WO2018203809A1

WO2018203809A1 - Methods and apparatus for random-access transmissions in a wireless communication network

Info

Publication number: WO2018203809A1
Application number: PCT/SE2018/050447
Authority: WO
Inventors: Jan Christoffersson; Jinhua Liu; Min Wang
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-05-05
Filing date: 2018-05-02
Publication date: 2018-11-08

Abstract

Numerous methods and apparatuses are disclosed. One method, in a terminal device for a wireless communication network, comprises: obtaining a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities; obtaining a resource configuration for a random access response window associated with the random-access transmission window; responsive to a determination of a need to perform a random-access procedure, transmitting, to a network node of the wireless communication network, a plurality of random-access preamble messages in the plurality of random-access preamble transmission opportunities; and listening for one or more random-access response messages in the random access response window.

Description

METHODS AND APPARATUS FOR RANDOM-ACCESS TRANSMISSIONS IN A WIRELESS COMMUNICATION NETWORK

Technical Field

Embodiments of the present disclosure relate to methods and apparatus in a wireless communication network, and particularly to methods and apparatus relating to random-access transmissions in a wireless communication network.

Background

Efforts are on-going to develop and standardize communications networks and protocols intended to meet the requirements set out for the fifth generation (5G) of wireless systems, as defined by the Next Generation Mobile Networks Alliance. The new system (also known as "New Radio" or "NR") is being designed to be able to support use cases with diverse requirements such as ultra-reliable low-latency communications (URLLC), enhanced mobile broadband (eMBB) and massive machine- type communications (mMTC) etc. Compared to eMBB and mMTC services, URLLC traffic is very delay-sensitive.

Random access is a procedure by which a terminal device seeks to access the wireless communication network without first having any radio resources (i.e. frequency bands, time slots, etc) scheduled to it. One significant part of the latency associated with communications is therefore the latency associated with random access. Particularly for traffic requiring low latency (e.g. URLLC traffic), there is a desire to reduce the amount of time required for a terminal device to carry out a successful random-access process.

Separately, those skilled in the art will appreciate that future wireless communications systems are expected to make greater use of directional beams in the downlink (i.e. communications from a network node such as an eNodeB or a gNodeB to a terminal device) and also the uplink (i.e. communications from a terminal device to a network node such as an eNodeB or a gNodeB). The future systems may utilize higher frequencies for their transmissions, and the use of beam-forming techniques serves to mitigate the higher signal attenuation that occurs at such frequencies. In general, narrower beams will propagate further from the transmitter but need to be directed accurately towards an intended receiver; wider beams do not need to be directed so accurately (and may not need to be directed at all), but will have a shorter range. More advanced terminal devices may support Tx/Rx reciprocity, which means that they can determine the best uplink (UL) transmission beam based on the best received beam in downlink (e.g., determined during reception of synchronization signal (SS) blocks transmitted by the network node). However, less advanced terminal devices without such capability may need an alternative solution.

Summary

Embodiments of the disclosure provide methods and apparatus, such as wireless terminal devices and network nodes (e.g. eNodeBs or gNodeBs, or servers coupled to such nodes), that alleviate one of more of the problems identified above.

In one aspect, there is disclosed a method in a terminal device for a wireless communication network, the method comprising: obtaining a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities; obtaining a resource configuration for a random access response window associated with the random-access transmission window; responsive to a determination of a need to perform a random-access procedure, transmitting, to a network node of the wireless communication network, a plurality of random-access preamble messages in the plurality of random-access preamble transmission opportunities; and listening for one or more random-access response messages in the random access response window.

Another aspect provides a method in a network node for a wireless communication network, the method comprising: providing to a terminal device a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities; providing to the terminal device a resource configuration for a random access response window associated with the random-access transmission window; controlling a radio access network node for the wireless communication network to listen for a plurality of random-access preamble messages in the plurality of random-access preamble transmission opportunities; and, responsive to receipt by the radio access network node of at least one random-access preamble message in the plurality of random-access preamble transmission opportunities, initiating transmission by the radio access network node of a random- access response message in the random access response window. A further aspect provides a method in a terminal device for a wireless communication network, the method comprising: responsive to a determination of a need to perform a random-access procedure, transmitting a first random access preamble message to a network node of the wireless communication network using a first transmit power; and, responsive to a determination that no random-access response message has been received to the first random-access preamble message, transmitting a second random access preamble message to the network node using a second, higher transmit power.

The disclosure also includes apparatus, such as terminal devices and network nodes, for performing the methods outlined above.

The concepts disclosed herein may provide a way for the network to efficiently control random-access transmission and reception for each terminal device based on the individual situation of each terminal device.

Some embodiments may enable a timely stop of beam sweeping or repetitions to save random-access transmission resources. For example, the network node may have the opportunity to transmit a random access response message to the terminal device (particularly in time division duplex, TDD, operation mode) as soon as a random- access preamble message is detected by the network node. Meanwhile, the terminal device (again, particularly in TDD operation mode) may have the opportunity to receive a random-access response message before the maximum number of random-access preamble transmissions is reached. Hence some random-access transmissions can be saved.

Some embodiments may improve the diversity gain for repeated random-access transmissions in the time domain.

Note that the discussion below focuses on a technical solution for LTE and those networks intended to meet the requirements set out for the fifth generation (5G) of wireless systems, as defined by the Next Generation Mobile Networks Alliance. However, those skilled in the art will appreciate that it is also possible to apply the methods and apparatus described herein to other networks and access technologies. In other networks, nodes and interfaces may have different names. Brief Description of the Drawings

Figure 1 shows a wireless communications network;

Figure 2 shows a random-access configuration according to embodiments of the disclosure;

Figure 3 shows a random-access configuration according to further embodiments of the disclosure; Figure 4 shows a random-access configuration according to yet further embodiments of the disclosure;

Figure 5 shows a random-access configuration according to yet further embodiments of the disclosure;

Figure 6 is a flow chart of a method in a terminal device according to embodiments of the disclosure;

Figure 7 is a flow chart of a method in a terminal device according to further embodiments of the disclosure;

Figure 8 is a flow chart of a method in a network node according to embodiments of the disclosure; Figure 9 is a schematic diagram of a terminal device according to embodiments of the disclosure;

Figure 10 is a schematic diagram of a terminal device according to further embodiments of the disclosure;

Figure 1 1 is a schematic diagram of a network node according to embodiments of the disclosure; and

Figure 12 is a schematic diagram of a network node according to further embodiments of the disclosure. Detailed Description

The following sets forth specific details, such as particular embodiments for purposes of explanation and not limitation. But it will be appreciated by one skilled in the art that other embodiments may be employed apart from these specific details. In some instances, detailed descriptions of well-known methods, nodes, interfaces, circuits, and devices are omitted so as not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry (e.g., analog and/or discrete logic gates interconnected to perform a specialized function, ASICs, PLAs, etc.) and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers that are specially adapted to carry out the processing disclosed herein, based on the execution of such programs. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.

Hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions. In terms of computer implementation, a computer is generally understood to comprise one or more processors, one or more processing modules or one or more controllers, and the terms computer, processor, processing module and controller may be employed interchangeably. When provided by a computer, processor, or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed. Moreover, the term "processor" or "controller" also refers to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above. Although the description is given for a wireless terminal device, or user equipment (UE), it should be understood by the skilled in the art that "UE" is a non-limiting term comprising any mobile or wireless device, terminal or node equipped with a radio interface allowing for at least one of: transmitting signals in uplink (UL) and receiving and/or measuring signals in downlink (DL). A UE herein may comprise a UE (in its general sense) capable of operating or at least performing measurements in one or more frequencies, carrier frequencies, component carriers or frequency bands. It may be a "UE" operating in single- or multi-radio access technology (RAT) or multi-standard mode. As well as "UE", the terms "mobile station" ("MS"), "mobile device", "terminal device" and "wireless terminal device" may be used interchangeably in the following description, and it will be appreciated that such a device does not necessarily have to be 'mobile' in the sense that it is carried by a user. Examples of UE are target device, device to device (D2D) UE, machine type UE or UE capable of machine to machine (M2M) communication, PDA, tablet computer, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, ProSe UE, V2V UE, V2X UE, MTC UE, eMTC UE, FeMTC UE, UE Cat 0, UE Cat M1 , narrowband Internet of Things (NB-loT) UE, UE Cat NB1 , etc.

In some embodiments a more general term "network node" is used and it can correspond to any type of radio access node or any network node, which communicates with a UE and/or with another network node. Examples of network nodes are NodeB, MeNB, SeNB, a network node belonging to MCG or SCG, base station (BS), multi-standard radio (MSR) radio node such as MSR BS, eNodeB, gNodeB, network controller, radio network controller (RNC), base station controller (BSC), relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission points, transmission nodes, RRU, RRH, nodes in distributed antenna system (DAS), core network node (e.g. MSC, MME, etc.), O&M, OSS, SON, positioning node (e.g. E-SMLC), MDT, test equipment, etc. Moreover, where the following description refers to steps taken in or by a network node or a radio access node, this also includes the possibility that some or all of the processing and/or decision making steps may be performed in a device that is physically separate from the radio antenna of the node, but is logically connected thereto. Thus, where processing and/or decision making is carried out "in the cloud", the relevant processing device is considered to be part of the node for these purposes. The embodiments are described for LTE or LTE based systems such as machine-type communication (MTC), evolved MTC (eMTC), NB-loT etc. As an example MTC UE, eMTC UE and NB-loT UE also called UE category 0, UE category M1 and UE category NB1. However, the embodiments are applicable to any RAT or multi-RAT systems, where the UE receives and/or transmit signals (e.g. data) e.g. LTE FDD/TDD, WCDMA/HSPA, GSM/GERAN, Wi-Fi, WLAN, CDMA2000, 5G, NR, etc. It is recalled that 5G, the fifth generation of mobile telecommunications and wireless technology is not yet fully defined but in an advanced draft stage within 3GPP. It includes work on 5G New Radio (NR) Access Technology. LTE terminology is used in this disclosure in a forward looking sense, to include equivalent 5G entities or functionalities although a different term is specified in 5G. A general description of the agreements on 5G New Radio (NR) Access Technology so far is contained in most recent versions of the 3GPP 38-series Technical Reports. Figure 1 shows a network 10 that may be utilized to explain the principles of embodiments of the present disclosure. The network 10 comprises a network node 12 which is connected, via a backhaul network 20, to a core network 18. Figure 1 also shows a wireless terminal (or UE, etc) 14 that is in wireless communication with the network node 12.

The wireless terminal 14 is thus operable to communicate with the network 10 and particularly the network node 12. Messages transmitted by the wireless terminal 14 to the network node 12 are said to be transmitted in the "uplink" (UL), while messages transmitted by the network node 12 to the wireless terminal 14 are said to be transmitted in the "downlink" (DL). In particular, the wireless terminal 14 may comprise a plurality of antennas and corresponding tx/rx circuitry that allow the wireless terminal 14 to generate a plurality of beams 16 using beamforming techniques. For example, the wireless terminal 14 may be operable to generate relatively narrow beams directed along different directions (i.e. beams 16a, 16b, 16c and 16d in Figure 1), as well as relatively wide beams which may propagate in all directions (i.e. beam 16e in Figure 1). In general, the relatively narrow beams in general will propagate further from the wireless terminal 14 than the relatively wide beam, owing to beamforming gain.

Embodiments of the present disclosure relate to a random-access procedure, in which the wireless terminal 14 attempts to communicate with the network node 12. A wireless terminal may perform a random-access procedure in a number of different situations. For example, a wireless terminal may perform random access during initial access, when the terminal first attempts to access the network (i.e. on power up, or when in an idle state). A wireless terminal may perform random access when attempting to re-establish a connection, or upon handover from one network node to another. A wireless terminal may perform random access when it has no radio resources (e.g. frequency bands, time slots or sub-frames, etc) scheduled to it for uplink transmissions. Random access may thus be performed in a wide range of different scenarios and the embodiments disclosed herein are not limited to any particular scenario.

According to embodiments of the disclosure, the wireless terminal 14 is configured with a random-access transmission window comprising a plurality of random-access preamble transmission opportunities. The wireless terminal 14 is also configured with a random-access response window associated with the random-access transmission window.

Upon determining a need to perform a random-access procedure, the wireless terminal 14 transmits a plurality of random-access preamble messages to the network node 12 using the plurality of random-access preamble transmission opportunities. The random-access preamble messages may comprise a selected one of a plurality of available random-access preambles, such that the same preamble is sent in each of the random-access preamble messages. After transmitting at least one of the plurality of random-access preamble messages, the wireless terminal 14 listens for one or more random-access response messages transmitted by the network node 12 during the random-access response window. As will be discussed below, the random-access response window may not begin until after the random-access transmission window has ended. However, in other embodiments the random-access response window may overlap with the random-access transmission window. In the latter case, the wireless terminal 14 may receive a random-access response message before transmitting messages in each of the plurality of random-access preamble transmission opportunities. The wireless terminal 14 may even receive a random-access response message before transmitting more than one random-access preamble message (i.e. only one random-access preamble message is transmitted). In such embodiments, the wireless terminal 14 may halt further transmissions of random-access preamble messages upon receipt of the random-access response message.

Figure 2 shows a random-access configuration according to embodiments of the disclosure. The drawing comprises a plurality of boxes representing radio resources for random-access transmissions between the wireless terminal 14 and the network node 12. The random-access messages may be transmitted using a physical random- access channel (PRACH). Each box represents radio resources in one transmission time unit, i.e. one time slot, one slot, one mini-slot or sub-frame.

The configuration for the PRACH and the plurality of transmission opportunities may be obtained via signalling from the network node, e.g. via system information broadcasts, or dedicated signalling to the wireless terminal 14 (e.g. RRC signalling). In the example of Figure 2, the random-access transmission window and the random- access response window do not overlap in time, i.e. are not interleaved. The wireless terminal 14 selects a preamble from a plurality of available preambles, and transmits the preamble in a first transmission opportunity (black box). In subsequent transmission opportunities (striped boxes), the wireless terminal 14 transmits the same preamble (i.e. such that the first message and subsequent messages are copies of each other).

In one embodiment, each preamble is transmitted using a different beam of the plurality of beams available to the wireless terminal 14. Such embodiments may be termed "beam sweeping" herein. In this example, the wireless terminal 14 may continue to transmit preamble messages using the transmission opportunities until at least one preamble message has been transmitted using each possible beam that is available to the wireless terminal 14, or until there are no further transmission opportunities available in the transmission window. In one embodiment, the wireless terminal 14 may execute a beam-sweeping procedure in which random-access preamble messages are transmitted on beams directed in substantially different directions so as to maximize the likelihood that a network node will receive at least one of the messages. Such embodiments may enable the wireless terminal 14 to determine the best beam on which to transmit wireless communications to the network. In an alternative embodiment, each preamble is transmitted using the same beam. Such embodiments may be termed "repetition" herein. The beam may be relatively wide (i.e. broadcast, without a defined direction), or narrow along a particular direction. For example, if the wireless terminal 14 has low mobility or is stationary, it may have previously determined the appropriate beam to utilize for connecting to the network 10.

