Communication between devices in a license exempt spectrum

Abstract

A method of communication between nodes on a plurality of channels within an unlicensed frequency spectrum is disclosed, wherein coordination of acquisition of different channels is provided in order to acquire a further channel before the occupancy time of a currently used channel expires. The method involves determining at a node that a channel in the unlicensed frequency band has been acquired for a predetermined occupancy time. A scan of at least one further channel within the unlicensed frequency spectrum is initiated to determine whether the further channel is available. Once the predetermined time has elapsed and for the predetermined occupancy time, the available channel is acquired by transmitting a signal thereon.

Description

TECHNICAL FIELD

[0001] Various example embodiments relate to communication within unlicensed spectrum. BACKGROUND

[0002] Unlicensed spectrum provides an opportunity to increase the available bandwidth for signals to be transmitted. However, as this bandwidth is shared with other devices, it can be necessary to scan before transmission to reduce interference. Furthermore, there can be rules about how often a device can scan to allow the spectrum to be fairly shared, and these issues can result in increased latency.

[0003] Unlicensed frequency bands are divided into sub-bands or channels, each sub-band or channel covering a certain frequency band, and a scanning procedure, such as listen before talk, involves sensing of the channel to determine if the channel is available before transmitting a signal. In the case that it is, the channel can be acquired by a node for a channel occupancy time, COT. During this time, signals can be transmitted and other nodes are prevented from using the channel.

[0004] Increasingly, devices are able to transmit and receive on more than one channel, and this can be used to increase throughput and / or increase reliability. Disruptions in communication can potentially be problematic when an occupancy period in one channel expires and a further channel is to be acquired.

[0005] It would be desirable to provide a system for communicating in unlicensed spectrum in a manner that is both efficient and allows co-existence with other systems. SUMMARY

[0006] The independent claims define the scope of the invention. Embodiments and features that are not part of the independent claims, if any, are to be interpreted as examples useful in understanding the invention various embodiments. The independent claims define the scope of the invention. Embodiments and features that are not part of the independent claims, if any, are to be interpreted as examples useful in understanding the invention various embodiments.

[0007] According to various, but not necessarily all, embodiments of the invention, according to a first aspect, there is provided a method performed at an apparatus, the method comprising: determining, at the apparatus, that a channel in unlicensed spectrum has been acquired by the apparatus or by a further apparatus for a predetermined occupancy time, the channel being one of a plurality of channels within the unlicensed spectrum; initiating scanning of at least one further channel within the unlicensed spectrum to determine whether the scanned at least one further channel is available; determining whether a predetermined time has elapsed since the channel was acquired, the predetermined time being less than or equal to the predetermined occupancy time; and in response to the scanning indicating that at least one of the scanned at least one further channel is available, and when the predetermined time is determined to have elapsed, initiating acquisition of one of the available scanned channels for a predetermined occupancy time.

[0008] Using unlicensed spectrum can require scanning of channels prior to use to allow coexistence between different devices using the spectrum. This scanning adds delay and can be a particular problem in cases where the scanning process requires a device to wait until the unlicensed medium is free for a defined period of time, which can be long before the spectrum can be accessed if there are a large number of devices in the neighbourhood. This is the case, for example, with listen-before-talk.

[0009] The inventors have recognised that there are many channels within the unlicensed spectrum that can be used for communication and that there is an increasing number of devices that support multi-link operating modes. Embodiments seek to exploit this ability to transmit on different channels while addressing the problems that can arise when switching between inter-channel communication, particularly in cases where a requirement to wait for a channel to become available must be met.

[0010] Accordingly, one aspect provides a method that starts scanning one or more further channels within an unlicensed spectrum while using a first channel acquired at an occupancy period for communication between two devices. Once the scanning indicates that a channel is available, rather than acquiring the channel immediately, the method waits until a predetermined time has elapsed since the first channel was acquired and only then acquires the further channel. In this way, there is coordination between the acquisition of different channels and the acquisition of the next channel to be used for communication can be controlled to be within the occupancy time of the first channel so that any gaps and associated discontinuous communication are prohibited.

[0011] In some embodiments, the above method includes, prior to initiating the above scanning, determining whether a second predetermined period of time has elapsed since the above channel was acquired and initiating the above scanning when the above second predetermined time is determined to have elapsed, the above second predetermined period of time being shorter than the above predetermined period of time.

[0012] While scanning can be performed in the background on many of the channels for most of the time, in some embodiments, the scanning is performed at a set time. This time can be chosen to be a certain time after the first channel was acquired or to be a certain time before the occupancy time is determined to be due to expire or to be a certain time before a new occupancy period is determined to be expected to start. In this regard, a subsequent channel is required before the occupancy period of the first channel expires but only shortly before. Furthermore, if the scanning of channels indicates that a channel is available at some time before it is required, the likelihood that the channel is no longer available at the time of requirement increases. However, a channel being scanned can initially be unavailable and many scanning methods, such as listen-before-talk, back off for a period of time if the channel is unavailable so the amount of time required for scanning cannot be fully predicted. Accordingly, it can be advantageous to wait for a certain time before the scanning starts and the preferred waiting time can depend on the conditions.

[0013] In some embodiments, the value of the second predetermined time period is specific to a particular channel.

[0014] The amount of time required to scan and find an available channel is unpredictable and will be influenced by factors such as channel load and channel occupancy, and as such, it will be specific to a particular channel, and in some cases, the second predetermined time period can depend on the channel being scanned. In other cases, it can be simpler to use a set second determined time period for all channels.

[0015] In some embodiments, the method comprises determining the second predetermined time for the at least one further channel to be scanned in dependence on at least one of:

[0016] the determined channel load and channel occupancy of the at least one further channel; and

[0017] stored historical data indicative of a delay between the start of a scan and the at least one further channel being determined to be available.

