WO2016072908A1

WO2016072908A1 - Dynamic listen before talk in license-assisted access

Info

Publication number: WO2016072908A1
Application number: PCT/SE2015/051138
Authority: WO
Inventors: Oscar Zee; Ashim Biswas; Daniel FIGUEIREDO; Damanjit Singh
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-11-06
Filing date: 2015-10-28
Publication date: 2016-05-12

Abstract

A method by a network node in a telecommunications system includes performing (602) a plurality of Listen Before Talk, LBT,attempts to access an air interface of a communication medium according to a first pattern, in response to the number of LBT attempts exceeding a threshold, performing (614) LBT according to a second pattern that is different from the first pattern, determining (624) that the air interface is available for transmission of data frames in response to performing LBT according to the second pattern and sending (606) a data frame over the air interface in response to determining that the air interface is available for transmission of the data frames.

Description

DYNAMIC LISTEN BEFORE TALK IN LICENSE-ASSISTED ACCESS

CLAIM OF PRIORITY

[0001] The present application claims the benefit of and priority to U.S. Provisional Patent Application No. 62/076,035, filed November 6, 2014, entitled "CONGESTION BASED DYNAMIC LISTEN BEFORE TALK (LBT)," the disclosure of which is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure is directed to communications and, more particularly, to wireless communication methods, networks, and network nodes.

BACKGROUND

[0003] License-Assisted Access via LTE (LAA-LTE) has been proposed as a technology for co-existence of 3rd-Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems on licensed carriers with unlicensed communication systems, such as wireless local area network (WLAN) communications systems.

[0004] IEEE 802.11 is a set of Media Access Control (MAC) and Physical layer (PHY) specifications for implementing WLAN computer communication in the 2.4, 3.6, 5 and 60 GHz frequency bands. The specifications are created and maintained by the IEEE Standards

Committee IEEE 802. The base version of the standard was released in 1997 and has had subsequent amendments. The standard and amendments provide the basis for wireless network products using Wi-Fi.

[0005] A wireless local area network (WLAN) links two or more devices using a wireless distribution method, and may also provide a connection through an access point to another network. This gives users the ability to move around within a local coverage area and still be connected to the network. All devices that can connect to the WLAN are referred to as stations. The wireless stations fall into one of two categories: access points and clients. Access points (AP), normally routers, are base stations for the wireless network. They transmit and receive signals at radio frequencies for wireless enabled devices. Wireless clients can be mobile devices, such as laptops, personal digital assistants, IP phones and other smartphones, or fixed devices, such as desktops and workstations, that are equipped with a wireless network interface. The IEEE 802.11 has two basic modes of operation: an ad hoc mode and an infrastructure mode. In the ad hoc mode, clients communicate directly peer-to-peer. In the infrastructure mode, clients communicate through an AP that serves as a bridge to other networks such as the Internet or a Local Area Network (LAN). The following sections summarize some IEEE 802.11 characteristics.

[0006] Wi-Fi systems based on the IEEE 802.11 standards have many aspects in common with cellular systems. One difference is the MAC protocol, which for cellular systems typically is scheduled, and for Wi-Fi is contention-based. This means that a receiving station does not know in advance which of the transmitting stations it will receive data from and what transmission format is used for this received data. The IEEE 802.11 MAC protocol is described in some more detail below.

[0007] The basic IEEE 802.11 MAC, the so-called Distributed Coordination Function (DCF), employs a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)-based MAC. The same protocol is applied by all stations including the APs, i.e. in both downlink and uplink transmissions. The standard also supports a Point Coordination Function (PCF) mode, in which APs have more control over the medium usage. Supporting the PCF mode is however optional, and rarely implemented.

[0008] As illustrated in Figure 1, a station using the DCF mode (User A) and wishing to transmit a frame first senses the medium. If the medium is sensed to be idle for a certain minimum time, i.e. a so-called Distributed Inter Frame Space (DIFS), the frame is transmitted. The DIFS is 50μ≤ in release IEEE 802.11b. If the medium is busy, as it is for user C in Figure 1, the station first waits until the medium is sensed idle (defer). When this occurs, the station defers the transmission during a DIFS. As an immediate transmission after the expiration of the DIFS may lead to collisions if more than one station is waiting to transmit data, each station sets a back-off timer to a random delay, and transmits only when this back-off timer has expired instead of transmitting immediately at the expiration of the DIFS. The back-off timer is only activated when the medium is sensed idle. Whenever the medium is sensed busy, a deferral state is entered in which the back-off timer is not activated. When the back-off timer expires, the frame is transmitted. If the frame is successfully received by a station, the receiving station responds with an acknowledgement to the transmitting station. The acknowledgement is sent a Short Inter Frame Space (SIFS) after the data frame is received. The SIFS is 10μ≤ in the release IEEE 802.11b. Since a SIFS is shorter than a DIFS, no other station will access the medium during this time. If no acknowledgement is received by the transmitting station, the transmitting station generates a new back-off timer value, and retransmits the frame when the new back-off timer has expired. The reason for not receiving any acknowledgement may be either because the transmitted frame is lost resulting in that no acknowledgement is returned or because the acknowledgement itself is lost. Even if the frame is successfully acknowledged, the transmitting station must generate a back-off timer value and wait for it to expire before transmitting the next frame. To avoid congestion when collisions occur, back-off timer values are drawn from distributions with larger and larger expected values every retransmission attempt. For the nth transmission attempt, the back-off timer value is drawn from the uniform distribution

U[0,min((CWmin)*2n-l - 1, CWmax)]. CWmin and CWmax are constants with values that depend on the physical layer. For the release IEEE 802.11b the values are CWmin = 31 and CWmax = 1023. The back-off timer value is measured in units of slot times, which for release IEEE 802.11b are 20 μ≤ long.

[0009] In the Enhanced DCF mode, defined in release IEEE 802. lie standard, service prioritization is introduced. This is done by using back-off and deferral parameters that depend on a service type.

[0010] Since frames are transmitted after a DIFS when the medium is free, the minimum delay is equal to the transmission time plus a DIFS, which for release IEEE 802.11b is about 1 ms for a 1500 byte frame. The almost immediate acknowledgement, with a

transmission time of around 0.1ms, means that the Round Trip Time (RTT) on layer 2 may be of the order of 1 ms. [0011] Because of the back-off and deferral times between transmissions, the medium is not fully used even at high traffic loads. The maximum link utilization reached depends on the frame size, and varies between 50% for voice traffic to 70-80% for data traffic.

[0012] The approaches described in the Background section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in the Background section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in the Background section.

SUMMARY

[0013] A method by a network node in a telecommunications system includes performing (602) a plurality of Listen Before Talk (LBT) attempts to access an air interface of a communication medium according to a first pattern, in response to the number of LBT attempts exceeding a threshold, performing (622) LBT according to a second pattern that is different from the first pattern, determining (624) that the air interface is available for transmission of data frames in response to performing LBT according to the second pattern, and sending (606) a data frame over the air interface in response to determining that the air interface is available for transmission of data frames.

[0014] Performing LBT in this manner may enhance the effectiveness of LBT in gaining the use of a secondary channel for data transmission by a network node using license-assisted access.

