Communication System

Abstract

The above describes an apparatus, method and computer program: determining a coupling gain of a user equipment within a cell of a mobile communication system; comparing the determined coupling gain with a coupling gain threshold; if the determined coupling gain is less than the coupling gain threshold, setting the user equipment to operate in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment is configured to use a device-specific reference signal transmission for determining channel state information; and if the determined coupling gain is not less than the coupling gain threshold, setting the user equipment to operate in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment is configured to use a cell-specific reference signal transmission for determining channel state information.

Description

Technical Field

[0001] This specification relates to communication systems. Background Art

[0002] Downlink reference signals can be used to determine channel state information of user equipment operating within a cell of a mobile communication system. Further development is still needed in this area. Summary of the invention

[0003] In a first aspect, the specification describes an apparatus comprising a component for performing the following operations: determining (e.g., measuring) a coupling gain of a user equipment within a cell of a mobile communication system (e.g., the user equipment can measure a reference signal and report the measurement to the cell); comparing the determined coupling gain with a coupling gain threshold; in the case where the determined coupling gain is less than the coupling gain threshold, setting the user equipment to operate in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment is configured to use a device-specific reference signal transmission for determining channel state information; and in the case where the determined coupling gain is not less than the coupling gain threshold, setting the user equipment to operate in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment is configured to use a cell-specific reference signal transmission for determining channel state information. In some example embodiments, the component is also configured to perform: setting the above-mentioned coupling gain threshold.

[0004] The coupling gain threshold may be based at least in part on a defined coupling gain threshold, the defined coupling gain threshold being based on the number of connected user equipment within a cell of the mobile communication system. In addition, the component may be further configured to perform: determining or obtaining the number of connected users within a cell of the mobile communication system; and setting the defined coupling gain threshold according to the number of connected users. The defined coupling gain threshold may be set periodically, but this is not required for all example embodiments.

[0005] The coupling gain threshold may be based at least in part on the minimum threshold. In addition, the coupling gain threshold may be the greater of the coupling gain threshold defined above and the minimum threshold described above. The minimum threshold may be a lower limit, below which the device-specific CSI-RS is always used.

[0006] In some example embodiments, while the user equipment remains within a cell of the mobile communication system, the set CSI-RS operation mode may be maintained (eg, until a handover to another cell occurs).

[0007] In some example embodiments, the set CSI-RS operation mode may be re-evaluated periodically or in response to an event, wherein the re-evaluation of the CSI-RS operation mode is based on a coupling gain and a coupling gain threshold of the user equipment when the CSI-RS operation mode is re-evaluated.

[0008] In some example embodiments, the component is further configured to perform: providing a downlink reference signal transmission according to the configured CSI-RS operation mode; and determining channel state information in response to the provided downlink reference signal transmission.

[0009] In some example embodiments, all user equipment within a cell operating in a device-specific CSI-RS mode of operation uses orthogonal resources (e.g., orthogonal downlink resources) for CSI-RS reference signal transmission. In some example embodiments, all user equipment within a cell operating in a cell-specific CSI-RS mode of operation uses the same resources (e.g., the same downlink resources) for CSI-RS reference signal transmission.

[0010] The above-mentioned components may include: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program being configured to cause the operation of the apparatus together with the at least one processor.

[0011] In a second aspect, the present specification describes a system comprising: multiple user equipments operating within a cell of a mobile communication system, wherein: one or more of the above-mentioned user equipments are configured to operate in a device-specific CSI-RS operation mode, in which the corresponding user equipment uses a device-specific reference signal transmission for determining channel state information; and one or more of the above-mentioned user equipments are configured to operate in a cell-specific CSI-RS operation mode, in which the corresponding user equipment uses a cell-specific reference signal transmission for determining channel state information, wherein: when the coupling gain of the user equipment determined for the corresponding user equipment is less than a coupling gain threshold, the user equipment operates in the device-specific CSI-RS operation mode; and when the coupling gain determined for the corresponding user equipment is not less than the coupling gain threshold, the user equipment operates in the cell-specific CSI-RS operation mode.

[0012] The respective coupling gain threshold may be based at least in part on a defined coupling gain threshold based on the number of connected user equipments within a cell of the mobile communication system. The defined coupling gain threshold may be set periodically, but this is not necessary for all example embodiments.

[0013] The corresponding coupling gain threshold may be based at least in part on the minimum threshold. In addition, the coupling gain threshold may be the greater of the coupling gain threshold defined above and the minimum threshold described above. The minimum threshold may be a lower limit, below which the device-specific CSI-RS is always used.

[0014] In some example embodiments, while the user equipment remains within a cell of the mobile communication system (eg, until a handover to another cell occurs), the CSI-RS operation mode set for the user equipment may be maintained.

[0015] In some example embodiments, a CSI-RS operation mode set for a user equipment may be re-evaluated periodically or in response to an event, wherein the re-evaluation of the CSI-RS operation mode is based on a coupling gain and a coupling gain threshold of the user equipment when the CSI-RS operation mode is re-evaluated.

[0016] In some example embodiments, all user equipment within a cell operating in a device-specific CSI-RS mode of operation uses orthogonal resources (e.g., orthogonal downlink resources) for CSI-RS reference signal transmission. In some example embodiments, all user equipment within a cell operating in a cell-specific CSI-RS mode of operation uses the same resources (e.g., the same downlink resources) for CSI-RS reference signal transmission.

[0017] In a third aspect, the specification describes a method comprising: determining a coupling gain of a user equipment within a cell of a mobile communication system; comparing the determined coupling gain with a coupling gain threshold; in a case where the determined coupling gain is less than the coupling gain threshold, setting the user equipment to operate in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment is configured to use a device-specific reference signal transmission for determining channel state information; and in a case where the determined coupling gain is not less than the coupling gain threshold, setting the user equipment to operate in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment is configured to use a cell-specific reference signal transmission for determining channel state information. Some example embodiments also include setting the coupling gain threshold.

