GB2550200A

GB2550200A - Methods and devices for supporting access to unlicensed radio resources in wireless communication systems

Info

Publication number: GB2550200A
Application number: GB1608407.1A
Authority: GB
Inventors: Liu Guang
Original assignee: TCL Communication Ltd
Current assignee: TCL Communication Ltd
Priority date: 2016-05-13
Filing date: 2016-05-13
Publication date: 2017-11-15
Anticipated expiration: 2036-05-13
Also published as: GB201608407D0; CN109417792A; CN114095941A; CN109417792B; GB2550200B; WO2017193843A1

Abstract

Supporting more efficiently access to an unlicensed communications channel includes parameters in a Downlink Control Information, DCI, message sent from an eNB (101) to a User Equipment, UE, (103a). The eNB is arranged to configure a Licensed Assisted Access (LAA) uplink channel wherein at least one symbol of a sub-frame is blanked to create a gap during which the UE can perform a Listen Before Talk, LBT, procedure and wherein the eNB is further arranged to configure a Maximum Channel Occupancy Time (MCOT) period during which a channel of the unlicensed radio resource may be occupied. The DCI message includes information relating to at least one of: (i) the position of the gap; (ii) a remaining duration of the MCOT period which is available to the wireless communication device; (iii) an instruction for the wireless communication device to switch from a Category 4 to a Category 2 LBT procedure; (iv) an instruction for the wireless communication device to postpone a Category 4 LBT procedure following a previous LBT procedure failure. A Category 2 LBT procedure is always preferred for LAA uplink as it helps a UE to grab an unlicensed channel with a higher probability compared with other categories.

Description

Methods and Devices for Supporting Access to Unlicensed Radio Resources in

Wireless Communication Systems

Technical Field

Embodiments of the present invention generally relate to wireless communication systems and in particular to devices and methods for supporting access to an unlicensed communications channel using a Listen Before Talk (LBT) procedure. The invention has particular application, though is not limited to, enhanced Licenced Assisted Access (eLAA) technologies in an LTE (Long Term Evolution) advanced wireless communication system.

Background

Wireless communication systems, such as the third-generation (3G) of mobile telephone standards and technology are well known. Such 3G standards and technology have been developed by the Third Generation Partnership Project (3GPP). The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Such macro cells utilise high power base stations (NodeBs) to communicate with wireless communication devices within a relatively large geographical coverage area. Typically, wireless communication devices, or User Equipment (UEs) as they are often referred to, communicate with a Core Network (CN) of the 3G wireless communication system via a Radio Network Subsystem (RNS). A wireless communication system typically comprises a plurality of radio network subsystems, each radio network subsystem comprising one or more cells to which UEs may attach, and thereby connect to the network. Each macro-cellular RNS further comprises a controller, in a form of a Radio Network Controller (RNC), operably coupled to the one or more NodeBs. Communication systems and networks have developed towards a broadband and mobile system. The 3rd Generation Partnership Project has developed the so-called Long Term Evolution (LTE) and LTE advanced solutions, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN), for a mobile access network, and a System Architecture Evolution (SAE) solution, namely, an Evolved Packet Core (EPC), for a mobile core network. A macrocell in an LTE system is supported by a base station known as an eNodeB or eNB (evolved NodeB).

Current wireless communications networks operate using licensed radio spectrum in which multiple accesses to the communications resources of the licensed radio spectrum is strictly controlled. Each user of the network is essentially provided a “slice” of the spectrum using a variety of multiple access techniques such as, by way of example only but not limited to, frequency division multiplexing, time division multiplexing, code division multiplexing, and space division multiplexing or a combination of one or more of these techniques. Even with a combination of these techniques, with the popularity of mobile telecommunications, the capacity of current and future networks is still very limited, especially when using licensed radio spectrum.

The use of unlicensed radio spectrum may also be used by network operators in order to increase or supplement capacity. For example, a network based on the Long Term Evolution (LTE)/LTE advanced standards has an enhanced downlink that uses a Licensed-Assisted-Access (LAA) procedure to operate on unlicensed spectrum. All communication devices need to complete a LBT (Listen Before Talk) procedure before accessing an unlicensed channel.