[0018] As previously mentioned, the time required for a scan depends on many factors specific to a channel and the prevailing conditions of that channel. It can therefore be advantageous for it to be specific to a particular channel, and / or determined based on historical data for that channel and / or the determined channel load and channel occupancy.

[0019] In this way, the second predetermined time period can be selected in dependence on the characteristics of the channel being scanned, with the apparatus selecting a shorter second predetermined time period to provide potentially longer scan times when the channel load and occupancy are determined to be high. In some embodiments, the second predetermined time can be estimated for a plurality of channels, and a value selected for all channels which is estimated to be likely to have at least one channel available within that time period.

[0020] In some embodiments, the predetermined time is selected in dependence on an expected overlap of the occupancy times.

[0021] In some embodiments, the predetermined time is dependent on network load and can be controlled to be within a certain percentage range of the occupancy time, in some embodiments the predetermined time comprises 70% to 99.5% of the occupancy time.

[0022] The predetermined time between the current channel being acquired and the acquisition of the subsequent channel will affect the overlap in occupancy time that occurs when the device acquires both channels. In this regard, in many cases it is desirable to have little overlap in the occupancy time, as low overlap can efficiently utilize the channels and allow for more time for scanning of the subsequent available channels. However, depending on the device and the type of communication, some overlap can be advantageous and can increase the chances of having no gaps in the communication. In one example, it is desirable that the overlap can be selected according to the buffer size of the device and the other device.

[0023] The second predetermined time can also be selected according to the desired overlap, as any overlap will affect the amount of scanning time available. In some cases, the second predetermined time can be selected according to the predetermined time, which itself can depend on the desired overlap. In this regard, the amount of scanning time available will depend on the difference between the predetermined time and the second predetermined time, so if the preferred scanning time remains the same, a change in the predetermined time due to a change in the desired overlap can trigger the same change in the second predetermined time.

[0024] In some embodiments, the device described above performs the initial steps of at least one of:

[0025] initiating transmission of an indication to the other device that multi-channel communication within the unlicensed spectrum between the device and the other device is to be performed; and

[0026] receiving an indication from the other device that multi-channel communication within the unlicensed spectrum between the device and the other device is to be performed.

[0027] Before multi-link communication occurs between a device and another device, an agreement typically needs to be reached that such communication will occur. This can be achieved by one device sending a multi-link communication request and the other device accepting the multi-link communication request, and / or can be achieved by a configuration signal configuring the devices for multi-link communication. In this regard, each device should recognize that they are working in this manner, such that they scan for the multiple channels on which the other device can be transmitting.

[0028] In some embodiments, the step of determining at the device that a channel in the unlicensed spectrum has been acquired by the device or by the other device comprises acquiring the channel, the method further comprising:

[0029] The steps of scanning for channels and acquiring available scanned channels for a predetermined occupancy time are repeated multiple times during a period of multi-channel communication between the device and the other device.

[0030] Although the step of acquiring a channel can be performed by each of the devices in the communication link, in some embodiments there can be a controlling device, for example a gNB, in which case it can be used to acquire a channel each time a channel switch occurs. It thus controls the scanning and acquisition of multiple channels and any overlap of occupancy time.

[0031] In some embodiments the above method further comprises:

[0032] Upon acquiring the one of the above available scanned channels, requesting an uplink transmission from the above further device; and

[0033] If the above uplink transmission is not received within a set time:

[0034] selecting a further one of the above scanned available channels and acquiring the further one of the above scanned available channels for a predetermined occupancy time period; and

[0035] marking the one of the above available scanned channels as unavailable.

[0036] In some embodiments, for example if one device is a gNB, there can be different devices in communication with the gNB, such as user equipment, and the channel acquired for communication can not be particularly suitable for one of these devices, for example there is a hidden device. In some cases it can therefore be advantageous if a signal is initially transmitted to request a response. If no response is received within a certain period, it indicates that the device did not receive the signal and another alternative channel can be acquired.

[0037] In some embodiments the above predetermined time is selected to provide a set overlap period for the above occupancy time, the above step of selecting and acquiring the further one of the above scanned available channels being performed within the above set overlap period.

[0038] If there is a step of determining whether the selected channel is suitable, it can be advantageous for the device to operate for an occupancy overlap period which is set to be long enough for the test process of determining whether the acquired channel is suitable for the further device to be performed within that period. In this way, if another channel is required, it can be selected within the occupancy overlap period without a gap in the communication. Unsuitable scanned channels can be marked as unavailable so that this does not occur again. In this regard, this can be within a predetermined time, or for a particular device or group of devices.

[0039] In some embodiments, the step of determining at the apparatus that the channel in the unlicensed frequency band has been acquired by the apparatus or by the further apparatus for the predetermined occupancy time comprises receiving a signal from the further apparatus indicating that the further apparatus has acquired the channel.

[0040] In some embodiments, the apparatuses can take turns acquiring channels, so after receiving a communication from an apparatus indicating that the apparatus has acquired a channel, the receiving apparatus can scan one or more other channels within the unlicensed spectrum and acquire one of these channels during the occupancy period of the previously acquired channel, which can then be used for a subsequent portion of the communication. This process is repeated as each receiving apparatus scans for available channels for a subsequent portion of the communication. This can occur, for example, when one apparatus is an access point in a Wi-Fi system and the further apparatus can be a user device.

[0041] In some embodiments, the method comprises, after acquiring the scanned available channel, transmitting an indication to the further apparatus that the scanned available channel has been acquired for the predetermined occupancy time; and

[0042] receiving a signal from the further apparatus indicating that the further apparatus has acquired a further one of the plurality of channels in the unlicensed spectrum prior to or at the expiration of the predetermined occupancy time for which the scanned available channel was acquired.

[0043] As mentioned above, the apparatus and the further apparatus can take turns acquiring channels and scan for further channels during the occupancy time of the previously acquired channel.

