Method for initiating a random access procedure of a wireless device in a communication network

Abstract

A method for initiating a random access procedure of a wireless device (14a, 14b, 14c; 14), preferably an ambient Internet of Things (loT) device, in a communication network (10), the method comprising: transmitting, by the wireless device (14a, 14b, 14c; 14), a first message of the random access procedure to a node (12) of the communication network (10), wherein the first message comprises a random value and / or a device identification information for requesting access to a transmission medium of the communication network (10), preferably for requesting transmission resources from the node (12); detecting, by the wireless device (14a, 14b, 14c; 14), a failure of the access request if no response message comprising the random value and / or the device identification information is received by the wireless device (14a, 14b, 14c; 14); determining, by the wireless device (14a, 14b, 14c; 14), based on the detected failure, a backoff termination condition for transmitting a further first message of the random access procedure to the node (12); and transmitting, by the wireless device (14a, 14b, 14c; 14), the further first message of the random access procedure to the node (12) when the backoff termination condition is fulfilled.

Description

[0001] R. 416257

[0002] - 1 -

[0003] Specification

[0004] Title

[0005] Method for initiating a random access procedure of a wireless device in a communication network

[0006] The invention concerns a method for initiating a random access procedure of a wireless device, preferably an ambient Internet of Things (loT) device, in a communication network. Further, the invention concerns a wireless device, preferably an ambient loT device, a computer program and a non-transitory computer readable medium.

[0007] Background

[0008] The state of the art in ambient loT devices, as currently studied by 3GPP, encompasses low-complexity, low-energy demanding wireless devices designed for various use-cases, such as inventory management, localization, and sensor data exchange within indoor and outdoor environments. These wireless devices are categorized into three main groups, each with different power consumption and transmission characteristics.

[0009] Type 1 devices have a peak power consumption of approximately 1 pW, comprise an energy storage, and have an initial sampling frequency offset (SFO) of up to 10X ppm. They do not have amplification in the device for either downlink (DL) or uplink (UL) transmission, and their UL transmission is based on backscattering an externally provided carrier wave.

[0010] Type 2a and Type 2b devices have peak power consumption of a few hundred pW, comprise an energy storage, and have an initial SFO of up to 10X ppm. Both types have amplification for DL and / or UL transmission, with Type 2a devices generating UL transmissions by backscattering externally provided carrier waves and Type 2b devices generating UL transmission internally. R. 416257

[0011] - 2 -

[0012] The ambient loT device may be configured to directly and bidirectionally communicate with a user equipment or a base station. The ambient loT device may also be configured to indirectly and bidirectionally communicate with a base station via at least one intermediate node, e.g., a user equipment (UE) or a reader or a relay.

[0013] The ambient loT device may also be configured for receiving downlink transmissions directly from a base station, and for receiving uplinks transmissions to the base station via at least one assisting node. The ambient loT device may alternatively be configured for receiving downlink transmission from the base stations via at least one assisting node, and for transmitting uplinks transmissions directly to the base station.

[0014] The random access procedure for these ambient loT devices may be based on a slotted ALOHA Medium Access (MAC) protocol, where devices access the channel only at the start of a time slot when triggered by the network. In the event of a collision, a resolution mechanism is required to address the simultaneous channel access by multiple ambient loT devices.

[0015] The random access procedure for ambient loT devices can be categorized based on the number of message exchanges and the approach to contention resolution: The procedure may be classified as two-step, three-step, or four-step, depending on the specific sequence of message exchanges involved in initiating and completing the random access process. Additionally, the procedure may be categorized as contention-based or contention-free, based on whether specific mechanisms are employed to mitigate contention and resolve collisions during channel access.

[0016] In conventional wireless networks with random access transmission, UEs transmit a random access preamble via the uplink random access channel. The network responds with a random access response. The U Es respond with a contention resolution identifier (CRID) to be identified by the network. The network then grants the channel to a specified UE based on resources and priority, while other UEs attempt to access the channel at a later random time. R. 416257

[0017] - 3 -

[0018] When an ambient loT device does not receive an access response message in response to transmitting an access preamble or only receives an access response message with the random number and / or device identifier of another wireless device, it may attempt to re-access the transmission medium by transmitting a further access preamble. Such a failure in accessing the channel may occur repeatedly for the same wireless device. For low-energy wireless device, an efficient channel access mechanism is crucial.