Some LAA techniques use a clear channel assessment (CCA) check on channels of the unlicensed spectrum to determine the presence or absence of other signals prior to using the channel. The base stations (eNBs) can start the downlink transmissions on the carriers which are clear and the user equipment or terminals need to monitor the downlink carriers indicated by the base station with signalling. Typically, a UE performs a CAA check by using energy detection to determine the presence or absence of other signals on a particular carrier, resource block and/or channel to determine if that carrier, resource block and/or channel is occupied or clear to use. The LBT procedure may be used for LAA carriers from the unlicensed spectrum. Normally carriers from the licensed spectrum are specifically reserved for each UE and thus typically do not require the LBT procedure and/or CCA check.

Currently, for LAA in LTE, DL (downlink) and UL (uplink) are implemented in different ways, and an eNB can start a DL transmission any time on any channel while UEs can only start an UL transmission on specific subframes of specific channels allocated by the eNB with UL Grant messages. Hence, a UE has comparatively fewer chances to access unlicensed carriers and UL performance may also be disadvantaged as a result.

It would be advantageous to provide a means for improving the efficiency of a UE’s access to an unlicensed wireless communications channel.

Summary

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

According to a first aspect of the present invention there is provided a network element for supporting communications in a wireless communication system, the network element comprising a transmitter circuit arranged to transmit a message, for reception by a wireless communication device in the wireless communication system, comprising information for assisting the wireless communication device to access an unlicensed radio resource, wherein the network element is arranged to configure a Licensed Assisted Access (LAA) uplink channel comprising subframes, each subframe having “n” OFDM symbols, where “n” is an integer, and wherein at least one symbol is blanked to create a gap during which the wireless communication device can perform a Listen Before Talk procedure and wherein the network element is further arranged to configure a Maximum Channel Occupied Time (MCOT) period during which a channel of the unlicensed radio resource may be occupied, and wherein said message includes information relating to at least one of: the position of the gap;, a remaining duration of the MCOT period which is available to the wireless communication device; an instruction for the wireless communication device to switch from a Category 4 to a Category 2 Listen Before Talk procedure; an instruction for the wireless communication device to postpone a Category 4 Listen Before Talk procedure following a previous Listen Before Talk procedure failure.

The network element may be an eNB.

The message may be included in Downlink Control Information.

In one embodiment, the network element and wireless communication device are arranged to support a Listen Before Talk (LBT) procedure. In one particular embodiment, the wireless communication system is an LTE advanced system in which Licensed Assisted Access is supported and which uses a Listen Before Talk procedure. It has been agreed that Listen Before Talk will be classified into four categories. Category 1 has no LBT; Category 2 has LBT without random back-off, Category 3 has LBT with random back-off with fixed size of contention window, Category 4 has LBT with random back-off with variable size of contention window. In 3GPP Release 13, Category 4 has been adopted as the only LBT type for downlink.

The instruction for the wireless communication device to switch from a Category 4 to a Category Listen Before Talk procedure may comprise a single bit indicator per subframe.

The instruction to postpone a Category 4 Listen Before Talk procedure following a previous Listen Before Talk procedure failure may be indicated by a single bit per subframe.

In some embodiments, the message transmitted by the network element may include information relating to at least one of an uplink subframe size and an uplink subframe location.

The message may include information indicating in which subframe a gap needs to be blanked for LBT procedures for a plurality of wireless communication devices multiplexed onto the LAA uplink channel.

According to a second aspect of the invention, there is provided a wireless communication device adapted to perform a Listen Before Talk (LBT) procedure and having a receiver circuit for receiving a message from a network element supporting communication in a wireless communication system, wherein the message includes information for assisting the wireless communication device to access an unlicensed radio resource using a Licensed Assisted Access (LAA) uplink channel comprising subframes, each subframe having “n” OFDM symbols, where “n” is an integer, and wherein at least one symbol is blanked to create a gap during which the wireless communication device can perform a Listen Before Talk procedure, and wherein said message includes information relating to at least one of: (i) the position of the gap; (ii) a remaining duration of a Maximum Channel Occupied Time MCOT period which is available to the wireless communication device; (iii) an instruction for the wireless communication device to switch from a Category 4 to a Category Listen Before Talk procedure; (iv) an instruction for the wireless communication device to postpone a Category 4 Listen Before Talk procedure following a previous Listen before talk procedure failure.

The wireless communication device may be a User Equipment or similar mobile communications device.

In one embodiment, the message further includes information indicating in which subframe a gap needs to be blanked for LBT procedure for a plurality of wireless communication devices multiplexed onto the LAA uplink channel.