[0018] The coupling gain threshold may be based at least in part on a defined coupling gain threshold based on the number of connected user equipment within a cell of the mobile communication system. In addition, the method may include: determining or obtaining the number of connected users within the cell of the mobile communication system; and setting the defined coupling gain threshold according to the number of connected users. The defined coupling gain threshold may be set periodically, but this is not required for all example embodiments.

[0019] The coupling gain threshold may be based at least in part on the minimum threshold. In addition, the coupling gain threshold may be the greater of the coupling gain threshold defined above and the minimum threshold described above. The minimum threshold may be a lower limit, below which the device-specific CSI-RS is always used.

[0020] In some example embodiments, while the user equipment remains within a cell of the mobile communication system (eg, until a handover to another cell occurs), the set CSI-RS operation mode may be maintained.

[0021] In some example embodiments, the set CSI-RS operation mode may be re-evaluated periodically or in response to an event, wherein the re-evaluation of the CSI-RS operation mode is based on a coupling gain and a coupling gain threshold of the user equipment when the CSI-RS operation mode is re-evaluated.

[0022] Some example embodiments further include: providing a downlink reference signal transmission according to the configured CSI-RS operation mode; and determining channel state information in response to the provided downlink reference signal transmission.

[0023] In some example embodiments, all user equipment within a cell operating in a device-specific CSI-RS mode of operation uses orthogonal resources (e.g., orthogonal downlink resources) for CSI-RS reference signal transmission. In some example embodiments, all user equipment within a cell operating in a cell-specific CSI-RS mode of operation uses the same resources (e.g., the same downlink resources) for CSI-RS reference signal transmission.

[0024] In a fourth aspect, the present specification describes a method comprising: operating a first group of one or more user equipment within a cell of a mobile communication system in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment in the first group uses a device-specific reference signal transmission for determining channel state information, wherein when a coupling gain determined for the corresponding user equipment is less than a coupling gain threshold, the user equipment operates in the device-specific CSI-RS operation mode; and operating a second group of one or more of the above-mentioned user equipment within a cell of the mobile communication system in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment in the second group uses a cell-specific reference signal transmission for determining channel state information, wherein when the coupling gain determined for the corresponding user equipment is not less than the coupling gain threshold, the user equipment operates in the cell-specific CSI-RS operation mode.

[0025] The respective coupling gain threshold may be based at least in part on a defined coupling gain threshold based on the number of connected user equipments within a cell of the mobile communication system. The defined coupling gain threshold may be set periodically, but this is not necessary for all example embodiments.

[0026] The corresponding coupling gain threshold may be based at least in part on the minimum threshold. In addition, the coupling gain threshold may be the greater of the coupling gain threshold defined above and the minimum threshold described above. The minimum threshold may be a lower limit, below which the device-specific CSI-RS is always used.

[0027] In some example embodiments, the CSI-RS operation mode set for the user equipment may be maintained while the user equipment remains within a cell of the mobile communication system (eg, until a handover to another cell occurs).

[0028] In some example embodiments, a CSI-RS operation mode set for a user equipment may be re-evaluated periodically or in response to an event, wherein the re-evaluation of the CSI-RS operation mode is based on a coupling gain and a coupling gain threshold of the user equipment when the CSI-RS operation mode is re-evaluated.

[0029] In some example embodiments, all user equipment within a cell operating in a device-specific CSI-RS mode of operation uses orthogonal resources (e.g., orthogonal downlink resources) for CSI-RS reference signal transmission. In some example embodiments, all user equipment within a cell operating in a cell-specific CSI-RS mode of operation uses the same resources (e.g., the same downlink resources) for CSI-RS reference signal transmission.

[0030] In a fifth aspect, the present specification describes an apparatus configured to perform any method as described with reference to the third aspect or the fourth aspect.

[0031] In a sixth aspect, the present specification describes computer readable instructions that, when executed by a computing device, cause the computing device to perform any of the methods described with reference to the third aspect or the fourth aspect.

[0032] In a seventh aspect, the specification describes a computer program, the computer program including instructions for causing an apparatus to at least perform the following operations: determine a coupling gain of a user equipment within a cell of a mobile communication system; compare the determined coupling gain with a coupling gain threshold; if the determined coupling gain is less than the coupling gain threshold, set the user equipment to operate in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment is configured to use a device-specific reference signal transmission for determining channel state information; and if the determined coupling gain is not less than the coupling gain threshold, set the user equipment to operate in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment is configured to use a cell-specific reference signal transmission for determining channel state information. Some example embodiments also include setting the above-mentioned coupling gain threshold.

[0033] In an eighth aspect, the present specification describes a computer program comprising instructions for causing an apparatus to perform at least the following operations: operating a first group of one or more user equipment within a cell of a mobile communication system in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment in the first group uses a device-specific reference signal transmission for determining channel state information, wherein when a coupling gain determined for the corresponding user equipment is less than a coupling gain threshold, the user equipment operates in the device-specific CSI-RS operation mode; and operating a second group of one or more of the above-mentioned user equipment within a cell of a mobile communication system in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment in the second group uses a cell-specific reference signal transmission for determining channel state information, wherein when a coupling gain determined for the corresponding user equipment is not less than a coupling gain threshold, the user equipment operates in the cell-specific CSI-RS operation mode.

[0034] In a ninth aspect, the present specification describes a computer-readable medium (such as a non-transitory computer-readable medium) including program instructions stored thereon, the program instructions for performing at least the following operations: determining a coupling gain of a user equipment within a cell of a mobile communication system; comparing the determined coupling gain with a coupling gain threshold; in the case where the determined coupling gain is less than the coupling gain threshold, setting the user equipment to operate in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment is configured to use a device-specific reference signal transmission for determining channel state information; and in the case where the determined coupling gain is not less than the coupling gain threshold, setting the user equipment to operate in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment is configured to use a cell-specific reference signal transmission for determining channel state information. Some example embodiments also include setting the above-mentioned coupling gain threshold.

