Patent Description:
In wireless communications, multiple-input and multiple-output (MIMO) technology is becoming more and more popular and has been incorporated into wireless broadband standards like <NUM>th Generation (<NUM>) Long Term Evolution (LTE) and <NUM>th Generation (<NUM>) New Radio (NR). Downlink (DL) multi-user MIMO or simply DL MU-MIMO allows one network node (e.g., eNB or gNB) to communicate with multiple wireless devices (e.g., user equipment (UE)) simultaneously using the same time frequency resource. Downlink MU-MIMO is usually a close-loop MIMO system, i.e., the downlink channel state information (CSI) perceived on the wireless device is feedback to the network node and used by network node to determine downlink transmission format, i.e., transmission block size (TBS), rank and modulation and coding rate scheme (MCS). The CSI reporting as specified in Third Generation Partnership Project (3GPP) <NUM> LTE and <NUM> NR assumes single user (SU) MIMO transmission as a wireless device does not know, when it sends the CSI report, how and which multiple wireless devices it will be paired with in future transmissions. This SU CSI report is not accurate if it is directly used to determine MU MIMO transmission format when multiple wireless devices are paired together for downlink transmission. The reason is that, first, the downlink transmit power will be shared by all paired wireless devices; and second, multiple paired wireless devices together using same time/frequency resource for transmission will introduce additional inter-stream interference. Both power sharing and inter-stream interference from other paired wireless devices will contribute to the decrease of signal to interference plus noise ratio (SINR) for each paired wireless device and create a gap between actual MU-MIMO CSI and wireless device reported CSI.

To help accurately determine downlink transmission format and achieve optimal throughput and block error rate, additional downlink CSI estimation may need to be performed on and/or by the network node for MU MIMO transmission. This additional downlink CSI estimation on the network node uses wireless device reported CSI as input to set an absolute reference for downlink signal power as well as noise and interference power, based on what is perceived by wireless device. Note that channel quality indication (CQI) can be considered as quantized downlink post equalization SINR. One issue with wireless device's CSI report is CQI saturation. In case actual downlink post equalization SINR is higher than the SINR corresponding to highest CQI, i.e., CQI of <NUM>, the reported CQI SINR will be capped. This will happen with massive MIMO systems with large number of antennas which provide very high beamforming gain. <FIG> illustrates such a system. A typical massive MIMO system consists of two-dimensional antenna elements array with M rows, N columns and K polarizations (K=<NUM> in case of cross-polarization).

Using capped SINR for MU-MIMO CSI estimation will result in over conservative SINR estimation for MU-MIMO transmission. In practical wireless communication systems, this kind of CSI estimation error will be compensated by an outer-loop link adaptation which is driven by downlink ACK/NACK, feedbacked by wireless device after transport block detection. When CSI estimation error is big, outer-loop link adaptation needs long time to converge and results in degraded performance.

A CSI report includes channel quality indication (CQI), precoding matrix indication (PMI) and rank indication (RI) and CSI-RS resource indication (CRI). CQI can be considered as quantized SINR to achieve as closely as possible the desired coding rate indicated by CQI index for reported PMI and RI (3GPP TS <NUM> for LTE and 3GPP TS38. <NUM> for NR). The highest CQI index <NUM> represents SINR needed to achieved highest coding rate supported by standard for given PMI and RI, which is roughly 20dB for LTE and NR when 64QAM is used and about <NUM> dB when 256QAM is configured.

Let γCQI<NUM> be the SINR corresponding to CQI <NUM>. In case the actual downlink post equalization SINR is higher than γCQI<NUM>, CQI <NUM> will be reported as illustrated in <FIG>. That is, CQI <NUM> to the first instance of CQI <NUM> in <FIG> corresponds to a linear or substantially linear region where increased SINR corresponds to an increase in CQI, which corresponds to a non-saturated region. However, after the first instance of CQI <NUM>, every increase in SINR does not correspond to an increase in CQI as the maximum reportable CQI is <NUM>, which corresponds to a saturated region. This means, for example, that SINR of <NUM> will be reported as CQI <NUM> even though the first instant of CQI <NUM> corresponds to an SINR of <NUM>. Hence the network node has no knowledge of the actual downlink SINR when CQI <NUM> is reported.

As previously described, when multiple wireless devices are paired together for MU transmission, the wireless device reported CQI will be reduced due to the power split between wireless devices and due to extra inter-stream interference between paired wireless devices. In case the actual downlink SINR is much higher than γCQI<NUM>, the estimated MU-MIMO SINR on and/or by the network node will be conservative (i.e., lower or substantially lower than the actual DL SINR) as illustrated in <FIG> and result in poor system performance.

There currently exist certain challenge(s) with respect to trying to resolve the CQI saturation issue.

To solve the CQI saturation issue, one solution is to configure multiple CSI-RS resources for each wireless device to an extended CQI linear range at low end and high end of SINR. As one alternative, for different CSI-RS resources, a different powerControlOffset is configured for different CSI-RS resources. With the help of powerControlOffset, the wireless device can scale down (or up) the signal first and then estimate the SINR, so that the wireless device can shift the SNR range in the CQI report from [-9dB, 20dB] to [(-<NUM>+ powerControlOffset)dB, (<NUM>+ powerControlOffset)dB], thereby helping reduce the CQI saturation probability. As another alternative, different number of CSI-RS antenna ports and/or different beamforming are performed for different CSI-RS resources. By reducing the beamforming gain, the CQI can tolerate higher received signal, thus reduce the CQI saturation probability.

Configuring multiple CSI-RS resources generally need for the wireless device to support more CSI-RS ports. For example, most of existing commercial networks utilize <NUM>-port CSI-RS to achieve optimum performance. Therefore, when two CSI-RS resources are configured, the total Tx ports the wireless device needs to support is <NUM> (<NUM>+<NUM>). However, due to CSI-RS complexity restriction, most of commercial wireless devices only support up to <NUM> ports in total.

To combat the wireless device capability constraint, one low complexity solution is to configure two CSI-RS resources and each with less antenna ports, i.e., <NUM> ports or less. Since less CSI-RS antenna ports are used for CSI feedback, this will negatively impact the CSI feedback accuracy and thus introduce some performance loss for type-I codebook based SU-MIMO performance. Furthermore, if <NUM> ports are configured for MU-MIMO and <NUM> ports are configured for SU-MIMO, this will break the smooth switch between SU-MIMO and MU-MIMO which is important for real world systems.

Document <CIT> discloses methods and for facilitating dynamic measurement power offset adjustments for use in reporting channel quality feedback. A user equipment may generate and send a plurality of channel quality indicator (CQI) values to a base station. The base station determines whether at least some of the received CQI values are outside of an upper or lower threshold value. If at least some of the received CQI values are outside the upper or lower threshold value, the base station can transmit an adjusted measurement power offset to the user equipment. On receipt of the adjusted measurement power offset, the user equipment generates sub-sequent CQI values using the adjusted measurement power offset.

Document <CIT> discloses methods and apparatuses for channel state information (CSI) feedback in a wireless network. A method includes receiving signaling including a first Non-Zero Power (NZP) CSI-reference signal (RS) configuration for channel measurement; a second NZP CSI-RS configuration; and a CSI interference measurement (CSI-IM) configuration for interference measurement. The method includes receiving a CSI feedback request and estimating the CSI based on at least the signaled first NZP CSI-RS configuration, the second NZP CSI-RS configuration, and the CSI-IM configuration.

The invention is defined by the subject-matter of independent claims <NUM>, <NUM>, <NUM> and <NUM>, which define a method at a network node, a method at a wireless device, a network node and a wireless device, respectively, for CQI saturation mitigation.

In the present disclosure, given limited wireless device capability to mitigate the CQI saturation issue, multiple embodiments are described herein that help mitigate CQI saturation. Certain aspects of the present disclosure and their embodiments may provide solutions to these or other challenges. The present disclosure includes several embodiments of methods, which can be deployed jointly, to mitigate the CQI saturation issue for wireless devices with limited CSI feedback capability for downlink massive MIMO systems. These embodiments may include:.

It should be noted that any of the above-mentioned transmission powers can be zero. When the transmission power is zero, this means that nothing is transmitted on that CSI-IM or nzp-CSI-RS-ResourcesForInterference.

There are, described herein, various embodiments which address one or more of the issues described above.

Certain embodiments may provide one or more of the following technical advantage(s). Embodiments of the methods disclosed herein enable a wireless device with limited capability to have multiple CSI report(s) to mitigate the SINR saturation issue encountered in downlink massive MU-MIMO system. With these embodiments, the CSI estimation on the base station will be more accurate which may improve massive MU-MIMO performance in <NUM> LTE and <NUM> NR systems, for example.

Before describing in detail example embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to CQI saturation mitigation. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

The term "network node" used herein can be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi-standard radio (MSR) radio node such as MSR BS, multi-cell/multicast coordination entity (MCE), integrated access and backhaul (IAB) node, relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd party node, a node external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also comprise test equipment. The term "radio node" used herein may be used to also denote a wireless device (WD) such as a wireless device (WD) or a radio network node.

In some embodiments, the non-limiting terms wireless device (WD) and a user equipment (UE) may be used interchangeably herein. The WD may also be a radio communication device, target device, device to device (D2D) WD, machine type WD or WD capable of machine to machine communication (M2M), low-cost and/or low-complexity WD, a sensor equipped with WD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (IoT) device, or a Narrowband IoT (NB-IOT) device, etc..

Some embodiments provide for CQI saturation mitigation. In one or more embodiments, mitigating CQI saturation refers to reducing a likelihood for CQI saturation and/or preventing CQI saturation.

Referring again to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in <FIG> a schematic diagram of a communication system <NUM>, according to an embodiment, such as a 3GPP-type cellular network that may support standards such as LTE and/or NR (<NUM>), which comprises an access network <NUM>, such as a radio access network, and a core network <NUM>. The access network <NUM> comprises a plurality of network nodes 16a, 16b, 16c (referred to collectively as network nodes <NUM>), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (referred to collectively as coverage areas <NUM>). Each network node 16a, 16b, 16c is connectable to the core network <NUM> over a wired or wireless connection <NUM>. A first wireless device (WD) 22a located in coverage area 18a is configured to wirelessly connect to, or be paged by, the corresponding network node 16a. A second WD 22b in coverage area 18b is wirelessly connectable to the corresponding network node 16b. While a plurality of WDs 22a, 22b (collectively referred to as wireless devices <NUM>) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole WD is in the coverage area or where a sole WD is connecting to the corresponding network node <NUM>. Note that although only two WDs <NUM> and three network nodes <NUM> are shown for convenience, the communication system may include many more WDs <NUM> and network nodes <NUM>.

A network node <NUM> is configured to include a configuration unit <NUM> which is configured to perform one or more network node <NUM> functions as described herein such as with respect to CQI saturation mitigation. A wireless device <NUM> is configured to include a CQI unit <NUM> which is configured to perform one or more wireless device <NUM> functions as described herein such as with respect to CQI saturation mitigation.

The host application <NUM> may be operable to provide a service to a remote user, such as a WD <NUM> connecting via an OTT connection <NUM> terminating at the WD <NUM> and the host computer <NUM>. The "user data" may be data and information described herein as implementing the described functionality. In one embodiment, the host computer <NUM> may be configured for providing control and functionality to a service provider and may be operated by the service provider or on behalf of the service provider. The processing circuitry <NUM> of the host computer <NUM> may enable the host computer <NUM> to observe, monitor, control, transmit to and/or receive from the network node <NUM> and or the wireless device <NUM>. The processing circuitry <NUM> of the host computer <NUM> may include an information unit <NUM> configured to enable the service provider to process, analyze, forward, relay, transmit, receive, store, etc., information related to CQI saturation mitigation.

Thus, the network node <NUM> further has software <NUM> stored internally in, for example, memory <NUM>, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node <NUM> via an external connection. The processing circuitry <NUM> may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by network node <NUM>. Processor <NUM> corresponds to one or more processors <NUM> for performing network node <NUM> functions described herein. The memory <NUM> is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software <NUM> may include instructions that, when executed by the processor <NUM> and/or processing circuitry <NUM>, causes the processor <NUM> and/or processing circuitry <NUM> to perform the processes described herein with respect to network node <NUM>. For example, processing circuitry <NUM> of the network node <NUM> may include configuration unit <NUM> configured to perform one or more network node <NUM> functions as described herein such as with respect to CQI saturation mitigation.

The processing circuitry <NUM> may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by WD <NUM>. The processor <NUM> corresponds to one or more processors <NUM> for performing WD <NUM> functions described herein. The WD <NUM> includes memory <NUM> that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software <NUM> and/or the client application <NUM> may include instructions that, when executed by the processor <NUM> and/or processing circuitry <NUM>, causes the processor <NUM> and/or processing circuitry <NUM> to perform the processes described herein with respect to WD <NUM>. For example, the processing circuitry <NUM> of the wireless device <NUM> may include a CQI unit <NUM> configured to perform one or more wireless device <NUM> functions as described herein such as with respect to CQI saturation mitigation.

In some embodiments, the measurements may be implemented in that the software <NUM>, <NUM> causes messages to be transmitted, in particular empty or 'dummy' messages, using the OTT connection <NUM> while it monitors propagation times, errors, etc..

Although <FIG> and <FIG> show various "units" such as configuration unit <NUM>, and CQI unit <NUM> as being within a respective processor, it is contemplated that these units may be implemented such that a portion of the unit is stored in a corresponding memory within the processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry.

<FIG> is a flowchart illustrating an example method implemented in a communication system, such as, for example, the communication system of <FIG> and <FIG>, in accordance with one embodiment. The communication system may include a host computer <NUM>, a network node <NUM> and a WD <NUM>, which may be those described with reference to <FIG>. In a first step of the method, the host computer <NUM> provides user data (Block S100). In an optional substep of the first step, the host computer <NUM> provides the user data by executing a host application, such as, for example, the host application <NUM> (Block S102). In a second step, the host computer <NUM> initiates a transmission carrying the user data to the WD <NUM> (Block S104). In an optional third step, the network node <NUM> transmits to the WD <NUM> the user data which was carried in the transmission that the host computer <NUM> initiated, in accordance with the teachings of the embodiments described throughout this disclosure (Block S106). In an optional fourth step, the WD <NUM> executes a client application, such as, for example, the client application <NUM>, associated with the host application <NUM> executed by the host computer <NUM> (Block S108).

<FIG> is a flowchart illustrating an example method implemented in a communication system, such as, for example, the communication system of <FIG>, in accordance with one embodiment. The communication system may include a host computer <NUM>, a network node <NUM> and a WD <NUM>, which may be those described with reference to <FIG> and <FIG>. In a first step of the method, the host computer <NUM> provides user data (Block S110). In an optional substep (not shown) the host computer <NUM> provides the user data by executing a host application, such as, for example, the host application <NUM>. In a second step, the host computer <NUM> initiates a transmission carrying the user data to the WD <NUM> (Block S112). In an optional third step, the WD <NUM> receives the user data carried in the transmission (Block S114).

<FIG> is a flowchart illustrating an example method implemented in a communication system, such as, for example, the communication system of <FIG>, in accordance with one embodiment. The communication system may include a host computer <NUM>, a network node <NUM> and a WD <NUM>, which may be those described with reference to <FIG> and <FIG>. In an optional first step of the method, the WD <NUM> receives input data provided by the host computer <NUM> (Block S116). In an optional substep of the first step, the WD <NUM> executes the client application <NUM>, which provides the user data in reaction to the received input data provided by the host computer <NUM> (Block S118). Additionally or alternatively, in an optional second step, the WD <NUM> provides user data (Block S120). In an optional substep of the second step, the WD provides the user data by executing a client application, such as, for example, client application <NUM> (Block S122). In providing the user data, the executed client application <NUM> may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the WD <NUM> may initiate, in an optional third substep, transmission of the user data to the host computer <NUM> (Block S124). In a fourth step of the method, the host computer <NUM> receives the user data transmitted from the WD <NUM>, in accordance with the teachings of the embodiments described throughout this disclosure (Block S126).

<FIG> is a flowchart illustrating an example method implemented in a communication system, such as, for example, the communication system of <FIG>, in accordance with one embodiment. The communication system may include a host computer <NUM>, a network node <NUM> and a WD <NUM>, which may be those described with reference to <FIG> and <FIG>. In an optional first step of the method, in accordance with the teachings of the embodiments described throughout this disclosure, the network node <NUM> receives user data from the WD <NUM> (Block S128). In an optional second step, the network node <NUM> initiates transmission of the received user data to the host computer <NUM> (Block S130). In a third step, the host computer <NUM> receives the user data carried in the transmission initiated by the network node <NUM> (Block S132).

<FIG> is a flowchart of a method in a network node <NUM> according to the claimed embodiment. One or more blocks described herein may be performed by one or more elements of network node <NUM> such as by one or more of processing circuitry <NUM> (including the configuration unit <NUM>), processor <NUM>, radio interface <NUM> and/or communication interface <NUM>. Network node <NUM> is configured to configure (Block S134) a first measurement resource for channel measurements, as described herein. Network node <NUM> is configured to configure (Block S136) a second measurement resource for interference measurements, as described herein. Network node <NUM> is configured to cause (Block S138) transmission of a first signal with a first predefined power level in a transmission occasion of the first measurement resource, as described herein. Network node <NUM> is configured to cause (Block S140) transmission of a second signal with a second predefined power level in a transmission occasion of the second measurement resource where at least one of the first predefined power level and the second predefined power level is configured to at least in part mitigate channel quality indication, CQI, saturation, as described herein.

According to one or more embodiments, the first measurement resource is a non-zero power channel state information-reference signal, NZP CSI-RS, resource. According to one or more embodiments, the second measurement resource is a channel state information-interference measurement, CSI-IM, resource. According to one or more embodiments, the second measurement resource is a non-zero power channel state information-reference signal, NZP CSI-RS, resource.

According to one or more embodiments, the processing circuitry is further configured to cause transmission of a third signal with a third predefined power level in another transmission occasion of the second measurement resource, receive a first reported CQI associated with the second signal, and receive a second reported CQI associated with the third signal, the first reported CQI being different than the second reported CQI. The processing circuitry is further configured to estimate a signal to interference plus noise ratio, SINR, based on at least one of the first reported CQI and second reported CQI, and perform at least one action based at least in part on the estimated SINR. According to one or more embodiments, the processing circuitry is further configured to receive a first reported CQI associated with the first signal and the second signal, estimate a signal to interference plus noise ratio, SINR, based on the first reported CQI, and perform at least one action based at least in part on the estimated SINR. According to one or more embodiments, the at least one action includes performing at least one of link adaptation and a modulation and coding rate decision.

According to the claimed embodiment, the at least one of the first predefined power level and second predefined power level is configured to at least in part mitigate CQI saturation by causing a signal to interference plus noise ratio, SINR, observed by a wireless device <NUM> to change, the observed SINR mapping to a reportable CQI. According to the claimed embodiment, the at least in part mitigating of CQI saturation corresponds to causing a reportable CQI to change from saturated CQI to non-saturated CQI by changing a signal to interference plus noise ratio, SINR, observed by the wireless device <NUM>. According to one or more embodiments, the processing circuitry is further configured to configure a third measurement resource for interference measurements, cause transmission of a third signal with a third predefined power level in a transmission occasion of the third measurement resource, and at least one of the first predefined power level where the second predefined power level and the third predefined power level is configured to at least in part mitigate channel quality indication, CQI, saturation.

<FIG> is a flowchart of a method in a wireless device <NUM> according to the claimed embodiment, One or more blocks described herein may be performed by one or more elements of wireless device <NUM> such as by one or more of processing circuitry <NUM> (including the CQI unit <NUM>), processor <NUM>, radio interface <NUM> and/or communication interface <NUM>. Wireless device <NUM> is configured to perform (Block S142) channel measurements based on a first signal with a first predefined power level that is received in a transmission occasion of a first measurement resource that is configured for channel measurements, as described herein. Wireless device <NUM> is configured to perform (Block S144) interference measurements based on a second signal with a second predefined power level that is received in a transmission occasion of a second measurement resource that is configured for interference measurements where at least one of the first predefined power level and the second predefined power level is configured to at least in part mitigate channel quality indication, CQI, saturation, as described herein. Wireless device <NUM> is configured to report (Block S146) a first CQI based at least on one of the channel measurements of the first signal and the interference measurements of the second signal, as described herein.

According to one or more embodiments, the first measurement resource is a non-zero power channel state information reference signal, NZP CSI-RS, resource. According to one or more embodiments, the second measurement resource is a channel state information-interference measurement, CSI-IM, resource. According to one or more embodiments, the second measurement resource is a non-zero power channel state information reference signal, NZP CSI-RS, resource.

According to one or more embodiments, the processing circuitry is further configured to perform interference measurements based on a third signal with a third predefined power level that is received in another transmission occasion of the second measurement resource that is configured for interference measurements, and report a second CQI associated with the interference measurements of the third signal where the first CQI is a different than the second CQI and is associated with the interference measurements of the second signal.

According to one or more embodiments, the processing circuitry is further configured to observe CQI that has been changed by the at least one of the first predefined power level and second predefined power level for at least in part mitigating CQI saturation. According to the claimed embodiment, the at least in part mitigating of CQI saturation corresponds to reporting a CQI that has changed from saturated CQI to a non-saturated CQI. According to one or more embodiments, the processing circuitry is further configured to perform interference measurements based on a third signal with a third predefined power level that is received in a transmission occasion of a third measurement resource that is configured for interference measurements, and where at least one of the first predefined power level, the second predefined power level and the third predefined power level is configured to at least in part mitigate channel quality indication, CQI, saturation, as described herein.

Having generally described arrangements for CQI saturation mitigation, details for these arrangements, functions and processes are provided as follows, and which may be implemented by the network node <NUM>, wireless device <NUM> and/or host computer <NUM>.

Some embodiments provide CQI saturation mitigation. Network node <NUM> functionality described below may be performed by at least one of processing circuitry <NUM>, radio interface <NUM>, processor <NUM>, configuration unit <NUM>, etc. Wireless device <NUM> functionality described below may be performed by at least one of processing circuitry <NUM>, processor <NUM>, radio interface <NUM>, CQI unit <NUM>, etc..

One or more embodiments will now be described more fully with reference to the accompanying drawings.

In one embodiment of the method of the present disclosure, one NZP CSI-RS resource for channel measurement and one CSI-IM resource for interference measurement is configured. In some embodiments, in CSI-IM, a signal with a transmission power is transmitted where the transmission power is non-zero. The transmission power is adjusted to control the wireless device <NUM> observed SINR, thus change/modifying the wireless device <NUM> reported CQI. In other embodiments, in the time domain, in a first CSI-IM resource transmission occasion, a signal with a first transmission power is transmitted, whereas in a second CSI-IM resource transmission occasion, a signal with a second transmission power level is transmitted so that wireless device <NUM> can provide two or more kinds of feedbacks, each report is with different SINR where some report(s) may be with a higher SINR, and some report(s) with lower SINR, while a time restrictions for interference measurements may be configured (i.e., configuring "timeRestrictionForInterferenceMeasurements") to avoid the wireless device <NUM> from performing any interference average across time.

In an embodiment, as shown in <FIG>, for each PRBs, there are <NUM> subcarriers in frequency domain and <NUM> OFDM symbols in time domain, one <NUM>-port CSI-RS resource for channel measurements is configured, marked as blocks with one style of hatching or fill pattern, and one CSI-IM resource for interference measurements is configured, marked as blocks with another style of hatching or fill pattern. As one example, in the x0 subframe, transmission power p<NUM> is transmitted on CSI-IM, in the subframe x1,. , xn, transmission power p<NUM>,. , pn are applied, respectively, where n is any integer number larger than <NUM>. The pattern can be repetitive with a periodicity. As another example for Alternative <NUM>, assume n=<NUM>, the power allocation pattern for CSI-IM could be p<NUM>,p<NUM>,p<NUM>,p<NUM>,···,p<NUM>,p<NUM>. As one example for Alternative <NUM>, assume n=<NUM>, the power allocation pattern for CSI-IM could be <MAT>.

At the wireless device <NUM> side, the wireless device <NUM> can use the CSI-RS for channel measurements to acquire the channel and use CSI-IM to measure interference and noise, and further derive CQI based on the measured channel and measured the interference and noise. As one example for the CQI derivation, CQI can be given by quantized SINR and SINR could be given by <MAT> where H is the channel, SCSI_IM is the transmitted signal on the CSI-IM, and I is the interference signal on REs of CSI-IM coming from neighbor cells, f(·) is a function, as one simple example for the f(·) could be: <MAT> where P is the best precoding matrix selected by the wireless device <NUM> based on codebook, <MAT> is the port to antenna mapping matrix configured in and/or by the network node <NUM>. Assuming the total number of transmission antenna at network node <NUM> is nTx and the number of Rx antenna at wireless device <NUM> is nRx, the number of CSI-RS ports is nPorts and the number of layers for PDSCH is nLayers, then matrix P is with dimension nPorts x nLayers, <MAT> is with dimension nTx x nPorts, H is with dimension nRx x nTx. (·)H is the conjugate transposition of (·), trace(·) represents the trace of the matrix (·). Given the above equation, on the subframe xk, the interference measured on CSI-IM is given by: <MAT> where pk is the transmission power for CSI-IM in the subframe xk, and <MAT> is the port to antenna mapping matrix for CSI-IM. Taking into consideration of I, the SINR could be given as: <MAT>.

From the above equation, it is illustrated that adjusting pk can adjust the SINR value, thus further adjust feedback CQI. Setting a proper value for pk can avoid the CQI saturation.

At the network node <NUM> side, based on obtained CQI, network node <NUM> can estimate the SINR and further estimate the I since all the parameters are known except I. As one example, <MAT> where g(-) is a function to predict SINR based on CQI report. After I in the example above is calculated, network node <NUM> may subtract I from CQI to get the true or actual SINR by SINR Network Node <NUM> = SINR_CQI * (CSI_IM/I+ <NUM>), which now may be higher than the SINR of CQI <NUM>. The basic procedure is shown in the signalling diagram of <FIG> that is discussed below.

With respect to <FIG>, network node <NUM> is configured to configure (Block S148) one CSI-RS source for channel measurement and one CSI-IM resource for interference measurement, as described herein. Network node <NUM> is configured to cause (Block S150) transmission of a signal with a transmission power p on CSI-IM, as described herein. Wireless device <NUM> is configured to estimate (Block S152) CQI based on CSI-RS and CSI-IM considering the transmitted signal on the CSI-IM and interference signal on REs of CSI-IM, as described herein. Wireless device <NUM> is configured to feedback (Block S154) the CQI, as described herein.

The network node <NUM> is configured to estimate (Block S156) an interference signal on REs of CSI-IM by removing the transmitted signal impact based on the CQI report, as described herein. The network node <NUM> is configured to perform (Block S158) link adaptation based on the estimated interference signal on RES of CSI-IM, as described herein.

In one embodiment, in case N=<NUM> and two reports can be obtained by network node <NUM>, network node <NUM> can set p<NUM> to zero and set p<NUM> to non-zero, so that the first report can be used for SU-MIMO, rank-decision, etc. Further, in case CQI is saturated in the lower SINR range for the second report, the first report can be used for interference estimation.

In another embodiment, network node <NUM> may dynamically decide the transmission power pn injected on CSI-IM resource in subframe n based on received CQI reports which were determined by the wireless device <NUM> based on CSI-IM measurement in subframe n-<NUM> (where the injected transmission power on the CSI-IM was pn-<NUM>). For instance, network node <NUM> may start by setting p<NUM> equal to zero. If the CQI reported based on CSI-IM measurement in subframe <NUM> corresponds to the highest CQI value (i.e., CQI=<NUM>) and so is saturated, network node <NUM> may for the subsequent CSI-IM occasion in subframe <NUM> inject a non-zero transmission power p<NUM> > <NUM>. Otherwise, if the reported CQI is not saturated, network node <NUM> may set the transmission power in subframe <NUM> to zero. Network node <NUM> may further, in the case where a non-zero transmission power pn was injected in subframe n and the corresponding reported CQI still was saturated, inject a larger transmission power in subframe n+<NUM> and continue to increase the transmission power injected on CSI-IM resources on subsequent subframes as long as the CQI is saturated.

The beam ( <MAT>) of the CSI-IM can be wide and non- wireless device <NUM> specific or be narrow and wireless device-specific. When using wide beam for CSI-IM, it allows wireless devices <NUM> in the cell to use the same CSI-IM signal to derive CQI. When using narrow beam for CSI-IM, there is a benefit in that it allows wireless devices <NUM> to measure potential interference from a certain Tx direction. By sweeping the narrow CSI-IM beams, as the CQI saturation issue is alleviated, network node <NUM> may also obtain measurements of interference from interested Tx directions.

In an embodiment, the method includes configuring one CSI-RS resource for channel measurements and two or more CSI-IM resources for interference measurements. In some embodiments, in a first CSI-IM resource, a signal with the first transmission power is transmitted. In a second CSI-IM resource, a signal with a second transmission power is transmitted. Multiple trigger states are defined for CSI report. At least one trigger state is associated with the report with the first CSI-IM resource and another trigger state is associated with the report with the second CSI-IM resource. Thus, multiple CQIs can be reported by wireless device <NUM> by triggering different trigger states at different time occasions.

As shown in <FIG>, one <NUM>-port CSI-RS resource for channel measurements is configured, marked as blocks with a particular hatching or filled pattern style, two CSI-IM resources for interference measurements, wherein the first CSI-IM resource is marked with another hatching or fill pattern style and the second CSI-IM resource is marked with yet another hatching or fill pattern style. On the first CSI-IM resource, the signal with transmission power p<NUM> is transmitted, whereas, on the second CSI-IM resource, the signal with transmission p<NUM> is transmitted.

As one example, p<NUM> can be set to zero and p<NUM> can be set into a non-zero value. Thus, the first CSI-IM can be used to avoid low-SNR saturation issue, and the second CSI-IM can be used for high-SNR saturation issue.

In order to reduce the wireless device <NUM> capability requirements, CSI trigger states, CSI-RS resource sets and CSI report setting may be taken into account and particularly designed.

According to 3GPP TS <NUM>, for a CSI report, a wireless device <NUM> is configured by higher layers with N≥<NUM> CSI-ReportConfig Reporting Settings, M≥<NUM> CSI-ResourceConfig Resource Settings, and one or two list(s) of trigger states (given by the higher layer parameters CSI-AperiodicTriggerStateList and CSI-SemiPersistentOnPUSCH-TriggerStateList). Each trigger state in CSI-AperiodicTriggerStateList contains a list of associated CSI-ReportConfigs indicating the Resource Set IDs for channel and optionally for interference. For aperiodic CSI report triggering, a single set of CSI triggering states are higher layer configured. A trigger state is initiated using the CSI request field in DCI. For a wireless device <NUM> configured with the higher layer parameter CSI-AperiodicTriggerStateList, if a Resource Setting linked to a CSI-ReportConfig has multiple aperiodic resource sets, only one of the aperiodic CSI-RS resource sets from the Resource Setting is associated with the trigger state, and the wireless device <NUM> is higher layer configured per trigger state per Resource Setting to select the one CSI-IM/NZP CSI-RS resource set from the Resource Setting.

Based on the above rules, one CSI-ReportConfig can be defined. In the CSI-ReportConfig, it associates the CSI report with a plurality of CSI-ResourceConfig Resource Settings. In the CSI-ResourceConfig Resource Setting, one NZP-CSI-RS-Resource set (NZP-CSI-RS-ResourceSet#<NUM>) for channel measurements and two csi-IM-ResourceSets (csi-IM-ResourceSet#<NUM> and CSI-IM-ResourceSet#<NUM>) for interference measurements are defined. Two trigger states in CSI-AperiodicTriggerStateList are configured, one trigger state (TriggerState#<NUM>) is used to select NZP-CSI-RS-ResourceSet#<NUM> for channel measurements and csi-IM-ResourceSet#<NUM> for interference measurements, and the other trigger state (TriggerState#<NUM>) is used to select NZP-CSI-RS-ResourceSet#<NUM> for channel measurements and csi-IM-ResourceSet#<NUM> for interference measurements. In a first slot, TriggerState#<NUM> is initiated using DCI in one downlink slot and TriggerState#<NUM> is initiated using DCI in another downlink slot. The SINR corresponding to the TriggerState#<NUM> can be given by <MAT>.

And the SINR corresponding to the triggerState#<NUM> can be given by: <MAT>.

The difference between the two trigger states is the transmit power of CSI-IM is different. With the above-mentioned method/embodiment(s), assuming p<NUM> < p<NUM>, SINR<NUM> can be used for SU-MIMO link adaptation, or used to avoid the lower SINR saturation issue, SINR<NUM> can be used for MU-MIMO link adaptation or used to avoid the higher SINR saturation issue.

In a variant of the previous embodiment, two aperiodic CSI Report Settings, a first and a second, are configured and mapped to individual trigger states. The first CSI Report Setting is associated with one periodic NZP CSI-RS resource for channel measurement and one periodic CSI-IM resource for interference measurement, where a first transmission power (which may typically be equal to zero) is injected on the periodic CSI-IM resource. Since these resources are periodic, they are transmitted with a certain periodicity and slot offset.

The second CSI Report Setting is associated with one aperiodic NZP CSI-RS resource for channel measurement and one aperiodic CSI-IM resource for interference measurement, where a second transmission power (which may typically be larger than zero) is injected on the aperiodic CSI-IM resource. The aperiodic CSI-RS resource is configured to occupy the same resource element within a slot as the periodic CSI-RS resource while the aperiodic CSI-IM resource do not occupy the same resource elements as the periodic CSI-IM resource. Since these resources are aperiodic, they are only present from a wireless device <NUM> perspective in the slot wherein the triggering DCI is transmitted.

With such configuration, network node <NUM> can trigger the second CSI Report Setting in the same slot wherein an occasion of the periodic CSI-RS resource is present. The periodic and aperiodic CSI-RS resource will thus "overlap" from wireless device <NUM> perspective, implying that network node <NUM> only needs to transmit one CSI-RS resource which reduces CSI-RS overhead.

In an embodiment, one CSI-RS resource for channel measrurements and one nzp-CSI-RS-Resource for interfernece measurements are configured. For the power transmission for the nzp-CSI-RS-ResourceForInterference, there are two alternatives. In the first alternative, a fixed transmission power is used for nzp-CSI-RS-ResourceForInterference. The power is determined so that the wireless device <NUM>'s CQI is not saturated. As a further embodiment, in order to provide wireless device <NUM> specific CQI determination, the transmission power for nzp-CSI-RS-ResourceForInterference is fixed, and a different wireless device <NUM> may use different powerControlOffset. For cell-center wireless device <NUM>, larger powerControlOffset may be informed, and for cell-edge wireless device <NUM>, smaller powerControlOffset may be informed.

In an additional embodiment, different transmission power is applied for the nzp-CSI-RS-Resource for interference measurements over time. More specifically, in a first nzp-CSI-RS-ResourcesForInterference resource transmission occasion, a signal with a first transmission power is transmitted, whereas in a second nzp-CSI-RS-ResourcesForInterference resource transmission occasion, a signal with a second transmission power level is transmitted, so that the wireless device <NUM> can provide two or more kinds of feedbacks, each report is with different SINR, some is with higher SINR and some is with lower SINR. In order to avoid wireless device <NUM> to perform any interference average across time, where a time restriction for interference measurements is configured, i.e., "timeRestrictionForInterferenceMeasurements" is configured.

In an additional embodiment, at network node <NUM> side, since the transmission power of nzp-CSI-RS-ResourcesForInterference is known, and the channel for the nzp-CSI-RS-ResourcesForInterference is known as well, thus, the interference of other cells can be estimated. Similarly, controlling the power of nzp-CSI-RS-ResourcesForInterference, the SINR range can be controlled, thus control the CQI range.

In an additional embodiment, in a first nzp-CSI-RS-ResourceForInterference, signal with the first transmission power is transmitted. A second nzp-CSI-RS-ResourceForInterference, a signal with a second transmission power is transmitted, so that the wireless device <NUM> can feedback a plurality of feedback where each feedback is associated with a different SINR, thus the CQI saturation issue can be eliminated.

In an additional embodiment, same REs and same transmission power is applied to two nzp-CSI-RS-ResourcesForInterference, but different powerControlOffset is associated with nzp-CSI-RS-ResourcesForInterference. In some embodiments, powerControlOffset is not necessarily equal to the transmission power and may only be used for CSI calculation. Since the same REs are used, although two nzp-CSI-RS-ResourcesForInterference are configured, the overhead to transmit two nzp-CSI-RS-ResourcesForInterference is the same as that for one nzp-CSI-RS-ResourceForInterference. As a result, the CSI-RS overhead is reduced.

The corresponding CSI report configuration and CSI resource configuration is described herein. More specifically, In the CSI-ResourceConfig Resource Setting, one NZP-CSI-RS-Resource set (NZP-CSI-RS-ResourceSet#<NUM>) for channel measurements and two sets of nzp-CSI-RS-ResourcesForInterference (nzp-CSI-RS-ResourcesForInterference#<NUM> and nzp-CSI - RS- ResourcesFor Interference# <NUM>) are defined. Two trigger states in CSI-AperiodicTriggerStateList are configured, one trigger state (TriggerState#<NUM>) is used to select NZP-CSI-RS-ResourceSet#<NUM> for channel measurements and nzp-CSI-RS-ResourcesForInterference#<NUM> for interference measurements, and the other trigger state (TriggerState#<NUM>) is used to select NZP-CSI-RS-ResourceSet#<NUM> for channel measurements and nzp-CSI-RS-ResourcesForInterference#<NUM> for interference measurements. In a first slot, TriggerState#<NUM> is initiated using downlink control information (DCI) in one downlink slot and TriggerState#<NUM> is initiated using DCI in another downlink slot. The SINR corresponding to the TriggerState#<NUM> can be given by <MAT>.

And the SINR corresponding to the triggerState#<NUM> can be given by: <MAT> where <MAT> is the port to antenna mapping for nzp-CSI-RS-ResourcesForInterference. For alternative <NUM>, p<NUM> and p<NUM> are the actual transmitted power for nzp-CSI-RS-ResourcesForInterference. For alternative <NUM>, p<NUM> and p<NUM> are the powerControlOffset for the first and second set of nzp-CSI-RS-Resources For Interference.

In an embodiment, upon checking the wireless device <NUM> CQI report, if the CQI report is larger than a first threshold for a first time-duration, network node <NUM> uses RRC to configure the first powerControlOffset for the CSI-RS resource for channel measurements for the given wireless device <NUM>. Otherwise, network node <NUM> uses RRC to configure the second powerControlOffset for the CSI resource for channel measurements, so that wireless device <NUM> can have different back off for the CQI report. Thus, the CQI saturation issues can be mitigated.

At least some of the above-mentioned embodiments can be combined to mitigate the CQI saturation issue.

In some embodiments, the following are configured: one CSI-RS resource for channel measurements, one csi-IM-ResourcesForInterference, and two nzp-CSI-RS-ResourcesForInterference. These two nzp-CSI-RS-ResourcesForInterference can be with different transmission power or different powerControlOffset.

In some embodiments, the following are configured: one CSI-RS resource for channel measurements, two csi-IM-ResourcesForInterference, and one nzp-CSI-RS-ResourcesForInterference. These two csi-IM-ResourcesForInterference can be with different transmission power.

One or more embodiments described herein may be applied to TDD systems. One or more embodiments described herein that, for example, use RRC to reconfigure the offset may be applied to TDD and/or FDD systems.

Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Python, Java® or C++.

Claim 1:
A method implemented by a network node (<NUM>) that is configured to communicate with a wireless device (<NUM>), the method comprising:
configuring (S134) a first measurement resource for channel measurements;
configuring (S136) a second measurement resource for interference measurements;
causing (S138) transmission of a first signal with a first predefined power level in a transmission occasion of the first measurement resource; and
causing (S140) transmission of a second signal with a second predefined power level in a transmission occasion of the second measurement resource, at least one of the first predefined power level and the second predefined power level is configured to at least in part mitigate channel quality indication, CQI, saturation, wherein the at least in part mitigating of CQI saturation corresponds to causing a reportable CQI to change from saturated CQI to non-saturated CQI by changing a signal to interference plus noise ratio, SINR, observed by the wireless device (<NUM>) and mapped to the reportable CQI, wherein the reportable CQI is saturated when it corresponds to a highest reportable CQI value.