WO2019036909A1

WO2019036909A1 - Method, computer program and apparatus

Info

Publication number: WO2019036909A1
Application number: PCT/CN2017/098534
Authority: WO
Inventors: Mieszko Chmiel; Ji Heng ZHANG; Hui Peng; Steffen Schulz
Original assignee: Nokia Technologies Oy
Priority date: 2017-08-22
Filing date: 2017-08-22
Publication date: 2019-02-28

Abstract

A method of a node accessing an unlicensed channel comprising: performing, by the node, a determination of whether an unlicensed channel the node requires access to is expected to be busy or idle in a period during which the node wants to transmit data, or in a period during which the node wants to perform clear channel assessment prior to transmission of data from the node; and accessing the channel in a manner dependent upon a result of the determination, the accessing the channel including performing a clear channel assessment of the channel.

Description

Method, Computer Program and Apparatus

Field

This disclosure relates to communications, and more particularly to a method, computer program and apparatus in a wireless communication system. More particularly the present invention relates to clear channel access timing in a wireless communication system.

Background

A communication system can be seen as a facility that enables communication between two or more devices such as user terminals, machine-like terminals, base stations and/or other nodes by providing communication channels for carrying information between the communicating devices. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication may comprise, for example, communication of data for carrying data for voice, electronic mail (email) , text message, multimedia and/or content data communications and so on. Non-limiting examples of services provided include two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

In a wireless system at least a part of communications occurs over wireless interfaces. Examples of wireless systems include public land mobile networks (PLMN) , satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN) . A local area wireless networking technology allowing devices to connect to a data network is known by the tradename WiFi (or Wi-Fi) . WiFi is often used synonymously with WLAN. The wireless systems can be divided into cells, and are therefore often referred to as cellular systems. A base station provides at least one cell.

A user can access a communication system by means of an appropriate communication device or terminal capable of communicating with a base station. Hence nodes like base stations are often referred to as access points. A communication device of a user is often referred to as user equipment (UE) . A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling communications with the base station and/or communications directly with other user devices. The communication device can communicate on appropriate channels, e.g. listen to a channel on which a station, for example a base station of a cell, transmits.

A communication system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. Communication protocols and/or parameters which shall be used for the connection are also typically defined. Non-limiting examples of standardised radio access technologies include GSM (Global System for Mobile) , EDGE (Enhanced Data for GSM Evolution) Radio Access Networks (GERAN) , Universal Terrestrial Radio Access Networks (UTRAN) and evolved UTRAN (E-UTRAN) . An example communication system architecture is the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The LTE is standardized by the third Generation Partnership Project (3GPP) . The LTE employs the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access and a further development thereof which is sometimes referred to as LTE Advanced (LTE-A) .

Since introduction of fourth generation (4G) services increasing interest has been paid to the next, or fifth generation (5G) standard. 5G may also be referred to as a New Radio (NR) network. Standardization of 5G or New Radio networks is an on-going study item.

3GPP LTE Rel-13 specifies a functionality know as Licensed Assisted Access (LAA) . LAA allows for an increase in transmission/reception bandwidth by aggregating cells or component carriers. Typically the primary cell is on a licensed carrier while the secondary cell (s) are on unlicensed carrier (s) . An unlicensed carrier may be, for example, a Wi-Fi connection. LAA may enable increased peak data rates, fast load balancing and fair coexistence with other technologies (for example Wi-Fi) without the additional costs of SCell (s) in the licensed spectrum.

Statement of invention

According to a first aspect there is provided: a method of a node accessing an unlicensed channel comprising: performing, by the node, a determination of whether an unlicensed channel the node requires access to is expected to be busy or idle in a period during which the node wants to transmit data, or in a period during which the node wants to perform clear channel assessment prior to transmission of data from the node； and accessing the channel in a manner dependent upon a result of the determination, the accessing the channel including performing a clear channel assessment of the channel.

According to some embodiments, the determination of whether the channel is expected to be busy or idle being based upon whether the channel was busy or idle during one or more previous clear channel assessments.