During the random-access response window, the wireless terminal 14 listens for a random-access response message from the network node 12. The random-access response message may be transmitted by the network node 12 in response to the successful detection of a random-access preamble message on the PRACH.

The random-access response window may be defined using a start time (RAR window start in Figure 2) and a window length (RAR window length). The start time may be defined relative to the start of the random-access transmission window, or relative to an initial transmission opportunity within the random-access transmission window. The start time may be defined in terms of a number of transmission time units, such as a number of time slots, slots, mini-slots or sub-frames. Similarly, the window length may be defined in terms of a number of time units, such as a number of time slots, slots, mini-slots or sub-frames.

If the network node 12 received at least one of the random-access preamble messages, a random-access response message is prepared and transmitted to the wireless terminal 14 in the random-access response window. In beam-sweeping embodiments, the random-access response message may comprise an indication of the preamble message which was received with the best value of some signal metric by the network node 12, or an indication of the beam over which that preamble message was transmitted. Alternatively, the random-access response message may comprise an indication of the first preamble message of those transmitted by the wireless terminal 14 which was received by the network node 12 with a signal metric that exceeded a threshold. Suitable signal metrics may include received signal strength, received signal received power, received signal quality, signal to interference ratio, signal to interference and noise ratio, or pathloss). In repetition embodiments, the random-access response message may comprise an indication of the number of repetitions (i.e. the number of random-access preamble messages) that were required before the random-access preamble message could be decoded by the network node 12. For example, in low-quality transmission environments, or where the wireless terminal 14 and the network node 12 are separated by a large distance, it may be necessary to accumulate the received energy from multiple transmissions in order to decode the data contained within the transmission (i.e. to decode the preamble).

Upon receipt of the random-access response message, the wireless terminal 14 can use the indicated beam, or the indicated number of repetitions, for future communication with the network node 14.

Figure 3 shows a random-access configuration according to further embodiments of the disclosure. Again, the boxes indicate time resources for random-access transmissions between the wireless terminal 14 and the network node 12. In this embodiment, the random-access transmission window and the random-access response window overlap in time, and thus the transmission opportunities are interleaved with time periods during which the wireless terminal 14 may listen for random-access response messages from the network node 12. The RAR window start (i.e. the offset between the start of the random-access transmission window or the first transmission opportunity and the start of the random-access response window) is shorter than the length of the random-access transmission window.

As in Figure 2, the wireless terminal 14 selects a preamble from the plurality of preambles available, and transmits the preamble in a first transmission opportunity (black box) of the random-access transmission window. Also as in Figure 2, the wireless terminal 14 may repeat the transmission of the selected preamble using the same beam (repetition) or different beams (beam sweeping) in subsequent transmission opportunities (striped boxes). During the random-access response window, the wireless terminal 14 also listens for response messages from the network node 12 during those time slots, slots, mini-slots or sub-frames which do not coincide with transmission opportunities (clear boxes).

The wireless terminal 14 may continue to transmit the preamble message using the defined transmission opportunities until a preamble message has been transmitted on all of the beams available to the wireless terminal 14, or until there are no further transmission opportunities available, or until a random-access response message is received.

A random-access response message may be transmitted by the network node 12 in a time slot, slot, mini-slot or sub-frame during the random-access response window that does not coincide with one of the plurality of transmission opportunities (referred to as "RAR receiving opportunities" in Figures 4 and 5 below).

In beam-sweeping embodiments, the random-access response message may comprise an indication of the preamble message which was received with the best value of some signal metric by the network node 12, or an indication of the beam over which that preamble message was transmitted. Alternatively, the random-access response message may comprise an indication of the first preamble message of those transmitted by the wireless terminal 14 which was received by the network node 12 with a signal metric that exceeded a threshold (or the beam over which that message was transmitted). Suitable signal metrics may include received signal strength, received signal received power, received signal quality, signal to interference ratio, signal to interference and noise ratio, or pathloss. In embodiments where the response message indicates a first preamble message which was received having a signal metric above a threshold, the indication of the preamble message or the beam may be implicitly provided by the relative timing between the transmission of the response message and the preamble message. For example, the network node 12 may be configured to transmit a random-access response message a predetermined time (i.e. a predetermined number of time slots, slots, mini-slots or sub-frames) after receipt of a preamble message that is decodable, i.e. for which a signal metric exceeds a threshold. The wireless terminal 14 may similarly be provided with this information, such that the selected preamble message or beam can be determined based on the timing of the receipt or transmission of the random-access response message.

In repetition embodiments, the random-access response message may again comprise an indication of the number of repetitions (i.e. the number of random-access preamble messages) that were required before the random-access preamble message could be decoded by the network node 12. However, again this random-access preamble message may be transmitted by the network node 12 before the preamble transmission opportunities have been exhausted.

The examples in Figures 2 and 3 have shown random-access configurations in which the transmission opportunities are configured periodically throughout the random- access transmission window. In these examples, the transmission opportunities may be configured every nth time slot, slot, mini-slot or sub-frame, where n is an integer greater than one. Figures 4 and 5 show alternative configurations in which transmission opportunities are configured more frequently at certain instances during the random-access transmission window.

In Figure 4, transmission opportunities are configured in consecutive time slots, slots, mini-slots or sub-frames at the start of the transmission window. Thus, after the initial transmission opportunity (black box), a second transmission opportunity (also black box) is defined in the immediately following time slot, slot, mini-slot or sub-frame. Subsequent transmission opportunities (e.g., "additional PRACH TX opportunities" in Figure 4) are defined at a lower periodicity in the transmission window.

Those skilled in the art will appreciate that different numbers of transmission opportunities may be provided than those illustrated, with different periodicities. In general, the transmission opportunities following this example may comprise subsets of transmission opportunities with different periodicities. A first subset (e.g. at the start of the transmission window) may define transmission opportunities every mth time slot, slot, mini-slot or sub-frame, while a second subset (e.g. subsequent to the first subset) may define transmission opportunities every nth time slot, slot, mini-slot or sub-frame, where m and n are both integers and n > m.

According to such embodiments, the transmission opportunities are thus more frequent towards the start of the transmission window, increasing the likelihood that a preamble message will be detected quickly by the network node 12 and latency in the random- access procedure can be reduced.

As with the example of Figure 3, the response window and the transmission window in Figure 4 overlap. As with the example of Figures 2 and 3, the wireless terminal 14 may transmit random-access preamble messages using the same beam (repetition) or different beams (beam sweeping). Figure 5 shows a further random-access configuration according to embodiments of the disclosure. The configuration has some similarities with previous embodiments, which will not be described in further detail. For example, the wireless terminal 14 may transmit preamble messages using the same beam (repetition) or different beams (beam sweeping); the response window and the transmission window overlap, such that a response message may be received before all of the transmission opportunities have been utilized; and multiple transmission opportunities are configured in consecutive time slots, slots, mini-slots or sub-frames at the start of the transmission window.

In the example shown in Figure 5, the transmission window comprises a plurality of transmission sub-windows, each comprising multiple transmission opportunities. In the illustrated example, four transmission sub-windows are shown, each comprising two transmission opportunities; however, any number of sub-windows may be provided and any number of transmission opportunities within those sub-windows. Also in the illustrated example, the transmission opportunities within each sub-window are in consecutive time slots, slots, mini-slots or sub-frames; however, in general the transmission opportunities within each sub-window may be defined non-periodically or with a periodicity that is less frequent than consecutive time slots, slots, mini-slots or sub-frames.