[0015] The method may further include sending a clear-to-send-to-self (CTS-to-self) message over the air interface in response to determining that the air interface is available for transmission of the data frames.

[0016] Performing LBT according to the second pattern may include listening (701) to the air interface continuously until an earlier occurrence of at least one of an expiration of a timeout duration or a determination that the air interface is available for transmission of the data frames. [0017] The method may further include indicating (801) that the data frame should be discarded and/or retransmitted, based on a determination that the air interface is not available during the timeout duration.

[0018] The method may further include waiting (612) for expiration of a back-off time before performing LBT according to the second pattern. The back-off time may include a random time period. The method may further include defining (901) the back-off time duration based on a fixed Transmission Time Interval (TTI).

[0019] The method may further include defining (1001) the threshold number of LBT attempts and/or the timeout duration based on Quality of Service (QoS) requirements for the data frames.

[0020] The method may further include determining (1101) a back-off period of time to wait before performing LBT according to the second pattern in response to a number of unsuccessful LBT attempts. The back-off period of time may further be determined (1201) based on prioritization of data frames and/or or based on Quality of Service (QoS)

requirements.

[0021] Performing LBT according to the first pattern may include performing LBT with a first periodicity, and performing LBT according to the second pattern may include performing LBT with a second periodicity that is smaller than the first periodicity.

[0022] Performing LBT according to the first pattern may include performing LBT with a first periodicity, and performing LBT according to the second pattern may include performing LBT with a second periodicity that decreases with time.

[0023] The method may further include waiting for a back-off time between the performing LBT according to the first pattern and the performing LBT according to the second pattern. The back-off time may include a random back-off time.

[0024] The method may further include ceasing to perform LBT according to the second pattern in response to the expiration of a timeout duration, and indicating (801) that the data frame should be discarded and/or retransmitted, based on a determination that the air interface was not available during the timeout duration. [0025] The air interface may include a primary channel in a licensed band and a secondary channel in an unlicensed band, wherein the data frames are transmitted in the secondary channel in the unlicensed band.

[0026] The first LBT pattern may include listening to the air interface periodically, and the second LBT pattern may include listening to the air interface continuously.

[0027] The first LBT pattern may include listening to the air interface periodically, and

[0028] the second LBT pattern may include listening to the air interface in time periods increasing in frequency.

[0029] A network node according to some embodiments includes a processor circuit (1902, 2002), a transceiver (1920, 2030) coupled to the processor circuit, and a memory circuit (1910, 2010) comprising computer readable program code (1912, 2012). The computer readable program code is configured to cause the processor circuit to execute the operations of performing (602) a number of Listen Before Talk (LBT) attempts to access an air interface of a communication medium according to a first LBT pattern, in response to the number of LBT attempts exceeding a threshold number of LBT attempts, performing (622) LBT according to a second pattern that is different from the first pattern, determining (624) that the air interface is available for transmission of data frames in response to performing LBT according to the second pattern, and sending (606) a data frame over the air interface in response to

determining that the air interface is available for transmission of the data frames.

[0030] A network node according to some embodiments includes a processor circuit (1902, 2002), a memory circuit (1910, 2010) coupled to the processor and comprising computer readable program code (1912, 2012), and a transceiver (1920, 2030) coupled to the processor circuit. The computer readable program code may include an LBT module (2014) for performing (602) a number of Listen Before Talk (LBT) attempts to access an air interface of a communication medium according to a first LBT pattern, in response to the number of LBT attempts exceeding a threshold number of LBT attempts, performing (622) LBT according to a second pattern that is different from the first pattern, and determining (624) that the air interface is available for transmission of data frames in response to performing LBT according to the second pattern, and a sending module (2018) for sending (606) a data frame over the air interface in response to determining that the air interface is available for transmission of the data frames.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which are included to provide a further

understanding of the disclosure and are incorporated in and constitute a part of this

application, illustrate certain non-limiting embodiment(s) of inventive concepts. In the drawings:

[0032] Figure 1 illustrates a Distributed Coordination Function (DCF) for a user attempting to transmit a data frame.

[0033] Figure 2 illustrates a hidden node in a wireless communication network, according to some embodiments.

[0034] Figure 3 illustrates an LAA-LTE system using LBT where a network node has increased latency in accessing the medium, according to some embodiments.

[0035] Figures 4, 5A and 5B illustrates LAA-LTE systems using LBT according to some embodiments.

[0036] Figures 6A to 17 are flowcharts of operations and methods by a network node configured according to some embodiments.

[0037] Figure 18 is a block diagram of a UE configured according to some embodiments.

[0038] Figure 19 is a block diagram of a network node configured according to some embodiments.

[0039] Figure 20 is a block diagram of a radio node configured according to some embodiments.

[0040] Figure 21 is a block diagram that illustrates computer readable program code modules according to some embodiments. DETAILED DESCRIPTION

[0041] Inventive concepts will now be described more fully hereinafter with reference to the accompanying drawings, in which examples of embodiments of inventive concepts are shown. Inventive concepts may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of present inventive concepts to those skilled in the art. It should also be noted that these embodiments are not mutually exclusive. Components from one embodiment may be tacitly assumed to be present/used in another embodiment.

[0042] Although various embodiments are disclosed herein in the context of being performed by a UE and/or a network node, they are not limited thereto and instead can be performed in any type of electronic communication device or system.

[0043] One problem that is unique to WLANs, compared to wired networks, is the hidden node problem. Because the radio for each device in a WLAN network has only a limited coverage area, it is possible that a device within the network may not "hear" hidden devices that are transmitting to a device within its coverage area. Figure 2 illustrates this problem of a hidden node. In the system of Figure 2, both a first station 12 and a second station 14 may communicate over a wireless LAN with an access point 10, which may, for example, be a wireless base station. However, the first and second stations 12, 14 are outside each other's coverage area, which means that the first station cannot receive transmissions from the second station, and vice versa. Thus, the first station 12 and the second station 14 are hidden from one another. A collision will occur if the first station 12 and the second station 14 transmit data to the access point 10 at the same time.

[0044] A solution to this problem is use a RTS (Request To Send)-CTS (Clear To Send) protocol for transmission. For example, referring to Figure 2, when the first station 12 wants to transmit data to the access point 10, the first station 12 may transmit a RTS signal, and all devices within the coverage area 12A of the first station 12 will avoid transmission until the data transmission (data + ACK) is finished. The transmission avoidance time may be available as a parameter within the RTS signal. Note, however that the second station 14 is not within the coverage area 12A of the first station 12, and therefore will not receive the RTS signal.

[0045] After reception of the RTS, the access point 10 may transmit a CTS, and all devices within coverage area 10A of the access point 10 (including the second station 14) will avoid transmission until the data transmission (data + ACK) is finished. This transmission avoidance time may be available as parameter within the CTS signal.

[0046] The first station 12 then transmits data to the access point 10, and the access point 10 acknowledges the data by transmitting an ACK signal to the first station 12.

