WO2014064322A1

WO2014064322A1 - Interference avoidance and power savings for coexistence among different radio access technologies

Info

Publication number: WO2014064322A1
Application number: PCT/FI2012/051008
Authority: WO
Inventors: Fuad JUNIOR; Erika ALMEIDA; Robson DOMINGOS; Rafael PAIVA; Fabiano CHAVES; Andre Cavalcante; Felipe Costa; Sayantan Choudhury
Original assignee: Nokia Corporation
Priority date: 2012-10-22
Filing date: 2012-10-22
Publication date: 2014-05-01

Abstract

A network operating in a 1st radio access technology RAT (e.g., Wi-Fi) can avoid interference to/from another network operating in a 2^nd RAT (e.g., LTE) by detecting within a predefined interval, of a resource allocation of the coexisting 2^nd RAT, whether the resource allocation (e.g., one subframe) is occupied or vacant. Only when the resource allocation was detected to be vacant, then transmissions according to the 1^st RAT are restricted to occur within boundaries of the resource allocation of the coexisting 2^nd RAT that was determined to be vacant. When the resource allocation was detected to be occupied, nodes in the 2^nd RAT can enter a sleep mode for power savings. The nodes can compare an energy level sensed during the predefined interval against a predefined threshold for the detecting. All of these procedures can be independent of cooperation with any network node operating in the coexisting 2^nd RAT.

Description

INTERFERENCE AVOIDANCE AND POWER SAVINGS FOR COEXISTENCE AMONG DIFFERENT RADIO ACCESS TECHNOLOGIES

TECHNICAL FIELD:

[0001] This invention relates generally to wireless communications, and more specifically is directed toward avoiding interference among coexisting radio access technologies, and also power savings for portable user equipments in such coexistence environments.

BACKGROUND:

[0002] In wireless communications typically coexistence problems occur when different systems operate by sharing the same communication resources, such as time and frequency resources. One recent area of study concerns license exempt spectrum such as television whitespaces TVWS in the VHF and UHF bands which is becoming available with the widespread adoption of digital television. In this unlicensed spectrum, typically devices access a whitespace database (WSD) to obtain a list of unoccupied spectrum in which these devices can transmit and receive data. There is also coexistence between IEEE 802.11 (wireless local area network WLAN) and 802.15.4 radios deployed in the Industrial, Scientific, and Medical(ISM) 2.4GHz band has already been established. This sets a high probability that in the near future there will be coexistence between the long term evolution (LTE) and Wi-Fi radio access technologies. For example, there is a clear difference among the frame structures, physical PHY layers, media access control MAC layers and application layers of the coexisting systems, so coexistence mechanisms with interference avoidance and energy saving strategies will be greatly important in this scenario.

[0003] Since its inception, the IEEE 802.11 family of standards has considered power savings for the ST As. The original IEEE 802.11 specification from November 1997 defines a power saving mode (PSM) in which the Wi-Fi STAs may request to be always in a sleep mode, which they leave temporarily to enter an awake mode for data exchange with the AP. The introduction in July 2003 of IEEE 802.1 le defined the unscheduled automatic power save delivery (U-APSD) mode which allows nodes to sleep for a specified amount of time after a period of traffic inactivity, while making use of enhanced distributed channel access (EDCA). The Wi-Fi Alliance has defined in 2004 a wireless multimedia power save (WMM-PS), which is based on U-APSD and which also adds a scheduled (synchronous) version (S-APSD). The introduction of IEEE 802.11η defined the power save multi-poll (PSMP) in which traffic depends on a schedule published by the AP, based on STA-published requirements. IEEE 802.1 In also defined a dynamic MIMO power save that allows MIMO-based radios to downshift to less-aggressive radio configurations when traffic loads are light, for example from a 2x2 configuration to a lxl configuration.

[0004] In practice, coexisting radio access technologies may not always be implementing some form of coordination for occupying the TVWS spectrum, apart from what might be mandated by standards or regulations. In other instances, even if there is some coordination mechanism it may not work effectively at all times. The inventors are aware of no existing solutions for uncoordinated interference minimization and power saving for Wi-Fi nodes operating in coexistence with LTE nodes. The solutions detailed herein can be deployed wherever there is coexistence in the same frequency band, whether the band is licensed (such as when the vacant spectrum spaces are opportunistically exploited by users), unlicensed, or unused bands.

SUMMARY:

[0005] In accordance with a first aspect of these teachings there is a method comprising: detecting within a predefined interval of a resource allocation of a coexisting second radio access technology whether the resource allocation is occupied or vacant; and only when the resource allocation was detected to be vacant, restricting transmissions according to a first radio access technology to occur within boundaries of the resource allocation of the coexisting second radio access technology that was determined to be vacant.

[0006] In accordance with a second aspect of these teachings there is an apparatus comprising at least one computer readable memory storing a set of executable instructions, and at least one processor. In this aspect the at least one computer readable memory is configured with the set of executable instructions and with the at least one processor to cause the apparatus at least to: detect within a predefined interval of a resource allocation of a coexisting second radio access technology whether the resource allocation is occupied or vacant; and only when the resource allocation was detected to be vacant, restrict transmissions according to a first radio access technology to occur within boundaries of the resource allocation of the coexisting second radio access technology that was determined to be vacant. [0007] In accordance with a third aspect of these teachings there is a computer readable memory tangibly storing a set of executable instructions, wherein the set of executable instructions comprises: code for detecting within a predefined interval of a resource allocation of a coexisting second radio access technology whether the resource allocation is occupied or vacant; and code for restricting transmissions according to a first radio access technology to occur within boundaries of the resource allocation of the coexisting second radio access technology that was determined to be vacant, only when the resource allocation was detected to be vacant.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0008] Figure 1A is a timing diagram illustrating the different frame timing as between a Wi-Fi system and a coexisting LTE system and showing how transmissions in the LTE system can block transmission in the Wi-Fi system, a problem which is resolved by embodiments of these teachings.

[0009] Figure IB is a timing diagram illustrating a Wi-Fi frame interfering with an LTE subframe when the initially non-interfering Wi-Fi transmissions go beyond the end of the vacant LTE subframe, and is another problem is resolved by embodiments of these teachings.

[0010] Figure 2 is a signaling diagram that illustrates switching from a regular/conventional 802.11 operation mode to a LTE coexistence mode according to an embodiment of these teachings.

[0011] Figure 3 is an exemplary signaling diagram illustrating how a STA#2 that is not blocked may be notified that the AP is experiencing blockage by the coexisting LTE system according to an embodiment of these teachings. [0012] Figure 4 is similar to Figure 3 but illustrating Wi-Fi nodes using the vacant LTE subframe according to an embodiment of these teachings.

[0013] Figure 5 is similar to Figure 3 but illustrating wasted radio resources due to STA#1 being blocked, and is a problem that is resolved by exemplary embodiments of these teachings.

[0014] Figure 6 is similar to Figure 3 but illustrating traffic where a LTE interference blockage check is performed according to an embodiment of these teachings.

[0015] Figure 7 is a flow diagram illustrating procedures for a Wi-Fi AP selecting between LTE coexistence mode and regular/conventional Wi-Fi mode according to an embodiment of these teachings.

[0016] Figure 8 is a flow diagram illustrating procedures for a Wi-Fi STA operating in the LTE coexistence mode according to an embodiment of these teachings.

[0017] Figure 9 is a flow diagram illustrating procedures for carrier sense multiple access with collision avoidance (CSMA/CA) operation within a vacant LTE subframe according to an embodiment of these teachings.

[0018] Figure 10 is a flow diagram illustrating procedures for a LTE interference blockage check according to an embodiment of these teachings.

[0019] Figure 11 is a simplified block diagram of two STAs and an AP which are exemplary devices suitable for use in practicing the exemplary embodiments of the invention.