[0019] Disclosure of the invention

[0020] According to a first aspect, there is provided a method for initiating a random access procedure of a wireless device, preferably an ambient Internet of Things (loT) device, in a communication network.

[0021] The method according to the first aspect comprises:

[0022] Transmitting, by the wireless device, a first message of the random access procedure to a node of the communication network, wherein the first message comprises a random value and / or a device identification information for requesting access to a transmission medium of the communication network, preferably for requesting transmission resources from the node;

[0023] Detecting, by the wireless device, a failure of the access request if no response message comprising the random value and / or the device identification information is received by the wireless device (within a defined period);

[0024] Determining, by the wireless device, based on the detected failure, a backoff termination condition for transmitting a further first message of the random access procedure to the node; and

[0025] Transmitting, by the wireless device, the further first message of the random access procedure to the node when the backoff termination condition is fulfilled, wherein the further first message comprises the random value and / or a further random value and / or the device identification information. R. 416257

[0026] - 4 -

[0027] The method according to the first aspect can be understood as a method for wireless communications, specifically of operating the wireless device, preferably the ambient loT device, of the communication network.

[0028] According to a second aspect, there is provided a wireless device, preferably an ambient loT device, of a communication network. The wireless device is configured to execute the method according to the first aspect, or its embodiments.

[0029] According to a third aspect, there is provided a computer program comprising machine-readable instructions to cause the wireless device as defined by the third aspect to execute the method according the first aspect, and / or its embodiments.

[0030] According to a fourth aspect, there is provided a non-transitory computer readable medium having stored thereon the computer program as defined by the sixth aspect.

[0031] The communication network may comprise a wireless network and a core network. The communication network may be configured as a cellular network, preferably according to 3GPP specifications, e.g., according to 3GPP release 18 or beyond, or as a wireless Local Area Network (LAN), preferably according to IEEE specifications. The communication network comprises at least the wireless device and the node.

[0032] The wireless device may be configured as a low-energy or low-power device. The wireless device may have a peak power consumption of less than 1 mW, preferably less than 500 pW, specifically less than 100 pW, according to an embodiment, less than 10 pW, e.g., approximately 1 pW.

[0033] The wireless device is preferably configured for energy harvesting, thus exploiting ambient energy sources, e.g., radio waves, thermal radiation, mechanical vibrations etc. as power supply. The wireless device may or may not comprise an energy storage, e.g., a battery. R. 416257

[0034] - 5 -

[0035] Specifically, the wireless device is different from a Reduced Capability (Redcap) device, a narrow band loT (NB-loT) device, a device for enhanced machine-type communication (eMTC), e.g., due to its lower hardware complexity and / or lower costs, and / or smaller form factors. Additionally, a communication between the wireless device and the node may not be controlled by a Radio Resource Control (RRC) layer. Particularly, a Hybrid Automated Repeat Request (HARQ) procedure may not be deployed or deployable for the communication between the wireless device and the node.

[0036] The wireless device may be arranged on or part of an environmental sensor, e.g., deployed in smart buildings, industrial facilities, and urban infrastructure to enable environmental monitoring and control, a smart home device to enable remote monitoring and control of home environments for energy efficiency, security, and convenience, a wearable health and / or fitness tracker to enable personal health and fitness tracking, as well as remote patient monitoring in healthcare applications, an asset tracking device to enable monitoring the location and status of assets, vehicles, and inventory in logistics, transportation, and supply chain management applications, an industrial loT sensor and / or actuator to enable monitoring and controlling machinery, equipment, and processes, a smart agriculture device to enable optimizing resource usage and improving crop yields, a smart city infrastructure unit to enable smart street lighting, traffic monitoring, waste management, public safety, and environmental monitoring.

[0037] The node of the communication network may be a radio or wireless node, or a core network node. The radio node may be a base station or a user equipment, e.g., configured as a reader for ambient loT devices, or a relay or an integrated access and backhaul (IAB).

[0038] The random access procedure preferably comprises at least the transmission of the first message of the random access procedure from the wireless device to the R. 416257

[0039] - 6 - node and the transmission of the second message of the random access procedure from the node to the wireless device.