[0047] License Assisted Access LTE (LAA-LTE)

[0048] LAA-LTE is an evolving standard under the umbrella of 3GPP. LAA-LTE proposes to use unlicensed bands (e.g. 2.4GHz and 5.1GHz) for LTE or LTE-like transmission, while coexisting with other wireless standards, such as WLAN IEEE 802.11 and Bluetooth. The primary channel of LTE in the licensed band may still be used, and the secondary carrier(s) in the unlicensed band may be used to boost the throughput to the user. However, most of these unlicensed bands are used by WLANs, which can significantly reduce the use of LTE in these bands. LTE transmissions in an unlicensed band can also become impaired without a coexistence protocol that limits interference in the unlicensed band. In particular, in the 5GHz unlicensed band, there are many channels available that can be used for LTE transmission if a suitable protocol is used.

[0049] LTE and WLAN compared

[0050] WLAN transmissions are asynchronous when compared to LTE, because WLAN transmissions can happen at any time the channel is free, while LTE transmissions are aligned to the Transmission Time Interval (TTI) of 1ms. Also, the duration of WLAN transmissions is variable, while the duration of a transmission of LTE signals may be in multiples of the TTI.

[0051] A feature than can be potentially useful in LAA-LTE, and that is different from WLAN communications, is that the licensed carrier can be used to transmit control channel information (such as grants), ACK signals, etc., while data may be offloaded to the secondary channel when it is free. This will potentially allow more users to use the licensed spectrum, which may reduce latency and/or result in fewer link drops. A further benefit of offloading data to a secondary, unlicensed channel may provide a more reliable control channel on the primary, licensed carrier by reducing lost control signals, risk of collision and/or interference experienced by the control signals. Loss of control signals may result in degradation of overall performance caused by factors such as link drops, lost data, etc.

[0052] Listen-Before-Talk (LBT)

[0053] Listen-Before-Talk (LBT) is a protocol in which the wireless medium in the desired channel is sensed for the presence of energy, such as due to WLAN transmissions, before the medium is used to transmit data. If the medium is found to be free, then the transmitter can start using the medium. This protocol potentially avoids collision with other devices from the same class or other classes (such as Bluetooth communications, or even interference from a microwave oven which operates on a frequency of 2.4GHz). The IEEE 802.11 standard uses CSMA/CA as mentioned above. This approach, along with DCF

(mentioned above), forms a powerful way of avoiding collisions and increasing throughput. However, because of alignment requirements, LBT is usually done at the transmitter side.

[0054] Even when LBT is used, the hidden node problem illustrated in Figure 2 may also affect LAA-LTE if the medium is not sensed properly. Some embodiments described herein perform LBT at the receiver (instead of at the transmitter as the name suggests), and inform the transmitter in a reasonably short time given LTE constraints that the medium is available for transmission.

[0055] Since the WLAN protocol transmissions are asynchronous (both start time and duration), the sharing of the same spectrum by an LTE synchronous transmission in the form of LAA-LTE creates an efficiency problem. There have been proposals for an LAA-LTE node to perform LBT at a fixed position within each TTI of 1 msec, whether that is at the start of the TTI, at the end of the TTI, or at a position within the TTI. However, in a densely loaded environment where there are WLAN nodes competing for the same medium, the occupancy time of the channel may be very high and the time for measuring a free channel may be in the range of 20 μsec to 50 μsec or less, as seen in the MAC Protocol or in WLAN standards.

Hence, the probability that an LAA-LTE node can obtain a free channel to be scheduled may be very low, as the probability that the air interface is "silent" during LBT with an with an LBT period of close to 1 msec may be very low.

[0056] For example, Figure 3 illustrates a case where LBT is performed at the end of each 1 msec TTI interval. An eNodeB 301 performs LBT 22 in an attempt to access the air interface to transmit data to a UE 302. However, at the time the eNB 301 performs LBT, an interfering Wi-Fi Node 303 is transmitting data 24 on the air interface at the same time. The eNodeB 301 may obtain access to the air interface on the third of the 1 msec intervals after the interfering Wi-Fi Node 303 finishes transmitting. At that point, the eNB may send a CTS- to-self message 25 to reserve the WLAN channel, and transmit downlink data 26 to the UE 302. In other words, the eNodeB 301 may experience increased latency based on performing LBT at regular intervals within the fixed 1 msec TTI.

[0057] A brute force approach to avoid the situation described above is to

continuously listen to the channel via LBT until the channel is free. However, running LBT continuously may be energy inefficient and may drain the UE battery. Additionally, continuously listening to the channel may also increase power requirements for the eNB and WLAN nodes, thereby increasing base station power requirements. Hence, these existing LBT approaches, using a fixed TTI period and/or continuous listening, may suffer from efficiency problems.

EMBODIMENTS OF THE PRESENT DISCLOSURE MAY OVERCOME THESE POTENTIAL PROBLEMS

[0058] Embodiments of the present disclosure may overcome one or more of the potential problems explained above with existing approaches by performing dynamic LBT on unlicensed spectrum. As described herein, these approaches may achieve a balance between the TTI-periodic LBT and the continuous LBT methods described above by establishing a prioritization measure to enhance the periodicity of the LBT activity before the requested transmission. [0059] Specifically, two new modes of Dynamic Listen Before Talk for LAA-LTE transmissions on unlicensed spectrum are discussed herein, for improving the competition against WLAN communication.

[0060] The two modes are protocols for LBT that aim at finding a balance between the TTI-periodic LBT and the continuous LBT. For this purpose, each of these protocols establishes a prioritization measure to regulate the periodicity of the LBT activity before the requested transmission.

[0061] The accompanying figures illustrate LBT applied at the eNB, as a non-limiting example. However, the approaches described herein may be applied to the UE by performing LBT at the UE in order to avoid the hidden node problem discussed above.

OPERATIONS AND METHODS ACCORDING TO THE PRESENT DISCLOSURE

[0062] Figures 4, 5A and 5B illustrate operations and methods by a network node configured according to some embodiments. Two modes of operation, Extended Listen Before Talk (E-LBT) and Scalable Listen Before Talk (S-LBT) are illustrated in Figures 4 and 5, as will now be discussed in detail.

[0063] Referring to Figure 4, a block diagram illustrating an operating environment including an eNodeB (or eNB) base station 301 that communicates with a UE 302 is illustrated. An interfering Wi-Fi node 303 may be present in the proximity of the eNodeB 301 and/or UE 302 and may produce interfering transmissions on the unlicensed WLAN spectrum. An Extended Listen Before Talk (E-LBT) mode may be utilized by the eNodeB to improve performance by reducing data latency and power requirements.

[0064] The E-LBT mode may be activated after a number of consecutive unsuccessful normal LBT attempts 32 have occurred. According to some embodiments, after a

predetermined number N of unsuccessful LBT attempts, the eNB may wait for a back-off time, after which a continuous LBT channel 36 measurement may be performed until the channel is found to be clear. The back-off time may be a fixed time period or a random time period. [0065] Once the eNB 301 determines that the WLAN channel is free, the eNB 301 sends a CTS-to-self message 38 over the WLAN interface to reserve the WLAN interface for data transmission, and then sends downlink data 39 to the UE 302 via the WLAN interface.

[0066] Several parameters may be controlled by system design to allow prioritization of traffic and/or different QoS categories. These parameters may include N, a number of initial LBT retries, that provide a maximum number of consecutive failed periodic LBT attempts that are allowed. Another parameter may be Q, a number of TTIs from which the back-off period is taken such that no sensing of the air interface occurs during the back-off period. In some embodiments a Timeout (TO) period may be defined, after which period the transmission of the packet is discarded or signaled for retransmission.

