Method, apparatus, and medium for transmitting subspace selection

Abstract

Embodiments of the present disclosure provide techniques for a user equipment (UE) to receive reference signals from a base station in a downlink channel and to transmit a linear combination index from the UE to the base station. Specifically, the linear combination index identifies a beam combination selected from a beam set based on the RS.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to U.S. Non - Provisional Application No. 15 / 800,955, filed on November 1, 2017, entitled "System and Method for Transmitting a Sub - Space Selection", which in turn claims priority to U.S. Provisional Patent Application No. 62 / 417,832, filed on November 4, 2016, entitled "System and Method for Transmitting a Sub - Space Selection", the entire contents of which are incorporated herein by reference. Field of the Invention

[0003] The present disclosure generally relates to systems and methods for subspace selection and, in particular embodiments, to systems and methods for transmitting subspace selection. Background of the Invention

[0004] Wireless signals for high - carrier - frequency communications, such as millimeter - wave (MMW) signals, tend to exhibit high free - space path loss. To compensate for the high path - loss rate, next - generation telecommunication networks may utilize beamforming at the base station and the UE to take advantage of multipath propagation and improve system throughput and / or reliability. Implementing beamforming at the base station and the UE may significantly increase the complexity of underlying beam - management techniques. Summary of the Invention

[0005] Technical advantages are generally achieved by embodiments of the present disclosure that describe methods for transmitting subspace selection.

[0006] According to one embodiment, a method for subspace selection is provided. In this embodiment, the method includes a user equipment (UE) receiving a reference signal (RS) from a base station in a downlink channel, and transmitting a linear combination index from the UE to the base station. In this embodiment, the linear combination index identifies a beam combination selected from a beam set according to the RS. In one example, the linear combination index identifies the selected beam combination without identifying or explicitly indicating individual beams within the selected beam combination. Optionally, in this example, or in another example, the linear combination index belongs to a predefined set of linear combination indexes, and each predefined linear combination index in the predefined set of linear combination indexes identifies a different beam combination in the beam set. Optionally, in any of the above examples, or in another example, the method further includes the UE transmitting a rotation index to the base station. The rotation index identifies a selected rotation angle of a channel space that includes the beam set. The method further includes transmitting a channel quality index (CQI) corresponding to a weighted combination of the selected beams from the UE to the base station. Optionally, in any of the above examples, or in another example, the method further includes the UE calculating a channel estimate of the downlink channel according to the RS, wherein the UE selects the beam combination according to the channel estimate, and the UE transmits the selected rotation index to the base station. The beam combination is selected according to the calculated channel estimate. Optionally, in any of the above examples, or in another example, the RS is received in the downlink channel through different beams in the beam set. Optionally, in any of the above examples, or in another example, the RS is received in the downlink channel without precoding.

[0007] According to another embodiment, a method for subspace selection is provided. In this embodiment, the method includes transmitting RS from a base station to a user equipment (UE), and the base station receiving a linear combination index from the UE. In this embodiment, the linear combination index identifies a beam combination selected by the UE from a beam set according to the RS. In an example, the linear combination index identifies the selected beam combination without identifying individual beams within the selected beam combination. Optionally, in this example, or in another example, the linear combination index belongs to a predefined set of linear combination indexes, and each predefined linear combination index in the predefined set of linear combination indexes identifies a different beam combination in the beam set. Optionally, in any of the above examples, or in another example, the method further includes the base station receiving a rotation index from the UE, where the rotation index identifies a selected rotation angle of the beam set. In this embodiment, the method further includes the base station receiving a channel quality index (CQI) corresponding to a weighted combination of the selected beams. Optionally, in any of the above examples, or in another example, the RS is transmitted through different beams in the beam set. Optionally, in any of the above examples, or in another example, the RS is received in the downlink channel without precoding.

[0008] According to another embodiment, a user equipment is provided, which includes a processor and a non-transitory computer-readable medium storing a program for execution by the processor. In this embodiment, the program includes instructions for receiving RS from a base station in a downlink channel and transmitting a linear combination index to the base station, where the linear combination index identifies a beam combination selected from a beam set according to the RS. In an example, the linear combination index identifies the selected beam combination without identifying or explicitly indicating individual beams within the selected beam combination. Optionally, in this example, or in another example, the linear combination index belongs to a predefined set of linear combination indexes, and each predefined linear combination index in the predefined set of linear combination indexes identifies a different beam combination in the beam set. Optionally, in any of the above examples, or in another example, the program further includes instructions for transmitting a rotation index to the base station. The rotation index identifies a selected rotation angle of the beam set. The program further includes transmitting a channel quality index (CQI) corresponding to a weighted combination of the selected beams. Optionally, in any of the above examples, or in another example, the program further includes instructions for calculating a channel estimate of the downlink channel according to the RS, selecting a rotation index according to the calculated channel estimate, and transmitting the selected rotation index to the base station. The beam combination is selected according to the calculated channel estimate. Optionally, in any of the above examples, or in another example, the RS is received in the downlink channel through different beams in the beam set. Optionally, in any of the above examples, or in another example, the RS is received in the downlink channel without precoding.

[0009] According to another embodiment, a base station is provided, the base station includes a processor and a non-transitory computer-readable medium, the non-transitory computer-readable medium stores a program for execution by the processor. In this embodiment, the program includes instructions for transmitting RS to a user equipment (UE) and receiving a linear combination index from the UE. The linear combination index identifies a beam combination selected by the UE from a beam set according to the RS. In an example, the linear combination index identifies the selected beam combination without identifying or indicating individual beams within the selected beam combination. Optionally, in any of the above examples, or in another example, the linear combination index belongs to a predefined set of linear combination indexes. Each predefined linear combination index in the predefined set of linear combination indexes identifies a different beam combination in the beam set. Optionally, in any of the above examples, or in another example, the program further includes instructions for receiving a rotation index from the UE. The rotation index identifies a selected rotation angle of the beam set. The program further includes instructions for receiving a channel quality index (CQI) corresponding to a weighted combination of the selected beams. Optionally, in any of the above examples, or in another example, the RS is transmitted through different beams in the beam set. Optionally, in any of the above examples, or in another example, the RS is received in the downlink channel without precoding.

