WO2016048798A1

WO2016048798A1 - Listen before talk arrangement for a multi-operator scenario

Info

Publication number: WO2016048798A1
Application number: PCT/US2015/050768
Authority: WO
Inventors: Esa Tiirola; Timo Lunttila; Kari Hooli; Klaus Hugl
Original assignee: Nokia Technologies Oy; Nokia Usa Inc.
Priority date: 2014-09-25
Filing date: 2015-09-17
Publication date: 2016-03-31

Abstract

Certain communication systems may benefit from listen before talk (LBT) arrangements. For example, long term evolution advanced (LTE-Advanced) and specifically LTE deployed on Unlicensed Bands (LTE Licensed Assisted Access, LTE LAA) may benefit from an LBT arrangement for a multi-operator scenario. A method can include providing multiple clear channel assessment slots at an end of an idle period. The method can also include assigning a clear channel assessment pattern for each cell of a plurality of cells.

Description

LISTEN BEFORE TALK ARRANGEMENT FOR A MULTI-OPERATOR SCENARIO CROSS-REFERENCE TO RELATED APPLICATION:

[0001] This application is related to and claims the benefit and priority of U.S. Provisional Patent Application No. 62/055,361, filed September 25, 2014, the entirety of which is hereby incorporated herein by reference.

BACKGROUND:

Field:

[0002] Certain communication systems may benefit from listen before talk (LBT) arrangements. For example, long term evolution advanced (LTE- Advanced) and specifically LTE deployed on Unlicensed Bands (also known as LTE Licensed Assisted Access, LAA) may benefit from an LBT arrangement for a multi-operator scenario. Description of the Related Art:

[0003] Different regions have different regulatory requirements for unlicensed band operation. These regulations are summarized in third generation partnership project (3GPP) document RP- 140054 ("Review of Regulatory Requirements for Unlicensed Spectrum"), which is hereby incorporated herein by reference in its entirety. Despite of the regulatory rules, LTE has not yet been deployed in unlicensed spectrum.

[0004] EN 301 893 defines European regulatory requirements unlicensed band on 5GHz band. EN 301 893 is hereby incorporated herein by reference in its entirety. EN 301 893 defines two types of operation modes: (1) Frame Based Equipment (FBE) and (2) Load Based Equipment (LBE). Frame based equipment is the equipment where the transmit/receive structure is not directly demand-driven but has fixed timing. A listen before talk (LBT) procedure for FBE and/or LBE may, for example, be based on European regulatory rules defined for 5 GHz ISM band.

[0005] In a load based equipment, the transmit/receive structure is not fixed in time but demand- driven. If the load based equipment finds an operating channel occupied (through some LBT/CCA procedure), it conventionally shall not transmit in that channel. Conventionally, the equipment shall then perform an Extended CCA check, in which the Operating Channel(s) is/are observed for the duration of a random factor N multiplied by the CCA observation time. N defines the number of clear idle slots resulting in a total Idle Period that need to be observed before initiation of the transmission. The value of N shall be randomly selected in the range l..q every time an Extended CCA is required. The value may be stored in a counter. The counter is decremented every time a CCA slot is considered to be unoccupied. When the counter reaches zero, the equipment may transmit. The value of q may be selected by the manufacturer in the range 4..32. The total time that an equipment makes use of an Operating Channel is the Maximum Channel Occupancy which shall be less than (13/32) x q ms, after which the device shall perform the Extended CCA.

[0006] While regulatory rules may define the boundary conditions of the system operating on the respective spectrum, they do not provide a detailed solution as to how to define and operate the system.

[0007] Synchronizing CCA timing between neighboring nodes (eNBs) poses certain challenges. In a synchronized scenario, nobody is transmitting during the CCA slot before the start of the frame transmission. That will cause a high collision probability for the data transmission. For example, all nodes that need to transmit will see the channel as not occupied and will be allowed to transmit.

[0008] ETSI Rules present an approach for equipment following regulatory rules for load based equipment in terms of the eCC A operation. However, that approach does not appear fully to support coordinated operation (frequency reuse- 1) within one operator, as each equipment would select randomly the extended CCA duration parameter N.

[0009] LTE License Assisted Access (LTE LAA) enables carrier aggregation using one or multiple unlicensed band LTE SCell(s) with a licensed band PCell and thereby increase the potential UE and system throughput.