[0067] The E-LBT mode illustrated in Figure 4 may follow the following sequence of events.

1. If LBT fails for a number of sub-frames or attempts or retries N (for example, N=2 in an example embodiment in Figure 4), the LAA-LTE node (in this case, the eNB 301) will enter E-LBT mode, where after random back-off, the eNB 301 will listen to the air interface continuously, and perform Wi-Fi like Collision Avoidance.

2. The E-LBT mode may have time-out period at which the eNB 301 ceases to perform continuous LBT. After the time-out period expires, the packet may be signaled for retransmission or discard.

3. If the air interface becomes free before the time-out period expires, the LAA-LTE node (eNB 301 in this example) will send a CTS-to-self signal 38 in order to occupy the air interface immediately.

4. The LAA-LTE node will then be able to transmit the data 39 in the coming sub-frame(s).

5. The values of initial retries and/or attempts, random back-off time and the time-out may be adjusted to be of different values for different quality-of-service requirements (QoS) and/or based on a fixed TTI.

6. As a non-limiting example, for a large value of N, a medium random back-off time and medium timeout period may be assigned for best-effort category packets. [0068] Referring to Figure 5A, a block diagram illustrating an operating environment including an eNodeB (or eNB) base station 301 that communicates with a UE 302 is illustrated. An interfering Wi-Fi node 303 may be present in the proximity of the eNodeB 301 and/or UE 302 to produce interfering transmissions. A Scalable Listen Before Talk (S-LBT) mode may be applied to the eNodeB 301 to improve performance by reducing data latency and/or power requirements.

[0069] Still referring to Figure 5A, the S-LBT is activated (similarly to E-LBT) after a number of consecutive unsuccessful normal LBT processes have occurred. S-LBT introduces a non-uniform period for back-off to run normal LBT processes until the channel is found clear. In some embodiments, the back-off period of time is determined as a reduced value when a subsequent number of consecutive unsuccessful attempts is greater than the number of consecutive unsuccessful attempts. One parameter, k, can be controlled by system design to allow prioritization and different QoS categories.

[0070] In the example of Figure 5A, an LAA-LTE node, in this case eNB 301, has data to send to a UE 302 via a WLAN secondary channel. The eNB 301 performs a first LBT measurement 42 and determines that the WLAN channel is occupied by data 44 transmitted by an interfering WLAN node 303. However, on the second LBT the channel is found to be free, so the eNB sends a CTS-to-self message 46 to reserve the WLAN channel and begins transmission of downlink data 48 to the UE 302.

[0071] When the eNB 301 has additional data to send, the eNB again performs LBT 50 on the WLAN channel. However, in this example, the WLAN channel is occupied during at least a predetermined number N of initial LBT attempts. The LAA-LTE node eNB 301 then enters S-LBT mode, in which the period of successive LBT approaches is reduced after each unsuccessful LBT attempt. When the WLAN channel is found to be free, the eNB 301 sends a CTS-to-self message 54 and then transmits the downlink data 56 to the UE 302 over the WLAN interface.

[0072] Accordingly, the S-LBT protocol may follow this sequence of events:

1. Initially, LBT is performed at a fixed periodicity (e.g., 1 ms). 2. If the initial LBT attempts fail at least N times, then the LAA-LTE node enters S-LBT mode in which the periodicity of LBT attempts decreases with each failure. The rate at which the periodicity of LTE attempts decrease may depend on the number of past failures and/or the urgency of data transmission. The period of LBT attempts during S- LBT can be modeled, for example, by the following formula:

LBT Period,

where k is a constant, Λ//_σ,·_/ is number of last consecutive LBT failures and « is greed/urgency factor.

3. Once the air interface is free, the LAA-LTE node will send a CTS-to-self signal in order to occupy the air interface.

4. The LAA-LTE node will then be able to transmit the data in the coming sub-frame(s).

5. The greed-factor can be different for different QoS requirements. For example, larger values (such as 1.5) may be used for low latency requirements, and smaller values (such as 0.1) may be used for best effort categories.

[0073] In some embodiments, the parameter k may be related to the LTE frame time, a period to transmit the frame, and/or the TTI. This parameter k may be controlled by the operator for desired system design and/or based upon the TTI.

[0074] Figure 5B illustrates an example of S-LBT according to further embodiments. In the example of Figure 5B, an LAA-LTE node (eNB 301), has data to send to a UE 302 via a WLAN secondary channel. The eNB 301 performs LBT according to a first LBT pattern in which LBT is performed with an initial periodicity Tl, e.g., 1 ms. LBT may be repeated a total of N times using the first LBT pattern. In the example illustrated in Figure 5B, N=2.

[0075] In the initial LBT pattern, the eNB 301 performs an LBT measurement 62 and determines that the WLAN channel is occupied by data 64 transmitted by an interfering WLAN node 303. After LBT has been repeated N times at the initial periodicity Tl, the LAA- LTE node may wait for an optional random back-off time before attempting LBT using a second pattern having a second periodicity T2 that is less than the first periodicity Tl. For example, the second periodicity T2 may be 0.5 ms.

[0076] The random back-off time may be omitted in some embodiments, such that the LAA-LTE node may transition directly from the first LBT pattern to a second LBT pattern without a delay in between the patterns.

[0077] The amount of reduction in periodicity from the first LBT pattern to the second LBT pattern may be based on a number of factors, including the number of previous LBT failures, the priority of the data packet, latency requirements, QoS requirements, or other factors.

[0078] When the eNB 301 begins to perform LBT using the second pattern, the eNB 301 performs LBT 70 on the WLAN channel with a second periodicity T2 that is smaller than the first periodicity Tl.

[0079] In the example of Figure 5B, the WLAN channel is occupied during the N initial LBT attempts. The LAA-LTE node eNB 301 then enters S-LBT mode after an optional random back-off period. In the S-LBT mode, the LAA-LTE node performs LBT 70 with a second periodicity T2 that is smaller than the first periodicity Tl until the WLAN channel is free or a timeout occurs. When the WLAN channel is found to be free, the eNB 301 sends a CTS-to-self message 74 and then transmits the downlink data 76 to the UE 302 over the WLAN interface.

[0080] Figures 6-18 are flowcharts of operations and methods by a network node configured according to some embodiments. Two modes of operation, Extended Listen Before Talk (E-LBT) and Scalable Listen Before Talk (S-LBT) are illustrated in Figures 6-18 and will now be discussed in detail. Figure 6A is a flowchart illustrating operations of

systems/methods according to some embodiments. In particular, an LAA-LTE node first performs a number of LBT attempts to access an air interface of a communication medium according to a first LBT pattern (block 602).

[0081] After each LBT attempt, the LAA-LTE node determines if the air interface is available for the transmission of data frames (block 604). If the air interface is available, the LAA-LTE proceeds to send a CTS-to-self signal (block 606), and to transmit the data frames (block 608). [0082] If the air interface is determined not to be available at block 604, the LAA-LTE node checks to see if the number of initial LBT attempts has exceed a threshold number N (block 610). If the threshold number has not been exceeded, operations return to block 602, where the LAA-LTE node again performs LBT according to the first LBT pattern.