[0010] According to another embodiment, a method for transmitting channel state information is provided, the method includes a user equipment (UE) selecting a first set of beams from a beam codebook, wherein the first set of beams has a predefined order. The method further includes the UE transmitting a first set of indexes to a base station (BS), the first set of indexes uniquely identifying the first set of beams selected from the beam codebook, a first number of bits being used to represent the first set of beams, the first number being equal to where N is the number of codewords in the beam codebook and M is the number of beams in the first set of beams. In an example, each beam in the first set of beams is represented by a vector or a matrix. Optionally, in this example, or in another example, each beam of the beam codebook is represented by a vector or a matrix. Optionally, in any of the above examples, or in another example, the first number of bits is the number of bits before potential coding. Optionally, in any of the above examples, or in another example, the group index is determined by C1 + l, where x0, x1... x M-1 are the M beam indexes to be reported, C1 is an arbitrary constant, and l is equal to Optionally, in any of the above examples, or in another example, the group index is determined by C2–l, where x0, x1... x M-1 are the M beam indices to be reported, C2 is an arbitrary constant, and l is equal to Optionally, in any of the above examples, or in another example, the predefined order is specified in the standard text. Optionally, in any of the above examples, or in another example, the method further includes the UE receiving the predefined order in a signaling message. Optionally, in any of the above examples, or in another example, the predefined order is an ascending order list of beam indices. Optionally, in any of the above examples, or in another example, the predefined order is a descending order list of beam indices. Optionally, in any of the above examples, or in another example, in response to the first group index being adjacent to the second group index, the first group of beams is adjacent to the second group of beams, where the first group of beams is mapped to the first group index and the second group of beams is mapped to the second group index. Optionally, in any of the above examples, or in another example, in response to the last beam index of the first group of beams being adjacent to the last beam index of the second group of beams, and each of the other beam indices of the first group of beams being equal to the corresponding one of the other beam indices of the second group of beams, the first group of beams is adjacent to the second group of beams. Optionally, in any of the above examples, or in another example, in response to the first group index being sequentially before or after the second group index, the first group index is adjacent to the second group index. Optionally, in any of the above examples, or in another example, in response to the last beam index of the first group of beams having an index greater than or less than one of the last beam indices of the second group of beams, the last beam index of the first group of beams is adjacent to the last beam index of the second group of beams. Optionally, in any of the above examples, or in another example, in response to the first group index being greater than the second group index, the first group of beams is greater than the second group of beams, where the first group of beams is mapped to the first group index and the second group of beams is mapped to the second group index. Optionally, in any of the above examples, or in another example, in response to the N-ary representation of the second group index having M beam indices being greater than the N-ary representation of the first group index, the second group of beams is greater than the first group of beams, where the N-ary representation is equal to x1×N (M-1) +x (2) ×N (M-2) +…+x (M-1) ×N (10 +x (M0 ×N (0) , and x yis the beam index corresponding to the y-th beam index. Optionally, in any of the above examples, or in another example, the first set of beams and the second set of beams are one of the beam groups. Optionally, in any of the above examples, or in another example, in response to the second set of indices being greater than the first set of indices, the first set of beams is less than the second set of beams, where the first set of beams is mapped to the first set of indices and the second set of beams is mapped to the second set of indices. Optionally, in any of the above examples, or in another example, in response to the N-ary representation of the second set of indices having M beam indices being less than the N-ary representation of the first set of indices, the second set of beams is less than the first set of beams, where the N-ary representation is equal to x1×N (M-1) +x (2) ×N (M-2) +…+x (M-1) ×N (1) +x (M) ×N (0) , and x y is the beam index corresponding to the y-th beam index. Optionally, in any of the above examples, or in another example, the first set of beams and the second set of beams are one of the beam groups. Optionally, in any of the above examples, or in another example, the method further includes the UE transmitting a rotation index to the base station, the rotation index identifying a selected rotation angle of the channel space, the channel space including the beam set. In this embodiment, the method further includes the UE transmitting a channel quality index (CQI) corresponding to a weighted combination of the selected beams. Optionally, in any of the above examples, or in another example, the method further includes the UE calculating a channel estimate of the downlink channel based on a reference signal (RS), where a beam combination is selected according to the channel estimate; the UE selects a rotation index according to the channel estimate; and the UE transmits the rotation index to the base station.

[0011] According to another embodiment, a method for receiving channel state information is provided, the method including an access node receiving a first set of indices from a user equipment (UE), where the first set of indices uniquely identifies a first set of beams selected from a beam codebook, a first number of bits is used to represent the first set of beams, and the first number is equal to N is the number of codewords in the beam codebook, M is the number of beams in the first set of beams; and the access node maps the received first set of indices to the first set of beams selected from the beam codebook, wherein the first set of beams has a predefined order. In one example, each beam in the first set of beams is represented by a vector or a matrix. Optionally, in any of the above examples, or in another example, each beam of the beam codebook is represented by a vector or a matrix. Optionally, in any of the above examples, or in another example, the first number of bits is the number of bits before potential coding. Optionally, in any of the above examples, or in another example, the group index is determined by C1 + l, where x0, x1... x M-1 are the M beam indices to be reported, C1 is an arbitrary constant, and l is equal to Optionally, in any of the above examples, or in another example, the group index is determined by C2 – l, where x0, x1... x M-1 are the M beam indices to be reported, C2 is an arbitrary constant, and l is equal to

