Channel state information reference signal resource mapping

Apparatuses and methods are disclosed for Channel State Information Reference Signal (CSI-RS) resource mapping. According to one embodiment, a method in a network node includes allocating at least one resource for CSI Interference Measurement (CSI-IM) within a predetermined IM region of a Resource Block (RB) of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood of overlap with at least one resource allocated for CSI-IM in a neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal (NZP CSI-RS) of the neighboring cell.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Submission Under 35 U.S.C. § 371 for U.S. National Stage Patent Application of International Application Number: PCT/IB2018/057127, filed Sep. 17, 2018 entitled “CHANNEL STATE INFORMATION REFERENCE SIGNAL RESOURCE MAPPING,” the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

Wireless communication and in particular, Channel State Information (CSI) reference signal resource mapping.

BACKGROUND

The 3rdGeneration Partnership Project (3GPP) New Radio (NR) standard is currently under discussion and development. As with Long Term Evolution (LTE), Channel State Information (CSI) area will be used. CSI may include the following aspects:Define signals that are used for the wireless device (WD), e.g., user equipment (UE) to measure and estimate channel and interference, and to perform time/frequency synchronization;Define the resource mapping for the defined signals discussed above;Define the channel characteristics to be measured by the WD; andDefine how channel state information is reported to the access network node (e.g., gNB)

NR specifications introduce a new framework for the WD to measure and report CSI. At least the following WD-specific resources have been defined in the NR CSI framework:Non-Zero-Power CSI Reference Signal (NZP CSI-RS) resources: These resources may be used for channel and interference measurement. When used for interference measurement, these resources may be used to measure intra-cell interference, or interference in Multi-User Multiple Inputs Multiple Outputs (MU-MIMO). A special type of NZP CSI-RS is the CSI-RS for tracking, which can be used for fine time and frequency synchronization. In this disclosure, this signal is referred to as “Tracking RS” or “TRS”. These NZP CSI-RS resources can be periodic or aperiodic (the TRS can only be periodic). For a periodic resource, a period and a slot offset may be specified. The number of resource elements (REs) in a CSI-RS resource can be determined by the number and density of CSI-RS ports, and the resource(s) can be mapped to a specific location within a resource block (RB);Zero-Power CSI-RS (ZP CSI-RS) resources: These resources may be used for rate matching for the Physical Downlink Shared Channel (PDSCH); andCSI Interference Measurement (CSI-IM) resources: These are normally used to measure inter-cell interference. Each CSI-IM resource may have 4 Resource Elements (REs), and can have a pattern of 4×1 (i.e., 4 consecutive REs in an Orthogonal Frequency Division Multiplexing (OFDM) symbol), or a pattern of 2×2 (i.e., 2 consecutive OFDM symbols, with 2 REs on each symbol).

However, existing specifications and the resources defined by these specifications do not establish processes and arrangements for CSI-RS resource mapping to lessen or minimize the impact on channel and interference measurements due to inter-cell interference.

SUMMARY

Some embodiments of this disclosure advantageously provide methods and apparatuses for CSI-RS resource mapping that may lessen or minimize the impact on channel and interference measurements due to inter-cell interference as compared with known implementations.

According to one aspect, a network node for serving a cell in a wireless network with at least one neighboring cell is provided. The network node includes processing circuitry configured to cause the network node to allocate at least one resource for Channel State Information Interference Measurement, CSI-IM, within a predetermined IM region of a Resource Block, RB, of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood that the allocated at least one resource overlaps with at least one resource allocated for CSI-IM in a neighboring cell as compared to allocating a common set of resources for CSI-IM in each neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal, NZP CSI-RS, of the neighboring cell.

In some embodiments of this aspect, the processing circuitry is further configured to identify the at least one resource for the CSI-IM within the predetermined IM region of the RB of the cell based at least in part on an identifier of the cell. In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to select at least one resource for Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, in a predetermined Reference Signal, RS, region of the RB of the cell, the predetermined RS region of the RB not overlapping with the predetermined IM region of the RB; and transmit the NZP CSI-RS on the selected at least one resource. In some embodiments of this aspect, the predetermined IM region of the RB is a dedicated region for at least one CSI-IM resource, the dedicated region not comprising any NZP CSI-RS resources. In some embodiments of this aspect, the predetermined RS region is a region of the RB configured for at least one CSI-RS resource, the predetermined RS region not comprising any CSI-IM resources.

In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to determine a slot offset for the CSI-IM based on a cell identifier, ID, of the cell being served by the network node. In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to determine a period for the CSI-IM, the period for the CSI-IM being common to a group of cells, the group of cells including at least the cell and the neighboring cell. In some embodiments of this aspect, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to the determined period for the CSI-IM and the determined slot offset. In some embodiments of this aspect, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to a random selection algorithm. In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to allocate at least one resource for Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, to at least partially overlap with at least one NZP CSI-RS resource of the neighboring cell. In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to determine a period and a slot offset for the at least one NZP CSI-RS that is the same as a period and a slot offset for the at least one NPZ CSI-RS associated with the neighboring cell.

In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to transmit at least one Tracking Reference Signal, TRS, to at least partially overlap with at least one TRS of the neighboring cell. In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to determine a period and a slot offset for at least one Tracking Reference Signal, TRS, that is the same as a period and a slot offset for at least one TRS associated with the neighboring cell; and transmit the at least one TRS according to the determined period and the determined slot offset. In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to transmit at least one Tracking Reference Signal, TRS, in a fixed time domain location, the fixed time domain location being the same as a fixed time domain location of the neighboring cell. In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to configure Tracking Reference Signal, TRS, resources in the RB of the cell by, for each TRS symbol in the RB, dividing a plurality of subcarriers into at least four sets of subcarriers, each of the at least four sets of subcarriers corresponding to a TRS power level that is different from a TRS power level of the other of the at least four sets of subcarriers. In some embodiments of this aspect, the at least four sets of subcarriers comprise a first set of subcarriers that is assigned for transmitting TRS at a regular TRS power level; a second set of subcarriers that is assigned for transmitting TRS at a power level that is 3 decibels, dB, higher than the regular TRS power level; a third set of subcarriers that is assigned for transmitting TRS at a power level that is 4.8 dB higher than the regular TRS power level; and a fourth set of subcarriers that is assigned for transmitting TRS at a power level that is 6 dB higher than the regular TRS power level. In some embodiments of this aspect, TRS resources associated with the neighboring cell are also configured with the at least four sets of subcarriers for aligning Tracking Reference Signals, TRSs, of the same power level on the same set of the at least four sets of subcarriers. In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to transmit at least one TRS on one of the at least four sets of subcarriers; and if the at least one TRS is transmitted on one of the second set, the third set and the fourth set of subcarriers, transmit a Zero-Power, ZP, Channel State Information Reference Signal, CSI-RS, on at least the first set of subcarriers.

According to another aspect, a method in a network node for serving a cell in a wireless network with at least one neighboring cell is provided. The method including allocating at least one resource for Channel State Information Interference Measurement, CSI-IM, within a predetermined IM region of a Resource Block, RB, of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood that the allocated at least one resource overlaps with at least one resource allocated for CSI-IM in a neighboring cell as compared to allocating a common set of resources for CSI-IM in each neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal, NZP CSI-RS, of the neighboring cell.

