Method for performing channel state measurement, user equipment

Abstract

The subject of this invention is "a method, user equipment, and network node for performing channel state measurements". The invention relates to determining channel state performed by a user equipment (UE) (12) in a mobile network, including determining (S21) one or more time intervals available for channel measurements, performing (S22) multiple signal power measurements, each associated with one of the time intervals to be used for channel measurements, and generating channel state information as a function of the multiple signal power measurements; the invention also relates to generating (S11) information containing indications of multiple time intervals available for receiving signal power measurements to be sent from an access node (eNB) (14) to the UE (12), and evaluating a measurement report received from the UE (12), wherein the report includes received signal power measurements, each associated with one of the time intervals; the invention also relates to the UE (12), the eNB (14), and corresponding computer programs.

Description

[0001] This application is a divisional application of patent application filed on September 23, 2016, with application number 201680069047.0 and entitled "Method for Performing Channel State Measurement, User Equipment and Network Node". Technical Field

[0002] This disclosure generally relates to communication on unlicensed spectrum. More specifically, without limitation, it provides apparatus and methods for measuring channel state information on unlicensed carriers. Background Technology

[0003] In a typical cellular system (also known as a wireless communication network or radio access network), a wireless (communication) terminal (also known as a mobile station or user equipment (UE)) communicates with one or more core networks via a radio access network (RAN). The radio access network may include an access point (AP) or a base station (BS), which communicates with the user equipment (UE) via radio signals and provides access to the core network.

[0004] The 3GPP (3rd Generation Partnership Project) has established multiple generations of mobile communication standards. The Universal Mobile Telecommunications System (UMTS) is a third-generation mobile communication system that evolved from the Global System for Mobile Communications (GSM) to provide mobile communication services based on Wideband Code Division Multiple Access (WCDMA) technology. Long Term Evolution (LTE), often referred to as fourth generation, has been specified to increase capacity and speed using different radio interfaces along with core network improvements.

[0005] LTE uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform (DFT) Extended OFDM (also known as Single-Carrier Frequency Division Multiple Access (SC-FDMA)) in the uplink. Therefore, the basic LTE downlink physical resources can be viewed as a time-frequency grid, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. Uplink subframes have the same subcarrier spacing as the downlink and the same number of SC-FDMA symbols in the time domain as the OFDM symbols in the downlink. In the time domain, LTE downlink transmission is organized into 10ms radio frames, each consisting of ten subframes of length T_subframe = 1ms. Each subframe includes two time slots with a duration of 0.5ms each, and the time slot numbers within the frame range from 0 to 19. For a normal cyclic prefix, a subframe consists of 14 OFDM symbols. The duration of each symbol is approximately 71.4μs.

[0006] In LTE, resource allocation is typically described using resource blocks, where one resource block corresponds to a time slot in the time domain and 12 adjacent subcarriers in the frequency domain. Two adjacent resource blocks in the time direction are considered symmetrical resource block pairs. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth.

[0007] Downlink transmissions are dynamically scheduled within the current downlink subframe; that is, in each subframe, the base station transmits control information relating to which terminals to transmit data and on which resource blocks the data will be transmitted. Downlink subframes also contain common reference symbols, which are known to the receiver and used for, for example, consistent demodulation of control information.

[0008] Typically, spectrum licensed by mobile carriers for cellular networks (such as LTE) and unlicensed spectrum for wireless local area networks (WLANs) have been largely separate. However, with the increasing number of mobile nodes and data rates per mobile node, there has been growing interest in transmitting LTE channels in smaller cells within unlicensed spectrum bands (or carriers).

[0009] Examples of unlicensed spectrum bands are the commonly referred to "WiFi bands" of approximately 2.4 GHz, 5 GHz, and 60 GHz. These are free to use, provided certain regulatory constraints are met when transmitting on them. These bands are not dedicated to any specific Radio Access Technology (RAT).

[0010] Recently, Licensed Assisted Access via LTE (LAA-LTE) has been proposed for coexistence with LTE, such as WLAN, on unlicensed carriers. This means that a User Equipment (UE) can connect to the LTE network on licensed spectrum (also known as the primary carrier). Additionally, it can also connect to the same network on unlicensed spectrum (also known as the secondary carrier).

[0011] The possibility of reliably utilizing unlicensed spectrum lies in transmitting critical control signals and channels on licensed carriers. Therefore, a UE can connect to a primary cell (PCell) in a licensed band and one or more secondary cells in an unlicensed band. These secondary cells are also referred to as Licensed Assisted Access Secondary Cells (LAA SCells).