[0012] Optionally, in any of the above examples, or in another example, the predefined order is specified in a standard text. Optionally, in any of the above examples, or in another example, the method further includes the UE receiving the predefined order in a signaling message. Optionally, in any of the above examples, or in another example, the predefined order is an ascending order list of beam indices. Optionally, in any of the above examples, or in another example, the predefined order is a descending order list of beam indices. Optionally, in any of the above examples, or in another example, in response to the first set of indices being adjacent to the second set of indices, the first set of beams is adjacent to the second set of beams, where the first set of beams is mapped to the first set of indices and the second set of beams is mapped to the second set of indices. Optionally, in any of the above examples, or in another example, in response to the last beam index of the first set of beams being adjacent to the last beam index of the second set of beams and each of the other beam indices of the first set of beams being equal to the corresponding one of the other beam indices of the second set of beams, the first set of beams is adjacent to the second set of beams. Optionally, in any of the above examples, or in another example, in response to the first set of indices being sequentially before or after the second set of indices, the first set of indices is adjacent to the second set of indices. Optionally, in any of the above examples, or in another example, in response to the last beam index of the first set of beams having an index greater than or less than one of the last beam indices of the second set of beams, the last beam index of the first set of beams is adjacent to the last beam index of the second set of beams. Optionally, in any of the above examples, or in another example, in response to the first set of indices being greater than the second set of indices, the first set of beams is greater than the second set of beams, where the first set of beams is mapped to the first set of indices and the second set of beams is mapped to the second set of indices. Optionally, in any of the above examples, or in another example, in response to the N - ary representation of the second set of indices having M beam indices being greater than the N - ary representation of the first set of indices, the second set of beams is greater than the first set of beams, where the N - ary representation is equal to x1×N (M-1) +x (2) ×N (M-2) +…+x (M-1) ×N (1) +x (M) ×N (0) ; and x yis the beam index corresponding to the y-th beam index. Optionally, in any of the above examples, or in another example, the first set of beams and the second set of beams are one of the beam groups. Optionally, in any of the above examples, or in another example, in response to the second set of indices being greater than the first set of indices, the first set of beams is less than the second set of beams, where the first set of beams is mapped to the first set of indices, and the second set of beams is mapped to the second set of indices. Optionally, in any of the above examples, or in another example, in response to the N-ary representation of the second set of indices having M beam indices being less than the N-ary representation of the first set of indices, the second set of beams is less than the first set of beams, where the N-ary representation is equal to x1×N (M-1) +x (2) ×N (M-2) +…+x (M-1) ×N (1) +x (M) ×N (0) ; and x y is the beam index corresponding to the y-th beam index. Optionally, in any of the above examples, or in another example, the first set of beams and the second set of beams are one of the beam groups. Optionally, in any of the above examples, or in another example, the method further includes the access node receiving a rotation index from the UE, where the rotation index identifies a selected rotation angle of a beam set in the beam codebook; and the access node receiving a channel quality index (CQI) corresponding to the first set of beams.

[0013] According to a first exemplary embodiment of the present disclosure, a method for subspace selection is provided. The method includes a user equipment (UE) selecting a first combination of beams from N different beams, where the N different beams form a basis for a channel space, and the beams form a basis for a subspace of the channel space. The method further includes the UE transmitting a descriptor of the first combination to a base station. The descriptor includes a linear combination index or a bitmap. The bitmap will include N bits, each bit corresponding to a different one of the N beams, where N is an integer greater than 1.

[0014] According to a second exemplary embodiment of the present disclosure, a user equipment is provided. The user equipment includes a processor and a non-transitory computer-readable medium storing a program for execution by the processor. The program includes instructions for selecting a first combination of beams from N different beams, the N different beams forming a basis for a channel space, and the beams forming a basis for a subspace of the channel space. The program further includes instructions for transmitting a descriptor of the first combination to a base station. The descriptor includes a linear combination index or a bitmap. The bitmap will include N bits, each bit corresponding to a different one of the N beams, where N is an integer greater than 1.

[0015] According to a third exemplary embodiment of the present disclosure, a base station is provided. The base station includes a processor and a non-transitory computer-readable medium storing a program for execution by the processor. The program includes instructions for transmitting a reference signal to a user equipment (UE) via a communication channel corresponding to a channel space formed by a basis including N different beams. The program further includes instructions for receiving a descriptor of a first combination of beams from the UE, the beams forming a basis for a subspace of the channel space. The descriptor includes a linear combination index or a bitmap. The bitmap will include N bits, each bit corresponding to a different one of the N beams. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To more fully understand the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0017] Figure 1 is a diagram of an exemplary wireless communication network;

[0018] Figure 2 is a flowchart of an exemplary method for operating a user equipment (UE) and transmitting a linear combination index;

[0019] Figure 3 is a flowchart of an exemplary method for operating a base station and receiving a linear combination index;

[0020] Figure 4 is a flowchart of an exemplary method for operating a UE and transmitting CSI feedback;

[0021] Figure 5 is a flowchart of an exemplary method for operating a base station and receiving CSI feedback;

[0022] Figure 6It is a schematic diagram with bundling for an implementation example of channel weighting;

[0023] Figure 7 It is a flowchart of another embodiment method for operating a base station and receiving CSI feedback;

[0024] Figure 8 It is a schematic diagram of an embodiment processing system; and

[0025] Figure 9 It is a schematic diagram of an embodiment transceiver. Detailed Description of the Embodiments

[0026] The present disclosure provides many applicable inventive concepts that can be embodied in a variety of specific situations. The specific embodiments discussed are merely illustrative of particular configurations and do not limit the scope of the present disclosure. For example, although the embodiments of the present disclosure will be described in the specific context of a downlink channel from a base station to a User Equipment (UE), these embodiments are equally applicable to the uplink from a multi-antenna UE to a base station, or to any other air communication link originating from a device with multiple antennas. As used herein, the term "beam direction" refers to a set of radio antenna patterns or beamforming weights for directional signal transmission and / or reception. The terms "beam direction" and "beam" may be used interchangeably herein.