[0010] In LTE LAA depending on the regulatory requirements, before being permitted to transmit, a user or an access point (such as eNodeB) may need to monitor the given radio frequency for a short period of time to ensure the spectrum is not already occupied by some other transmission. This requirement is referred to as Listen-bef ore-talk (LBT). The requirements for LBT vary depending on the geographic region. For example, in the US such requirements do not exist, whereas in other places such as Europe the network elements operating on unlicensed bands need to comply with LBT requirements.

SUMMARY:

[0011] According to a first embodiment, a method can include providing multiple clear channel assessment slots at an end of an idle period. The method can also include assigning a clear channel assessment pattern for each cell of a plurality of cells.

[0012] In a variant, the clear channel assessment pattern comprises a CCA slot number to indicate in which CCA slot to perform clear channel assessment.

[0013] In a variant, the clear channel assessment pattern comprises a counter value.

[0014] In a variant, the assigning includes generating the clear channel assessment pattern with a pseudo-random generator.

[0015] In a variant, the assigning is performed in dependence on at least one of a public land mobile network identifier (PLMN ID), a subframe number, or a slot number.

[0016] In a variant, multiple clear channel assessment slots can each have a clear channel assessment slot length equal to an orthogonal frequency division multiple access symbol.

[0017] In a variant, multiple clear channel assessment slots can each have a clear channel assessment slot length equal to a fraction of an orthogonal frequency division multiple access symbol.

[0018] According to a second embodiment, a method can include performing clear channel assessment before starting data transmitting. The method can also include conditionally transmitting data based on a result of the clear channel assessment and a clear channel assessment pattern.

[0019] In a variant, the method includes monitoring the CCA slot to determine whether the channel is unoccupied.

[0020] In a variant, the method includes transmitting data from the beginning of the frame period when the clear channel assessment indicates that the channel is unoccupied.

[0021] In a variant, the method includes when the clear channel assessment indicates that the channel is unoccupied, transmitting a reservation signal from the beginning of next CCA slot until the end of the idle period.

[0022] In a variant, the method includes transmitting data immediately when the clear channel assessment indicates that the channel is unoccupied.

[0023] In a variant, the method includes decrementing a counter when a value of the counter is greater than zero and the clear channel assessment indicates that the channel is unoccupied.

[0024] In a variant, the method includes transmitting data when the counter is equal to zero.

[0025] In a variant, multiple clear channel assessment slots can each have a clear channel assessment slot length equal to an orthogonal frequency division multiple access symbol.

[0026] In a variant, multiple clear channel assessment slots can each have a clear channel assessment slot length equal to a fraction of an orthogonal frequency division multiple access symbol.

[0027] In a variant, the clear channel assessment pattern comprises a counter value.

[0028] In a variant, the assigning includes generating the clear channel assessment pattern with a pseudo-random generator.

[0029] In a variant, the assigning is performed in dependence on at least one of a public land mobile network identifier (PLMN ID), a subframe number, or a slot number.

[0030] In a variant, the clear channel assessment pattern can indicate to a given network node a pseudo-random factor N, upon starting the extended clear channel assessment procedure.

[0031] In a variant, a counter for N can be reset with a pseudo-random clear channel assessment pattern value at predefined time instances, regardless of an enhanced clear channel assessment procedure state.

[0032] In a variant, the counter reset time instances can be predetermined by standard or configurable.

[0033] In a variant, in the case of configurable reset time instances, the resetting frequency may adapt to the current interference or load situation.

[0034] In a variant, the counter resetting may also be enabled or disabled. [0035] In a variant, the counter resetting can be enabled or disabled based on current interference or load situation.

[0036] In variant, resetting of counter N value may be dynamically triggered.

[0037] In a variant, the dynamic trigger can be provided by DCI used for UL scheduling.

[0038] According to third and fourth embodiments, an apparatus can include means for performing the method of the first or second embodiment in any of their variants, respectively.

[0039] According to fifth and sixth embodiments, an apparatus can include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code can be configured to, with the at least one processor, cause the apparatus at least to perform the method according to the first or second embodiment in any of their variants, respectively.

[0040] A non-transitory computer-readable medium can, in seventh and eighth embodiments, be encoded with instructions that, when executed in hardware, perform a process. The process can include the method according to the first or second embodiment in any of their variants, respectively.

[0041] A computer program product, in ninth and tenth embodiments, can encode instructions for performing a process. The process can include the method according to the first or second embodiment in any of their variants, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0042] For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:

[0043] Figure 1 illustrates a scenario according to certain embodiments for frame based equipment.

[0044] Figure 2 illustrates a method according to certain embodiments.

[0045] Figure 3 illustrates the principle of the CCA slot arrangement with FBE and DL scenario, according to certain embodiments.