[0040] The first message may comprise or consist of the random access preamble. The random access preamble may comprise a random number and / or a device identification information.

[0041] The second message may comprise of consist of the random access response. The random access response may be an echo of the random number and / or the device identification information comprised by the random access preamble.

[0042] Messages of the random access procedure transmitted between the node and the wireless device, i.e., messages transmitted from the wireless device and received by the node and / or messages transmitted from the node and received by the wireless device, may either be transmitted directly, specifically, on the physical random access channel (PRACH), or indirectly via an intermediate or assisting node of the communication network. As an example, a message received by the wireless device may be transmitted from a core node of the communication network via a radio node, e.g., a base station, of the communication network, to the wireless device, and vice versa.

[0043] The failure of the access request is preferably detected if no response message, specially no second message of the random access procedure, comprising the random value and / or the device identification information is received by the wireless device within a defined period. The defined period may be represented by a defined number of access occasions, preferably by a defined number of slots.

[0044] More precisely, the period corresponds to a duration a slot times multiplied with a natural number. The period may be one slot or N slots corresponding to one round of random access channel contention. The number N of slots defining a contention round of the random access procedure may be configured by the network or a reader node. The period may correspond to the number of slots of the current or next random channel access contention round. The period may be set as a timer or counter or duration of a scheduled time slot for receiving the response message. R. 416257

[0045] - 7 -

[0046] Receiving no response message comprising the random value and / or the device identification information can be understood as either receiving no response message to the first message at all, or receiving a response message which however does not comprise the random value and / or the device identification information contained in the first message.

[0047] In the first case, the same random value, i.e., the same access occasion, e.g., the same slot, may have been selected by at least two wireless devices. Consequently, the same first message / the same random access preamble is sent by at least two devices, thus generating interference on the random access channel. As a result, the first message(s) cannot be successfully received by the node, no response to the first message(s) is transmitted by the node.

[0048] In the second case, the first message may have been received by the node. However, instead of the wireless device, another wireless device has been selected for channel access by the node. As a result, a response to the first message may be received by the wireless device which, however, comprise the random value and / or the device identification of the other wireless device.

[0049] Transmitting the further first message can be understood as an attempt, by the wireless device, for re-accessing the transmission medium or channel. Here, the further first message is transmitted when the backoff termination condition is fulfilled. In other words, the method may comprise backing off or refraining from attempting to re-access the transmission medium or channel during a backoff interval or backoff period, and attempting to re-access by transmitting the further first message after termination of the backoff. In other words, the wireless device’s attempt to re-access the channel is delayed until the backoff is terminated. Preferably, the further first message comprises the random value and / or a further random value and / or the device identification information

[0050] The proposed solution effectively addresses access failures in a random access procedure of a wireless device by mitigating repeated collisions. To this end, a customizable backoff mechanism is provided which may be tailored to device or network specific conditions, thus enhancing the efficiency of channel re-access R. 416257

[0051] - 8 - attempts and improving overall system performance in wireless communication networks.

[0052] According to an embodiment, the backoff termination condition indicates a reception of one or multiple successive trigger messages, wherein the trigger message(s) may indicate a start of at least one of a paging round comprising multiple access rounds, an access round comprising multiple sets of access occasions, a set of access occasions.

[0053] The trigger message may be transmitted by the node or a further node of the communication network. The trigger message may be a paging message transmitted prior to or at the beginning of a / each paging round. The trigger message may be a round trigger message transmitted prior to or at the beginning of an I each access round. The trigger message may be an occasion trigger message transmitted prior to or at the beginning of a / each set of access occasions. Here, the backoff termination condition may require delaying the transmission of the further first message until the receipt of the next trigger message, or the trigger message following the next one, or the trigger message following the one after next. As an example, backing off until receipt of the next paging trigger message may comprise receiving one or multiple round trigger messages and multiple access occasion trigger messages without re-accessing the channel.

[0054] In other words, transmitting the further first message when the backoff termination condition is fulfilled may comprise:

[0055] Backing off for an entire current set of access occasions, preferably slots, and re-accessing the transmission medium upon reception of the next trigger message from the node. Here, multiple access occasions, preferably slots, can occur after each trigger message. If accessing the transmission medium fails in one occasion, backing off and re-accessing the transmission medium may occur in the next occasion within the same round.