[0044] In some embodiments, the method further comprises performing a further check that the scanned available channel is still available immediately prior to initiating acquisition of the channel.

[0045] If the scan for a channel indicates that the channel will be available for a short period of time before the predetermined time elapses, a further check can be needed when that time is about to elapse and the channel should be acquired. Such a further check is typically much quicker than the previous scan, as there is no back-off period, and the check can be a simple scan to check for any signals. This can be performed a set time before the predetermined time elapses, the set time being close to the end of the predetermined time, so that if the channel is determined to still be free, the channel can be acquired immediately. In this regard, a second predetermined time is selected relative to the start of the scan to the end of the occupancy time, so as to estimate that the scan should be completed close to the end of the occupancy time, so the channel is unlikely to not be free. However, if not free, another channel needs to be acquired, or the system needs to check again.

[0046] According to various, but not necessarily all, embodiments of the application, according to a second aspect, there is provided a computer program comprising computer readable instructions configured to, when executed by a processor on a device, cause the device to perform the method according to the first aspect.

[0047] According to various, but not necessarily all, embodiments of the application, according to a third aspect, there is provided a device comprising means configured to:

[0048] determine that a channel in an unlicensed frequency spectrum has been acquired by the device or by a further device for a predetermined occupancy time, the channel being one of a plurality of channels within the unlicensed frequency spectrum;

[0049] initiate a scan of at least one further channel within the unlicensed frequency spectrum to determine whether the scanned at least one further channel is available;

[0050] determine whether a predetermined time has elapsed since the channel was acquired, the predetermined time being less than or equal to the predetermined occupancy time; and

[0051] initiate acquisition of one of the available scanned channels for the predetermined occupancy time after the scan indicates that at least one of the scanned at least one further channel is available and when the predetermined time is determined to have elapsed.

[0052] In some embodiments, the means are configured to determine, prior to initiating the scan, whether a second predetermined time period has elapsed since the channel was acquired, the second predetermined time period being less than the predetermined time period.

[0053] In some embodiments, the second predetermined time period is specific to a particular channel.

[0054] In some embodiments, the means are configured to determine the second predetermined time for the at least one further channel to be scanned in dependence on at least one of: a determined channel load and channel occupancy of the at least one further channel; and stored historical data of a delay time between a start of a scan on the at least one further channel and the at least one further channel being determined to be available.

[0055] In some embodiments, the predetermined time is selected in dependence on an expected overlap of the occupancy time.

[0056] In some embodiments, the above-mentioned means are configured to control the above-mentioned apparatus to perform at least one of the following initial steps: initiating transmission of an indication to the above-mentioned further apparatus that multi-channel communication in the unlicensed spectrum between the above-mentioned apparatus and the above-mentioned further apparatus is to be performed; and receiving an indication from the above-mentioned further apparatus that multi-channel communication in the unlicensed spectrum between the above-mentioned apparatus and the above-mentioned further apparatus is to be performed.

[0057] In some embodiments, the above-mentioned means are configured to, when acquiring the one of the above-mentioned available scanned channels, initiate transmission of a signal requesting uplink transmission from the above-mentioned further apparatus; and if the above-mentioned uplink transmission is not received within a set time: select a further one of the above-mentioned scanned available channels, and initiate transmission to acquire the further one of the above-mentioned scanned available channels for a predetermined occupation time period; and mark the one of the above-mentioned available scanned channels as unavailable.

[0058] In some embodiments, the above-mentioned predetermined time is selected to provide a set overlap period for the occupation time, the above-mentioned step of selecting and acquiring the further one of the above-mentioned scanned available channels being performed within the set overlap period.

[0059] In some embodiments, the above-mentioned means are configured to, during the above-mentioned predetermined occupation time period, initiate transmission of a signal indicating a further channel to be used during a subsequent predetermined occupation time period of the communication.

[0060] In some embodiments, if the above-mentioned apparatus is configured to control acquisition of channels, and the further apparatus can only communicate on one channel at a time, the apparatus can be configured to indicate to the further apparatus a subsequent channel to acquire next during a current channel occupation time period. In this way, the other apparatus can switch to the channel in order to receive a subsequent signal at or near the end of the current channel occupation time period.

[0061] In some embodiments, the means comprise: at least one processor; and at least one memory including computer program code, the above-mentioned at least one memory and computer program code configured to, with the above-mentioned at least one processor, cause the apparatus to perform.

[0062] In some embodiments, the above-mentioned apparatus further comprises means for transmitting and receiving signals, and means for scanning channels in the unlicensed spectrum.

[0063] According to various, but not necessarily all, embodiments of the invention there is provided an apparatus comprising control circuitry configured to: determine that a channel in an unlicensed spectrum has been acquired by the apparatus or by a further apparatus for a predetermined occupancy time, the channel being one of a plurality of channels within the unlicensed spectrum; initiate a scan of at least one further channel within the unlicensed spectrum to determine whether the scanned at least one further channel is available; determine whether a predetermined time has elapsed since the channel was acquired, the predetermined time being less than or equal to the predetermined occupancy time; and initiate acquisition of one of the available scanned channels for a predetermined occupancy time after the scan indicates that at least one of the scanned at least one further channel is available and when the predetermined time is determined to have elapsed.

[0064] In some embodiments the apparatus further comprises: a transmitter configured to transmit signals to the at least one further node in a plurality of channels of an unlicensed spectrum; a receiver configured to receive signals from at least one further node in the plurality of channels of the unlicensed spectrum; and scan circuitry configured to scan the plurality of channels in the unlicensed spectrum.

[0065] In some embodiments the control circuitry is configured to determine that a second predetermined period of time has elapsed since the channel was acquired before controlling the scan, the second predetermined period of time being less than the predetermined period of time.