The wireless communication device may include a signal processor for determining whether a Category 4 Listen Before Talk procedure can be postponed following a previous Listen Before Talk procedure failure on receipt of a message from the network element including information relating to the position of the gap and a remaining duration of the Maximum Channel Occupation Time.

In one embodiment, the signal processor is arranged to determine if such a a Category 4 Listen Before Talk procedure can be postponed on a subframe by subframe basis.

In one embodiment the signal processor is arranged to postpone the Category 4 Listen before talk procedure by one subframe if a Listen Before Talk procedure failed on a previous subframe with a single UE indicated.

In another embodiment, the wireless communication device includes a signal processor for determining whether the wireless communication device can switch from a Category 4 Listen Before Talk procedure to a Category 2 Listen Before Talk procedure depending on information received from the network element relating to a remaining duration of an Maximum Channel Occupation Time and, optionally, the position of the gap.

According to a third aspect of the invention, there is provided a method for enabling communications in a wireless communication device in a wireless communication system, the method comprising, at a network element of the wireless communication system, transmitting to the wireless communication device, a message comprising information for assisting the wireless communication device to access an unlicensed radio resource; configuring a Licensed Assisted Access (LAA) uplink channel comprising subframes, each subframe having “n” OFDM symbols, where “n” is an integer, and wherein at least one symbol is blanked to create a gap during which the wireless communication device can perform a Listen Before Talk procedure, configuring a Maximum Channel Occupied Time (MCOT) period during which a channel of the unlicensed radio resource can be occupied, and including in said message information relating to at least one of: (i) the position of the gap; (ii) a remaining duration of the MCOT period which is available to the wireless communication device; (iii) an instruction for the wireless communication device to switch from a Category 4 to a Category 2 Listen Before Talk procedure; (iv) an instruction for the wireless communication device to postpone a Category 4 Listen Before Talk procedure following a previous Listen Before Talk procedure failure.

The method may also include, at the wireless communication device, determining if a Category 4 Listen Before Talk procedure can be postponed following a previous Listen Before Talk procedure failure.

According to a fourth aspect of the invention, there is provided a non-transitory computer readable medium having computer readable instructions stored thereon for execution by a processor to perform the method according to the third aspect.

The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an

Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory.

Brief description of the drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

Figure 1 is a simplified block diagram of a part of a cellular communication system and operating in accordance with an example embodiment;

Figure 2 is a first timing diagram illustrating an example of a Licensed Assisted Access method utilising Listen Before Talk procedures;

Figures 3 and 4 are second and third timing diagrams illustrating an example of a Licensed Assisted Access method for multiple User Equipments; and

Figure 5 is a table illustrating relevant parameters utilised by a User Equipment when accessing unlicensed spectrum.

Detailed description of the preferred embodiments

Those skilled in the art will recognise and appreciate that the specifics of the examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings.

Referring now to FIG.1, an example of part of an LTE cellular communication system operating in accordance with embodiments of the invention is illustrated and indicated generally at 100 and comprises an evolved Node B (eNB) 101 supporting an LTE cell 102. In other embodiments, the eNB 101 may support a multiplicity of cells. The evolved Node B 101 comprises a part of a radio access network which in this example is an E-UTRAN. User Equipments 103a, 103b, 103c are located within the area of coverage of the cell 102. Just three User Equipments are shown in FIG. 1 but more or fewer User Equipments may be located in the cell 102 and be in a connected mode at any given time. An evolved packet core (EPC) of the Wireless Communications System of FIG.1 includes a Packet Gateway P-GW 104 and a Serving GPRS (General Packet Radio System) Support Node (SGSN) 105. The P-GW 104 is responsible for interfacing the radio access network with a packet data network, eg. a Packet Switched Data Network (PSDN) (such as the Internet). The SSGN 105 performs a routing and tunnelling function for traffic to and from the cell 102, while the P-GW 104 links with external packet networks. The EPC also comprises a Mobility Management Entity 106. The eNB 101 is linked to the SSGN 105 through the Mobility Management Entity (MME) 106. The eNB 101 is also connected with the P-GW 104 through the MME 106 and a Service Gateway S-GW 107. The MME 106 handles signalling control and mobility while the S-GW 107 is a local anchor point for user data. The eNB 101 is provided with a receiver circuit 108 and also a transmitter circuit 109 for transmitting messages to one or more User Equipments 103a, 103b, 103c. The messages transmitted include certain information (to be described in further detail below) for assisting a User Equipment to access an unlicensed radio resource which is provided by the eNB in addition to licensed carriers. Unlicensed carriers work together with licensed carriers in Carrier Aggregation. The messages may be included in Downlink Control Information. Each User Equipment 103a, 103b and 3B, 103c includes a receiver 110 for receiving messages from the eNB 101 and a signal processor 111 for determining certain factors, to be described below, based on the information contained in the received messages.

