WO2017128045A1

WO2017128045A1 - Method and apparatus for data transmission

Info

Publication number: WO2017128045A1
Application number: PCT/CN2016/072195
Authority: WO
Inventors: Ming Li; Yanqiang LI; Jinhua Liu
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2016-01-26
Filing date: 2016-01-26
Publication date: 2017-08-03

Abstract

Embodiments of the present disclosure provide a method (500) for data transmission at a communications device operable in an unlicensed spectrum. The communications device comprises a digital unit and a radio unit. The method (500) comprises selecting (510), at the radio unit, at least one unlicensed carrier from a set of candidate carriers in the unlicensed spectrum for channel sensing, in response to a data transmission request from the digital unit and performing (520) channel sensing on the at least one unlicensed cartier according to predetermined timing for data transmission. The method (500) further comprises transmitting (530) a data block prepared at the digital unit on a selected unlicensed carrier which is determined to be available by the channel sensing. There is also provided a corresponding communications device and a corresponding radio unit.

Description

METHOD AND APPARATUS FOR DATA TRANSMISSION

TECHNICAL FIELD

The non-limiting and exemplary embodiments of the present disclosure generally relate to the field of wireless communications， and specifically to a method and an apparatus for data transmission at a communications device operable in an unlicensed spectrum.

BACKGROUND

This section introduces aspects that may facilitate better understanding of the present disclosure. Accordingly， the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.

he fast uptake of the Third Generation Partnership Project (3GPP) -Long Term Evolution (LTE) in various regions of the world shows both that demand for wireless broadband data is increasing， and that LTE is a successful platform to meet that demand. The existing and new spectrum licensed for exclusive use by International Mobile Telecommunications (IMT) technologies will remain fundamental for providing seamless coverage， achieving the higher spectral efficiency， and ensuring the higher reliability of cellular networks through careful planning and deployment of high-quality network equipment and devices.

In order to meet the ever increasing data traffic demand from users， particularly in concentrated high traffic buildings or hot spots， more mobile broadband bandwidth will be needed. Given a large amount of spectrum available in unlicensed bands around the globe， the unlicensed spectrum is more and more considered by cellular operators as complementary means to augment their service provisioning. While the unlicensed spectrum may not match qualities of the licensed regime， solutions that allow efficient use of it as a complement to licensed deployments have a potential to bring a great value to 3GPP operators， and ultimately to the 3GPP industry as a whole. This type of solutions would enable operators and vendors to leverage the existing or planned investments in LTE/Evolved Package Core (EPC) hardware in radio and core networks.

It has been agreed to study Licensed-Assisted Access (LAA) technologies in the 3GPP at RP-141664. This LAA framework builds on carrier aggregation (CA) solutions introduced in LTE Release-10 to access the additional bandwidth in the unlicensed spectrum. FIG. 1 shows an illustrative LTE network that configures a user equipment (UE) to aggregate additional secondary cells (SCells) which are using frequency carriers in the unlicensed spectrum. A primary cell (PCell) maintains exchange of essential control messages and also offers an always-available robust spectrum， i.e. the licensed spectrum， for real-time and high-value traffic. Via the high-quality and robust licensed spectrum， the PCell may also provide mobility handling and management for the UE. The aggregated SCells in the unlicensed spectrum， when available， can be utilized as a bandwidth booster to serve， e.g. the best effort traffic. The LAA SCells may operate in a downlink (DL) -only mode or operate with both uplink (UL) and DL traffic.

Since there are a plenty of unlicensed carriers below 6GHz， LAA has become an important feature for LTE evolution. In 3GPP， further enhancement for CA is standardized to support 32 Component Carriers (CCs) . As low frequency resources become scarce with the mobile wireless network development， it becomes more important to develop a method to improve resource utilization efficiency and harmonious coexistence of multiple radio systems. Meanwhile， since different wireless communication systems compete for the same set of unlicensed carriers， each one has to try its best to seize up a channel as quickly as possible without violating channel access rules.

There are two specific channel management functions adopted in a communications device， like a base station operable in an LAA system， for co-existing with Wi-Fi or other LAA systems.

The first channel management function refers to candidate cartier selection performed at a digital unit (DU) that is used for baseband signal processing. As there is a large available bandwidth in the unlicensed spectrum， it may not be possible to perform channel sensing for all channels due to a hardware restriction， since there could be a very large delay if all CCs in the unlicensed spectrum are sensed each time. Therefore， one or more candidate CCs may be selected by the DU based on a report from a radio unit (RU) and the channel sensing will be performed for the selected one or more CCs only.

The second channel management function refers to clear channel sensing (which may be implemented via Listen-before-Talk (LBT) ) performed by a RU that is used for radio frequency (RF) and digital signal processing. Channel sensing via the LBT will lead to fair sharing of the unlicensed spectrum. Hence， it is considered to be a vital feature for a fair and friendly operation with co-existence of multiple systems in the same set of shared unlicensed carriers. The LBT is defined as a mechanism by which equipment applies a clear channel assessment (CCA) check before using a candidate unlicensed carrier. The CCA is usually performed according to a configuration from the DU. The CCA utilizes at least energy detection to determine presence or absence of a signal on a channel so as to determine whether the channel is occupied or free. The LBT is mandatory for Wi-Fi access and LAA access currently.

For easy understanding of the present disclosure， a procedure for data transmission carried out between a DU and a RU in a communications device operable in the unlicensed spectrum is sketched as follows： when there is data ready for transmission at the DU， the DU will send a data transmission request to the RU to initiate LBT over a selected channel. Then the RU performs CCA for the selected channel and then reports a CCA result to the DU. Subsequently， the DU may decide availability of the channel based on the report. If the channel is available， the DU may transmit a reservation signal to the RU to reserve the channel for data transmission.

FIG. 2 shows a diagram illustrating channel management allocation between a RU and a DU. As shown， the candidate channel selection is performed in the DU by a pre-scheduler， while the channel sensing is performed in the RU. The channel scheduling which carries channel selection information and a reservation signal are instructed from the DU to the RU.

SUMMARY

Various embodiments of the present disclosure mainly aim at providing a solution for fast grasping an unlicensed channel without violating channel access rules for LAA systems or any radio system involving competition for a shared unlicensed spectrum and possibly requiring a substantive synchronization. Other features and advantages of embodiments of the present disclosure will also be understood from the following description of specific embodiments when read in conjunction with the accompanying drawings， which illustrate the principles of embodiments of the present disclosure.

In a first aspect of the present disclosure， there is provided a method for data transmission. The method is performed at a communications device operable at least in an unlicensed spectrum. The communications device may also be operable in a licensed spectrum， for example in an LAA system. The communications device comprising a digital unit and a radio unit. The method comprises selecting at least one unlicensed carrier from a set of candidate carriers in the unlicensed spectrum for channel sensing， in response to a data transmission request from the digital unit and then performing channel sensing on the at least one unlicensed carrier according to predetermined timing for data transmission. For example， the predetermined timing may be defined by an LTE frame structure. The method further comprises transmitting a data block prepared at the digital unit on a selected unlicensed carrier which is determined to be available by the channel sensing.

By means of this method， the communications device may have a higher autonomy and flexibility to perform channel sensing at the radio unit side. Thus， the possibility to grasp an unlicensed carrier may be enhanced even though with a limitation of the predetermined timing.

In an embodiment， the set of candidate carriers may be configured by the digital unit to the radio unit. In this embodiment， the set of candidate carriers may comprise a preferred unlicensed carrier selected by the digital unit and thus the preferred unlicensed carrier may be first selected from the set of candidate carriers when information regarding the preferred unlicensed carrier is notified from the digital unit. Preferably， the preferred unlicensed carrier may be an unlicensed carrier for which the data block is prepared at the digital unit.

In another embodiment， if the selected unlicensed carrier which is determined to be available is different from the unlicensed carrier for which the data block was prepared at the digital unit， the method may further comprise reserving a channel on the selected unlicensed carrier which is determined to be available by the channel sensing and notifying the digital unit of information regarding the reserved channel. Also， the data block prepared at the digital unit for the reserved channel is received from the digital unit at the radio unit. In this way， the channel can be more timely grasped even though the digital unit needs to be notified and then prepares the data block again for the reserved channel.

In yet another embodiment， the data block may be prepared at the digital unit according to a worst channel quality for the set of candidate carriers and a specific transmission mode so that the prepared data block can be transmitted on any of the set of candidate carriers with a target block error rate less than a predetermined threshold. In such an embodiment， the prepared data block may be transmitted on the selected unlicensed carrier which is determined to be available without further processing by the digital unit on the prepared data block. The method may further comprise notifying the digital unit of the selected unlicensed carrier which is determined to be available. In this way， the data may be fast transmitted without any delay caused by signalling transmission between the radio and digital units or by further processing of the digital unit on the data to be transmitted.

In yet another embodiment， the set of candidate carriers may be determined based on at least one of the following： historical measurement results， measurement reports from other communications devices communicating with said communications device， capabilities of the other communications devices， configured carriers for the other communications devices and quality of service requirements.

In yet another embodiment， each of the set of candidate carriers may have a corresponding priority. In such an embodiment， the at least one unlicensed carrier may be selected from the set of candidate carriers according to the corresponding priorities. The method may further comprise maintaining the set of candidate carriers at the radio unit.

In a second aspect of the present disclosure， there is provided a communications device that is operable at least in an unlicensed spectrum. The communications device may also be operable in a licensed spectrum， for example in an LAA system. The communications device may be embodied as a base station to perform data transmission towards a terminal device or embodied as a terminal device to perform data transmission towards a base station.

Particularly， the communications device comprises a digital unit and a radio unit. The digital unit is configured to prepare a data block for transmission and send a data transmission request to the radio unit. The radio unit is configured to select at least one unlicensed carrier from a set of candidate carriers in the unlicensed spectrum for channel sensing， in response to the data transmission request from the digital unit. The radio unit is further configured to perform channel sensing on the at least one unlicensed carrier according to predetermined timing for data transmission， for example， which may be defined according to an LET frame structure， and to transmit the data block prepared at the digital unit on an selected unlicensed carrier which is determined to be available by the channel sensing.

In an embodiment， if the selected unlicensed carrier which is determined to be available is different from the unlicensed carrier for which the data block was prepared at the digital unit， the radio unit may be further configured to reserve a channel on the selected unlicensed carrier which is determined to be available by the channel sensing， to notify the digital unit of information regarding the reserved channel， and to receive the data block prepared at the digital unit for the reserved channel. Correspondingly， the digit unit may be further configured to prepare the data block for the reserved channel.

In another embodiment， the digital unit may be further configured to prepare the data block according to a worst channel quality for the set of candidate carriers and a specific transmission mode so that the prepared data block can be transmitted on any of the set of candidate carriers with a target block error rate less than a predetermined threshold.

In a further embodiment， the radio unit may be further configured to enable the data block to be transmitted on the selected unlicensed carrier which is determined to be available without further processing by the digital unit on the data block and to notify the digital unit of the selected unlicensed carrier which is determined to be available.

In a third aspect of the present disclosure， there is provided a radio unit. The radio unit may be embodied as the radio unit of the communications device of the second aspect that is operable at least in an unlicensed spectrum and also comprises a digital unit. The communications device may also be operable in a licensed spectrum， for example in an LAA system.

Particularly， the radio unit comprises a selecting module， a channel sensing module and a transmitting module. The selecting module is configured to select at least one unlicensed carrier from a set of candidate carriers in the unlicensed spectrum for channel sensing， in response to a data transmission request from the digital unit. The channel sensing module is configured to perform channel sensing on the at least one unlicensed carrier according to predetermined timing for data transmission， for example， which may be defined according to an LET frame structure. The transmitting module is configured to transmit a data block prepared at the digital unit on a selected unlicensed carrier which is determined to be available by the channel sensing.

In an embodiment， if the selected unlicensed carrier which is determined to be available is different from the unlicensed carrier for which the data block was prepared at the digital unit， the radio unit may further comprise a reserving module， a notifying module and a receiving module. The reserving module is configured to reserve a channel on the selected unlicensed carrier which is determined to be available by the channel sensing. The notifying module is configured to notify the digital unit of information regarding the reserved channel. The receiving module is configured to receive the data block prepared at the digital unit for the reserved channel.

In another embodiment， the data block may be prepared at the digital unit according to a worst channel quality for the set of candidate carriers and a specific transmission mode so that the prepared data block can be transmitted on any of the set of candidate carriers with a target block error rate less than a predetermined threshold.

In a further embodiment， the transmitting module may be further configured to enable the prepared data block to be transmitted on the selected unlicensed carrier which is determined to be available without further processing by the digital unit on the prepared data block. In this embodiment， the radio unit may further comprise a notifying module that is configured to notify the digital unit of the selected unlicensed carrier which is determined to be available.

In a fourth aspect of the present disclosure， there is provided an apparatus for data transmission at a communications device operable at least in an unlicensed spectrum. The apparatus comprises a processor and a memory. The memory contains instructions executable by the processor， whereby the apparatus is operative to perform the method according to the first aspect of the present disclosure.

In a fifth aspect of the present disclosure， there is provided an apparatus for data transmission at a communications device operable at least in an unlicensed spectrum. The apparatus comprises processing means that is adapted to perform the method according to the first aspect of the present disclosure.

It shall be appreciated that various embodiments of the first aspect may be applied to the second， third， fourth and fifth aspect of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects， features， and benefits of various embodiments of the present disclosure will become more fully apparent， by way of example， from the following detailed description with reference to the accompanying drawings， in which：

FIG. 1 shows an illustrative LTE network that can configure a UE to aggregate additional secondary cells which are using frequency carriers in the unlicensed spectrum；

FIG. 2 shows a diagram illustrating channel management allocation between a RU and a DU；

FIG. 3 illustrates a delay problem of the existing solution with an exemplary circuitry；

FIG. 4 shows an LTE radio frame structure；

FIG. 5 illustrates a flowchart of a method for data transmission according to embodiments of the present disclosure；

FIG. 6 illustrates an example of channel management allocation between a RU and a DU of a communications device according to an embodiment of the present disclosure；

FIG. 7 shows a comparison between a practical example of data transmission using the existing LBT solution and a practical example of data transmission using the method of FIG. 5；

FIG. 8 illustrates a schematic block diagram of a communications device according to embodiments of the present disclosure；

FIG. 9 illustrates a schematic block diagram of a radio unit according to embodiments of the present disclosure；

FIG. 10 illustrates a schematic block diagram of an apparatus according to embodiments of the present disclosure.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

Hereinafter， the principle and spirit of the present disclosure will be described with reference to illustrative embodiments. It should be understood， all these embodiments are given merely for one skilled in the art to better understand and further practice the present disclosure， but not for limiting the scope of the present disclosure. For example， features illustrated or described as part of one embodiment may be used with another embodiment to yield still a further embodiment. In the interest of clarity， not all features of an actual implementation are described in this specification.

References in the specification to “one embodiment， ” “an embodiment， ” “another embodiment， ” etc. indicate that the embodiment described may include a particular feature， structure， or characteristic， but every embodiment may not necessarily include the particular feature， structure， or characteristic. Moreover， such phrases are not necessarily referring to the same embodiment. Further， when a particular feature， structure， or characteristic is described in connection with an embodiment， it is submitted that it is within the knowledge of one skilled in the art to affect such a feature， structure， or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that， although the terms “first” and “second” etc. may be used herein to describe various elements， these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example， a first element could be termed a second element， and similarly， a second element could be termed a first element， without departing from the scope of example embodiments. As used herein， the term “and/or” includes any and all combinations of one or more of the associated listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the embodiments. As used herein， the singular forms “a” ， “an” and “the” are intended to include the plural forms as well， unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” ， “comprising” ， “has” ， “having” ， “includes” and/or “including” ， when used herein， specify the presence of stated features， elements， and/or components etc.， but do not preclude the presence or addition of one or more other features， elements， components and/or combinations thereof.

In the following description and claims， unless defined otherwise， all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs. For example， the term “base station” (BS) ， used herein may also be referred to as e.g. eNB， eNodeB， NodeB or base transceiver station (BTS) ， Access Node (AN) or Access Point (AP) etc. depending on the technology and terminology used. The term “communications device” may refer to either a base station or a terminal device， which can establish wireless communications at least in the unlicensed spectrum. The term “terminal device” used herein may refer to any terminal or UE having wireless communication capabilities at least in the unlicensed spectrum， including but not limited to， mobile phones， cellular phones， smart phones， or personal digital assistants (PDAs) ， portable computers， image capture devices such as digital cameras， gaming devices， music storage and playback appliances and any portable units or terminals that have wireless communications capabilities， or Internet appliances permitting wireless Internet access and browsing and the like.

In the Background Section， an existing solution for channel management is introduced as being performed cooperatively between a DU and a RU in a communications device， such as a base station. However， there may be some problems with the existing solution. For example， FIG. 3 illustrates a delay problem of the existing solution with an exemplary circuitry.

As illustrated， on a failure of the channel sensing (e.g. by LBT) for a candidate channel selected by the DU， the RU reports the failure to the DU and waits for a new candidate channel indication from the DU. After the new candidate channel indication is received， the RU may start channel sensing for the new candidate channel as indicated. Due to reporting of the LBT failure and receiving the new candidate channel indication， a considerable delay may be caused before performing the channel sensing for the new candidate channel. A signaling transmission and processing delay may also be quite considerable between the RU and the DU. In the case that there is a large distance between the RU and the DU， the delay could be even larger.

As a consequence， such a delay may result in a lower probability to grasp a channel in a system， like an LAA system， where the channel sensing or LBT needs to be performed according to a predetermined timing， e.g. defined by an LTE radio frame structure， which provides a longer gap between two sensing opportunities as compared with Wi-Fi systems.

FIG. 4 shows an example LTE radio frame structure. As shown， the LTE radio frame has 10 LTE subframes， while each subframe may have 14 symbols. According to the current specification， the first three symbols in each subframe may be used for channel sensing， after which data transmission may be performed. Based on this frame structure， the channel sensing opportunities for a communications device operable in the LAA system may be limited compared to normal Wi-Fi systems. Even though it is not in the LAA system， the channel sensing may still need to follow a predetermined timing so as to facilitate such operations as cell selection or switching which have to be implemented based on substantively synchronization in some cellular systems operable in the unlicensed spectrum (which may be referred to as LAA-like systems so as to differentiate from normal Wi-Fi systems) . Therefore， when competing for the unlicensed spectrum against other co-existing systems that also utilize the unlicensed spectrum， like Wi-Fi systems， the LAA or LAA-like systems may be in an inferior position.

Accordingly， a solution for fast grasping an unlicensed channel without violating the channel access rules is very important for LAA and LAA-like systems， particularly when there is a high traffic load over the unlicensed spectrum.

Hereafter， various embodiments of the present disclosure provide an efficient solution applicable to radio systems involving the unlicensed spectrum competition. For the illustrative purpose only， several embodiments of the present disclosure will be described in the LAA scenario. Those skilled in the art will appreciate， however， that several embodiments of the present disclosure may be more generally applicable to other scenarios in which data transmission can be performed over the unlicensed spectrum and a predetermined timing is followed for data transmission so as to ensure substantive system synchronization.

FIG. 5 illustrates a flowchart of a method 500 for data transmission according to embodiments of the present disclosure. The method 500 is performed at a communications device， e.g. a base station or a terminal device， which is operable at least in an unlicensed spectrum. The communications device may also be operable in a licensed spectrum， for example in an LAA system. The communications device comprises a digital unit for baseband signal processing and a radio unit for RF and digital processing. Hereafter， for easy description and understanding of this method， the communications device performing the method 500 may be referred to as a base station， while another communications device communicating with that communications device may be referred to as a UE. However， those skilled in the art shall understand that the method 500 can also be performed at a UE to implement data transmission to a base station.

As illustrated， the method 500 enters at block 510， in which the radio unit of the base station selects at least one unlicensed carrier from a set of candidate carriers in the unlicensed spectrum for channel sensing， in response to a data transmission request from the digital unit. Then， the radio unit performs， at block 520， channel sensing on the at least one unlicensed carrier according to predetermined timing for data transmission. For example， in an LAA-LTE system， the predetermined timing may be the timing defined according to the frame structure as shown in FIG. 4. When there is more than one unlicensed carrier selected for channel sensing， the channel sensing may be performed sequentially or in parallel among the selected unlicensed carriers.

It shall be appreciated that， in practical implementations， the selecting step at block 510 may not be explicitly separated from the channel sensing step at block 520 and rather be implicitly included in the channel sensing step. For example， sometimes， it seems that the radio unit performs the channel sensing directly for a certain unlicensed carrier， in response to the data transmission request. Actually， in order to implement the channel sensing operation， the certain unlicensed carrier must have been selected. In particular， the certain unlicensed carrier may be selected via frequency hopping (FH) from the set of candidate carriers. In various embodiments， the unlicensed carrier may be selected randomly or according to priorities of respective candidate carriers.

In an embodiment that each of the set of unlicensed carriers has a corresponding priority， which for example may be assigned based on the channel sensing results or measurement reports from UEs， all candidate carriers may be listed according to their respective priorities so that the RU can select initially at least one candidate carrier with a higher priority for channel sensing or can finally choose a best unlicensed carrier， if more than one carrier is determined to be available by the channel sensing， for data transmission.

In some embodiments， the set of candidate carriers may be configured by the digital unit to the radio unit， for example when the communications device is turned on or by being notified with the data transmission request.

In these embodiments， the set of unlicensed carriers may be determined at the digital unit based on historical measurement results， e.g. previous channel sensing results of the base station or measurement reports from other communications devices communicating with said communications device， e.g. Channel Quality Indication (CQI) reported from UEs. For example， the carriers on which the channels have lower interference plus noise may be included in the set of candidate carriers.

Alternatively or additionally， the set of candidate carriers may be determined based on QoS requirements. For example， a size of the set of candidate carriers may be smaller for a lower rate non-delay sensitive service compared to a higher rate delay sensitive service.

In addition， since different communications devices may support a different number of unlicensed carriers or different unlicensed carriers， the set of candidate carriers may be determined based on capabilities of the other communications devices， e.g. UEs. Furthermore， since different communications device may be configured with a different number of unlicensed carriers or different unlicensed carriers， the set of candidate carriers may also be determined based on the configured carriers of the other communications devices， e.g. UEs. In these cases， the set of candidate carriers may be UE specific or user specific.

Alternatively， when the channel sensing results of the base station is used to determine the set of candidate carriers， the set may be specific to a cell. Likewise， if the measurement report of a UE is used to determine the set of candidate carriers， the set may be specific to the UE.

In some further or alternative embodiments， the set of candidate carriers may also be maintained (e.g. adjusted or updated) dynamically at the radio unit based on at least one of the following： historical measurement results， measurement reports from other communications devices (e.g. UEs) communicating with said communications device (e.g. base station) ， capabilities of the other communications devices， configured carriers for the other communications devices and QoS requirements. For example， according to the measurement reports from the UEs， the priorities of candidate carriers may be adjusted and accordingly the order of the candidate carriers in the set may also be adjusted. For another example， the number of candidate carriers may be adjusted according to the number of unlicensed carriers configured for the communicating UE.

In an extreme case， the set of candidate carriers may cover a full bandwidth of the unlicensed spectrum.

In some embodiments， the digital unit may select or appoint a preferred unlicensed carrier for a data block to be transmitted and notify the radio unit of the preferred unlicensed carrier. In the above embodiment where each candidate carrier has a corresponding priority， the preferred candidate carrier of the digital unit may be listed at the first position in the candidate carrier set and all carriers are listed in the set according to corresponding priorities in a descending order. By this way， the preferred unlicensed carrier does not need to be notified in a separate message from the digital unit to the radio unit.

In these embodiments that the preferred unlicensed carrier is known by the radio unit， the set of candidate carriers may comprise the preferred unlicensed cartier. When the radio unit selects the at least one unlicensed carrier from the set of candidate carriers at block 510， it may select the preferred unlicensed carrier first to do channel sensing thereon. Particularly， the preferred unlicensed cartier may be an unlicensed carrier for which the data block was prepared at the digital unit. The term “prepared” used herein may comprise being “coded” and “modulated” according to a certain Modulation and Coding Scheme (MCS) and additionally may comprise being “pre-coded” according to a certain precoding vector.

Once there is a selected unlicensed carrier that is determined to be available by the channel sensing， the radio unit can transmit， at block 530， a data block prepared at the digital unit on that unlicensed carrier.

If none of unlicensed carriers in the set of candidate carriers is determined to be available， which means the channel sensing fails， the radio unit may report the failure to the digital unit. Meanwhile， another set of candidate carriers may be used for further carrier selection and channel sensing， or it will wait for a next opportunity to repeat the above procedure until there is a free channel for data transmission.

In some other embodiments， before the radio unit can transmit the prepared data block over the available unlicensed carrier， some additional operations may need to be performed， which will be described in the following embodiments.

In a first embodiment， if the selected unlicensed carrier which is determined to be available is different from the unlicensed cartier for which the data block was prepared at the digital unit， the radio unit may reserve， at block 522， a channel on the available unlicensed carrier， for example by transmitting a reservation signal over that channel.

Additionally， the radio unit may also notify， at block 524， the digital unit of information regarding the reserved channel. Based on the information regarding the reserved channel， the digital unit may adjust the data block with regard to the reserved channel， for example by selecting a new MCS and optional precoding parameters according to the channel condition of the reserved channel， and then send the newly prepared data block to the radio unit. From the perspective of the radio unit， it receives， at block 526， the data block prepared at the digital unit with regard to the reserved channel. Then， the radio unit transmits the newly prepared data block over the reserved channel.

Please note that although the step 522 is shown before the step 524 in the figure， the step 522 may be performed after or in parallel with the step 524.

FIG. 6 illustrates an example of the channel management allocation between a radio unit and a digital unit of the communications device according to the first embodiment of the present disclosure.

As illustrated， the pre-scheduler of the digital unit schedules a data transmission. The digital unit may prepare a data block for a preferred channel， for example by performing coding， modulating and/or precoding on the data block with a selected MCS and precoding parameters. Then the digital unit transmits a data transmission request with the prepared data block to the radio unit.

In response to receipt of the data transmission request， the radio unit starts a channel sensing procedure， including selecting at least one unlicensed carrier from the set of candidate carriers for channel sensing and then performing the channel sensing on the selected at least one unlicensed carrier one by one or in parallel. The channel sensing may be implemented via the LBT， i.e. by performing CCA on the selected unlicensed carrier. The first selected carrier may be the preferred carrier appointed by the digital unit.

If there is only one channel determined to be available according to the CCA result for the corresponding carrier， the radio unit may reserve the channel by transmitting a reservation signal on it and notifies the digital unit of the reserved channel.

If there is more than one channel determined to be available according to the CCA results for corresponding carriers， the radio unit may choose one available channel to reserve for data transmission. Meanwhile， the radio unit also reports the chosen available channel to the digital unit.

At DU side， if the reserved channel is different from the channel for which the digital unit already prepared the data block， based on the information regarding the reserved channel， e.g. the index of the corresponding carrier and/or the channel condition of the reserved channel， the digital unit may adapt the data block with regard to the reserved channel， for example by selecting a new MCS and precoding parameters according to the channel condition， and then send the newly prepared data block to the radio unit for transmission over the reserved channel.

Optionally， the digital unit may also inform another communications device of the reserved channel via a licensed carrier (if available) so that the other communications device can decode the data received from said communications device on the reserved channel， rather than decode over the full bandwidth. Thus， the decoding efficiency at the receiving side may be improved.

In a second embodiment， the data block may be prepared at the digital unit according to a worst channel quality for the set of candidate carriers and a specific transmission mode (e.g. TM2， TM3 etc. ) so that the prepared data block can be transmitted on any of the set of candidate carriers with a target block error rate (BLER) less than a predetermined threshold.

In this embodiment， the digital unit may or may not notify the radio unit of the preferred carrier. Ifthe radio unit has the knowledge of the preferred carrier， the radio unit may select the preferred carrier first to perform channel sensing on it. If the channel is determined to be available on the preferred carrier， the radio unit may transmit the prepared data block directly on the preferred available carrier. Otherwise， if the channel on the preferred carrier is not available， while another one or more candidate carriers are determined to be available， then the radio unit may select any one of the available channel to transmit the data block directly. Alternatively， the radio unit may select an available channel with the best channel quality or with the highest priority to transmit the data block.

Otherwise， if the radio unit has no knowledge of the preferred carrier of the digital unit， the radio unit may select any one or more candidate carriers to do channel sensing thereon. Alternatively， the radio unit may select one or more candidate carriers with higher priorities to do channel sensing thereon. If there is only one candidate carrier is determined to be available， the radio unit may transmit the data block directly on that carrier. If more than one candidate carrier is determined to be available by the channel sensing， the radio unit may select one available carrier to transmit the data block directly without further processing by the digital unit on the data block.

The channel sensing may be regarded as a failure only when none of the set of the candidate carriers is determined to be available. In this case， the radio unit may report the failure to the digital unit. Likewise， another set of candidate carriers may be used for further carrier selection and channel sensing， or it will wait for a next opportunity to repeat the above procedure until there is a free channel for data transmission.

In addition， since a channel that is already occupied can be used for up to several milliseconds (ms) (e.g. 4ms， which equals to 4 subframes according to the LTE frame structure) ， the digital unit may perform link adaptation with regard to the occupied channel during this period， for example， by selecting a new MCS or precoding parameters more appropriate to the occupied channel. As an example， if a channel on a certain carrier is occupied in the first subframe， then the digital unit may perform link adaptation in the following three subframes for the certain carrier so as to improve transmission performance.

Optionally， the digital unit may send precoding vectors to the radio unit in advance for each carrier in the set of candidate carriers. In this case， the prepared data block is not precoded. Once an available unlicensed carrier is chosen by the radio unit for data transmission， the radio unit may perform precoding on the non-procoded data block with the precoding vector corresponding to the chosen available channel before transmitting it over that channel.

The method 500 as discussed above may be enabled based on a traffic load on the unlicensed carriers. For example， if a high load is determined on the unlicensed carriers， then the method 500 may be enabled to compete for a channel with a higher probability. If a low traffic load is determined on the unlicensed carriers， then the method 500 may be disabled to save power for channel sensing at the base station side and to save possible power for blind decoding at the UE side.

Alternatively， the method 500 may be enabled based on an indication from the digital unit. For example， an enabler bit may be set in the data transmission request. Different values of the enabler bit may instruct to enable or disable the method 500 in the communications device. The enabler bit may be set differently for various data blocks.

Alternatively， the method 500 may be enabled for some certain communications devices but disabled for other communications devices， i.e. in a user specific way according to respective performance requirements.

For better understanding of the present disclosure， FIG. 7 shows a comparison between a practical example of data transmission using the existing LBT solution and a practical example of data transmission using the method 500.

According to the existing LBT solution as shown in FIG. 7 (a) ， before transmission on a channel， the communications device shall perform a CCA check using ″energy detect″ . The communications device may observe the operating channel (s) for a CCA observation time period which shall be not less than 20 μs. The CCA observation time period used by the communications device may be declared by a manufacturer of the communications device. The channel will be determined to be occupied or busy if the energy level on that channel exceeds a certain threshold. If the communications device finds a channel occupied， it will not transmit data on that channel. Usually， the communications device performs an extended CCA check in which the channel is observed for a duration of the CCA observation time period multiplied by a random factor N. N defines a number of clear slots (i.e. the CCA check on which is successful) that need to be observed before start of the transmission. The value of N may be randomly selected in a range of 1 to q for each time of performing the extended CCA and the value is stored in a counter. The value of q is selected by the manufacturer from a range of 4 to 32. This selected value shall be declared by the manufacturer. The counter is decremented every time a CCA slot is considered to be ″unoccupied″ or “free” . When the counter reaches zero， the communications device may start the transmission. In FIG. 7 (a) ， N is set to 3. Therefore， after three times of success in CCA during the CCA observation time period， the transmission can be started.