According to some embodiments, when the channel is expected to be idle, the method comprises starting clear channel assessment as late as possible.

According to some embodiments, starting clear channel assessment as late as possible comprises a minimum clear channel assessment time before a data transmission period.

According to some embodiments, a duration of a reservation signal transmission period for the channel is based on a determination of whether the clear channel assessment is performed within a threshold time.

According to some embodiments the threshold time comprises a minimum clear channel assessment time.

According to some embodiments, the reservation signal duration is zero if the clear channel assessment is performed in a time that is less than or equal to the threshold time, and the reservation signal duration is greater than zero when the clear channel assessment is performed in a time that is greater than the threshold time.

According to some embodiments, when the channel is expected to be busy the method comprises starting the clear channel assessment as soon as possible.

According to some embodiments starting the clear channel assessment as soon as possible comprises starting the clear channel assessment immediately after a previous transmission has been completed.

According to some embodiments starting the clear channel assessment as soon as possible comprises starting the clear channel assessment within a minimum clear channel assessment time plus one slot duration before a data transmission period.

According to some embodiments starting the clear channel assessment as soon as possible comprises starting the clear channel assessment within a minimum clear channel assessment time plus one subframe duration before a data transmission period.

According to some embodiments, the reservation signal duration is greater than zero if the clear channel assessment is performed in a time that is less than or equal to the threshold time, and the reservation signal duration is greater than or equal to zero when the clear channel assessment is performed in a time that is greater than the threshold time.

According to some embodiments, the channel is expected to be idle if, during the one or more previous clear channel assessments, the channel was continuously idle.

According to some embodiments, the channel is expected to be busy if, during the one or more previous clear channel assessments, the channel was busy at least once.

According to some embodiments, the node comprises a user equipment.

According to some embodiments, the node comprises a base station.

According to some embodiments, the base station comprises an eNB.

According to a second aspect there is provided a computer program comprising program code means adapted to perform the steps of the first aspect when the program is run on a data processing apparatus.

According to a third aspect there is provided 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: perform a determination of whether an unlicensed channel the apparatus requires access to is expected to be busy or idle in a period during which the apparatus wants to transmit data, or in a period during which the apparatus wants to perform clear channel assessment prior to transmission of data from the apparatus； and access the channel in a manner dependent upon a result of the determination, the accessing the channel including performing a clear channel assessment of the channel.

According to some embodiments, the channel is expected to be idle, the apparatus is configured to start clear channel assessment as late as possible.

According to some embodiments, a duration of a reservation signal transmission period for the channel is based on a determination by the apparatus of whether the clear channel assessment is performed within a threshold time.

According to some embodiments, the reservation signal duration is zero if the clear channel assessment is performed by the apparatus in a time that is less than or equal to the threshold time, and the reservation signal duration is greater than zero when the clear channel assessment is performed by the apparatus in a time that is greater than the threshold time.

According to some embodiments, when the channel is expected to be busy the apparatus is configured to start the clear channel assessment as soon as possible.

According to some embodiments, the reservation signal duration is greater than zero if the clear channel assessment is performed by the apparatus in a time that is less than or equal to the threshold time, and the reservation signal duration is greater than or equal to zero when the clear channel assessment is performed by the apparatus in a time that is greater than the threshold time.

According to some embodiments, the apparatus comprises a user equipment.

According to some embodiments, the apparatus comprises a base station.

According to some embodiments, the base station comprises an eNB.

Brief description of Figures

The invention will now be described in further detail, by way of example only, with reference to the following examples and accompanying drawings, in which:

Figure 1 shows a schematic example of a wireless communication system where the invention may be implemented；

Figure 2 shows an example of a communication device；

Figure 3 shows an example of a control apparatus；

Figure 4 shows a timing diagram according to an example；

Figure 5 shows a timing diagram according to an example；

Figure 6 shows a timing diagram according to an example；

Figures 7A and 7B show an example of determining a minimum CCA time；

Figure 8 shows a flow chart of a method according to an example.

Detailed description

Before explaining in detail the examples, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figures 1 to 2 to assist in understanding the technology underlying the described examples.