[0027] As described above, implementing beamforming at the UE and the base station can increase the complexity of beam management techniques such as beam scanning and / or beam tracking. Beam scanning is typically performed during or just before link establishment in order to identify which pair of beam directions will be used for initial data transmission / reception. Conventional beam scanning schemes typically require the UE to select a subset of beams based on reference signals received from the base station, and subsequently feedback a corresponding list of beam indices to the base station. The selected subset of beams can then be used to schedule sounding reference signal (SRS) transmissions, which can be evaluated to produce a better estimate of the channel in order to select an appropriate TX and RX beam pair for initial data transmission.

[0028] Embodiments of the present disclosure reduce the signaling overhead associated with beam scanning by feeding back a linear combination index that identifies the selected subset of beams rather than a list of indices of individual beams in the subset. Since the linear combination index identifies the selected beam "combination", the number of bits used to represent the linear combination index is typically less than the number of bits required to transmit the corresponding list of individual beam indices, thereby reducing the signaling overhead. In some embodiments, the linear combination index belongs to a predefined set of linear combination indices, and each predefined linear combination index in the set identifies a different combination of available beams.

[0029] In one embodiment, the UE receives a reference signal (RS) from the base station in the downlink channel and calculates a channel estimate based on the RS. The UE selects a beam combination from a set of available beams according to the calculated channel estimate. The UE transmits a linear combination index to the base station, and the linear combination index identifies the selected beam combination. In one embodiment, the UE transmits a channel quality index (CQI) corresponding to the selected beam combination to the base station. In this embodiment, the UE selects a rotation angle for rotating the channel space, and the channel space includes the set of available beams. The UE then transmits a rotation index to the base station, and the rotation index identifies the rotated channel space. The UE selects the rotation angle according to the channel estimate.

[0030] In one embodiment, the base station transmits the RS to the UE in the downlink channel. In this embodiment, the base station receives a linear combination index from the UE, for example as CSI feedback. The base station uses the linear combination index to identify the beam combination selected by the UE from the set of available beams. The base station uses the identified beam combination to communicate with the UE. In one embodiment, the linear combination index identifies the selected beam combination without explicitly indicating or identifying individual beams in the selected beam combination. In another example, the linear combination index belongs to a set of predefined linear combination indexes. In this example, each predefined linear combination index in the set of predefined linear combination indexes identifies a different beam combination in the set of available beams. In yet another example, the RS is transmitted through different beams in the beam set in the downlink channel. In yet another embodiment, the base station receives a rotation index from the UE. In this embodiment, the rotation index identifies the rotation angle of the rotated channel space, and the channel space includes the set of available beams selected by the UE. In one embodiment, the base station receives the CQI corresponding to the selected beam combination from the UE. In some embodiments, each beam in the linear combination index is represented by a vector. In some other embodiments, each beam in the linear combination index is represented by a bit matrix.

[0031] In one embodiment, in the case of a DFT codebook, the UE may receive RS transmitted from 32 ports of the base station, resulting in a full-space basis of 16 beams due to polarization. Then, the UE may feedback a beam index for each of the 4 selected beams, where each of these beam indices must include at least 4 bits since there are a total of 16 beams. The total number of bits required to feedback the subspace descriptor will be 4 x 4 = 16 bits. If this system is only designed for no more than 16-bit feedback of the subspace descriptor, when using a separate beam index feedback scheme, the UE may select no more than 4 beams. Alternatively, if a 16-bit bitmap is used as the subspace descriptor, the UE may change the number of selected beams from 1 to 16 based on local conditions without additional signaling.

[0032] Advantageously, compared to feedbacking all selected beam indices, the linear combination index used as the subspace descriptor can reduce the overhead. For example, when the UE is to select 4 beams from a channel space fully represented by 16 beams, there may be different combinations. Accordingly, this linear combination index can be represented with as few bits as possible. Therefore, compared to feedbacking all 4 selected beam indices, this linear combination index can reduce the overhead, as previously mentioned, this linear combination would require at least 16 bits.

[0033] The equation: can be used to calculate the number of bits representing each group of beams in the linear combination index of the beams. In this equation, the smallest integer of the logarithm (base 2) of the binomial coefficient represents the number of bits for a group. The formula can be used to calculate the binomial coefficient In this embodiment, N represents the number of codewords in the beam codebook, and M is the number of beams in the beam group.

[0034] Figure 1A network 100 for transmitting data is shown. The network 100 includes a base station 110 having a coverage area 101, a plurality of UEs 115, and a backhaul network 130. As shown, the base station 110 establishes an uplink (dashed line) and / or a downlink (dotted line) connection with the UEs 115, which are used to transmit data from the UEs 115 to the base station 110 and vice versa. The data carried through the uplink / downlink connection may include data transmitted between the UEs 115, as well as data transmitted to or from a remote terminal (not shown) through the backhaul network 130. As used herein, the term "base station" refers to any component (or collection of components) used to provide wireless access to a network, such as an enhanced base station (eNB), a macro cell, a femtocell base station, a Wi-Fi access point (AP), or other wireless-enabled devices. The base station may provide wireless access according to one or more wireless communication protocols, such as Long Term Evolution (LTE), LTE Advanced (LTE-A), High Speed Packet Access (HSPA), Wi-Fi 802.11a / b / g / n / ac, etc. As used herein, the term "UE" refers to any component (or collection of components) capable of establishing a wireless connection with a base station, such as a mobile device, a mobile station (STA), and other wireless-enabled devices. In some embodiments, the network 100 may include various other wireless devices, such as repeaters, low-power nodes, etc.