In some embodiments of this aspect, the method further includes identifying the at least one resource for the CSI-IM within the predetermined IM region of the TTI of the cell based at least in part on an identifier of the cell. In some embodiments of this aspect, the process further includes selecting at least one resource for Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, in a predetermined Reference Signal, RS, region of the TTI of the cell, the predetermined RS region of the RB not overlapping with the predetermined IM region of the TTI; and transmitting the NZP CSI-RS on the selected at least one resource. In some embodiments of this aspect, the predetermined IM region of the RB of the cell is a dedicated region for at least one CSI-IM resource, the dedicated region not comprising any NZP CSI-RS resources. In some embodiments of this aspect, the predetermined RS region is a region of the RB of the cell configured for at least one CSI-RS resource, the predetermined RS region not comprising any CSI-IM resources.

In some embodiments of this aspect, the process further includes determining a slot offset for the CSI-IM based on a cell identifier, ID, of the cell being served by the network node. In some embodiments of this aspect, the method further includes determining a period for the CSI-IM, the period for the CSI-IM being common to a group of cells, the group of cells including at least the cell and the neighboring cell. In some embodiments of this aspect, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to the determined period for the CSI-IM and the determined slot offset. In some embodiments of this aspect, wherein the CSI-IM is mapped to the at least one resource of the predetermined IM region according to a random selection algorithm. In some embodiments of this aspect, the method further includes allocating at least one resource for Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, to at least partially overlap with at least one NZP CSI-RS resource of the neighboring cell. In some embodiments of this aspect, the process further includes determining a period and a slot offset for the at least one NZP CSI-RS that is the same as a period and a slot offset for the at least one NPZ CSI-RS associated with the neighboring cell.

In some embodiments of this aspect, the method further includes transmitting at least one Tracking Reference Signal, TRS, to at least partially overlap with at least one TRS of the neighboring cell. In some embodiments of this aspect, the method further includes determining a period and a slot offset for at least one Tracking Reference Signal, TRS, that is the same as a period and a slot offset for at least one TRS associated with the neighboring cell; and transmitting the at least one TRS according to the determined period and the determined slot offset. In some embodiments of this aspect, the method further includes transmitting at least one Tracking Reference Signal, TRS, in a fixed time domain location, the fixed time domain location being the same as a fixed time domain location of the neighboring cell. In some embodiments of this aspect, the method further includes configuring Tracking Reference Signal, TRS, resources in the RB of the cell by, for each TRS symbol in the RB, dividing a plurality of subcarriers into at least four sets of subcarriers, each of the at least four sets of subcarriers corresponding to a TRS power level that is different from a TRS power level of the other of the at least four sets of subcarriers. In some embodiments of this aspect, the at least four sets of subcarriers comprise: a first set of subcarriers that is assigned for transmitting TRS at a regular TRS power level, a second set of subcarriers that is assigned for transmitting TRS at a power level that is 3 decibels, dB, higher than the regular TRS power level, a third set of subcarriers that is assigned for transmitting TRS at a power level that is 4.8 dB higher than the regular TRS power level, and a fourth set of subcarriers that is assigned for transmitting TRS at a power level that is 6 dB higher than the regular TRS power level. In some embodiments of this aspect, TRS resources associated with the neighboring cell are also configured with the at least four sets of subcarriers for aligning Tracking Reference Signals, TRSs, of the same power level on the same set of the at least four sets of subcarriers. In some embodiments of this aspect, the method further includes transmitting at least one TRS on one of the at least four sets of subcarriers; and if the at least one TRS is transmitted on one of the second set, the third set and the fourth set of subcarriers, transmitting a Zero-Power, ZP, Channel State Information Reference Signal, CSI-RS, on at least the first set of subcarriers.

According to yet another aspect of this disclosure, a wireless device, WD, for communicating with a network node serving a cell in a wireless network with at least one neighboring cell is provided. The WD includes processing circuitry configured to cause the WD to receive a signal on at least one resource for Channel State Information Interference Measurement, CSI-IM, the at least one resource for CSI-IM being allocated within a predetermined IM region of a Resource Block, RB, of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood that the allocated at least one resource overlaps with at least one resource allocated for CSI-IM in a neighboring cell as compared to allocating a common set of resources for CSI-IM in each neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal, NZP CSI-RS, of the neighboring cell; and transmit a Channel State Information, CSI, report, the CSI report based at least in part on inter-cell interference measured on the at least one resource for the CSI-IM of the cell.

In some embodiments of this aspect, the processing circuitry is further configured to receive at least one Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, in a predetermined Reference Signal, RS, region of the RB of the cell, the predetermined RS region of the RB not overlapping with the predetermined IM region of the RB. In some embodiments of this aspect, the predetermined IM region of the RB of the cell is a dedicated region for at least one CSI-IM resource, the dedicated region not comprising any NZP CSI-RS resources. In some embodiments of this aspect, the predetermined RS region is a region of the RB of the cell configured for at least one CSI-RS resource, the predetermined RS region not comprising any CSI-IM resources. In some embodiments of this aspect, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to at least a slot offset, the slot offset based at least in part on a cell identifier, ID. In some embodiments of this aspect, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to a random selection algorithm. In some embodiments of this aspect, the processing circuitry is further configured to cause the WD to receive at least one Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, that at least partially overlaps with at least one NZP CSI-RS of at least a neighboring cell.

In some embodiments of this aspect, a period and a slot offset for the received at least one NZP CSI-RS is the same as a period and a slot offset for the at least one NPZ CSI-RS associated with the neighboring cell. In some embodiments of this aspect, the processing circuitry is further configured to cause the WD to receive at least one Tracking Reference Signal, TRS, that at least partially overlaps with at least one TRS of a neighboring cell. In some embodiments of this aspect, a period and a slot offset for the at least one TRS is the same as a period and a slot offset for the at least one TRS of the neighboring cell. In some embodiments of this aspect, the received at least one TRS is in a fixed time domain location, the fixed time domain location being the same as a fixed time domain location of the neighboring cell. In some embodiments of this aspect, the processing circuitry is further configured to cause the WD to receive at least one Tracking Reference Signal, TRS, on one of at least four sets of subcarriers in the RB, the at least four sets of subcarriers comprising a first set of subcarriers that is assigned for transmitting TRS at a regular TRS power level, a second set of subcarriers that is assigned for transmitting TRS at a power level that is 3 decibels, dB, higher than the regular TRS power level, a third set of subcarriers that is assigned for transmitting TRS at a power level that is 4.8 dB higher than the regular TRS power level, and a fourth set of subcarriers that is assigned for transmitting TRS at a power level that is 6 dB higher than the regular TRS power level. In some embodiments of this aspect, the processing circuitry is further configured to cause the WD to receive the at least one TRS on one of the at least four sets of subcarriers; and if the at least one TRS is transmitted on one of the second set, the third set and the fourth set of subcarriers, receive a Zero-Power, ZP, Channel State Information Reference Signal, CSI-RS, on at least the first set of subcarriers.

According to another aspect of this disclosure, a method in a wireless device, WD, for communicating with a network node serving a cell in a wireless network with at least one neighboring cell is provided. The method includes receiving a signal on at least one resource for Channel State Information Interference Measurement, CSI-IM, the at least one resource for CSI-IM being allocated within a predetermined IM region of a Resource Block, RB, of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood that the allocated at least one resource overlaps with at least one resource allocated for CSI-IM in a neighboring cell as compared to allocating a common set of resources for CSI-IM in each neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal, NZP CSI-RS, of the neighboring cell; and transmitting a Channel State Information, CSI, report, the CSI report based at least in part on inter-cell interference measured on the at least one resource for the CSI-IM of the cell.