[0083] If the threshold number has been exceeded, the LAA-LTE node may optionally wait for a random back-off time (block 612). The LAA-LTE node then proceeds to perform LBT according to a second LBT pattern until the air interface is available for data transmission (block 614). The second pattern may, for example, be continuous LBT as illustrated in Figure 4, or LBT with decreasing periodicity as illustrated in Figure 5.

[0084] In some embodiments the number of attempts may be one attempt more than the number of retries. The LBT attempts may be performed by the network node. I n response to the number of LBT attempts exceeding a threshold number of LBT attempts, the network node may listen to the air interface to determine if the air interface is available for transmission of data frames (block 602). If the air interface is determined to be available for transmission of the data frames, a Clear-to-Send-to-self (CTS-to-self) signal may be sent (block 603). The CTS-to-self message reserves the WLAN channel for a period of time to allow the LAA-LTE node to transmit data to a receiver.

[0085] In some embodiments, performing the number of LBT attempts may include performing LBT attempts according to a first LBT pattern, and listening to the air interface may include performing LBT attempts according to a second LBT pattern. The first pattern may be different from the second pattern. According to some embodiments, the first LBT pattern may include listening to the air interface periodically with a fixed period, and the second LBT pattern may include listening to the air interface continuously. According to some embodiments, the first LBT pattern may include listening to the air interface periodically with a fixed period, and the second LBT pattern may include listening to the air interface in time periods increasing in frequency.

[0086] Figure 6B illustrates the operations of block 614 in Figure 6A in more detail. In particular, after the LAA-LTE node has performed at least a threshold number of unsuccessful LBT attempts according to the first LBT pattern, the LAA-LTE node may first initiate a timeout counter (block 620) and commence to perform LBT according to a second LBT pattern (block 622). Each time LBT is performed, the LAA-LTE node checks to see if the air interface is available (block 624). If the air interface is available, operations proceed to block 606, where the LAA-LTE transmits data frames over the air interface. If the LAA-LTE node determines at block 624 that the air interface is not available, the LAA-LTE node then checks to see if the timeout counter has expired (block 630). If the timeout counter has expired, the LAA-LTE may mark the packet for discard or retransmission. If the timeout counter has not expired, the operations return to block 622, where the LAA-LTE node again performs LBT according to the second LBT pattern.

[0087] Referring to Figure 7, these operations may apply to E-LBT mode. The method may further include listening (block 701) to the air interface continuously until expiration of a timeout duration or determining that the air interface is available for transmission of the data frames.

[0088] In some embodiments, referring to Figure 8, the method may include indicating (block 801) that the data frames should be discarded and/or retransmitted, based on a determination that the air interface is not available during the timeout duration. Referring to Figure 9, the random back-off time duration may be defined based on a fixed Transmission Time Interval (TTI) (block 901). Referring to Figure 10, the method may include defining (block 1001) the threshold of LBT attempts, the random back-off time duration, and/or the timeout duration based on Quality of Service (QoS) requirements for the data frames.

[0089] Referring to Figure 11, these operations may apply to S-LBT mode. According to some embodiments, the method may include determining (block 1101) a back-off period of time to wait before listening to the air interface based on the number of consecutive unsuccessful attempts.

[0090] Referring to Figure 12, the back-off period of time may be further determined (block 1201) based on prioritization of data frames and/or or based on Quality of Service (QoS) requirements. Referring to Figure 13, the back-off period of time may be determined (block 1301) as a reduced value when a subsequent number of consecutive unsuccessful attempts is greater than the number of consecutive unsuccessful attempts. [0091] Referring to Figure 14, according to some embodiments, sending the CTS signal may include sending (block 1401) an indication that reserves the air interface for transmission of a specified number of data frames, a specified number of data bytes, and/or for a specified amount of time of transmission. Referring to Figure 15, the data frames on the air interface may be transmitted responsive to determining that the air interface is available for transmission (block 1501). According to some embodiments, the air interface may include a primary channel in a licensed band and a secondary channel in an unlicensed band. The data frames may be transmitted in the secondary channel in the unlicensed band.

[0092] Referring to Figure 16, the method may include performing (block 1601) the LBT periodically at a fixed period of time. According to some embodiments, referring to Figure 17, listening to the air interface may include sensing (1701) presence of a carrier on the air interface. According to some embodiments the CTS signal may include a Clear to Send-to-self (CTS-to-self) signal.

EXAMPLE USER EQUIPMENT AND NETWORK NODE

[0093] Figure 18 is a block diagram of a UE 1900, for use in a telecommunications system, that is configured to perform operations according to one or more embodiments disclosed herein. The UE 1900 includes a transceiver 1920, a processor circuit 1902, and a memory circuit 1910 containing computer readable program code 1912. The UE 1900 may further include a display 1930, a user input interface 1940, and a speaker 1950.

[0094] The transceiver 1920 is configured to communicate with a network node, the example of which is an eNB, through a wireless air interface using one or more of the radio access technologies disclosed herein. The processor circuit 1902 may include one or more data processing circuits, such as a general purpose and/or special purpose processor, e.g., microprocessor and/or digital signal processor. The processor circuit 1902 is configured to execute the computer readable program code 1912 in the memory circuit 1910 to perform at least some of the operations described herein as being performed by a UE.

[0095] Figure 19 is a block diagram of a radio access network (RAN) node 2000, for use in a telecommunications system, that is configured according to one or more embodiments disclosed herein for an eNB, radio network node, or other network node. The network node 2000 can include a transceiver 2030, a network interface 2020, a processor circuit 2002, and a memory circuit 2010 containing computer readable program code 2012.

[0096] The transceiver 2030 is configured to communicate with the UE 1900 using one or more of the radio access technologies disclosed herein, when the network node 2000 is a radio network node. The processor circuit 2002 may include one or more data processing circuits, such as a general purpose and/or special purpose processor, e.g., microprocessor and/or digital signal processor, that may be collocated or distributed across one or more networks. The processor circuit 2002 is configured to execute the computer readable program code 2012 in the memory 2010 to perform at least some of the operations and methods of described herein as being performed by a network node. The network interface 2020 communicates with other network nodes and/or a core network.

[0097] Figure 20 illustrates a network node 2100, such as the UE 1900 or RAN 2000 in more detail. In particular, the network node 2100 includes an LBT module 1914 for performing (602) a plurality of Listen Before Talk (LBT) attempts to access an air interface of a communication medium according to a first pattern, and in response to the number of LBT attempts exceeding a threshold number of LBT attempts, performing (614) LBT according to a second pattern that is different from the first pattern. The network node 2100 may include a sending module 1918 for sending (606) a data frame over the air interface in response to determining that the air interface is available for transmission of the data frames.

[0098] Figure 21 illustrates the computer readable program code 2200. The computer readable program code 2100 may correspond to the computer readable program code 1912 in the UE 1900 or to the computer readable program code 2012 in the radio network node 2000. In particular, the computer readable program code 2012 includes a performing module 2014 for performing (602) a plurality of Listen Before Talk (LBT) attempts to access an air interface of a communication medium according to a first pattern, and in response to the number of LBT attempts exceeding a threshold number of LBT attempts, performing (614) LBT according to a second pattern that is different from the first pattern. The computer readable program code 2012 may include a sending module 2018 for sending (606) a data frame over the air interface in response to determining that the air interface is available for transmission of the data frames.

[0099] E-LBT and S-LBT each may find a balance between the sub-frame periodic LBT and the continuous LBT. This may result in a more energy efficient use of the unlicensed spectrum while sharing the spectrum with WLAN devices.

[00100] Each of the proposed protocols adapts the system to different QoS categories and avoids LAA-LTE communication from being blocked or starved from

transmissions in the unlicensed spectrum bands. The proposed method may also be tailored for different QoS level of requirements.

[00101] E-LBT may be tailored for a wider range of QoS categories and with larger back-off periods. E-LBT may be more energy efficient than existing solutions at the expense of a lower QoS target.

[00102] S-LBT is a highly efficient process to find clear channels in dense WLAN environments by decreasing the period of the back-off time to the next LBT. The slope of the decreasing period may be controlled by a parameter to adjust to different QoS targets.

[00103] Examples on how to secure LAA LTE downlink unlicensed carriers were illustrated by Figures 4 and 5. Two procedures, E-LBT and S-LBT, were described above.

These procedures for LAA-LTE may be applied to work with the primary cell (Pcell) on the dedicated licensed spectrum and the secondary cell (Scell) on the unlicensed carrier. These procedures for E-LBT and S-LBT may be included in a system design as follows:

1. When eNB has data to transmit to UE through SCell, the eNB will use a control channel on PCell to indicate UE. eNB will now perform LBT before the sub-frame boundary to find an available opportunity for transmission.

2. If the LBT fails then the eNB can either choose Extended-LBT or Scalable-LBT as illustrated in Figures 4 and 5.

3. If E-LBT is chosen then eNB will keep listening to the channel continuously until it is free. The eNB will then immediately transmit Wi-Fi CTS-to-self in order to occupy the channel. 4. If S-LBT is chosen then eNB will keep listening to the channel in 20us durations with decreasing periodicity until it is free. The eNB will then immediately transmit Wi-Fi CTS- to-self in order to occupy the channel.

5. The eNB will transmit data on secondary carrier in the next available sub-frame. Additional steps may be performed at the receiving network node (such as a UE). The duration or periodicity may be controlled as discussed by the solution proposed above.

[00104] Various embodiments of the present disclosure are applicable to a LAA- LTE system. As explained above, Dynamically adjusting the LBT requirements for LAA-LTE may improve performance. Usage of licensed carriers to implement CTS on a receiver to protect the air interface against a WLAN interfering node on the receiver side may improve the data reception characteristics. The techniques described herein may be applicable for both uplink and downlink at a user equipment or at a network node. Overall, the strategies described herein allow LBT to be applied in a more energy efficient manner.

ABBREVIATIONS

eNB Enhanced Node conforming to 3GPP LTE standards

UE User Equipment - usually and LTE client device

WLAN Wireless Local Area Network conforming to IEEE 802.11 a/g/n spec

LBT Listen-Before-Talk; a generic term for sensing wireless medium

LAA-LTE License Assisted Access for LTE

RTS Request to Send

CTS Clear to Send

DCF Distributed Co-ordination Function

QoS Quality of Service

TTI Transmission time interval FURTHER DEFINITIONS AND EMBODIMENTS

[00105] In the above-description of various embodiments of present inventive concepts, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of present inventive concepts. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which present inventive concepts belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[00106] When an element is referred to as being "connected", "coupled", "responsive", or variants thereof to another element, it can be directly connected, coupled, or responsive to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected", "directly coupled", "directly responsive", or variants thereof to another element, there are no intervening elements present. Like numbers refer to like elements throughout. Furthermore, "coupled", "connected",

"responsive", or variants thereof as used herein may include wirelessly coupled, connected, or responsive. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Well-known functions or constructions may not be described in detail for brevity and/or clarity. The term "and/or" includes any and all combinations of one or more of the associated listed items.

[00107] It will be understood that although the terms first, second, third, etc. may be used herein to describe various elements/operations, these elements/operations should not be limited by these terms. These terms are only used to distinguish one element/operation from another element/operation. Thus a first element/operation in some embodiments could be termed a second element/operation in other embodiments without departing from the teachings of present inventive concepts. The same reference numerals or the same reference designators denote the same or similar elements throughout the specification. [00108] As used herein, the terms "comprise", "comprising", "comprises", "include", "including", "includes", "have", "has", "having", or variants thereof are open-ended, and include one or more stated features, integers, elements, steps, components or functions but does not preclude the presence or addition of one or more other features, integers, elements, steps, components, functions or groups thereof. Furthermore, as used herein, the common abbreviation "e.g.", which derives from the Latin phrase "exempli gratia," may be used to introduce or specify a general example or examples of a previously mentioned item, and is not intended to be limiting of such item. The common abbreviation "i.e.", which derives from the Latin phrase "id est," may be used to specify a particular item from a more general recitation.

[00109] Example embodiments are described herein with reference to block diagrams and/or flowchart illustrations of computer-implemented methods, apparatus

(systems and/or devices) and/or computer program products. It is understood that a block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by computer program instructions that are performed by one or more computer circuits. These computer program instructions may be provided to a processor circuit of a general purpose computer circuit, special purpose computer circuit, and/or other programmable data processing circuit to produce a machine, such that the instructions, which execute via the processor of the computer and/or other programmable data processing apparatus, transform and control transistors, values stored in memory locations, and other hardware components within such circuitry to implement the functions/acts specified in the block diagrams and/or flowchart block or blocks, and thereby create means (functionality) and/or structure for implementing the functions/acts specified in the block diagrams and/or flowchart block(s).

[00110] These computer program instructions may also be stored in a tangible computer-readable medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer- readable medium produce an article of manufacture including instructions which implement the functions/acts specified in the block diagrams and/or flowchart block or blocks. Accordingly, embodiments of present inventive concepts may be embodied in hardware and/or in software (including firmware, resident software, micro-code, etc.) that runs on a processor such as a digital signal processor, which may collectively be referred to as "circuitry," "a module" or variants thereof.

[00111] It should also be noted that in some alternate implementations, the functions/acts noted in the blocks may occur out of the order noted in the flowcharts. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the

functionality/acts involved. Moreover, the functionality of a given block of the flowcharts and/or block diagrams may be separated into multiple blocks and/or the functionality of two or more blocks of the flowcharts and/or block diagrams may be at least partially integrated.

Finally, other blocks may be added/inserted between the blocks that are illustrated, and/or blocks/operations may be omitted without departing from the scope of inventive concepts. Moreover, although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows.

[00112] Many variations and modifications can be made to the embodiments without substantially departing from the principles of the present inventive concepts. All such variations and modifications are intended to be included herein within the scope of present inventive concepts. Accordingly, the above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended examples of embodiments are intended to cover all such modifications, enhancements, and other embodiments, which fall within the spirit and scope of present inventive concepts. Thus, to the maximum extent allowed by law, the scope of present inventive concepts are to be determined by the broadest permissible interpretation of the present disclosure, and shall not be restricted or limited by the foregoing detailed description.