[0035] Figure 2 It is a flowchart of an exemplary method 200 that can be executed by a UE for receiving RS and transmitting a selected beam group to a base station. In step 202, the UE receives RS from the base station in a downlink channel. In one embodiment, the UE may receive RS from the base station through a receiving beam. In another embodiment, the RS may be received without beamforming, such as in a non-precoded channel state information reference signal (CSI-RS) in an LTE network. In yet another embodiment, the RS may be beamformed in the downlink channel, but the UE may receive the RS without receiving beamforming, such as in multiple-input multiple-output (MIMO) type B in an LTE network.

[0036] In step 204, the UE calculates a channel estimate of the downlink channel based on the RS. In step 206, in a subspace of the channel space between the UE and the base station, where the channel space has a basis formed by a set of available beams, the UE selects a beam combination that forms the subspace basis. The beam combination selected by the UE is consistent with the channel estimate calculated in step 204. In step 208, the UE determines a linear combination index from a predefined set of linear combination indices, where the linear combination index identifies the selected beam combination. In the predefined set of linear combination indices, each predefined linear combination index identifies a different combination of the beams of the set of available beams. The linear combination index identifies the selected combination of beams without identifying or explicitly indicating each individual beam in the selected combination of beams. In step 210, the UE transmits the linear combination index to the base station.

[0037] Figure 3 is a flowchart of an exemplary method 300 that can be performed by a base station for transmitting the RS and receiving the selected beam set from the UE. In step 302, the base station transmits the RS to the UE in the downlink channel. As previously described, with reference to Figure 2 , in some embodiments, the RS can be transmitted via beams, and in other embodiments, the RS can be transmitted to the UE without beamforming. In step 304, the base station receives a linear combination index from the UE in response to the transmitted RS. In step 306, the base station identifies a beam set in the channel space that beamforms the basis of the subspace that the UE has selected. In step 308, the base station can use the same predefined set of linear combination indices to identify the beam set. The base station then communicates with the UE using the beam set.

[0038] Figure 4 is a flowchart of an exemplary method 400 that can be performed by a UE for receiving the RS and sending the selected beam set as CSI feedback to the base station. In step 402, the UE receives the RS from the base station in the downlink channel. As previously described, with reference to Figure 2 , in some embodiments, the RS can be received via beams, and in other embodiments, the RS can be received without beamforming.

[0039] In step 404, the UE calculates a channel estimate of the downlink channel based on the RS. In some embodiments, the UE can also perform channel estimation through the channel space, where the UE models the channel space as having an orthogonal basis of, for example, N different beams. In one embodiment, when calculating the channel estimate, the channel space model can also be rotated P times.

[0040] In one embodiment, the channel space model can be rotated P times to support P - fold oversampling in the spatial domain. This rotation is used to better align the channel space model with the optimal signal path. The codebook used for this channel estimation can be, for example, a discrete Fourier transform (DFT) - based codebook, such as the DFT - based codebook used in LTE Release 13.

[0041] In a massive MIMO environment where a large number of base stations and UEs utilize MIMO technology, channel statistics such as channel correlation or the channel covariance matrix (CCM) are typically used to determine channel state information (CSI). The CCM can be used to estimate high - dimensional channels and / or transform high - dimensional channels into low - dimensional subspaces, which reduces the effective channel size. In step 406, the UE derives a downlink channel covariance matrix (DCCM) based on a channel space model with a full - space basis. In step 408, the UE selects one or more eigenvectors in the covariance matrix. In step 410, in a subspace of the channel space where the channel space has a basis formed by a set of available beams, the UE selects the subspace. The beam combination selected by the UE is at least consistent with the principal eigenvectors of the covariance matrix determined in step 406. As the rank of the channel covariance matrix increases, an increasing number of eigenvectors can be used for subspace selection.

[0042] In one embodiment with oversampling, where the basis of the channel subspace can have a non - orthogonal basis, the UE can also select one of the P rotation angles of the rotated channel space. The channel subspace has a basis of M different beams selected from N total beams, where M is less than or equal to N. The UE maps the eigenvectors onto the selected M - beam subspace to calculate M channel weights. The channel weights can include quantized phase and amplitude coefficients, and the base station uses these phase and amplitude coefficients to precode transmissions over a specific frequency band. When the frequency band is divided into sub - bands, various channel weighting protocols can be used to provide different granularities of channel weights for different sub - bands, either increased or decreased. In an exemplary channel weighting protocol, the UE feeds back different phase and amplitude coefficients for each corresponding sub - band. Thus, the channel quality can be improved at the cost of high feedback overhead. For example, when a 20 - MHz frequency band is divided into 13 sub - bands and 3 - bit phase coefficients and 3 - bit amplitude coefficients are used for each sub - band, then 13×(3 + 3)=78 bits are used for channel weight feedback.

[0043] In step 412, the UE determines a linear combination index that identifies a subspace from a set of predefined linear combination indices. In the set of predefined linear combination indices, each predefined linear combination index identifies a subspace of the entire spatial basis. The linear combination index identifies the subspace without identifying or explicitly indicating each individual beam within the subspace. In step 414, the UE determines a channel quality index (CQI) for the subspace corresponding to each set of channel weights.