As mentioned above, downlink and uplink LBT procedures are implemented in different ways. A downlink LBT has been specified in 3GPP TS 36.213 and defines four priority classes. A contention window is also defined for each priority and a random value is chosen and used to determine the number of CCAs to be done within one LBT procedure. Choosing a random value minimises the chances of collisions between different eNBs attempting to access the same unlicensed channel. The contention window size can depend on loading of the channel and although a small contention window size can help an eNB to grab a channel quickly, it also limits the time available to the eNB for transmission of data to a comparatively short period. In accordance with currently proposed downlink LBT procedures, the eNB 101 listens to the unlicensed channel to determine if the channel is already in use by some other device. Once the channel is detected to be free, the eNB 101 starts a defer period followed by a CCA countdown. If, during the countdown period, a signal is detected, then the eNB suspends the countdown until the signal has gone whereupon the countdown procedure is resumed after expiry of another defer period. When the countdown value is equal to zero, the eNB can start its transmission but for no more than a certain number of milliseconds as permitted by the prevailing priority class. The downlink LBT is Category 4.

An LBT procedure as agreed by the 3GPP defines a Maximum Channel Occupied Time (MCOT) which identifies a maximum length of a downlink burst that an eNB can transmit on an unlicensed channel. In practice, however, the eNB 101 may not use all of this MCOT period and so it has also been agreed that the remaining part can be shared by one or more of the UEs 103a, 103b, 103c in a so-called one-shot or Category 2 LBT procedure. Unlike the downlink, the uplink requires multiplexing of multiple UEs and so the eNB 101 needs to coordinate these multiple devices to access the same channel at the same time. In order to support multi-UE multiplexing, all UEs must start transmission exactly at the same time otherwise signals from a UE that starts earliest will cause all other UE LBT procedure is to fail. A Licensed Assisted Access uplink transmission in this example is arranged in subframes. Each subframe has ”n” OFDM symbols and at least one symbol is blanked to create a gap. In these gaps, UEs may perform an LBT procedure and start transmission immediately after the gap. In one embodiment, each subframe is 1ms long with 14 symbols and either the first and/or second symbol are blanked. In accordance with one embodiment of the invention, the eNB indicates the position of the gaps to the UEs 103a, 103b, 103c. During the gaps, a UE may either perform a Category 2 LBT when its following transmission burst lies within an existing MCOT, or a Category 4 LBT when its following transmission burst cannot be finished within an existing MCOT. If the Category 4 LBT cannot be completed within one gap, it has to continue its LBT procedure in the next gap which will be at least 1 ms later and so on.

In order for a UE to select the more appropriate LBT procedure (for example, Category 2 as opposed to Category 4) it is advantageous for a UE to know how much of the MCOT is remaining. For example, a UE will know how long it requires to transmit its data and therefore if it also knows the duration of the remaining MCOT it will be able to deduce if the transmission can be completed within the remaining MCOT window or not. For example, if the UE determines that the transmission would not fall outside the MCOT window then it can perform a Category 2 LBT procedure. If on the other hand the UE determines that its transmission would fall outside the MCOT window, then the UE can choose to perform a Category 4 LBT. A Category 4 LBT may be postponed after a Category 2 LBT fail and under certain circumstances to be explained in more detail below.

In one embodiment, the remaining MCOT is signalled to the UE by the eNB 101. This information may comprise, for example, 3 bits and is included in the message sent from the eNB in Downlink Control Information. Alternatively, the remaining MCOT can be inferred by the signal processor 111 in the UE by counting down one subframe from the predefined MCOT value whenever the UE detects a downlink transmission. This alternative has a drawback however in the case of a missed detection of a downlink transmission. In such a case, the remaining MCOT would not be decremented. This could result in the UE occupying the unlicensed channel time with an improper LBT. A Category 2 LBT procedure is always preferred for LAA uplink as it helps a UE to grab an unlicensed channel with a higher probability compared with other categories. In one example of the invention, the eNB 101 sends an instruction to a UE instructing the UE to switch from a Category 4 to a Category 2 LBT procedure under certain circumstances. The instruction can be included in the message transmitted by the eNB in Downlink Control Information. A single bit indication per subframe can be used. If such bit is not sent, then the UE continues to use Category 4 LBT. Alternatively, the UE can deduce whether or not to switch from a Category 4 to a Category 2 LBT procedure from other signalling fields.