[0035] In a tenth aspect, the present specification describes a computer-readable medium (such as a non-transitory computer-readable medium), which includes program instructions stored thereon, and the program instructions are used to perform at least the following operations: operating a first group of one or more user equipment within a cell of a mobile communication system in a device-specific CSI-RS operation mode, in which the user equipment in the first group uses a device-specific reference signal transmission to determine channel state information, wherein when the coupling gain determined for the corresponding user equipment is less than a coupling gain threshold, the user equipment operates in the device-specific CSI-RS operation mode; and operating a second group of one or more of the above-mentioned user equipment within a cell of the mobile communication system in a cell-specific CSI-RS operation mode, in which the user equipment in the second group uses a cell-specific reference signal transmission to determine channel state information, wherein when the coupling gain determined for the corresponding user equipment is not less than the coupling gain threshold, the user equipment operates in the cell-specific CSI-RS operation mode.

[0036] In an eleventh aspect, the present specification describes an apparatus comprising: at least one processor; and at least one memory comprising computer program code, which, when executed by the at least one processor, causes the apparatus to: determine a coupling gain of a user equipment within a cell of a mobile communication system; compare the determined coupling gain with a coupling gain threshold; in the case where the determined coupling gain is less than the coupling gain threshold, set the user equipment to operate in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment is configured to use a device-specific reference signal transmission for determining channel state information; and in the case where the determined coupling gain is not less than the coupling gain threshold, set the user equipment to operate in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment is configured to use a cell-specific reference signal transmission for determining channel state information. Some example embodiments also include setting the above-mentioned coupling gain threshold.

[0037] In a twelfth aspect, the present specification describes an apparatus comprising: at least one processor; and at least one memory comprising computer program code, which, when executed by the at least one processor, causes the apparatus to: operate a first group of one or more user equipment within a cell of a mobile communication system in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment in the first group uses a device-specific reference signal transmission for determining channel state information, wherein in a case where a coupling gain determined for the corresponding user equipment is less than a coupling gain threshold, the user equipment operates in the device-specific CSI-RS operation mode; and operate a second group of one or more of the above-mentioned user equipment within a cell of the mobile communication system in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment in the second group uses a cell-specific reference signal transmission for determining channel state information, wherein in a case where the coupling gain determined for the corresponding user equipment is not less than a coupling gain threshold, the user equipment operates in the cell-specific CSI-RS operation mode.

[0038] In a thirteenth aspect, the present specification describes an apparatus comprising: a component (such as a first processor) for determining a coupling gain of a user equipment within a cell of a mobile communication system; a component (such as a comparator) for comparing the determined coupling gain with a coupling gain threshold; a component (such as a first output) for setting the user equipment to operate in a device-specific CSI-RS operation mode when the determined coupling gain is less than the coupling gain threshold, wherein in the device-specific CSI-RS operation mode, the user equipment is configured to use a device-specific reference signal transmission for determining channel state information; and a component (such as a first output) for setting the user equipment to operate in a cell-specific CSI-RS operation mode when the determined coupling gain is not less than the coupling gain threshold, wherein in the cell-specific CSI-RS operation mode, the user equipment is configured to use a cell-specific reference signal transmission for determining channel state information. Some example embodiments also include setting the above-mentioned coupling gain threshold.

[0039] In a fourteenth aspect, the present specification describes an apparatus comprising: a component (such as a control module) for operating a first group of one or more user equipment within a cell of a mobile communication system in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment in the first group uses a device-specific reference signal transmission for determining channel state information, wherein when a coupling gain determined for the corresponding user equipment is less than a coupling gain threshold, the user equipment operates in the device-specific CSI-RS operation mode; and a component (such as the above-mentioned control module) for operating a second group of one or more of the above-mentioned user equipment within a cell of a mobile communication system in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment in the second group uses a cell-specific reference signal transmission for determining channel state information, wherein when the coupling gain determined for the corresponding user equipment is not less than the coupling gain threshold, the user equipment operates in the cell-specific CSI-RS operation mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Example embodiments will now be described, by way of example only, with reference to the following schematic drawings, in which:

[0041] Figure 1 is a block diagram of a system according to an example embodiment;

[0042] Figure 2 is a flow chart illustrating an algorithm according to an example embodiment;

[0043] Figures 3 to 6 is a diagram according to an example embodiment;

[0044] Figures 7 to 9is a flow chart illustrating an algorithm according to an example embodiment;

[0045] Fig.10 is a diagram according to an example embodiment;

[0046] Fig.11 shows simulation results according to example embodiments;

[0047] Fig.12 is a flow chart illustrating an algorithm according to an example embodiment;

[0048] Fig.13 is a block diagram of components of a system according to an example embodiment; and

[0049] Fig.14A and Fig. 14B Tangible media storing computer readable codes, which when executed by a computer perform operations according to example embodiments, are shown, respectively, a removable nonvolatile memory unit and a compact disk (CD). DETAILED DESCRIPTION

[0050] The scope of protection sought by various embodiments of the present invention is defined by the independent claims. Embodiments and features described in the specification that do not belong to the scope of the independent claims, if any, are to be interpreted as examples useful for understanding various embodiments of the present invention.

[0051] In the specification and drawings, like reference numerals refer to like elements throughout.

[0052] Figure 1 is a block diagram of a system according to an example embodiment, which is generally indicated by reference numeral 10. The system shows a portion of a mobile communication cell, including a base station 12 and first to fourth user equipments 14 to 17 in communication with the base station.

[0053] In the system 10, the first user equipment 14 is using downlink reference signal transmissions (particularly channel state information reference signal (CSI-RS) transmissions 18) to estimate the downlink channel and report CSI (channel state information) to the cell, including, for example, PMI (precoding matrix indicator), CQI (channel quality indicator) and RI (rank indicator). The channel state information reported by the user equipment 14 can be used to determine the transmission rank, precoder and modulation coding scheme (MCS) for data transmission to the user on the downlink.

[0054] The CSI-RS transmission 18 may take the form of a cell-specific CSI-RS transmission or a device-specific CSI-RS transmission.