In some embodiments of this aspect, the method further includes receiving at least one Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, in a predetermined Reference Signal, RS, region of the RB of the cell, the predetermined RS region of the RB not overlapping with the predetermined IM region of the RB. In some embodiments of this aspect, the predetermined IM region of the RB of the cell is a dedicated region for at least one CSI-IM resource, the dedicated region not comprising any NZP CSI-RS resources. In some embodiments of this aspect, the predetermined RS region is a region of the RB of the cell configured for at least one CSI-RS resource, the predetermined RS region not comprising any CSI-IM resources. In some embodiments of this aspect, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to at least a slot offset, the slot offset based at least in part on a cell identifier, ID. In some embodiments of this aspect, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to a random selection algorithm. In some embodiments of this aspect, the method further includes receiving at least one Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, that at least partially overlaps with at least one NZP CSI-RS of at least a neighboring cell.

In some embodiments of this aspect, a period and a slot offset for the received at least one NZP CSI-RS is the same as a period and a slot offset for the at least one NPZ CSI-RS associated with the neighboring cell. In some embodiments of this aspect, the method further includes receiving at least one Tracking Reference Signal, TRS, that at least partially overlaps with at least one TRS of a neighboring cell. In some embodiments of this aspect, a period and a slot offset for the at least one TRS is the same as a period and a slot offset for the at least one TRS of the neighboring cell. In some embodiments of this aspect, the received TRS is in a fixed time domain location, the fixed time domain location being the same as a fixed time domain location of the neighboring cell. In some embodiments of this aspect, the method further includes receiving at least one Tracking Reference Signal, TRS, on one of at least four sets of subcarriers in the RB, the at least four sets of subcarriers including a first set of subcarriers that is assigned for transmitting TRS at a regular TRS power level, a second set of subcarriers that is assigned for transmitting TRS at a power level that is 3 decibels, dB, higher than the regular TRS power level, a third set of subcarriers that is assigned for transmitting TRS at a power level that is 4.8 dB higher than the regular TRS power level, and a fourth set of subcarriers that is assigned for transmitting TRS at a power level that is 6 dB higher than the regular TRS power level. In some embodiments of this aspect, the method further includes receiving the at least one TRS on one of the at least four sets of subcarriers; and if the at least one TRS is transmitted on one of the second set, the third set and the fourth set of subcarriers, receiving a Zero-Power, ZP, Channel State Information Reference Signal, CSI-RS, on at least the first set of subcarriers.

According to yet another aspect of this disclosure, a computer program, program product or computer readable storage medium is provided that includes instructions which when executed on at least one processor of a network node perform any one of the methods of the network node.

According to another aspect of this disclosure, a computer program, program product or computer readable storage medium is provided that includes instructions which when executed on at least one processor of a wireless device perform any one of the methods of the wireless device.

DETAILED DESCRIPTION

Resource mapping can affect the performance of a network. With improper resource mapping, user and cell performance degradation may occur. For example, when a WD's CSI-IM resource collides with CSI-IM resources of a neighbor cell, the inter-cell interference may be underestimated. In this case, the Channel Quality Indicator (CQI) values reported by the WD may be overly optimistic. This can cause an aggressive link adaptation and a high error rate, and can eventually reduce the user's throughput.

Accordingly, some embodiments of this disclosure provide for CSI-RS resource mapping that may advantageously minimize/reduce the impact on channel and interference measurements due to e.g., inter-cell interference.

Some embodiments of this disclosure allow WDs to perform channel and interference measurements more accurately, as compared to existing resource mapping techniques, which can be a foundation for improving user throughput.

Some embodiments of this disclosure are based on an ideal condition or neighbor cell resource allocation in which there is:no overlap between one cell's CSI-IM with the neighbor cell's NZP CSI-RS; and/orno overlap between one cell's CSI-IM with the neighbor cell's CSI-IM.

With some existing techniques, a slot offset may be assigned for one cell's CSI-IM, and a network node may attempt to make the slot offset different from those used for CSI-IM by neighbor cells. Furthermore, a different slot offset may be used for NZP CSI-RS for the cell, and this offset may be different from the offsets used for NZP CSI-RS of the neighbor cells. Some problems with this technique may include:difficulty in managing multiple sets of slot offsets; andvery difficult to eliminate any type of overlap (between CSI-IM and NZP CSI-RS, or between CSI-IM and CSI-IM).

Accordingly, the principles of this disclosure are provided to create a simpler and/or more efficient solution for reference signal resource allocation, as compared to existing techniques. Thus, some advantages of this disclosure include one or more of the following:simplicity: a network node may only be required to try (e.g., reduce a likelihood of overlap) to make the CSI-IM offsets different between neighbor cells;overlap between one cell's CSI-IM with the neighbor cell's NZP CSI-RS may be completely eliminated;with only one set of offsets, the probability of offset colliding between neighbor cells is smaller/reduced as compared to when each cell has more than one offset to manage; andin addition to the slot offset, there are multiple resources in the IM region, which further reduces the probability of CSI-IM resource overlapping in neighboring cells.

In some embodiments, the term “resource” is used in a general way. It may indicate any radio resource, such as, a Resource Element (RE), or, in some embodiments, a combination of subcarriers, time slots, symbols, codes and/or spatial dimensions. In some embodiments, the “resource” may indicate a frequency and/or time resource associated with radio communications. Non-limiting examples of time resources include symbol, time slot, subframe, radio frame, TTI, interleaving time, etc.

A RE may represent a smallest time-frequency resource, e.g. representing the time and frequency range covered by one symbol or a number of bits represented in a common modulation. A RE may e.g. cover a symbol time length and a subcarrier, in particular in 3GPP, NR and/or LTE standards.

A cell may be generally a communication cell, e.g., of a cellular or mobile communication network, provided by a node, such as a network node. A serving cell may be a cell on or via which a network node (the node providing or associated to the cell, e.g., base station or eNodeB) transmits and/or may transmit data (which may be data other than broadcast data) to a WD, in particular control, configuration, allocation and/or user or payload data, and/or via or on which a WD transmits and/or may transmit data to the node. A serving cell may be a cell for or on which the WD is configured and/or to which it is synchronized and/or has performed an access procedure, e.g., a random access procedure, and/or in relation to which it is in a RRC_connected or RRC_idle state, e.g., in case the network node and/or WD and/or network follow the a standard such as LTE and/or NR. One or more carriers (e.g., uplink and/or downlink carrier/s and/or a carrier for both uplink and downlink) may be associated to a cell.

In some embodiments, a neighboring cell is a cell that may or can be expected to cause inter-cell interference with another cell and which inter-cell interference may affect network performance.