[0046] Figure 4 illustrates a system according to certain embodiments.

DETAILED DESCRIPTION:

[0047] Certain embodiments relate to a way how to facilitate Listen Before Talk (LBT) and related Clear Channel Assessment (CCA) procedures in a LTE LAA scenario with multiple operators and synchronized network. The logic behind the scenario includes that in a typical LTE LAA scenario, multiple operators share the same unlicensed spectrum.

[0048] An assumption made here is that the network is synchronized. This is a typical assumption in time division duplex (TDD) deployments in general and a prerequisite for effective interference management. Also, in FDD deployments, more and more synchronized network operation is used to enable enhanced LTE features as intercell interference coordination, enhanced UE receivers, and the like. The synchronization assumption covers both intra-operator and inter-operator cases here. Another possible scenario is such where synchronization assumption covers only intra-operator case but not inter-operator case.

[0049] The exact way to achieve synchronism is outside the scope of this discussion. Any available method, such as global positioning system (GPS), Ethernet based synchronization solutions, and Radio Interface Based Synchronization (RIBS) developed in Rel-12, is permitted. Generally speaking, synchronized operation provides better performance compared asynchronous operation. Although the network may be synchronized, such synchronization may not be necessary for all embodiments.

[0050] Certain embodiments provide a way to facilitate Listen Before Talk (LBT) in, for example, an LAA scenario with multiple operators and a synchronized network. The considered scenario is depicted in the Figure 1 for frame based equipment (FBE) according to the EU/ETSI regulations. The figure assumes that downlink (DL) subframe/symbol timing is aligned between neighbouring cells. This assumption may apply both to frame based equipment (FBE) as well as to load based equipment (LBE).

[0051] Figure 1 illustrates a scenario according to certain embodiments for frame based equipment. As shown in Figure 1, for each of cells A, B, and C, there can be a fixed frame period of, for example, 10 ms. The frame period includes the Channel Occupancy time (i.e. the transmission) and an idle period. The idle period may be, for example, about 1 ms out of the 10 ms or less.

[0052] Certain embodiments define a CCA arrangement for LTE LAA scenario with multiple operators and synchronized network operating according to the regulations defined for either FBE or

LBE. Thus, certain embodiments include the steps illustrated in Figure 2.

[0053] Figure 2 illustrates a method according to certain embodiments. As shown in Figure 2, at 210 the method can include providing multiple CCA slots at the end of an idle period. Each CCA slot can have a predefined time duration, T_cca. T_cca can be, for example, 18 or 20 μβ. CCA slots may be numbered. For example, they can be numbered as ... , 6, 5, 4, 3, 2, 1, 0. Figure 3 provides an illustration of such numbering.

[0054] As also shown in Figure 2, at 220 the method can include assigning a CCA pattern for each cell. The CCA pattern can be made up of pseudo-random numbers. The pattern may be derived based on various input parameters such as cell_id, subframe number, radio frame number, service provider id (operator_id), or the like.

[0055] Moreover, the CCA Pattern can be defined for each cell, for example on a per-cell basis. Frequency reuse- 1 can be realized by assigning the same CCA Pattern for multiple cells, which might make sense for multiple cells of a single operator. LBT among cells can be realized by assigning distinct CCA patterns for each of the multiple cells, for example for different operators.

[0056] In certain embodiments, a separate CCA Pattern can be defined for each of the uplink and downlink operations in the cell. In another embodiment, all UEs in a certain cell can utilize the same CCA pattern for their uplink operation. Thus, in certain embodiments the uplink CCA Patterns can be cell specific but not UE specific.

[0057] In the case of FBE, the CCA pattern can indicate the CCA slot in which the given network node is to perform CCA. The CCA slot indicated by the CCA Pattern can vary from one idle period to another in a pseudo-random manner.

[0058] In the case of LBE, the CCA pattern can indicate to the given network node the (pseudo) random factor N, upon starting the extended CCA procedure. In yet another embodiment targeted for LBE, the counter for N can be reset with the pseudo-random CCA pattern value at predefined time instances, regardless of the eCCA procedure state.

[0059] Before starting transmission, at 230 a network node can perform CCA LBT. Network node here can broadly refer to such devices as an eNB or UE. If the network node finds the operating channel occupied, at 232 the network node can avoid transmitting on that channel immediately. If the network node finds the operating channel unoccupied, it may, at 234, attempt to occupy the channel according to the following procedures.