[0066] In some embodiments the control circuitry is configured to determine the second predetermined time for the at least one further channel to be scanned in dependence on at least one of: a determined channel load and channel occupancy of the at least one further channel; and stored historical data of a delay time between a start of a scan on the at least one further channel and the at least one further channel being determined to be available.

[0067] In some embodiments the control circuitry is configured to control the apparatus to perform at least one of an initial step of: initiating transmission of an indication to the further apparatus that multi-channel communication within the unlicensed spectrum between the apparatus and the further apparatus is to be performed; and receiving an indication from the further apparatus that multi-channel communication within the unlicensed spectrum between the apparatus and the further apparatus is to be performed.

[0068] According to various, but not necessarily all, embodiments of the invention there is provided a method and apparatus for providing communication between nodes which use different sub-bands in succession within an unlicensed spectrum. Acquisition of sub-bands is arranged so that there is at least some overlap in the occupation of sub-bands, and any gaps in the communication are suppressed. There is provided a method performed at a second node for coordinating multi-channel communication between a first node and the second node, the method comprising: while communicating with the first node on a first channel, scanning at least one further channel to determine whether the at least one further channel is available, acquiring one of the at least one further scanned channels after a predetermined time, before an occupation period of the first channel expires. The method further comprises transmitting a signal to the first node on the first channel, the signal indicating the at least one further channel to be acquired during the channel occupation period.

[0069] Further specific and preferred aspects are set out in the appended dependent and independent claims. Features of dependent claims can be combined with features of the independent claims as appropriate and combinations other than those explicitly set out in the claims are also envisaged.

[0070] If apparatus features are described as operable to provide functionality, it will be appreciated that this includes apparatus features which provide that functionality, or apparatus features which are adapted or configured to provide that functionality. BRIEF DESCRIPTION OF DRAWINGS

[0071] Some example embodiments will now be described with reference to the accompanying drawings, in which:

[0072] Figures la, lb and Figure 1C Discontinuous communication problems which can arise with multi-link communication are illustrated;

[0073] Figure 2 Multi-link communication according to one embodiment is schematically illustrated;

[0074] Figure 3 A flow diagram illustrating steps in a method of performing multi-link communication according to one embodiment is illustrated;

[0075] Figure 4 Multi-link communication according to another embodiment is schematically illustrated;

[0076] Figure 5 Constraints on COT start times in further channels are schematically illustrated;

[0077] Figure 6 Scan times required to find available channels are schematically illustrated; and

[0078] Figure 7A node according to one embodiment is shown schematically. DETAILED DESCRIPTION

[0079] Before discussing example embodiments in more detail, first an overview will be provided.

[0080] Embodiments provide apparatuses or nodes configured to communicate using multiple channels in the unlicensed spectrum in such a way that the delay in transmissions is reduced and discontinuity is inhibited. Communication between nodes is performed continuously on different channels in the unlicensed spectrum.

[0081] Coordination of acquisition of different channels is provided so that a further channel is acquired before the occupancy time of the currently used channel expires.

[0082] In some embodiments, a node receiving signals from a further node in a first channel acquired by the further node for an occupancy period, scans one or more other channels during the occupancy period and when it determines that one of the scanned other channels is available, and when the occupancy period of the acquired channel is about to expire, the node acquires the available channel, in this way, communication between the two nodes can continue uninterrupted, or at least the chances of interruption can be reduced. In this regard, if multiple channels are scanned and the load of the channels is not too high, it is likely that a channel will be available and can be acquired during the occupancy period of the previously acquired channel, so that there will be no gap in the transmission.

[0083] In other embodiments, one of the nodes in the communication can control the acquisition of channels. In one example, the node can be a gNB (5G radio node) communicating with user equipment. In this case, the gNB controls the acquisition of different channels and it will scan multiple channels during the occupancy period of the previously acquired channel and acquire a channel in the unlicensed spectrum before the occupancy period of the previously acquired channel expires. In this way, by controlling the selection of the time of scanning and the selection of the time of channel acquisition, continuous communication using different channels within the unlicensed spectrum can be achieved.

[0084] Figure 1A 、 Figure 1B and Figure 1C shows the potential problem of delay that can arise in the communication between two nodes if there is no coordination of acquisition of different channels within the unlicensed spectrum. Figure 1A synchronous multi-link channel access is shown in which a multi-link device controls channel access to ensure that channel occupancy times (COTs) in different links a) start at the same time, and / or b) end at the same time. From a channel access perspective, the implementation of synchronous multi-link channel access results in almost deterministic discontinuous communication (see Figure 1Across marks in

[0085] Another alternative is an asynchronous and independent multi-link channel access, as Figure 1B shown. A device implementing this mode of operation will perform channel access independently per link, i.e. as long as a link is available, the multi-link device will initiate a COT. It should be noted that the COT in different links can be initiated by different devices. For example, while this figure covers many scenarios, one can imagine that a gNB (gNB1) initiates a first COT in link A to communicate with one of its associated UEs (UE1) and that UE1 initiates a first COT in link B to communicate with gNB1. This can thus provide high throughput. However, from a latency perspective, this mode of operation can not be the most efficient as it is almost certain that there will be periods without COT (see cross marks in Figure 1B ). Moreover, depending on the implementation of the transceivers, and whether the links are within the same band and / or there is sufficient frequency separation between the links, a device can not be able to perform LBT on one link while transmitting and / or receiving on another link. This makes the above observation even more true.

[0086] Figure 1C An alternative multi-link channel access is shown, where a multi-link device will only attempt to perform channel access in a different link after the active COT in the other link has completed. While this mode of operation can be the best choice from a latency perspective if a device cannot transmit / receive in different links at the same time, it can not be the best approach if a device does not have such a constraint. This is because this mode of operation does not guarantee that there is at least one COT ongoing / available at any time when there is interference (see cross marks in Figure 1C ).

[0087] Figure 2 The timing of the scanning and acquisition of the channel by two nodes according to one embodiment is shown schematically. As Figure 2 indicated by the arrows in , the objective of the proposed solution, called "continuous multi-link mode of operation", is to have at least one COT ongoing / available at any time.

[0088] In the example in Figure 2 , the communication is between a multi-link capable 802.11 compliant access point (AP) and a multi-link capable 802.11 compliant enhanced / virtual reality station (STA). The embodiments are particularly suitable for enhanced / virtual reality traffic, which imposes strict latency / reliability constraints that should be met in order to get a satisfactory end-user experience.

[0089] Although the examples of AP and STA are given above, the communication can be between any two nodes configured to communicate using multiple channels in the unlicensed spectrum. For example, the communication can be a cellular sidelink communication, where a cellular device communicates directly with another device without relaying its traffic through a base station. In this setup, one of the devices will play the role of the AP (and thus become the dominant device), while the other device plays the role of the STA. Of course, these roles can be interchanged as the communication proceeds, especially if both devices cannot transmit and receive in multiple links at the same time due to self-interference / hardware constraints. For these devices, to establish the above operations in a sidelink context, explicit signaling is used.

[0090] For the purpose of this embodiment, the links can be interpreted as 20MHz channels, the multi-link AP and the multi-link STA operate in two links (Link 1 and Link 2) located in different frequency bands (e.g., low 5GHz and high 5GHz). The device initiating the COT (AP or STA in this embodiment) will perform a continuous data transmission to the other communication end, with a maximum COT duration of 6ms.

[0091] Figure 3 A flowchart illustrating steps in a method according to one embodiment is shown. In this example, “Device A” is the AP, while “Device B” is the STA.

[0092] Step S1 : After identifying the traffic needs of the STA, the AP indicates to the STA:

[0093] The continuous multi-link operation mode should be enabled, and

[0094] The AP itself will be the “initiating” device in the first transmission of the continuous multi-link operation mode, the “following” device should be the device receiving data in Link P. In practice, this means that the role of the “following” device will alternate between the AP and the STA, and both devices should implement the components of the proposed method.

[0095] In a sidelink context, if the devices are two UEs communicating directly, the device playing the role of the AP signals to the device playing the role of the STA the above behavior. Since this behavior requires a configuration between the two devices, in some embodiments, this is done through a PC5 RRC reconfiguration message exchange (where PC5 denotes the sidelink interface between the two devices, and the RRC reconfiguration message corresponds to a Radio Resource Control message, which in a cellular context is responsible for all configuration parameters and their exchange between the affected devices).

[0096] Step S2: The STA (Device B) replies to the AP (Device A) to indicate that it agrees to operate in the continuous multi-link operation mode.

[0097] In the sidelink context, step S2 corresponds to the device playing the role of STA replying with a PC5 RRC reconfiguration acknowledgement (actually only a HARQ acknowledgement needs to be received).

[0098] If device B accepts the multi-link operation mode, then at step S3: it is first determined who is the initiating device and who is the following device. In this case, the AP will be the "initiating" device in the first COT and the STA will be the "following" device in the first COT.

[0099] Step S4: After contending for channel access with LBT in both links, the AP gets the COT and initiates a downlink transmission to the STA in link 1 (now labelled "link P"). As a "following" device, the STA initializes the COT timer to t = 0.

[0100] When the two devices are directly communicating UEs, in order to inform the device playing the role of STA, the device playing the role of AP includes control information in its transmission. Such control information states at least that the AP device has acquired the COT and its duration.

[0101] Step S5: Since the STA is considered as a "following" device, it checks whether it should start scanning. It determines that it should start scanning in the following cases:

[0102] t > (COT P-S Start time - LBT S Period length), for all S ≠ P

[0103] (Equation 1)

[0104] For link S = 2, the above operations must be performed independently, COT P-S is defined as the time from the start of the COT in link P, during which the multi-link device is allowed to initiate a transmission in a different link (link S). This depends on the time of overlap required by the two COTs.

[0105] The value of this parameter varies depending on the pair of links considered, i.e. link P and link S are different for the device, and in the present embodiment should be dynamically and independently adjusted by the relevant devices (both the AP and the STA).

[0106] LBT S is defined as the time spent by a device between 1) the start of the channel access contention in link S and 2) the start of the transmission in link S. Thus, the "LBT period length" includes the time during which such a device performs the following operations 1) sensing the channel free with a backoff counter equal to a non-zero value, and 2) sensing the channel busy.

[0107] In practice, it is determined according to the length of the COT and the estimated time that a channel scan can be performed and the channel is considered available to be determined, at which time the scanning procedure should be initiated, so that the channel will likely be available. The time in which the scan of a particular channel should be completed can be estimated according to channel history and / or current load and / or channel occupancy, and this time is denoted as LBTsfor channel s. Thus, when it is estimated that the COT has this time remaining, the scan of a particular channel is started so that the scan should be completed before the end of the COT, or more precisely, when the multi-link device is allowed to start transmission in another link.

[0108] In other, simpler embodiments, the device will continuously perform LBT and can not use this parameter.

[0109] In this embodiment, it is considered that even in the case of invalid continuous multi-link operation mode, the device with the capability to implement the proposed operation mode contains a continuous estimation of the COT P-S Start time and LBT S Both the function blocks of the period length parameter. This allows them to be able to provide an initial estimate that can then be refined as described later.

[0110] For ease of illustration, assume that (COT P-S Start time - LBT S Period length) = 3 ms, and COT P-S Start time = 5 ms. Thus, as soon as t = 3 ms, the STA will enter step S6.

[0111] In step S6, the STA starts the LBT in link s = 2 at t = 3 ms.

[0112] In step S7: When the LBT backoff counter in link s = 2 reaches 0, the STA, which is currently the following device, checks whether the following is true

[0113] t > = COT P-S Start time

[0114] (Equation 2)

[0115] For ease of illustration, and since this is a random process, assume that the LBT counter of the STA of link s = 2 reaches 0 at t = 4 ms. This means that the device has to wait 1 ms to continue with step S8.

[0116] Step S8: When t = 5ms, the STA makes sure that the link S = 2 is still considered as free. In the embodiment where the follower device scans more than one channel, i.e. in step S6, it starts LBT in more than one link (e.g. S2, S3 and S4), then in step S8, the device will stop LBT scanning in the other links (see description of NR-U compatible gNB below).

[0117] Step S9: The STA becomes the "initiator" device and the link S = 2 is now labelled as link P.

[0118] Step S10: According to the initial agreement between the AP and the STA, the AP will next play the role of "follower" device as it is receiving data in link P. The STA goes back to step S4 to act as initiator device.

[0119] Sidelink aspect: This agreement is part of the exchange of PC5 RRC reconfiguration.

[0120] In another embodiment, we consider a scenario with a multi-link capable NR-U compatible gNB and two NR-U compatible UEs, i.e. one enhanced / virtual reality UE with multi-link capability and one UE generating best effort traffic.

[0121] For the purpose of this embodiment,

[0122] A link can be interpreted as a 20MHz channel,

[0123] The multi-link gNB and the multi-link UE operate in four links (links 1 to 4) within the same frequency band (e.g. low 5GHz),

[0124] The maximum COT duration is 6ms,

[0125] The multi-link UE has simultaneous transmission and reception constraints, i.e. it cannot simultaneously receive in one link and transmit in a different link due to intra-device inter-channel interference,

[0126] The serving gNB is aware of this simultaneous transmission and reception constraint, and

[0127] Figure 3 "Device A" in is the gNB, while Figure 3 "Device B" in is the UE.

[0128] For ease of description, in the following we will focus on the differences and complements of this embodiment with the previous one.

[0129] Step S1 : After identifying the traffic requirements of the concerned UEs, the gNB suggests the enhanced / virtual reality UE to enable the continuous multi-link operation mode and the gNB itself is always both the "initiator" and "follower" device.

[0130] Step S2: The enhanced / virtual reality UE replies to the AP to indicate that it agrees to operate in the continuous multi-link operation mode.

[0131] Step S3: According to the agreement, the gNB will play both the "initiating" and "following" device roles in the first COT.

[0132] Step S4: After contending for channel access with LBT in all four links, the gNB acquires the COT and initiates a downlink transmission to the best effort UE in link 1, which is now labeled as "link P". As a "following" device, the gNB initializes the COT timer to t = 0.

[0133] Figure 4 It is shown how transmissions to / from multi-link capable UEs with strict delay / reliability / throughput requirements can be scheduled at the beginning of the COT and / or after the COT start time of link P, as these UEs would benefit from the possibility to replicate / aggregate data in different links. This also provides a time for single-link capable UEs to switch from link A to link B based on the signaling received in the COT on link A. This mechanism can be based on standard signaling to support BWP (Bandwidth Part) switching in 5G NR, or alternative methods.

[0134] In other embodiments, the gNB can decide to stop the COT acquired in link P immediately after acquiring the COT in link S.

[0135] Step S5: Since the gNB is considered as a "following" device, it checks if the following holds:

[0136] t > (COT P-S start time - LBT S period length) for all S ≠ P

[0137] (Eq. 1) where for links S = 2, S = 3 and S = 4, the above operation is performed independently.

[0138] For ease of illustration, assume that (COT P-S start time - LBT S period length) = 3 ms for all links, and COT P-S start time = 5 ms. Thus, as soon as t = 3 ms, the gNB enters step S6.

[0139] Step S6: The gNB starts LBT in links S = {2, 3, 4} at t = 3 ms.

[0140] Step S7: When the LBT backoff counter in links S = {2, 3, 4} reaches 0, the gNB checks whether the following is true

[0141] t > = COT P-S Start time

[0142] (Eq. 2)

[0143] For the sake of illustration, and since this is a random process, it is assumed that the LBT counter of the gNB for links S = {2, 3, 4} reaches 0 at t = 5 ms.

[0144] Step S8: When t = 5 ms, the gNB makes sure that links S = {2, 3, 4} are still considered free. The gNB randomly decides to initiate transmission in link S = 2, and to stop LBT in the other links. In this regard, since the gNB can initiate COT in multiple links, the gNB can select the location to initiate COT based on, for example, random selection or pre-defined channel selection metrics.

[0145] Step S8.1. (not shown): Before the end of the COT, the AP performs uplink and downlink transmissions in link S = 2 to / from enhanced / virtual reality UEs.

[0146] If the scheduled UEs perform the requested uplink transmission(s), go to step S9.

[0147] If the scheduled UEs do not perform the requested uplink transmission (e.g. due to the presence of a hidden device), the gNB can determine that link S = 2 is not suitable, and, if there is enough time until the end of the COT in at least link P, and taking into account the carrier sensing status in the other links, e.g. whether they are available or will be available, it will

[0148] Consider link S = 2 as unavailable, and remove it from the list of candidate links, and

[0149] Re-perform step S8. In this case, the gNB decides to initiate transmission in link S = 3.

[0150] Step S9: Link S = 3 is now marked as link P.

[0151] Step S10: The gNB goes back to step 4.

[0152] Figure 5 And Figure 6 It is schematically shown how to determine the predetermined time COT P-S Start time, and how to determine the estimated length needed for LBT scanning to set the second predetermined time for the start of channel scanning.

[0153] When switching between links, COT P-S The parameter will determine the overlap of COTs. Figure 5 Different facts that affect it are shown, and how they increase or decrease the overlap of COTs.