In a wireless communication system 100, such as that shown in Figure 1, a wireless communication devices, for example, user equipment (UE) or

MTC devices

102, 104, 105 are provided wireless access via at least one base station or similar wireless transmitting and/or receiving wireless infrastructure node or point. Such a node can be, for example, a base station or an eNodeB (eNB) , or other wireless infrastructure node. These nodes will be generally referred to as base stations. Base stations are typically controlled by at least one appropriate controller apparatus, so as to enable operation thereof and management of mobile communication devices in communication with the base stations. The controller apparatus may be located in a radio access network (e.g. wireless communication system 100) or in a core network (CN) (not shown) and may be implemented as one central apparatus or its functionality may be distributed over several apparatus. The controller apparatus may be part of the base station and/or provided by a separate entity such as a Radio Network Controller. In Figure 1

control apparatus

108 and 109 are shown to control the respective macro

level base stations

106 and 107. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller. Other examples of radio access system comprise those provided by base stations of systems that are based on technologies such as 5G or new radio, wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access) . A base station can provide coverage for an entire cell or similar radio service area.

In Figure 1

base stations

106 and 107 are shown as connected to a wider communications network 113 via gateway 112. A further gateway function may be provided to connect to another network.

The

smaller base stations

116, 118 and 120 may also be connected to the network 113, for example by a separate gateway function and/or via the controllers of the macro level stations. The

base stations

116, 118 and 120 may be pico or femto level base stations or the like. In the example,

stations

116 and 118 are connected via a gateway 111 whilst station 120 connects via the controller apparatus 108. In some embodiments, the smaller stations may not be provided.

A possible wireless communication device will now be described in more detail with reference to Figure 2 showing a schematic, partially sectioned view of a communication device 200. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a “smart phone” , a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle) , personal data assistant (PDA) or a tablet provided with wireless communication capabilities, or any combinations of these or the like. A mobile communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email) , text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services comprise two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content comprise downloads, television and radio programs, videos, advertisements, various alerts and other information.

A wireless communication device may be for example a mobile device, that is, a device not fixed to a particular location, or it may be a stationary device. The wireless device may need human interaction for communication, or may not need human interaction for communication. In the present teachings the terms UE or “user” are used to refer to any type of wireless communication device.

The wireless device 200 may receive signals over an air or radio interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the wireless device.

A wireless device is typically provided with at least one data processing entity 201, at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 204. The user may control the operation of the wireless device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a wireless communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto. The

communication devices

102, 104, 105 may access the communication system based on various access techniques.

Figure 3 shows an example of a control apparatus for a communication system, for example to be coupled to and/or for controlling a station of an access system, such as a RAN node, e.g. a base station, eNB, a central unit of a cloud architecture or a node of a core network such as an MME or S-GW, a scheduling entity such as a spectrum management entity, or a server or host. The control apparatus may be integrated with or external to a node or module of a core network or RAN. In some embodiments, base stations comprise a separate control apparatus unit or module. In other embodiments, the control apparatus can be another network element such as a radio network controller or a spectrum controller. In some embodiments, each base station may have such a control apparatus as well as a control apparatus being provided in a radio network controller. The control apparatus 300 can be arranged to provide control on communications in the service area of the system. The control apparatus 300 comprises at least one memory 301, at least one

data processing unit

302, 303 and an input/output interface 304. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. The receiver and/or the transmitter may be implemented as a radio front end or a remote radio head. For example the control apparatus 300 or processor 201 can be configured to execute an appropriate software code to provide the control functions.

The present disclosure relates to timing of Clear Channel Assessment (CCA) , also known as listen before talk (LBT) . In CCA an assessment is made of a channel state before performing a transmission. For example the assessment may involve checking that the channel is free from other transmissions. An LAA node may be, for example, a user equipment.

The present inventors have recognised that an LAA node needs to successfully complete a Clear Channel Assessment before transmitting on an unlicensed carrier. CCA timing is not specified by 3GPP.