In some embodiments, the allocation of resources for one or more WDs in a cell may be performed by the network node. In some embodiments, the resources that are allocated by the network node are for the one or more WDs to perform measurements on, which measurements can be used for channel state information. In some embodiments, a set of resources, such as, a Resource Block (RB), a Transmission Time Interval (TTI) or a subframe, may be divided into one or more regions dedicated/predetermined for specific reference signals (e.g., CSI-RS, CSI-IM, etc.) and/or channels. In some embodiments, the allocation of reference signal resources (e.g., CSI-RS, CSI-IM, etc.) for a cell may include the network node16selecting or determining which subset of resources in a predetermined/dedicated region should be used by the WD to perform measurements on. In some embodiments, the network node may select or determine such resources according to the principles in this disclosure to e.g., reduce the impact on channel and interference measurement due to inter-cell interference caused by neighboring cells. It is also noted that any two or more embodiments described in this disclosure may be combined in any way with each other. In the present disclosure, the terms Resource Block (RB), Transmission Time Interval (TTI) and subframe may be used interchangeably.

A network node16is configured to include a resource allocation unit32which is configured to cause the network node16to allocate at least one resource for Channel State Information Interference Measurement, CSI-IM, within a predetermined IM region of a Resource Block, RB (or, equivalently, a Transmit Time Interval, TTI), of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood that the allocated at least one resource overlaps with at least one resource allocated for CSI-IM in a neighboring cell as compared to allocating a common set of resources for CSI-IM in each neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal, NZP CSI-RS, of the neighboring cell.

A wireless device22is configured to include a measurement unit34which is configured to cause the WD22to receive a signal on at least one resource for Channel State Information Interference Measurement, CSI-IM, the at least one resource for CSI-IM being allocated within a predetermined IM region of Resource Block, RB, (or, equivalently, a Transmit Time Interval, TTI), of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood that the allocated at least one resource overlaps with at least one resource allocated for CSI-IM in a neighboring cell as compared to allocating a common set of resources for CSI-IM in each neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal, NZP CSI-RS, of the neighboring cell; and to transmit a Channel State Information, CSI, report, the CSI report based at least in part on inter-cell interference measured on the at least one resource for the CSI-IM of the cell.

Thus, the network node16further has software74stored internally in, for example, memory72, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node16via an external connection. The software74may be executable by the processing circuitry68. The processing circuitry68may 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 node16. Processor70corresponds to one or more processors70for performing network node16functions described herein. The memory72is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software74may include instructions that, when executed by the processor70and/or processing circuitry68, causes the processor70and/or processing circuitry68to perform the processes described herein with respect to network node16. For example, processing circuitry68of the network node16may include resource allocation unit32configured to cause the network node to16to allocate at least one resource for Channel State Information Interference Measurement, CSI-IM, within a predetermined IM region of a Resource Block, RB (or, equivalently, a Transmit Time Interval, TTI), of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood that the allocated at least one resource overlaps with at least one resource allocated for CSI-IM in a neighboring cell as compared to allocating a common set of resources for CSI-IM in each neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal, NZP CSI-RS, of the neighboring cell.

In some embodiments, the processing circuitry68is further configured to identify the at least one resource for the CSI-IM within the predetermined IM region of the RB of the cell based at least in part on an identifier of the cell. In some embodiments, the processing circuitry68is further configured to cause the network node16to select at least one resource for Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, in a predetermined Reference Signal, RS, region of the RB of the cell, the predetermined RS region of the RB not overlapping with the predetermined IM region of the RB; and transmit the NZP CSI-RS on the selected at least one resource. In some embodiments, the predetermined IM region of the RB is a dedicated region for at least one CSI-IM resource, the dedicated region not comprising any NZP CSI-RS resources. In some embodiments, the predetermined RS region is a region of the RB configured for at least one CSI-RS resource, the predetermined RS region not comprising any CSI-IM resources. In some embodiments, the processing circuitry68is further configured to cause the network node16to determine a slot offset for the CSI-IM based on a cell identifier, ID, of the cell being served by the network node16.

In some embodiments, the processing circuitry68is further configured to cause the network node16to determine a period for the CSI-IM, the period for the CSI-IM being common to a group of cells, the group of cells including at least the cell and the neighboring cell. In some embodiments, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to the determined period for the CSI-IM and the determined slot offset. In some embodiments, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to a random selection algorithm. In some embodiments, the processing circuitry68is further configured to cause the network node16to allocate at least one resource for Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, to at least partially overlap with at least one NZP CSI-RS resource of the neighboring cell. In some embodiments, the processing circuitry68is further configured to cause the network node16to determine a period and a slot offset for the at least one NZP CSI-RS that is the same as a period and a slot offset for the at least one NPZ CSI-RS associated with the neighboring cell. In some embodiments, the processing circuitry68is further configured to cause the network node16to transmit at least one Tracking Reference Signal, TRS, to at least partially overlap with at least one TRS of the neighboring cell. In some embodiments, the processing circuitry68is further configured to cause the network node16to determine a period and a slot offset for at least one Tracking Reference Signal, TRS, that is the same as a period and a slot offset for at least one TRS associated with the neighboring cell; and transmit the at least one TRS according to the determined period and the determined slot offset. In some embodiments, the processing circuitry68is further configured to cause the network node16to transmit at least one Tracking Reference Signal, TRS, in a fixed time domain location, the fixed time domain location being the same as a fixed time domain location of the neighboring cell.

In some embodiments, the processing circuitry68is further configured to cause the network node16to configure Tracking Reference Signal, TRS, resources in the RB of the cell by, for each TRS symbol in the RB, dividing a plurality of subcarriers into at least four sets of subcarriers, each of the at least four sets of subcarriers corresponding to a TRS power level that is different from a TRS power level of the other of the at least four sets of subcarriers. In some embodiments, the at least four sets of subcarriers include a first set of subcarriers that is assigned for transmitting TRS at a regular TRS power level; a second set of subcarriers that is assigned for transmitting TRS at a power level that is 3 decibels, dB, higher than the regular TRS power level; a third set of subcarriers that is assigned for transmitting TRS at a power level that is 4.8 dB higher than the regular TRS power level; and a fourth set of subcarriers that is assigned for transmitting TRS at a power level that is 6 dB higher than the regular TRS power level. In some embodiments, TRS resources associated with the neighboring cell are also configured with the at least four sets of subcarriers for aligning Tracking Reference Signals, TRSs, of the same power level on the same set of the at least four sets of subcarriers. In some embodiments, the processing circuitry68is further configured to cause the network node16to transmit at least one TRS on one of the at least four sets of subcarriers; and if the at least one TRS is transmitted on one of the second set, the third set and the fourth set of subcarriers, transmit a Zero-Power, ZP, Channel State Information Reference Signal, CSI-RS, on at least the first set of subcarriers.

The communication system10further includes the WD22already referred to. The WD22may have hardware80that may include a radio interface82configured to set up and maintain a wireless connection64with a network node16serving a coverage area18in which the WD22is currently located. The radio interface82may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers.

The processing circuitry84may 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 the WD22. The processor86corresponds to one or more processors86for performing WD22functions described herein. The WD22includes memory88that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software90and/or the client application92may include instructions that, when executed by the processor86and/or processing circuitry84, causes the processor86and/or processing circuitry84to perform the processes described herein with respect to WD22. For example, the processing circuitry84of the wireless device22may include a measurement unit34configured to cause the WD22to receive a signal on at least one resource for Channel State Information Interference Measurement, CSI-IM, the at least one resource for CSI-IM being allocated within a predetermined IM region of a Resource Block, RB (or, equivalently, a Transmit Time Interval, TTI), of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood that the allocated at least one resource overlaps with at least one resource allocated for CSI-IM in a neighboring cell as compared to allocating a common set of resources for CSI-IM in each neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal, NZP CSI-RS, of the neighboring cell; and transmit a Channel State Information, CSI, report, the CSI report based at least in part on inter-cell interference measured on the at least one resource for the CSI-IM of the cell.