[00113] Embodiment 1. A method by a network node in a telecommunications system, the method comprising: performing a number of Listen Before Talk (LBT) attempts to access an air interface of a communication medium;

listening (602), in response to the number of LBT attempts exceeding a threshold of LBT attempts, to the air interface to determine if the air interface is available for transmission of data frames; and

sending a Clear to Send (CTS) signal in response to determining that the air interface is available for transmission of the data frames.

[00114] Embodiment 2. The method of Embodiment 1, wherein the performing the number of LBT attempts comprises performing LBT attempts according to a first LBT pattern, wherein the listening to the air interface comprises performing LBT attempts according to a second LBT pattern, wherein the first pattern is different from the second pattern.

[00115] Embodiment 3. The method of any of Embodiments 1-2, wherein the listening to the air interface comprises: listening to the air interface continuously until an earlier occurrence of at least one of an expiration of a timeout duration or a determination that the air interface is available for transmission of the data frames.

[00116] Embodiment 4. The method of Embodiment 3, further comprising: waiting (801), prior to the listening to the air interface continuously, for expiration of a random backoff time duration following the number of LBT attempts exceeding the threshold of LBT attempts.

[00117] Embodiment s. The method of Embodiment 3, further comprising: indicating that the data frames should be discarded and/or retransmitted, based on a determination that the air interface is not available during the timeout duration.

[00118] Embodiment 6. The method of Embodiment 3, further comprising defining the random backoff time duration based on a fixed Transmission Time Interval (TTI).

[00119] Embodiment ?. The method of Embodiment 3, further comprising defining (1101) the threshold of LBT attempts, the random backoff time duration, and/or the timeout duration based on Quality of Service (QoS) requirements for the data frames. [00120] Embodiment s. The method of any of Embodiments 1-2, wherein the listening to the air interface comprises: determining a backoff period of time to wait before listening to the air interface based on the number of LBT attempts.

[00121] Embodiment 9. The method of Embodiment 8, wherein the backoff period of time is further determined based on prioritization of data frames and/or or based on Quality of Service (QoS) requirements.

[00122] Embodiment 10. The method of Embodiment 8, wherein the backoff period of time is determined as a reduced value when a subsequent number of consecutive unsuccessful attempts is greater than the number of consecutive unsuccessful attempts.

[00123] Embodiment 11. The method of any of Embodiments 1-10, wherein the sending the CTS signal comprises sending an indication that reserves the air interface for transmission of a specified number of data frames, a specified number of data bytes, and/or for a specified amount of time of transmission.

[00124] Embodiment 12. The method of any of Embodiments 1-11, further comprising: transmitting the data frames on the air interface responsive to determining that the air interface is available for transmission.

[00125] Embodiment 13, The method of any of Embodiments 1-12, wherein the air interface comprises a primary channel in a licensed band and a secondary channel in an unlicensed band, wherein the data frames are transmitted in the secondary channel in the unlicensed band.

[00126] Embodiment 14. The method of any of Embodiments 1-13, further comprising performing the LBT periodically at a fixed period of time.

[00127] Embodiment 15. The method of any of Embodiments 1-14, wherein listening to the air interface comprises sensing presence of a carrier on the air interface.

[00128] Embodiment 16. The method of any of Embodiments 1-15, wherein the CTS signal comprises a Clear to Send-to-self (CTS-to-self) signal.

[00129] Embodiment 17. The method of Embodiment 2, wherein the first LBT pattern comprises listening to the air interface periodically, and wherein the second LBT pattern comprises listening to the air interface continuously. [00130] Embodiment 18. The method of Embodiment 2, wherein the first LBT pattern comprises listening to the air interface periodically, and wherein the second LBT pattern comprises listening to the air interface in time periods increasing in frequency.

[00131] Embodiment 19. A network node comprising:

a processor circuit;

a transceiver coupled to the processor circuit; and

a memory circuit comprising computer readable program code that is configured to cause the processor circuit to execute the operations of: performing a number of Listen Before Talk (LBT) attempts to access an air interface of a communication medium; listening, in response to the number of LBT attempts exceeding a threshold of LBT attempts, to the air interface to determine if the air interface is available for transmission of data frames; and sending a Clear to Send (CTS) signal in response to determining that the air interface is available for transmission of the data frames.

[00132] Embodiment 20. A network node, comprising:

[00133] a processor circuit;

[00134] a memory circuit coupled to the processor and comprising computer readable program code; and

[00135] a transceiver coupled to the processor circuit;

[00136] wherein the computer readable program code comprises: a performing module for determining a number of Listen Before Talk (LBT) attempts to access an air interface of a communication medium; a listening module for listening, in response to the number of LBT attempts exceeding a threshold of LBT attempts, to the air interface to determine if the air interface is available for transmission of data frames; and a sending module for sending a Clear to Send (CTS) signal in response to determining that the air interface is available for transmission of the data frames.

[00137] Embodiment 21. A method by a network node in a telecommunications system, the method comprising:

performing a number of Listen Before Talk, LBT, attempts to access an air interface of a communication medium according to a first pattern; in response to the number of LBT attempts exceeding a threshold, performing LBT according to a second pattern that is different from the first pattern;

determining that the air interface is available for transmission of data frames in response to performing LBT according to the second pattern; and

sending a data frame over the air interface in response to determining that the air interface is available for transmission of data frames.

[00138] Embodiment 22. The method of Embodiment 21, further comprising sending a clear-to-send-to-self (CTS-to-self) message over the air interface in response to determining that the air interface is available for transmission of the data frames.

[00139] Embodiment 23. The method of any of Embodiments 21-22, wherein performing LBT according to the second pattern comprises listening to the air interface continuously until an earlier occurrence of at least one of an expiration of a timeout duration or a determination that the air interface is available for transmission of the data frames.

[00140] Embodiment 24. The method of Embodiment 23, further comprising indicating that the data frame should be discarded and/or retransmitted, based on a determination that the air interface is not available during the timeout duration.

[00141] Embodiment 25. The method of Embodiment 23, further comprising waiting for expiration of a back-off time before performing LBT according to the second pattern.

[00142] Embodiment 26. The method of Embodiment 25, wherein the back-off time comprises a random time period.

[00143] Embodiment 27. The method of Embodiment 25, further comprising defining the back-off time duration based on a fixed Transmission Time Interval (TTI).

[00144] Embodiment 28. The method of Embodiment 23, further comprising defining the threshold number of LBT attempts and/or the timeout duration based on Quality of Service (QoS) requirements for the data frames.

[00145] Embodiment 29. The method of any of Embodiments 21-22, further comprising determining a back-off period of time to wait before performing LBT according to the second pattern in response to a number of unsuccessful LBT attempts. [00146] Embodiment 30. The method of Embodiment 29, wherein the back-off period of time is further determined based on prioritization of data frames and/or or based on Quality of Service (QoS) requirements.

[00147] Embodiment 31. The method of Embodiment 21, wherein the performing LBT according to the first pattern comprises performing LBT with a first periodicity, and wherein performing LBT according to the second pattern comprises performing LBT with a second periodicity that is smaller than the first periodicity.

[00148] Embodiment 32. The method of Embodiment 21, wherein performing LBT according to the first pattern comprises performing LBT with a first periodicity, and wherein performing LBT according to the second pattern comprises performing LBT with a second periodicity that decreases with time.