[0060] In the case of LBE, a reservation signal may be used to occupy the channel until the start of the next LTE subframe, at 240, to align the LBE transmission with the symbol/subframe grid of LTE (for example with the symbol and subframe timing of the licensed band LTE PCell) in a predetermined way of the intended synchronized network operation.

[0061] Moreover, at 242 the node can start transmitting data when the extended CCA procedure has determined the channel to be available for transmission. For example, in LBE the node can start transmitting after the node has observed the channel to be unoccupied N times. A pseudo-random CCA pattern can determine the initial value of N. If the eCCA procedure determines the channel to be free, N can be decremented by one, otherwise N can stay the same. When N reaches zero, namely the channel has been found to be unoccupied N times, the node may transmit.

[0062] For example, if the value of N > 0, when the node observes that the operating channel is unoccupied, the node can decrement N by one and the extended CCA procedure can continue. Else, when the node observes that the operating channel is occupied, N is not decremented. When N = 0, the node can start transmitting data as soon as it can start the transmission, taking into account time required for Rx-Tx switching.

[0063] As mentioned above, a reservation signal can be used to align the LBE transmission with the symbol/subframe grid in a predetermined way of the intended synchronized network operation.

[0064] In the case of FBE, at 245 the node can start transmitting a reservation signal until the beginning of the (fixed) frame period.

[0065] Moreover, at 247 the node can start transmitting data from the beginning of the (fixed) frame period when the CCA slot monitored is the last CCA slot within the idle period, such as CCA slot #0 in Figure 3.

[0066] Thus, for example, if the CCA slot monitored is the last CCA slot within the Idle period (for example, CCA slot #0), then the node can start transmitting data from the beginning of the frame period. Otherwise, the node can start transmitting a reservation signal as soon as it can start the transmission taking into account time required for Rx-Tx switching.

[0067] A channel reservation signal can be transmitted until beginning of the (fixed) frame period and the UE can start transmitting data after that.

[0068] Figure 3 illustrates the principle of the clear channel assessment (CCA) slot arrangement with FBE and DL scenario, according to certain embodiments. As shown in Figure 3, there can be at least four cells (Cell A, Cell B, Cell C, and Cell D). There can be an idle period between a previous channel occupancy and a next channel occupancy, i.e. the next frame boundary.

[0069] During the idle period, at CCA slot 3, Cell A can conduct CCA, followed by reservation signals in CCA slots 2, 1, and 0 if the channel was found unoccupied in the CCA. Similarly, Cell B can conduct CCA in CCA slot 2, followed by reservation signals in CCA slots 1 and 0. Likewise, Cell C can conduct CCA in CCA slot 1, followed by a reservation signal in CCA slot 1. Cell D can simply conduct CCA in CCA slot 0.

[0070] Thus, Figure 3 depicts a DL scenario in which different network nodes can correspond to different eNBs. Each network node can be given a CCA pattern, which can indicate a CCA slot for each idle period in the range of 0...(F-1), where Y equals the number of CCA slots configured.

[0071] The relative index of the CCA slot can essentially indicate a current cell priority when compared to other neighboring cells when reserving the channel. For example, nodes with earlier CCA slots effectively have higher priority when accessing the spectrum. In the example of Figure 3, Cell A is most likely to gain access to spectrum.

[0072] In a typical implementation, eNBs of the same operator may have the same priority. Such an implementation can allow frequency reuse- 1 type operation within an operator. To keep things fair, the CCA slot allocation and the priority can change deterministically from one LBT occasion/idle period to another. The change can be made, for example, in a pseudo-random manner so that network operators are more or less equally happy or unhappy. This approach can, at the same time, help to prevent unnecessary collisions of a fully synchronized multi-operator FBE scenario.

[0073] As for collisions / number of offsets required, there may be a fundamental limit that if there are large number of cells / Public Land Mobile Network (PLMN) competing for the spectrum in the same area, and the cells all want to use spectrum, at least one of the cells may not get served in a given LBT occasion/idle period. The randomization of the offsets can help in guaranteeing that every cell or node gets access sometimes.

[0074] Implementations can be somewhat different for load based equipment. For example, in certain embodiments each network node can be given a CCA pattern. Based on the CCA pattern, the network node can determine the value of N that the UE should assume in an extended CCA procedure.

[0075] Thus, in such embodiments, the pattern can be used in initializing the value of N. Moreover, the pattern can result in N being time dependent and varying. The values of N can be uniformly distributed over a range l ..q, where q is defined as described above. With LBE, the same parameter value q may be selected for multiple nodes in the network. This may be beneficial at least in the case when different nodes are configured with the same CCA pattern.