[0044] In an embodiment with oversampling, a rotation index that describes the selected rotation angle is selected. In step 416, the UE determines a rotation index that corresponds to the selected rotation angle of a rotated space that includes the full spatial basis. For example, a 3-bit rotation index can indicate up to 8 different rotation angles to support 8-fold oversampling in the spatial domain.

[0045] In step 418, the UE transmits CSI feedback to the base station, and the CSI feedback includes the linear combination index, the channel quality index (CQI), and the rotation angle of the rotated space.

[0046] Figure 5 is a flowchart of an exemplary method 500 that can be performed by a base station for transmitting RSs and receiving CSI feedback from a UE. In step 502, the base station transmits RSs to the UE in a downlink channel. As described above, with reference to Figure 2 , in some embodiments, the RSs can be transmitted via beams, and in other embodiments, the RSs can be transmitted to the UE without beamforming. The base station transmits reference signals to the UE. In step 504, the base station receives CSI feedback from the UE. The CSI feedback can include the linear combination index, the rotation index, and the weighting factor, as well as the associated channel quality index. In step 506, the base station can use the linear combination index in the CSI feedback to identify a beam combination that forms the basis of the subspace of the channel space. A channel subspace is selected from the channel space identified by the UE. In step 508, the base station uses the channel quality index to identify the channel quality index of the selected beam combination, where the selected beam combination is identified using the linear combination index. In step 510, the base station can use the rotation index to identify the selected rotation angle in the channel space model and rotate the selected rotation angle to support oversampling in the spatial domain. The base station communicates with the UE using the information from the CSI feedback and at least one of the channel subspace, the rotation angle, the weighting factor, and the channel quality index.

[0047] In some embodiments, the descriptor of the selected beam combination can be an N-bit bitmap. In this bitmap, each bit corresponds to the selection of a beam; if a specific bit element in the bitmap is set to 1, this value indicates that the corresponding beam is selected, while a bit with a value of zero indicates that the corresponding beam is not selected. In other embodiments, the reverse of this logic can be used.

[0048] Relative to a single index that feedbacks all the selected beams, the bitmap used as the subspace descriptor can increase system flexibility by allowing the number of selected beams to vary. Allowing the number of selected beams to vary can achieve a better performance-overhead tradeoff. In some deployment scenarios, for example, in line-of-sight conditions, the UE will only need to feedback one selected path from the base station to the UE. However, in other deployments, a cluster of paths covering a larger angular spread may be required to effectively represent the communication channel. To cover this larger angular spread, several beams may need to be selected as the basis of the channel subspace. However, if the indices of all the selected beams are feedback, the number of feedback bits required increases as the number of selected beams increases.

[0049] Figure 6 An embodiment showing a band 600 subdivided into subbands 604 is presented, where the previously described exemplary channel weighting protocol is modified to allow subband bundling. Subbands 604 within a specific frequency range can be grouped together into bundles with potentially different bandwidths. The UE can then calculate different phase and amplitude coefficients for each bundle 604. In Figure 6 the embodiment, the frequency range 602 can be, for example, 20 MHz wide. This frequency range 602 is divided into 13 subbands 604, which are labeled S1 to S13. S1 and S2 are grouped as a first subband bundle 606, S3 to S12 are grouped as a second subband bundle 608, and S13 is a third subband bundle 610. CSI feedback can then include 3 amplitude bits and 3 phase bits for each of these three bundles, resulting in (3 + 3) x 3 = 18 channel weighting bits. In one embodiment, the base station can direct subband bundling based on channel conditions to provide a performance-overhead tradeoff. For example, the base station can bundle subbands at a granularity sufficient to provide a minimum number of feedback bits to achieve a predetermined performance level.

[0050] Figure 7 is a flowchart of an exemplary method 700 that can be performed by a base station for transmitting descriptors of RS and subband bundling to a UE and receiving CSI feedback. In step 702, the base station selects a subband bundling in a frequency band and divides the frequency band into subbands according to channel conditions. Each subband can be bundled as part of a subband bundle, as previously referenced Figure 6As described above. In step 704, the base station transmits a sub-band bundle descriptor with RS in the downlink channel to the UE. In one embodiment, the RS may be LTE unprecoded CSI-RS. In another embodiment, the RS may be in a MIMO Class B LTE network. In some embodiments, the sub-band bundle descriptor may be included in a transmission that is different and distinct from the reference signal. In step 706, the base station receives CSI feedback transmitted by the UE. The CSI feedback indicates the subspace selected by the UE and the channel weights calculated by the UE based on the selected sub-band bundle. The channel subspace selected by the UE has a basis of M different beams selected from N total beams in the entire channel space, where M is less than or equal to N. In embodiments where the UE uses spatial oversampling, the CSI feedback may further include a rotation index that describes the rotation angle selected from P rotation angles. The descriptor of the selected subspace included in the CSI may be an N-bit bitmap or a linear combination index.

[0051] In step 708, the base station uses the CSI feedback to identify the selected channel subspace. The base station may use the linear combination index in the CSI feedback to identify the beam combination that forms the basis of the subspace of the channel space. The channel subspace is selected from the channel space identified by the UE. In step 710, the base station identifies the channel weights based on the CSI feedback. In addition to the channel weighting protocols already described, other channel weighting protocols may also be used. In another exemplary protocol, the same amplitude coefficients are used across the entire frequency band, but different phase coefficients are used on different sub-bands, which may reduce the channel quality while saving overhead. For example, a 20 MHz frequency band may have 3-bit amplitude coefficients and may be divided into 13 sub-bands, each with 3-bit phase coefficients, resulting in (13×3)+3 = 42 channel weighting bits, with a performance loss of approximately 6% compared to using all 78 channel weighting bits. In yet another exemplary protocol, the differential amplitude of each corresponding sub-band may be used in combination with the amplitude over the entire frequency range, while different phase coefficients are still used for each corresponding sub-band. For example, 2 wideband amplitude bits, 1 differential amplitude bit per sub-band, and 3 phase bits per sub-band may be used. For 13 sub-bands, this example will result in a feedback of 13×(1+3)+2 = 54 channel weighting bits.