Typically an LAA node can start data transmission only on a subframe (1ms) or a slot boundary (0.5ms) which is coarser compared to, for example, Wi-Fi timing. Therefore the channel may be grabbed by another node or nodes using the Wi-Fi, meaning that the LAA node is unable to use the channel, or is at least delayed in using the channel. 3GPP currently implements two ways of attempting to deal with this.

A first way, as disclosed in TS36.213, Rel-13, section 15.1.1, may be considered CCA with self-deferral where, after completing CCA, the LAA node remains silent until the next subframe/slot-boundary, and then performs another short CCA before the slot/subframe boundary. This options gives a relatively low overhead, but there is a risk that other nodes with much finer timing (e.g. Wi-Fi) will take or grab the available medium while the LAA node waits in an idle state.

A second way, as disclosed in R1-153873, “Reservation Signal Design for LAA” , Qualcomm, may be considered CCA with a reservation signal where, after completing CCA, the LAA node transmits a reservation signal (or initial signal) until the next subframe/slot boundary, and then transmits useful data in the slot/subframe boundary. In this option the reservation signal prevents other nodes from grabbing or assuming the channel, although there is relatively higher overhead compared to the first way discussed above.

Additionally, a total transmission duration of one burst (including the reservation signal (if any) and data transmission) is limited by Maximum Channel Occupancy Time (T_mcot, p) , defined in TS 36.213, Rel-13, section 15.1.1.

Generally speaking, as identified by the present inventors, current proposals have a disadvantage that either the probability of accessing the medium is reduced, or peak data rate/channel occupancy is reduced.

Accordingly, and as explained in more detail below, it is proposed that if a channel is expected to be idle during CCA then the channel occupancy time can be maximised by starting the CCA as late as possible to avoid or reduce reservation signal overhead. “As late as possible” may also be referred to as a minimum CCA time before the intended data transmission. Otherwise (i.e. if the channel is not expected to be idle during the CCA) , then the probability of accessing or grabbing the channel can be maximised by starting the CCA as soon as possible. “As soon as possible” may be considered immediately after a previous transmission has been completed. That is the CCA may be started in response to determining that a previous data transmission has been completed. Alternatively as soon as possible may be considered to mean a minimum CCA time plus one slot duration (e.g. 0.5 ms) before the intended useful transmission. Alternatively as soon as possible may be considered to mean a minimum CCA time plus one subframe duration (e.g. 1ms) before the intended useful transmission.

The “as late as possible” timing may be determined based upon how long it takes for CCA to be completed. For example:

IF the CCA is completed within a minimum or threshold time

THEN

reservation signal duration ＝0

ELSE

the reservation signal duration >＝0

With the “as soon as possible” timing,

IF the CCA is completed within a minimum or threshold time

THEN

the reservation signal duration > 0

ELSE

the reservation signal duration >＝0

The “minimum” time is not necessarily fixed to a specific value. The “minimum” CCA time may be considered a quickest time in which CCA can be completed. That is the minimum CCA time may be considered a quickest possible time in which CCA can be completed. In some examples, the minimum CCA time may only be possible when the channel is idle during that time. The minimum time could take different values dependent on situation. The attached tables shown in Figure 7A and Figure 7B show some examples. In some examples the min CCA time depends on the access priority class p and on the random draw N_init as shown in the Tables. The Tables only show minimum CCA time for min and max N_init but N_init can be any integer from 0 to CW_p, max. In the Figure 7A example N_init is minimal. In the Figure 7B example N_init is maximal.

Figure 4 shows an example UML timing diagram. This timing diagram assumes a typical case of channel access priority p ＝ 3, and maximum channel occupancy T_mcot, p ＝ 8ms, (RX-TX and TX-RX switching time is assumed to be <＝5 us i.e. fully hidden in the CCA state) .

As shown, this timing diagram shows four states of an LAA node: idle 402, CCA 404, TX reservation signal 406 and TX data 408.

