WO2014064322A1 - Évitement de brouillage et économies d'énergie pour une coexistence parmi différentes technologies d'accès radio - Google Patents

Évitement de brouillage et économies d'énergie pour une coexistence parmi différentes technologies d'accès radio Download PDF

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Publication number
WO2014064322A1
WO2014064322A1 PCT/FI2012/051008 FI2012051008W WO2014064322A1 WO 2014064322 A1 WO2014064322 A1 WO 2014064322A1 FI 2012051008 W FI2012051008 W FI 2012051008W WO 2014064322 A1 WO2014064322 A1 WO 2014064322A1
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WIPO (PCT)
Prior art keywords
radio access
access technology
coexistence
coexisting
resource allocation
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PCT/FI2012/051008
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English (en)
Inventor
Fuad JUNIOR
Erika ALMEIDA
Robson DOMINGOS
Rafael PAIVA
Fabiano CHAVES
Andre Cavalcante
Felipe Costa
Sayantan Choudhury
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Nokia Corporation
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Priority to PCT/FI2012/051008 priority Critical patent/WO2014064322A1/fr
Publication of WO2014064322A1 publication Critical patent/WO2014064322A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/14—Spectrum sharing arrangements between different networks
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/541—Allocation or scheduling criteria for wireless resources based on quality criteria using the level of interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/10—Small scale networks; Flat hierarchical networks
    • H04W84/12—WLAN [Wireless Local Area Networks]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Definitions

  • 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.
  • 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.
  • PSM power saving mode
  • U-APSD unscheduled automatic power save delivery
  • EDCA enhanced distributed channel access
  • WMM-PS wireless multimedia power save
  • S-APSD scheduled (synchronous) version
  • IEEE 802.11 ⁇ 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.
  • 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.
  • an apparatus comprising at least one computer readable memory storing a set of executable instructions, and at least one processor.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Figure 4 is similar to Figure 3 but illustrating Wi-Fi nodes using the vacant LTE subframe according to an embodiment of these teachings.
  • 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.
  • 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.
  • FIG. 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.
  • 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.
  • 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.
  • CSMA/CA carrier sense multiple access with collision avoidance
  • Figure 10 is a flow diagram illustrating procedures for a LTE interference blockage check according to an embodiment of these teachings.
  • FIG 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.
  • any underlying lower-power Wi-Fi nodes operating on the same channel typically suffer from interference.
  • the minimal LTE allocation units are the LTE subframes 102, which are larger than the duration of a standard Wi-Fi slot.
  • 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.
  • CSMA carrier sense multiple access
  • 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.
  • 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.
  • 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).
  • MCS modulation and coding scheme
  • 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.
  • LTE coexisting technology
  • the Wi-Fi frame will need to be re-transmitted, resulting in a throughput degradation for both technologies.
  • 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".
  • 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.
  • 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;
  • the Wi-Fi network is operating in the coexisting technology operation mode and it is sharing the spectrum at that location with another technology;
  • the Wi-Fi network is operating in the coexisting technology operation mode and it is the single technology using the spectrum at that location;
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Wi-Fi/IEEE 802.11 -type system operating with a coexisting LTE system.
  • the Wi-Fi nodes coexisting with other technologies LTE in the specific non-limiting examples
  • 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.
  • 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.
  • 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.
  • 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.
  • 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).
  • the Wi-Fi node concludes the detected LTE subframe/resource unit is vacant, and so it may enter the coexisting technology operation mode.
  • 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.
  • 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.
  • a predefined interval the coexistence detection space CxDS
  • the predefined interval is within a LTE subframe
  • 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.
  • 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.
  • a first radio access technology e.g., Wi-Fi/IEEE 802.11
  • 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.
  • a contention interframe space CxIFS between the coexistence detection space and the coexistence beacon.
  • 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.
  • 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.
  • the Wi-Fi AP sends a clear-to-send message to reserve the channel for itself
  • CTS-to-self message (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.
  • 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.
  • All Wi-Fi nodes (AP and STAs) will perform the LTE Detection procedure to
  • the Wi-Fi nodes will acquire time offset information about when the LTE sub frame starts.
  • 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.
  • the Wi-Fi AP sends in broadcast to all STAs the output/result of the LTE detection decision in a Coexistence Detection Result message.
  • All the Wi-Fi nodes then enter into the LTE Coexistence Operation Mode after the time offset specified by the Wi-Fi AP.
  • the AP detects energy from another radio access technology in the channel (or otherwise detects presence of a LTE or other network).
  • 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.
  • 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.
  • the AP and STAs 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.
  • 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.
  • 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.
  • CSMA/CA carrier sense multiple access with collision avoidance
  • 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).
  • 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.
  • 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.
  • FIG. 2 illustrates one exemplary embodiment of this checking procedure.
  • the AP sends a clear-to-send (CTS) message 202 (CTS-to-self) to reserve the channel for itself.
  • CTS clear-to-send
  • BSS basic service set
  • NAV network allocation vector
  • 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.
  • the Wi-Fi nodes 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.
  • 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.
  • 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.
  • 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.
  • the Wi-Fi AP does not sense a LTE transmission, but at least one STA reports the presence of a LTE signal.
  • 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.
  • 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.
  • 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.
  • 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.
  • FIGS 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.
  • 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:
  • all Wi-Fi nodes 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.
  • 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).
  • CxIFS Coexistence Inter-Frame Space
  • this Wi-Fi node 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.
  • a Coexistence Beacon shown as 306 in Figure 3
  • a special frame which is also referred to herein as a Coexistence Beacon
  • 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.
  • 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.
  • 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.
  • 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).
  • CCA Clear Channel Assessment
  • 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.
  • 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).
  • 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.
  • 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.
  • 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.
  • 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:
  • 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).
  • 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
  • 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.
  • 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).
  • BRST Blockage Report Slot Time
  • 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.
  • 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.
  • 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.
  • the Wi-Fi node shall enter in Clear
  • CCA Channel Assessment
  • the Wi-Fi node 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Block 708 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.
  • a blockage check is done in Figure 7 at block 714 and is detailed more fully with respect to Figure 10.
  • this blockage check 714 shows the AP and at least one STA as not being blocked by LTE transmissions
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Figure 10 summarizes the LTE Interference Blockage Check according to an exemplary but non- limiting embodiment of these teachings.
  • 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.
  • 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.
  • FIGS. 1-10 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.
  • 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.
  • 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.
  • 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.
  • FIG. 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.
  • 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).
  • 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.
  • processing means such as at least one data processor (DP) 20A
  • MEM computer-readable memory
  • PROG computer program
  • 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.
  • the STA 20 may comprise only one, or even more than the two illustrated antennas 20F.
  • the TX 20D, RX 20E and antenna(s) 20F are for bidirectional wireless communications with the AP 22.
  • the MEM 20B 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • digital devices having wireless communication capabilities such as smartphones, radio devices with sensors operating in a machine-to -machine type environment
  • 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.
  • 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.

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Abstract

Selon la présente invention, un réseau fonctionnant dans une première technologie d'accès radio RAT (par exemple, WiFi) peut éviter un brouillage vers/depuis un autre réseau fonctionnant dans une 2nde RAT (par exemple, LTE) par détection à l'intérieur d'un intervalle prédéfini, d'une affectation de ressources de la 2nde RAT coexistante, si l'affectation de ressources (par exemple, une sous-trame) est occupée ou vacante. Seulement lorsque l'affectation de ressources a été détectée comme vacante, des émissions selon la 1ère RAT sont restreintes pour se produire à l'intérieur de frontières de l'affectation de ressources de la 2nde RAT coexistante qui a été déterminée comme vacante. Lorsque l'affectation de ressources a été détectée comme occupée, des nœuds dans la 2nde RAT peuvent entrer dans un mode de sommeil pour des économies d'énergie. Les nœuds peuvent comparer un niveau d'énergie détecté durant l'intervalle prédéfini à un seuil prédéfini pour la détection. Toutes ces procédures peuvent être indépendantes d'une coopération avec n'importe quel nœud de réseau fonctionnant dans la 2nde RAT coexistante.
PCT/FI2012/051008 2012-10-22 2012-10-22 Évitement de brouillage et économies d'énergie pour une coexistence parmi différentes technologies d'accès radio WO2014064322A1 (fr)

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