DETAILED DESCRIPTION:

[0020] To better appreciate practical deployments for these teachings, first are explored some specific details of specific coexistence scenarios. When there is a traditional cellular wireless broadband base station (BS) operating in the unlicensed band, any underlying lower-power Wi-Fi nodes operating on the same channel typically suffer from interference. As shown in Figure 1 A for the case of LTE, the minimal LTE allocation units are the LTE subframes 102, which are larger than the duration of a standard Wi-Fi slot. As a result, the LTE downlink (DL) frames arriving at Wi-Fi nodes with reception power above the carrier sense multiple access (CSMA) sensing threshold causes the CSMA sensing algorithm to determine that the Wi-Fi channel is occupied. The standard CSMA response to the channel being occupied is for the user device to keep on sensing the radio medium and wait until it becomes idle, followed by counting down a random timer (termed an exponential back-off window) before trying again to send a packet. And when a Wi-Fi node is under the interference of another technology such as LTE, the clear channel assessment (CCA) phase takes longer than when the channel is disputed only among Wi-Fi nodes. Interfaces on such LTE -blocked Wi-Fi nodes have to remain turned on for the CSMA sensing operation for as long as the LTE subframe lasts, and since its duration is known, this represents unnecessary power consumption. Therefore this procedure is not efficient for the coexistence scenario on the TVWS band.

[0021] Another problem may arise when a Wi-Fi node gains access to the channel within a period of inactivity of the coexisting technology, shown in Figure 1A as a "blank" LTE subframe 104B, and does not take into account the amount of time required to transmit data at the current modulation and coding scheme (MCS). If a Wi-Fi node is coexisting with LTE in this example, it can be sure that the minimal resource granularity unit is the LTE subframe 104 A, because in LTE either the whole LTE subframe is occupied 104 A or it is not occupied at all 104B. In the situation where the coexisting technology (e.g. LTE) does not occupy a single resource unit, the CCA would enable a Wi-Fi transmission 106 which may easily trespass the limits 106A of this vacant resource unit 104B, depending on the current Wi-Fi MCS, packet size and time to gain access to the channel. In this case, not only the coexisting technology (LTE) suffers from interference, but also the Wi-Fi frame will need to be re-transmitted, resulting in a throughput degradation for both technologies.

[0022] Embodiments of these teachings exploit properties of the coexisting technology (for example, Wi-Fi blockage due to LTE transmissions and LTE subframe resource granularity) to define a uncoordinated strategy for Wi-Fi nodes avoiding interference to and interference from the coexisting/LTE technology, while at the same time enabling power savings when there may be some unavoidable interference blockage due to transmissions in the coexisting technology. This uncoordinated strategy is denoted herein as a "coexisting technology operation mode".

[0023] In order to optimize power consumption and avoid unnecessary exchange of messages between Wi-Fi nodes, it is advantageous to have some mechanism to switch between this coexisting technology operation mode and the regular/conventional 802.11 operation mode. For convenience, below are listed some example scenarios in which the above switching mechanism would be useful in order to put the Wi-Fi node into one mode or the other. In general the Wi-Fi node can be the network access node/access point AP or a non-AP station STA; the description below stipulates the aspects of these teachings that are specific to one or the other.

a) The Wi-Fi network is operating in the regular /conventional 802.11 operation mode and it is the single technology using the spectrum at that location;

b) The Wi-Fi network is operating in the coexisting technology operation mode and it is sharing the spectrum at that location with another technology;

c) The Wi-Fi network is operating in the coexisting technology operation mode and it is the single technology using the spectrum at that location;

d) The Wi-Fi network is operating in the regular /conventional 802.11 operation mode and it is sharing the spectrum at that location with another technology.

[0024] Scenario a is optimal in the sense that Wi-Fi nodes do not use nor require any additional overhead for coexisting with another technology. Scenario b is also optimal, but in the sense that there will be necessary some additional overhead for coexisting with another technology being used by Wi-Fi nodes, given that these Wi-Fi nodes are actually coexisting with another technology and as such some overhead ensures they optimally perform coexistence procedures. Scenarios a and b may not demand switching of the operation modes.

[0025] To the contrary, in scenario c there is the absence of another technology sharing the spectrum. If the Wi-Fi nodes do not have a mechanism to switch back from coexisting technology operation mode to regular /conventional 802.11 operation mode, the Wi-Fi nodes are likely to waste a significant amount of scarce radio resources in order to coordinate transmissions during the non-cooperative Wi-Fi network time-span, and also to waste a significant amount of time silencing the Wi-Fi nodes so as to avoid interference to the non-cooperative network.

[0026] In a similar vein, for scenario d if the nodes operating in the Wi-Fi system do not have a mechanism to switch from regular/conventional 802.11 operation mode to coexisting technology operation mode, the overall system is highly likely to consume unnecessary resources performing channel measurements when Wi-Fi transmissions are blocked anyway by the coexisting other network, and increase their back-off timer (which may cause the Wi-Fi network to be inactive during the silent periods that exists between LTE transmissions).

[0027] Scenarios c and d are therefore non-optimal, and may lead to an unnecessary wasting of resources for both the Wi-Fi nodes and for the nodes operating according to the coexisting other radio access technology. Therefore, an operational mode switching may be necessary. To do this operational mode switching most effectively (at the proper moments) for both scenarios c and d, below are also detailed specific ways according to an example embodiment to trigger the switch from one operation mode to another, depending on whether there is present or not a (non-cooperating) network from a different radio access technology sharing channel resources with a Wi-Fi network. As will be seen, these triggering mechanisms account for the possibility that only a subset of the ST As associated to a given AP may be suffering from interference from the other/LTE network so not all associated STAs on all of the AP's Wi-Fi channels need to move to the coexisting technology operation mode. Also detailed is a mechanism to monitor those STAs and continue using the channel in the coexisting technology operation mode.

[0028] With the above fuller understanding of the environment and the possible scenarios as presently contemplated by the inventors, now are described embodiments of these teachings in the specific context of a Wi-Fi/IEEE 802.11 -type system operating with a coexisting LTE system. As noted above these are only example radio access technologies and the broader principles herein can be deployed with other pairs of coexisting radio access technologies. As noted above the Wi-Fi nodes coexisting with other technologies (LTE in the specific non-limiting examples) in a non-cooperative environment will implement what is termed herein as a coexisting technology operation mode. In this mode the Wi-Fi nodes can avoid their own Wi-Fi transmissions interfering on the coexisting technology as well avoid interference from transmissions in the coexisting technology.

[0029] For this operation mode, the Wi-Fi transmissions shall only occur within the boundaries of resource unit allocations defined by the coexisting technology that the Wi-Fi nodes can determine as being vacant. In the examples below these boundaries can be for a minimal (smallest) resource unit allocation defined by the coexisting technology, but in other embodiments the boundaries might be some integer multiple of the minimum. For LTE this minimal resource unit allocation is a LTE subframe, and in different embodiments the boundaries can be the boundaries of one subframe or of 2 or more consecutive subframes. The Wi-Fi nodes can determine such a LTE subframe as being vacant for example by using a criteria of the energy, detected during a certain interval in the start of this resource unit, being above a certain threshold that is termed herein for convenience a coexistence carrier sensing threshold. This interval is referred to below as a coexistence detection space and is shown in Figures 3-6 as detailed below.

[0030] If the energy in the coexistence detection space exceeds the coexistence carrier sensing threshold, the Wi-Fi node concludes the detected LTE sub frame/resource unit is occupied by transmissions from the coexisting technology, and so it enters a sleep mode through at least the end of the detected LTE subframe/resource unit that is occupied (or more generally until the end boundary of the resource unit allocation). A Wi-Fi ST A in the sleep mode depowers some of its circuitry to achieve a lower overall power consumption level, until the next triggering of the Coexistence Vacancy Sensing Timer (which occurs at the start of the next LTE subframe). If the energy in the coexistence detection space does not exceed the coexistence carrier sensing threshold, the Wi-Fi node concludes the detected LTE subframe/resource unit is vacant, and so it may enter the coexisting technology operation mode. When the Wi-Fi AP detects this resource unit as vacant, according to an exemplary implementation the AP will send a special coexistence beacon frame (still at the start of the vacant resource unit). This special coexistence beacon frame is understood by the Wi-Fi STAs as a signal that the AP is experiencing no blocking by transmissions of the coexisting technology.

[0031] From the AP's perspective the above steps may be summarized as follows. The AP detects within a predefined interval (the coexistence detection space CxDS) of a resource allocation of a coexisting second radio access technology (e.g., the predefined interval is within a LTE subframe) whether the resource allocation is occupied or vacant. One non-limiting way to implement this detecting is to compare an energy level sensed during the coexistence detection space against a predefined coexistence carrier sensing threshold. In this manner the detecting is independent of cooperation by any network node operating in the coexisting second radio access technology. Only when the resource allocation was detected to be vacant, the AP restricts transmissions according to a first radio access technology (e.g., Wi-Fi/IEEE 802.11) to occur within boundaries of the resource allocation (e.g., LTE subframe where the boundaries are of a minimum LTE resource allocation) of the coexisting second radio access technology (e.g., LTE) that was determined to be vacant. Otherwise, when the resource allocation is detected to be occupied, the AP can enter a sleep mode until the end of the LTE subframe that was detected as being occupied, and no transmissions according to the first radio access technology (e.g., Wi-Fi) occur within those LTE subframe boundaries.

[0032] For the case in which the LTE subframe is determined to be vacant, then after the coexistence detection space the AP may in an embodiment broadcast a coexistence beacon according to the first radio access technology/Wi-Fi that informs user devices /STAs operating according to the first radio access technology that the access node/AP is not being blocked by the coexisting second radio access technology/LTE. As will be detailed below, in an embodiment there is a contention interframe space CxIFS between the coexistence detection space and the coexistence beacon. [0033] In an exemplary embodiment there is also an optional procedure for the AP to check if the STAs to which it intends to transmit data (within this resource unit that the AP detected as vacant) are themselves being blocked by transmissions from the coexisting technology. This can occur for example when the AP itself does not see interference from the LTE network in the subframe it detected as vacant, but the STAs nearer to the LTE access node see interference from it as is detailed more particularly below with respect to Figure 5 where only STA#1 is blocked by LTE signals. In this embodiment the AP sends a poll to the STAs to which it intends to transmit, and the STAs reply to the AP's poll if they are not experiencing blocking by the LTE system. The AP interprets successful reception of a reply from a polled STA as meaning this STA was not blocked by a transmission from the coexisting technology/LTE in this resource unit that was determined to be vacant. This is detailed more particularly below with respect to Figure 6 where the blocked STA#1 does not reply to the AP's poll. The STAs can detect the LTE subframe the same as the AP; sense energy in the predefined interval/coexistence detection space and compare it to the coexistence carrier sensing threshold.

[0034] In order to ensure that Wi-Fi transmissions starting on a vacant resource unit from the coexisting techno logy/LTE do not cause interference on adjacent resource units of the coexisting technology as is shown at Figure IB (past the time 106A), in an embodiment of these teachings all of the participating Wi-Fi nodes (those which are in the coexisting technology operating mode) should keep track of the amount or available time until the end of the current vacant resource unit so as to ensure their transmission after the clear channel assessment (CCA) will not trespass the boundaries (106A of Figure IB) of this vacant resource unit.

[0035] To provide optimum efficiency these procedures need not be used when there is no nearly coexisting radio access technology network, and so there is a mechanism for Wi-Fi nodes to switch between the two described operation modes. This switchover procedure needs to be completed at the same time by the AP and by all the STAs operating on the channel or channels which are coexisting in both the Wi-Fi and the LTE systems. According to one exemplary embodiment this mechanism to change the operational mode is summarized as follows and detailed more particularly below with respect to Figure 2.

A. The Wi-Fi AP sends a clear-to-send message to reserve the channel for itself

(sometimes referred to as a CTS-to-self message). This operates to reserve the channel for an amount of time sufficient for performing the LTE detection.

B. The Wi-Fi AP sends a Coexistence Detection Request message in broadcast to all STAs in that basic service set (BSS). This coexistence detection request message defines a LTE Detection Interval and optionally also indicates the scheduling for the order in which each STA shall respond with its Coexistence Detection Report after the LTE Detection Interval.

C. All Wi-Fi nodes (AP and STAs) will perform the LTE Detection procedure to

identify presence of a coexisting LTE network. If there is a coexisting LTE network present then the Wi-Fi nodes will acquire time offset information about when the LTE sub frame starts.

D. All scheduled Wi-Fi STAs will send their Coexistence Detection Report in the order scheduled.

E. The Wi-Fi AP uses its own LTE Detection result and also the responses from the reporting ST As to determine whether LTE signaling is present, and also what is the time set to be used in order to synchronize with the LTE subframes.

F. The Wi-Fi AP sends in broadcast to all STAs the output/result of the LTE detection decision in a Coexistence Detection Result message.

G. All the Wi-Fi nodes then enter into the LTE Coexistence Operation Mode after the time offset specified by the Wi-Fi AP.

[0036] Since this process for identifying whether the Wi-Fi nodes should switch over from the normal to the coexistence operation mode takes time and consumes network radio resources for the signaling, it is advantageous to provide a triggering mechanism to avoid repeating this procedure unnecessarily. Following are some non-limiting examples of triggering mechanisms for triggering when the Wi-Fi nodes (or only the AP) will check whether or not to switch from the normal/conventional IEEE 802.1 1 operation mode to the LTE coexistence operation mode.

A. After a pre-determined amount of time (for example, once each 100 ms).

B. Upon a loss of a large number of packets addressed to a given ST A (which the AP will recognize by not receiving ACKs from that STA).

C. A message from a geo-location database informing that there is another secondary network using the channel near the location of the AP.

D. A special beacon sent by a blocked STA, during the LTE 'silent' period.

E. The AP observes that it has lost a connection with a STA.

F. The AP detects energy from another radio access technology in the channel (or otherwise detects presence of a LTE or other network).

[0037] One technical aspect of these teachings is the delimitation of Wi-Fi usage only within the bounds of vacant resource units from the coexisting technology, allied with the enforcement of the policy that each and every Wi-Fi transmission does not trespass those boundaries of the resource units found vacant. Both of these techniques operate to enable interference minimization without needing to coordinate among the coexisting technologies.

[0038] In an example embodiment, a trigger for enabling sleep mode for the Wi-Fi node may be defined as the detection of a transmission from the coexisting technology at the start of a given coexisting technology's resource unit. At the same time, this trigger is self-contained in the sense that the Wi-Fi network does not rely on cooperation from nodes or entities in the coexisting technology network for the detection to occur.

[0039] In an example embodiment, once the AP and STAs are in the LTE Coexistence Mode, they may switch back to the regular/conventional IEEE 802.11 Mode when the LTE system is not present. This enables one to avoiding unnecessarily requiring the signaling overhead that comes with the LTE Coexistence Mode, when the LTE signal is not present.

[0040] Figure 2 illustrates procedures for checking the channel to see whether the Wi-Fi nodes should transition from the regular/conventional IEEE 802.11 operation mode to the LTE coexistence operation mode. Figures 3-6 present different scenarios for a Wi-Fi system represented as one AP and two stations (STA#1 and STA#2) with a coexisting LTE system in the same TVWS band. These Wi-Fi nodes are in the LTE Coexistence Mode, which according to these teachings is characterized by the synchronization of the Wi-Fi operation to the periodicity and duration of LTE subframes. This is in contrast to the regular/conventional Wi-Fi mode operation which is guided by the carrier sense multiple access with collision avoidance (CSMA/CA) algorithm alone, and might be triggered once Wi-Fi nodes determine they are coexisting with a LTE system within the same channel. [0041] The examples presented herein make the following three assumptions.

• The Wi-Fi nodes have the capability for identifying operation with a coexisting wireless standard/technology, and are able to switch to a Technology Coexistence Mode.

• The coexisting technology occupies the channel based on a minimal time-slot resource unit granularity, in such a way that it either occupies the whole minimal resource unit (LTE subframe for the LTE system) or let it vacant.

• The Wi-Fi nodes know a priori the duration of the minimal resource unit of the coexisting technology, and are able to synchronize to the start of each of such resource units from the coexisting technology (and know the duration of the resource unit to which they synchronized).

[0042] Wi-Fi nodes are assumed to be aware when they are coexisting with another technology such as LTE in the same band and some non-limiting examples of sensing energy in the channel are given herein. Wi-Fi transmission opportunities might be created either by the interference from LTE being below a certain coexistence carrier sensing threshold, or by LTE occasionally rescinding from using the shared medium (i.e. TVWS channel band) for a given minimal resource unit (LTE sub frame). This rescinding by the LTE system can be for various and diverse reasons, such as for example a lack of demand or the purposeful decision to enable coexistence on the TVWS channel with other technologies such as Wi-Fi.

[0043] Now are examined more detailed examples of the different coexistence scenarios with the Wi-Fi nodes starting in the regular/conventional Wi-Fi operation mode, in order to demonstrate the trigger for checking whether the Wi-Fi nodes should switch to the coexistence mode, and also the actual switching to the LTE coexistence operation mode. The trigger can be any one or more of the following, but these are non-limiting and presented for example only. A first implementation of the trigger is that the Wi-Fi AP has detected, through energy sensing on the selected channel, the presence of a LTE network. A second implementation of the trigger is that the Wi-Fi AP observes that it has lost connection with one of the associated STAs, for example the AP notices that it has not received x consecutive ACKs from a specific STA (x is an integer greater than one). A third implementation of the trigger is that some predefined time has elapsed since the previous periodic LTE coexistence check. Several other non-limiting examples are listed at bullets A through F above.

[0044] Once a LTE detection trigger has been fired, on the next Wi-Fi AP transmission opportunity the AP will then perform the check to see if the Wi-Fi nodes should change to the LTE coexistence operation mode. Figure 2 illustrates one exemplary embodiment of this checking procedure. After a short interframe space SIFS following regular IEEE 802.11 operation (for example, conventional Wi-Fi data transmission) the AP sends a clear-to-send (CTS) message 202 (CTS-to-self) to reserve the channel for itself. This is the mechanism that operates to guarantee that all Wi-Fi nodes within that basic service set (BSS) will refrain from competing for the channel for an amount of time large enough for the whole LTE coexistence detection to be performed. That amount of time is shown at Figure 2 as the network allocation vector (NAV), shown by shading for each of the AP, STA#1 and STA#2.

[0045] Then immediately after the CTS-to-self 202 and waiting another SIFS, the AP sends a Coexistence Detection Request message 204, which informs that all Wi-Fi nodes are required to sense the channel for a pre-determined period. This period is termed herein as the coexistence detection window (or LTE Detection Window when the coexisting radio access technology is LTE). In an exemplary embodiment this message 204 includes at least one of a) the duration of the detection period 206 (shown in Figure 2 as 206- AP, 201-1 and 206-2), b) the detection mechanism, and c) the scheduling order in which each STA shall transmit (208-1, 208-2) their outcome from the LTE detection.

[0046] After receiving the coexistence detection request 204, all associated STAs and the AP will sense the channel, so that LTE transmissions (if any) are detected. During the "LTE Detection" shown at 208-AP, 208-1 and 208-2, the Wi-Fi nodes are assumed to be able to sense the spectrum such that they are able to determine whether LTE transmissions are occurring, and at which transmission power; and to synchronize with an LTE subframe, such that the Wi-Fi nodes are able to measure the time offset between the beginning 206-B of the LTE detection window and the beginning of LTE subframes.

[0047] Based on the outcome of the LTE Detection Window, the STAs will then send to the AP a Coexistence Detection Report message 208-1, 208-2 at their proper transmission order as specified in the scheduling order on the Coexistence Detection Request message 204. The coexistence Detection Reports each include information about at least one of a) whether a LTE transmission was detected, and b) the time-offset measured between the LTE frame and the beginning 206-B of the LTE Detection window.

[0048] There are at least three distinct cases after the LTE Detection window. In a first case neither Wi-Fi AP nor any STA sense LTE transmission, and the AP receives a coexistence detection report from each of the STAs. In this case the regular/conventional IEEE 802.11 operation mode is maintained.

[0049] In a second case the Wi-Fi AP senses a LTE transmission, and after waiting for the period reserved for receiving the Coexistence Detection Reports 208-1, 208-2 from the Wi-Fi STAs, the Wi-Fi AP sends a Coexistence Detection Result message 210, informing that all STAs should enter the LTE coexistence mode after some time offset. If for instance a STA is not able to decode the Coexistence Detection Result 210, it shall always assume that the AP may have detected LTE presence, and as such that STA shall enter the LTE coexistence mode and wait during a certain timeout period for a Coexistence Beacon in order to synchronize with LTE subframe. [0050] In a third case the Wi-Fi AP does not sense a LTE transmission, but at least one STA reports the presence of a LTE signal. In Figure 2 this sensing station is STA#2, and so after the AP receives this report 208-2, and waits for the remaining reports if any, the AP sends a Coexistence Detection Result message 210 informing that all STAs should enter the LTE coexistence mode after some time offset. If for instance the AP is not able to receive a Coexistence Detection Report from a STA at that STA's scheduled slot, then the AP shall assume that there is a chance that this STA might be blocked by LTE interference, and as such it shall repeat this LTE Coexistence Check again.

[0051] The switch back from the LTE coexistence mode to the regular 802.11 operation mode happens for example after the AP senses a given number of successive subframes that are not occupied by LTE signals. Such a given number may be termed a Coexistence Clearance Threshold. After this initial trigger is fired, the Wi-Fi AP needs to be reasonably certain that its STAs are also not being blocked by LTE subframe. As such, a mandatory LTE Interference Blockage Clearance Check with all STAs should be performed. Only after that all STAs reported that they are not coexisting with LTE, then the AP may assume that LTE transmission is no longer detectable. If for instance at least a single STA reports they have been blocked by LTE, then the AP assumes that all nodes in that BSS should keep operating in the LTE coexistence mode. If instead all STAs reported they are clear from LTE interference, then in the next coexistence subframe the AP may inform all STAs that the operation mode should be switched back to regular 802.11 operation by simply sending a conventional 802.11 beacon. After receiving this conventional 802.11 beacon, all STAs shall assume they should switch their operation mode back to regular 802.11 operation, meaning they should no longer need to be synchronized with LTE subframes. In order to increase confidence that such non-blockage reports from STAs are an accurate reflection of the coexisting LTE network not interfering, the AP might perform successive LTE Interference Blockage Clearance Check with all STAs not only after the Coexistence Clearance Threshold, but indeed within such threshold. So for example if the Coexistence Clearance Threshold is 200 subframes, then this check can be performed with 50, 100, 150 and 200 subframes.

[0052] Figures 3-6 present different scenarios for a Wi-Fi system represented as one AP and two stations (STA#1 and STA#2) in the LTE Coexistence Mode, with a coexisting LTE system in the same TVWS band. Once the Wi-Fi nodes are in LTE Coexistence Mode, each synchronizes an internal timer clock, which we term as a Coexistence Vacancy Sensing Timer. This timer is fired at the start of each LTE subframe and is used to determine the execution of the following actions:

A. At the start of every LTE subframe, all Wi-Fi nodes (AP and STAs) shall determine whether LTE is transmitting for the duration of this LTE subframe by performing an energy detection during a time interval which is termed herein as a Coexistence Detection Space (CxDS, shown as 302 in Figure 3), adjacent to the firing of the Coexistence Vacancy Sensing Timer. This energy detection can be quite simple in order to save energy at the portable Wi-Fi nodes since it is only used to determine whether an LTE signal is present, but in other embodiments it can be more complex.

B. If a Wi-Fi node (either AP or ST A) determines that the energy reception within the CxDS was above a certain LTE Interference Threshold, then this Wi-Fi node refrains from receiving or transmitting Wi-Fi traffic for the rest of the LTE subframe, and may preferably enter a lower power consumption level (known as Sleep Mode) until the next triggering of the Coexistence Vacancy Sensing Timer (which occurs at the start of the next LTE subframe).

C. If, instead a Wi-Fi node (either AP or STA) determines that the energy reception within the CxDS was below a certain LTE Interference Threshold, then this node waits for a certain Coexistence Inter-Frame Space (CxIFS, shown as 304 in Figure 3), which in these teachings can be far shorter than the conventional WLAN inter- frame spaces specified in IEEE 802.11 standards (specifically, the distributed inter- frame space DIFS and the short inter-frame space SIFS of conventional IEEE 802.11), before proceeding with operation in LTE Coexistence Mode;

• If this Wi-Fi node is a Wi-Fi AP, it shall send a Coexistence Beacon (shown as 306 in Figure 3), composed by a special frame, which is also referred to herein as a Coexistence Beacon, right after waiting the CxIFS, and which shall be composed by a Coexistence Preamble and a Coexistence Header.

• If this Wi-Fi node is a Wi-Fi STA, it shall expect the successful reception of a Coexistence Beacon from its Wi-Fi AP right after waiting the CxIFS.

[0053] If the Wi-Fi STA does not succeed in receiving a Coexistence Beacon from the Wi-Fi AP right after the CxIFS, then the Wi-Fi STA shall determine that the whole BSS is blocked by LTE interference, and as such it shall refrain from reception or transmission of Wi-Fi traffic and enter into a Sleep Mode for the rest of the LTE subframe. This scenario is shown in Figure 3; the AP and STA#1 are blocked by LTE subframe interference in LTE subframe n-1, while STA #2 is not blocked. STA #2 is notified of the AP being blocked by the lack of a coexistence beacon (CxBeacon 306) from the AP right after the coexistence detection space CxDS 302 at the start of the LTE subframe n-1 (with the CxIFS 304 between them). The bounds 354 and 356 of LTE subframe n-1 are shown to extend to the whole portion of Figure 3 representing activity in the Wi-Fi system. The AP and STA #1 become aware that there is LTE interference right after the end of the coexistence detection space CxDS 302 since they detect the LTE traffic occupancy directly. STA#2 does not detect the LTE interference directly, and so STA #2 still has to wait for the coexistence interframe space CxIFS 304 prior to expecting to receive a coexistence beacon CxBeacon 306, and so only becomes aware of LTE interference after STA#2 does not successfully receive the expected coexistence beacon CxBeacon 306.

[0054] If instead the Wi-Fi STA does succeed in receiving the Coexistence Beacon from the Wi-Fi AP, then it shall determine that the whole BSS is free from interference from LTE for the rest of the LTE subframe. This scenario is shown in Figure 4, which more particularly illustrates a situation where the LTE system refrains from using a given LTE subframe n. Following the CxBeacon 306 there is a contention for the channel among STA#1 and STA#2. This contention may be conventional; every Wi-Fi node waits a DIFS 308 and then contends for the channel in a contention slot 310. This is a conventional Clear Channel Assessment (CCA) which the relevant nodes do prior to accessing the channel (wait DIFS plus the chosen number of contention slots). STA#2 loses that contention and so both AP and STA #1 engage in traffic exchange with the AP sending downlink data 312D to STA#1, STA#1 sending uplink an acknowledgement (ACK 314U) after a SIFS, and after the STA#1 wins the contention in the subsequent contention slot following a DIFS the STA#1 sends uplink data 312U which the AP replies with a downlink ACK 314D after waiting a SIFS. Both AP and STA #1 observe the limit of the remaining time within the vacant LTE subframe n (limits 354, 356 shown for subframe n-1 in Figure 3). STA #2 loses the contentions and so is unable to send or receive data in the Wi-Fi system within the bounds of this n-1 subframe despite the channel being available in Figure 4, so STA#2 simply refrains from transmitting or receiving until the start of the next LTE subframe.

[0055] Figures 5-6 illustrate how the lack of a feedback mechanism for STA blockage generates a waste of resources (Figure 5), and demonstrates how the LTE Interference Blockage Check allows resource optimization by enabling the AP to transmit only to non-blocked Wi-Fi STAs (Figure 6).

[0056] First consider the lack of the feedback mechanism for STA blockage in Figure 5. There, after the Wi-Fi AP determined that it (but has not determined that the STAs) was not blocked by a transmission in the n+1 LTE subframe, and has transmitted a Coexistence Beacon 306, it sends data to STA#1 assuming STA#1 is also not blocked. But in the Figure 5 hypothetical case STA#1 is blocked by transmissions in the n+1 LTE subframe and so STA#1 does not receive the data transmission from the AP. STA#1 cannot ACK the data it did not receive, and since the LTE transmission in LTE subframe n+1 which blocked STA#1 fills the whole LTE subframe, then also STA#1 will be unable to send its uplink data to the AP as it was able to do in Figure 4 during LTE subframe n. The entire channel from the end of the beacon 306 to the start of the next LTE subframe is wasted in the Wi-Fi system and the nodes are not even in the sleep mode, except perhaps STA#1 since it never received the coexistence beacon 306. This situation can arise when the relative position of the nodes are generally as shown at the inset at the left side of Figure 5.

[0057] Figure 6 illustrates the exact same channel interference situation as Figure 5 but showing how the feedback mechanism can more efficiently utilize the available (non- interfered) radio resources. After the Wi-Fi AP determined that it was not blocked by a transmission in the n+1 LTE subframe, and has transmitted a Coexistence Beacon 306, the AP in Figure 6 has optionally decided to perform a LTE Interference Blockage Check procedure in order to determine whether a given set of Wi-Fi STAs is being blocked by LTE subframe transmission or not. At Figure 6 the AP sends a LTE Interference Blockage Clearance Poll message 602 after a CxIFS following the CxBeacon 306, which makes all STAs set their NAV timers (shown in shading at the bottom of the STA#1 and STA#2 rows within the Overhead' interval) so the STAs do not contend for the channel. Also, notice that each LTE Interference Blockage Clearance Reply message 604-1, 604-2 from the respective STAs has the exact duration of a Blockage Report Slot Time (BRST). Finally after this entire LTE Interference Blockage Clearance procedure is over (when the NAV timers are expired), all Wi-Fi nodes return to the CSMA contention for channel access as was detailed above for Figure 4. [0058] In an exemplary embodiment of these teachings the LTE Interference Blockage Clearance Check procedure is as follows:

A. The LTE Interference Blockage Clearance Check procedure starts by the Wi-Fi AP sending a LTE Interference Blockage Clearance Poll frame 602 after a CxIFS succeeding the Coexistence Beacon 306. This LTE Interference Blockage Clearance

Poll frame 602 shall contain at least a mandatory list of unique STA identifiers, relative to the set of STAs the AP wants to poll for blockage clearance in this LTE sub frame (n+1 in Figure 6).

B. As the CxIFS is smaller than a DIFS, the Wi-Fi STAs will receive the LTE Interference Blockage Clearance Poll frame 602 from the Wi-Fi AP before managing to make the first transmission. After the transmission of this clearance poll frame 602, all STAs shall understand that a LTE Interference Blockage Clearance Polling Schedule was created, such that after a CxIFS succeeding this LTE Interference Blockage Clearance Poll frame 602 the AP shall expect to receive a set of LTE Interference Blockage Clearance Reply frames 604- 1 , 604-2 from the polled

STAs, each to be sent within a given LTE Interference Blockage Clearance Slots in the number equal to the number of polled STAs.

1. All STAs in that BSS shall set their NAV timer after the reception of the LTE Interference Blockage Clearance Poll frame 602 to the duration of a CxIFS plus the duration of LTE Interference Blockage Clearance Slots (the BRSTs in Figure 6), such that they do not attempt to contend for the channel during that period of time and simply suspend their DIFS counters prior to proceeding with clear channel assessment CCA right after the LTE Interference Blockage Clearance Poll procedure is finished.

2. If the STA was NOT blocked by LTE subframe interference and was included in the list of polled STAs within the LTE Interference Blockage Clearance Poll frame 602 as is the case for STA#2 in Figure 6, it shall wait for an amount of time equal to a CxIFS after the reception of the LTE Interference Blockage Clearance Poll frame 602, and use its position within the informed set of STAs to be polled at the header of the LTE Interference Blockage Clearance Poll frame 602 as an indication of which LTE Interference Blockage Clearance Slot it shall use to send its LTE Interference Blockage Clearance Reply frame 604-2.

• Each LTE Interference Blockage Clearance Slot shall have the exact duration of the minimal amount of information required to transmit a LTE Interference Blockage Clearance Reply frame 604-2, herein called Blockage Report Slot Time (BRST).

3. If the STA was blocked by LTE subframe interference or was not able to receive correctly the Coexistence Beacon 206 from the AP as is the case for STA#1 in Figure 6, the steps herein described mandate this STA should refrain from contending for the channel during that LTE subframe, and may optionally sleep for the rest of this LTE subframe n+1.

The Wi-Fi AP shall understand the lack of reception of the LTE Interference Blockage Clearance Reply frames (the AP does not receive poll reply frame 604-1 in Figure 6) on the expected LTE Interference Blockage Clearance Slots as an indication of the polled STA or STAs detecting LTE subframe transmissions during the CxDS interval (i.e. being blocked by LTE subframe transmission, and therefore these STAs are now sleeping), and shall use such information to decide to which STAs it shall transmit Data frames in the remaining time within this vacant LTE subframe n+1.

[0059] After the determination that the BSS is free from LTE interference for the rest of the LTE subframe (that is, detection during the CxDS, silent period in CxIFS and the transmission of the Coexistence Beacon) and the optional execution of the LTE Interference Blockage Check, both the Wi-Fi AP and Wi-Fi STAs which have not been blocked by LTE subframe transmission may engage in CSMA/CA or any other IEEE 802.11 operation (such as power save multi-poll PSMP) for the remaining time within this vacant LTE subframe as was detailed for Figure 4. In this case, for each Wi-Fi node wishing to transmit during this period, calculations should be made to ensure that the amount of time required to transmit the given data frame and receive the ACK frame using the current modulation and coding scheme (MCS) is less than or equal to the amount of remaining interference-free time from the coexisting technology.

A. For a given contention slot randomly chosen by the Wi-Fi node, if the amount of time required for the contention plus the transmission of the Data frame and the reception of the ACK frame is greater than the amount of remaining time within this LTE subframe, then the Wi-Fi node shall decide whether it enters on contention and employs fragmentation to diminish the Data frame or simply refrain from entering in contention for the channel for the rest of the LTE subframe.

B. If instead the amount of time required for the contention, transmission of the data frame and the reception of the ACK is less than or equal than the amount of time remaining in the interference- free period, then the Wi-Fi node shall enter in Clear

Channel Assessment (CCA) by listening to the channel for a DIFS to ensure the channel is clear prior to contending (using regular/conventional IEEE 802.11 procedures) for the channel. 1. If the Wi-Fi node wins the contention, then it performs the transmission of a data frame and waits for the reception of the ACK frame.

2. If instead the Wi-Fi node loses the contention, it shall perform a conventional IEEE 802.11 exponential back-off, taking care that if the back-off window is larger than the time remaining in the LTE subframe then the back-off window shall be frozen at the end of this LTE subframe and re-started just after another vacant LTE subframe is detected and the corresponding Coexistence Beacon is successfully received from the Wi-Fi AP. [0060] In an example embodiment, the Coexistence Preamble is a special signal, which may be implemented to be similar to conventional IEEE 802.11 preambles, which shall be easily detected via correlation by the Wi-Fi STAs and also enable easy time and frequency synchronization for entering Wi-Fi STAs that are not yet synchronized. The Coexistence Header uniquely identifies the current BSS (for example, using the service set identifier SSID) such that entering Wi-Fi STAs can determine whether the current BSS is the one they are looking for. This coexistence header may also in an embodiment contain any additional information that may help the Wi-Fi STAs performing operation during LTE Coexistence Mode.

[0061] The LTE Interference Blockage Clearance Poll frame contains a list of unique ST A identifiers (for example, MAC addresses) that the AP wants to poll for blockage clearance in this LTE subframe, and the exact order of the STAs within this list shall be interpreted by the polled STAs as a scheduling order for when the transmission of the LTE Interference Blockage Clearance Reply frames should occur within the LTE Interference Blockage Clearance Slots. Optionally, the LTE Interference Blockage Clearance Poll frame may also indicate that the STAs can incorporate on their respective LTE Interference Blockage Clearance Reply frames information other than their unique identifiers, such as for example the size of their uplink buffers so the AP knows how much data they have to send.

[0062] The LTE Interference Blockage Clearance Reply frames should contain a mandatory unique STA identifier (for example, MAC addresses), and optionally may contain any type of additional information requested by the AP on the LTE Interference Blockage Clearance Poll frame.

[0063] Flowcharts for the operation within LTE coexistence mode for both the Wi-Fi AP and Wi-Fi STAs are represented respectively on Figure 7 and Figure 8, while Figure 9 and Figure 10 present respectively how CSMA/CA could be implemented within vacant LTE subframes and how the LTE Interference Blockage Check are to be implemented. These Figures provide a summary of the procedures for which further details were presented above. [0064] Figure 7 begins with the AP synchronizing to the start of the LTE subframe at block 702 and then sensing the channel at block 704. The AP decides at block 706 is the channel is blocked or not by LTE transmissions. If no then the flow proceeds to block 708 where the AP waits a CxlFS before transmitting a CxBeacon at block 710, after which the AP can decide at block 712 whether or not to do a blockage check. Such a blockage check is done in Figure 7 at block 714 and is detailed more fully with respect to Figure 10. Assuming this blockage check 714 shows the AP and at least one STA as not being blocked by LTE transmissions, then the AP can proceed to occupy the channel using Wi-Fi technology at block 716, for example using the conventional CSMA/CA procedures as are further summarized at Figure 9. If instead the decision by the AP at block 706 is that the channel is blocked by LTE transmissions, then the AP can sleep at block 718. Whether the AP occupies the channel as in block 716 or sleeps as in block 718, the occupy/sleep status continues until the end of the LTE subframe 720, after which the AP begins again at the start of Figure 7 for the next LTE subframe.

[0065] Figure 8 is similar to Figure 7 except from the STA's perspective, so the first several process blocks are the same for the STA as for the AP and are not again expanded upon. The STA receives the AP's CxBeacon at block 810 if initial sensing shows that the channel is not blocked, and assuming it is correctly received at block 812 (that is, this STA is not itself blocked by LTE transmissions in the subframe) then this STA can participate in the interference blockage check at 814 and with the AP occupy the channel at block 816 with Wi-Fi transmissions. If the initial sensing shows there are LTE transmissions in the channel, or the STA does not successfully receive the AP's CxBeacon, then the STA at block 818 can sleep until the end of the LTE subframe at 820.

[0066] The flow diagram at Figure 9 illustrates exemplary steps for how CSMA/CA could be implemented within vacant LTE subframes and gives further detail of blocks 716 and 816 of respective Figure 7 and 8. If the check at block 904 indicates the end of the LTE subframe then block 904 tells the Wi-Fi node to finish the CSMA/CA exchange process within the vacant LTE subframe, else block 906 checks whether the node executing Figure 9 has data to send. If no then the node prepares to receive data at block 910, else the node checks if it has started a new contention timer at block 912. IF there is a new contention timer then the node selects a random contention slot at block 914, else it resumes its existing/ongoing contention timer at block 916. At block 918 the node fragments its packet to send so as not to exceed the end of the vacant LTE subframe at 920. If this is not possible and the LTE subframe will be exceeded then at block 922 the node refrains from transmitting its data at block 922 and updates its contention timer at block 924.

[0067] If instead at block 920 it is determined that the packet can fit within the remaining portion of the LTE subframe, then if the node executing Figure 9 is the AP (block 926) it waits a SIFS at block 928 A and it the node is a STA it waits a DIFS at block 928B. After waiting for the contention slot at block 930, if the node did not win the channel contention at block 932 then it updates its contention timer at block 934, receives data at block 910 and sends an ACK for the received data at block 936. If the node executing Figure 9 won the contention at block 932, then it resets its contention timer at block 938, sends it data at block 940, and receives an ACK from the receiving party (AP or STA) at block 942. [0068] Figure 10 summarizes the LTE Interference Blockage Check according to an exemplary but non- limiting embodiment of these teachings. If the node executing Figure 10 is the AP at block 1002 then the flow proceeds to block 1004 in which the AP sends a LTE interference blockage check poll to the STAs, waits a CxIFS at block 1006 and at block 1008 receives the replies from the STAs to the poll from block 1004 and then determines from those replies which STAs are not blocked by LTE transmissions at block 1010. If data is to be exchanged in the vacant LTE frame the AP will restrict such data exchanges with those STAs determined at block 1010 to not be blocked by LTE transmissions.

[0069] If instead it is a STA which is performing the process flow of Figure 10, then the STA at block 1012 receives the AP's LTE interference blockage check poll and if it was not successfully decoded at block 1014 (such as may happen due to LTE interference) then the STA is finished with its part of the blockage check at 1010. If the poll form the AP is correctly received and decoded at 1014 then the STA checks the decoded poll at 1016 to see if it is one of the polled STAs. If no then the STA can skip 1018 the remainder of the blockage check process and is finished 1010. IF the STA is polled then it waits a CxIFS at block 1020, waits at block 1022 for its slot to send its blockage clearance report (since the order of these reports is given by the poll itself) and at the proper slot the STA sends its LTE interference blockage clearance reply at block 1024. [0070] The logic flow diagrams of Figures 7-10 summarize some of the non- limiting and exemplary embodiments of the invention from the perspective of the AP or STA or similar such nodes of another non- Wi-Fi network (or certain components thereof if not performed by the entire AP/STA). These Figures may each be considered to illustrate the operation of a method, and a result of execution of a computer program stored in a computer readable memory, and a specific manner in which components of an electronic device are configured to cause that electronic device to operate, whether such an electronic device is the access node in full or one or more components thereof such as a modem, chipset, or the like.

[0071] The various blocks shown at Figures 7-10 may also be considered as a plurality of coupled logic circuit elements constructed to carry out the associated function(s), or specific result of strings of computer program code or instructions stored in a memory. Such blocks and the functions they represent are non-limiting examples, and may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

[0072] Exemplary embodiments of these teachings provide the technical effect of allowing Wi-Fi nodes to coexist with LTE while avoiding both interfering with the LTE system and avoiding the Wi-Fi signals suffering from LTE interference, which might cause packed drops for Wi-Fi. In the examples above the whole operation is autonomous to LTE, which in essence eases coexistence. The Wi-Fi nodes may additionally save power when sleeping, instead of keeping awake for CCA when LTE subframe transmissions are occurring. The described blockage notification mechanism allows both AP and STAs to optimize their resources, no matter whether they are blocked by LTE subframe interference or not. And finally the mechanisms for triggering the activation and deactivation of the described LTE coexistence mode ensure that they are only used when Wi-Fi nodes are actually coexisting with LTE. [0073] Reference is now made to Figure 11 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing the exemplary embodiments of this invention. In Figure 11 an AP 22 is adapted for communication over a wireless medium/link 10 with an apparatus, such as a mobile device/terminal or a radio-equipped sensor or a user equipment, all of which stand in the place of the STA in the examples above. Figure 11 shows only two STAs 20-1 and 20-2 but there may many STAs served by a single AP 22. The AP 22 may be any access node (including frequency selective repeaters) of any wireless network such as WLAN/Wi-Fi in the examples above, or it may be an access node that utilizes some other (first) radio access technology such as for example cellular technologies LTE, LTE-A, GSM, GERAN, WCDMA, and the like which may be coexisting with a second radio access technology. The AP 22 provides the STAs 20-1, 20-2 with connectivity to further networks via data link 14 (for example, a data communications network/Internet as shown and/or a publicly switched telephone network).

[0074] One STA 20-1 is detailed below (referred to as STA 20) but the other STA 20-2 is functionally similar though it may be not be physically identical or even made by the same manufacturer. The STA 20 includes processing means such as at least one data processor (DP) 20A, and storing means such as at least one computer-readable memory (MEM) 20B storing at least one computer program (PROG) 20C or other set of executable instructions. In some embodiments the STA 20 may also include communicating means such as a transmitter TX 20D and a receiver RX 20E that may be embodied for example in a chipset or RF front end chip. In other embodiments the STA 20 may comprise only one, or even more than the two illustrated antennas 20F. In either case the TX 20D, RX 20E and antenna(s) 20F are for bidirectional wireless communications with the AP 22. Also stored in the MEM 20B at reference number 20G is the UE's algorithm or function or selection logic for implementing coexistence of the first radio access technology and some second radio access technology such as LTE in the above non-limiting examples, as detailed above. The STA 20 uses this algorithm or function or selection logic 20G in conjunction with the AP 22.

[0075] The AP 22 may comprise processing means such as at least one data processor (DP) 22A, storing means such as at least one computer-readable memory (MEM) 22B storing at least one computer program (PROG) 22C or other set of executable instructions. The AP22 may also comprise communicating means such as a transmitter TX 22D and a receiver RX 22E for bidirectional wireless communications with the STA 20, for example via one or more antennas 22F. The AP 22 may store at block 22G the algorithm or function or selection logic for implementing coexistence of the first radio access technology with some second radio access technology such as LTE in the above non-limiting examples, as detailed above. The AP 22 uses this algorithm or function or selection logic 22G in conjunction with the ST As 20-1 and 20-2.

[0076] At least one of the PROGs 22C/22G in the AP 22, and PROGs 20C/20G in the STA 20, is assumed to include a set of program instructions that, when executed by the associated DP 22A/20A, may enable the device to operate in accordance with the exemplary embodiments of this invention, as detailed above. In these regards the exemplary embodiments of this invention may be implemented at least in part by computer software stored on the MEM 20B, 22B which is executable by the DP 20A of the STA 20 and/or by the DP 22A of the AP 22, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware). Electronic devices implementing these aspects of the invention need not be the entire devices as depicted at Figure 11 but may be one or more components of same such as the above described tangibly stored software, hardware, firmware and DP, or a system on a chip SOC or an application specific integrated circuit ASIC.

[0077] In general, the various embodiments of the STA 20 can include, but are not limited to digital devices having wireless communication capabilities such as smartphones, radio devices with sensors operating in a machine-to -machine type environment; and personal portable radio devices such as but not limited to cellular telephones, navigation devices, laptop/palmtop/tablet computers, digital cameras and music devices, and Internet appliances.

[0078] Various embodiments of the computer readable MEMs 20B, 22B include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the DPs 20A, 22A include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and multi-core processors.

[0079] Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description. While the exemplary embodiments have been described above in the context of the WLAN/Wi-Fi/IEEE 802.11 system in the position of the first radio access technology and LTE in the position of the coexisting second radio access technology, as noted above the exemplary embodiments of this invention may be used with various other types of wireless communication systems that are currently in use or as may be adapted over time in the future.

[0080] Further, some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

Claims

CLAIMS: We claim:

1. A method comprising:

detecting within a predefined interval of a resource allocation of a coexisting second radio access technology whether the resource allocation is occupied or vacant; and

only when the resource allocation was detected to be vacant, restricting transmissions according to a first radio access technology to occur within boundaries of the resource allocation of the coexisting second radio access technology that was determined to be vacant.

2. The method according to claim 1, the method further comprising:

when the resource allocation was detected to be occupied, entering a sleep mode.

3. The method according to claim 1 or 2, wherein the predefined interval is of a minimum resource allocation of the coexisting second radio access technology.

4. The method according to any of claims 1-3, wherein:

the predefined interval is a coexistence detection space;

the detecting comprises comparing an energy level sensed during the coexistence detection space against a predefined coexistence carrier sensing threshold; and

the detecting is independent of cooperation with any network node operating in the coexisting second radio access technology.

5. The method according to claim 4, in which the method is executed by an access node operating according to the first radio access technology and the method further comprises: after the coexistence detection space, broadcasting according to the first radio access technology a coexistence beacon that informs user devices operating according to the first radio access technology that the access node is not being blocked by the coexisting second radio access technology.

6. The method according to claim 5, the method further comprising, after broadcasting the coexistence beacon, performing a carrier sense multiple access with collision avoidance CSMA/CA operation for channel contention during a remainder of the resource allocation that was detected to be vacant.

7. The method according to claims 5 or 6, the method further comprising:

sending an interference blockage check poll after broadcasting the coexistence beacon; and

during a remainder of the resource allocation that was detected to be vacant, restricting data exchange to only those nodes which have replied to the interference blockage check poll indicating that they are not experiencing blockage by the second radio access technology.

8. The method according to any of claims 1-7, in which the method is executed by an access node operating according to the first radio access technology and the method further comprises:

prior to the detecting, the access node sending a clear-to-send message to reserve a channel in which the detecting is performed.

9. The method according to claim 8, further comprising:

after sending the clear-to-send message, the access node broadcasting a coexistence detection request message which indicates duration of a coexistence detection window and which schedules an order for stations to reply to the coexistence detection request message with their respective coexistence detection reports after the coexistence detection window.

10. The method according to claim 9, further comprising: utilizing at least coexistence detection reports received from the respective stations to determine whether to switch to a coexistence operation mode.

11. The method according to any of claims 8-10, wherein the sending of the clear-to-send message is triggered by at least one of:

expiration of a periodic timer running for a predetermined amount of time;

packet loss of packets addressed to a given station exceeding a threshold;

determining that a wireless connection with a station is lost;

information received from a geo-location database informing that another network is operating using other than the first radio access technology and near an access node executing the method;

sensing by the access node executing the method that another network is operating using other than the first radio access technology and near the access node; and

a beacon that is received from a station at an access node executing the method during a silent period defined for the coexisting second radio access technology.

12. The method according to any of claims 1-4, in which the method is executed by a station operating according to the first radio access technology,

and wherein the restricting of the transmissions according to the first radio access technology is only when the resource allocation was detected to be vacant and the station successfully receives a coexistence beacon from an access node operating according to the first radio access technology.

13. The method according to any of claims 1 -4 or 12, in which the method is executed by a station operating according to the first radio access technology, the method further comprising:

receiving an interference blockage check poll from an access node operating according to the first radio access technology; and

indicating to the access node that the station is not experiencing blockage by the second radio access technology in response to the received interference blockage check poll.

14. The method according to any of claims 1-4 or 12-13, in which the method is executed by a station operating according to the first radio access technology, the method further comprising:

receiving a coexistence detection request message which indicates duration of a coexistence detection window and which schedules an order for stations to reply to the coexistence detection request message;

and transmitting a coexistence detection reports after the coexistence detection window.

15. The method according to any of claims 1-4 or 12-14, in which the method is executed by a station operating according to the first radio access technology, the method further comprising:

receiving an instruction from an access node to switch to a coexistence operation mode.

16. The method according to any of claims 1-15, wherein:

the first radio access technology is IEEE 802.11, and

the transmissions according to the first radio access technology, that are restricted to occur within boundaries of the resource allocation of the coexisting second radio access technology that was determined to be vacant, are made without explicit coordination with any network entity operating and coexisting on the second radio access technology.

17. An apparatus comprising:

at least one computer readable memory storing a set of instructions; and

at least one processor;

wherein the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least to:

detect within a predefined interval of a resource allocation of a coexisting second radio access technology whether the resource allocation is occupied or vacant; and

only when the resource allocation was detected to be vacant, restrict transmissions according to a first radio access technology to occur within boundaries of the resource allocation of the coexisting second radio access technology that was determined to be vacant.

18. The apparatus according to claim 17, wherein the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least further to:

when the resource allocation was detected to be occupied, enter a sleep mode.

19. The apparatus according to claim 17 or 18, wherein the predefined interval is of a minimum resource allocation of the coexisting second radio access technology.

20. The apparatus according to any of claims 17-19, wherein:

the predefined interval is a coexistence detection space;

21. The apparatus according to claim 20, wherein the apparatus comprises an access node operating according to the first radio access technology and the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least further to:

after the coexistence detection space, broadcast according to the first radio access technology a coexistence beacon that informs user devices operating according to the first radio access technology that the access node is not being blocked by the coexisting second radio access technology.

22. The apparatus according to claim 21, wherein the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least further to, after broadcasting the coexistence beacon, perform a carrier sense multiple access with collision avoidance CSMA/CA operation for channel contention during a remainder of the resource allocation that was detected to be vacant.

23. The apparatus according to claims 21 or 22, wherein the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least further to:

send an interference blockage check poll after broadcasting the coexistence beacon; and

during a remainder of the resource allocation that was detected to be vacant, restrict data exchange to only those nodes which have replied to the interference blockage check poll indicating that they are not experiencing blockage by the second radio access technology.

24. The apparatus according to any of claims 17-23, wherein the apparatus comprises an access node operating according to the first radio access technology and the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least further to: prior to the detecting, send a clear-to-send message to reserve a channel in which the detecting is performed.

25. The apparatus according to claim 24, wherein the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least further to:

after sending the clear-to-send message, broadcast a coexistence detection request message which indicates duration of a coexistence detection window and which schedules an order for stations to reply to the coexistence detection request message with their respective coexistence detection reports after the coexistence detection window.

26. The apparatus according to claim 25, wherein the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least further to: utilize at least coexistence detection reports received from the respective stations to determine whether to switch to a coexistence operation mode.

27. The apparatus according to any of claims 24-26, wherein sending of the clear-to-send message is triggered by at least one of:

expiration of a periodic timer running for a predetermined amount of time;

packet loss of packets addressed to a given station exceeding a threshold;

determining that a wireless connection with a station is lost;

28. The apparatus according to any of claims 17-20, wherein the apparatus comprises a station operating according to the first radio access technology,

and wherein the restricting of the transmissions according to the first radio access technology is only when the resource allocation was detected to be vacant and the station successfully receives a coexistence beacon from an access node operating according to the first radio access technology

29. The apparatus according to any of claims 17-20 or 28, wherein the apparatus comprises a station operating according to the first radio access technology and the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least further to:

receive an interference blockage check poll from an access node operating according to the first radio access technology; and

indicate to the access node that the station is not experiencing blockage by the second radio access technology in response to the received interference blockage check poll.

30. The apparatus according to any of claims 17-20 or 28-29, wherein the apparatus comprises a station operating according to the first radio access technology and the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least further to:

receive a coexistence detection request message which indicates duration of a coexistence detection window and which schedules an order for stations to reply to the coexistence detection request message;

and transmit a coexistence detection reports after the coexistence detection window.

31. The apparatus according to any of claims 17-20 or 28-30, wherein the apparatus comprises a station operating according to the first radio access technology and the at least one computer readable memory with the set of instructions is configured with the at least one processor to cause the apparatus at least further to:

receive an instruction from an access node to switch to a coexistence operation mode.

32. The apparatus according to any of claims 17-31, wherein:

the first radio access technology is IEEE 802.11, and

33. A computer readable memory storing a set of executable instructions comprising: code for detecting within a predefined interval of a resource allocation of a coexisting second radio access technology whether the resource allocation is occupied or vacant; and

code for restricting transmissions according to a first radio access technology to occur within boundaries of the resource allocation of the coexisting second radio access technology that was determined to be vacant, only when the resource allocation was detected to be vacant.

34. The computer readable memory according to claim 33, wherein the set of executable instructions further comprises:

code for entering a sleep mode when the resource allocation was detected to be occupied.

35. The computer readable memory according to claim 33 or 34, wherein the predefined interval is of a minimum resource allocation of the coexisting second radio access technology.

36. The computer readable memory according to any of claims 33-35, wherein:

the predefined interval is a coexistence detection space;

37. The computer readable memory according to claim 36, wherein the memory is a part of an access node operating according to the first radio access technology and the set of executable instructions further comprises:

code for broadcasting according to the first radio access technology, after the coexistence detection space, a coexistence beacon that informs user devices operating according to the first radio access technology that the access node is not being blocked by the coexisting second radio access technology.

38. The computer readable memory according to claim 37, wherein the set of executable instructions further comprises code for performing, after broadcasting the coexistence beacon, a carrier sense multiple access with collision avoidance CSMA/CA operation for channel contention during a remainder of the resource allocation that was detected to be vacant.

39. The computer readable memory according to claims 37 or 38, wherein the set of executable instructions further comprises:

code for sending an interference blockage check poll after broadcasting the coexistence beacon; and

code for restricting, during a remainder of the resource allocation that was detected to be vacant, data exchange to only those nodes which have replied to the interference blockage check poll indicating that they are not experiencing blockage by the second radio access technology.

40. The computer readable memory according to any of claims 33-39, wherein the memory is a part of an access node operating according to the first radio access technology and the set of executable instructions further comprises:

code for sending, prior to the detecting, a clear-to-send message to reserve a channel in which the detecting is performed.

41. The computer readable memory according to claim 40, wherein the set of executable instructions further comprises:

code for broadcasting, after sending the clear-to-send message, a coexistence detection request message which indicates duration of a coexistence detection window and which schedules an order for stations to reply to the coexistence detection request message with their respective coexistence detection reports after the coexistence detection window.

42. The computer readable memory according to claim 41 , wherein the set of executable instructions further comprises:

code for utilizing at least coexistence detection reports received from the respective stations to determine whether to switch to a coexistence operation mode.

43. The computer readable memory according to any of claims 40-42, wherein the sending of the clear-to-send message is triggered by at least one of:

expiration of a periodic timer running for a predetermined amount of time;

packet loss of packets addressed to a given station exceeding a threshold;

determining that a wireless connection with a station is lost;

44. The computer readable memory according to any of claims 33-36, wherein the memory is a part of a station operating according to the first radio access technology, and wherein the restricting of the transmissions according to the first radio access technology is only when the resource allocation was detected to be vacant and the station successfully receives a coexistence beacon from an access node operating according to the first radio access technology.

45. The computer readable memory according to any of claims 33-36 or 44, wherein the memory is a part of a station operating according to the first radio access technology and the set of executable instructions further comprises:

code for receiving an interference blockage check poll from an access node operating according to the first radio access technology; and

code for indicating to the access node that the station is not experiencing blockage by the second radio access technology in response to the received interference blockage check poll.

46. The computer readable memory according to any of claims 33-36 or 44-45, wherein the memory is a part of a station operating according to the first radio access technology and the set of executable instructions further comprises: code for receiving a coexistence detection request message which indicates duration of a coexistence detection window and which schedules an order for stations to reply to the coexistence detection request message;

and code for transmitting a coexistence detection reports after the coexistence detection window.

47. The computer readable memory according to any of claims 33-36 or 44-46, wherein the memory is a part of a station operating according to the first radio access technology and the set of executable instructions further comprises:

code for receiving an instruction from an access node to switch to a coexistence operation mode.

48. The computer readable memory according to any of claims 33-47, wherein:

the first radio access technology is IEEE 802.11, and