[0055] If cell-specific CSI-RS transmission is used, all relevant user equipment within the cell use the same downlink resources for CSI-RS reference signal transmission. Therefore, the cell does not need to allocate independent, mutually exclusive downlink resources for CSI-RS transmission to each radio resource control (RRC) connected user in the cell. Instead, all connected user equipment in the cell can use the same CSI-RS resources (e.g., periodically transmitted) to estimate their corresponding channels.

[0056] If device-specific CSI-RS transmission is used, all relevant user equipment within the cell typically use orthogonal downlink resources for CSI-RS reference signal transmission. Therefore, CSI-RS transmission to each user equipment will be performed on a user-specific beam, such as the user's best eigenbeam or the user's best refined beam grid (GoB) beam. This can bring greater beamforming gain and higher SINR (signal to interference and noise ratio) to the user equipment, thereby bringing better throughput performance to the user equipment. However, device-specific CSI-RS transmission typically requires mutually exclusive CSI-RS resources for each RRC-connected user in the cell, which has an adverse impact on user throughput performance when there are a large number of RRC-connected users.

[0057] Figure 2 is a flow chart illustrating an algorithm, generally indicated by reference numeral 20 , according to an example embodiment.

[0058] Algorithm 20 begins at operation 22, where downlink reference signal transmission is provided according to a CSI-RS operation mode (eg, cell-specific CSI-RS or device-specific CSI-RS).

[0059] At operation 24 , channel state information (CSI) is determined in response to the downlink reference signal transmission provided in operation 22 .

[0060] Figure 3 is a graph, generally indicated by reference numeral 30, according to an example embodiment. Graph 30 plots the percentage of downlink resources used to implement device-specific CSI (graph 32) and cell-specific CSI (graph 34) relative to the number of connected devices.

[0061] As described above, independent and mutually exclusive resources are used to transmit device-specific CSI-RS. Therefore, when using device-specific CSI-RS, the overhead increases linearly with the number of RRC-connected users in the cell (as shown in Figure 32). For example, Figure 3As shown in the example, for the example CSI-RS configuration, with only 180 RRC connected users in the cell, 50% of the available downlink resources will be used for CSI-RS transmission. Obviously, if hundreds or even thousands of users are assigned to a cell, it may become impractical to use device-specific CSI-RS transmission within that cell.

[0062] In contrast, when cell-specific CSI-RS transmission is used instead, the overhead is limited to less than about 1% of the available downlink resources (see Figure 34). Thus, the CSI-RS overhead is negligible when cell-specific CSI-RS transmission is used.

[0063] Figure 4 is a graph, generally indicated by reference numeral 40, in accordance with an example embodiment. Graph 40 illustrates a comparison of system performance gain with device-specific CSI-RS compared to cell-specific CSI-RS in a system where there are 10 RRC-connected devices in a cell. Graph 40 is based on 10 RRC-connected devices, such that the overhead incurred by allocating device-specific CSI-RS resources to user equipment is small.

[0064] As shown in Figure 40, when the number of RRC connected user devices is small (10 in this case), using cell-specific CSI-RS transmission generally results in worse geometric mean performance. Simulation data shows that for larger inter-site distances, the cell edge throughput may be poor when using cell-specific CSI-RS, but the user can obtain reasonable throughput when using device-specific CSI-RS. This is because using cell-specific beams will have poor beamforming gain in the direction of the user due to the use of cell-specific CSI-RS transmission. The sector-specific beams combined with the split-panel architecture for cell-specific CSI-RS transmission have lower beamforming gain, thereby limiting the coverage area of ​​the beam and resulting in lower performance in the case of cell-specific CSI-RS. On the other hand, device-specific CSI-RS will produce better performance due to the use of device-specific beams, such as the user's best eigenbeam or the user's best GoB beam. This can better match the beam in the direction of the user's channel, resulting in better SINR and throughput for the user.

[0065] Therefore, for a small number of RRC connected devices (making the overhead of using device-specific CSI-RS very low), using device-specific CSI-RS resources can significantly improve system performance because the user beam is better matched to the user channel, resulting in better beamforming gain.

[0066] Figure 55 is a graph according to an exemplary embodiment, generally indicated by reference numeral 50. Graph 50 shows a geometric mean of user throughput versus the number of RRC connected users. The graph includes a first graph 52 in which device-specific CSI-RS transmission is used and a second graph 54 in which cell-specific CSI-RS transmission is used.

[0067] As described above, the CSI-RS overhead in the case of device-specific CSI-RS transmission increases as the number of RRC-connected users increases. As shown in the first graph 52, when device-specific CSI-RS transmission is used, the user throughput performance decreases as the number of RRC-connected user devices increases. Graphs 52 and 54 show that for a small number of connected user devices, the performance of device-specific CSI-RS is better than that of cell-specific CSI-RS, but as the number of connected devices increases, the performance of device-specific CSI-RS transmission decreases linearly, and ultimately, the cell-specific CSI-RS scheme is better than the device-specific CSI-RS. Figure 5 In the simulation data shown, for 300 RRC connected users, the geometric mean of the throughput with the device-specific CSI-RS is about 75% lower than the geometric mean of the throughput with the cell-specific CSI-RS scheme.

[0068] Figure 6 is a graph, generally indicated by reference numeral 60, according to an example embodiment. Graph 60 shows a comparison of user throughput gain with device-specific CSI-RS when compared to cell-specific CSI-RS for different numbers of RRC-connected devices in a cell.

[0069] Graph 60 shows the gain in user throughput when all users in a cell use device-specific CSI-RS instead of cell-specific CSI-RS (but ignoring CSI-RS overhead). This enables determination of which user equipment benefits most from using device-specific CSI-RS. It is found that the user equipment with lower throughput with cell-specific CSI-RS is the one that obtains the largest gain by using device-specific CSI-RS. This is because, with device-specific CSI-RS, the reference signal can better match the primary channel direction of the user, resulting in a higher SINR and thus improved throughput. Since cell-edge user equipment typically have poorer throughput to begin with, their percentage gain tends to be larger.

[0070] Based on these results, it can be concluded that cell edge user equipment should preferentially receive device-specific CSI-RS configurations. Therefore, as described in detail below, a hybrid CSI-RS scheme can be designed, in which user equipment with coupling gain less than a threshold uses device-specific CSI-RS transmission, while other users use cell-specific CSI-RS transmission.