Initially the LAA node is in a transmission state, as shown at 410. At time t＝0 the LAA node enters an idle state, as shown at 412. In this example the channel is expected to be idle, so CCA starts as late as possible (ALAP) . That is, according to some embodiments, when the channel is expected to be idle, clear channel assessment is started as late as possible. In this example the CCA is completed in the minimum CCA time. This assumes N_init＝31 i.e. 43+ (31*9) ＝ 322us. In this example the value of 43 is calculated from T_d_p ＝ T_f (＝16us) + m_p (＝3) *T_sl (＝9us) (see Tables in Figures 7A and 7B) . T_d_p T_f and T_sl and m_p are defined in 3GPP 36.213. N_init is a random initialization of the CCA back-off counter N (uniform random draw from [0, CW_p] ) . Then the CCA starts at time a-322us, as shown at 414. “a” is a time value. In the time scale of Figure 4, a ＝ 1ms.

Assuming the channel is clear, the LAA node can move to a Tx data state, as shown at 416. In this example the data transmission duration ＝ 8ms ＝ T_mcot, p, where T_mcot, p is the maximum channel occupancy time. That is the LAA node occupies the channel for the maximum time possible.

Following this the LAA node enters the idle state again, as shown at 418. The LAA node starts CCA again at time b-322us (assuming N_init＝31 and 10 collisions) . The “collisions” may be with other nodes attempting to access the channel, as shown at 420. Again, the channel is expected to be idle, and the CCA starts ALAP but in this case takes longer than the minimum or threshold CCA time. That is in this example case the CCA takes 752us. Accordingly, as explained above, the LAA node transmits a Tx reservation signal as shown at 422, to reserve space on the channel for transmission.

In some embodiments, a duration of a reservation signal transmission period for the channel is based on a determination of whether the clear channel assessment is performed within the threshold (or minimum) time.

In some examples the reservation signal duration is zero if the clear channel assessment is performed in a time that is less than or equal to the threshold (or minimum) time, and the reservation signal duration is greater than zero when the clear channel assessment is performed in a time that is greater than the threshold (or minimum) time.

In some examples the reservation signal duration is greater than zero if the clear channel assessment is performed in a time that is less than or equal to the threshold time, and the reservation signal duration is greater than or equal to zero when the clear channel assessment is performed in a time that is greater than the threshold time.

Following on from this the LAA node enters the Tx data state as shown at 424. The Tx data state 424 lasts for a duration of 7ms (i.e. <T_mcot, p) . That is the Tx data duration 424 is less than Tx data duration 416, at least in part due to time spent in sending the Tx reservation signal as shown at 422.

Following this, as shown at 426 the LAA node reverts to the CCA state, as shown at 426. The node reverts to the CCA state rather than the idle state because the channel is expected to be busy. Since the channel is expected to be busy, the CCA starts ASAP (as soon as possible) , and the LAA does not revert to the idle state. In this example the CCA takes longer than the minimum or threshold CCA time (assuming N_init＝31 and 10 collisions i.e. 43 + (31*9) + (10*43) ＝ 752us. Due to the channel being expected to be busy, the LAA node transmits a Tx reservation signal as shown at 428, so as to reserve transmission time on the channel. The data transmission is shown at 430. In this example the Tx data transmission has a duration of 7ms which is < T_mcot, p. Again, this is at least in part due to the time spent in sending the reservation signal.

As shown at 432, the node then returns to an idle state.

Although Figure 4 shows three set-up and transmission phases in succession (shown generally at 434, 436 and 438) , it will be understood that this is by way of example only. Each or any number of these “phases” or instances can occur in isolation from each other, or in any order or combination. Furthermore in Figure 4 the N_init and number of collisions is considered constant, which may in some scenarios be unrealistic but is useful for the purposes of example at least (and such a scenario is not excluded) .

Figure 5 shows a similar UML timing diagram, although in this example N_init and the number of collisions are variable, which may be considered more realistic. Again, the LAA node has an idle state 502, a CCA state 504, a Tx reservation signal state 506, and a Tx data state 508. In a first transmission set-up phase 534 the channel is expected to be idle and therefore CCA starts ALAP. The CCA is completed in the minimum or threshold CCA time (assuming N_init ＝ 31 i.e. 43 +(31*9) ＝ 322us) . Accordingly the data duration for transmission can equal the maximum channel occupancy time, which in this example is 8ms, as shown at 516.