[0012] Data transmission on unlicensed frequency bands is typically controlled using a Listen-Before-Talk (LBT) mechanism. In a typical WLAN deployment, Carrier Sense Multiple Access (CSMA / CA) with collision avoidance is used for media access. This means that the channel is detected to perform a Blank Channel Assessment (CCA), and transmission is initiated only if the channel is declared idle. If the channel is declared busy, transmission is essentially postponed until the channel is deemed idle. When the ranges of several base stations or access points (APs) using the same frequency overlap, this means that in cases where transmissions to / from another AP (which is within range) on the same frequency can be detected, all transmissions associated with one AP may be postponed. In practice, this means that if several APs are within range, they will have to share the channel in time, and the throughput of individual APs may be severely degraded. A diagram illustrating the Listen-Before-Talk (LBT) mechanism is provided below. Figure 1 As shown in the image.

[0013] In cellular communication systems, downlink pilots, reference signals (RS), or so-called cell-specific reference symbols (CRS) with predefined and known characteristics are periodically transmitted from the radio access network infrastructure access point or base station to user equipment. Reference signals are used by idle and active user equipment for purposes such as channel estimation, mobility measurement, and cell association for certain transmission modes (e.g., measurement).

[0014] According to 3GPP technical specification 36.213 (current version 12.5.0, hereinafter referred to as TS 36.213), the UE will perform periodic and / or aperiodic reporting of the channel state indicator. This information can be used by the radio access network for scheduling decisions (e.g., including the selection of the modulation and coding scheme (MCS) to be used by the UE to transmit a certain transport block and the allocation of resource blocks (RBs) to the UE) to ensure efficient use of radio resources.

[0015] According to Section 7.2 of 3GPP TS 36.213, the CSI to be reported by the UE includes the so-called Channel Quality Indicator (CQI) and may include other indicators such as the so-called Precoding Matrix Indicator (PMI) and the so-called Rank Indicator (RI). The UE will report to the radio terminating node (eNB) of the radio access network the highest wideband CQI value within a range that matches the appropriate CQI value experienced by the UE under the transient radio conditions given the UE's receiver capabilities, resulting in a block error rate (BLER) equal to or less than 10%. The BLER can represent the ratio of the number of erroneous data blocks to the corresponding total number of received data blocks. The radio access network will use the reported CQI value as an input to its scheduling algorithm. As defined in Table 7.2.3-1 of TS 36.213 above, there are 15 CQI values ​​from 0 to 15, each associated with a certain efficiency, which increases efficiently with that value.

[0016] These CSI measurements can be based on Channel State Information Reference Signal (CSI-RS) or CRS. Channel State Information Interference Measurement (CSI-IM) can be used for interference measurements in so-called Transport Mode 10. Furthermore, CRS or Discovery Reference Signal (DRS) can be used as the basis for Radio Resource Management (RRM) measurements such as RSRP and RSRQ, while CSI-RS can be used for RSRP. In the current LTE specification, the UE can average CRS-based pair measurements across multiple subframes, and average CSI-RS and CSI-IM pair measurements across different CSI-RS and CSI-IM timings, and for RRM measurements to be averaged across multiple DRS timings. Reference Signal Received Power (RSRP) is defined as a linear average of the power share (in [W]) of the resource element carrying the cell-specific reference signal in the considered measurement frequency bandwidth. RSRQ is defined as the ratio N × RSRP / (E-UTRA carrier RSSI), where N is the number of RBs in the E-UTRA carrier RSSI measurement bandwidth. Measurements in the numerator and denominator will be performed on the same set of resource blocks. The Received Signal Strength Indicator (RSSI) includes the linear average of the total received power (in [W]) observed by the UE over N resource blocks from all sources (including co-channel serving and non-serving cells) only in certain OFDM symbols of the measurement subframe, along with adjacent channel interference, thermal noise, etc. If a higher layer indicates a DRS-based measurement, the RSSI is measured from all OFDM symbols in the DL portion of the subframe during the configured DRS timing. Summary of the Invention

[0017] The present application recognizes that CSI, RRM measurements and / or reliance on DL reference signals or any other measurements across multiple subframes according to the prior art can cause insufficient accuracy in the measurements determined by the UE CSI associated with LAA:

[0018] In LAA, the reference signal may be present as required to perform LBT before DL transmission instead of as specified for LTE, and / or the power on CRS / CSI-RS of different subframes may vary, for example if power compensation is applied to all REs in a subframe when utilizing higher-order modulation, or dynamic power sharing across multiple DL component carriers is used in the case of carrier aggregation.