[00149] Embodiment 33. The method of Embodiment 31 or 32, further comprising waiting for a back-off time between the performing LBT according to the first pattern and the performing LBT according to the second pattern.

[00150] Embodiment 34. The method of Embodiment 33, wherein the back-off time comprises a random back-off time.

[00151] Embodiment 35. The method of Embodiment 31 or 32, further comprising ceasing to perform LBT according to the second pattern in response to the expiration of a timeout duration, and indicating that the data frame should be discarded and/or retransmitted, based on a determination that the air interface was not available during the timeout duration.

[00152] Embodiment 36. The method of any of Embodiments 21-35, wherein the air interface comprises a primary channel in a licensed band and a secondary channel in an unlicensed band, wherein the data frames are transmitted in the secondary channel in the unlicensed band.

[00153] Embodiment 37. The method of Embodiment 21, wherein the first LBT pattern comprises listening to the air interface periodically, and wherein the second LBT pattern comprises listening to the air interface continuously. [00154] Embodiment 38. The method of Embodiment 21, wherein the first LBT pattern comprises listening to the air interface periodically, and wherein the second LBT pattern comprises listening to the air interface in time periods increasing in frequency.

[00155] Embodiment 39. A network node comprising:

a processor circuit;

a transceiver coupled to the processor circuit; and

a memory circuit comprising computer readable program code that is configured to cause the processor circuit to execute the operations of:

performing a number of Listen Before Talk, LBT, attempts to access an air interface of a communication medium according to a first LBT pattern;

in response to the number of LBT attempts exceeding a threshold, performing LBT according to a second pattern that is different from the first pattern;

[00156] Embodiment 40. A network node, comprising:

a processor circuit;

a memory circuit coupled to the processor and comprising computer readable program code; and

a transceiver coupled to the processor circuit;

wherein the computer readable program code comprises an LBT module for performing a number of Listen Before Talk, LBT, attempts to access an air interface of a communication medium according to a first LBT pattern, and in response to the number of LBT attempts exceeding a threshold, performing LBT according to a second pattern that is different from the first pattern; and determining that the air interface is available for transmission of data frames in response to performing LBT according to the second pattern; and a sending module for sending a data frame over the air interface in response to determining that the air interface is available for transmission of data frames. [00157] Embodiment 41. A network node configured to perform the method of any of Embodiments 21-38.

[00158] Embodiment 42. A method by a network node in a telecommunications system, the method comprising:

performing (602) a number of Listen Before Talk, LBT, attempts to access an air interface of a communication medium according to a first pattern;

in response to the number of LBT attempts exceeding a threshold, performing (622) LBT according to a second pattern that is different from the first pattern;

determining (624) that the air interface is available for transmission of data frames in response to performing LBT according to the second pattern; and

sending (606) a data frame over the air interface in response to determining that the air interface is available for transmission of data frames.

[00159] Embodiment 43. A network node comprising:

a processor circuit (1902, 2002);

a transceiver (1920, 2030) coupled to the processor circuit; and

a memory circuit (1910, 2010) comprising computer readable program code (1912, 2012) that is configured to cause the processor circuit to execute the operations of:

performing (602) a number of Listen Before Talk, LBT, attempts to access an air interface of a communication medium according to a first LBT pattern;

[00160] Embodiment 44. A network node, comprising:

a processor circuit (1902, 2002); a memory circuit (1910, 2010) coupled to the processor and comprising computer readable program code (1912, 2012); and

a transceiver (1920, 2030) coupled to the processor circuit;

wherein the computer readable program code comprises:

an LBT module (2014) for performing (602) a number of Listen Before Talk, LBT, attempts to access an air interface of a communication medium according to a first LBT pattern, in response to the number of LBT attempts exceeding a threshold, performing (622) LBT according to a second pattern that is different from the first pattern, and determining (624) that the air interface is available for transmission of data frames in response to performing LBT according to the second pattern; and

a sending module (2018) for sending (606) a data frame over the air interface in response to determining that the air interface is available for transmission of data frames.

[00161]

Claims

CLAIMS:

1. A method by a network node in a telecommunications system, the method comprising:

2. The method of claim 1, further comprising sending a clear-to-send-to-self, CTS- to-self, message over the air interface in response to determining that the air interface is available for transmission of the data frames.

3. The method of any of claims 1-2, wherein performing LBT according to the second pattern comprises:

listening (701) to the air interface continuously until an earlier occurrence of at least one of an expiration of a timeout duration or a determination that the air interface is available for transmission of the data frames.

4. The method of claim 3, further comprising:

indicating (801) that the data frame should be discarded and/or retransmitted, based on a determination that the air interface is not available during the timeout duration.

5. The method of claim 3, further comprising: waiting (612) for expiration of a back-off time before performing LBT according to the second pattern.

6. The method of claim 5, wherein the back-off time comprises a random time period.

7. The method of claim 5, further comprising defining (901) the back-off time duration based on a fixed Transmission Time Interval, TTI.

8. The method of claim 3, further comprising defining (1001) the threshold number of LBT attempts and/or the timeout duration based on Quality of Service, QoS, requirements for the data frames.

9. The method of any of claims 1-2, further comprising:

determining (1101) a back-off period of time to wait before performing LBT according to the second pattern in response to a number of unsuccessful LBT attempts.

10. The method of claim 9, wherein the back-off period of time is further

determined (1201) based on prioritization of data frames and/or or based on Quality of Service, QoS, requirements.

11. The method of claim 1, wherein the performing LBT according to the first pattern comprises performing LBT with a first periodicity, and wherein performing LBT according to the second pattern comprises performing LBT with a second periodicity that is smaller than the first periodicity.

12. The method of claim 1, wherein performing LBT according to the first pattern comprises performing LBT with a first periodicity, and wherein performing LBT according to the second pattern comprises performing LBT with a second periodicity that decreases with time.

13. The method of claim 11 or 12, further comprising waiting for a back-off time between the performing LBT according to the first pattern and the performing LBT according to the second pattern.

14. The method of claim 13, wherein the back-off time comprises a random back-off time.

15. The method of claim 11 or 12, further comprising:

ceasing to perform LBT according to the second pattern in response to the expiration of a timeout duration, and

indicating (801) that the data frame should be discarded and/or retransmitted, based on a determination that the air interface was not available during the timeout duration.

16. The method of any of claims 1-15,

wherein the air interface comprises a primary channel in a licensed band and a secondary channel in an unlicensed band,

wherein the data frames are transmitted in the secondary channel in the unlicensed band.

17. The method of claim 1,

wherein the first LBT pattern comprises listening to the air interface periodically, and wherein the second LBT pattern comprises listening to the air interface continuously.

18. The method of claim 1,

wherein the first LBT pattern comprises listening to the air interface periodically, and wherein the second LBT pattern comprises listening to the air interface in time periods increasing in frequency.

19. A network node comprising:

a processor circuit (1902, 2002);

a transceiver (1920, 2030) coupled to the processor circuit; and

20. A network node, comprising:

a processor circuit (1902, 2002);

a memory circuit (1910, 2010) coupled to the processor and comprising computer readable program code (1912, 2012); and

a transceiver (1920, 2030) coupled to the processor circuit;

wherein the computer readable program code comprises:

21. A network node (1900, 2000) configured to perform the method of any of claims 1-18.