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WO2018167566A1 - Sélection de mode d'évaluation de canal libre pour entrée multiple sortie multiple (mimo) dans des bandes de fréquences sans license - Google Patents

Sélection de mode d'évaluation de canal libre pour entrée multiple sortie multiple (mimo) dans des bandes de fréquences sans license Download PDF

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Publication number
WO2018167566A1
WO2018167566A1 PCT/IB2018/000340 IB2018000340W WO2018167566A1 WO 2018167566 A1 WO2018167566 A1 WO 2018167566A1 IB 2018000340 W IB2018000340 W IB 2018000340W WO 2018167566 A1 WO2018167566 A1 WO 2018167566A1
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WIPO (PCT)
Prior art keywords
user equipment
cca
mode
channel
lbt
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Ceased
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PCT/IB2018/000340
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English (en)
Inventor
Giovanni GERACI
Adrian GARCIA RODRIGUEZ
David LOPEZ-PEREZ
Lorenzo GALATI GIORDANO
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Alcatel Lucent SAS
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Alcatel Lucent SAS
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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0808—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • 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

Definitions

  • Unlicensed frequency bands are portions of the radiofrequency spectrum that do not require a license for use and may therefore be used by any device compliant with regulations to transmit or receive radiofrequency signals.
  • Wireless communication devices that transmit or receive signals in licensed or unlicensed frequency bands are typically referred to as nodes, which include Wi-Fi access points that operate according to IEEE 802.1 1 standards in the unlicensed spectrum.
  • Nodes also include base stations that operate in the licensed spectrum according to standards such as Long Term Evolution (LTE) standards defined by the Third Generation Partnership Project (3GPP).
  • Base stations that operate according to LTE can implement supplementary downlink (SDL) channels in the unlicensed spectrum to provide additional bandwidth for downlink communications to user equipment that are also communicating with the base station using channels in a licensed frequency band.
  • SDL supplementary downlink
  • the licensed frequency bands may be referred to as LTE-L bands and the unlicensed frequency bands may be referred to as LTE-U bands.
  • Other base stations operate in the unlicensed frequency bands according to Licensed Assisted Access (LAA) standards. Some base stations operate solely in the unlicensed frequency bands without support in licensed frequency bands, e.g., according to emerging standards such as MuLTEFire.
  • LAA Licensed Assisted Access
  • Some base stations operate solely in the unlicensed frequency bands without support in licensed frequency bands, e.g., according to emerging standards such as MuLTEFire.
  • Demand for the unlicensed frequency bands is growing and guaranteeing seamless inter-technology coexistence is essential to support the broad range of technologies operating in the unlicensed frequency bands. Access to the unlicensed frequency band is therefore strictly regulated and nodes operating within the unlicensed frequency bands must comply with well- defined regulatory requirements.
  • FIG. 1 is a block diagram of a wireless communication system that includes a base station that provides wireless connectivity via a multiple-input, multiple-output (M IMO) array according to some embodiments.
  • FIG. 2 is a block diagram of the wireless communication system that performs enhanced clear channel assessment (CCA) using spatial nulls to filter received energy in an unlicensed frequency band according to some embodiments.
  • CCA enhanced clear channel assessment
  • FIG. 3 is a flow diagram of a method for classifying user equipment in a conventional CCA mode or an enhanced CCA mode according to some embodiments.
  • FIG. 4 illustrate a sequence of messages including request-to-send pilot (RSTP) messages and pilot signals transmitted by user equipment according to some embodiments.
  • RSTP request-to-send pilot
  • FIG. 5 is a flow diagram of a method for acquiring a channel of an unlicensed frequency band using a conventional CCA mode or an enhanced CCA mode according to some embodiments.
  • channels in the unlicensed frequency bands are reused by nodes that operate according to different radio access technologies (RATs) such as Wi-Fi access points and LTE base stations.
  • RATs radio access technologies
  • Communication by the nodes that operate according to the different RATs is coordinated using clear channel assessment (CCA) techniques to reduce interference between transmissions by the different nodes.
  • CCA clear channel assessment
  • LBT listen before talk
  • LBT coexistence rules require that each node monitors a channel (e.g., "listens") to detect energy on the channel prior to transmitting information on the channel. If the detected energy level is below a threshold level, the channel is considered clear and the node is free to transmit on the channel for a predetermined time interval.
  • M IMO arrays include large number of antennas to provide a large number of spatial degrees of freedom that support spatially multiplexed communication with multiple user equipment.