In some embodiments, the processing circuitry84is further configured to receive at least one Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, in a predetermined Reference Signal, RS, region of the RB of the cell, the predetermined RS region of the RB not overlapping with the predetermined IM region of the RB. In some embodiments, the predetermined IM region of the RB of the cell is a dedicated region for at least one CSI-IM resource, the dedicated region not comprising any NZP CSI-RS resources. In some embodiments, the predetermined RS region is a region of the RB of the cell configured for at least one CSI-RS resource, the predetermined RS region not comprising any CSI-IM resources. In some embodiments, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to at least a slot offset, the slot offset based at least in part on a cell identifier, ID. In some embodiments, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to a random selection algorithm.

In some embodiments, the processing circuitry84is further configured to cause the WD22to receive at least one Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, that at least partially overlaps with at least one NZP CSI-RS of at least a neighboring cell. In some embodiments, a period and a slot offset for the received at least one NZP CSI-RS is the same as a period and a slot offset for the at least one NPZ CSI-RS associated with the neighboring cell. In some embodiments, the processing circuitry84is further configured to cause the WD22to receive at least one Tracking Reference Signal, TRS, that at least partially overlaps with at least one TRS of a neighboring cell. In some embodiments, a period and a slot offset for the at least one TRS is the same as a period and a slot offset for the at least one TRS of the neighboring cell. In some embodiments, the received at least one TRS is in a fixed time domain location, the fixed time domain location being the same as a fixed time domain location of the neighboring cell. In some embodiments, the processing circuitry84is further configured to cause the WD22to receive at least one Tracking Reference Signal, TRS, on one of at least four sets of subcarriers in the RB, the at least four sets of subcarriers including a first set of subcarriers that is assigned for transmitting TRS at a regular TRS power level, a second set of subcarriers that is assigned for transmitting TRS at a power level that is 3 decibels, dB, higher than the regular TRS power level, a third set of subcarriers that is assigned for transmitting TRS at a power level that is 4.8 dB higher than the regular TRS power level, and a fourth set of subcarriers that is assigned for transmitting TRS at a power level that is 6 dB higher than the regular TRS power level. In some embodiments, the processing circuitry84is further configured to cause the WD22to receive the at least one TRS on one of the at least four sets of subcarriers; and if the at least one TRS is transmitted on one of the second set, the third set and the fourth set of subcarriers, receive a Zero-Power, ZP, Channel State Information Reference Signal, CSI-RS, on at least the first set of subcarriers.

In some embodiments, the inner workings of the network node16, WD22, and host computer24may be as shown inFIG.2and independently, the surrounding network topology may be that ofFIG.1.

In some embodiments, the host computer24includes processing circuitry42and a communication interface40that is configured to a communication interface40configured to receive user data originating from a transmission from a WD22to a network node16. In some embodiments, the WD22is configured to, and/or comprises a radio interface82and/or processing circuitry84configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the network node16, and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the network node16.

AlthoughFIGS.1and2show various “units” such as resource allocation unit32, and measurement unit34as 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.7is a flowchart of an example method performed by a network node16for CSI-RS resource mapping. The process includes allocating, by for example the resource allocation unit32of the processing circuitry68, at least one resource for Channel State Information Interference Measurement, CSI-IM, within a predetermined IM region of a Resource Block, RB (or, equivalently, a Transmit Time Interval, TTI), of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood that the allocated at least one resource overlaps with at least one resource allocated for CSI-IM in a neighboring cell as compared to allocating a common set of resources for CSI-IM in each neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal, NZP CSI-RS, of the neighboring cell (block S134). In some embodiments, the process further includes identifying, by for example the resource allocation unit32, the at least one resource for the CSI-IM within the predetermined IM region of the RB of the cell based at least in part on an identifier of the cell. In some embodiments, the process further includes selecting at least one resource for Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, in a predetermined Reference Signal, RS, region of the RB of the cell, the predetermined RS region of the RB not overlapping with the predetermined IM region of the RB; and transmitting, such as via radio interface62, the NZP CSI-RS on the selected at least one resource. In some embodiments, the predetermined IM region of the RB of the cell is a dedicated region for at least one CSI-IM resource, the dedicated region not comprising any NZP CSI-RS resources.

In some embodiments, predetermined RS region is a region of the RB of the cell configured for at least one CSI-RS resource, the predetermined RS region not comprising any CSI-IM resources. In some embodiments, the process further includes determining a slot offset for the CSI-IM based on a cell identifier, ID, of the cell being served by the network node16. In some embodiments, the process further includes determining, such as via resource allocation unit32, a period for the CSI-IM, the period for the CSI-IM being common to a group of cells, the group of cells including at least the cell and the neighboring cell. In some embodiments, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to the determined period for the CSI-IM and the determined slot offset. In some embodiments, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to a random selection algorithm. In some embodiments, the process further includes allocating at least one resource for Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, to at least partially overlap with at least one NZP CSI-RS resource of the neighboring cell. In some embodiments, the process further includes determining, such as via resource allocation unit32, a period and a slot offset for the at least one NZP CSI-RS that is the same as a period and a slot offset for the at least one NPZ CSI-RS associated with the neighboring cell. In some embodiments, the process further includes transmitting, such as via radio interface62, at least one Tracking Reference Signal, TRS, to at least partially overlap with at least one TRS of the neighboring cell. In some embodiments, the process further includes determining, such as via resource allocation unit32, a period and a slot offset for at least one Tracking Reference Signal, TRS, that is the same as a period and a slot offset for at least one TRS associated with the neighboring cell; and transmitting, such as via radio interface62, the at least one TRS according to the determined period and the determined slot offset. In some embodiments, the process further includes transmitting, such as via radio interface62, at least one Tracking Reference Signal, TRS, in a fixed time domain location, the fixed time domain location being the same as a fixed time domain location of the neighboring cell. In some embodiments, the process further includes configuring, such as via resource allocation unit32, Tracking Reference Signal, TRS, resources in the RB of the cell by, for each TRS symbol in the RB, dividing a plurality of subcarriers into at least four sets of subcarriers, each of the at least four sets of subcarriers corresponding to a TRS power level that is different from a TRS power level of the other of the at least four sets of subcarriers.

In some embodiments, the at least four sets of subcarriers includes a first set of subcarriers that is assigned for transmitting TRS at a regular TRS power level, a second set of subcarriers that is assigned for transmitting TRS at a power level that is 3 decibels, dB, higher than the regular TRS power level, a third set of subcarriers that is assigned for transmitting TRS at a power level that is 4.8 dB higher than the regular TRS power level, and a fourth set of subcarriers that is assigned for transmitting TRS at a power level that is 6 dB higher than the regular TRS power level. In some embodiments, TRS resources associated with the neighboring cell are also configured with the at least four sets of subcarriers for aligning Tracking Reference Signals, TRSs, of the same power level on the same set of the at least four sets of subcarriers. In some embodiments, the process further includes transmitting, such as via radio interface62, at least one TRS on one of the at least four sets of subcarriers; and if the at least one TRS is transmitted on one of the second set, the third set and the fourth set of subcarriers, transmitting, such as via radio interface62, a Zero-Power, ZP, Channel State Information Reference Signal, CSI-RS, on at least the first set of subcarriers.