The transmission sub-windows represent a granularity with which the wireless terminal 14 may transmit preamble messages using the transmission opportunities. That is, in the example of Figure 5, the wireless terminal 14 transmits preamble messages in the first two transmission opportunities, which in the illustration are both before the response window has begun. If no random-access response message is received to either of those transmitted preamble messages, the wireless terminal 14 proceeds to transmit preamble messages in each of the transmission opportunities in the subsequent transmission sub-window. If no random-access response message is received to those messages or previous messages, the wireless terminal 14 proceeds to transmit preamble messages in each of the transmission opportunities in the subsequent transmission sub-window, and so on until a response message is received (e.g. in one of the RAR receiving opportunities), or the transmission opportunities are all utilized, or all beams have been utilized. Thus a number of random-access configurations are disclosed which a wireless terminal may use to perform a random-access procedure with a network node.

Figure 6 is a flow chart of a method according to embodiments of the disclosure. The method may be carried out in a terminal device, such as the wireless terminal 14 shown in Figure 1.

The method begins in step 600, in which the terminal device obtains a configuration of a random-access transmission window. The configuration may relate to a physical random-access channel (PRACH), i.e. indicating a transmission window for the PRACH. The configuration may be obtained via signalling from a network node of a wireless communication network (such as an eNodeB or a gNodeB, etc). The signalling may be broadcast to all terminal devices (e.g. via system information broadcast) or dedicated to the terminal device (e.g. via radio resource control, RRC, signalling, etc).

The random-access transmission window comprises a plurality of transmission opportunities. At least a subset of the transmission opportunities may be defined periodically within the transmission window. For example, in some embodiments all of the transmission opportunities may be defined periodically within the transmission window. In other embodiments, the plurality of transmission opportunities may comprise first and second subsets of transmission opportunities, each of which has different periodicity. For example, a first (initial) subset may have a relatively higher periodicity than a second (subsequent) subset of transmission opportunities. The first subset of transmission opportunities may be arranged in every mth time slot, slot, mini- slot or sub-frame, while the second subset may be arranged in every nth time slot, slot, mini-slot or sub-frame, where n and m are integers and n > m. In some embodiments, m may be equal to one, such that transmission opportunities in the first subset are arranged in consecutive time slots, slots, mini-slots or sub-frames.

The configuration for the transmission opportunities may comprise a time slot, slot, mini-slot or sub-frame for the first (i.e. initial) transmission opportunity, and a number of repetitions. The configuration may further comprise a periodicity, or multiple periodicities in the case of subsets (see above). In further embodiments, the random-access transmission window comprises a plurality of random-access transmission sub-windows, each comprising multiple random-access preamble transmission opportunities. Within each sub-window, the transmission opportunities may be arranged periodically or non-periodically.

In step 602, the terminal device obtains a configuration of a random-access response window associated with the random-access transmission window. The configuration may relate to a physical random-access channel (PRACH), i.e. indicating a response window for the PRACH. Again, the configuration may be obtained via signalling from a network node of a wireless communication network (such as an eNodeB or a gNodeB, etc), and the signalling may be broadcast to all terminal devices (e.g. via system information broadcast) or dedicated to the terminal device (e.g. via radio resource control, RRC, signalling, etc). The configuration for the random-access response window may comprise an indication of one or more time slots, slots, mini-slots or sub-frames. The indication may comprise a start time of the random-access response window and a duration of the random- access response window (e.g. defined in terms of a number of time slots, slots, mini- slots or sub-frames). The start time may be defined relative to a start time of the random-access transmission window or an initial random-access preamble transmission opportunity of the plurality of random-access preamble transmission opportunities.

The response window may be scheduled later in time than the transmission window, such that random-access response messages can be transmitted in response to receipt of a random-access preamble message transmitted using one of the transmission opportunities. In one embodiment, the response window at least partially overlaps the transmission window, such that a response message may be received by the terminal device before all of the transmission opportunities have been utilized.

The random-access transmission window and the random-access response window may each repeat within some defined time frame for the wireless communications in the network. For example, the random-access transmission window and the random- access response window may be defined relative to the start of a system frame (or similar repeating time structure), and repeat with each system frame. In step 604, the terminal device determines whether a random-access procedure is required. As noted above, a random-access procedure may be required in a number of different situations. For example, a terminal device may perform random access during initial access, when the terminal first attempts to access the network (i.e. on power up, or when in an idle state). A terminal device may perform random access when attempting to re-establish a connection, or upon handover from one network node to another. A terminal device may perform random access when it has no radio resources (e.g. frequency bands, time slots, slots, mini-slots or sub-frames, etc) scheduled to it for uplink transmissions. Random access may thus be performed in a wide range of different scenarios and the embodiments disclosed herein are not limited to any particular scenario.

If no random-access procedure is required, the flow repeats step 604 until a random- access procedure is required.

If a random-access procedure is required, the method proceeds to step 606, in which the terminal device selects a random-access preamble from the random-access preambles that are available to it, and utilizes the plurality of transmission opportunities in the random-access transmission window to transmit the selected random-access preamble to a network node. In one embodiment, the same preamble is transmitted in each transmission opportunity. The random-access preamble messages may be transmitted using a physical random-access channel (PRACH), or any other suitable physical channel for which random-access is configured. The terminal device may utilize a plurality of beams propagating in different directions to transmit the random-access preamble messages, such that the random-access preamble messages are transmitted in different directions. Alternatively, the terminal device may utilize the same beam to transmit the random-access preamble messages. The transmission of random-access preamble messages may continue until no transmission opportunities are left (i.e. a random-access preamble message has been transmitted in each of the transmission opportunities), or until at least one random- access preamble message has been transmitted using each of the beams available to the terminal device. In further embodiments, however, step 606 may be linked with step 608 such that the transmission of random-access preamble messages halts when a random-access response message is received. In step 608, the terminal device listens (e.g. monitors the physical channel) for a random-access response message from the network node during the random-access response window.

In embodiments where the response window and the transmission window overlap, step 608 may comprise the terminal device listening for random-access response messages in time slots, slots, mini-slots or sub-frames in the random access response window which do not comprise a transmission opportunity.

If a random-access response message is received during the transmission window, i.e. before all of the transmission opportunities have been utilized, the terminal device may halt further transmission of random-access preamble messages, saving resources at the terminal device.

Steps 606 and 608 may be further linked in embodiments where the transmission window comprises a plurality of transmission sub-windows. In such embodiments, the terminal device may transmit random-access preamble messages in each of the transmission opportunities of a sub-window before listening for a random-access response message. If no response message is received, the terminal device may transmit random-access preamble messages in each of the transmission opportunities of a subsequent sub-window before listening for a response, and so on until a response is received, or no transmission opportunities are left, or until at least one random-access preamble message has been transmitted using each of the beams available to the terminal device.

In beam-sweeping embodiments, the random-access response message may comprise an indication of the preamble message which was received with the best value of some signal metric by the network node, or an indication of the beam over which that preamble message was transmitted. Alternatively, the random-access response message may comprise an indication of the first preamble message of those transmitted by the terminal device which was received by the network node with a signal metric that exceeded a threshold. Suitable signal metrics may include received signal strength, received signal received power, received signal quality, signal to interference ratio, signal to interference and noise ratio, or pathloss. The indication may be implicit by way of the relative timing of transmission of the random-access response message.

In repetition embodiments, the random-access response message may comprise an indication of the number of repetitions (i.e. the number of random-access preamble messages) that were required before the random-access preamble message could be decoded by the network node. For example, in low-quality transmission environments, or where the terminal device and the network node are separated by a large distance, it may be necessary to accumulate the received energy from multiple transmissions in order to decode the data contained within the transmission (i.e. to decode the preamble).

The terminal device may then utilize the indicated beam, or the indicated number of repetitions, for future communication with the network node.

Figure 7 is a flowchart of a method according to further embodiments of the disclosure. The method may be carried out in a terminal device, such as the wireless terminal 14. The method may be carried out in conjunction with the method described above with respect to Figure 6.

The method begins step 700, in which the terminal device determines that a random- access procedure is required. As noted above, random-access procedures may be required in a large number of different scenarios, and the concepts described herein are not limited to any particular scenario. This step may therefore be substantially similar to step 604 described above.

Responsive to a determination that a random-access procedure is required, the method proceeds to step 602, in which the terminal device selects a random-access preamble from the plurality of preambles available to it, and transmits the selected preamble. The transmission may be over a physical random-access channel (PRACH) or any suitable physical channel configured for random-access.

The random-access preamble is transmitted using a first transmit power, determined by the terminal device. For example, the first transmit power may be a default transmit power. The random-access preamble may be transmitted a single time in step 702, over a wide or narrow beam. In the latter case, the narrow beam may be selected based on a beam which was previously used to communicate with a network node.

In step 704, the terminal device determines whether a random-access response message has been received from a network node. The terminal device may listen for such random-access response messages in a defined random-access response window, e.g. a window defined related to the transmission of the random-access preamble message, on the same physical channel over which the random-access preamble message was transmitted, or a different physical channel.

If a random-access response message is received, the method proceeds to step 706 in which further communication takes place with the network node on the basis of information contained within the received random-access response message. For example, the random-access response message may contain an indication of radio resources (e.g. frequency channels and/or time slots, slots, mini-slots or sub-frames) which the terminal device can use for uplink transmissions to the network node.

If no response is received, the method proceeds to step 708 in which the terminal device determines whether a maximum transmit power was used to transmit the random-access preamble message, or whether a predetermined maximum number of random-access preamble messages have been transmitted. As this is the first transmission of a random-access preamble message, it is unlikely (although not impossible) that either of these criteria is satisfied, and therefore the method proceeds to step 710 in which the transmit power is increased (i.e. increased relative to the first transmit power), and then to step 702 in which a second random-access preamble message is transmitted using the increased transmit power. In some embodiments, the terminal device carries out a further selection of a random-access preamble from the plurality of preambles available to it, and therefore the second preamble may be different from the first.

The higher transmit power increases the likelihood that a network node will be able to receive and decode the second random-access preamble message. However, if no response is received to the second random-access preamble message, it will be seen that the method continues to increase the transmit power until a maximum transmit power is reached (step 708), a maximum number of preamble transmissions is reached (step 708) or a random-access response message is received to one of the transmitted random-access preamble messages (step 704).

If, in step 708, the maximum transmit power or the maximum number of transmissions is reached, the method proceeds to step 712 in which the terminal device transmits a plurality of random-access preamble messages using a plurality of configured transmission opportunities (e.g. in a random-access transmission window), i.e. substantially as described in steps 606 and 608 above. It will be noted that the terminal device may previously have been configured with a random-access transmission window and a random-access response window as outlined in steps 600 and 602.

It can therefore be seen that the method of Figure 7, if carried out, ensures that the method of Figure 6 is only carried out when necessary, i.e. when other methods of performing random-access have failed. Although this may increase the latency of communications in some cases, performance of the network as a whole is improved.

Figure 8 is a flowchart of a method according to embodiments of the disclosure. The method may be carried out in a network node of a wireless communication network. For example, the method may be carried out in a network node such as the network node 12 described above with respect to Figure 1. Alternatively, the method may be carried out in a server that is remote from the network node 12 but communicatively coupled to it. Such a server may be operative to obtain data which is received wirelessly by the network node 12, and to instruct the network node 12 to transmit communications.

The method begins in step 800, in which the network node configures a terminal device of the wireless communication network with a random-access transmission window. The configuration may relate to a physical random-access channel (PRACH), i.e. indicating a transmission window for the PRACH. The configuration may be provided via signalling from the network node or a radio access network node coupled to the network node (such as an eNodeB or a gNodeB, etc). The signalling may be broadcast to all terminal devices (e.g. via system information broadcast) or dedicated to the terminal device (e.g. via radio resource control, RRC, signalling, etc). The random-access transmission window comprises a plurality of transmission opportunities. At least a subset of the transmission opportunities may be defined periodically within the transmission window. For example, in some embodiments all of the transmission opportunities may be defined periodically within the transmission window. In other embodiments, the plurality of transmission opportunities may comprise first and second subsets of transmission opportunities, each of which has different periodicity. For example, a first (initial) subset may have a relatively higher periodicity than a second (subsequent) subset of transmission opportunities. The first subset of transmission opportunities may be arranged in every mth time slot, slot, mini- slot or sub-frame, while the second subset may be arranged in every nth time slot, slot, mini-slot or sub-frame, where n and m are integers and n > m. In some embodiments, m may be equal to one, such that transmission opportunities in the first subset are arranged in consecutive time slots, slots, mini-slots or sub-frames. The configuration for the random-access response window may comprise an indication of one or more time slots, slots, mini-slots or sub-frames. The indication may comprise a start time of the random-access response window and a duration of the random- access response window (e.g. defined in terms of a number of time slots, slots, mini- slots or sub-frames). The start time may be defined relative to a start time of the random-access transmission window or an initial random-access preamble transmission opportunity of the plurality of random-access preamble transmission opportunities.

In further embodiments, the random-access transmission window comprises a plurality of random-access transmission sub-windows, each comprising multiple random-access preamble transmission opportunities. Within each sub-window, the transmission opportunities may be arranged periodically or non-periodically.

In step 802, the network node configures the terminal device with a random-access response window associated with the random-access transmission window. The configuration may relate to a physical random-access channel (PRACH), i.e. indicating a response window for the PRACH. Again, the configuration may be provided via signalling from the network node or a radio access network node coupled to it (such as an eNodeB or a gNodeB, etc), and the signalling may be broadcast to all terminal devices (e.g. via system information broadcast) or dedicated to the terminal device (e.g. via radio resource control, RRC, signalling, etc). The configuration for the random-access response window may comprise an indication of one or more time slots, slots, mini-slots or sub-frames. The indication may comprise a start time of the random-access response window and a duration of the random- access response window (e.g. defined in terms of a number of time slots, slots, mini- slots or sub-frames). The start time may be defined relative to a start time of the random-access transmission window or an initial random-access preamble transmission opportunity of the plurality of random-access preamble transmission opportunities.

The response window may be scheduled later in time than the transmission window, such that random-access response messages can be transmitted in response to receipt of a random-access preamble message transmitted using one of the transmission opportunities. In one embodiment, the response window at least partially overlaps the transmission window, such that a response message may be transmitted by the network node (or a radio access network node coupled to it) before all of the transmission opportunities have been utilized.

The random-access transmission window and the random-access response window may each repeat within some defined time frame for the wireless communications in the network. For example, the random-access transmission window and the random- access response window may be defined relative to the start of a system frame (or similar repeating time structure), and repeat with each system frame. In step 804, the network node listens for one or more random-access preamble messages transmitted by the terminal device in the random-access transmission window, using the configured transmission opportunities. In some embodiments, a message is received when it is received with sufficient strength or quality to be decoded. In step 806, if no random-access preamble message is received (or not received with sufficient strength or quality), the method moves back to step 804 until a message is received.

It will be apparent from the discussion above that in some embodiments the terminal device may transmit the same preamble message using the same beam (so-called repetition). In these embodiments, step 806 may comprise accumulating the energy from multiple transmissions until the message can be decoded. Once at least one random-access preamble message has been received, the method proceeds to step 808 in which the network node selects a preferred configuration for uplink transmissions based on the received preamble messages.

In some embodiments, e.g. where the terminal device transmits random-access preamble messages over different beams, the network node may select a beam over which uplink communications should take place. For example, the network node may select the beam based on the first message received in step 806 for which a signal metric exceeded a threshold. Alternatively, the network node may receive multiple messages in step 806 and select the beam for which the received signal had the best signal metric. Suitable metrics may include received signal strength, received signal received power, received signal quality, signal to interference ratio, signal to interference and noise ratio, or pathloss.

In other embodiments (e.g. repetition embodiments), the network node may determine in step 808 a required number of repetitions of the random-access preamble message before the contents of the message can be decoded. In step 810, the network node transmits, or initiates the transmission of, a random- access response message to the terminal device in the configured random-access response window. The random-access response message may comprise an indication of the number of repetitions required for future UL communications, or a beam over which UL communications should take place. In the latter case, the indication may be implicit based on a timing of the random-access response message transmission. The random-access response message may further comprise an indication of radio resources (e.g. frequencies and time slots, slots, mini-slots or sub-frames) scheduled to the terminal device for UL communications. Figure 9 is a schematic diagram of a terminal device 900 according to embodiments of the disclosure. The terminal device 900 may be suitable to perform the methods shown in Figures 6 and 7, for example, and may correspond to the wireless terminal 14 described above with respect to Figure 1. The terminal device 900 comprises processing circuitry 902 and a machine-readable medium 904 (such as memory) which is coupled to the processing circuitry 902. In one embodiment, the machine-readable medium 904 comprises instructions which, when executed by the processing circuitry 902, cause the terminal device to: obtain a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities; obtain a resource configuration for a random access response window associated with the random-access transmission window; responsive to a determination of a need to perform a random- access procedure, transmit, to a network node of the wireless communication network, a plurality of random-access preamble messages in the plurality of random-access preamble transmission opportunities; and listen for one or more random-access response messages in the random access response window.

In another embodiment, the machine-readable medium 904 comprises instructions which, when executed by the processing circuitry 902, cause the terminal device to: responsive to a determination of a need to perform a random-access procedure, transmit a first random access preamble message to a network node of the wireless communication network using a first transmit power; and, responsive to a determination that no random-access response message has been received to the first random- access preamble message, transmit a second random access preamble message to the network node using a second, higher transmit power.

The terminal device 900 may also generally comprise hardware and/or software for transmitting and receiving wireless signals, such as one or more antennas, and transceiver circuitry coupled to the one or more antennas.

Figure 10 is a schematic diagram of a terminal device 1000 according to further embodiments of the disclosure. The terminal device 1000 may be suitable to perform the methods shown in Figures 6 and 7, for example, and may correspond to the wireless terminal 14 described above with respect to Figure 1.

The terminal device 1000 comprises a configuration module 1002, a transmission module 1004, and a listening module 1006.

In one embodiment, the configuration module 1002 is configured to obtain a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities, and to obtain a resource configuration for a random access response window associated with the random- access transmission window. The transmission module 1004 is configured to, responsive to a determination of a need to perform a random-access procedure, transmit, to a network node of the wireless communication network, a plurality of random-access preamble messages in the plurality of random-access preamble transmission opportunities. The listening module 1006 is configured to listen for one or more random-access response messages in the random access response window.

In another embodiment, the transmission module 1004 is configured to, responsive to a determination of a need to perform a random-access procedure, transmit a first random access preamble message to a network node of the wireless communication network using a first transmit power; and, responsive to a determination that no random-access response message has been received to the first random-access preamble message, transmit a second random access preamble message to the network node using a second, higher transmit power.

The terminal device 1000 may also generally comprise hardware for the transmission and reception of wireless signals, such as one or more antennas, and one or more transceiver modules coupled to the one or more antennas.

In one embodiment, the random-access transmission window and the random access response window at least partially overlap in time. In such embodiments, the terminal device may be configured to listen for one or more random-access response messages in the random access response window by listening for one or more random-access response messages in time slots, slots, mini-slots or sub-frames in the random access response window which do not comprise a random-access preamble transmission opportunity. The terminal device (e.g. the transmission module) may further be caused to, responsive to receipt of a random-access response message in the random-access response window, halt transmission of further random-access preamble messages in the plurality of random-access preamble transmission opportunities.

In one embodiment, at least a subset of the plurality of random-access preamble transmission opportunities are configured periodically within the random-access transmission window. The plurality of random-access preamble transmission opportunities may be configured periodically within the random-access transmission window. For example, a first subset of the plurality of random-access preamble transmission opportunities may be configured with a first periodicity, and a second subset of the plurality of random-access preamble transmission opportunities may be configured with a second periodicity, wherein the first periodicity is more frequent than the second periodicity. The first subset may be an initial subset and the second subset a subsequent subset. The random-access preamble transmission opportunities in the first subset may be arranged in consecutive time slots, slots, mini-slots or sub-frames.

The random-access preamble transmission opportunities in the second subset may be arranged in every nth time slot, slot, mini-slot or sub-frame, wherein n is an integer greater than 1.

In one embodiment, the random-access transmission window comprises a plurality of random-access transmission sub-windows, each comprising multiple random-access preamble transmission opportunities of the plurality of random-access preamble transmission opportunities. In such an embodiment, the terminal device may be configured to transmit a plurality of random-access preamble messages by transmitting a respective random-access preamble message in each of the multiple random-access preamble transmission opportunities of a first random-access transmission sub- window, and, responsive to a determination that no random-access response message has been received, transmitting a respective random-access preamble message in each of the multiple random-access preamble transmission opportunities of a second random-access transmission sub-window.

In an embodiment, the resource configuration for the plurality of random-access preamble transmission opportunities comprises one or more of time slots, slots, mini- slots or sub-frames, and frequency bands.

In an embodiment, the resource configuration for the random access response window comprises one or more of time slots, slots, mini-slots or sub-frames, and frequency bands. The resource configuration for the random-access response window may be defined by a start time of the random-access response window and a duration of the random-access response window. The start time may be defined relative to a start time of the random-access transmission window or an initial random-access preamble transmission opportunity of the plurality of random-access preamble transmission opportunities. In one embodiment, the terminal device is configured to transmit the plurality of random-access preamble messages by transmitting the plurality of random-access preamble messages using the same beam. The plurality of random-access preamble messages may be copies of each other. In such embodiment, the terminal device (e.g. listening module 1006) may receive a random access response message from the network node, the random access response message comprising an indication of a number of repetitions of the random access preamble message required for successful decoding of the random access preamble message by the network node. The terminal device (e.g. the transmission module 1004) may then transmit a further wireless message using the number of repetitions indicated in the random access response message.

In an alternative embodiment, the terminal device is configured to transmit the plurality of random-access preamble messages by transmitting the plurality of random-access preamble messages using a plurality of beams. For example, the terminal device (e.g. the transmission module 1004) may be configured to transmit the plurality of random- access preamble messages by transmitting respective random-access preamble messages using respective beams of the plurality of beams. The terminal device may then receive a random access response message from the network node, the random access response message comprising an indication of a random-access preamble message of the plurality of random-access preamble messages which was first received by the network node with a signal metric above a threshold, or the beam of the plurality of beams using which the random-access preamble message of the plurality of random-access preamble messages was received first by the network node with a signal metric above a threshold. Alternatively, the terminal device may then receive a random access response message from the network node, the random access response message comprising an indication of the random-access preamble message of the plurality of random-access preamble messages which was received by the network node with a best signal metric, or the beam of the plurality of beams using which the random-access preamble message with the best signal metric was received. In either case, the signal metric may be one or more of: received signal strength, received signal received power, received signal quality, signal to interference ratio, signal to interference and noise ratio, and pathloss. In one embodiment, the terminal device (e.g. the transmission module 1004), responsive to a determination of a need to perform a random-access procedure, first transmits a single first random access preamble message using a first transmit power; and, responsive to a determination that no random-access response message has been received to the single first random-access preamble message, transmits a single second random access preamble message using a second, higher transmit power. For example, responsive to a determination that no random-access response message has been received, the terminal device may transmit further single random access preamble messages progressively higher transmit powers. The terminal device (e.g., the transmission module 1004) may further, responsive to a determination that a maximum transmit power has been reached, transmit the plurality of random-access preamble messages in the plurality of random-access preamble transmission opportunities. Preambles for the single first random access preamble message and the single second random access preamble message may each be the result of random selection processes. Figure 11 is a schematic diagram of a network node 1100 according to embodiments of the disclosure. The network node 1 100 may be suitable to perform the method shown in and described with respect to Figure 8, for example. The network node 1100 may correspond to a radio access network node, such as the network node 12 described above with respect to Figure 1 , or may correspond to a node which is connected to and controls such a radio access network node.

The network node 1100 comprises processing circuitry 1102 and a machine-readable medium 1104 (such as memory) which is coupled to the processing circuitry 1102. The machine-readable medium 1 104 comprises instructions which, when executed by the processing circuitry 1 102, cause the network node to: provide to a terminal device a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities; provide to the terminal device a resource configuration for a random access response window associated with the random-access transmission window; control a radio access network node for the wireless communication network to listen for a plurality of random-access preamble messages in the plurality of random-access preamble transmission opportunities; and, responsive to receipt by the radio access network node of at least one random-access preamble message in the plurality of random-access preamble transmission opportunities, initiate transmission by the radio access network node of a random- access response message in the random access response window. The network node 1100 may also generally comprise interface circuitry (i.e. hardware and/or software) for transmitting and receiving signals, such as one or more antennas, and transceiver circuitry coupled to the one or more antennas for transmitting and receiving wireless signals, or optical and/or electrical circuitry for transmitting and receiving optical or electrical signals.

Figure 12 is a schematic diagram of a network node 1200 according to embodiments of the disclosure. The network node 1200 may be suitable to perform the method shown in and described with respect to Figure 8, for example. The network node 1200 may correspond to a radio access network node, such as the network node 12 described above with respect to Figure 1 , or may correspond to a node which is connected to and controls such a radio access network node.

The network node 1200 comprises a configuration module 1202, a listening module 1206, and a transmission module 1204.

The configuration module 1202 is configured to provide to a terminal device a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities; and to provide to the terminal device a resource configuration for a random access response window associated with the random-access transmission window. The listening module 1204 is configured to control a radio access network node for the wireless communication network to listen for a plurality of random-access preamble messages in the plurality of random-access preamble transmission opportunities. The transmission module 1206 is configured to, responsive to receipt by the radio access network node of at least one random-access preamble message in the plurality of random-access preamble transmission opportunities, initiate transmission by the radio access network node of a random- access response message in the random access response window. The network node 1200 may also generally comprise one or more interface modules for transmitting and receiving signals, such as one or more antennas, and transceiver modules coupled to the one or more antennas for transmitting and receiving wireless signals, or optical and/or electrical modules for transmitting and receiving optical or electrical signals. In one embodiment, the random-access transmission window and the random access response window at least partially overlap in time.

In one embodiment, the network node is configured to initiate transmission by the radio access network node of a random-access response message in the random access response window responsive to successful decoding of at least one random-access preamble message. For example, the network node may combine multiple received random-access preamble messages in order to decode at least one of the random- access preamble messages. In such an embodiment, the random-access response message may comprise an indication of the number of random-access preamble messages required to decode at least one of the random-access preamble messages.

In an alternative embodiment, the network node is configured to initiate transmission by the radio access network node of a random-access response message in the random access response window responsive to an initial successful decoding of a random- access preamble message.

In a further alternative embodiment, the network node receives multiple random-access preamble messages in the plurality of random-access preamble transmission opportunities. The random-access response message comprises an indication of which random-access preamble message of the multiple random-access preamble messages was received by the radio access network node with a best signal metric, or an indication of a beam of a plurality of beams over which the random-access preamble message with the signal with the best signal metric was received. In such an embodiment, the signal metric may comprise one or more of: received signal strength, received signal received power, received signal quality, signal to interference ratio, signal to interference and noise ratio, and pathloss.

In another alternative embodiment, the network node is configured to initiate transmission by the radio access network node of a random-access response message in the random access response window responsive to receipt of a random-access preamble message having one or more signal metrics above a threshold. The one or more signal metrics may comprise one or more of: received signal strength, received signal received power, received signal quality, signal to interference ratio, signal to interference and noise ratio, and pathloss. In one embodiment, at least a subset of the plurality of random-access preamble transmission opportunities are configured periodically within the random-access transmission window. For example, the plurality of random-access preamble transmission opportunities may be configured periodically within the random-access transmission window. Alternatively, a first subset of the plurality of random-access preamble transmission opportunities may be configured with a first periodicity, and a second subset of the plurality of random-access preamble transmission opportunities configured with a second periodicity, wherein the first periodicity is more frequent than the second periodicity. In such an embodiment, the first subset may be an initial subset and the second subset a subsequent subset. The random-access preamble transmission opportunities in the first subset may be arranged in consecutive time slots, slots, mini-slots or sub-frames. Additionally or alternatively, the random-access preamble transmission opportunities in the second subset may be arranged in every nth time slot, slot, mini-slot or sub-frame, wherein n is an integer greater than 1.

In one embodiment, the random-access transmission window comprises a plurality of random-access transmission sub-windows, each comprising multiple random-access preamble transmission opportunities of the plurality of random-access preamble transmission opportunities.

In one embodiment, the resource configuration for the plurality of random-access preamble transmission opportunities comprises one or more of time slots, slots, mini- slots or sub-frames, and frequency bands. In one embodiment, the resource configuration for the random access response window comprises one or more of time slots, slots, mini-slots or sub-frames, and frequency bands. For example, the resource configuration for the random-access response window may be defined by a start time of the random-access response window and a duration of the random-access response window. The start time may be defined relative to a start time of the random-access transmission window or an initial random-access preamble transmission opportunity of the plurality of random-access preamble transmission opportunities.

The network node may be the radio access network node or a network node which is communicatively coupled to the radio access network node. Thus embodiments of the disclosure provide methods and apparatus that increase the likelihood that a random-access procedure will be successful, while achieving low latency if conditions allow.

Claims

1. A method in a terminal device (14, 900, 1000) for a wireless communication network, the method comprising:

obtaining (600) a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities; obtaining (602) a resource configuration for a random access response window associated with the random-access transmission window;

responsive to a determination (604) of a need to perform a random-access procedure, transmitting (606), to a network node (12) of the wireless communication network, a plurality of random-access preamble messages in the plurality of random- access preamble transmission opportunities; and

listening (608) for one or more random-access response messages in the random access response window.

2. The method according to claim 1 , wherein the random-access transmission window and the random access response window at least partially overlap in time.

3. The method according to claim 2, wherein the step of listening (608) for one or more random-access response messages in the random access response window comprises listening for one or more random-access response messages in time slots, slots, mini-slots or sub-frames in the random access response window which do not comprise a random-access preamble transmission opportunity.

4. The method according to claim 2 or 3, further comprising, responsive to receipt of a random-access response message in the random-access response window, halting transmission of further random-access preamble messages in the plurality of random- access preamble transmission opportunities.

5. The method according to any one of the preceding claims, wherein the resource configuration for the random access response window comprises one or more of time slots, slots, mini-slots or sub-frames, and frequency bands.

6. The method according to claim 5, wherein the resource configuration for the random-access response window is defined by a start time of the random-access response window and a duration of the random-access response window.

7. The method according claim 6, wherein the start time is defined relative to a start time of the random-access transmission window or an initial random-access preamble transmission opportunity of the plurality of random-access preamble transmission opportunities.

8. The method according to any one of the preceding claims, wherein the step of transmitting (606) the plurality of random-access preamble messages comprises transmitting the plurality of random-access preamble messages using the same beam.

9. The method according to claim 8, wherein the plurality of random-access preamble messages are copies of each other.

10. The method according to any one of claims 1 to 7, wherein the step of transmitting (606) the plurality of random-access preamble messages comprises transmitting the plurality of random-access preamble messages using a plurality of beams (16a-16e).

1 1. The method according to claim 10, wherein the step of transmitting (606) the plurality of random-access preamble messages comprises transmitting respective random-access preamble messages using respective beams of the plurality of beams (16a-16e).

12. The method according claim 10 or 11 , further comprising receiving a random access response message from the network node, the random access response message comprising an indication of a random-access preamble message of the plurality of random-access preamble messages which was first received by the network node with a signal metric above a threshold, or the beam of the plurality of beams using which the random-access preamble message of the plurality of random-access preamble messages was received first by the network node with a signal metric above a threshold.

13. A method in a network node (12, 1 100, 1200) for a wireless communication network, the method comprising: providing (800) to a terminal device a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities;

providing (802) to the terminal device a resource configuration for a random access response window associated with the random-access transmission window; controlling a radio access network node for the wireless communication network to listen (804) for a plurality of random-access preamble messages in the plurality of random-access preamble transmission opportunities; and

responsive to receipt (806) by the radio access network node of at least one random-access preamble message in the plurality of random-access preamble transmission opportunities, initiating transmission (810) by the radio access network node of a random-access response message in the random access response window.

14. The method according to claim 13, wherein the resource configuration for the random access response window comprises one or more of time slots, slots, mini-slots or sub-frames, and frequency bands.

15. The method according to claim 14, wherein the resource configuration for the random-access response window is defined by a start time of the random-access response window and a duration of the random-access response window.

16. The method according claim 15, wherein the start time is defined relative to a start time of the random-access transmission window or an initial random-access preamble transmission opportunity of the plurality of random-access preamble transmission opportunities.

17. A terminal device (14, 900, 1000) for a wireless communication network, the terminal device being configured to perform the method of any one of claims 1 to 12.

18. A terminal device (900) for a wireless communication network, the terminal device comprising processing circuitry (902) and a machine-readable medium (904) storing instructions which, when executed by the processing circuitry, cause the terminal device to:

obtain a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities; obtain a resource configuration for a random access response window associated with the random-access transmission window;

responsive to a determination of a need to perform a random-access procedure, transmit, to a network node of the wireless communication network, a plurality of random-access preamble messages in the plurality of random-access preamble transmission opportunities; and

listen for one or more random-access response messages in the random access response window.

19. The terminal device according to claim 18, wherein the random-access transmission window and the random access response window at least partially overlap in time.

20. The terminal device according to claim 19, wherein the terminal device is configured to listen for one or more random-access response messages in the random access response window by listening for one or more random-access response messages in time slots, slots, mini-slots or sub-frames in the random access response window which do not comprise a random-access preamble transmission opportunity.

21. The terminal device according to claim 19 or 20, wherein the machine-readable medium further stores instructions which, when executed by the processing circuitry, cause the terminal device to, responsive to receipt of a random-access response message in the random-access response window, halt transmission of further random- access preamble messages in the plurality of random-access preamble transmission opportunities.

22. The terminal device according to any one of claims 18 to 21 , wherein the resource configuration for the random access response window comprises one or more of time slots, slots, mini-slots or sub-frames, and frequency bands.

23. The terminal device according to claim 22, wherein the resource configuration for the random-access response window is defined by a start time of the random-access response window and a duration of the random-access response window.

24. The terminal device according claim 23, wherein the start time is defined relative to a start time of the random-access transmission window or an initial random-access preamble transmission opportunity of the plurality of random-access preamble transmission opportunities.

25. The terminal device according to any one of claims 18 to 24, wherein the terminal device is configured to transmit the plurality of random-access preamble messages by transmitting the plurality of random-access preamble messages using the same beam.

26. The terminal device according to claim 25, wherein the plurality of random- access preamble messages are copies of each other.

27. The terminal device according to any one of claims 18 to 24, wherein the terminal device is configured to transmit the plurality of random-access preamble messages by transmitting the plurality of random-access preamble messages using a plurality of beams.

28. The terminal device according to claim 27, wherein the terminal device is configured to transmit the plurality of random-access preamble messages by transmitting respective random-access preamble messages using respective beams of the plurality of beams.

29. The terminal device according claim 27 or 28, wherein the machine-readable medium further stores instructions which, when executed by the processing circuitry, cause the terminal device to receive a random access response message from the network node, the random access response message comprising an indication of a random-access preamble message of the plurality of random-access preamble messages which was first received by the network node with a signal metric above a threshold, or the beam of the plurality of beams using which the random-access preamble message of the plurality of random-access preamble messages was received first by the network node with a signal metric above a threshold.

30. A network node (12, 1 100, 1200) for a wireless communication network, the network node being configured to perform the method according to any one of claims 13 to 16.

31. A network node (1 100) for a wireless communication network, the network node comprising processing circuitry (1 102) and a machine-readable medium (1 104) storing instructions which, when executed by the processing circuitry, cause the network node to:

provide to a terminal device a resource configuration for a random-access transmission window comprising a plurality of random-access preamble transmission opportunities;

provide to the terminal device a resource configuration for a random access response window associated with the random-access transmission window;

control a radio access network node for the wireless communication network to listen for a plurality of random-access preamble messages in the plurality of random- access preamble transmission opportunities; and

responsive to receipt by the radio access network node of at least one random- access preamble message in the plurality of random-access preamble transmission opportunities, initiate transmission by the radio access network node of a random- access response message in the random access response window.

32. The network node according to claim 31 , wherein the resource configuration for the random access response window comprises one or more of time slots, slots, mini- slots or sub-frames, and frequency bands.

33. The network node according to claim 32, wherein the resource configuration for the random-access response window is defined by a start time of the random-access response window and a duration of the random-access response window.

34. The network node according claim 33, wherein the start time is defined relative to a start time of the random-access transmission window or an initial random-access preamble transmission opportunity of the plurality of random-access preamble transmission opportunities.