Reference will now be made to the timing diagram of figure 2. It will be understood that gaps between transmissions during the same MCOT period which are larger than 25 microseconds need not be included in the total transmission duration. Therefore it can be said that the subframes for which a UE performed an LBT but failed do not form part of the MCOT.

In the example of figure 2, for one frame 201 having a total duration of 10 ms, there are 4 downlink subframes (0 to 3) and six uplink subframes (4 to 9) which are allocated to only one UE and a downlink LBT initiates a MCOT of 8 ms. The single UE needs to finish a 25 ps LBT (that is a one shot/Category 2 LBT) before its uplink transmission commences and if the first 25 ps LBT fails, the UE needs to wait until the beginning of the next subframe before it can perform another LBT.

Two cases are illustrated in figure 2. Case 1 illustrates how a Category 4 LBT can be postponed following an LBT failure. In case 1, a UE (such as 103a of figure 1) has failed its first LBT at the commencement of subframe 4 but succeeded in its second LBT one subframe later. So it starts its uplink transmissions from subframe number 5 and keeps transmitting without a break up to the start of subframe 9 whereupon the eNB-initiated MCOT expires. In case 2, the UE succeeded in its first LBT and so it can start uplink transmissions from subframe number 4 and keep transmitting up to the start of subframe 8 where the eNB MCOT expires. In both case 1 and case 2, the total transmission duration is no more than the MCOT which has been initiated by the eNB. So a UE can continue another transmission after successful category 4 LBT at the beginning of either subframe 9 for case 1 or subframe 8 for case 2. A Category 4 LBT must be performed in order to comply with regulations. Hence, a category 4 LBT can be deferred in such circumstances such as that in case 1. A signalling indicator is transmitted in a message from the eNB to the UEs to indicate, for each uplink subframe, if a Category 4 LBT can be postponed by one subframe when an LBT failed on this subframe. Alternatively, the signal processing capability of the UE can determine by how many subframes a category 4 LBT can be postponed following an LBT failure by receiving the message indicating the remaining MCOT duration and knowing the number of subframes which have been allocated and their location.

In one example, the eNB sends to the UEs in a broadcast manner, one or more parameters indicating how many uplink subframes are allocated and where they are. Such an indicator could be designated “subframe’s size” and could comprise 3 to 4 bits. The allocated subframes for a particular UE do not have to be contiguous. The size of a subframe has to be known to the UE is so it can correctly configure the uplink channel. For multiple UEs, an information field designated “multiple UEs bitmap (one bit per scheduled uplink subframe) is used to indicate to the UEs in which subframes a gap needs to be blanked for an LBT procedure.

In another example, the eNB sends to the UE one or more parameters in a unicast manner indicating how many uplink subframes are allocated and where they are. The allocated subframes for a particular UE do not have to be contiguous. For multiple UEs, and information field designated “multiple UEs bitmap (one bit per scheduled uplink subframe) is used to indicate to the UE in which subframes a gap needs to be blanked for an LBT procedure. A further information field designated “MCOT remaining duration” which may comprise 3 bits is used to send information relating to the remaining MCOT duration which can be utilised by UEs after an eNB has completed its downlink transmissions. In one example, this remaining duration is indicated in units of subframe and indicates the remaining duration of the MCOT which was initiated by the eNB. If an uplink transmission can be completed within this remaining period, a category 2 LBT is required. Otherwise, a category 4 LBT is required. This information field could be sent in either a broadcast manner or a unicast manner and if it is sent in the unicast manner to a UE, the eNB can adjust its value according to which subframes the specific UE is scheduled on.