[0052] In step 712, the base station transmits precoded data to the UE based on the selected M beams and the identified channel weights.

[0053] In an embodiment where the descriptor for beam combination is a linear combination index, the UE selects M beams (M less than or equal to N) from a set of N available beams. In this embodiment, an M×1 index vector x can be formed. The index vector x includes M elements, each element including the corresponding index of a different one of the M selected beams. The N beams are classified according to a certain order, and the beam order is known to both the base station and the UE. The beam order of the M selected beams in x follows the same order, and a linear function can then uniquely map all possible values of the index vector x to a unique scalar l in R 1 In other words, the linear combination index l = a0x0 + a1x1 + … + a M-1 x M-1 is a scalar with a value that provides a unique mapping to R 1 where a0, a1, …, a M-1 .

[0054] For example, when N equals 16 and M equals 4, the UE can calculate the linear combination index by using Equation 1 below:

[0055]

[0056] More generally, for any number M of beams selected from N total beams, the linear combination index can be calculated using Equation 2 below:

[0057]

[0058] In another embodiment, where the beam reporting index is where the combined number can be calculated using Equation 3 below:

[0059]

[0060] Use a combined coefficient table to report the index i 1,2 , where for a given L and (N1, N2), rows 0, …, N1N2 - 1 and columns 1, ……, L are used.

[0061] In the mapping from [n1, n2] to i 1,2 the beam ordering can be identified as (assigning the index i such that n (i) increases as i increases). Thus the index where C(x, y) is the set of combined coefficients.

[0062] In the mapping from i 1,2 to [n1, n2], use i 1,2and obtain i = 0,.., L-1, e from the combination coefficient table i = C(x * , L-i).

[0063] n (i) = N1N2 - 1 - x *

[0064]

[0065] When iterating through i = 0, 1,.., L-1, where s1 = 0, the maximum x * ∈ {L-1-i, …, N1N2-1-i} belongs to i 1,2 - s i-1 ≥ C(x * , L-i), for calculating e i = C(x * , L-i), s i = s i-1 + e i .

[0066] It should be noted that Equation 2 is equal to Equation 3. Assuming N = N1N2 and n = n (i) , Equation 2 = C(N, M) - Equation 3.

[0067] The beam indices in the predefined linear combination of indices can have a predefined order or sorting. In one embodiment, the predefined order of the beams can be ascending. In this embodiment, each beam in the linear combination has an increasingly ordered number, where the first beam index is less than the last beam index. In an alternative embodiment, the predefined order of the beams can be descending. In this embodiment, each beam in the linear combination has a decreasing order, where the first beam index is greater than the last beam index. In one embodiment, the order is specified in the standard text. In another embodiment, a signaling message can be used to signal the predefined order of the predefined index linear combination from the base station to the UE.

[0068] When the corresponding group indices are adjacent to each other, the beam groups in the linear combination of indices can be referred to as adjacent to each other. When the last beam indices of each group of beams are adjacent to each other and all other indices of the group match, the group of beams can also be referred to as adjacent to each other. In this embodiment, the last beam indices of adjacent groups are separated by a single index.

[0069] In one embodiment, the index of each group of beams is directly related to its corresponding beam group. For example, a group of beams with an index greater than the second group of beams also has a larger group of beams. The reverse is also true.

[0070] The group size can be determined by the N-ary representation of the group. The N-ary representation is equal to x1 × N(M-1) +x (2) ×N (M-2) +…+x (M-1) ×N (1) +x (M) ×N (0) In this equation, x y represents the y-th beam index of a set of beams having M beam indices.

[0071] Figure 8 FIG. shows a block diagram of a processing system 800 for performing the methods described herein. The processing system 800 may be installed in a host device. As shown, the processing system 800 includes a processor 804, a memory 806, and interfaces 810 - 814, and these components may (or may not) be arranged as shown in Figure 8 . The processor 804 may be any component or collection of components for performing computations and / or other processing-related tasks, and the memory 806 may be any component or collection of components for storing programs and / or instructions for execution by the processor 804. In one embodiment, the memory 806 includes a non-transitory computer-readable medium. The interfaces 810, 812, 814 may be any component or collection of components that allow the processing system 800 to communicate with other devices / components and / or users. For example, one or more of the interfaces 810, 812, 814 may be used to transfer data, control, or management messages from the processor 804 to an application installed on the host device and / or a remote device. As another example, one or more of the interfaces 810, 812, 814 may be used to allow a user or user device (e.g., a personal computer (PC), etc.) to interact / communicate with the processing system 800. The processing system 800 may include Figure 8 additional components not shown in

[0072] , such as long-term memory (e.g., non-volatile memory, etc.).

[0073] In some embodiments, one or more of interfaces 810, 812, 814 connect processing system 800 to a transceiver for transmitting and receiving signaling over a telecommunications network. Figure 9 A block diagram of transceiver 900 adapted to transmit and receive signaling over a telecommunications network is shown. The transceiver 900 may be installed in a host device. As shown, the transceiver 900 includes a network side interface 902, a coupler 904, a transmitter 906, a receiver 908, a signal processor 910, and a device side interface 912. The network side interface 902 may include any component or collection of components for transmitting or receiving signaling over a wireless or wired telecommunications network. The coupler 904 may include any component or collection of components for facilitating two-way communication over the network side interface 902. The transmitter 906 may include any component or collection of components for converting a baseband signal into a modulated carrier signal suitable for transmission over the network side interface 902 (e.g., an upconverter, a power amplifier, etc.). The receiver 908 may include any component or collection of components for converting a carrier signal received over the network side interface 902 into a baseband signal (e.g., a downconverter, a low noise amplifier, etc.). The signal processor 910 may include any component or collection of components for converting a baseband signal into a data signal suitable for communication over the device side interface 912, or vice versa. The device side interface 912 may include any component or collection of components for conveying data signals between the signal processor 910 and components within the host device (e.g., processing system 800, a local area network (LAN) port, etc.).

[0074] The transceiver 900 can transmit and receive signaling through any type of communication medium. In some embodiments, the transceiver 900 transmits and receives signaling through a wireless medium. For example, the transceiver 900 can be a wireless transceiver for communicating according to a radio communication protocol, such as a cellular protocol (e.g., Long Term Evolution (LTE), etc.), a wireless local area network (WLAN) protocol (e.g., Wi-Fi, etc.), or any other type of wireless protocol (e.g., Bluetooth, near field communication (NFC), etc.). In this embodiment, the network-side interface 902 includes one or more antennas / radiating elements. For example, the network-side interface 902 can include a single antenna, multiple separate antennas, or a multi-antenna array for multi-layer communication such as single-input multiple-output (SIMO), multiple-input single-output (MISO), multiple-input multiple-output (MIMO), etc. In other embodiments, the transceiver 900 transmits and receives signaling through a wired medium such as a twisted pair cable, coaxial cable, optical fiber, etc. A particular processing system and / or transceiver may utilize all of the illustrated components or only a subset of the illustrated components, and the degree of integration between devices may vary.

[0075] It should be understood that one or more steps of the method of the embodiments provided herein can be performed by corresponding units or modules. For example, a signal can be transmitted by a transmitting unit or a transmitting module. A signal can be received by a receiving unit or a receiving module. A signal can be processed by a processing unit or a processing module. A signal can be selected by a selecting unit or a storage module. The corresponding unit / module can be hardware, software, or a combination thereof. For example, one or more unit / module can be an integrated circuit, such as an FPGA or an ASIC.

[0076] Although the description has been detailed, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. In addition, the scope of the present invention is not intended to be limited to the specific embodiments described herein, and those of ordinary skill in the art will readily appreciate from the present invention that processes, machines, manufacturing processes, compositions of matter, components, methods, or steps (including those that exist currently or will be developed in the future) can perform substantially the same functions as the corresponding embodiments described herein or achieve substantially the same effects as the corresponding embodiments described herein. Accordingly, the scope of the appended claims includes such processes, machines, manufactures, compositions of matter, components, methods, and steps.

[0077] The advantage of the illustrative embodiments is that using CSI feedback in a communication network provides a higher channel resolution for improved precoding and / or multi-user scheduling. Relative to codebook feedback or beam index feedback, the embodiments provide the advantages of reduced overhead and / or improved beam selection flexibility while still maintaining communication performance.

[0078] Although the invention has been described with reference to the illustrative embodiments, such description is not intended to limit the invention. Those skilled in the art will appreciate various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, after reference to this description. Accordingly, the appended claims are intended to cover any such modifications or embodiments.

Claims

1. A communication method, characterized in that, Comprising: Receiving a reference signal RS from a base station BS; Selecting M beams from N beams according to the reference signal RS, any one of the M beams corresponding one-to-one to one of M indexes; Transmit a first index to the base station BS, where the first index is determined based on the M indices, the first index is carried by a first bit, the first index indicates the M beams through the first bit, and the first bit occupies bits; Wherein, the first index is determined according to the following formula ； Among them, the M indexes include x0, x 1, …, x M-1 , where M is an integer greater than 1 and less than or equal to N, and N is an integer greater than or equal to 2.

2. The method according to claim 1, wherein When M = 2, the formula is as follows: .

3. The method according to claim 1 or 2, characterized in that, Any two of the M indexes are different, and any two of the M beams are different.

4. The method according to claim 1 or 2, characterized in that less than , .

5. A communication method, characterized in that, Comprising: Sending a reference signal RS to a user equipment UE on N beams; Receive a first index from the UE, where the first index indicates M beams through a first bit, and the first bit occupies bits; Determining M indexes according to the first index; Wherein, the first index is determined according to the following formula ； Among them, the M indexes include x0, x 1, …, x M-1 , where M is an integer greater than 1 and less than or equal to N, and N is an integer greater than or equal to 2.

6. The method according to claim 5, wherein When M = 2, the formula is as follows: .

7. The method according to claim 5 or 6, characterized in that, Any two of the M indexes are different, and any two of the M beams are different.

8. The method according to claim 5 or 6, characterized in that, Less than , .

9. A communication device, characterized in that, Comprising a module for implementing the method according to any one of claims 1-4.

10. The communication device according to claim 9, wherein The communication device comprises a user equipment UE.

11. A communication device, characterized in that, Comprising a module for implementing the method according to any one of claims 5-8.

12. The communication device according to claim 11, wherein The communication device comprises an access point device.

13. A computer-readable storage medium, characterized in that, The computer storage medium stores computer-readable instructions, which when executed, cause the method according to any one of claims 1-4 to be implemented.

14. A computer-readable storage medium, characterized in that, The computer storage medium stores computer-readable instructions, which when executed, cause the method according to any one of claims 5-8 to be implemented.

15. A computer program product, characterized in that, When the computer program product is run, the method according to any one of claims 1-4 is caused to be implemented.

16. A computer program product, characterized in that, When the computer program product is run, the method according to any one of claims 5-8 is caused to be implemented.

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