In the second phase 536, the channel is again expected to be idle so the CCA starts ALAP, but in this case it takes longer than the minimum CCA time (in this example assuming N_init ＝ 15 and 10 collisions) . That is according to some embodiments if the minimum CCA time is exceeded (with ALAP timing) , then a reservation signal is deemed to be required until the next subframe or slot start. Accordingly the LAA node enters the Tx reservation signal state 506, in which a reservation signal is transmitted. Following this, the LAA node enters the transmission state 508, and has a data duration of 7ms as shown at 524. This duration is less than the maximum occupancy window, due to the set-up time in reserving the channel. If the channel is busy then the CCA continues and the node is unable to transmit the reservation signal. When the reservation signal is transmitted there is no further checking of the channel, because this is a transmission rather than reception period. If the node has been through the Tx reservation signal state then the node may, in some embodiments, consider it a certainty that the node will enter the Tx data state. Following the Tx data phase 524, the LAA node reverts to CCA state 504. This is because, in this example, the channel is expected to be busy. In this example the channel is expected to be busy because there was at least one collision in the previous CCA. Alternatively, whether a channel is expected to be busy can be based on contention window size CW_p. Either method (collision or contention window size) can look back to the directly preceding CCA, or multiple previous CCAs (for example with some averaging) . Since the channel is expected to be busy the CCA is started ASAP. In this example the CCA takes longer than the minimum CCA time (Assuming N_init ＝ 10 and 15 collisions i.e. 43 + (10*9) + (15*43) ＝ 778us. Due to the CCA taking longer than the threshold or minimum time for the CCA, the LAA node then moves to the Tx reservation signal state 506 in order to reserve space on the channel. After this, the LAA node then enters the Tx data state 508 as shown at 530. The Tx data duration is, in this example phase, 7ms which is less than the maximum channel occupancy class. Following this the LAA node reverts to the idle state 502.

A further example is shown in Figure 6. In this example, in the first phase 634 the channel is expected to be busy so, following initial Tx state 608 the LAA node assumes CCA state 604 rather than idle state 602. The CCA state lasts longer than expected (in this example 752us) , due at least in part to there being collisions (10 in this example) . Due to the busy channel (or expectation that the channel will be busy) the LAA node transmits a reservation signal 606 to reserve space on the channel prior to entering data transmission phase 616.

After this, the LAA node reverts to the CCA state rather than the idle state, because again the channel is expected to be busy. In the second phase 636 the CCA is completed relatively quickly (in this example 178us) , at least in part due to there being no or relatively few collisions, and after Tx reservation signalling 606 is completed the LAA node enters the Tx data state 608 as shown at 624.

After the transmission phase 624 the LAA node reverts to idle state 602. In this example the node has reverted to idle, rather than CCA mode, due to the late start. In this example the minimum CCA time is 178us before the next subframe, so the node has 1000-178us ＝ 822us to be idle. Then, in the third phase 638 the channel is expected to be idle so the CCA starts ALAP and in this example is completed relatively quickly (178us) and within the minimum or threshold time. Due to completing the CCA within the threshold time it is determined by the LAA node that there is no need for transmitting a reservation signal for the channel, and so the LAA node moves from the CCA state 604 directly to the Tx data state 608. The LAA node can then occupy the channel for the maximum time available. Following this the LAA node reverts to the idle state 602.

From the above described examples it can be seen that the manner in which the node accesses the channel is dependent on an expected state of the channel. More particularly the method comprises determining whether an unlicensed channel the node requires access to is expected to be busy or idle: (a) in a period during which the node wants to transmit data, or (b) in a period during which the node wants to perform clear channel assessment prior to transmission of data from the node. The channel can then be accessed in a manner dependent on a result of the determination. The clear channel assessment is performed before the channel is accessed.