[0056] Backing off for an entire current set of occasions and re-accessing the transmission medium upon reception of the trigger message following the next one or the one after next. In other words, re-accessing the R. 416257

[0057] - 9 - transmission medium may be attempted upon reception of one of the subsequent trigger messages received from the node.

[0058] Backing off for a current round and re-accessing the transmission medium in the round that follows, preferably upon reception of a round trigger message.

[0059] Backing off for a current paging round and re-accessing the transmission medium upon reception of the next paging message from the node.

[0060] This allows for dynamic adaptation of the channel re-access by utilizing trigger messages to indicate a termination of a backoff interval.

[0061] According to an embodiment, the backoff termination condition indicates an occurrence of a defined access occasion, specifically a defined slot, for transmitting the further first message. In other words, the backoff termination condition requires to backoff until a defined access occasion, e.g., represented by an access occasion or slot index, occurs. Specifically, according to this embodiment, the backoff termination condition may be independent from the receipt of trigger messages, like paging trigger, round trigger, or access occasion trigger messages. This allows for assigning specific access occasions to the wireless device, thus providing the chance to further reduce channel collisions.

[0062] According to an embodiment, the method further comprises:

[0063] Determining, by the wireless device, the defined access occasion, specifically the defined slot, for transmitting the further first message, specifically based on the random number and / or the further random number, using a mapping policy.

[0064] The wireless device may comprise a random number generator for generating the random number and / or the further random number. The random number may be generated by using a uniform random distribution or another distribution.

[0065] The wireless device may further comprise a mapping policy, e.g., a mapping function or a mapping table, for mapping input data, specifically the random number and / or the further random number, to an index of an access occasion, preferably of a slot. In other words, the mapping policy is configured to map input data like the random number to an index of an access occasion, preferably of a slot. As an alternative to the random number, an index of an access occasion, R. 416257

[0066] - 10 - preferably of a slot, used for transmitting the first message may be used as input data for the mapping policy.

[0067] The mapping policy may be configured as a modulo function. A modulus of the modulo function may be set to the number of slots, e.g., in a paging period (as configured by the node using a paging trigger message) or a round period (as configured by the node using a round trigger message). Here, the respective mapping policy maps a defined set of random numbers to a defined set of indices of access occasions. In other words, random number generation is followed by mapping the generated random number with help of the mapping policy.

[0068] The method may comprise, prior to transmitting the first message, determining the random number and mapping the random number to an index of an access occasion, preferably of slot, using the mapping policy, wherein the first message is transmitted in the access occasion with the index derived from the random number. The first message may comprise the determined random number or a random number different from the determined random number.

[0069] The method may further comprise, in response to the detected failure, determining the further random number and mapping the further random number to an index of a further access occasion, preferably a further slot, using the mapping policy, wherein the further first message comprises the further random number and is transmitted in the further access occasion, preferably the further slot, with the index derived from the further random number.

[0070] The method may further comprise, in response to the detected failure, mapping the random number to an index of a different access occasion, preferably by using another mapping policy, wherein the further first message comprises the random number and is transmitted in the further access occasion with the index derived from the further random number. A set of mapping policies may be provided to the wireless device by configuration or pre-configuration. The set of mapping policies is preferably also provided to the node.

[0071] Using a mapping policy for determining the backoff termination condition allows for dynamically adjusting the wireless device’s re-access strategy in response to detected access failures. R. 416257

[0072] - 11 -

[0073] According to an embodiment, the method further comprises:

[0074] Selecting, by the wireless device, the mapping policy from a group comprising at least two mapping policies, wherein the selection is performed based on at least one of o a failure information, preferably indicating a number of failed access attempts, of the wireless device, or o an energy information, preferably indicating an energy level, of the wireless device, or o a buffer information, preferably indicating a size or a fill level of a buffer, of the wireless device, or o a data information, preferably indicating a criticality of data, specifically in a / the buffer, of the wireless device, or o a location information of the wireless device, preferably indicating an identifier of a zone comprising the wireless device, or o a use case information of the wireless device, preferably indicating a use case as part of which the method is performed, o an access occasion for transmitting the first message.

[0075] The group of mapping policies may comprise at least a modulo function and a uniform random distribution. The selection of the mapping policy may be performed in response to the detected failure. The use case as part of which the method is performed may be a command use case or an inventory use case, e.g., according to 3GPP specifications for ambient loT devices.

[0076] As an example, if the energy information indicates a low energy level, a mapping policy may be selected which increases a duration of a backoff interval but decreases a risk of a channel collision resulting in a further failure. Accordingly, if the energy information indicates a high energy level, a mapping policy may be selected which shortens a duration of a backoff interval at the cost of an increased risk of a channel collision.

[0077] As a further example, if the buffer information indicates a low buffer fill level, a mapping policy may be selected which increases a duration of a backoff interval but decreases a risk of a channel collision resulting in a further failure.

[0078] Accordingly, if the buffer information indicates a high buffer fill level, a mapping R. 416257

[0079] - 12 - policy may be selected which shortens a duration of a backoff interval at the cost of an increased risk of a channel collision.

[0080] By introducing a dynamic selection of the mapping policy based on a variety of parameters, the wireless device’s backing off strategy may be adapted to devicebased and / or network based conditions.

[0081] According to an embodiment, the method further comprises:

[0082] Selecting, by the wireless device, the mapping policy from a group comprising at least two mapping policies, wherein the selection is performed randomly.

[0083] The group of mapping policies may comprise at least a modulo function and a uniform random distribution. The selection of the mapping policy may be performed in response to the detected failure. As an example, each time a failure is detected, a new mapping policy may be randomly selected from the group. This allows to avoid a purely deterministic backoff procedure, thus significantly reducing a risk of repeated access failure due to successive channel collisions of the same wireless devices.

[0084] According to an embodiment, the method further comprises:

[0085] Selecting, by the wireless device, an access occasion configuration based on the detected failure from a set comprising at least two access occasion configurations, wherein the at least two access occasion configurations differ by a duration of individual access occasions, and;

[0086] Changing, by the wireless device, a current access occasion configuration to the selected access occasion configuration, wherein the defined access occasion, specifically the defined slot, for transmitting the further first message is based on the selected access occasion configuration.

[0087] The at least two access occasion configurations may have fixed access occasion duration each. As an example, a first access configuration may have an access occasion duration of 0,1 ms, and a second access configuration may have an access occasion duration of 0,01 ms. R. 416257

[0088] - 13 -

[0089] The at least two access occasion configurations may be synchronized such that at least a subset of the access occasions of the respective configurations start at the same point in time. The synchronization may be ensured prior to the random access procedure, e.g., during paging, or regularly, e.g., periodically, by known mechanisms, e.g., precision time protocol (PTP), white rabbit, etc. For the above example, a start of an access occasion of the first configuration may be aligned with a start of every tenth access occasion of the second configuration.

[0090] According to an example, a first access occasion configuration may be selected and changed to after a failure of the access request is detected and a second access occasion configuration may be selected and changed to after a subsequent failure of the further access request is detected. Here, a duration of the individual access occasions of the configurations is preferably fixed. Further, the duration of the access occasions of the first configuration may be longer or shorter than the duration of the access occasions of the second configuration.

[0091] Specifically, a third access occasion configuration may be selected and changed to after a subsequent failure of an access request following the further access request is detected. Here, a duration of the individual access occasions of the third configuration is preferably also fixed. Further, the duration of the access occasions of the second configuration may be longer or shorter than the duration of the access occasions of the third configuration.

[0092] The dynamic selection and change of access occasion configurations by the wireless device based on detected failures allows to dynamically switch between configurations with different durations of access occasions, thus further enhancing the adaptability and efficiency of the wireless device's access attempts.

[0093] According to an embodiment, the set of access occasion configurations is preconfigured by the communication network and / or depends on a type of the wireless device. This allows to enable different types of wireless devices with different adaptability for re-access attempts.

[0094] According to an embodiment, the access occasion configuration is selected, by the wireless device, further based on a received configuration message. The message can be an access occasion configuration message and / or a paging R. 416257

[0095] - 14 - trigger message and / or a round trigger message and / or an access occasion trigger message transmitted from the node or a further node of the communication network. The configuration message may indicate an index of the access occasion configuration, e.g., a number of access occasions within a defined duration, e.g., 10 slots per millisecond. This allows for a device individual selection of the access occasion configuration, thus enabling individualized and flexible configuration selection.