[0154] In a preferred embodiment, a device implementing the proposed method will adjust this parameter to take into account:

[0155] Downlink / Uplink buffer size (i.e. traffic load) - constraints are set in the minimum COT overlap to provide a given throughput;

[0156] The specific value of the COT overlap needed to deliver a given amount of data can be easily calculated based on the total transmission / reception time on all active links;

[0157] The previous success rate of guaranteeing consecutive COTs when transitioning from link S to any other link - for example, a smaller COT start time can result in a smaller success rate of guaranteeing consecutive COTs, as COTs in different links will finish at similar times and the likelihood of having at least one COT immediately after is smaller. In some embodiments, various predefined COT start times can be used and tested before picking the one that maximizes or at least improves the success rate mentioned above;

[0158] The time needed to detect link selection problems and implement a fast reselection (see additional step 8.1 in the second embodiment) - for example, some embodiments can perform uplink and downlink transmissions at the start of a partially overlapping COT to determine if there are any problems with the initial link selection attempt and a new link should be selected.

[0159] Figure 6 How to determine the parameter LBT S The value of the period length to provide the desired probability that a scanned channel will be available at the desired COT start time. While the value of the LBT parameter varies from embodiment and depends on the specific link or channel considered, it should be noted that its value will depend on the channel load and occupancy. In general, a device can generate a conservative bound based on, for example, previous channel access statistics, and use it at the most appropriate point in time to start the LBT (taking into account the current backoff counter value) to achieve the desired COT start time.

[0160] In some embodiments, a device implementing the proposed method will determine the LBT Sa value of the listen time length. For example, as shown in Figure 10, the device can select a value that guarantees, with a given probability (0.999 in the figure), that the LBT succeeds within the listening time period (2ms).

[0161] In other embodiments, a device implementing the proposed method will determine the LBT value for all links in which the device operates based on joint statistical information of the LBT durations on the multiple links. For example, if the device can perform LBT in 3 links at the same time, the device can select a value that provides that the LBT in at least one link will succeed with a given probability in the listening time period.

[0162] In summary, embodiments provide a node that establishes an agreement among nodes that specifies which node(s) should attempt to initiate a COT at a given time.

[0163] Embodiments define and regulate a link-dependent "COT start time" so that the start of COTs in different links are not too close to each other.

[0164] Embodiments provide that a new COT can only start after a certain time period after the start of the current COT, which is regulated to increase the chances that at least one COT is available at any time.

[0165] Embodiments control the "LBT start time" per link by considering the expected "LBT time length" and "COT start time".

[0166] Embodiments control the "LBT time length" as a function of the channel load and occupancy. The LBT time length can be estimated, and LBT is started at the most appropriate point in time to achieve the desired COT start time.

[0167] Both end-user devices and infrastructure network components can implement components of the invention.

[0168] Figure 7 An apparatus according to one embodiment is shown. The apparatus is a network node 10 configured to transmit and receive signals 21 on multiple channels within an unlicensed spectrum, and can be, for example, an access point, user equipment, gNB, or station. The node 10 includes transmission circuitry 30 and reception circuitry 32 configured to transmit and receive signals on the multiple channels of the unlicensed spectrum through an antenna 20. The node 10 includes scanning circuitry 40 configured to scan the multiple channels in the unlicensed spectrum using a listen-before-talk procedure to determine whether they are available. In other embodiments, other scanning circuitry can be used that uses other scanning procedures, such as clear channel assessment.

[0169] The node 10 comprises control circuitry configured to control the transmission, reception and scanning circuitry to perform the methods shown in Figure 3 as described above, where the node communicates with another node using a different channel within the unlicensed spectrum. The node can acquire the first channel itself, or can receive a signal from another node on a first channel acquired by that node, at which point it can scan for an available other channel in the unlicensed spectrum, and then acquire that other channel before the expiry of the COT period for the first channel, so that communication between the nodes can continue without an interval.

[0170] It will be readily apparent to those skilled in the art that steps of various above-described methods can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, e.g., digital data stores, tangible machine-readable or computer- readable storage media such as digital memories, magnetic or optical storage media such as magnetic disks and magneto-optical disks, hard drive and enterprise storage, or compact discs readable by a computer. The program storage devices are non-transitory in the sense that they do not rely on propagation of signals through space or through a medium such as waves deposited on a physical medium or a computer network. The program storage devices are readable by a machine for executing or for further processing the instructions to perform the methods.

[0171] Although embodiments of the application have been described in the preceding paragraphs in the context of various examples, it should be noted that modifications to those examples could be made by a person skilled in the art without departing from the scope of the application as defined by the appended claims.

[0172] Features described in the preceding description can be used in combinations other than the combinations explicitly provided.

[0173] Although functions have been described with reference to certain features, those functions can be performed by other features whether or not the other features are described.

[0174] Although features have been described with reference to certain embodiments, those features can also be present in other embodiments whether or not the other embodiments are described.

[0175] Although efforts have been made to accurately describe the features of the application, it will be understood that the application is capable of modification without departing from the spirit of the application as set out in the appended claims.

Claims

1. A method for communication performed at a device, the method comprising: The device determines that a channel in the unlicensed spectrum has been acquired by the device or by another device for a predetermined period of time, and the channel is one of a plurality of channels in the unlicensed spectrum; While the acquired channel is being used for communication between the device and the other device, a scan of at least one additional channel within the unlicensed spectrum is initiated to determine whether the at least one additional channel is available; Determine whether a predetermined time has elapsed since the channel was acquired, wherein the predetermined time is less than or equal to the predetermined occupancy time; as well as After the scan indicates that at least one of the at least one additional channel is available, and when the predetermined time is determined to have elapsed, the acquisition of one of the available channels among the at least one additional channel is initiated within the predetermined occupancy time.

2. The method according to claim 1, wherein the method comprises: Before initiating the scan, it is determined whether a second predetermined time period has elapsed since the channel was acquired, and when the second predetermined time period is determined to have elapsed, the scan is initiated, wherein the second predetermined time period is shorter than the predetermined time period.