[0076] For DL operation, the pattern may be PMLN specific, such as a function of the PLMN ID. For UL operation, the pattern may be cells specific, such as a function of the cell ID, potentially in combination with the PLMN ID. The pattern for UL operation may also or alternatively be PMLN specific.

[0077] The CCA pattern may be generated with a pseudo-random generator at each network node. Each time the value N is initialized, the pseudo-random generator can be initialized according to the assigned CCA pattern. Thus, for example, the pseudo-random generator initialization may depend on PLMN ID and a time instance, such as subframe number or slot number.

[0078] Before a transmission or a burst of transmissions on an operating channel, the equipment can perform a Clear Channel Assessment (CCA) check using energy detect. If the equipment finds the Operating Channel(s) to be clear, the equipment may transmit immediately. The total time that an equipment makes use of an Operating Channel is the Maximum Channel Occupancy Time. This maximum time may be set to be less than (13/32) x q ms, where q = {4...32}. Thus, for example when q = 32, the Maximum Channel Occupancy Time may be 13 ms.

[0079] If the equipment finds an operating channel occupied, the equipment can perform an extended CCA check. For example, the equipment can continue monitoring operating the channel, until the channel becomes unoccupied. A counter can be decremented every time a CCA slot is considered to be unoccupied. When the counter reaches zero, the equipment may transmit.

[0080] Network elements may see different interference levels and, hence, have different interpretations whether a particular CCA slot is occupied or not, based on an energy detection approach to determining occupancy. Thus, counters for N on different network elements may be decremented at a different pace, although initialized with the same CCA pattern value. Differences in

N counter value means that network element would start transmission at different time instances, and the network element first to transmit would block transmission from other network elements. Reuse- 1 between cells or FDMed UL may not be achieved in that case.

[0081] To avoid that situation or for other reasons, the counter for N can be reset with the pseudo- random CCA pattern value at predefined time instances, regardless of the eCCA procedure state. The counter reset time instances may be predetermined by standard or configurable. In the case of configurable reset time instances, the resetting frequency may adapt to the current interference or load situation. The counter resetting may also be enabled or disabled. This may be done based on current interference or load situation for example. Further, in the case of UL, resetting of counter N value may be dynamically triggered, for example with DCI used for UL scheduling.

[0082] Dimensioning of the CCA procedure and idle period done in a variety of ways for Frame based Equipment (FBE). For example, in certain embodiments, an eNB's reservation signal can be counted as part of the channel occupancy time when defining the LTE LAA frame length. This approach may ensure that the minimum Idle Period is at least 5 % of the Channel Occupancy Time used by the equipment for the current Fixed Frame Period.

[0083] After pseudorandom allocation of the CCA slot, two eNBs under different operators may have the same CCA slot. The probability of CCA collisions can be reduced by increasing the number of CCA slots.

[0084] Channel reservation signals for FBE and LBE can implemented in at least two ways.

According to a first approach, a CCA slot length can equal one OFDMA symbol. Thus, the CCA slot length including Rx-Tx time can be defined to be one OFDMA symbol. In such a case, existing signals can be used as reservation signals. For example, current LTE signals such as CRS can be used as a reservation signal.

[0085] According to a second approach, CCA slot length can equal a fraction of an OFDMA symbol. In order to minimize the overhead due to plurality of CCA slots, the eNB may support transmission of reservation signal outside the regular symbol grid.

[0086] There are different ways to make the signal. For example, one way is frequency domain generation of the signal, for example based on pre-calculated sequences. Those sequences can be configured to have a desired time domain behavior.

[0087] Another way is time domain generation of the signal. Constant amplitude zero

autocorrelation (CAZAC) sequences are examples of sequences that can be used. Time domain gating or cutting can be applied for the sequences defined in the frequency domain.

[0088] In one embodiment, the duration of CCA slot (T_cca) including Rx-Tx time can be defined to be TJN, where T_s the duration of an OFDMA symbol and N is a positive integer, N £ { 1 ,2,3, ... } . This choice may allow maximal usage of existing signals as reservation signals. Thus, at maximum one fractional signal may be needed, at the beginning of a reservation signal, and remaining part can be made using current LTE principles.

[0089] If coordination of the CCA Operation is desired, X2 signalling can be used to facilitate the desired coordination between eNBs. The coordination may be desired in the following areas. For FBE only, alignment of CCA slots between different operators for frame based equipment may be desired. This may include duration of a CCA slot (T_cca) or the number of CCA slots (Y). For both FBE and LBE, X2 signaling can be used to facilitate similar or different random selection /CCA pattern within one operator's network.

[0090] Figure 4 illustrates a system according to certain embodiments of the invention. It should be understood that each block of the flowchart of Figure 2 may be implemented by various means or their combinations, such as hardware, software, firmware, one or more processors and/or circuitry. In one embodiment, a system may include several devices, such as, for example, network element 410 and user equipment (UE) or user device 420. The system may include more than one UE 420 and more than one network element 410, although only one of each is shown for the purposes of illustration. A network element can be an access point, a base station, an eNode B (eNB), or any other network element. Each of these devices may include at least one processor or control unit or module, respectively indicated as 414 and 424. At least one memory may be provided in each device, and indicated as 415 and 425, respectively. The memory may include computer program instructions or computer code contained therein. One or more transceiver 416 and 426 may be provided, and each device may also include an antenna, respectively illustrated as 417 and 427. Although only one antenna each is shown, many antennas and multiple antenna elements may be provided to each of the devices. For example, a two-dimensional array of antenna elements may be used by network element 410. Other configurations of these devices, for example, may be provided. For example, network element 410 and UE 420 may be additionally configured for wired communication, in addition to wireless communication, and in such a case antennas 417 and 427 may illustrate any form of communication hardware, without being limited to merely an antenna.

[0091] Transceivers 416 and 426 may each, independently, be a transmitter, a receiver, or both a transmitter and a receiver, or a unit or device that may be configured both for transmission and reception. The transmitter and/or receiver (as far as radio parts are concerned) may also be implemented as a remote radio head which is not located in the device itself, but in a mast, for example. It should also be appreciated that according to the "liquid" or flexible radio concept, the operations and functionalities may be performed in different entities, such as nodes, hosts or servers, in a flexible manner. In other words, division of labor may vary case by case. One possible use is to make a network element to deliver local content. One or more functionalities may also be implemented as a virtual application that is as software that can run on a server.

[0092] A user device or user equipment 420 may be a mobile station (MS) such as a mobile phone or smart phone or multimedia device, a computer, such as a tablet, provided with wireless communication capabilities, personal data or digital assistant (PDA) provided with wireless communication capabilities, portable media player, digital camera, pocket video camera, navigation unit provided with wireless communication capabilities or any combinations thereof. The user device or user equipment 420 may be a sensor or smart meter, or other device that may usually be configured for a single location.

[0093] In an exemplifying embodiment, an apparatus, such as a node or user device, may include means for carrying out embodiments described above in relation to Figure 2.

[0094] Processors 414 and 424 may be embodied by any computational or data processing device, such as a central processing unit (CPU), digital signal processor (DSP), application specific integrated circuit (ASIC), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), digitally enhanced circuits, or comparable device or a combination thereof. The processors may be implemented as a single controller, or a plurality of controllers or processors. Additionally, the processors may be implemented as a pool of processors in a local configuration, in a cloud configuration, or in a combination thereof.

[0095] For firmware or software, the implementation may include modules or unit of at least one chip set (e.g., procedures, functions, and so on). Memories 415 and 425 may independently be any suitable storage device, such as a non-transitory computer-readable medium. A hard disk drive (HDD), random access memory (RAM), flash memory, or other suitable memory may be used. The memories may be combined on a single integrated circuit as the processor, or may be separate therefrom. Furthermore, the computer program instructions may be stored in the memory and which may be processed by the processors can be any suitable form of computer program code, for example, a compiled or interpreted computer program written in any suitable programming language. The memory or data storage entity is typically internal but may also be external or a combination thereof, such as in the case when additional memory capacity is obtained from a service provider. The memory may be fixed or removable.

[0096] The memory and the computer program instructions may be configured, with the processor for the particular device, to cause a hardware apparatus such as network element 410 and/or UE 420, to perform any of the processes described above (see, for example, Figure 2).

Therefore, in certain embodiments, a non-transitory computer-readable medium may be encoded with computer instructions or one or more computer program (such as added or updated software routine, applet or macro) that, when executed in hardware, may perform a process such as one of the processes described herein. Computer programs may be coded by a programming language, which may be a high-level programming language, such as objective-C, C, C++, C#, Java, etc., or a low-level programming language, such as a machine language, or assembler. Alternatively, certain embodiments of the invention may be performed entirely in hardware.

[0097] Furthermore, although Figure 4 illustrates a system including a network element 410 and a UE 420, embodiments of the invention may be applicable to other configurations, and configurations involving additional elements, as illustrated and discussed herein. For example, multiple user equipment devices and multiple network elements may be present, or other nodes providing similar functionality, such as nodes that combine the functionality of a user equipment and an access point, such as a relay node.

[0098] Certain embodiments may have various advantages and/or benefits. For example, certain embodiments may provide maximum scalability with small overhead. Furthermore, in certain embodiments there may be no extra signaling required between different operators. Additionally, certain embodiments may provide the possibility of coordinated operation ("Reuse- 1") within one operator. Also, certain embodiments may provide fair interference avoidance between different operators.

[0099] Certain embodiments may be applicable for both frame based equipment as well as load based equipment and may be equally applicable for DL and UL operation. Additionally, certain embodiments may facilitate frequency domain multiplexing of multiple UEs in the case of UL operation.

[0100] Certain embodiments make an assumption that listen before talk (LBT) procedure is based on European regulatory rules defined for 5 GHz ISM band. However, certain embodiments may also be relevant to other implementations.

[0101] Although certain embodiments have been described relative to LAA, it should be understood that various embodiments may be applicable to scenarios other than those in LAA. For example, certain embodiments may be applicable to co-primary sharing between operators, flexible spectrum usage, and the like.

[0102] An LBT solution applicable to LAA, for example including both multi-operator LTE and WiFi, may be useful for those scenarios. Nevertheless, it should be understood that those other scenarios are not excluded. Thus, the above illustrations can also be applied, in certain embodiments, to non-LAA situations, such as other co-existence scenarios.

[0103] For example, Licensed Shared Access (LSA) is an example of such another scenario. LSA is spectrum sharing concept enabling access to spectrum that is identified for IMT but not cleared for IMT deployment. LSA is focused on bands subject to harmonization and standardized by 3GPP (2.3 GHz in EU & China, 1.7 GHz and 3550-3650 MHz in US).

[0104] Co-primary sharing is another example. Co-primary sharing refers to spectrum sharing where several primary users or operators share the spectrum dynamically or semi-statically. Suitable spectrum, for example for small cells, may exist at 3.5 GHz. Spectrum sharing between operators may happen if regulators enforce it and/or operators need it.

[0105] One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention.

[0106] Partial Glossary

[0107] 3GPP Third Generation Partnership Program

[0108] ACK Acknowledgement

[0109] CC Component Carrier

[0110] CCA Clear Channel Assessment or Assignment

[0111] CP Cyclic Prefix

[0112] CRS Common Reference Signal

[0113] CRW Channel Reservation Window

[0114] CSI-RS Channel State Information Reference Signal

[0115] DL Downlink

[0116] DTX Discontinuous Transmission [0117] DwPTS Downlink Pilot Time Slot

[0118] eCCA extended CCA

[0119] e.i.r.p. equivalent isotropically radiated power

[0120] elMTA Enhanced Interference Mitigation and Traffic Adaptation (the name of

WI tar geting to flexible UL/DL adaptation for TD-LTE)

[0121] eNB enhanced or evolved Node B (base station according to LTE terminology)

[0122] EPDCCH Enhanced PDCCH

[0123] FBE Frame Based Equipment

[0124] HARQ Hybrid Automatic Repeat ReQuest

[0125] ISM Industrial, Scientific and Medical

[0126] LAA License Assisted Access

[0127] LBE Load Based Equipment

[0128] LBT Listen Before Talk

[0129] LTE Long Term Evolution

[0130] LTE LAA LTE License Assisted Access

[0131] NCT New Carrier Type

[0132] OFDM Orthogonal Frequency Division Multiplexing

[0133] OFDMA OFDM Access

[0134] PCell Primary Cell

[0135] PDCCH Physical Downlink Control Channel

[0136] PHICH Physical HARQ Indicator Channel

[0137] PLMN Public Land Mobile Network

[0138] PSS Primary Synchronization Signal

[0139] PUCCH Physical Uplink Control Channel

[0140] PUSCHPhysical Uplink Shared Channel

[0141] RAN Radio Access Network

[0142] Rel Release

[0143] SCell Secondary Cell

[0144] SDL Supplementary DL

[0145] SI Study Item

[0146] sss Secondary Synchronization Signal

[0147] TD, TDD Time Division duplex

[0148] TL Threshold Level

[0149] UL Uplink

[0150] UpPTS Uplink Pilot Time Slot

X2 X2 is an interface used to communication between eNBs

Claims

CLAIMS WE CLAIM:

1. A method, comprising:

providing multiple clear channel assessment slots at an end of an idle period; and assigning a clear channel assessment pattern for each cell of a plurality of cells.

2. The method of claim 1, wherein the clear channel assessment pattern comprises a clear channel assessment slot number to indicate in which clear channel assessment slot to perform clear channel assessment.

3. The method of claim 1, wherein the clear channel assessment pattern comprises a counter value.

4. The method of claim 1, wherein the assigning comprises generating the clear channel assessment pattern with a pseudo-random generator.

5. The method of claim 1, wherein the assigning is performed in dependence on at least one of a public land mobile network identifier, a subframe number, or a slot number.

6. The method of claim 1, wherein multiple clear channel assessment slots have a clear channel assessment slot length equal to an orthogonal frequency division multiple access symbol.

7. The method of claim 1, wherein multiple clear channel assessment slots have a clear channel assessment slot length equal to a fraction of an orthogonal frequency division multiple access symbol.

8. A method, comprising:

performing clear channel assessment before starting data transmitting; and

conditionally transmitting data based on a result of the clear channel assessment and a clear channel assessment pattern.

9. The method of claim 8, further comprising:

monitoring a clear channel assessment slot to determine whether the channel is unoccupied.

10. The method of claim 9, further comprising:

transmitting data from the beginning of the frame period when the clear channel assessment indicates that the channel is unoccupied.

11. The method of claim 9, further comprising:

when the clear channel assessment indicates that the channel is unoccupied, transmitting a reservation signal from the beginning of next clear channel assessment slot until the end of the idle period.

12. The method of claim 9, further comprising:

transmitting data immediately when the clear channel assessment indicates that the channel is unoccupied.

13. The method of claim 9, further comprising: decrementing a counter when a value of the counter is greater than zero and the clear channel assessment indicates that the channel is unoccupied.

14. The method of claim 13, further comprising:

transmitting data when the counter is equal to zero.

15. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to

provide multiple clear channel assessment slots at an end of an idle period; and

assign a clear channel assessment pattern for each cell of a plurality of cells.

16. The apparatus of claim 15, wherein the clear channel assessment pattern comprises a clear channel assessment slot number to indicate in which clear channel assessment slot to perform clear channel assessment.

17. The apparatus of claim 15, wherein the clear channel assessment pattern comprises a counter value.

18. The apparatus of claim 15, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to, in assigning the clear channel assessment pattern, generate the clear channel assessment pattern with a pseudo- random generator.

19. The apparatus of claim 15, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to perform the assignment in dependence on at least one of a public land mobile network identifier, a subframe number, or a slot number.

20. The apparatus of claim 15, wherein multiple clear channel assessment slots have a clear channel assessment slot length equal to an orthogonal frequency division multiple access symbol.

21. The apparatus of claim 15, wherein multiple clear channel assessment slots have a clear channel assessment slot length equal to a fraction of an orthogonal frequency division multiple access symbol.

22. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

perform clear channel assessment before starting data transmitting; and

conditionally transmit data based on a result of the clear channel assessment and a clear channel assessment pattern.

23. The apparatus of claim 22, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to monitor a clear channel assessment slot to determine whether the channel is unoccupied.

24. The apparatus of claim 23, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to transmit data from the beginning of the frame period when the clear channel assessment indicates that the channel is unoccupied.

25. The apparatus of claim 23, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to, when the clear channel assessment indicates that the channel is unoccupied, transmit a reservation signal from the beginning of next clear channel assessment slot until the end of the idle period.

26. The apparatus of claim 23, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to transmit data immediately when the clear channel assessment indicates that the channel is unoccupied.

27. The apparatus of claim 23, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to decrement a counter when a value of the counter is greater than zero and the clear channel assessment indicates that the channel is unoccupied.

28. The apparatus of claim 27, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to transmit data when the counter is equal to zero.

29. The apparatus of claim 23, wherein the clear channel assessment pattern comprises a clear channel assessment slot number to indicate in which clear channel assessment slot to perform clear channel assessment.

30. The apparatus of claim 23, wherein the clear channel assessment pattern comprises a counter value.

31. The apparatus of claim 30, wherein the counter value is reset with a pseudo-random clear channel assessment pattern value at predefined time instances, regardless of an enhanced clear channel assessment procedure state.

32. The apparatus of claim 31, wherein the resetting frequency of the counter value adapts to the current interference or load situation.

33. A non-transitory computer-readable medium encoded with instructions that, when executed in hardware, perform a process, the process comprising the method according to any of claims 1-14.