FIG.8is a flowchart of an example method performed by a wireless device22according to some embodiments of the present disclosure. The process includes receiving, such as via radio interface82, a signal on at least one resource for Channel State Information Interference Measurement, CSI-IM, the at least one resource for CSI-IM being allocated within a predetermined IM region of a Resource lock, RB (or, equivalently, a Transmit Time Interval, TTI), of the cell, the predetermined IM region encompassing a plurality of resources of the RB of the cell, the allocated at least one resource being selected from among the plurality of resources of the IM region to reduce a likelihood that the allocated at least one resource overlaps with at least one resource allocated for CSI-IM in a neighboring cell as compared to allocating a common set of resources for CSI-IM in each neighboring cell, the predetermined IM region at least partially overlapping with a respective predetermined IM region of a RB of the neighboring cell, and the predetermined IM region of the cell not overlapping resources allocated for Non-Zero Power Channel State Information Reference Signal, NZP CSI-RS, of the neighboring cell (block S136). The process includes transmitting, such as via radio interface82, a Channel State Information, CSI, report, the CSI report based at least in part on inter-cell interference measured on the at least one resource for the CSI-IM of the cell (block S138).

In some embodiments, the process includes receiving, such as via radio interface82and/or the measurement unit34, at least one Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, in a predetermined Reference Signal, RS, region of the RB of the cell, the predetermined RS region of the RB not overlapping with the predetermined IM region of the RB. In some embodiments, the predetermined IM region of the RB of the cell is a dedicated region for at least one CSI-IM resource, the dedicated region not comprising any NZP CSI-RS resources. In some embodiments, the predetermined RS region is a region of the RB of the cell configured for at least one CSI-RS resource, the predetermined RS region not comprising any CSI-IM resources. In some embodiments, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to at least a slot offset, the slot offset based at least in part on a cell identifier, ID. In some embodiments, the CSI-IM is mapped to the at least one resource of the predetermined IM region according to a random selection algorithm. In some embodiments, the process includes receiving, such as via radio interface82and/or the measurement unit34, at least one Non-Zero Power, NZP, Channel State Information Reference Signal, CSI-RS, that at least partially overlaps with at least one NZP CSI-RS of at least a neighboring cell.

In some embodiments, a period and a slot offset for the received at least one NZP CSI-RS is the same as a period and a slot offset for the at least one NPZ CSI-RS associated with the neighboring cell. In some embodiments, the process further includes receiving, such as via radio interface82and/or the measurement unit34, at least one Tracking Reference Signal, TRS, that at least partially overlaps with at least one TRS of a neighboring cell. In some embodiments, a period and a slot offset for the at least one TRS is the same as a period and a slot offset for the at least one TRS of the neighboring cell. In some embodiments, the received TRS is in a fixed time domain location, the fixed time domain location being the same as a fixed time domain location of the neighboring cell. In some embodiments, the process further includes receiving, such as via radio interface82and/or the measurement unit34, at least one Tracking Reference Signal, TRS, on one of at least four sets of subcarriers in the RB, the at least four sets of subcarriers comprising a first set of subcarriers that is assigned for transmitting TRS at a regular TRS power level, a second set of subcarriers that is assigned for transmitting TRS at a power level that is 3 decibels, dB, higher than the regular TRS power level, a third set of subcarriers that is assigned for transmitting TRS at a power level that is 4.8 dB higher than the regular TRS power level, and a fourth set of subcarriers that is assigned for transmitting TRS at a power level that is 6 dB higher than the regular TRS power level. In some embodiments, the process further includes receiving, such as via radio interface82and/or the measurement unit34, the at least one TRS on one of the at least four sets of subcarriers; and if the at least one TRS is transmitted on one of the second set, the third set and the fourth set of subcarriers, receiving a Zero-Power, ZP, Channel State Information Reference Signal, CSI-RS, on at least the first set of subcarriers.

Having described some embodiments of this disclosure for CSI-RS resource mapping, a more detailed description of some of the embodiments is described below.

The resources for CSI-IM may be used (e.g., by the WD22) for measuring inter-cell interference. If a cell's CSI-IM REs overlap with NZP CSI-RS (including TRS) of neighbor cells, the WDs22in the cell may observe the interference from the neighbor's NZP CSI-RS regardless of the traffic load of the neighboring cells, which can lead to over-estimation of the interference. On the other hand, if the cell's CSI-IM REs overlap completely with the CSI-IM of neighbor cells, WDs22in the cell are not able to detect any interference from the neighbor cells, which can lead to under-estimation of the interference.

Thus, the present disclosure provides at least two resource allocation rules that may be used by e.g., the network node16for allocating reference signal resources in a communication network with neighboring cells. In one embodiment of this disclosure, for CSI-IM resource allocation, the network node16(e.g., via resource allocation unit32) serving a cell may allocate resources for CSI-IM to avoid (or at least minimize) overlapping the cell's CSI-IM with a neighbor cell's NZP CSI-RS, including TRS. Further, in one embodiment, the network node16, such as via the resource allocation unit32, may allocate resources for CSI-IM to avoid (or at least minimize) overlapping the cell's CSI-IM with the neighbor cell's CSI-IM.

In some embodiments, for periodic resources, it is possible to use a period and a slot offset to implement the resource allocation rules above, but it may be complicated to coordinate the period and slot offset configurations between all neighboring cells. In some embodiments, for aperiodic resources, if the network node16, such as via the resource allocation unit32, attempts to configure resources according to the resource allocation rules above, the scheduling of interference measurements may become very complicated.

One technique for addressing one or more of these issues is to have a predetermined or dedicated IM region for CSI-IM within a physical resource, such as, for example, a resource block (RB), a subframe, a slot, or a Transmission Time Interval (TTI). In one embodiment, the NZP CSI-RS (including TRS) of any cell should not be mapped to this dedicated IM region. The PDSCH may still be able to be mapped to the REs in the IM region though, if such REs are not allocated for CSI-IM. In one embodiment, in addition to the predetermined IM region for CSI-IM, there may be a predetermined reference signal region in e.g., the TTI or RB of the cell for NZP CSI-RS. The predetermined reference signal (RS) region may be configured to not overlap with the IM region of the TTI. Thus, according to these embodiments, avoiding overlapping the cell's CSI-IM with a neighboring cell's NZP CSI-RS may be accomplished. It is noted that it may be possible to have multiple CSI-IM resources within a CSI-IM region.

For allocating resources for CSI-IM to avoid (or at least minimize) overlapping the cell's CSI-IM with the neighbor cell's CSI-IM, with periodic CSI-IM resources, the network node16, such as via resource allocation unit32, may determine a CSI-IM period and a CSI-IM slot offset. The CSI-IM period may be configured by operators. Thus, in one embodiment, the CSI-IM period may be a period that is a common CSI-IM period to at least a group of neighboring cells. However, the slot offset can be determined based on, for example, a cell identifier (ID), or another parameter that can be used to differentiate one cell from a neighboring cell e.g., for purposes of avoiding or minimizing allocating CSI-IM resources that overlap with CSI-IM resources allocated in the neighboring cell. For example, the network node16, such as via the resource allocation unit32, may determine the slot offset according to: slot offset=(cell ID) mod (configured CSI-IM period). It should be understood that, in some embodiments, overlapping of CSI-IM resources of neighboring cells may not be completely or entirely avoidable. However, by using at least some of the principles of the present disclosure, such overlap of CSI-IM resources of neighboring cells may be minimized, as compared to existing CSI reference signal resource allocation techniques.