[0071] Figure 7 is a flow chart illustrating an algorithm according to an example embodiment, the algorithm being generally indicated by reference numeral 70. Algorithm 70 is an example of a hybrid CSI-RS scheme.

[0072] At operation 72, the coupling gain of the user equipment within the cell of the mobile communication system is determined (e.g., measured). Typically, the user equipment measures a reference signal and reports the measurement to the base station. For example, operation 72 may be implemented for the user equipment when the user equipment first enters the cell.

[0073] Coupling gain can be defined as the gain from the transmitter to the receiver taking into account the attenuation of the transmitted signal due to the distance between the devices and the transmitter and receiver antenna gains, and is therefore inversely proportional to the path loss.

[0074] At operation 74, the coupling gain determined in operation 72 is compared to a coupling gain threshold. (An example method for setting the coupling gain threshold is described below.)

[0075] If the determined coupling gain is less than the coupling gain threshold, algorithm 70 moves to operation 76, where the user equipment is configured to operate in a device-specific CSI-RS operation mode. In the device-specific CSI-RS operation mode, the user equipment is configured to use device-specific reference signal transmissions for determining channel state information.

[0076] If the determined coupling gain is not less than the coupling gain threshold, algorithm 70 moves to operation 78, where the user equipment is configured to operate in a cell-specific CSI-RS operation mode. In the cell-specific CSI-RS operation mode, the user equipment is configured to use cell-specific reference signal transmissions for determining channel state information.

[0077] Once set (in operation 76 or operation 78), the user equipment may maintain the CSI-RS operation mode until it leaves the cell. In another embodiment, the coupling gain may be periodically rechecked in an event-triggered manner to determine whether the CSI-RS configuration should be changed for a given device (e.g., based on the coupling gain of the user equipment and the coupling gain threshold when the CSI-RS operation mode is re-evaluated).

[0078] Algorithm 70 thus provides a hybrid CSI-RS scheme that has some advantages of cell-specific CSI-RS transmission (e.g., reduced overhead when the number of connected user devices is large) and some advantages of device-specific CSI-RS transmission (e.g., improved throughput performance when the number of connected user devices is small).

[0079] Figure 8 is a flow chart illustrating an algorithm according to an example embodiment, which is generally indicated by reference number 80. Algorithm 80 illustrates an example method for setting a coupling gain threshold used in operation 74 described above.

[0080] The algorithm 80 begins at operation 82, where the number of user equipment connected within the associated cell is determined.

[0081] At operation 84, a coupling gain threshold is set. In one example embodiment, the coupling gain threshold (CG thresh ) is given by the following formula:

[0082] CG thresh =max(CG optim (#RRC connected UEs), CGMin thresh )

[0083] Function CG optim (#RRC connected UEs) indicates the optimal coupling gain threshold for a given number of RRC connected users in the cell (i.e., the number of connected users determined in operation 82). CG optim The function may depend on the radio propagation environment within the cell and may be implemented as a look-up table.

[0084] Variable CGMin thresh is the minimum value of the coupling gain threshold. It provides a lower limit below which device-specific CSI-RS can always be used (regardless of the number of connected devices in the cell). Setting a minimum coupling gain threshold ensures good cell-edge performance and coverage by using device-specific CSI-RS for extreme cell-edge user devices.

[0085] Therefore, the coupling gain threshold may be set to the maximum value of the coupling gain threshold defined based on the number of users of the RRC connection and the above minimum threshold.

[0086] Algorithm 80 may be repeated periodically to update the coupling gain threshold used in algorithm 70. However, this is not necessary for all example embodiments, as non-periodic updating of the coupling gain threshold is possible.

[0087] Fig. 9is a flow chart illustrating an algorithm, generally indicated by reference numeral 90 , according to an example embodiment.

[0088] Algorithm 90 begins at operation 92, where a coupling gain threshold CG thresh is set to a large value so that when the number of RRC connected users in the cell is small, any user admitted to the cell is configured with a device-specific CSI-RS resource.

[0089] At operation 94, the minimum coupling gain CGMin thresh is set to a specific value so that the coupling gain is less than CGMin thresh The very poor RF user is always configured with a device-specific CSI-RS resource, regardless of the number of RRC-connected users in the cell. This value can be found using simulations.

[0090] At operation 96, CSI-RS resources are allocated when the user is admitted to the cell. Operation 94 may be implemented using algorithm 70 described above.

[0091] In operation 96, the coupling gain is less than CG thresh Any user that is admitted to the cell will be assigned a device-specific CSI-RS resource, in which case the CSI-RS transmission and subsequent PDSCH transmission to the user will use the device-specific eigenbeam or the best GoB beam for the user. Furthermore, in one example embodiment, the user's assigned device-specific CSI-RS resources will continue to use the assigned resources for CSI-RS transmissions for the time that it is associated with the cell. In another embodiment, the device-specific CSI-RS resources may be assigned based on the current value of the coupling gain of the device and the CG thresh The current value of CG is used to re-evaluate the CSI-RS configuration of the user in a periodic or event-triggered manner. thresh A user) is allocated a common cell-specific CSI-RS resource, typically using a split-panel approach using a cell-specific beam, and the PDSCH transmission to the user will use the PMI reported by the user equipment.

[0092] At operation 98, the coupling gain threshold CG thresh Operation 98 may be implemented using algorithm 80 described above.

[0093] Coupling gain threshold CG thresh The value of depends on the propagation environment, load, number of RRC connected users, etc., and can be set independently in each cell. If there are significant differences in load or propagation environment across cells, different thresholds can be used across cells. The coupling gain threshold CG thresh You can find CG optim(#RRC connected UE) to periodically update, CG optim is a non-increasing function of the number of RRC-connected users in the cell. optim (#RRC connected UEs) can be implemented as a lookup table and is typically obtained from simulation results.