By contrast， according to the method 500 of the present disclosure， the LBT procedure will be changed as follows.

Before transmission on a channel， the communications device has an opportunity to perform CCA over an entire receiving instant bandwidth (RX IBW) ， for example on three channels over the RX IBW.

It is assumed that the three channels experience different blocking situations as shown in FIG. 7 (b) . Therefore， as illustrated in FIG. 7 (c) ， within the same CCA observation time period， the first channel is considered as a “not allowed channel” since its noise floor is higher than a 3GPP defined threshold and the CCA in only one CCA slot is successful. The second channel is considered as an “allowed channel” since its noise floor is lower than the 3GPP defined threshold and the CCA checks in three CCA slots are successful. The third channel is considered as a “clearest allowed channel” since its noise floor is much lower than the 3GPP defined threshold and the CCA checks in more than three CCA slots are successful. If the existing LBT procedure is followed and the first channel happens to be selected by the DU， then the CCA check in this CCA observation time period fails and thus the transmission cannot be started. It has to wait for another CCA observation time period to find an available channel for transmission. Clearly， a delay is incurred.

Differently， according to the method 500， during a single CCA observation time period， there are two channels (i.e. the second and third) that can be considered available based on the CCA check results. In such a case， the clearest allowed channel may be chosen for the better transmission performance. In FIG. 7 (c) ， a FH period may be needed for notifying the DU of the chosen available channel， and meanwhile the DU can prepare data with regard to the chosen channel so as to start the transmission. During this FH period， the RU transmits a reservation signal until the prepared data arriving at the RU.

FIG. 8 illustrates a schematic block diagram of a communications device 800 according to embodiments of the present disclosure. The communications device 800 is operable at least in an unlicensed spectrum. The communications device may also be operable in a licensed spectrum， for example in an LAA system. The communications device 800 may be embodied as a base station to perform data transmission towards a terminal device or embodied as a terminal device to perform data transmission towards a base station.

Particularly， the communications device 800 comprises a digital unit 810 and a radio unit 820. The digital unit 810 is configured to prepare a data block for transmission and send a data transmission request to the radio unit. The radio unit 820 is configured to select at least one unlicensed carrier from a set of candidate carriers in the unlicensed spectrum for channel sensing， in response to the data transmission request from the digital unit 810. The radio unit 820 is further configured to perform channel sensing on the at least one unlicensed carrier according to predetermined timing for data transmission， for example， which may be defined according to an LET frame structure， and to transmit the data block prepared at the digital unit on an selected unlicensed carrier which is determined to be available by the channel sensing.

In an embodiment， the digital unit 810 may be further configured to configure the set of candidate carriers to the radio unit 820. In this embodiment， the set of candidate carriers may comprise a preferred unlicensed carrier selected by the digital unit 810. The radio unit 820 is configured to first select the preferred unlicensed carrier if information regarding the preferred unlicensed carrier is notified from the digital unit. Preferably， the preferred unlicensed carrier may be an unlicensed carrier for which the data block was prepared at the digital unit.

Additionally， if the selected unlicensed carrier which is determined to be available is different from the unlicensed carrier for which the data block was prepared at the digital unit， the radio unit 820 may be further configured to reserve a channel on the selected unlicensed carrier which is determined to be available by the channel sensing， to notify the digital unit 810 of information regarding the reserved channel， and to receive the data block prepared at the digital unit 810 for the reserved channel. Correspondingly， the digit unit 810 may be further configured to prepare the data block for the reserved channel.

In another embodiment， the digital unit 810 may be further configured to prepare the data block according to a worst channel quality for the set of candidate carriers and a specific transmission mode so that the prepared data block can be transmitted on any of the set of candidate carriers with a target block error rate less than a predetermined threshold.

In a further embodiment， the radio unit 820 may be further configured to enable the data block to be transmitted on the selected unlicensed carrier which is determined to be available without further processing by the digital unit 810 on the data block and to notify the digital unit 810 of the selected unlicensed carrier which is determined to be available.

In yet another embodiment， the set of candidate carriers may be determined based on at least one of the following： historical measurement results， measurement reports from other communications devices communicating with said communications device， capabilities of the other communications devices， configured carriers for the other communications devices， and quality of service requirements.

In yet another embodiment， each of the set of candidate carriers may have a corresponding priority. In such an embodiment， the at least one unlicensed carrier may be selected from the set of candidate carriers according to the corresponding priorities. The radio unit 820 may be further configured to maintain the set of candidate carriers.

The digital unit 810 and the radio unit 820 may be configured to implement the corresponding operations or steps as described with reference to FIG. 5 and thus will not be detailed herein for the sake of brevity.

FIG. 9 illustrates a schematic block diagram of a radio unit 900 according to embodiments of the present disclosure. The radio unit 900 may be embodied as the radio unit 810 of the communications device 800 that is operable at least in an unlicensed spectrum and comprises a digital unit. The communications device may also be operable in a licensed spectrum， for example in an LAA system.

Particularly， the radio unit 900 comprises a selecting module 910， a channel sensing module 920 and a transmitting module 930. The selecting module 910 is configured to select at least one unlicensed carrier from a set of candidate carriers in the unlicensed spectrum for channel sensing， in response to a data transmission request from the digital unit. The channel sensing module 920 is configured to perform channel sensing on the at least one unlicensed carrier according to predetermined timing for data transmission， for example， which may be defined according to an LET frame structure. The transmitting module 930 is configured to transmit a data block prepared at the digital unit on a selected unlicensed carrier which is determined to be available by the channel sensing.

In an embodiment， the set of candidate carriers may be configured by the digital unit to the radio unit. In such an embodiment， the set of candidate carriers may comprise a preferred unlicensed carrier selected by the digital unit. The selecting module 910 may be further configured to first select the preferred unlicensed carrier if information regarding the preferred unlicensed carrier is notified from the digital unit. Preferably， the preferred unlicensed carrier may be an unlicensed carrier for which the data block is prepared at the digital unit.

Additionally， if the selected unlicensed carrier which is determined to be available is different from the unlicensed carrier for which the data block was prepared at the digital unit， the radio unit 900 may further comprise a reserving module 940， a notifying module 950 and a receiving module 960. The reserving module 940 may be configured to reserve a channel on the selected unlicensed carrier which is determined to be available by the channel sensing. The notifying module 950 may be configured to notify the digital unit of information regarding the reserved channel. The receiving module 960 may be configured to receive the data block prepared at the digital unit for the reserved channel.

In a further embodiment， the transmitting module 930 may be further configured to enable the prepared data block to be transmitted on the selected unlicensed carrier which is determined to be available without further processing by the digital unit on the prepared data block. In this embodiment， the radio unit may further comprise a notifying module 950 that is configured to notify the digital unit of the selected unlicensed carrier which is determined to be available.

In yet another embodiment， each of the set of candidate carriers may have a corresponding priority. The selecting module 910 may be further configured to select the at least one unlicensed carrier from the set of candidate carriers according to the corresponding priorities. In such an embodiment， the radio unit may further comprise a maintaining module 970 that is configured to maintain the set of candidate carriers at the radio unit.

The above units 910-970 may be configured to implement the corresponding operations or steps as described with reference to FIG. 5 and thus will not be detailed herein for the sake of brevity.

FIG. 10 illustrates a schematic block diagram of an apparatus 1000 according to embodiments of the present disclosure. The apparatus 1000 may be embodied at a communications device， e.g. a base station or a terminal device， which is operable at least in an unlicensed spectrum. The communications device may also be operable in a licensed spectrum， for example in an LAA system.

The apparatus 1000 comprises at least one processor 1010， such as a data processor (DP) and at least one memory (MEM) 1020 coupled to the processor 1010. The apparatus 1000 may further comprise a transmitter TX and receiver RX 1030 coupled to the processor 1010 for establishing wireless communications with other apparatuses. The MEM 1020 stores a program (PROG) 1040. A combination of the at least one processor 1010 and the at least one MEM 1020 may form processing means 1050 adapted to implement some embodiments of the present disclosure.

The PROG 1040 may include instructions that， when executed on the associated processor 1010， enable the apparatus 1000 to operate in accordance with the embodiments of the present disclosure， for example to perform the method 500 as described with reference to FIGs. 5-6. Alternatively， the processing means 1050 may be adapted to implement some embodiments of the present disclosure as described with reference to FIGs. 5-6.

The MEM 1020 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology， such as semiconductor based memory devices， magnetic memory devices and systems， optical memory devices and systems， fixed memory and removable memory， as non-limiting examples.

The processors 1010 may be of any type suitable to the local technical environment， and may include one or more of general purpose computers， special purpose computers， microprocessors， digital signal processors DSPs and processors based on multicore processor architecture， as non-limiting examples.

In addition， the present disclosure may also provide a carrier containing the computer program as mentioned above， wherein the carrier is one of an electronic signal， optical signal， radio signal， or computer readable storage medium. The computer readable storage medium can be， for example， an optical compact disk or an electronic memory device like a RAM (random access memory) ， a ROM (read only memory) ， Flash memory， magnetic tape， CD-ROM， DVD， Blue-ray disc and the like.

The techniques described herein may be implemented by various means so that an apparatus implementing one or more functions of a corresponding apparatus described with an embodiment comprises not only prior art means， but also means for implementing the one or more functions of the corresponding apparatus described with the embodiment and it may comprise separate means for each separate function， or means that may be configured to perform two or more functions. For example， the functional modules/units described as embodiments of the present disclosure may be implemented in hardware (one or more apparatuses) ， firmware (one or more apparatuses) ， software (one or more modules) ， or combinations thereof. For a firmware or software， implementation may be made through modules (e.g.， procedures， functions， and so on) that perform the functions described herein.

Exemplary embodiments herein have been described above with reference to block diagrams and flowchart illustrations of methods and apparatuses. It will be understood that each block of the block diagrams and flowchart illustrations， and combinations of blocks in the block diagrams and flowchart illustrations， respectively， can be implemented by various means including computer program instructions. These computer program instructions may be loaded onto a general purpose computer， special purpose computer， or other programmable data processing apparatus to produce a machine， such that the instructions which execute on the computer or other programmable data processing apparatus create means for implementing the functions specified in the flowchart block or blocks.

While this specification contains many specific implementation details， these should not be construed as limitations on the scope of any implementation or of what may be claimed， but rather as descriptions of features that may be specific to particular embodiments of particular implementations. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely， various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover， although features may be described above as acting in certain combinations and even initially claimed as such， one or more features from a claimed combination can in some cases be excised from the combination， and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

It will be obvious to a person skilled in the art that， as the technology advances， the inventive concept can be implemented in various ways. The above described embodiments are given for describing rather than limiting the disclosure， and it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the disclosure as those skilled in the art readily understand. Such modifications and variations are considered to be within the scope of the disclosure and the appended claims. The protection scope of the disclosure is defined by the accompanying claims.

Claims

A method (500) for data transmission at a communications device operable in an unlicensed spectrum， the communications device comprising a digital unit and a radio unit， the method comprising：

selecting (510) ， at the radio unit， at least one unlicensed cartier from a set of candidate carriers in the unlicensed spectrum for channel sensing， in response to a data transmission request from the digital unit；

performing (520) channel sensing on the at least one unlicensed carrier according to predetermined timing for data transmission； and

transmitting (530) a data block prepared at the digital unit on a selected unlicensed carrier which is determined to be available by the channel sensing.
The method according to Claim 1， wherein

the set of candidate carriers is configured by the digital unit to the radio unit；

the set of candidate carriers comprises a preferred unlicensed carrier selected by the digital unit； and

selecting at least one unlicensed carrier from the set of candidate carriers comprises first selecting the preferred unlicensed carrier if information regarding the preferred unlicensed carrier is notified from the digital unit.
The method according to Claim 2， wherein

the preferred unlicensed carrier is an unlicensed carrier for which the data block is prepared at the digital unit.
The method according to any of Claims 1-3， further comprising， if the selected unlicensed carrier which is determined to be available is different from the unlicensed carrier for which the data block was prepared at the digital unit：

reserving (522) a channel on the selected unlicensed carrier which is determined to be available by the channel sensing；

notifying (524) the digital unit of information regarding the reserved channel； and

receiving (526) the data block prepared at the digital unit for the reserved channel.
The method according to Claim 1 or 2， wherein

the data block is prepared at the digital unit according to a worst channel quality for the set of candidate carriers and a specific transmission mode so that the prepared data block can be transmitted on any of the set of candidate carriers with a target block error rate less than a predetermined threshold.
The method according to Claim 5， wherein

transmitting the data block prepared at the digital unit on the selected unlicensed carrier comprises enabling the prepared data block to be transmitted on the selected unlicensed carrier which is determined to be available without further processing by the digital unit on the prepared data block； and

the method further comprises notifying the digital unit of the selected unlicensed carrier which is determined to be available.
The method according to any of Claims 1-6， wherein

the set of candidate carriers is determined based on at least one of the following： historical measurement results， measurement reports from other communications devices communicating with said communications device， capabilities of the other communications devices， configured carriers for the other communications devices and quality of service requirements.
The method according to any of Claims 1-7， wherein

each of the set of candidate carriers has a corresponding priority；

the at least one unlicensed carrier is selected from the set of candidate carriers according to the corresponding priorities； and

the method further comprising maintaining (540) the set of candidate carriers at the radio unit.
A communications device (800) operable in an unlicensed spectrum， comprising：

a digital unit (810) configured to prepare a data block for transmission and to send a data transmission request to a radio unit (820) ； and

the radio unit (820) configured to：

select at least one unlicensed carrier from a set of candidate carriers in the unlicensed spectrum for channel sensing， in response to the data transmission request from the digital unit；

perform channel sensing on the at least one unlicensed carrier according to predetermined timing for data transmission； and

transmit the data block prepared at the digital unit on a selected unlicensed carrier which is determined to be available by the channel sensing.
The communications device according to Claim 9， wherein

the digital unit is further configured to configure the set of candidate carriers to the radio unit；

the set of candidate carriers comprises a preferred unlicensed carrier selected by the digital unit； and

the radio unit is configured to first select the preferred unlicensed carrier if information regarding the preferred unlicensed carrier is notified from the digital unit.
The communications device according to Claim 10， wherein

the preferred unlicensed carrier is an unlicensed carrier for which the data block is prepared at the digital unit.
The communications device according to any of Claims 9-11， wherein

if the selected unlicensed carrier which is determined to be available is different from the unlicensed carrier for which the data block was prepared at the digital unit，

the radio unit is further configured to reserve a channel on the selected unlicensed cartier which is determined to be available by the channel sensing， notify the digital unit of information regarding the reserved channel， and receive the data block prepared at the digital unit for the reserved channel； and

the digit unit is further configured to prepare the data block for the reserved channel.
The communications device according to Claim 9 or 10， wherein

the digital unit is further configured to prepare the data block according to a worst channel quality for the set of candidate carriers and a specific transmission mode so that the prepared data block can be transmitted on any of the set of candidate carriers with a target block error rate less than a predetermined threshold.
The communications device according to Claim 13， wherein the radio unit is further configured to：

enable the data block to be transmitted on the selected unlicensed carrier which is determined to be available without further processing by the digital unit on the data block； and

notify the digital unit of the selected unlicensed carrier which is determined to be available.
The communications device according to any of Claims 9-14， wherein

the set of candidate carriers is determined based on at least one of the following： historical measurement results， measurement reports from other communications devices communicating with said communications device， capabilities of the other communications devices， configured carriers for the other communications devices， and quality of service requirements.
The communications device according to any of Claims 9-15， wherein

each of the set of candidate carriers has a corresponding priority；

the at least one unlicensed carrier is selected from the set of candidate carriers according to the corresponding priorities； and

the radio unit is further configured to maintain the set of candidate carriers.
A radio unit (820， 900) at a communications device operable in an unlicensed spectrum and comprising a digital unit， the radio unit comprising：

a selecting module (910) configured to select at least one unlicensed carrier from a set of candidate carriers in the unlicensed spectrum for channel sensing， in response to a data transmission request from the digital unit；

a channel sensing module (920) configured to perform channel sensing on the at least one unlicensed carrier according to predetermined timing for data transmission； and

a transmitting module (930) configured to transmit a data block prepared at the digital unit on a selected unlicensed carrier which is determined to be available by the channel sensing.
The radio unit according to Claim 17， wherein

the set of candidate carriers is configured by the digital unit to the radio unit；

the set of candidate carriers comprises a preferred unlicensed carrier selected by the digital unit； and

the selecting module (910) is further configured to first select the preferred unlicensed carrier if information regarding the preferred unlicensed carrier is notified from the digital unit.
The radio unit according to Claim 18， wherein

the preferred unlicensed carrier is an unlicensed carrier for which the data block is prepared at the digital unit.
The radio unit according to any of Claims 17-19， further comprising， if the selected unlicensed carrier which is determined to be available is different from the unlicensed carrier for which the data block was prepared at the digital unit：

a reserving module (940) configured to reserve a channel on the selected unlicensed carrier which is determined to be available by the channel sensing；

a notifying module (950) configured to notify the digital unit of information regarding the reserved channel； and

a receiving module (960) configured to receive the data block prepared at the digital unit for the reserved channel.
The radio unit according to Claim 17 or 18， wherein

the data block is prepared at the digital unit according to a worst channel quality for the set of candidate carriers and a specific transmission mode so that the prepared data block can be transmitted on any of the set of candidate carriers with a target block error rate less than a predetermined threshold.
The radio unit according to Claim 23， wherein：

the transmitting module (930) is further configured to enable the prepared data block to be transmitted on the selected unlicensed carrier which is determined to be available without further processing by the digital unit on the prepared data block； and

the radio unit further comprises a notifying module (950) configured to notify the digital unit of the selected unlicensed carrier which is determined to be available.
The radio unit according to any of Claims 17-22， wherein

the set of candidate carriers is determined based on at least one of the following： historical measurement results， measurement reports from other communications devices communicating with said communications device， capabilities of the other communications devices， configured carriers for the other communications devices and quality of service requirements.
The radio unit according to any of Claims 17-23， wherein

each of the set of candidate carriers has a corresponding priority；

the selecting module is further configured to select the at least one unlicensed carrier from the set of candidate carriers according to the corresponding priorities； and

the radio unit further comprises a maintaining module (970) configured to maintain the set of candidate carriers at the radio unit.
An apparatus (1000) for data transmission at a communications device operable at least in an unlicensed spectrum， the apparatus comprising a processor (1010) and a memory (1020) ， said memory containing instructions executable by said processor， whereby said apparatus is operative to perform the method of any of claims 1-8.
An apparatus (1000) for data transmission at a communications device operable at least in an unlicensed spectrum， the apparatus comprising processing means (1050) adapted to perform the method of any of claims 1-8.