From the above described examples it can be seen that whether the channel is expected to be idle during the CCA can be determined based on the channel busy/collision occurrences in the previous CCA instance (s) . For example, if the channel was detected as busy at least once during the previous CCA (i.e. the CCA took longer than the minimum CCA time) then the channel is not expected to be idle during the next CCA. Or in other words it is determined or predicted that the channel will be busy. If the channel was detected as idle all the time during the previous CCA then the channel is expected to be idle during the next CCA. Or in other words it is determined or predicted that the channel will be idle (or not busy) . Therefore in some examples the determination of whether the channel is expected to be busy or idle is based upon whether the channel was busy or idle during one or more previous clear channel assessments. In an example, the channel is expected to be idle if, during the one or more previous clear channel assessments, the channel was continuously idle. In an example, the channel is expected to be busy if, during the one or more previous clear channel assessments, the channel was busy at least once.

In an alternative or complementary approach, determining if the channel is expected to be idle or busy during the CCA can be based on a contention window size (CW_p) and whether it increases/decreases. In some examples the contention window is used to initialize the back-off counter N by N_init randomly selected from 0..CW_p.

In some embodiments the LAA node comprises a UE. In some embodiments the LAA node comprises a base station, for example an eNB. In some embodiments the functionality may be implemented at the RF (radio frequency) and baseband. For example the baseband may select the timing options. Alternatively the functionality may be implemented at the RF level only. In such an example the RF may select the timing options.

In one alternative embodiment, instead of “Start the CCA as late as possible” , CCA with self-deferral may be used.

Alternatively an approach may be followed whereby “Start the CCA as soon as possible” is used, and if during this CCA the channel is continuously idle then self-deferral may be used instead of the reservation signal (as defined in 3GPP, or by not decrementing back-off counter N from 1 to 0 until immediately before the start of the next subframe/slot) . If the channel is busy during some instances of the CCA, then the reservation signal may be used from the time when the CCA is successfully completed until the next subframe/slot.

According to some embodiments, peak data rate is maximized in idle channel conditions. Channel occupancy may also be maximized in idle channel conditions. Furthermore, the probability of grabbing or using the unlicensed channel is maximized in busy channel conditions. According to some embodiments an algorithm providing the functionality automatically adapts to the current idle/busy channel conditions. The embodiments may also provide a relatively simple implementation because only one CCA method is implemented, but with a smartly controlled starting time. According to some examples, the support of partial starting subframe and/or partial ending subframe (optional UE features) are not required to implement the described functionality.

The phrase “as soon as possible” (ASAP) may be considered to mean that the CCA is entered immediately after, or in response to determination of, a given event. For example the event may be the determination of whether the channel is expected to be idle or busy. If the channel is expected to be busy, then the CCA is entered immediately (or in direct response) to the determination that the channel is expected to be busy (i.e. ASAP) .

The phrase “as late as possible” (ALAP) may be considered to mean that the CCA is entered after a delay following (or in response to determination of) a given event. For example the event may be the determination of whether the channel is expected to be idle or busy. If the channel is expected to be idle, then the CCA is entered after a delay following the determination that the channel is expected to be idle (i.e. ALAP) . ALAP may additionally or alternatively be considered to mean as late as possible before the transmission time window in question but which still allows just enough time for CCA to be completed.

Figure 7 is a flow chart showing a method according to an example.

At S1, a node performs a determination of whether an unlicensed channel the node requires access to is expected to be busy or idle in a period during which the node wants to transmit data, or in a period during which the node wants to perform clear channel assessment prior to transmission of data from the node.

At S2, the node accesses the channel in a manner dependent upon a result of the determination. The accessing the channel includes performing clear channel assessment of the channel.

In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the invention may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The embodiments of this invention may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer-executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media.

The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) , application specific integrated circuits (ASIC) , FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples.

Embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention as defined in the appended claims. Indeed there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

A method of a node accessing an unlicensed channel comprising:

performing, by the node, a determination of whether an unlicensed channel the node requires access to is expected to be busy or idle in a period during which the node wants to transmit data, or in a period during which the node wants to perform clear channel assessment prior to transmission of data from the node； and

accessing the channel in a manner dependent upon a result of the determination, the accessing the channel including performing a clear channel assessment of the channel.
A method according to claim 1, the determination of whether the channel is expected to be busy or idle being based upon whether the channel was busy or idle during one or more previous clear channel assessments.
A method according to claim 1 or claim 2, wherein when the channel is expected to be idle, the method comprises starting clear channel assessment as late as possible.
A method according to claim 3, wherein a duration of a reservation signal transmission period for the channel is based on a determination of whether the clear channel assessment is performed within a threshold time.
A method according to claim 4, wherein the reservation signal duration is zero if the clear channel assessment is performed in a time that is less than or equal to the threshold time, and the reservation signal duration is greater than zero when the clear channel assessment is performed in a time that is greater than the threshold time.
A method according to claim 1 or claim 2, wherein when the channel is expected to be busy the method comprises starting the clear channel assessment as soon as possible.
A method according to claim 6, wherein a duration of a reservation signal transmission period for the channel is based on a determination of whether the clear channel assessment is performed within a threshold time.
A method according to claim 7, wherein the reservation signal duration is greater than zero if the clear channel assessment is performed in a time that is less than or equal to the threshold time, and the reservation signal duration is greater than or equal to zero when the clear channel assessment is performed in a time that is greater than the threshold time.
A method according to claim 2, wherein the channel is expected to be idle if, during the one or more previous clear channel assessments, the channel was continuously idle.
A method according to claim 2, wherein the channel is expected to be busy if, during the one or more previous clear channel assessments, the channel was busy at least once.
A method according to any of claims 1 to 10, wherein the node comprises a user equipment.
A method according to any of claims 1 to 10, wherein the node comprises a base station.
A computer program comprising program code means adapted to perform the steps of any of claims 1 to 12 when the program is run on a data processing apparatus.
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:

perform a determination of whether an unlicensed channel the apparatus requires access to is expected to be busy or idle in a period during which the apparatus wants to transmit data, or in a period during which the apparatus wants to perform clear channel assessment prior to transmission of data from the apparatus； and

access the channel in a manner dependent upon a result of the determination, the accessing the channel including performing a clear channel assessment of the channel.
An apparatus according to claim 1, the determination of whether the channel is expected to be busy or idle being based upon whether the channel was busy or idle during one or more previous clear channel assessments.
An apparatus according to claim 14 or claim 15, wherein when the channel is expected to be idle, the apparatus is configured to start clear channel assessment as late as possible.
An apparatus according to claim 16, wherein a duration of a reservation signal transmission period for the channel is based on a determination by the apparatus of whether the clear channel assessment is performed within a threshold time.
An apparatus according to claim 17, wherein the reservation signal duration is zero if the clear channel assessment is performed by the apparatus in a time that is less than or equal to the threshold time, and the reservation signal duration is greater than zero when the clear channel assessment is performed by the apparatus in a time that is greater than the threshold time.
An apparatus according to claim 14 or claim 15, wherein when the channel is expected to be busy the apparatus is configured to start the clear channel assessment as soon as possible.
An apparatus according to claim 19, wherein a duration of a reservation signal transmission period for the channel is based on a determination by the apparatus of whether the clear channel assessment is performed within a threshold time.
An apparatus according to claim 20, wherein the reservation signal duration is greater than zero if the clear channel assessment is performed by the apparatus in a time that is less than or equal to the threshold time, and the reservation signal duration is greater than or equal to zero when the clear channel assessment is performed by the apparatus in a time that is greater than the threshold time.
An apparatus according to claim 15, wherein the channel is expected to be idle if, during the one or more previous clear channel assessments, the channel was continuously idle.
An apparatus according to claim 15, wherein the channel is expected to be busy if, during the one or more previous clear channel assessments, the channel was busy at least once.
An apparatus according to any of claims 14 to 23, wherein the apparatus comprises a user equipment.
An apparatus according to any of claims 14 to 23, wherein the apparatus comprises a base station.