In one embodiment, the predetermined IM region is a region of a set of radio resources (e.g., RB, TTI, slot, subframe, etc.) that includes a plurality of CSI-IM resources. The predetermined IM region may overlap a corresponding IM region in a neighboring cell. However, within this predetermined region at least one CSI-IM resource may be allocated by the network node16, such as via the resource allocation unit32, for the CSI-IM of the cell and this at least one resource may be selected and allocated by the network node16serving the cell so that that allocated CSI-IM resource(s) do not overlap the corresponding resources allocated to CSI-IM in the neighboring cell.

Given that there may be multiple CSI-IM resources within the predetermined CSI-IM region, some resource selection algorithms may be used e.g., by the network node16to further minimize the CSI-IM resource overlap between neighbor cells. For example, one resource selection algorithm may be based at least in part on an identifier of the cell. Another resource selection algorithm may be a random selection algorithm or function. In other embodiments, other resource selection algorithms may be used to avoid or reduce the likelihood of overlap of allocated CSI-IM resources between neighbor cells according to the principles of this disclosure.

Accordingly, some embodiments of this disclosure may provide techniques for minimizing or avoiding overlapping of a cell's allocated resources for CSI-IM with at least one neighboring cell's allocated resources (e.g., NZP CSI-RS, TRS, CSI-IM) to advantageously reduce at least some of the drawbacks associated with inter-cell interference.

NZP CSI-RS can be used for channel and/or interference measurements by the WD22. When NZP CSI-RS is used for interference measurement, it is typically used for the measurement of intra-cell interference, or the interference between WDs22that are co-scheduled for MU-MIMO. For NZP CSI-RS, the network node16can transmit NZP CSI-RS in one of three forms: no beamforming, common beamforming, and WD-specific beamforming. Given that WD-specific beamforming is normally performed on the PDSCH, allowing the cell's NZP CSI-RS to collide with a neighbor cell's NZP CSI-RS may not be worse (e.g., in terms of performance) than allowing the cell's NZP CSI-RS to collide with the neighbor cell's PDSCH. In fact, in some cases, allowing such a collision/overlapping can result in a better performance, as compared with allocating resources to avoid the collision. For example, when a cell's non-beamformed NZP CSI-RS collides with the neighbor cell's non-beamformed NZP CSI-RS, the interference on the CSI-RS from the neighbor cell is likely less than that when the interference is from the neighbor cell's PDSCH, which can allow for a better channel measurement. Since these resources may not be used for interference measurement, NZP CSI-RS collision should not cause overestimation of interference.

Thus, the present disclosure provides another resource allocation rule for NZP CSI-RS. In one embodiment, the network node16, such as via the resource allocation unit32, may allocate NZP CSI-RS resources to align NZP CSI-RSs of neighboring cells. Stated another way, in one embodiment, the network node16may allocate NZP CSI-RS to at least partially overlap with NZP CSI-RS of at least one neighboring cell. In yet other embodiments, the network node16may not be configured to allocate NZP CSI-RS resources to avoid overlapping with NZP CSI-RSs of neighboring cells.

Thus, in one embodiment, performance may be improved as a result of NZP CSI-RS from all neighboring cells (or at least some neighboring cells) overlapping with one another. In some embodiments, the network node16, such as via the resource allocation unit32, can be configured to attempt to maximize the degree of overlapping. For example, for periodic NZP CSI-RS resources, NZP CSI-RS can have the same period and the same slot offset for all cells (or at least a group of neighboring cells). The network node16, such as via the resource allocation unit32, may also be configured to determine or identify at least some symbols as preferred symbols for NZP CSI-RS and, at least initially, use all REs in those preferred symbols for NZP CSI-RS before allocating other symbols for NZP CSI-RS. Accordingly, the network node16, such as via the resource allocation unit32, can be configured with rules designed to align, or maximize the overlap of NZP CSI-RS with neighboring cell NZP CSI-RS.

In one embodiment, assuming no WD-specific beamforming for TRS, one or more of the following rules are provided for TRS resource mapping by e.g., a resource allocation unit32in a network node16:use the same period and slot offset for all (or at least some neighboring) cells,have a fixed time domain location for TRS,align TRSs with the same power level, anduse different REs for TRSs with different power levels.

According to 3GPP specifications, for sub-6 GHz or frequency range 1, the TRS resource set may include four periodic CSI-RS resources in two consecutive slots with two CSI-RS resources in each of the two consecutive slots. The time-domain locations of the two CSI-RS resources in a slot may be given by one of {4, 8}, {5, 9}, or {6, 10}. For frequency range 2, other time-domain locations may also be allowed. In each OFDM symbol, 3 REs can be allocated for TRS, while the other REs can be configured as ZP CSI-RS if a TRS power boost is used.

Based on one or more of the TRS rules provided above, a fixed time domain location can be selected by e.g., the network node16(for example, {5, 9}) for all (or at least some neighboring) cells. In one embodiment, for each TRS symbol, the network node16may divide the 12 subcarriers into at least four sets of subcarriers as follows: one set for regular power level TRS; one set for 3 dB power boost TRS; one set for 4.8 dB power boost TRS; and one set for 6 dB power boost TRS (see e.g.,FIGS.14-17).

Specifically, according to one example embodiment, subcarriers 0, 4, and 8 may be configured e.g., by a resource allocation unit32in the network node16for regular power level TRS for all WDs22in all (or at least some neighboring) cells. If 3 dB power boost is configured for a cell, subcarriers 1, 5, 9 may be allocated for TRS while subcarriers 0, 4, 8 are configured as ZP CSI-RS. If 4.8 dB power boost is configured for a cell, subcarriers 2, 6, 10 may be allocated for TRS while subcarriers 0, 1, 4, 5, 8 and 9 are configured as ZP CSI-RS. If 6 dB power boost is configured for a cell, subcarriers 3, 7, 11 may be allocated for TRS while subcarriers 0, 1, 2, 4, 5, 6, 8, 9 and 10 are configured as ZP CSI-RS. By doing so, according to this embodiment, TRS with the same power level may be aligned amongst the neighboring cells and different REs may be used for TRSs with different power levels. For example, this example embodiment may result in the following resource configurations:TRS with the regular power level may overlap with—TRS with the regular power level from neighbor cells, for which TRS power boost is not configured, orZP CSI-RS from neighbor cells, for which TRS power boost is configured;TRS with 3 dB power boost may overlap with—TRS with 3 dB power boost from neighbor cells, for which 3 dB TRS power boost is configured, orPDSCH from neighbor cells, for which TRS power boost is not configured, orZP CSI-RS from neighbor cells, for which 4.8 dB or 6 dB TRS power boost is configured;TRS with 4.8 dB power boost may overlap with—TRS with 4.8 dB power boost from neighbor cells, for which 4.8 dB TRS power boost is configured, orPDSCH from neighbor cells, for which TRS power boost is less than 4.8 dB, orZP CSI-RS from neighbor cells, for which 6 dB TRS power boost is configured; andTRS with 6 dB power boost may overlap with—TRS with 6 dB power boost from neighbor cells, for which 6 dB TRS power boost is configured, orPDSCH from neighbor cells, for which TRS power boost is less than 6 dB.