Reference will now be made to the timing diagrams of figures 3 and 4 which consider the case of multiple UEs. In figures 3 and 4, for one frame 301 having a total duration of 10 ms, there are 4 downlink subframes (0 to 3) and six uplink subframes (4 to 9) which are allocated to two UEs, UE1 and UE2, (such as 103a and 103b of figure 1) and a downlink LBT initiates a MCOT of 8 ms. Each UE needs to finish a 25 ps LBT (that is a one shot/Category 2 LBT) before its uplink transmission commences and if the first 25 ps LBT fails, the UE needs to wait until the beginning of the next subframe before it can perform another LBT. If a subframe is not used by either UE, then it is not included in the remaining MCOT duration. If a subframe is used by either UE, then it is included in the remaining MCOT duration. In figure 3, subframes 4 to 9 are allocated for use by UE1 and subframes 6 to 8 are allocated for use by UE2. In figure 4, subframes 4 to 9 are allocated to UE1 and subframes 4 to 6 are allocated to UE2. Both UEs can use the same subframe but are allocated different resource blocks. In case 1 illustrated in figure 3, following failure of a Category 2 LBT by UE1 at subframe 4, the category 4 LBT can be postponed by one subframe because subframe number 4 is unused by either UE and therefore is not included in the MCOT. In case 1 of figure 4 on the other hand, the category 4 LBT for UE1 cannot be postponed because subframe 4 is allocated to (and therefore assumed to be used by) UE2 and so must be included in the MCOT.

Information fields for figures 3 and 4 can be as follows. A first information field is the ‘uplink subframe size’ and in these examples of figures 3 and 4, has a value of 6 meaning that a total number of 6 subframes are allocated. A second information field is ‘multiple UEs bitmap’ which identifies location of subframes used by one or multiple UEs. In the case of figure 3, this has the value 001110 meaning that the third, fourth and fifth subframes are allocated to multiple UEs (and the first, second and sixth subframes to one UE only). In the case of figure 4, the ‘multiple UEs bitmap has the value 111000 meaning that the first, second and third subframes are allocated to multiple UEs (and the fourth, fifth and sixth subframes are allocated to only one). A third information field is ‘MCOT remaining duration’ and has a value of 4 meaning that the remaining MCOT duration (after downlink transmissions have finished) comprises four subframes. These information fields can be sent from the eNB to the UEs with the uplink grant message or alternatively can be broadcast at the same time the uplink grant is sent.

Referring to figure 3 again, since the first two uplink subframes are allocated (or scheduled) to UE 1 only, the signal processing functionality of UE1 can deduce that the Category 4 LBT can be postponed by a least two successive subframes if LBT failure occurs. Referring to figure 4 again, since the first subframe is scheduled to multiple UEs, the signal processing functionality of both UE1 and UE2 can deduce that the Category 4 LBT cannot be postponed following an earlier LBT failure.

Referring now to the table of figure 5, a method describing how a UE can deduce whether or not it can postpone a category 4 LBT based on indicators from the eNB will now be described. In the example of figure 5, a remaining MCOT duration (after the eNB has completed its downlink transmissions) is equal to 3 (that is 3 ms or three subframes) and this value is transmitted to a UE by the eNB with the uplink grant. Uplink subframes are configured by the eNB and represented by row 501 in figure 5 and numbered 4 to 9. The ‘multiple UEs bitmap’ of 010000 shown in row 502 means that only subframe number 5 is used by more than one UE with the rest being used by one UE only (but not necessarily the same UE each time). In row 503 the shaded subframes 4, 5, 7, 8 and 9 are allocated to UE1. Row 503 represents LBT results with an ‘x’ signifying a Category 2 failure and a ‘V’ signifying a pass. Row 505 states whether or not a particular subframe is counted as a transmission as far as the remaining MCOT is concerned. Row 506 states the remaining MCOT duration at the end of each subframe as deduced by the UE1. Row 507 states the category of LBT carried out at a particular subframe.

At subframe 4 the UE1 performs a Category 2 (25 microsecond) LBT. This LBT fails. However, subframe 4 is scheduled to a single UE, (bitmap value 0) and UE 1 knows it is the only one scheduled on this subframe. So when the LBT fails, because the UE1 knows that this subframe is not used by any other UE, it can be excluded from the remaining MCOT duration. Hence, at the end of subframe 4 the remaining MCOT duration value has not changed and still remains at 3.

Subframe number 5 is scheduled to multiple UEs (bitmap value equal to 1) and the UE1 knows it is just one of the several UEs scheduled. So when the LBT fails, UE1 cannot know if this subframe is used by any other UE or not. Hence this subframe must be counted in the transmission duration. Therefore after subframe 5 the remaining MCOT duration is reduced by one and now equals 2.

