously monitors the PDCCH while the CR timer is running, and discontinuous monitoring is configured after the CR timer expires and stops when the CR timer restarts.

[0083] The method further comprises step 505, in which a contention resolution message (Msg4) is received during the "on" duration period.

[0084] Figure 6 FIG. 2 shows a contention resolution message flow involving blind Msg3 retransmission between UE 101 and NTN base station 102 according to an embodiment. Upon receiving an uplink grant ( Figure 6101 sends a first RRC connection request (Msg3) to the base station 102. Because of the long RTT between the UE 101 and the NTN base station 102, the UE postpones the start of the CR timer based on the RTT1 value. Once the CR timer CR1 is started, the UE 101 starts discontinuous monitoring of the PDCCH in order to receive blind retransmissions and / or Msg4. The discontinuous monitoring can be configured based on the configuration received in the system information and / or Msg2 message as detailed above. Therefore, when the "off duration" expires, the UE starts an active monitoring period "on duration", during which the UE 101 remains awake and monitors the UL grant (PDCCH) for blind retransmissions and Msg4. When the "on duration" expires, the UE starts the "off duration", during which the UE 101 does not monitor any PDCCH. Figure 4 It is further shown that UE 101 receives a retransmission of Msg2 during the "on duration" while contention resolution timer CRT1 is running, which includes a blind Msg3 retransmission grant (Msg2 RTX). UE 101 receiving the Msg2 RTX message triggers UE 101 to send a retransmission of Msg3 message (Msg3 RTX). When sending the Msg3 retransmission (Msg3 RTX), UE 101 schedules a delayed start of a new contention resolution timer CRT2, wherein the start of timer CRT2 is delayed based on the RTT value. Therefore, the start of timer CRT2 is scheduled after the expiration of the RTT2 period. In order to avoid any gap between the expiration of the CRT1 monitoring period and the start of timer CRT2, the CRT1 timer duration and the associated discontinuous monitoring are extended until the CRT2 timer is started. In this way, a longer CR timer can be configured without increasing the power consumption of the UE, so that a possible Msg4 that arrives later can be received.

[0085] Figure 7 FIG. 4 shows a contention resolution message flow involving blind Msg3 retransmission between UE 101 and NTN base station 102 according to another embodiment. Upon receiving an uplink grant ( Figure 7 After that, UE 101 sends a first RRC connection request (Msg3) to base station 102. Because of the long RTT between UE 101 and NTN base station 102, UE delays the start of the CR timer based on the RTT1 value. Once CR timer CRT1 starts, UE 101 starts continuous monitoring of PDCCH until CRT1 expires. Figure 7Further shown is a blind Msg3 retransmission grant (Msg2RTX) received by UE 101 while timer CRT1 is running. Reception of the blind Msg3 retransmission grant by UE 101 triggers the sending of the Msg3 retransmission, after which contention resolution schedules the start of a new timer (CRT2) after expiration of a delay (RTT2) based on the UE-gNB RTT. To avoid the CRT1 timer expiring before the RTT2 delay has elapsed, which could cause the UE to believe that contention resolution has failed, the CRT1 timer is extended (CRT1Ext) until the contention resolution timer is restarted (CRT2). During the extension of the CRT1 timer, UE 101 performs discontinuous monitoring of the PDCCH instead of continuous monitoring in order to limit power consumption. Therefore, the discontinuous monitoring period starts after the contention resolution timer expires and ends before the contention resolution timer is restarted after the retransmission. In this way, a longer CR timer can be configured without increasing the power consumption of the UE, so that a possible Msg4 that arrives later can be received.

[0086] Figure 8 A schematic architecture of the apparatus 800 suitable for implementing a method for performing a random access procedure between the apparatus 800 and a base station in a wireless communication network according to an embodiment is shown.

[0087] The apparatus 800 comprises a processor 801 and a memory 802, such as a random access memory (RAM). The processor 801 may be controlled by a computer program 803 stored in the memory 802, the computer program comprising instructions configured to implement a method for performing random access between the apparatus and a network node in a wireless network according to a particular embodiment.

[0088] More specifically, the computer program 803 includes instructions for implementing the following steps: transmitting a random access preamble to a network node; receiving a random access response; transmitting a contention resolution message; configuring discontinuous monitoring of a downlink channel to receive a response to the transmitted contention resolution message; and receiving a contention resolution message.

[0089] At initialization, the instructions of the computer program 803 may be loaded into the memory 802 before being executed by the processor 801. The processor 801 implements the steps of the method according to the instructions of the computer program 803.

[0090] The apparatus 800 includes a wireless transceiver unit 804, which can be configured by the processor 801 to establish radio communication with other devices. As an example, the wireless transceiver 804 can be a 5G NR compatible transceiver suitable for establishing communication with a 5G NR non-terrestrial access network. The transceiver unit 804 can be configured by program instructions of the computer program 803 to receive a system information block from a serving base station and exchange messages with the base station.

[0091] The apparatus 800 may further include a RACH unit 805. The RACH unit 805 may be implemented by computer program instructions configured to implement the steps of a contention-based random access procedure to achieve uplink synchronization between the apparatus 800 and a base station. The RACH unit 805 may be further configured to support blind Msg3 retransmission.

[0092] The apparatus 800 may further include a discontinuous reception configuration unit 806. The configuration unit 806 may be implemented by a computer program instruction configured to obtain discontinuous reception configuration parameters from a system information block broadcast by a network node. In some embodiments, the discontinuous reception configuration parameters may include a discontinuous reception cycle duration, and / or an inactive state duration and / or an inactive state duration, and / or a flag indicating whether the discontinuous reception cycle should start at an active period or an inactive period. The discontinuous reception configuration unit 806 may be further configured to obtain the configuration parameters from a Msg3 retransmission grant received by the communication unit 804.

[0093] Finally, the apparatus 800 may include a discontinuous reception unit 807 configured to perform discontinuous monitoring of a downlink channel (e.g., PDCCH) to receive blind Msg3 retransmissions and / or Msg4 messages. According to an embodiment, the discontinuous reception unit 807 may be configured by the discontinuous reception configuration unit 806 to discontinuously perform at least one monitoring period on the PDCCH when the contention timer is running, the monitoring period comprising an on-duration period (e.g., an active reception state) and an off-duration period (e.g., an inactive reception state). In some embodiments, discontinuous monitoring is maintained during the entire contention timer duration. According to an embodiment, the discontinuous reception unit 807 may be configured by the discontinuous reception configuration unit 806 to perform continuous monitoring of the PDCCH during the initial duration of the contention resolution timer triggered by the first transmission of Msg3, to perform discontinuous monitoring of the PDCCH during the extended duration of the contention resolution timer, and to stop discontinuous monitoring of the PDCCH when the contention resolution timer is restarted due to the retransmission of Msg3.

[0094] The present disclosure also contemplates a user equipment apparatus comprising such an apparatus 800 and a wireless system comprising the user equipment.

Claims

1. A wireless communication method performed by a user equipment for a random access procedure between the user equipment and a network node in a wireless communication network, the method comprising: transmitting (501) a random access preamble to the base station, receiving (502) a random access response, Send (503) a contention resolution message, configuring (504) at least one discontinuous monitoring period of the downlink channel to receive a response to the transmitted contention resolution message, and A contention resolution message is received (505) during an active period of the discontinuous monitoring cycle.

2. The method according to claim 1, wherein: Discontinuous monitoring is configured based on a configuration received from the network node.

3. The method according to claim 2, wherein: The discontinuous monitoring configuration is received in a system information message.

4. The method according to claim 2, wherein: The discontinuous monitoring configuration is received in a random access response message including a Msg3 retransmission uplink grant.

5. The method according to claim 2, wherein: The discontinuous monitoring configuration is received in both a random access response message including a Msg3 retransmission grant and a system information message.

6. The method according to claim 1, wherein: While the contention resolution timer is running, discontinuous monitoring of the downlink channel period is performed.

7. The method according to claim 1, wherein: Discontinuous monitoring of the downlink channel is performed from the expiration of a first contention resolution timer associated with the transmission of a first Msg3 message and the initiation of a second contention resolution timer associated with the retransmission of the Msg3 message.

8. An apparatus for performing random access between the apparatus and a network node in a wireless communication network, the apparatus comprising a processor (801) coupled to a memory (802), the memory comprising computer program instructions (803) stored thereon, the instructions being configured to implement the following steps: transmitting a random access preamble to the network node, receiving a random access response, Send a contention resolution message, configuring at least one discontinuous monitoring period of a downlink channel to receive a response to said transmitted contention resolution message, and Receive contention resolution messages.

9. A user equipment, comprising the apparatus according to claim 8.

10. A wireless communication system, comprising the user equipment according to claim 9.

11. A computer program comprising instructions configured to implement the steps of the method for a random access procedure between a user equipment and a network node in a wireless communication network according to claim 1 when the instructions are executed by a processor.

12. A non-transitory computer-readable information medium comprising computer program instructions for executing the steps of the method according to claim 1.

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