[0094] Algorithms 70 to 90 collectively describe a path loss based hybrid CSI-RS scheme that uses cell specific CSI-RS transmission for some RRC connected users in a cell and device specific CSI-RS transmission for other users, depending on the current number of RRC connected user devices and the path loss (or coupling gain) of the user devices. Based on the number of RRC connected user devices, the scheme may have three general regions as follows:

[0095] When the number of RRC-connected user equipments is small, the user equipments may be configured to use device-specific CSI-RS transmission.

[0096] When the number of RRC connected user equipment is large, most user equipment can use cell-specific CSI-RS transmission. The exception is user equipment with very large path loss (i.e., very small coupling gain) at the cell edge, whose performance will be very poor if device-specific CSI-RS transmission is not used.

[0097] In the middle region (i.e., between the two extremes above), there may be an adaptive threshold value that is used to determine which user equipment uses device-specific CSI-RS transmission and which user equipment uses cell-specific CSI-RS transmission. User equipment with coupling gain below the threshold receives device-specific CSI-RS, while user equipment with coupling gain above the threshold receives cell-specific CSI-RS configuration. The threshold value is also adapted so that the threshold value becomes smaller as the number of RRC-connected user equipment increases, thereby strengthening the requirement for user equipment to receive device-specific CSI-RS transmission.

[0098] Fig.10 1 is a graph according to an example embodiment, generally indicated by reference numeral 100. Graph 100 shows a geometric mean of user equipment throughput per cell as a function of the number of RRC connected user equipment for different values ​​of coupling gain threshold. As described above, the coupling gain threshold determines the user equipment that uses device-specific CSI-RS transmissions.

[0099] Specifically, the graph 100 includes a first graph 102 , a second graph 104 , a third graph 106 , and a fourth graph 108 , whose coupling gain thresholds are −130 dB, −138 dB, −142 dB, and −150 dB, respectively.

[0100] It can be clearly seen from the diagram 100 that in order to obtain the best performance when the number of RRC connected user equipment changes, the coupling gain threshold should be changed. In this way, it is possible to operate in the optimal envelope of all diagrams 102 to 108. Specifically, as the number of RRC connected user equipment increases, the optimal coupling gain threshold below which the user equipment should receive the device-specific CSI-RS is further reduced. Based on this, we can determine the above three solutions:

[0101] Region 1: UEs with a small number of RRC connections. The geometric mean performance in this region is best when all UEs use device-specific CSI-RS resources. Here, the higher beamforming gain associated with device-specific beams is more important than the larger CSI-RS resource overhead in the case of device-specific beams.

[0102] Region 2: User devices with a medium number of RRC connections. As the number of RRC connected users increases, the added CSI-RS overhead starts to impact throughput performance, so device-specific CSI-RS resources cannot be allocated to all users. As can be observed from graph 100, when there are more than about 100 RRC connected user devices, if the cell edge user devices exceed a certain path loss or fall below a coupling gain threshold, device-specific CSI-RS is used, and the remaining user devices use cell-specific CSI-RS, so that the best geometric mean performance can be achieved. This threshold gradually decreases as the number of RRC connected users increases, so as the number of RRC connected user devices increases, the user devices need to have a lower coupling gain to obtain device-specific CSI-RS resources.

[0103] Region 3: Large number of RRC connected user devices. As the number of RRC connected users increases further, it is better to switch to a scheme where all users in a cell use cell-specific CSI-RS resources, rather than using a hybrid scheme where a small fraction of users use device-specific CSI-RS resources. However, this may mean that the system may not be able to serve some poor RF users because the coverage of the cell-specific beams used with cell-specific CSI-RS transmissions is reduced. As mentioned above, this last problem can be solved by providing a minimum value for the coupling gain (CGMin thresh ) to solve the problem. For example, when the number of users connected by RRC is greater than a threshold (e.g., 500 users), the coupling gain threshold can be fixed to CGMin thresh , so that the coupling gain value is less than CGMin thresh All users of the cell are allocated device-specific CSI-RS resources, seeking to alleviate the very poor performance issue associated with cell-specific CSI-RS resources for extreme cell-edge user devices.

[0104] The adaptive thresholds in the current operating area and area 2 may be re-adjusted based on the current number of users in the RRC connection in the cell.

[0105] In addition, as described above, in order to avoid RRC reconfiguration messages, once a user is designated to use device-specific CSI-RS transmission, the user can continue to use device-specific CSI-RS transmission, that is, the user's CSI-RS resource remains unchanged until the handover occurs. In another embodiment, the user equipment can be based on the current coupling gain and parameter CG thresh The configuration of the cell-specific CSI-RS or device-specific CSI-RS of the user equipment is re-evaluated periodically or in an event-triggered manner based on the current value of

[0106] Fig.11 is a graph, generally indicated by reference numeral 110 , illustrating simulation results according to an example embodiment.

[0107] exist Fig.11 In , we compare the geometric mean performance (in the case of 10 active users) of the above hybrid (coupling gain based) CSI-RS transmission scheme with the hybrid (random) scheme against a baseline scheme where all users use cell-specific CSI-RS resources. Both hybrid schemes (i.e., path loss based and random hybrid schemes) allow the same number of users to receive device-specific CSI-RS transmissions. In addition, for the hybrid (random) scheme, a set of random user devices are configured for device-specific CSI-RS transmissions, while for the hybrid (coupling gain based) scheme, only users with path loss values ​​greater than a selected threshold (or, equivalently, coupling gain less than an appropriate threshold) are configured with device-specific CSI-RS resources. In both hybrid schemes, all other users are allocated cell-specific CSI-RS resources.

[0108] For the hybrid (coupling gain based) scheme, simulations were run for coupling gain thresholds of -130, -134, -138, and -146 dB corresponding to approximately 20%, 15%, 10%, and 5% of the users whose coupling gain was less than this threshold in the simulation. Accordingly, for the hybrid (random) scheme, simulations were performed with 20%, 15%, 10%, and 5% of the users randomly assigned device-specific CSI-RS resources. For each data point on graph 110, the percentage throughput gain of the hybrid (random) scheme relative to the baseline (cell-specific) transmission is plotted on the right, and the performance of the hybrid (coupling gain) scheme relative to the baseline transmission is plotted on the left.

[0109] exist Fig.11In Figure 2, we see that the hybrid (coupling gain based) scheme has a significant gain (>50%) at the cell edge compared to the baseline scheme, and has a 10-12% gain in the geometric mean of user equipment throughput. In contrast, the hybrid (random) scheme has only a 10-12% gain in terms of cell edge compared to the baseline scheme. As expected, the hybrid (random) scheme also performs better than the baseline scheme because a small fraction of users use device-specific CSI-RS transmissions (i.e., CSI-RS and data transmission) and these users will have higher rank and SINR and therefore higher throughput. The hybrid (random) scheme does not perform as well as the hybrid (coupling gain based) scheme because in the case of the hybrid (coupling gain based) scheme, cell edge users are preferentially allocated with device-specific CSI-RS resources.

[0110] Fig.12 is a flow chart illustrating an algorithm, generally indicated by reference numeral 120 , according to an example embodiment.

[0111] The algorithm 120 begins at operation 122, where a first group of one or more user equipment within a cell of a mobile communication system is operated in a device-specific CSI-RS operation mode, wherein the user equipment in the first group uses a device-specific reference signal transmission for determining channel state information. The user equipment may operate in the device-specific CSI-RS operation mode when a coupling gain determined for the corresponding user equipment is less than a coupling gain threshold.

[0112] At operation 124, a second group of one or more of the above user equipments within a cell of the mobile communication system is operated in a cell-specific CSI-RS operation mode, wherein the user equipments in the second group use a cell-specific reference signal transmission for determining channel state information in the cell-specific CSI-RS operation mode. In the case where the coupling gain determined for the corresponding user equipment is not less than a coupling gain threshold, the user equipment may operate in the cell-specific CSI-RS operation mode.

[0113] The algorithm 120 may be implemented using the system 10 in which the user equipment 14 to 17 operate in a device-specific operation mode or a cell-specific operation mode according to the coupling gain of the respective user equipment relative to a coupling gain threshold.

[0114] The above embodiments generally consider coupling gain and coupling gain threshold. As mentioned above, coupling gain is a measure of path loss, and the terms coupling gain and path loss can be used interchangeably in some cases.

[0115] For the sake of completeness, Fig.13is a schematic diagram of components of one or more of the previously described example embodiments, which are hereinafter collectively referred to as processing system 300. Processing system 300 may be, for example, an apparatus as recited in the following claims.

[0116] The processing system 300 may have a processor 302, a memory 304 tightly coupled to the processor and including a RAM 314 and a ROM 312, and an optional user input 310 and a display 318. The processing system 300 may include one or more network / device interfaces 308, which are used for connection to a network / device, for example, a wired or wireless modem. The network / device interface 308 may also operate as a connection with other devices, such as a device / device that is not a network-side device. Therefore, direct connection between devices / devices without network involvement is possible.

[0117] Processor 302 is connected to each of the other components to control their operation.

[0118] The memory 304 may include non-volatile memory, such as a hard disk drive (HDD) or a solid state drive (SSD). The ROM 312 of the memory 304 stores, among other things, an operating system 315, and may store software applications 316. The RAM 314 of the memory 304 is used by the processor 302 to temporarily store data. The operating system 315 may contain code that implements aspects of the algorithms 20, 70, 80, 90, and 120 described above when executed by the processor. Note that in the case of a small device / apparatus, the memory may be best suited for small size use, i.e., not always a hard disk drive (HDD) or a solid state drive (SSD).

[0119] Processor 302 may take any suitable form. For example, it may be a microcontroller, multiple microcontrollers, a processor, or multiple processors.

[0120] The processing system 300 may be a stand-alone computer, server, console or a network thereof. The processing system 300 and the required structural parts may all be inside a device / device such as an IoT device / apparatus, i.e., embedded in a very small size.

[0121] In some example embodiments, the processing system 300 may also be associated with external software applications. These may be applications stored on a remote server device / apparatus and may run partially or exclusively on the remote server device / apparatus. These applications may be referred to as cloud-hosted applications. The processing system 300 may communicate with the remote server device / apparatus in order to utilize the software applications stored there.

[0122] Fig.14A and Fig. 14B Tangible media storing computer readable code are shown, respectively a removable memory unit 365 and a compact disk (CD) 368, which can perform the method according to the above-described example embodiments when the computer is run. The removable memory unit 365 can be a memory stick, such as a USB memory stick, which has an internal memory 366 storing computer readable code. The internal memory 366 can be accessed by the computer system via a connector 367. The CD 368 can be a CD-ROM or DVD, etc. Other forms of tangible storage media can be used. The tangible medium can be any device / device capable of storing data / information that can be exchanged between devices / apparatus / networks.

[0123] Embodiments of the present invention may be implemented in software, hardware, application logic, or a combination of software, hardware, and application logic. The software, application logic, and / or hardware may reside in memory or on any computer medium. In an example embodiment, the application logic, software, or instruction set is maintained on any of a variety of conventional computer-readable media. In the context of this document, "memory" or "computer-readable medium" may be any non-transitory medium or device that can contain, store, convey, propagate, or transmit instructions for use by or in conjunction with an instruction execution system, device, or apparatus (such as a computer).

[0124] Where relevant, references to "computer-readable medium", "computer program product", "tangibly embodied computer program", etc., or "processor" or "processing circuit system", etc. should be understood to include not only computers with different architectures (such as single / multi-processor architectures and sequencer / parallel architectures), but also special-purpose circuits such as field-programmable gate arrays FPGAs, application-specific circuits ASICs, signal processing devices / apparatuses, and other devices / apparatuses. References to computer programs, instructions, codes, etc. should be understood to mean software for programmable processor firmware, such as programmable content of hardware devices / apparatuses as instructions for a processor, or configured settings or configuration settings for fixed-function devices / apparatuses, gate arrays, programmable logic devices / apparatuses, etc.

[0125] If desired, the different functions discussed herein may be performed in a different order and / or concurrently with each other. Furthermore, if desired, one or more of the above functions may be optional or may be combined. Similarly, it will also be understood that Figure 2 , Figure 7 , Figure 8 , Fig. 9 and Fig.12 The flowcharts are merely examples, and various operations described therein may be omitted, re-ordered, and / or combined.

[0126] It should be understood that the above exemplary embodiments are purely illustrative and do not limit the scope of the present invention.Other variations and modifications will be clear to those skilled in the art after reading this specification.

[0127] Furthermore, the disclosure of the present application should be understood to include any novel feature or any novel combination of features disclosed herein explicitly or implicitly, or any generalization thereof, and during the prosecution of the present application or any application derived therefrom, new claims may be formulated to cover any such feature and / or combination of such features.

[0128] Although various aspects of the invention are set out in the independent claims, further aspects of the invention comprise other combinations of features from the described example embodiments and / or the dependent claims with features of the independent claims, and not just the combinations explicitly set out in the claims.

[0129] It should also be noted herein that although various examples are described above, these descriptions should not be viewed in a limiting sense. Rather, several variations and modifications may be made without departing from the scope of the present invention as defined in the appended claims.

Claims

1. An apparatus for communication, comprising means for performing the following: determining a coupling gain of a user equipment within a cell of a mobile communication system, wherein the coupling gain is the gain from a transmitter to a receiver taking into account attenuation of a transmission signal due to distance between the equipment and transmitter and receiver antenna gains; comparing the determined coupling gain with a coupling gain threshold; In a case where the determined coupling gain is less than the coupling gain threshold, setting the user equipment to operate in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment is configured to use device-specific reference signal transmission for determining channel state information; as well as In a case where the determined coupling gain is not less than the coupling gain threshold, the user equipment is set to operate in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment is configured to use a cell-specific reference signal transmission for determining channel state information.

2. The apparatus of claim 1 , wherein the component is further configured to perform: The coupling gain threshold is set.

3. An apparatus according to claim 1 or claim 2, wherein the coupling gain threshold is at least partially based on a defined coupling gain threshold, the defined coupling gain threshold being based on the number of connected user equipments within the cell of the mobile communication system.

4. The apparatus of claim 3, wherein the component is further configured to perform: determining or obtaining the number of connected users within the cell of the mobile communication system; and The defined coupling gain threshold is set according to the number of connected users.

5. The apparatus of claim 3, wherein the coupling gain threshold is based at least in part on a minimum threshold. 6 . The apparatus of claim 5 , wherein the coupling gain threshold is the larger of the defined coupling gain threshold and the minimum threshold.

7. The apparatus according to claim 1 or claim 2, wherein when the user equipment remains in the cell of the mobile communication system, the set CSI-RS operation mode is maintained.

8. The apparatus according to claim 1 or claim 2, wherein the set CSI-RS operation mode is re-evaluated periodically or in response to an event, wherein the re-evaluation of the CSI-RS operation mode is based on the coupling gain and the coupling gain threshold of the user equipment when the CSI-RS operation mode is re-evaluated.

9. The apparatus of claim 1 or claim 2, wherein the component is further configured to perform: providing downlink reference signal transmission according to the set CSI-RS operation mode; and In response to providing the downlink reference signal transmission, channel state information is determined.

10. The apparatus of claim 1 or claim 2, wherein all user equipments within a cell operating in the device-specific CSI-RS operation mode use orthogonal resources for CSI-RS reference signal transmission.

11. The apparatus according to claim 1 or claim 2, wherein all user equipments within a cell operating in the cell-specific CSI-RS operation mode use the same resources for CSI-RS reference signal transmission.

12. The apparatus of claim 1 or claim 2, wherein the component comprises: at least one processor; as well as At least one memory including computer program code, the at least one memory and the computer program being configured to, together with the at least one processor, cause execution of the apparatus.

13. A method for communication, comprising: determining a coupling gain of a user equipment within a cell of a mobile communication system, wherein the coupling gain is the gain from a transmitter to a receiver taking into account attenuation of a transmission signal due to distance between the equipment and transmitter and receiver antenna gains; comparing the determined coupling gain with a coupling gain threshold; In a case where the determined coupling gain is less than the coupling gain threshold, setting the user equipment to operate in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment is configured to use device-specific reference signal transmission for determining channel state information; as well as In a case where the determined coupling gain is not less than the coupling gain threshold, the user equipment is set to operate in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment is configured to use a cell-specific reference signal transmission for determining channel state information.

14. A method for communication, comprising: operating a first group of one or more user equipments within a cell of a mobile communication system in a device-specific CSI-RS operation mode, wherein the user equipments in the first group use device-specific reference signal transmissions for determining channel state information, wherein the user equipments operate in the device-specific CSI-RS operation mode if a determined coupling gain for the respective user equipment is less than a coupling gain threshold, wherein the coupling gain is a gain from a transmitter to a receiver taking into account an attenuation of a transmission signal due to a distance between the devices and transmitter and receiver antenna gains; as well as One or more user equipments of a second group within the cell of the mobile communication system are operated in a cell-specific CSI-RS operation mode, wherein the user equipments in the second group use a cell-specific reference signal transmission for determining channel state information, wherein the user equipments operate in the cell-specific CSI-RS operation mode when the coupling gain determined for the corresponding user equipment is not less than the coupling gain threshold.

15. A computer program product comprising instructions for causing an apparatus to at least: determining a coupling gain of a user equipment within a cell of a mobile communication system, wherein the coupling gain is the gain from a transmitter to a receiver taking into account attenuation of a transmission signal due to distance between the equipment and transmitter and receiver antenna gains; comparing the determined coupling gain with a coupling gain threshold; In a case where the determined coupling gain is less than the coupling gain threshold, setting the user equipment to operate in a device-specific CSI-RS operation mode, wherein in the device-specific CSI-RS operation mode, the user equipment is configured to use device-specific reference signal transmission for determining channel state information; as well as In a case where the determined coupling gain is not less than the coupling gain threshold, the user equipment is set to operate in a cell-specific CSI-RS operation mode, wherein in the cell-specific CSI-RS operation mode, the user equipment is configured to use a cell-specific reference signal transmission for determining channel state information.

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