[0096] According to an embodiment, the method further comprises:

[0097] Receiving, by the wireless device, a message transmitted from the node, wherein the message indicates a set of access occasions, especially a set of slots, and the further message may only be transmitted, by the wireless device, in one of the access occasions comprised by the set.

[0098] The set of access occasions may be indicated in an access occasion configuration message and / or a paging trigger message and / or a round trigger message and / or an access occasion trigger message. By indicating different set of access occasions to different wireless devices with failed access attempts, the probability for channel collisions for re-access of multiple devices can be further reduced.

[0099] According to an embodiment, the method further comprises:

[0100] Receiving, by the wireless device, an access configuration message transmitted from the node, wherein the access configuration message is used for configuring the wireless device for accessing the transmission medium of the communication network, wherein the access configuration message may indicate o a number of access rounds per paging round, and / or o a number of sets of access occasions per access, and / or o a number of access occasions per set.

[0101] This allows the node to efficiently configure the devices with the access-relevant features or parameters.

[0102] According to an embodiment, the method further comprises: R. 416257

[0103] - 15 -

[0104] Performing energy harvesting, by the wireless device, based on the determined backoff condition to increase an energy level of the device for the transmission of the further first message.

[0105] Energy harvesting may comprise capturing and accumulating energy from the surrounding environment, such as ambient radio frequency waves, thermal radiation, or mechanical vibrations, and converting it into electrical energy to power the device. To this end, the wireless device may preferably comprise an energy storage, e.g., a battery. By utilizing the backoff interval for energy harvesting, the wireless device can replenish its energy reserves, thus ensuring that it has sufficient power to transmit the subsequent first message after the backoff interval.

[0106] According to an embodiment, the method further comprises:

[0107] Prior to transmitting the first message, receiving, by the wireless device, a trigger message transmitted from the node or a further node of the communication network for triggering the random access procedure, wherein the first message is transmitted in response to receiving the trigger message.

[0108] The further node may be a core network node or a radio node, e.g., a base station or a user equipment. The trigger message may part of a paging message transmitted over a paging channel of the communication network. This allows for an efficient and coordinated initiation of the random access procedure, thus reducing collisions and contention with other devices attempting to access the network.

[0109] According to an embodiment of the first aspect, the method further comprises: Receiving, by the wireless device, a second message transmitted from the node in response to receiving the further first message, wherein the second message comprises o the random value and / or the device identification information comprised by the first and / or the further first message and / or o a resource information about transmission resources allocated for the wireless device.

[0110] The second message may the random access response. The second message may comprise an echo of the random number and / or the device identification information. The second message may additionally or alternatively indicate R. 416257

[0111] - 16 - transmission resources of the network allocated for a transmission or a or multiple retransmission(s) of the wireless device. The resource information may indicate, e.g., a slot or a set of slots allocated for a transmission of the wireless device. Further, the second message may comprise control information. This allows for efficient signaling the wireless device to continue with step three of a three / four step random access procedure or to start with payload transmission in a two step random access procedure.

[0112] According to a further aspect of the invention, there is provided a (wireless) communication network comprising at least the wireless device and the node.

[0113] The non-transitory computer readable medium is preferably configured to store the computer program to be executed by a processor of the first LAN element and / or the second LAN element and / or the communication network. The non- transitory computer readable media may include RAM, ROM, EEPROM, and any other non-volatile storage device.

[0114] Description of the figures

[0115] Exemplary embodiments of the present invention are depicted in the figures, which are not to be construed as limiting the claims, and are explained in greater detail below.

[0116] Fig. 1 schematically illustrates a communication network according to an embodiment of the invention; and

[0117] Fig. 2 schematically illustrate a method according to an embodiment of the invention.

[0118] Fig. 1 schematically illustrates a communication network 10 according to an aspect of the invention. The communication network 10 is configured as a cellular communication network 10, preferably according to 3GPP specifications. The communication network 10 may comprise a core network and a wireless network.