  • a massive M IMO array of N antennas can provide a spatially multiplexed channel to each of K user equipment as long as N ⁇ K. Additional spatial degrees of freedom may be allocated to interference suppression to improve coexistence with other transmitters, such as interfering Wi-Fi nodes. For example, interference with D single-antenna interfering nodes is suppressed by allocating at least D degrees of freedom to spatial nulls that are placed onto spatial directions corresponding to the D interfering nodes, where D ⁇ N - K. Massive M IMO arrays are therefore able to place radiation nulls to suppress interference along directions towards other nodes during data transmission and during mandatory LBT phases. Thus, a node that implements a massive MIMO array with interference suppression becomes "invisible" to the nodes that have been nulled and does not interfere with the nulled nodes, thereby resulting in a larger reuse of the unlicensed frequency bands.
  • Nulling is used to enhance CCA techniques such as LBT because transmissions from nulled nodes are filtered out of the aggregate power of the signals that are received during the listening time interval.
  • the massive M IMO array is eligible to transmit if the received energy from other nodes, e.g., nodes that are not nulled, is less than the threshold level that indicates that the channel is occupied by another node, regardless of whether the nulled nodes are transmitting.
  • the enhanced LBT technique increases spectrum reuse in the spatial domain by allowing concurrent transmissions by the massive MIMO array and nulled nodes. However, the increased spectrum reuse comes with a trade-off.
  • the user equipment that are served by the massive MIMO array are not aware of the nulling performed by the massive MIMO array and are therefore able to receive signals transmitted by the nulled nodes, which can potentially interfere with the signals transmitted by the massive M IMO array.
  • conventional LBT supports lower spectrum reuse while providing minimal interference at the user equipment
  • enhanced LBT supports higher spectrum reuse while allowing for higher levels of interference at the user equipment.
  • either approach could provide for a higher data rate in transmissions from the massive MIMO array.
  • FIGs. 1 -5 disclose a base station that implements a MIMO array configured to selectively utilize a conventional CCA mode such as LBT or an enhanced CCA mode such as enhanced LBT based on a comparison of values of metrics calculated under the assumptions that conventional CCA is used and enhanced CCA is used.
  • the conventional CCA mode is performed without placing nulls on directions associated with interfering nodes.
  • the enhanced CCA mode places nulls on the directions associated with the interfering nodes.
  • a first metric is calculated based on a first data rate that is estimated assuming conventional LBT and a second metric is calculated based on a second data rate that is estimated assuming enhanced LBT.
  • the first and second metrics are calculated for each user equipment served by the base station.
  • the user equipment are associated with either conventional LBT or enhanced LBT based on the relative values of the first metric and the second metric for the corresponding user equipment.
  • the first and second metrics are calculated based on estimates of a spatial reuse factor, a power of a signal received on a channel supported by the massive MIMO array, powers of interfering signals, and a previous data rate received by the user equipment.
  • the estimates are performed based on parameters such as a received signal power from the massive M IMO array, interference from transmitting access points, previously achieved data rates, successful/unsuccessful reception of pilot signals after a request-to-send pilot message, quality-of- service (QoS) parameters for the user equipment, and the like.
  • QoS quality-of- service
  • the base station orders the user equipment based on scheduling priorities for the user equipment and the base station chooses between conventional LBT and enhanced LBT based on the ordered list of user equipment. For example, the base station can choose to utilize the LBT mode associated with the highest priority user equipment. For another example, the base station can select the LBT mode using combinations of the values of the metrics of the user equipment. The base station then attempts to gain access to the channels using the selected conventional or enhanced LBT technique and, if successful, the base station transmits data towards the user equipment via the massive MIMO array.
  • the data is transmitted omnidirectionally if conventional LBT was used for CCA or, in some embodiments, spatial multiplexing is used to point beams towards receiving devices, which may require reducing the overall transmission power so that the power in some directions is not increased by pointing the beams.
  • the user equipment associated with the conventional LBT mode have a larger priority to be scheduled in this case. If enhanced LBT was used for clear channel assessment, the spatial nulls, as well as any other beamforming or spatial multiplexing supported by the spatial degrees of freedom available at the massive M IMO array, are applied if enhanced LBT was used for the clear channel assessment. The user equipment associated with the enhanced LBT mode have a larger priority to be scheduled in this case.
  • FIG. 1 is a block diagram of a wireless communication system 100 that includes a base station 105 that provides wireless connectivity via a M IMO array 1 10 according to some embodiments.
  • the M IMO array 1 10 includes a plurality of antenna elements 1 15, only one indicated by a reference numeral in the interest of clarity. Transmission and reception by the plurality of antenna elements 1 15 is coordinated by the base station 1 05, which provides modulated baseband signals to the antenna elements 1 15 for transmission over an air interface and receives modulated baseband signals from the antenna elements 1 15.
  • the base station 105 demodulates and decodes the received signals and provides the information in the decoded signals to other entities (not shown) in the wireless communication system 100, e.g., using one or more processors 1 16 that execute instructions stored in one or more memories 1 17.