[0019] Therefore, the goal is to improve the above measurements.

[0020] According to one embodiment, a method for determining channel state performed by a user equipment (UE) in a radio access network is provided, comprising:

[0021] • Determine one or more time intervals that can be used for channel measurements.

[0022] Perform multiple signal power measurements, each associated with one of the time intervals to be used for channel measurements, and

[0023] • Generate channel state information as a function of multiple signal power measurements.

[0024] In another embodiment, a method is proposed to be performed at a network node (eNB) in a radio access network, comprising:

[0025] • Generate information containing indications of multiple time intervals that can be used for received signal power measurements to be sent to the UE, and

[0026] • Evaluate the measurement reports received from the UE, where the reports include received signal power measurements, each associated with one of the time intervals.

[0027] In another embodiment, a UE is proposed, comprising:

[0028] • Determine the module, adapted to determine one or more time intervals that can be used for channel measurements, and

[0029] • The measurement module is adapted to perform multiple signal power measurements, each associated with one of the time intervals to be used for channel measurements, and is adapted to generate channel state information as a function of the multiple signal power measurements.

[0030] In another embodiment, an eNB for a radio access network is proposed, comprising:

[0031] • Time interval indication module, adapted to generate information containing indications of multiple time intervals that can be used for receiving signal power measurement, and

[0032] • Channel state assessment module, adapted to assess measurement reports received from the UE, wherein the reports include received signal power measurements, each associated with one of the time intervals.

[0033] Other embodiments relate to computer programs, including portions of software code, to implement the methods described above when operated by a corresponding processor of the UE or eNB. The computer program can be stored on a computer-readable medium. The computer-readable medium can be a permanent or rewritable memory located within the UE or eNB or externally. The corresponding computer program can also be transferred to the corresponding UE or eNB, for example, as a sequence of signals via a cable or wireless link.

[0034] Detailed embodiments of the invention will be described below to provide those skilled in the art with a full and complete understanding. However, these embodiments are illustrative and not intended to be limiting. Attached Figure Description

[0035] The accompanying drawings illustrate several aspects of this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0036] Figure 1 This demonstrates a sample LBT mechanism associated with LAA;

[0037] Figure 2 This demonstrates a sample LAA SCell DL frame;

[0038] Figure 3 The diagram shows a radio network including access points or eNBs that communicate with the UE via PCell and SCell.

[0039] Figure 4 This illustrates a first sequence of messages and steps performed by the wireless device and the base station for channel state measurement;

[0040] Figure 5 This illustrates a second sequence of messages and steps performed by the wireless device and the base station for channel state measurement;

[0041] Figure 6 This is a block diagram of the structural units of a wireless device according to some embodiments of this application;

[0042] Figure 7 This is a block diagram of the functional units of a wireless device according to some embodiments of this application;

[0043] Figure 8 This is a block diagram of the structural units of a base station according to some embodiments of this application; and

[0044] Figure 9 This is a block diagram of the functional units of a base station according to some embodiments of this application. Detailed Implementation

[0045] like Figure 3 As shown, the example network may include one or more radio access nodes and one or more instances of wireless communication devices 12 (e.g., conventional user equipment (UE), machine-type communication (MTC), or machine-to-machine (M2M) devices). In the following example, wireless communication device 12 is referred to as UE, and radio access node 14 will be referred to as eNodeB or eNB14.

[0046] UE 12 can connect to a primary cell (PCell) in a licensed frequency band and one or more secondary cells in an unlicensed frequency band. Such secondary cells are also referred to as Licensed Auxiliary Access Secondary Cells (LAA SCells).

[0047] The eNB 14 is capable of communicating with the UE 12 along with any additional components suitable for supporting communication between wireless communication devices or between a wireless communication device and another communication device (e.g., a landline telephone). While the illustrated UE 12 may represent any suitable combination of hardware and / or software, such devices in specific embodiments may represent, for example, communication via… Figure 6 and Figure 7 The example wireless communication device is shown in more detail. Similarly, while the eNB 14 shown can represent any suitable combination of hardware and / or software, this node in a particular embodiment can represent, for example, a network node via... Figure 8 and Figure 9 The example base station apparatus is shown in more detail. It should be understood that a cellular communication network may include any number of radio access nodes serving any number of wireless communication devices. The eNB 14 is also connected to a core network (not shown).

[0048] Figure 2 The diagram shows a sample LAA DL frame comprising 10 subframes, some of which are unavailable for DL ​​transmission by the eNB due to being occupied by non-LTE devices (LBT failure). As an example, subframes #0, #1, #5, #6, and #9 are therefore unavailable for channel measurements in the UE.

[0049] In one embodiment, Figure 4 As shown, in the first step S11, the eNB sends an indication to the UE of multiple time intervals or slots that can be used for channel measurement. Figure 2 For example, the eNB can transmit identifiers for subframes #2, #3, #4, #7, and #8 of frame n. Alternatively, the eNB can transmit an indication of time intervals that cannot be used for channel measurements.

[0050] In the second step S12, the UE performs channel measurements in time intervals to be used for channel measurements, wherein each (time interval) measurement is associated with one of these time intervals.

[0051] In the third step S13, the UE may provide measurement results to the eNB, wherein the measurement results may be a function of multiple measurements. The function may be an averaging function that determines the average of measurements over multiple time intervals.

[0052] The time interval can be the OFDM symbol duration, subframe or transmission time interval (TTI) or any suitable time interval.

[0053] In one embodiment, the indication sent by the eNB includes multiple identifiers (e.g., multiple subframe identifiers) that identify the explicit time interval to be used for measurement. Additionally or alternatively, the indication includes a set of time intervals (subframes) or a range of valid subframes (to which measurements can be performed). The range of valid subframes may include subframes in which no UE is scheduled for reception on the Physical Downlink Shared Channel (PDSCH).

[0054] The scope of a valid subframe can span within a download (DL) transmission burst or across different DL transmission bursts. The eNB can also indicate (for which measurement averaging should be performed) a subset of symbols in the symbol set within a valid subframe.

[0055] Measurements can be performed according to CSI metrics (such as CQI). Another example is RSSI measurement. A valid subframe for averaging measurements can be temporally correlated with a DL reference subframe (for which CSI represents channel quality).

[0056] In one embodiment, the instruction is transmitted to the UE via the Physical Downlink Control Channel (PDCCH) using downlink control information (DCI), which may also provide information to the UE, such as UL scheduling authorization. Additionally, one or more new fields may be included in the resource-authorized DCI.

[0057] Alternatively, the indication can be transmitted via aperiodic CSI requests or broadcast in the common search space of the control channel.

[0058] In one embodiment, eNB 14 uses higher-order modulation data (e.g., 64QAM or 256QAM) to optimize the scheduling of UE 12 in order to reduce power variations across subframes.

[0059] In another embodiment, UEs scheduled using higher-order modulation are grouped together in the same burst. Furthermore, UEs can be down-selected based on which higher-order modulations are scheduled (e.g., between 64QAM and 256QAM). As an example, UEs using higher-order modulation data can be served in the same subframe of a DL burst, such that the remaining subframes of that burst have the same power. In another example, UEs using higher-order modulation data are served on licensed carriers.

[0060] In one embodiment, the eNB avoids scheduling higher-order modulated data in subframes where the UE expects the presence of reference signals (CSI-RS and / or CSI / IM). The eNB may (explicitly or implicitly) indicate to the UE that no higher-order modulated data is scheduled in these subframes.

[0061] In one embodiment, such as Figure 5 As shown, UE 12 autonomously determines which DL subframes to use for channel measurements.

[0062] Furthermore, in the first step S21, the UE may detect time intervals in which the estimated received power deviates from the measured received power (e.g., by detecting that the power difference between the estimated received power and the measured power exceeds a certain power threshold), and exclude such time intervals from the channel measurement.

[0063] In the second step S22, the UE can perform the following: Figure 4 The measurement described in step S11.

[0064] In the third step S23, with Figure 4 Similar to step S13, the UE can provide measurement results to the eNB, where the measurement results can be a function of multiple measurements. The function can be an averaging function that determines the average of measurements over multiple time intervals.

[0065] In one embodiment, the estimated received power is determined based on a set of previously received subframes (e.g., the average of a certain number of previously received subframes).

[0066] In one embodiment, UE 12 performs RSRP measurements on the CRS or CSI-RS and compares them to the average of a set of previously received subframes. If the power difference is too large (exceeding a certain or defined threshold), the subframe is excluded from the averaging.

[0067] In one embodiment, subframes in which UE 12 schedules data using higher-order modulation are excluded from the set of subframes (on which measurements are averaged).

[0068] In another example, measurement averaging at UE 12 is performed with power compensation considered when the UE uses higher-order modulation data for scheduling. For example, some scaling / calibration could be performed based on power compensation due to higher-order modulation to include these subframes along with those without power compensation when averaging measurements.

[0069] In one embodiment, UE 12 autonomously determines whether a power change has occurred based on the number of SCells in the TTI (on which UE 12 is scheduled to receive data) or the number of SCells on which UE 12 has detected the presence of CRS or an initial signal. The measurements are averaged and can then be performed across subframes with the same estimated number of active SCells.

[0070] In one embodiment, the averaging of measurements at UE 12 is performed while taking into account either the number of SCells in the TTI (on which UE 12 is scheduled to receive data) or the number of SCells on which UE 12 has detected the presence of CRS or an initial signal. For example, some scaling / calibration may be performed based on the number of SCells when averaging measurements.

[0071] In one embodiment, eNB 14 can avoid scheduling higher-order modulated data in subframes where the UE expects CSI-RS and / or CSI / IM to be present, allowing UE 12 to assume that no higher-order modulated data is scheduled in the subframe. If this scheduling constraint applies to all CSI-RS / IM transmissions from the eNB, additional explicit signaling for this purpose is not required.

[0072] like Figure 6 As shown, the example wireless communication device or UE 12 includes a baseband unit 120, a radio unit 121, and one or more antennas 122. The baseband unit 120 is coupled to the radio unit 121. The baseband unit 120 includes a device processor 1201 and a device memory 1202. The radio unit 121 includes a transceiver 1210 coupled to one or more antennas 122. The transceiver includes transmit circuitry TX 1211 and receiver circuitry RX 1212. In specific embodiments, some or all of the above-described functionalities, such as those provided by a UE, MTC, or M2M device and / or any other type of wireless communication device, can be provided by the device processor 1201 executing instructions stored on a computer-readable medium (e.g., device memory 1202). Alternative embodiments of the wireless communication device may include additional components beyond those shown herein, which may be responsible for providing certain aspects of the device's functionality, including any of the above-described functionalities and / or any functionality required to support the above-described solutions.

[0073] like Figure 7 As shown, example UE 12 includes the following exemplary functional units:

[0074] • Subframe determination module 124 adapts to identify multiple time intervals or time slots that can be used for channel measurements. This identification can be performed autonomously by the UE as described above or by evaluating an indication message received from the eNB;

[0075] • Measurement module 125, adapted to perform channel measurement (CSI measurement) during the time interval identified for use in channel measurement;

[0076] • Measurement Reporting Module 126, adapted to perform measurements (CQI) reported to the eNB as configured by the network.

[0077] like Figure 8As shown, the example network node or eNB 14 includes a node processor 141, a node memory 142, a node transceiver 143, one or more node antennas 144, and a network interface 145. The node processor 141 is coupled to the node memory 142, the network interface 145, and the node transceiver 143, and the node transceiver 143 is coupled to one or more node antennas 144. The node transceiver 143 includes transmit circuitry TX 1431 and receiver circuitry RX 1432. In specific embodiments, some or all of the above-described functionalities, such as those provided by a base station, Node B, enhanced Node B, and / or any other type of network node, can be provided by the node processor executing instructions stored on a computer-readable medium (e.g., node memory 142). Alternative embodiments of the radio access node may include additional components responsible for providing additional functionality including any of the functionalities identified above and / or any functionality required to support the solutions described above.

[0078] like Figure 9 As shown, the example eNB 14 includes the following exemplary functional units:

[0079] • The time interval indication module 146 is adapted to generate information containing indications of multiple time intervals or time slots that can be used for channel measurement, and the indications are sent to the UE;

[0080] • CSI report evaluation module 147, adapted for evaluating measurement reports (CSI reports) received from the UE.

[0081] The following presents some considerations and suggestions that may be based on or supplement the previous descriptions and / or provide other aspects.

[0082] CSI feedback based on CSI-RS and CSI-IM:

[0083] The CSI-RS framework is a UE-specific framework, meaning a particular UE is unaware of other UEs' CSI-RS. Furthermore, CSI-RS is currently configured with specific periodicity and offset. Additionally, there are three CSI procedures defined for CSI measurements. The number of CSI procedures a UE supports is a UE capability. UEs that do not measure CSI-RS will use ZP (Zero Power)-CSI-RS configuration at those times, and the PDSCH / EPDCCH mapping should function without any apparent drawbacks. The same approach is used for CSI-IM.

[0084] In the first scenario, we consider allowing the aperiodic presence of CSI-RS. In this scenario, the eNB can instruct the UE in some form that CSI-RS is present in the corresponding subframe. This may need to be done for both ZP (zero power)-CSI-RS and NZP (non-zero power)-CSI-RS. Furthermore, the same principle applies to CSI-IM. For each UE scheduled in the DL, the eNB can indicate ZP-CSI-RS for all used REs. Currently, the amount of CSI-RS available for configuration may be too large to be included in the DCI message.

[0085] Therefore, a simple and reliable approach is for the UE to assume that ZP CSI-RS, NZP-CSI-RS, and CSI-IM are configured and transmitted periodically, as in Rel-12. This avoids the risk of different assumptions between the eNB and the UE, and does not compromise DCI message capacity or the permissible number of CSI-RS configurations. Furthermore, if LBT adoption by the eNB is successful, the UE can perform measurements only on NZP CSI-RS and CSI-IM; thus, the availability of these resources can be effectively aperiodic.

[0086] Therefore, according to this embodiment, ZP-CSI-RS, NZP-CSI-RS, and CSI-IM are configured periodically, while NZP-CSI-RS and CSI-IM exist aperiodically (subject to LBT).

[0087] In one embodiment, the UE is configured with a relatively short periodicity for CSI-RS per CSI process, relative to the periodicity of CSI-RS timing, because the eNB cannot guarantee successful LBT implementation or occupy the channel for a longer duration corresponding to the CSI-RS configuration periodicity. More specifically, there may be a relationship between the transmission burst used by the eNB and the CSI-RS configuration. If the periodicity of CSI-RS ensures that a single CSI-RS timing is within a transmission burst from the eNB, then CSI-RS can occur at any time within the transmission burst. Currently defined CSI-RS periodicities are 5, 10, 20, 40, and 80 ms. Two of the transmission duration values ​​considered in the LAA discussion so far are 4 and 10 ms. A CSI-RS with a 5 ms periodicity can be supported with a 10 ms transmission duration. This assumes that CSI-RS can occur in any subframe within the transmission duration. It should be noted that DwPTS does not support CSI-RS configuration, allowing for the definition of a CSI-RS configuration for a subframe if the last DL subframe corresponds to a DwPTS subframe. For a 4ms transmission duration, a new, more compact periodicity for CSI-RS can be introduced. This ensures that there are CSI-RS opportunities available for the UE to perform measurements. UEs not performing CSI-RS measurements will be configured with ZP-CSI-RS at those opportunities, and the PDSCH / EPDCCH mapping should function without any apparent drawbacks. The same approach can be used for CSI-IM. Therefore, according to this embodiment, it is proposed to introduce (e.g., 4ms) CSI-RS periodicity.

[0088] For aperiodic CSI reports, when a UL grant is sent on a SCell cell (which also triggers an aperiodic CSI report), it is easy for the eNB to ensure that the CSI-RS is transmitted along with the UL grant. However, if the UL grant indicates an aperiodic CSI-RS report from a cell different from the cell on which the UL grant is sent, it may not be possible to transmit the NZPCSI-RS in the configured subframe of the CSI-RS. One possible reason is that the eNB has already occupied the channel due to the short processing time available between a successful LBT on a carrier (to which it needs to report) and the transmission time of the UL grant on a different carrier. Another possibility is that the eNB has been unable to access the channel due to an unsuccessful LBT. In such cases, the eNB will discard the corresponding aperiodic CSI report, and preferably, the UE has not used such noisy measurements to affect other measurements. It is also possible that the UE implicitly detects the presence of CSI-RS in such cases.

[0089] Another aspect to consider is the feasibility of interpolating CSI measurements across time intervals. In current LTE designs, the UE is allowed to average CSI-RS and CSI-IM measurements across different CSI-RS and CSI-IM timings. Another important aspect is to adequately support 64QAM and 256QAM in the DL for PDSCH transmission. Allowing power compensation values ​​from the maximum transmit power when the eNB schedules these higher modulation orders can be advantageous. Furthermore, in multi-carrier scenarios, varying the output power based on the number of carriers successfully used in the LBT or operated on the current TTI can be beneficial. If the UE will be able to measure CSI-RS across multiple subframes (where the power allocation differs from the eNB side), it may be difficult to utilize CSI reports from the eNB because the eNB will not know how the UE constructs the CSI reports. Therefore, one solution is that the UE should not autonomously interpolate measurements between different NZP-CSI-RS and CSI-IM timings unless instructed to do so by the eNB. Because the eNB has complete knowledge of any changes in its DL transmit power, it can indicate to the UE which and how many CSI-RS moments are suitable for averaging measurements. Alternatively, it can indicate to the UE whether higher-order modulation was used in subframes in which the UE expects CSI-RS and / or CSI / IM to exist, after which the UE can avoid measurement interpolation or take this information into account when constructing the CSI report. Therefore, according to this embodiment, the UE is configured to perform CSI measurements only in CSI reference resources. It is also configured to average CSI measurements only across different CSI reference resources (if explicitly indicated by the eNB).

[0090] Due to the unpredictability of LBT and restricted channel occupancy time, as well as channel conditions in unlicensed spectrum, updating CSI reports as quickly as possible is preferred; it is also preferable to minimize the delay between the triggering of aperiodic reporting and the availability of CSI-RS (if available due to LBT). This will allow the UE to always perform measurements and report only based on the most recent measurements. Alternatively, the UE can be configured to perform measurements only when the CSI of a particular cell should be reported. Furthermore, in one embodiment, it is proposed that aperiodic CSI reporting of the indicated LAA SCell triggered by UL authorization be based on NZP-CSI-RS and CSI-IM in the same subframe as the UL-authorized subframe. This embodiment can have the advantage of providing significant power savings in the UE.

[0091] CRS-based CSI feedback: A key aspect of CRS-based CSI feedback is how the UE detects the presence of CRS. Given the design goal of being able to perform a single DRS measurement based on CRS, it should therefore be possible for the UE to implicitly detect CRS for the purpose of CSI feedback. If this is found not to be possible, then the same mechanism proposed for CSI-RS can be used.

[0092] Similar to CSI measurements based on CSI-RS, the UE cannot assume the same power on the CRS between different subframes. Therefore, for CRS-based CSI feedback, the UE should not interpolate CRS measurements between different subframes unless explicitly indicated by the eNB.

[0093] Furthermore, in one embodiment, the UE can be configured to autonomously detect the presence of CRS for the purpose of CSI feedback.

[0094] In addition, the UE can be configured such that CSI measurements are performed only within the CSI reference resource, without averaging across different CSI reference resources, unless indicated or commanded by the eNB.

[0095] Considerations related to the periodicity of CSI reports (periodic vs. non-periodic CSI reports):

[0096] It can be assumed that interference conditions on the LAA SCell are highly variable over time. Furthermore, the scenario considered can be a low-mobility scenario. The fundamental spatial properties and channel quality (if interference conditions are excluded) are therefore quite static over time. Additionally, it can be assumed that the LAA SCell will primarily be used to increase the data rate; that is, if the eNB has a large amount of DL data to schedule to the UE, the eNB will utilize the LAA SCell. Therefore, the LAA SCell will be used for a significant period before the eNB clears its transmit buffer. Thus, it is perhaps unlikely that the eNB will activate the LAA SCell without scheduling data on it for a long period.

[0097] Periodic CSI reporting is primarily used to obtain a good starting point for link adaptation. When data is being continuously scheduled, the resolution of periodic CSI reporting is insufficient for reliable scheduling at high data rates. Furthermore, reliable transmission of the reference signal for periodic CSI on unlicensed bands is impossible due to the potential lack of channel access. In addition, interference conditions in unlicensed spectrum can be highly variable over short periods because the amount of available spectrum can be large. Therefore, it is desirable to support lightweight aperiodic CSI reporting (e.g., wideband aperiodic CSI reporting only) to maintain a reasonable aperiodic CSI payload.

[0098] Explanation of Abbreviations

[0099] CCA Blank Channel Evaluation

[0100] CRS Cell-Specific Reference Signal

[0101] CQI Channel Quality Indicator

[0102] CSI Channel Status Information

[0103] DCI downlink control information

[0104] DL downlink

[0105] DRS detected a reference signal.

[0106] eNB evolves into NodeB and base station

[0107] UE User Equipment

[0108] UL uplink

[0109] LAA Licensed Assisted Access

[0110] RSRP reference signal received power

[0111] RSRQ reference signal reception quality

[0112] RS reference signal

[0113] RSSI Received Signal Strength Indicator

[0114] SCell Auxiliary Community

[0115] LBT: Listen First, Then Speak

[0116] LTE in unlicensed LTE-U spectrum

[0117] PDCCH Physical Downlink Control Channel

[0118] PUSCH Physical Uplink Shared Channel

[0119] RRM Radio Resource Management

[0120] UCI uplink control information

Claims

1. A method for determining channel state performed at a user equipment (UE) in a radio access network, comprising: • Autonomously determine one or more subframes to be used for channel state measurements. Perform multiple signal power measurements, each of which is associated with one of the subframes to be used for channel state measurements. • Generate channel state information as a function of the plurality of signal power measurements. The one or more subframes to be used for channel state measurement are determined by detecting that the power difference between the measured received power and the estimated received signal power associated with the corresponding subframe does not exceed a certain power threshold, wherein the estimated received signal power is determined based on a set of previous received subframes.

2. The method of claim 1, comprising: • Provide the channel state information to the access node that provides the UE with access to the radio access network.

3. The method as described in claim 1, wherein, Generating the channel state information as a function of the plurality of signal power measurements includes determining the average of the plurality of signal power measurements.

4. The method of claim 1, wherein, The UE performs a reference signal received power measurement (RSRP) on the cell-specific reference symbol (CRS) or the channel state information reference signal (CSI-RS) in the current subframe, and compares the RSRP with the average value of the measurement set of previously received subframes.

5. The method of claim 4, wherein, If the power difference exceeds a certain threshold, the measurement of the current subframe is excluded from the averaging.

6. The method according to any one of claims 1-5, wherein, Channel state information is being determined on a radio channel associated with an unlicensed LTE frequency band controlled by the Listen-Before-Speak (LBT) mechanism.

7. The method as described in any one of claims 1-5, wherein, The one or more subframes are Orthogonal Frequency Division Multiplexing (OFDM) symbol intervals.

8. A user equipment (UE) adapted to perform any one of claims 1-7.

9. A user equipment (UE) for operation in a radio access network, comprising: • Determining the module, adapted to autonomously determine one or more subframes to be used for channel state measurements, and • A measurement module adapted to perform multiple signal power measurements, each associated with one of the subframes to be used for channel state measurement, and adapted to generate channel state information as a function of the multiple signal power measurements. The determining module is configured to determine the one or more subframes to be used for channel state measurement by detecting that the power difference between the measured received power and the estimated received signal power associated with the corresponding subframe does not exceed a certain power threshold, wherein the estimated received signal power is determined based on a set of previous received subframes.

10. The UE of claim 9, configured to provide the channel state information to an access node that provides the UE with access to the radio access network.

11. The UE of claim 9, wherein configuring the channel state information as a function of the plurality of signal power measurements includes determining an average of the plurality of signal power measurements.

12. The UE as described in any one of claims 9-11, configured to perform a reference signal received power measurement RSRP on a cell-specific reference symbol CRS or on a channel state information reference signal CSI-RS in the current subframe, and to compare the RSRP with the average value of a set of RSRP measurements from previously received subframes.

13. The UE of claim 12, configured to exclude the current subframe from averaging if the power difference exceeds a certain threshold.

14. A computer program product comprising instructions that, when executed on at least one processor of a UE, cause the at least one processor to perform the method according to any one of claims 1-7.

15. A computer-readable medium containing instructions that, when executed on at least one processor of a UE, cause the at least one processor to perform the method according to any one of claims 1-7.

16. A user equipment (UE) for operation in a radio access network, comprising: • At least one transceiver; • At least one processor; as well as • Memory, containing software executable by the at least one processor, wherein the UE is configured to: - Autonomously determine one or more subframes to be used for channel state measurements. - Perform multiple signal power measurements, each associated with one of the subframes to be used for channel state measurements, and - Generate channel state information as a function of the plurality of signal power measurements. The one or more subframes to be used for channel state measurement are determined by detecting that the power difference between the measured received power and the estimated received signal power associated with the corresponding subframe does not exceed a certain power threshold, wherein the estimated received signal power is determined based on a set of previous received subframes.

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