3. The method of claim 2, wherein the value of the second predetermined time period is specific to a particular channel.

4. The method according to claim 3, wherein the method comprises: The second predetermined time for the at least one additional channel to be scanned is determined based on at least one of the following: The determined channel load and channel occupancy of the at least one additional channel; as well as The stored historical data indicates the delay between the start of the scan and the determination that the at least one additional channel is available.

5. The method of claim 1, wherein the predetermined time is selected based on the expected overlap of the occupancy times.

6. The method of claim 1, wherein the apparatus performs at least one of the following initial steps: Initiating a transmission to the other device regarding an instruction that multichannel communication will be performed between the device and the other device within the unlicensed spectrum; and Receive from the other device an instruction that multichannel communication will be performed between the device and the other device in the unlicensed spectrum.

7. The method according to claim 1, wherein The determination at the device that a channel in the unlicensed spectrum has been acquired by the device or by the other device includes: The method for acquiring the channel further includes: During the period of multi-channel communication between the device and the other device, the process of initiating the channel scan and acquiring an available channel is repeated multiple times within a predetermined time period.

8. The method according to claim 7, further comprising: When acquiring one of the available channels, an uplink transmission is requested from the other device; as well as If the uplink transmission is not received within the set time, then: Select another channel from the available channels, and acquire the other channel from the available channels within a predetermined time period; as well as Mark one of the available channels as unavailable.

9. The method of claim 8, wherein the predetermined time is selected to provide a set overlapping period for the occupancy time, and the step of selecting and obtaining the other channel among the available channels is performed within the set overlapping period.

10. The method of claim 1, wherein The step of determining at the device that a channel in the unlicensed spectrum has been acquired by the device or by the other device within a predetermined occupancy time includes: Receive from the other device a signal indicating that the other device has acquired the channel.

11. The method of claim 10, wherein the method comprises: After acquiring the available channel, an indication is transmitted to the other device that the available channel has been acquired within a predetermined time. as well as The other device receives a signal indicating that it has acquired another channel of the plurality of channels in the unlicensed spectrum before the predetermined occupancy time when the available channel is acquired, or when the predetermined occupancy time expires.

12. The method according to any preceding claim, comprising: Perform further checks on the availability of the channels immediately before initiating the acquisition of the channels.

13. A computer program product comprising computer-readable instructions, which, when executed by a processor on a device, are configured to cause the device to perform the method according to any of the preceding claims.

14. An apparatus for communication, comprising components configured to perform the following operations: It is determined that a channel in the unlicensed spectrum has been acquired by the device or by another device within a predetermined occupancy time, and the channel is one of a plurality of channels in the unlicensed spectrum; While the acquired channel is being used for communication between the device and the other device, a scan of at least one additional channel within the unlicensed spectrum is initiated to determine whether the at least one additional channel is available; Determine whether a predetermined time has elapsed since the channel was acquired, wherein the predetermined time is less than or equal to the predetermined occupancy time; as well as After the scan indicates that at least one of the at least one additional channel is available, and when the predetermined time is determined to have elapsed, the acquisition of one of the available channels among the at least one additional channel is initiated within the predetermined occupancy time.

15. The apparatus of claim 14, wherein the component is configured to determine, before initiating the scan, whether a second predetermined time period has elapsed since the channel was acquired, the second predetermined time period being less than the predetermined time period.

16. The apparatus of claim 15, wherein the second predetermined time period is specific to a particular channel.

17. The apparatus of claim 16, wherein the component is configured to determine the second predetermined time period according to at least one of the following: The determined channel load and channel occupancy of the at least one additional channel; and The stored historical data is the time delay between the start of a scan on the at least one additional channel and the determination that the at least one additional channel is available.

18. The apparatus of claim 14, wherein the predetermined time is selected based on the expected overlap of the occupancy times.

19. The apparatus of claim 14, wherein the component is configured to perform at least one of the following initial steps: Initiating a transmission to the other device regarding an instruction that multichannel communication will be performed between the device and the other device within the unlicensed spectrum; and Receive from the other device an instruction that multichannel communication will be performed between the device and the other device in the unlicensed spectrum.

20. The apparatus of claim 19, wherein the component is configured to: When acquiring one of the available channels, a transmission of a signal is initiated to request uplink transmission from the other device; as well as If the uplink transmission is not received within the set time, then: Select another channel from the available channels and initiate a transmission to acquire the other channel from the available channels within a predetermined time period; as well as Mark one of the available channels as unavailable.

21. The apparatus of claim 20, wherein the predetermined time is selected to provide an overlap period for the occupancy time, and the component is configured to control the selection and acquisition of the other channel among the available channels within the overlap period.

22. The apparatus of claim 14, wherein the component comprises: At least one processor; as well as At least one memory, including computer program code, the at least one memory and the computer program code being configured together with the at least one processor to cause the apparatus to perform the method according to any one of claims 1-12.

23. The apparatus according to any one of claims 14 to 22, the apparatus further comprising components for transmitting and receiving signals, and components for scanning channels in the unlicensed spectrum.

24. An apparatus for communication, comprising a control circuit system configured to: It is determined that a channel in the unlicensed spectrum has been acquired by the device or by another device within a predetermined occupancy time, and the channel is one of a plurality of channels in the unlicensed spectrum; While the acquired channel is being used for communication between the device and the other device, a scan of at least one additional channel within the unlicensed spectrum is initiated to determine whether the at least one additional channel is available; Determine whether a predetermined time has elapsed since the channel was acquired, wherein the predetermined time is less than or equal to the predetermined occupancy time; as well as After the scan indicates that at least one of the at least one additional channel is available, and when the predetermined time is determined to have elapsed, the acquisition of one of the available channels among the at least one additional channel is initiated within the predetermined occupancy time.

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