Subframe number 6 is scheduled to a single UE and UE1 is not scheduled on this subframe (blank). So UE1 cannot know if this subframe is used by another UE or not. This subframe must be counted in the transmission duration. So after subframe 6, the MCOT remaining duration is reduced by 1 down to a value of 1.

Subframe number 7 is similar to subframe number 4 in that it is only scheduled to UE1 and UE1 failed its LBT on subframe 7 in this example and so this frame is not counted in the transmission duration. So after subframe 7 the remaining MCOT duration is not reduced and remains at 1.

Subframe number 8 is only scheduled to UE1 and UE1 passed its LBT (indicated by the letter V in the table) and occupied this subframe. After subframe 8 the remaining MCOT duration is reduced by 1 down to 0 which means from the beginning of subframe number 9 a Category 4 LBT is required.

Thus it can be seen from the above that the UE can determine when to perform a category 4 LBT. This determination can be performed by the signal processor in the UE.

In another embodiment, the UE is not configured to deduce remaining MCOT durations on a subframe by subframe basis as described above with reference to figure 5, but instead relies on signalling from the eNB. For example, a ‘remaining MCOT duration parameter’ can be included in one common DCI message to multiple UEs. In this embodiment, a UE monitors the downlink signalling. If no downlink signalling is received then the UE defaults to a Category 4 LBT. If downlink signalling is received and the ‘remaining MCOT duration parameter indicates a remaining duration of zero, then the UE must perform a Category 4 LBT. If downlink signalling is received and the ‘remaining MCOT duration’ parameter indicates a remaining duration of 1, then the UE performs a Category 2 LBT in the first subframe and a Category 4 LBT in the next subframe. If downlink signalling is received and the remaining MCOT duration parameter is of 2 or more, then a Category 2 LBT can be performed in the first two and/or the following subframes.

In another embodiment, the UE is not configured to determine whether a Category 4 LBT can be postponed or not but instead relies on signalling from the eNB. An additional field equalling either 0 or 1, where a 0 means that a postponement is permitted if LBT fails on this subframe and a 1 means that it is not permitted, can be used. Taking the example of Figure 5, the table below illustrates this.

Subframe number 5 is a no because another UE is multiplexed and may use this subframe. Subframe 6 is also a no because this subframe is scheduled to another UE. All the other subframes are yes, the Category 4 LBT can be postponed once the 25 ps LBT fails. The same number of subframes can be postponed as the number of subframes which have a failed LBT and a ‘yes’ at the same time. Alternatively, subframe number 6 can be removed from the above signalling as it is not scheduled to UE1 and UE1 knows that. This option uses more downlink signalling but keeps everything and under the control of the eNB.

The signal processing functionality of the embodiments of the invention may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface , such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

In this document, the terms ‘computer program product’, ‘computer-readable medium’ and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally referred to as ‘computer program code’ (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code), when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP), or application-specific integrated circuit (ASIC) and/or any other sub-system element.

It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organisation.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices. Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to ‘a’, ‘an’, ‘first’, ‘second’, etc. do not preclude a plurality.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ or “including” does not exclude the presence of other elements.

Claims

1. A network element for supporting communications in a wireless communication system, the network element comprising a transmitter circuit arranged to transmit a message, for reception by a wireless communication device in the wireless communication system, comprising information for assisting the wireless communication device to access an unlicensed radio resource, wherein the network element is arranged to configure a Licensed Assisted Access (LAA) uplink channel comprising subframes, each subframe having “n” OFDM symbols, where “n” is an integer, and wherein at least one symbol is blanked to create a gap during which the wireless communication device can perform a Listen Before Talk procedure and wherein the network element is further arranged to configure a Maximum Channel Occupied Time (MCOT) period during which a channel of the unlicensed radio resource may be occupied, and wherein said message includes information relating to at least one of: (i) the position of the gap;. (ii) a remaining duration of the MCOT period which is available to the wireless communication device; (iii) an instruction for the wireless communication device to switch from a Category 4 to a Category 2 Listen Before Talk procedure; (iv) an instruction for the wireless communication device to postpone a Category 4 Listen Before Talk procedure following a previous Listen Before Talk procedure failure.