[0119] The communication network 10 comprises a radio node 12, configured as a user equipment 12, or a reader 12 for an ambient Internet of Things (loT) device, or a R. 416257

[0120] - 17 - relay node acting as a reader, and a plurality of wireless devices 14a, 14b, 14c, preferably configured as ambient loT devices 14a, 14b, 14c, specifically according to 3GPP specifications. The wireless devices 14a, 14b, 14c are collectively represented by reference sign 14. The communication network 10 further comprises a radio node 16 configured as a base station 16.

[0121] For requesting access to a transmission medium of the communication network 10, the wireless devices 14 are configured to perform a method for initiating a preferably slot-based random access procedure. Here, the random access procedure may be based on a slotted ALOHA random access MAC protocol. I.e., the wireless devices 14 are configured to begin a transmission only at the beginning of a slot. The length of the slot preferably equals the sum of a packet transmission time and a maximum propagation delay in the network to ensure that both transmission and reception of a data packet can be completed within one slot.

[0122] The random access procedure may be established between the respective wireless device 14a, 14b, 14c and the reader 12, or between the respective wireless device 14a, 14b, 14c and the base station 16. For the latter case, transmission between the wireless devices 14 and the base station 16 may be routed or relayed via the reader 12.

[0123] According to an alternative embodiment, the base station 16 may be configured as a reader for the wireless devices 14. Consequently, messages of the random access procedure are transmitted directly between the base station 16 and the wireless devices 14a, 14b, 14c (i.e., without routing them via the radio node 12).

[0124] The wireless devices 14 are configured for initiating a random access procedure of the respective wireless device 14 by performing the method according to the first aspect of the invention, and / or its embodiments, as further described in Fig. 2. Specifically, the wireless devices 14 are configured for backing off upon detection of a failed channel access attempt.

[0125] Fig. 2 schematically illustrates a method 100 for initiating a preferably slot-based random access procedure of a wireless device, preferably an ambient Internet of Things (loT) device, in a communication network. R. 416257

[0126] - 18 -

[0127] The method 100 comprises a step 110 of transmitting, by the wireless device, a first message of the random access procedure to a node of the communication network. The first message comprises a random value and / or a device identification information for requesting access to a transmission medium of the communication network, preferably for requesting transmission resources from the node.

[0128] The method 100 comprises a step 120 of detecting, by the wireless device, a failure of the access request if no response message comprising the random value and / or the device identification information is received by the wireless device.

[0129] The method 100 comprise a step 130 of determining, by the wireless device, based on the detected failure, a backoff termination condition for transmitting a further first message of the random access procedure to the node.

[0130] According to an embodiment, the backoff termination condition indicates a reception of one or multiple successive trigger messages, wherein the trigger message(s) may indicate a start of at least one of

[0131] - a paging round comprising multiple access rounds,

[0132] - an access round comprising multiple sets of access occasions,

[0133] - a set of access occasions.

[0134] According to an alternative embodiment, the backoff termination condition indicates an occurrence of a defined access occasion, specifically a defined slot, for transmitting the further first message.

[0135] The method 100 comprises a step of 140 of transmitting, by the wireless device, the further first message of the random access procedure to the node when the backoff termination condition is fulfilled. The further first message comprises the random value and / or a further random value and / or the device identification information.

Claims

R. 416257- 19 -Claims1 . A method (100) for initiating a random access procedure of a wireless device (14a, 14b, 14c; 14), preferably an ambient Internet of Things (loT) device (14a, 14b, 14c; 14), in a communication network (10), the method (100) comprising:Transmitting (110), by the wireless device (14a, 14b, 14c; 14), a first message of the random access procedure to a node (12) of the communication network (10), wherein the first message comprises a random value and / or a device identification information for requesting access to a transmission medium of the communication network (10), preferably for requesting transmission resources from the node (12);Detecting (120), by the wireless device (14a, 14b, 14c; 14), a failure of the access request if no response message comprising the random value and / or the device identification information is received by the wireless device (14a, 14b, 14c; 14);Determining (130), by the wireless device (14a, 14b, 14c; 14), based on the detected failure, a backoff termination condition for transmitting a further first message of the random access procedure to the node (12); andTransmitting (140), by the wireless device (14a, 14b, 14c; 14), the further first message of the random access procedure to the node (12) when the backoff termination condition is fulfilled.

2. The method (100) according to claim 1 , wherein the backoff termination condition indicates a reception of one or multiple successive trigger messages, wherein the trigger message(s) may indicate a start of at least one of a paging round comprising multiple access rounds, an access round comprising multiple sets of access occasions, a set of access occasions.R. 416257- 20 -3. The method (100) according to one of the preceding claims, wherein the backoff termination condition indicates an occurrence of a defined access occasion, specifically a defined slot, for transmitting the further first message.

4. The method (100) according to claim 3, further comprising:Determining, by the wireless device (14a, 14b, 14c; 14), the defined access occasion, specifically the defined slot, for transmitting the further first message, specifically based on the random number and / or the further random number, using a mapping policy.

5. The method (100) according to claim 4, further comprising:Selecting, by the wireless device (14a, 14b, 14c; 14), the mapping policy from a group comprising at least two mapping policies, wherein the selection is performed based on at least one of o a failure information, preferably indicating a number of failed access attempts, of the wireless device (14a, 14b, 14c; 14), or o an energy information, preferably indicating an energy level, of the wireless device (14a, 14b, 14c; 14), or o a buffer information, preferably indicating a size or a fill level of a buffer, of the wireless device (14a, 14b, 14c; 14), or o a data information, preferably indicating a criticality of data, specifically in a / the buffer, of the wireless device (14a, 14b, 14c; 14), or o a location information of the wireless device (14a, 14b, 14c; 14), preferably indicating an identifier of a zone comprising the wireless device (14a, 14b, 14c; 14), or o a use case information of the wireless device (14a, 14b, 14c; 14), preferably indicating a use case as part of which the method (100) is performed, o an access occasion for transmitting the first message.

6. The method (100) according to claim 4, further comprising:Selecting, by the wireless device (14a, 14b, 14c; 14), the mapping policy from a group comprising at least two mapping policies, wherein the selection is performed randomly.R. 416257- 21 -7. The method (100) according to one of the preceding claims, further comprising:Selecting, by the wireless device (14a, 14b, 14c; 14), an access occasion configuration based on the detected failure from a set comprising at least two access occasion configurations wherein the at least two access occasion configurations differ by a duration of individual access occasions, and;Changing, by the wireless device (14a, 14b, 14c; 14), a current access occasion configuration to the selected access occasion configuration, wherein the defined access occasion, specifically the defined slot, for transmitting the further first message is based on the selected access occasion configuration.

8. The method (100) according to claim 7, wherein the set of access occasion configurations is preconfigured by the communication network (10) and / or depends on a type of the wireless device (14a, 14b, 14c; 14)9. The method (100) according to one of the preceding claims, wherein the access occasion configuration is selected, by the wireless device (14a, 14b, 14c; 14), further based on a received configuration message.

10. The method (100) according to one of the preceding claims, further comprising:Receiving, by the wireless device (14a, 14b, 14c; 14), a message transmitted from the node (12), wherein the message indicates a set of access occasions, especially a set of slots, and the further message may only be transmitted, by the wireless device (14a, 14b, 14c; 14), in one of the access occasions comprised by the set.11 . The method (100) according to one of the preceding claims, further comprising:Receiving, by the wireless device (14a, 14b, 14c; 14), an access configuration message transmitted from the node (12) for configuring the wireless device (14a, 14b, 14c; 14) for accessing the transmission medium of the communication network (10),R. 416257- 22 - wherein the access configuration message may indicate o a number of access rounds per paging round, and / or o a number of sets of access occasions per access, and / or o a number of access occasions per set.

12. The method (100) according to one of the preceding claims, further comprising:Performing energy harvesting, by the wireless device (14a, 14b, 14c; 14), based on the determined backoff condition to increase an energy level of the device for the transmission of the further first message.

13. A wireless device (14a, 14b, 14c; 14), preferably an ambient Internet of Things (loT) device, of a communication network (10) configured to execute the method (100) according to one of the preceding claims.

14. A computer program comprising machine-readable instructions to cause the wireless device (14a, 14b, 14c; 14) according to claim 13 to execute the method (100) according to one of claims 1 to 12.

15. A non-transitory computer readable medium having stored thereon the computer program according to claim 14.

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