  • the base station 105 and the M IMO array 1 10 are also referred to collectively as a node of the wireless communication system 100.
  • the term "base station” will be used herein to refer to the processors, memories, and other circuitry used to generate baseband signals for transmission by the M IMO array 1 10 and receive baseband signals from the MIMO array 1 10.
  • the base station 105 is configured to exchange signals with the user equipment 120, 121 , 122, 123 (collectively referred to herein as "the user equipment 120-123") in licensed or unlicensed frequency bands. Some embodiments of the base station 105 are therefore configured to operate in the licensed spectrum according to standards such as Long Term Evolution (LTE) standards defined by the Third Generation Partnership Project (3GPP). Some embodiments of the base station 1 05 also implement supplementary downlink (SDL) channels in the unlicensed spectrum to provide additional bandwidth for downlink communications to the user equipment 120-123. The base station 1 05 provides control signaling to the user equipment 120-123 for the SDL channels in a licensed frequency band.
  • LTE Long Term Evolution
  • 3GPP Third Generation Partnership Project
  • the licensed frequency bands are referred to as LTE-L bands and the unlicensed frequency bands are referred to as LTE-U bands.
  • Some embodiments of the base station 1 05 operate in the unlicensed frequency bands according to Licensed Assisted Access (LAA) standards.
  • Some embodiments of the base station 105 operate solely in the unlicensed frequency bands without support in licensed frequency bands, e.g., according to emerging standards such as MuLTEFire.
  • LAA Licensed Assisted Access
  • the base station 105 performs a clear channel assessment (CCA) prior to transmitting in the unlicensed frequency band.
  • CCA clear channel assessment
  • Some embodiments of the base station 105 perform a listen-before-talk (LBT) operation to detect energy on a channel in the unlicensed frequency band prior to transmitting information on the channel. If the base station 105 detects an energy level on the channel that is below a threshold level, the channel is considered clear and the base station 105 is free to transmit on the channel for a predetermined time interval. If the detected energy level is above the threshold level, which indicates that the channel is not clear because another node is transmitting on the channel, the base station 105 backs off until the energy level falls below the threshold.
  • LBT listen-before-talk
  • the energy detection threshold for Wi-Fi is -62 decibel-milliwatts (dBm) and the energy detection threshold for LTE-U, LAA is -72 dBm, and MuLTEFire is -72 dBm.
  • Wi-Fi nodes may also perform Wi-Fi preamble decoding on signals with detected energy levels below the energy detection threshold and above -82 dBm . The Wi- Fi node backs off if it successfully decodes preambles in transmissions by other Wi-Fi nodes at an energy level between -62 dBm and -82 dBm.
  • the base station 105 utilizes the spatial degrees of freedom of the M IMO array 1 10 to create spatial channels 125, 126, 127, 128 (collectively referred to herein as "the spatial channels 125-128") along one or more directions, such as the directions from the M IMO array 1 10 towards the user equipment 120-124.
  • the base station 1 05 uses conventional omnidirectional LBT to listen for transmissions by other nodes during a listening time interval.
  • the base station generates an aggregate general covariance matrix based on the energy detected during the listening time interval.
  • the aggregate general covariance matrix is used to generate spatial channels or nulls, generate precoding matrices, perform spatial multiplexing, or perform beamforming.
  • the wireless communication system 100 also includes access points 130, 135 that provide wireless connectivity in the unlicensed frequency band within corresponding geographic areas or cells 140, 145.
  • the energy detected by the base station 105 includes transmissions by the access points 130, 135. Consequently, the base station 1 05 bypasses transmission on a channel of the unlicensed frequency band and backs off if the energy transmitted by one or more of the access points 130, 135 exceeds the energy detection threshold for the conventional omnidirectional LBT process.
  • the conventional LBT process therefore ensures that the channel of the unlicensed frequency band is clear of transmissions by all nodes including the user equipment 120-124 and the access points 130, 135 while the base station 105 is transmitting signals via the M IMO array 1 1 0.
  • the conventional LBT process is overly conservative in some situations and prevents spatial reuse of the same channels of the unlicensed frequency band by the base station 105 and the access points 130, 135.
  • FIG. 2 is a block diagram of the wireless communication system 100 that performs enhanced clear channel assessment (CCA) using spatial nulls to filter received energy in an unlicensed frequency band according to some embodiments.
  • CCA enhanced clear channel assessment
  • the illustrated embodiment of the wireless communication system 100 differs from the embodiments depicted in FIG. 1 because the base station 1 05 uses a subset of the spatial degrees of freedom of the MIMO array 1 10 to place spatial nulls 150, 155 along directions corresponding to the access points 130, 135.
  • the spatial nulls 1 50, 155 and the spatial channels 125-128 are formed based on channel covariance matrices that are determined by measuring an aggregate power received by the MIMO array 1 10 on a channel of the unlicensed frequency band and filtered through the spatial nulls 150, 155.
  • the spatial nulls 1 50, 155 are well- placed, e.g., they successfully filter substantially all of the energy transmitted by the access points 130, 135 in the direction of the M IMO array 1 10, concurrent transmissions by the access points 130, 135 on the channel are not detected during the enhanced CCA.
  • the base station 105 therefore determines that the channel is clear (provided that no other nodes are transmitting on the channel during the listening time interval) and the base station 105 acquires the channel.
  • the base station 105 and the access points 130, 135 are therefore able to transmit concurrently on the channel of the unlicensed frequency band.
  • Downlink transmissions by the access points 130, 135 generate interference with downlink transmissions from the M IMO array 1 10 when the access points 130, 135 and the base station 105 are transmitting concurrently.
  • the base station 105 is transmitting towards the user equipment 120 in the unlicensed frequency band via the spatial channel 125.
  • the access point 130 is concurrently transmitting signals 160 in the unlicensed frequency band.
  • the signals 160 interfere with the signals transmitted via the spatial channel 125 at the user equipment 120.
  • the access point 135 is also concurrently transmitting signals 165 in the unlicensed frequency band.
  • the signals 165 interfere with the signals transmitted via the spatial channel 127 towards the user equipment 122.
  • an enhanced CCA such as enhanced LBT supports spectrum reuse in the spatial domain by allowing the base station 105 to access channels of the unlicensed frequency bands for downlink transmission even when one or more other nodes are transmitting.
  • the trade-off is that concurrent transmission by other nodes creates interference at user equipment 120-123 that are being served by the base station 105.
  • the embodiments of the wireless communication system 100 shown in FIG. 1 and FIG. 2 demonstrate that the conventional omnidirectional CCA and the enhanced CCA using spatial nulls to filter received signals are both able to provide performance benefits in particular circumstances, but neither conventional omnidirectional CCA nor enhanced CCA is optimal in all circumstances.
  • conventional CCA ensures low interference at the user equipment 120-123 being served by the base station 105 at the potential cost of decreasing the efficiency of the wireless communication system 100 by sacrificing spectrum reuse.
  • enhanced CCA increases the efficiency of the wireless communication system 100 by permitting spectrum reuse at the potential cost of increased interference at the user equipment 120- 123 being served by the base station 105.
  • Some embodiments of the base station 105 balance the competing demands for spectrum reuse and low interference at the user equipment 120-123 by selectively performing either conventional CCA or enhanced CCA based on estimated data rates for downlink transmissions on channels of the unlicensed frequency band that are acquired according to the different approaches.
  • embodiments of the base station 1 05 calculate first metrics based on first data rates that are estimated assuming that the conventional CCA mode is used to acquire the channel of the unlicensed frequency band for one or more of the user equipment 120-123.
  • the base station 105 also calculates second metrics based on second data rates that are estimated assuming that the enhanced CCA mode is used to acquire the channel of the unlicensed frequency band for the user equipment 1 20-1 23.
  • the base station 1 05 selects either the conventional CCA mode or the enhanced CCA mode based on the values of the first and second metrics.
  • the base station 1 05 uses the selected CCA mode to acquire the channel of the unlicensed frequency band for the user equipment 120-123.
  • FIG. 3 is a flow diagram of a method 300 for classifying user equipment in a conventional CCA mode or an enhanced CCA mode according to some embodiments.
  • the method 300 is implemented in some embodiments of the base station 1 05 shown in FIGs. 1 and 2.
  • the base station performs CCA using LBT processes.
  • the base station therefore classifies user equipment in an LBT mode or an enhanced LBT mode.
  • the base station accesses parameters that characterize signals that are transmitted or received via a M IMO array.
  • the parameters include one or more of, but are not limited to, a power of a signal received by the user equipment from the M IMO array, a measure of interference at the user equipment from neighboring nodes such as Wi-Fi devices, previous data rates achieved by the user equipment, whether the M IMO array receives a requested pilot signal from the user equipment, quality-of-service (QoS) parameters for the user equipment, and the like. Subsets of the parameters are combined to form different metrics to assess the relative benefits of classifying the user equipment as conventional LBT mode or enhanced LBT mode.
  • QoS quality-of-service
  • Some embodiments of the user equipment provide reports that indicate the powers of signals received from the M IMO array. This information is used to determine whether spatial reuse (e.g., according to the enhanced LBT mode) is likely to benefit the user equipment.
  • the received signal power is an indicator of the proxim ity of the user equipment to the M IMO array.
  • User equipment that are closer to the M IMO array are more likely to benefit from enhanced LBT because more proximate user equipment are less vulnerable to interference received from concurrent transmission by other nodes such as Wi-Fi devices.
  • Some embodiments of the user equipment provide reports indicating values of measurements of (interfering) signals received from neighboring nodes such as nearby Wi-Fi devices.
  • the user equipment can implement automatic neighbor relations (AN R) functionality that allows the user equipment to provide reports including information indicating identifiers of Wi-Fi access points that generate interfering signals that are detected using intra-frequency or inter-frequency measurements requested by the base station.
  • AN R automatic neighbor relations
  • Some embodiments of the base station use the previous data rates achieved by the user equipment to determ ine whether they are likely to benefit from enhanced LBT.
  • User equipment that have previously received low data rates after acquiring a channel in the unlicensed frequency band using enhanced LBT and have a received signal power larger than a given threshold are also likely receiving a high level of interference from a neighboring node that is hidden from the base station.
  • the base station may not be able to detect the neighboring node using AN R functionality. In that case, the user equipment is likely to benefit from being classified in the conventional LBT mode to ensure that the user equipment do not receive interference from the neighboring nodes.
  • Some embodiments of the base station transm it a request-to-send pilot (RSTP) message to the user equipment in response to the user equipment being scheduled for data transmission.
  • the user equipment is expected to transm it its pilot signal in response to receiving the RSTP message so that the base station can acquire a channel state information (CS I) for the user equipment.
  • the user equipment is also required to perform LBT before transmitting the pilot signal.
  • the LBT performed by the user equipment is not likely to be successful if there are neighboring nodes that are transmitting concurrently or if the user equipment has previously received a network allocation vector (NAV) message from the neighboring node indicating that the channel is occupied.
  • NAV network allocation vector
  • User equipment that do not convey pilot signals in response to the RSTP request should therefore be classified in the conventional LBT mode.
  • An example of a message exchange including an RSTP request and response is shown in FIG. 4.
  • Some embodiments of the base station use QoS parameters for the user equipment to classify the user equipment as conventional LBT or enhanced LBT because the different modes have distinct features that determine the type of traffic that should be managed using the different modes. For example, user equipment that are receiving delay sensitive data are likely to be better served using enhanced LBT because enhanced LBT has a larger probability of successfully acquiring a channel in the unlicensed frequency band, relative to conventional LBT, which reduces the data transm ission delay.
  • the base station estimates the first, conventional LBT metric based on the signal parameters.
  • Some embodiments of the base station estimate the conventional LBT metric m k l LBT according to the form ula: where R k denotes data transmission rates for user equipment /( served by a base station / ' and the terms P ik , P jk , and P lk denote power received from the serving M IMO base station, interfering M IMO base stations, and Wi-Fi access points, respectively, when the user equipment are served according to conventional LBT.
  • the first metric is therefore a ratio of the estimated data rate (E) to a previous data rate received by the user equipment.
  • the estimated data rate is determ ined based on the estimated spectral reuse gain ( LBT ) , received power on the intended channel of the unlicensed frequency band (P ik ) , a sum of the received power over neighboring devices that operate according to the same RAT ( ⁇ j ⁇ i P jk ), and a sum of the received powers over neighboring devices that operate according to different RATs ( ie£ z.Br P lk ) .
  • the base station estimates the second, enhanced LBT metric based on the signal parameters.
  • Some embodiments of the base station estimate the enhanced LBT metric m k eLBT according to the formula: where R k denotes data transmission rates for user equipment /( served by a base station / ' and the terms P ik , P jk , and P lk denote power received from the serving MIMO base station, interfering M IMO base stations, and Wi-Fi access points, respectively, when the user equipment are served according to enhanced LBT.
  • the second metric is therefore a ratio of the estimated data rate (E) to a previous data rate received by the user equipment.
  • the estimated data rate is determined based on the estimated spectral reuse gain (a eLBT ), received power on the intended channel of the unlicensed frequency band (P ik ) , a sum of the received power over neighboring devices that operate according to the same RAT ( ⁇ j ⁇ i Pjk), and a sum of the received powers over neighboring devices that operate according to different RATs ( ⁇ l e£ eLBr P lk ) .
  • a eLBT estimated spectral reuse gain
  • P ik received power on the intended channel of the unlicensed frequency band
  • ⁇ j ⁇ i Pjk a sum of the received power over neighboring devices that operate according to the same RAT
  • ⁇ l e£ eLBr P lk a sum of the received powers over neighboring devices that operate according to different RATs
  • the choice of mode between the conventional LBT mode or the enhanced LBT mode affects several of the parameters in the above equations for the first and second metrics.
  • the mode selection affects the interference received from neighboring nodes such as Wi-Fi devices, because more neighboring nodes are active concurrently with the base station in the enhanced LBT mode relative to the conventional LBT mode.
  • the actual value of the spatial reuse factor depends on the number of coexisting nodes. In some cases, the value can be set by assuming that the channel is shared for a fraction of the total time that is inversely proportional to the number of coexisting devices and, in contrast, conventional LBT does not provide any spatial reuse gain because the channel must be shared through discontinuous transmission with neighboring nodes.
  • the conventional LBT metric is compared to the enhanced LBT metric.
  • the first and second metrics are defined so that larger values of the metrics indicate higher estimated data rates.
  • the base station therefore sets the value of the metric for the user equipment equal to the maximum value of the first and second metrics: max(m£ BT ' , m BT ) If the first metric for conventional LBT is greater than the second metric for enhanced LBT, the method 300 flows to block 325. If the first metric for conventional LBT is less than the second metric for enhanced LBT, the method 300 flows to block 330.
  • the user equipment is classified in the conventional LBT mode.
  • the value of the metric for the user equipment is set equal to the value of the first metric that is calculated assuming that the user equipment is classified in the conventional LBT mode.
  • the user equipment is classified in the enhanced LBT mode.
  • the value of the metric for the user equipment is set equal to the value of the second metric that is calculated assuming that the user equipment is classified in the enhanced LBT mode.
  • the optimal LBT mode for a user equipment is likely to change in response to changes in
  • radiofrequency conditions changes in physical locations of the neighboring nodes or the user equipment, and the like.
  • Some embodiments of the method 300 are therefore performed periodically at predetermined time intervals, in response to events, or at other times.
  • FIG. 4 illustrates a sequence 400 of messages including request-to-send pilot (RSTP) messages and pilot signals transmitted by user equipment according to some embodiments.
  • a base station for a MIMO array (MIMO BS) transmits an RSTP message 405 to a user equipment (UE).
  • the user equipment responds to the RSTP by transmitting a pilot signal 410, which the base station uses to acquire a channel state information (CSI) for the user equipment.
  • CSI channel state information
  • the user equipment performs LBT to acquire a channel of the unlicensed frequency band before transmitting the pilot signal.
  • the base station subsequently transmits RSTP message 415 to the user equipment.
  • the user equipment performs LBT to attempt to acquire the channel of the unlicensed frequency band but, in this case, the user equipment is receiving an interfering signal 420 from a neighboring Wi-Fi node.
  • the LBT process is therefore unsuccessful and the user equipment is unable to acquire the channel of the unlicensed frequency band to transmit the pilot signal, as indicated by the dashed line 425.
  • Some embodiments of the base station therefore classify the user equipment in the conventional LBT mode for subsequent communication with the user equipment.
  • FIG. 5 is a flow diagram of a method 500 for acquiring a channel of an unlicensed frequency band using a conventional CCA mode or an enhanced CCA mode according to some embodiments.
  • the method 500 is implemented in some embodiments of the base station 105 shown in FIGs. 1 and 2.
  • the base station performs CCA using LBT processes.
  • the base station therefore acquires the channel of the unlicensed frequency band using an LBT mode or an enhanced LBT mode.
  • the enhanced LBT mode includes performing LBT concurrently with placing nulls on directions associated with neighboring nodes that transmit on the channel in the unlicensed frequency band or performing LBT while applying a receive filter that represents a beamforming pattern to the received "listen" signals.
  • the base station classifies the user equipment as conventional LBT mode or enhanced LBT mode. Some embodiments of the base station perform the classification using the method 300 shown in FIG. 3. An example of the CCA mode classification of the user equipment shown in FIGs. 1 and 2 is given in Table 1 .
  • the base station orders the user equipment based on priorities associated with the user equipment. In each transmission slot, the base station decides on a subset of user equipment to schedule for data transmission. Priorities of the user equipment are determined based on scheduling metrics, such as proportional fairness metrics, which are modified from the conventional practice to account for the classification of the user equipment in different CCA modes. For example, user equipment that are served after a channel in the unlicensed frequency band has been acquired using enhanced LBT are likely to experience interference from neighboring nodes. Moreover, the user equipment are potentially served with a reduced number of spatial degrees of freedom of the M IMO array because some of the spatial degrees of freedom are used to place nulls along the directions towards neighboring nodes.
  • scheduling metrics such as proportional fairness metrics
  • U Es that are served after the channel in the unlicensed frequency band has been acquired using conventional LBT do not experience interference from neighboring nodes and all of the spatial degrees of freedom of the MIMO array are available for beamforming and spatial multiplexing.
  • Some embodiments of the scheduling metrics are modified by incorporating one or more scaling factors along with a signal-plus-interference-to-noise ratio (SIN R) factor that is computed using conventional scheduling metrics.
  • SINR signal-plus-interference-to-noise ratio
  • the base station calculates a decision metric to determine whether to use the conventional LBT mode or enhanced LBT mode to acquire the channel of the unlicensed frequency band for one or more of the user equipment. Some embodiments of the base station acquire a channel using the mode associated with the highest rank user equipment. For example, the base station can acquire the channel of the unlicensed frequency band using the mode associated with the user equipment 122 that has the highest rank in Table 2. Some embodiments of the base station determine a value of the decision metric using the number or the priority of the user equipment that are associated with conventional LBT and enhanced LBT.
  • the base station can determine the decision metric by adding up values of the scheduling metrics for the number of user equipment that are to be spatially multiplexed. Addition of the scheduling metrics is done independently for user equipment that are associated with the conventional LBT mode and user equipment that are associated with the enhanced LBT mode. The base station would then acquire the channel of the unlicensed frequency band using the mode with the largest overall priority.
  • the base station determines whether the decision metric indicates that the conventional LBT mode or the enhanced LBT is used to acquire the channel of the unlicensed frequency band.
  • some embodiments of the base station choose the mode based only on the mode associated with the highest-ranking user equipment and some embodiments of the base station choose the mode based on numbers or priorities of the user equipment associated with the different modes.
  • entries in Table 1 indicate the modes associated with the user equipment 120-123 and entries in Table 2 indicate the values of the metrics associated with the user equipment 120-123.
  • the user equipment 120 and 122 are associated with the conventional LBT mode and the metric values m 1 and m 3 .
  • the user equipment 121 and 123 are associated with the enhanced LBT mode and the metric values m 2 and m 4 .
  • the base station selects the conventional LBT mode if: m 1 + m 3 > m 2 + m 4
  • the base station selects the enhanced LBT mode. If the conventional LBT mode is selected, the method 500 flows to block 525. If the enhanced LBT mode is selected, the method 500 flows to block 530.
  • the base station uses the conventional LBT mode to attempt to acquire the channel of the unlicensed frequency band. Some embodiments of the base station continue using the conventional LBT mode as long as the base station is unable to acquire the channel. For example, if a previous CCA has not yet completed because the random back off counter is still active, the base station continues performing the assessment using conventional LBT until the base station successfully acquires the channel. In some cases, the base station waits and freezes the back off counter because the base station has detected an ongoing transmission. This situation may occur if a neighboring node such as a Wi-Fi device wins contention for the channel and accesses the medium before the MIMO base station. The method 500 then flows to block 535.
  • a neighboring node such as a Wi-Fi device wins contention for the channel and accesses the medium before the MIMO base station.
  • the base station uses the enhanced LBT mode to attempt to acquire the channel of the unlicensed frequency band. Some embodiments of the base station continue using the enhanced LBT mode as long as the base station is unable to acquire the channel. For example, if a previous CCA has not yet completed because the random back off counter is still active, the base station continues perform ing the assessment using enhanced LBT until the base station successfully acquires the channel. In some cases, the base station waits and freezes the back off counter because the base station has detected an ongoing transmission. This situation may occur if an insufficient number of degrees of freedom are allocated for interference suppression during enhanced LBT or if the available channel estimates (e.g., the channel covariance matrices) towards neighboring nodes are not sufficiently accurate. The method 500 then flows to block 540.
  • the available channel estimates e.g., the channel covariance matrices
  • the base station transm its toward the user equipment using all the spatial degrees of freedom of the M IMO array for beamform ing and spatial multiplexing.
  • the user equipment that are associated with the conventional LBT mode are scheduled for transm ission.
  • the number of user equipment that are scheduled depends on the number of antennas implemented in the M IMO array. None of the degrees of freedom of the M IMO array are allocated for interference suppression because conventional LBT ensures that neighboring nodes are not transmitting during the time interval that has been acquired for transmission by the base station.
  • user equipment that are associated with the enhanced LBT mode are also scheduled for transmission, although they may experience reduced performance because transm ission is not performed in accordance with their preferred, enhanced LBT mode.
  • the base station transm its toward the user equipment using a first subset of the spatial degrees of freedom of the M IMO array for beamform ing and spatial multiplexing.
  • the user equipment that are associated with the enhanced LBT mode are scheduled for transmission.
  • the number of user equipment that are scheduled depends on the number of antennas implemented in the M IMO array and the number of spatial degrees of freedom in the first subset.
  • a second , mutually exclusive subset of the spatial degrees of freedom of the M IMO array are allocated for interference suppression .
  • the spatial nulls that were placed during the listening phase of the enhanced LBT procedure are preserved during data transm ission.
  • Some embodiments of the base station include a precoder that is designed to prevent interference towards neighboring nodes.
  • user equipment that are associated with the conventional LBT mode are also scheduled for transmission, although they may experience reduced performance because transm ission is not performed in accordance with their preferred, conventional LBT mode.
  • certain aspects of the techniques described above may implemented by one or more processors of a processing system executing software.
  • the software comprises one or more sets of executable instructions stored or otherwise tangibly embodied on a non-transitory computer readable storage medium .
  • the software can include the instructions and certain data that, when executed by the one or more processors, manipulate the one or more processors to perform one or more aspects of the techniques described above.
  • the non-transitory computer readable storage medium can include, for example, a magnetic or optical disk storage device, solid state storage devices such as Flash memory, a cache, random access memory (RAM) or other non-volatile memory device or devices, and the like.
  • the executable instructions stored on the non-transitory computer readable storage medium may be in source code, assembly language code, object code, or other instruction format that is interpreted or otherwise executable by one or more processors.
  • a computer readable storage medium may include any storage medium, or combination of storage media, accessible by a computer system during use to provide instructions and/or data to the computer system.
  • Such storage media can include, but is not limited to, optical media (e.g., compact disc (CD), digital versatile disc (DVD), Blu-Ray disc), magnetic media (e.g., floppy disc , magnetic tape, or magnetic hard drive), volatile memory (e.g., random access memory (RAM) or cache), nonvolatile memory (e.g., read-only memory (ROM) or Flash memory), or microelectromechanical systems (MEMS)-based storage media.
  • optical media e.g., compact disc (CD), digital versatile disc (DVD), Blu-Ray disc
  • magnetic media e.g., floppy disc , magnetic tape, or magnetic hard drive
  • volatile memory e.g., random access memory (RAM) or cache
  • nonvolatile memory e.g., read-only memory (ROM) or Flash memory
  • MEMS microelectro
  • the computer readable storage medium may be embedded in the computing system (e.g., system RAM or ROM), fixedly attached to the computing system (e.g., a magnetic hard drive), removably attached to the computing system (e.g., an optical disc or Universal Serial Bus (USB)-based Flash memory), or coupled to the computer system via a wired or wireless network (e.g., network accessible storage (NAS)).
  • system RAM or ROM system RAM or ROM
  • USB Universal Serial Bus
  • NAS network accessible storage

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

Selon l'invention, une station de base pour un réseau entrée multiple sortie multiple (MIMO) calcule des premières mesures sur la base de premiers débits de données qui sont estimés en supposant qu'un premier mode d'évaluation de canal libre (CCA) est utilisé pour acquérir un canal d'une bande de fréquences non autorisée pour une pluralité d'équipements utilisateurs. La station de base calcule des secondes mesures sur la base de seconds débits de données qui sont estimés en supposant qu'un second mode CCA est utilisé pour acquérir le canal de la bande de fréquences sans license pour la pluralité d'équipements utilisateurs. La station de base sélectionne le premier ou le second mode CCA sur la base des première et seconde mesures. La station de base effectue une CCA pour acquérir le canal de la bande de fréquences sans licence pour une transmission par le réseau MIMO selon le premier ou le second mode CCA sélectionné.
PCT/IB2018/000340 2017-03-17 2018-03-14 Sélection de mode d'évaluation de canal libre pour entrée multiple sortie multiple (mimo) dans des bandes de fréquences sans license Ceased WO2018167566A1 (fr)

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CN113395724A (zh) * 2021-08-13 2021-09-14 北京玻色量子科技有限公司 一种基站的模式优化方法及装置
CN114208379A (zh) * 2019-08-15 2022-03-18 索尼集团公司 用于无线通信系统的电子设备、方法和存储介质
WO2022080728A1 (fr) * 2020-10-15 2022-04-21 엘지전자 주식회사 Procédé d'exécution d'une procédure d'accès à un canal et dispositif associé

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US20160036578A1 (en) * 2014-07-31 2016-02-04 Qualcomm Incorporated Transmission of uplink control channels over an unlicensed radio frequency spectrum band

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US20130012134A1 (en) * 2011-07-07 2013-01-10 Cisco Technology, Inc. Dynamic Clear Channel Assessment Using Spectrum Intelligent Interference Nulling
US20160036578A1 (en) * 2014-07-31 2016-02-04 Qualcomm Incorporated Transmission of uplink control channels over an unlicensed radio frequency spectrum band

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Publication number Priority date Publication date Assignee Title
CN114208379A (zh) * 2019-08-15 2022-03-18 索尼集团公司 用于无线通信系统的电子设备、方法和存储介质
WO2022080728A1 (fr) * 2020-10-15 2022-04-21 엘지전자 주식회사 Procédé d'exécution d'une procédure d'accès à un canal et dispositif associé
CN113395724A (zh) * 2021-08-13 2021-09-14 北京玻色量子科技有限公司 一种基站的模式优化方法及装置
CN113395724B (zh) * 2021-08-13 2021-10-15 北京玻色量子科技有限公司 一种基站的模式优化方法及装置

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