2. The network element of claim 1 wherein said message is included in Downlink Control Information.

3. The network element of claim 1 or claim 2 wherein the instruction for the wireless communication device to switch from a Category 4 to a Category 2 Listen Before Talk procedure comprises a single bit indicator per subframe.

4. The network element of any preceding claim wherein the instruction to postpone a Category 4 Listen Before Talk procedure following a previous Listen Before Talk procedure failure is indicated by a single bit per subframe.

5. The network element of any preceding claim wherein said message further includes information relating to at least one of; an uplink subframe size and an uplink subframe location.

6. The network element of any preceding claim wherein said message further includes information indicating in which subframe a gap needs to be blanked for LBT procedure for a plurality of wireless communication devices multiplexed onto the LAA uplink channel.

7. A wireless communication device adapted to perform a Listen Before Talk procedure and having a receiver circuit for receiving a message from a network element supporting communication in a wireless communication system, wherein the message includes information for assisting the wireless communication device to access an unlicensed radio resource using a Licensed Assisted Access (LAA) uplink channel comprising subframes, each subframe having “n” OFDM symbols, where “n” is an integer, and wherein at least one symbol is blanked to create a gap during which the wireless communication device can perform a Listen Before Talk procedure, and wherein said message includes information relating to at least one of: (i) the position of the gap; (ii) a remaining duration of a Maximum Channel Occupied Time MCOT period which is available to the wireless communication device; (iii) an instruction for the wireless communication device to switch from a Category 4 to a Category Listen Before Talk procedure; (iv) an instruction for the wireless communication device to postpone a Category 4 Listen Before Talk procedure following a previous Listen Before Talk failure.

8. The wireless communication device of claim 7 wherein said message further includes information indicating in which subframe a gap needs to be blanked for an LBT procedure for a plurality of wireless communication devices multiplexed onto the LAA uplink channel.

9. The wireless communication device of claim 7 or 8 including a signal processor for determining whether a Category 4 Listen Before Talk procedure can be postponed following a previous Listen Before Talk procedure failure on receipt of a message from the network element including information relating to the position of the gap and a remaining duration of a Maximum Channel Occupation Time.

10. The wireless communication device of claim 9 wherein the signal processor is arranged to determine if a Category 4 Listen Before Talk procedure can be postponed following a previous Listen Before Talk procedure failure on a subframe by subframe basis.

11. The wireless communication device of claim 10 wherein the signal processor is arranged to postpone the Category 4 Listen Before Talk procedure by one subframe if an LBT failed on a previous subframe with a single UE indicated.

12. The wireless communication device of claim 7 including a signal processor for determining whether the wireless communication device can switch from a Category 4 Listen Before Talk procedure to a Category 2 Listen Before Talk procedure depending on information received from the network element relating to a remaining duration of a Maximum Channel Occupation Time.

13. The wireless communication device of claim 12 wherein the signal processor determines whether the wireless communication device can switch from a Category 4 Listen Before Talk procedure to a Category 2 Listen Before Talk procedure depending on information received from the network element relating to the position of the gap.

14. A method for enabling communications in a wireless communication device in a wireless communication system, the method comprising, at a network element of the wireless communication system, transmitting to the wireless communication device, a message comprising information for assisting the wireless communication device to access an unlicensed radio resource; configuring a Licensed Assisted Access (LAA) uplink channel comprising subframes, each subframe having “n” OFDM symbols, where “n” is an integer, and wherein at least one symbol is blanked to create a gap during which the wireless communication device can perform a Listen Before Talk procedure, configuring a Maximum Channel Occupied Time (MCOT) period during which a channel of the unlicensed radio resource can be occupied, and including in said message information relating to at least one of: (i) the position of the gap; (ii) a remaining duration of the MCOT period which is available to the wireless communication device; (iii) an instruction for the wireless communication device to switch from a Category 4 to a Category 2 Listen Before Talk procedure; (iv) an instruction for the wireless communication device to postpone a Category 4 Listen Before Talk procedure following a previous Listen Before Talk procedure failure.

15. The method of claim 14 comprising including said message In Downlink Control Information.

16. The method of either of claims 14 or 15 comprising, at the wireless communication device, determining if a Category 4 Listen before Talk procedure can be postponed following a previous Listen Before Talk procedure failure.

17. A non-transitory computer readable medium having computer readable instructions stored thereon for execution by a processor to perform the method according to claim 14.

18. The non-transitory computer readable medium of claim 17 comprising at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory.