Non-coherent joint transmission (NC-JT)

Abstract

A method for performing a non-coherent joint transmission, NC-JT, for a user equipment, UE, using up to N transmission and reception points, TRPs, where N > 1. The method includes, for each one of the N TRPs, obtaining a CSI report generated by the UE for the TRP, thereby obtaining N CSI reports, one for each one of the N TRPs. The method also includes, based on the N CSI reports, selecting X of the N TRPs to participate in the NC-JT for the UE, where X ≤ N. The method also includes, determining a modulation and coding scheme (MCS) for the NC-JT for the UE. The method also includes determining a precoder for each one of the X TRPs. The method further includes performing the NC-JT for the UE using the selected X TRPs and using the determined MCS and precoders.

Description

NON-COHERENT JOINT TRANSMISSION (NC-JT) TECHNICAL FIELD

[0001] Disclosed are embodiments related to non-coherent joint transmission. BACKGROUND

[0002] Joint transmission (JT) is a distributed Multiple-Input and Multiple-Output (D- MIMO) technique applied in the downlink (DL) in which a signal for a user equipment (UE) is transmitted from multiple and spatially distributed transmit / receive points (TRPs), such as, for example macro base stations, pico base stations, femto base station, radio heads, or antenna systems. In the framework of The Third Generation Partnership Project (3GPP), JT is categorized into coherent JT (C-JT) and non-coherent JT (NC-JT). In 3GPP New Radio (NR), the multiple TRPs are associated with a fifth generation (5G) base station (gNB).

[0003] In coherent joint transmission (C-JT) over multiple TRPs, each MIMO layer is transmitted over all the TRPs. A MIMO layer is precoded jointly across the TRPs such that the precoded signals from all the TRPs, for each layer, would be added constructively at the UE.

[0004] Such a scheme requires time and frequency synchronization between the TRPs such that co-phasing between TRPs is possible. It also requires instantaneous channel knowledge in order to control the co-phasing correctly.

[0005] In contrast to C-JT, in non-coherent joint transmission (NC-JT), each MIMO layer is only transmitted from one TRP and co-phasing between TRPs is not needed. Therefore, tight frequency synchronization between TRPs is not required. An example is shown in FIG. 1, where two Physical Downlink Shared Channel (PDSCH) layers, one over each TRP, are transmitted to a UE over two TRPs. Each PDSCH layer has an associated Demodulation Reference Signal (DMRS) port transmitted from the same TRP.

[0006] Channel State Information (CSI) Reference Signal (CSI-RS)

[0007] For CSI measurement and feedback, CSI-RSs are defined. A CSI-RS is transmitted on each transmit antenna (a.k.a., antenna port) and is used by the UE to estimate the downlink channel between each of the antenna ports and each of its receive antenna ports. Theantenna ports are also referred to as CSI-RS ports. The supported number of antenna ports in NR are {1,2,4,8,12,16,24,32}. By measuring the received CSI-RS, a UE can estimate the channel that the CSI-RS is traversing, including the radio propagation channel and antenna gains. The CSI-RS for the above purpose is also referred to as Non-Zero Power (NZP) CSI-RS.

[0008] A CSI-RS can be configured to be transmitted in certain resource elements (REs) in a slot and certain slots. FIG. 2 shows an example of CSI-RS REs for 12 antenna ports, where one RE per resource block (RB) per port is shown.

[0009] In addition, an interference measurement resource (IMR) is also defined in NR for a UE to measure interference. An IMR contains 4 REs, either 4 adjacent REs in frequency in the same OFDM symbol or 2 by 2 adjacent REs in both time and frequency in a slot.

[0010] By measuring the channel based on the NZP CSI-RSs and the interference based on an IMR, a UE can estimate the effective channel and noise plus interference to determine the CSI (e.g., to determine a rank, a precoding matrix, and a channel quality). Furthermore, a UE in NR may be configured to measure interference based on one or multiple NZP CSI-RS resources.

[0011] CSI framework in NR

[0012] In NR, a UE can be configured with multiple CSI reporting settings and multiple CSI-RS resource settings. Each CSI-RS resource setting can contain multiple resource sets, and each resource set can contain up to 8 CSI-RS resources. For each CSI reporting setting, a UE feeds back a CSI report containing CSI. The CSI included in the CSI report may include: a channel quality indicator (CQI) indicating the channel quality determined by the UE, a precoding matrix indicator (PMI) indicating the precoding matrix determined by the UE, a rank indicator (RI) indicating the rank determined by the UE, and / or other information.

[0013] Each CSI reporting setting contains at least the following information shown in table 1 below: TABLE 1 - CSI Reporting Setting • A CSI-RS resource set for channel measurement • An IMR resource set for interference measurement • Optionally, a CSI-RS resource set for interference measurement• Time-domain behavior, i.e., periodic, semi-persistent, or aperiodic reporting • Frequency granularity, i.e., wideband or subband • CSI parameters to be reported such as rank indicator (RI), precoding matrix indicator (PMI), channel quality indicator (CQI), and CSI-RS resource indicator (CRI) in case of multiple CSI-RS resources in a resource set • Codebook types, i.e., type I or II, and codebook subset restriction • Measurement restriction • Subband size. One out of two possible subband sizes is indicated, the value range depends on the bandwidth of the BWP. One CQI / PMI (if configured for subband reporting) is fed back per subband).

[0014] When the CSI-RS resource set in a CSI reporting setting contains multiple CSI- RS resources, one of the CSI-RS resources is selected by a UE and a CSI-RS resource indicator (CRI) is also reported by the UE to indicate to the gNB about the selected CSI-RS resource in the resource set, together with RI, PMI and CQI associated with the selected CSI-RS resource.

[0015] For aperiodic CSI reporting in NR, more than one CSI reporting settings, each with a different CSI-RS resource set for channel measurement and / or resource set for interference measurement, can be configured and triggered at the same time. In this case, multiple CSI reports are aggregated and sent from the UE to the gNB in a single Physical Uplink Shared Channel (PUSCH) transmission.

[0016] NR CSI capabilities

[0017] The NR CSI reporting capabilities reported by the UE are summarized in table 2 below. TABLE 2 • The maximum number of simultaneous CSI reports [simultaneousCSI-ReportsAllCC] (i.e. number of CSI processing units (CPUs)) and simultaneous NZP CSI-RS ports / resources [totalNumberPortsSimultaneousNZP-CSI-RS-ActBWP-AllCC / maxNumberSimultaneousNZP-CSI-RS-ActBWP-AllCC] are reported per band combination [CA-ParametersNR]o In addition, the maximum number of simultaneous CSI reports in a component carrier (CC) [simultaneousCSI-ReportsPerCC] and simultaneous NZP CSI-RS ports / resources in a CC [maxNumberSimultaneousNZP-CSI-RS-PerCC] is reported per band [MIMO-ParametersPerBand] o “Simultaneous” here means: ^ For CSI reports: • Simultaneously occupying CPUs ^ For CSI-RS: • “Simultaneously active” o For periodic resource: A configured resource is active until RRC release o For semi-persistent resource: An activated resource is active until MAC CE deactivation o For aperiodic resource: A triggered resource is active until PUSCH Transmission SUMMARY

[0018] Certain challenges presently exist. For instance, because most commercially available 5G NR UEs in the market are based on Rel-15, most commercially available UEs do not support the NC-JT features introduced in the 3GPP release 16 (Rel-16) standard, for example, CSI report for NC-JT containing TRP specific PMI, jointed rank and CQI, etc. Accordingly, how to improve downlink system performance with NC-JT for those UEs is a problem.

[0019] Accordingly, in one aspect there is provided a method for performing a non- coherent joint transmission, NC-JT, for a user equipment, UE, using up to N transmission and reception points, TRPs, where N > 1. The method includes, for each one of the N TRPs, obtaining a CSI report generated by the UE for the TRP, thereby obtaining N CSI reports, one for each one of the N TRPs. The method also includes, based on the N CSI reports, selecting X of the N TRPs to participate in the NC-JT for the UE, where X ≤ N. The method also includes determining a modulation and coding scheme (MCS) for the NC-JT for the UE. The method also includes determining a precoder for each one of the X TRPs. The method further includesperforming the NC-JT for the UE using the selected X TRPs and using the determined MCS and precoders.

[0020] In another aspect there is provided an apparatus that is configured to perform the methods disclosed herein. The apparatus may include memory and processing circuitry coupled to the memory.

[0021] In another aspect there is provided a computer program comprising instructions which when executed by processing circuitry of an apparatus causes the apparatus to perform any of the methods disclosed herein. In one embodiment, there is provided a carrier containing the computer program wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

[0022] An advantage of the embodiments disclosed herein is that they allow for implementation of NC-JT for any 5G NR UE without considering the UE’s category and capabilities, thereby providing greater flexibility than the currently specified 3GPP scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

[0024] FIG. 1 illustrates a non-coherent joint transmission to a UE.

[0025] FIG. 2 shows an example of CSI-RS REs for 12 antenna ports.

[0026] FIG. 3 is a flowchart illustrating a process according to an embodiment.

[0027] FIG. 4 illustrates a UE transmitting N CSI reports.

[0028] FIG. 5 illustrates simultaneous CSI reports for N TRPs.

[0029] FIG. 6 illustrates simultaneous CSI reports for N TRPs.

[0030] FIG. 7 illustrates a TRP sweep over time for CSI-RS signal and CSI report.

[0031] FIG. 8 illustrates a TRP sweep over time for CSI-RS signal and CSI report.

[0032] FIG. 9 illustrates an NC-JT for a UE.

[0033] FIG. 10 is a block diagram of a network node according to an embodiment. DETAILED DESCRIPTION

[0034] In a legacy, single TRP transmission-based CSI feedback, the typical procedure for a downlink data transmission has the following steps.

[0035] First, a UE measures the downlink channel between the UE and the TRP and sends a CSI report to the TRP’s gNB. The CSI report usually includes a rank indicator (RI), a precoding matrix indicator (PMI) and a channel quality indicator (CQI). RI represents the number of layers for a Physical Downlink Shared Channel (PDSCH) transmission. PMI indicates a precoder in a codebook of RI layers of transmission. CQI indicates a modulation and code rate index corresponding to a quantized signal to noise ratio (SNR) observed at the UE for the reported RI and PMI. CQI can usually be mapped to SNR by a lookup table.

[0036] Next, based on the RI and the CQI in the CSI report, the gNB determines a modulation and coding scheme (MCS) for the transmission of a signal on the PDSCH. The signal is encoded, and the encoded signal is further precoded over the transmit antennas by a precoder indicated by the PMI contained in CSI report. The gNB sends to the UE downlink control information (DCI), which carries scheduling information such as time and frequency resource and MCS for the PDSCH. Using the DCI, the UE receives and decodes the signal.

[0037] As noted above, most commercially available 5G NR UEs and do not support the NC-JT features introduced in the 3GPP release 16 (Rel-16) standard. Accordingly, how to improve downlink system performance with NC-JT for those UEs is a problem.

[0038] To solve this problem, this disclosure describes implementing NC-JT in a wireless network with 3GPP release 15 (Rel-15) UEs. The approach implements downlink (DL) NC-JT in 5G NR systems without help of the tools specified in the 3GPP standard and without needing to consider a UE’s capabilities.

[0039] FIG. 3 is a flow chart illustrating a method 300, according to one embodiment, for performing an NC-JT for a UE (e.g., UE 302 shown in FIG. 3) using up to N TRPs. The method 300 includes the following steps:

[0040] Step s302: For each one of the N TRPs, obtaining a CSI report for the TRP transmitted by the UE, thereby obtaining N CSI reports, one for each one of the TRPs. That is, for each one of the N TRPs potentially participating in the NC-JT for the UE (“potentially participating TRP”), a network node obtains a CSI report transmitted by the UE. For example, inthis step, a measurement configuration is provided to the UE for configuring the UE to transmit a single TRP CSI report for each one of the N potentially participating TRPs, where N > 1.

[0041] Step s304: Based on the N CSI reports, selecting X of the N potentially participating TRPs to take part in the NC-JT for the UE, where X ≤ N.

[0042] Step s306: Determining a modulation and coding scheme (MCS) for the NC-JT for the UE. For example, the MCS may be determined using the N CSI reports or may be determined using X of the CSI reports (i.e., the CSI report from each one of the TRPs selected in step s304).

[0043] Step s308: Determining precoders for the NC-JT for the UE.

[0044] Step s310: Performing the NC-JT for the UE. That is performing a PDSCH transmission using the selected X TRPs and using the determined MCS and determined precoders.

[0045] The benefit of the method is that NC-JT can be achieved with a legacy UE supporting only single TRP transmission without any changes in the UE.

[0046] Details of each of the steps are further discussed below.

[0047] Obtain the N CSI reports

[0048] FIG. 4 illustrates a UE 402 transmitting N CSI reports. In the example shown, the number of participating TRPs is three, hence N=3. More specifically, as shown in FIG. 4, each one of the three participating TRPs transmits an RS, i.e., in the example shown, TRP 404 transmits a CSI-RS, TRP 406 transmits a CSI-RS, and TRP 408 transmits a CSI-RS. The CSI- RSs are transmitted using different time and / or frequency resources.

[0049] In the embodiment shown in FIG. 4, a network node 410 (a.k.a., central controller or schedular) configures UE 402 to transmit the N CSI reports, receives the N CSI reports, and performs process 300. In one embodiment, network node 410 is co-located with one of the N TRPs (e.g., TRP 404) and connected via a link, such as, for example, a backhaul link, to the other TRPs. In another embodiment, network node 410 is connected to each one of the N TRPs via a link.

[0050] For each CSI-RS transmitted, UE 402 performs a measurement on the CSI-RS, determines CSI based on the measurement, and transmits a CSI report indicating the determined CSI. For example, as described in the Background section, each CSI report transmitted by the UE may include an RI, a PMI, and a CQI.

[0051] Option 1: Simultaneous Multiple CSI reports

[0052] If a UE supports multiple CSI-RS resources and multiple CSI reports, one solution is to use multiple-CSI reports. With this approach, if a UE indicates in capability signaling that it supports simultaneous reporting of multiple CSI reports in a carrier frequency and the number of supported simultaneous CSI reports is larger than or equal to N, which is the number of participating TRPs, then N CSI reports and N CSI-RS resource sets are configured for the UE. In one embodiment, each CSI reporting setting contains one CSI-RS resource set which is configured with one CSI-RS resource for channel measurement. CSI parameters configured to be included in the CSI report include at least RI, PMI, and CQI. In one embodiment, the CSI-RS for each CSI report setting is configured to transmit with periodicity T over one of N TRPs, as illustrated in FIG. 5.

[0053] According to the CSI reference resource definition in 3GPP, in time domain the CSI reference resource for a CSI reporting in uplink slot ^ is defined by a single downlink slot^ − ^^^^_^^^, where for periodic and semi-persistent CSI reporting, if a single CSI-RS resource isconfigured for channel measurement, ^^^^_^^^is the smallest value greater than or equal to 4 slots, such that it corresponds to a valid downlink slot. Based on this specification, the CSIreports should be configured in an uplink slot ^ (^ ≥ 4) slots after the CSI-RSs beingtransmitted in each period. An example is shown in FIG. 5, which illustrates simultaneous CSI reports for N TRPs.

[0054] FIG. 6 is a message flow diagram illustrating option 1. As shown in FIG. 6, the UE may first provide capability information to the network node. In this example, based on this capability information, the network node determines that the UE can provide N CSI reports in a single uplink transmission the uplink control channel. Accordingly, the network node then provides a measurement configuration, such as, for example the CSI-RS Report Config, to the UE to cause the UE to simultaneously transmit the N CSI reports after performing the N CSI-RS measurements. After transmitting the measurement configuration to the UE, the network nodecauses TRPs 404, 406, and 408 to perform the CSI-RS transmissions. The UE measures these CSI-RS transmission, generates the N CSI reports, and provides the N CSI reports to the network node.

[0055] Option2: Time-domain TRP sweeping

[0056] For UEs that don’t support reporting multiple CSI reports simultaneously, a time- domain TRP sweeping approach can be used, which is illustrated in FIG. 7.

[0057] With this approach, a periodic CSI-RS resource is configured for the UE. In the CSI-RS resource, CSI-RS is configured to transmit with a periodicity of T. The CSI-RS is transmitted from one TRP in each period, i.e., the CSI-RS is sent over the first TRP in a first period, and the CSI-RS is sent over the 2ndTRP in a second period, and so on until the CSI-RS being sent over the Nth TRP. This process is then repeated.

[0058] For each one of the N CSI-RS transmissions, the UE generates and transmits one CSI report. Hence, N CSI reports are transmitted, one for each of the N TRPs. To obtain a one- to-one mapping between a CSI report and a TRP over which CSI-RS is transmitted, the following additional configurations can be setup:

[0059] 1) To get channel state for a specific TRP, averaging of the channel estimation across multiple CSI-RS transmissions needs to be disabled at the UE. This can be done in NR by turning on the higher layer parameter timeRestrictionForChannelMeasurements in CSI- ReportConfig. Thus, according to 3GPP Technical Specification (TS) 38.214 V18.0.0 (“TS 38.214”), the UE shall derive the channel measurements for computing CSI reported in uplink slot ^ based only on the most recent, no later than the CSI reference resource, occasion of NZP CSI-RS associated with the CSI resource setting.

[0060] 2) To get per TRP CSI feedback, a periodic or semi-persistent CSI report can be synchronized with the CSI-RS transmission, i.e., the periodic and semi-persistent CSI report fora TRP can be configured to be reported in an uplink slot ^ slots, ^ ≥ 4, after a CSI-RStransmission over the TRP. This is illustrated in FIG. 7.

[0061] FIG. 8 is a message flow diagram illustrating option 2. As shown in FIG. 8, the UE may first provide capability information to the network node. In this example, based on this capability information, the network node determines that the UE is not capable of providing NCSI reports in a single uplink transmission the uplink control channel. Accordingly, the network node then provides a measurement configuration to the UE to cause the UE to transmit the N CSI reports one at a time after performing each respective CSI-RS measurement. In one embodiment, the measurement configuration configures the UE with one CSI-RS resource and sets the parameter timeRestrictionForChannelMeasurements so as to disable at the UE averaging of the channel estimation across multiple CSI-RS transmissions, thereby allowing the network node to get channel state for a specific TRP because each one of the N CSI reports will be for a specific TRP. In one embodiment, the measurement configuration sets a gap between CSI Reporting and the CSI-RS transmissions so that each CSI report is associated with just one TRP.

[0062] After transmitting the measurement configuration to the UE, the network node causes each of the TRPs 404, 406, and 408 to perform a CSI-RS transmission with a gap between each CSI-RS transmission as shown in FIG. 8. In the gap, the UE generates a CSI report based on its measurement of the CSI-RS and provides the CSI report to the network node. In this way, after N CSI-RS transmission, the network node will have obtained N CSI reports, one for each TRP.

[0063] TRP selection and Joint transmission Rank Selection

[0064] According to TS 38.214, codebook-based CSI report usually includes an RI, a PMI and a CQI. A CQI can usually be mapped to an SNR by a lookup table.

[0065] A normalized SNR for TRP n is defined as: ^(^) = ^^(^) × ^(^^^(^)), where^(∙)is a function that maps CQI(n) to a linear SNR for TRP n, ^^(^)is the UE reported rank for the nthTRP, and CQI(n) is the UE reported CQI for the nthTRP.

[0066] After the N CSI-reports are received, an initial estimation of the downlinktransmission rank, L, across all the TRPs can be made as: L = min^∑^^!"# ^^(^) , %&'(), where%&'(is a constant specifying the maximum number of layers allowedPDSCHtransmission, and %&'( ≥ *.

[0067] For the NC-JT for the UE, the number of layers, l(n), allocated to TRP ^ can be determined according to the normalized SNR associated to the TRP and the total normalized SNR across all TRPs, i.e.,^(^)+(^) = min ,round 1∑^^ ( )^( ) × % 2 , ^^ ^ 3!"# ^where round(∙)is a function which rounds the nearest integer. In the case of a tie,where an element has a fractional part of 0.5 (within roundoff error) in decimal, the round function rounds away from zero to the nearest integer with larger magnitude.

[0068] If M out of the N TRPs have +(^) > 0, then the M TRPs are sorted from thehighest6(!)7(!)to the lowest6(!)7(!)and put into a new list {TRP^#, TRP^ , …, TRP^8^}, ^&∈(0,1, … , * − 1) and < = 0,1, .. , > − 1. +(^&) is the number of layers of PDSCH data allocatedto TRP ^&in the new list. X number of TRPs are selected from the new list starting from the first TRP in the list, i.e., TRP ^#, then second, and so on, until the list is exhausted or L is reached. With the constraint that N ≤ Lmax, then M is at least 1, i.e., there is at least one value of n for which l(n) > 0.

[0069] Following pseudo code shows the PDSCH data layer allocation procedure: Initialization: La = 0, m = 0 / * La is the number of allocated layers * / WHILE %? < % AND < < >IF % − %? ≥ +(^&)Allocate layers %? to (%? + +(^&) − 1) to TRP ^&%? = %? + +(^&)ELSE Allocate layers %? to (% − %? − 1) to TRP ^&+(^&) = % − %?%? = %END <= < + 1END

[0070] The rank of PDSCH for joint transmission is %. Note that if +(^&) > 0 then TRP^& in the new list is selected for joint transmission of PDSCH. The case in which > = 1corresponds to single TRP transmission.

[0071] One PDSCH DMRS port shall be allocated and associated with each PDSCH layer as specified by 3GPP. In case of multiple TRP joint transmission, i.e., B > 1, if morethan one layer is allocated to one TRP, it is preferable to allocate the DMRS ports associated to those layers in a same DMRS CDM group as same QCL properties are expected for DMRS ports in each CDM group.

[0072] Determining MCS

[0073] Assuming that the M TRPs are selected above and the TRP indices of the selected TRP are ^^& ∈ (0,1, … , * − 1), < = 0,1, … , > − 1), then with CQI and RI reported by UE foreach TRP and also the number of layers determined for each TRP, the CQI and RI for TRP ^&can be converted to mutual information (MI) as follows: >^(<) = CD^^^(^&), ^^(^&)E, whereC(∙) is a function to map CQI and RI to mutual information.

[0074] Then an effective SNR can be obtained for joint transmission over the M TRPs as: F*^ ^GHH = C (∑8^&"# >^(<) , %), where C^ (∙) is inverse function of C(∙). F*^GHH can also be

[0075] The per layer SNR for TRP < selected for PDSCH transmission can be approximated as I(<) = 6(!J)7(!J) . One heuristic is to use the lowest of I(<), I&K!, of all TRPsselected for the link of joint tran ^ ( ))8^smission, i.e., F*^GHH = I&K! = m&in I < &"# .

[0076] Other heuristics could also be used, for example,, , of TRPs selected for joint transmission could also be used for link adaptation, i,e., F*^GHH= I&^'! = 8 ∑8^&"# I(<) .is then used to determine a MCS for non-coherent joint transmission over the multiple TRPs.

[0078] Determining Joint Transmission Precoder

[0079] Let LM8^J ∈ ℂ^O×P^(&) be the PDSCH precoder indicated by PMI in the CSIreport associatedCSI transmission over TRP ^&, < = 0,1, … , > − 1, where *' is thenumber of transmit antenna ports in TRP ^&, then for joint transmission with +(^&) layers overTRP ^&, any +(^&) columns in LM8^Jcan be used as the precoder for the +(^&) layers transmitted over TRP ^&. For the first +(^&)columns of LM8^Jmay be used.

[0080] Transmitting PDSCH jointly from the X TRPs

[0081] With the determined number of layers and the precoder for each of the selected TRPs and the MCS for joint transmission, a PDSCH can be precoded at each TRP with the determined precoder and jointly transmitted over the multiple TRPs with the determined MCS. This is illustrated in FIG. 9, which shows the network node using each selected TRP to transmit the PDSCH using the layers allocated to the TRP. More specifically, in the example shown, TRP 404 transmits the PDSCH using a first subset of the layers determined to be used for the NC-JT (e.g., layers l1and l2), TRP 406 transmits the PDSCH using a second subset of the layers (e.g., layers l3, l4, and l5), and TRP 408 transmits the PDSCH using a third subset of layers (e.g., layers l6 and l7). As a more specific example, if a set of 7 layers (l1, l2, l3, l4, l5, l6, and l7) was determined to be used for the NC-JT for the UE, then TRP 404 may transmit the PDSCH using layers l4and l5, TRP 406 may transmits the PDSCH using a layers l1, l2, and l3), and TRP 408 may transmits the PDSCH using layers l6 and l7.

[0082] FIG. 10 is a block diagram of network node 410, according to some embodiments. As shown in FIG. 10, network node 410 may comprise: processing circuitry (PC) 1002, which comprises one or more processors (P) 1055 (e.g., one or more general purpose microprocessors and / or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (e.g., network node 410 may be a distributed computing apparatus comprising two or more computers or a monolithic computing apparatus consisting of a single computer); at least one network interface 1048 (e.g., a physical interface or air interface) comprising a transmitter (Tx) 1045 and a receiver (Rx) 1047 for enabling network node 410 to transmit data to and receive data from other nodes connected to network 110 (e.g., an Internet Protocol (IP) network) to which network interface 1048 is connected (physically or wirelessly) (e.g., network interface 1048 may be coupled to an antenna arrangement comprising one or more antennas for enabling network node 410 to wirelessly transmit / receive data); and a storage unit (a.k.a., “data storage system”) 1008, which may include one or more non-volatile storage devices and / or one or more volatile storagedevices. In embodiments where PC 1002 includes a programmable processor, a computer readable storage medium (CRSM) 1042 may be provided. CRSM 1042 may store a computer program (CP) 1043 comprising computer readable instructions (CRI) 1044. CRSM 1042 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 1044 of computer program 1043 is configured such that when executed by PC 1002, the CRI causes network node 410 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, network node 410 may be configured to perform steps described herein without the need for code. That is, for example, PC 1002 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and / or software.

[0083] Conclusion

[0084] As described above, this disclosure proposes a method and a system to implement NC-JT in a wireless network with 3GPP Rel-15 UEs, i.e., UE transparent NC-JT. The method includes obtaining per TRP CSI report, selecting TRP and rank, and layer allocation for each selected TRP, estimating SNR and determining an MCS based on the estimated SNR, and precoding of PDSCH data for PDSCH joint transmission over the selected TRPs.

[0085] While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0086] As used herein transmitting a message “to” or “toward” an intended recipient encompasses transmitting the message directly to the intended recipient or transmitting the message indirectly to the intended recipient (i.e., one or more other nodes are used to relay the message from the source node to the intended recipient). Likewise, as used herein receiving a message “from” a sender encompasses receiving the message directly from the sender orindirectly from the sender (i.e., one or more nodes are used to relay the message from the sender to the receiving node). Further, as used herein “a” means “at least one” or “one or more.”

[0087] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.

Claims

CLAIMS 1. A method (300) for performing a non-coherent joint transmission, NC-JT, for a user equipment, UE, (302) using up to N transmission and reception points, TRPs, (404, 406, 408) where N > 1, the method comprising: for each one of the N TRPs, obtaining (s302) a CSI report generated by the UE for the TRP, thereby obtaining N CSI reports, one for each one of the N TRPs; based on the N CSI reports, selecting (s304) X of the N TRPs to participate in the NC-JT for the UE, where X ≤ N; determining (s306) a modulation and coding scheme, MCS, for the NC-JT for the UE; determining (s308) a precoder for each one of the X TRPs; and performing (s310) the NC-JT for the UE using the selected X TRPs and using the determined MCS and precoders.

2. The method of claim 1, wherein the method further comprises: prior to obtaining the N CSI reports, providing to the UE a measurement configuration for configuring the UE to transmit a single CSI report for each one of the N TRPs.

3. The method of claim 1 or 2, wherein selecting X of the N TRPs comprises: for each one of the N TRPs, allocating a transmission rank to the TRP, wherein the transmission rank indicates a number of layers of PDSCH data allocated to the TRP; selecting a first TRP within the set of N TRPs, wherein the first TRP has the highest allocated transmission rank; and selecting a second TRP within the set of N TRPs, wherein the second TRP has the highest allocated transmission rank or a next highest allocated transmission rank.

4. The method of claim 3, wherein the method further comprises: based on the N CSI reports, determining a set of L layers, l1, l2, ..., lL, to use for the NC- JT for the UE; allocating to the first TRP a first subset of the set of layers, the number of layers included in the first subset being equal to the transmission rank allocated to the first TRP; andallocating to the second TRP a second subset of the set of layers, the number of layers included in the second subset being equal to the transmission rank allocated to the second TRP, wherein the first subset and the second subset are disjoint.

5. The method of claim 3 or 4, wherein selecting X of the N TRPs further comprises: determining whether l(1) + l(2) is less than L; and as a result of determining that l(1) + l(2) is less than L, then selecting a third TRP within the set of N TRPs to participate in the transmission, wherein l(1) is the transmission rank allocated to the first TRP, and l(2) is the transmission rank allocated to the second TRP.

6. The method of claim 5, wherein selecting X of the N TRPs further comprises: determining whether l(1) + l(2) + l(3) is less than L; and as a result of determining that l(1) + l(2) + l(3) is less than L, then selecting a fourth TRP within the set of N TRPs to participate in the transmission, wherein l(3) is the transmission rank allocated to the third TRP.

7. The method of any one of claims 3-6, wherein allocating a transmission rank to the first TRP comprises: comparing RI(1) to RImax(1); and allocating to the first TRP a transmission rank equal to RImax(1) if RI(1) is greater than RImax(1), otherwise allocating to the first TRP a transmission rank equal to RI(1), wherein the CSI report for the first TRP includes an RI, RI(1) is the rank indicator included in the CSI report for the first TRP, and RImax(1) is a maximum RI for the first TRP.

8. The method of claim 7, wherein RI 6( )max(1) is equal to: round Q × % X, where^(1)is a normalized signal-to-noise ratio, SNR, for the first^(^)is a normalized SNR for the nthTP, and L is a determined transmission rank for the NC-JT for the UE.

9. The method of claim 8, wherein ^(^) = ^^(^) × ^(^^^(^)),^(∙)is a function that maps CQI(n) to a linear SNR for TRP n, ^^(^)is the UE reported rank for the nthTRP, and CQI(n) is the UE reported CQI for the nthTRP.

10. The method of claim 8 or 9, wherein %= min^∑^^!"# ^^(^) , %&'(), andallowed for the NC-JT for the UE.

11. A network node (410), the network node comprising: memory (1042); and processing circuitry (1002), wherein the memory stores a computer program (1043) comprising instructions (1044) which when executed by the processing circuitry (1002) causes the network node to perform a method for performing a non-coherent joint transmission, NC-JT, for a user equipment, UE, (302) using up to N transmission and reception points, TRPs, where N > 1, the method comprising: for each one of the N TRPs, obtaining a CSI report generated by the UE for the TRP, thereby obtaining N CSI reports, one for each one of the N TRPs; based on the N CSI reports, selecting X of the N TRPs to participate in the NC-JT for the UE, where X ≤ N; determining a modulation and coding scheme, MCS, for the NC-JT for the UE; determining a precoder for each one of the X TRPs; performing the NC-JT for the UE using the selected X TRPs and using the determined MCS and precoders.

12. The network node of claim 11, wherein the method further comprises: prior to obtaining the N CSI reports, providing to the UE a measurement configuration for configuring the UE to transmit a single CSI report for each one of the N TRPs.

13. The network node of claim 11 or 12, wherein selecting X of the N TRPs comprises: for each one of the N TRPs, allocating a transmission rank to the TRP, wherein the transmission rank indicates a number of layers of PDSCH data allocated to the TRP; selecting a first TRP within the set of N TRPs, wherein the first TRP has the highest allocated transmission rank; and selecting a second TRP within the set of N TRPs, wherein the second TRP has the highest allocated transmission rank or a next highest allocated transmission rank.

14. The network node of claim 13, wherein the method further comprises: based on the N CSI reports, determining a set of L layers, l1, l2, ..., lL, to use for the NC- JT for the UE; allocating to the first TRP a first subset of the set of layers, the number of layers included in the first subset being equal to the transmission rank allocated to the first TRP; and allocating to the second TRP a second subset of the set of layers, the number of layers included in the second subset being equal to the transmission rank allocated to the second TRP, wherein the first subset and the second subset are disjoint.

15. The network node of claim 13 or 14, wherein selecting X of the N TRPs further comprises: determining whether l(1) + l(2) is less than L; and as a result of determining that l(1) + l(2) is less than L, then selecting a third TRP within the set of N TRPs to participate in the transmission, wherein l(1) is the transmission rank allocated to the first TRP, and l(2) is the transmission rank allocated to the second TRP.

16. The network node of claim 15, wherein selecting X of the N TRPs further comprises: determining whether l(1) + l(2) + l(3) is less than L; and as a result of determining that l(1) + l(2) + l(3) is less than L, then selecting a fourth TRP within the set of N TRPs to participate in the transmission, wherein l(3) is the transmission rank allocated to the third TRP.

17. The network node of any one of claims 3-6, wherein allocating a transmission rank to the first TRP comprises: comparing RI(1) to RImax(1); and allocating to the first TRP a transmission rank equal to RImax(1) if RI(1) is greater than RImax(1), otherwise allocating to the first TRP a transmission rank equal to RI(1), wherein the CSI report for the first TRP includes an RI, RI(1) is the rank indicator included in the CSI report for the first TRP, and RImax(1) is a maximum RI for the first TRP.

18. The network node of claim 17, wherein RImax(1) is equal to: round Q 6( )∑RSTUVW 6(!) × % X,where^(1)is a normalized signal-to-noise ratio, SNR, for the first TP, ^(^)is a normalized SNR for the nthTP, and L is a determined transmission rank for the NC-JT for the UE.

19. The network node of claim 18, wherein ^(^) = ^^(^) × ^(^^^(^)),^(∙)is a function that maps CQI(n) to a linear SNR for TRP n, ^^(^)is the UE reported rank for the nthTRP, and CQI(n) is the UE reported CQI for the nthTRP.

20. The network node of claim 18 or 19, wherein %= min^∑^^!"# ^^(^) , %&'(), andallowed for the NC-JT for the UE.

21. A computer program (1043) comprising instructions (1044) which when executed by processing circuitry (1002) of a network node causes the network node to perform the method of any one of claims 1-10.

22. A carrier containing the computer program of claim 21, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium (1042).

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