Thus, if neighboring cells are configured with these TRS allocation rules, the overlapping of resources may be optimized to e.g., reduce inter-cell interference error. Some advantages for this kind of TRS configuration may include one or more of the following:TRS with the regular power level may not experience strong interference of PDSCH from neighbor cells. Since PDSCH is beamformed per WD22, the interference of PDSCH can be quite strong.TRS with power boost may experience interference from PDSCH from neighbor cells. The power boost level can be adjusted to handle the strong interference of PDSCH.TRS with power boost may collide with TRS from neighbor cells at the same power boost level. The assumption for TRS power boost is that TRS coverage may be limited while TRS interference is not a dominant factor. When TRS with the same power boost level collides, the signal to interference ratio is the same as with no power boost.When TRS power level is increased for a given cell, for example, from 3 dB to 4.8 dB, it doesn't change the interference to TRS of the neighbor cells, either without power boost or with power boost of 6 dB. The interference to TRS of the neighbor cells with power boost of 3 dB may be removed. The interference to TRS of the neighbor cells with power boost of 4.8 dB may be expected to be reduced since the interference is now due to TRS instead of PDSCH.

Having described some embodiments for CSI-RS resource mapping according to some embodiments of the present disclosure, some specific resource partition examples are provided inFIGS.9-19. In at least some of the resource partition examples, in addition to CSI-RS and CSI-IM being configured in separate regions and/or with non-overlapping resources, yet other signals and/or channels may be configured in separate regions and/or with non-overlapping resources, such as, for example, Physical Downlink Control Channel (PDCCH) and Physical Downlink Shared Channel (PDSCH) Demodulation Reference Signal (DMRS). It is noted that these examples are non-limiting and are intended to aid understanding of the disclosure and embodiments, and not as the only possible resource partition examples.

FIG.9illustrates a first example resource partition of a subframe. The example shows the OFDM symbols 2 and 3 being configured for PDSCH DMRS. The TRS is shown at OFDM symbols 5 and 9, with three REs in each OFDM symbol at subcarriers 0, 4 and 8. The last four OFDM symbols in the subframe are configured as the CSI-RS region. The CSI-IM region is at OFDM symbols 7 and 8.

FIG.10illustrates a second example resource partition of a subframe. In this example, the CSI-IM region is at OFDM symbols 4 and 6 and includes additional OFDM symbols for CSI-RS in OFDM symbols 7 and 8.

FIG.11illustrates a third example resource partition of a subframe. In this example, additional OFDM symbols are configured for PDSCH DMRS, namely OFDM symbols 2, 3 as well as 10 and 11. The CSI-RS region is at OFDM symbols 7, 8, 12 and 13. The CSI-IM region is at OFDM symbols 4 and 6.

FIG.12illustrates a fourth example resource partition of a subframe. In this example, the CSI-RS region is at OFDM symbols 4, 6, 7 and 8. The CSI-IM region is at OFDM symbols 12 and 13.

FIG.13illustrates a fifth example resource partition of a subframe. In this example, the CSI-RS region is at OFDM symbols 3, 4, 6 and 7. The PDSCH DMRS is at OFDM symbols 2 and 11.

FIG.14illustrates a sixth example resource partition of a subframe. In this example, the CSI-RS region is mapped to OFDM symbols 3, 4, 7 and 8.

FIG.15illustrates a seventh example resource partition of a subframe. In this example, resources are configured with a TRS power boost of 3 dB, where Zero Power (ZP) CSI-RS is required. The TRS is mapped to OFDM symbols 5 and 9 at subcarriers 1, 5 and 9. ZP CSI-RS is mapped to OFDM symbols 5 and 9 at subcarriers 0, 4 and 8, according to the embodiments discussed above for aligning TRSs with the same power levels.

FIG.16illustrates an eight example resource partition of a subframe. In this example, resources are configured with a TRS power boost of 4.8 dB, where ZP CSI-RS is required. The TRS is mapped to OFDM symbols 5 and 9 at subcarriers 2, 6 and 10. ZP CSI-RS is mapped to OFDM symbols 5 and 9 at subcarriers 0, 4 and 8, as well as, subcarriers 1, 5 and 9, according to the embodiments discussed above for aligning TRSs with the same power levels.

FIG.17illustrates a ninth example resource partition of a subframe. In this example, resources are configured with a TRS power boost of 6 dB, where ZP CSI-RS is required. The TRS is mapped to OFDM symbols 5 and 9 at subcarriers 3, 7 and 11. ZP CSI-RS is mapped to OFDM symbols 5 and 9 at subcarriers 0, 4 and 8, as well as, subcarriers 1, 5 and 9 and subcarriers 2, 6 and 10, according to the embodiments discussed above for aligning TRSs with the same power levels.

FIG.18illustrates a tenth example resource partition of a subframe. In this example, resources are configured with a TRS power boost; however, the CSI-IM region does not include all subcarriers in an OFDM symbol. Thus, TRS and the CSI-IM REs can be in the same OFDM symbol together. In this example, the CSI-IM pattern is a 2×2 pattern (e.g., 2 consecutive OFDM symbols, with 2 adjacent REs on each the 2 consecutive symbols).

FIG.19illustrates an eleventh example resource partition of a subframe. In this example, resources are configured with a TRS power boost; however, less ZP CSI-RS resources are used, as compared to the example resource partition ofFIG.18. Specifically, the number of ZP CSI-RS REs is reduced by 2. One potential issue is the error in inter-cell interference measured by the WDs22in the cell. For example, power boosted TRS from neighbor cells may be seen as interference.

In other embodiments of the principles of this disclosure, there may be resource partition configurations other than those shown inFIGS.9-19that may advantageously reduce interference from neighboring cells.

It should be understood that the reference signal resources allocated and/or configured (e.g., by the resource allocation unit32of the network node16) according to the embodiments and various arrangements discussed above may be used by e.g., the measurement unit34of the WD22to perform channel and/or interference measurements and to generate and send to the network node16corresponding CSI reports.

Accordingly, some embodiments in this disclosure provide solutions for performing resource mapping for CSI reference signals that may address the inter-cell interference problem to allow WDs to measure channel information more accurately. For example, in some embodiments, inter-cell interference error can be reduced by allocating resources for CSI-IM to avoid (or at least minimize) overlapping a cell's CSI-IM with a neighbor cell's NZP CSI-RS, including TRS and/or by allocating resources for CSI-IM to avoid (or at least minimize) overlapping the cell's CSI-IM with the neighbor cell's CSI-IM. Further, in some embodiments, improved channel estimation may be achieved by allocating NZP CSI-RS resources to align/overlap NZP CSI-RSs of neighboring cells, as compared to existing channel estimation techniques. In addition, in some embodiments, improved time and/or frequency synchronization may be achieved, as compared to existing time and frequency synchronization techniques, by TRS resource mapping that aligns TRSs of neighboring cells with the same power level, and uses different REs for TRSs of neighboring cells with different power levels. By reducing inter-cell interference error according to at least some of the principles in this disclosure, channel measurements may be more accurate and channel state information, such as CQI values, reported by the WD can be more accurate, which can improve user throughput as compared to existing CSI reference signal resource mapping techniques.

The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows.