WO2020030848A1

WO2020030848A1 - Exploiting receiver antenna correlation in time-compression-based csi feedback scheme

Info

Publication number: WO2020030848A1
Application number: PCT/FI2019/050561
Authority: WO
Inventors: Rana Ahmed Salem; Eugene Visotsky; Frederick Vook; William Hillery
Original assignee: Nokia Technologies Oy
Priority date: 2018-08-09
Filing date: 2019-07-26
Publication date: 2020-02-13

Abstract

A method includes receiving channel state information reference signals from a base station for computing channel state information feedback (1602); constructing a time domain channel matrix from the channel state information reference signals (1602); measuring a level of correlation among the received signals having a common polarization (1604); determining, depending on the measured level of correlation, whether to use a feedback reduction scheme or no feedback reduction scheme (1606); and informing the base station that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used (1608). An alternative method includes receiving channel state information reference signals from a base station for computing channel state information feedback; constructing a time domain channel matrix from the channel state information reference signals; measuring a level of correlation among the received signals having a common polarization; transmitting the level of correlation to the base station; receiving information from the base station whether to use a feedback reduction scheme or no feedback reduction scheme; and using the feedback reduction scheme or no feedback reduction scheme as instructed by the base station.

Description

EXPLOITING RECEIVER ANTENNA CORRELATION IN TIME-COMPRESSION-BASED CSI FEEDBACK SCHEME

TECHNICAL FIELD

This disclosure is related to the provision of channel state information feedback information from a user equipment to a base station.

BACKGROUND

In FDD (frequency-division duplex) systems, and in some TDD (time- division duplex) systems, such as those lacking proper calibration, a UE (user equipment) has to send DL (downlink) channel information back to the gNB (base station) due to the absence of channel reciprocity. The gNB uses this information to build DL precoding matrices. In LTE (long-term evolution) and NR (new radio) phase I, the UE sends back one or more indices known as PMIs (Precoding Matrix Indicators), which point to one or more code words in a predetermined codebook shared by the UE and gNB. The codebook is based on DFT (discrete Fourier transform) precoding (see 3GPP TS 36.211, Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 13), and 3GPP TS 38.211, VI.0.0 (2017-09), Technical Specification Group Radio Access Network; NR; Physical channels and modulation (Release 15)).

For NR phase II, in order to obtain a more accurate description of the channel at the gNB, there is a need for improved MU-MIMO (multi-user multi-input multi-output) performance and more advanced schemes, such as non-linear precoding, CoMP (coordinated multi-point) transmission or IFA (interference alignment).

The explicit feedback of the CIR (channel impulse response) can also be reported for an effective beam- formed channel, as is shown in Figure 1. For example, by employing a GoB (grid of beams)

precoder 100, the dimensions of the channel reduce from M X N, where M is the number of transmit antennas and N is the number of receive antennas to B X V, where B is the number of transmit beams employed, that is, 5 = 2i if two polarizations are used at the transmitter side where L is the number of beams per polarization. A natural consequence of that is having narrower beams with higher gains, and a sparser CIR in the time domain, due to channel hardening (see Marzetta, T., Larsson, E., Yang, H., & Ngo, H. (2016). Fundamentals of Massive MIMO. Cambridge: Cambridge University Press). In addition, the number of reference signals needed to train the whole system is reduced accordingly. The CIR sent back (CIR feedback 102) is then of dimension , where N_T is the whole time delay range of the CIR (sampled

in taps) in one path. Note that the sparsity of the time domain signal means that B*N*N_T is much higher than the actual number of significant channel taps across all paths, which we denote here by k_taps, that is,

.

The time domain channel information can be represented using the time domain channel matrix:

where c_p(n_s) is the complex coefficient on the p^tn path (out of N X B paths) and significant tap # ¾. A path is defined as the channel between transmit antenna (or transmit beam) and a receive antenna (or a receive beam). Note that the elements in should be normalized to the strongest element such that the maximum element is

normalized to 1 at 0 degrees. The time domain channel matrix can also be built such that the different paths are assigned in columns and the different taps are assigned to rows, i.e. of d . Depending on the way the time domain channel matrix is built, the

overhead reduction schemes will operate on rows (in case of or on columns

It has been proposed in International Application No.

PCT/CN2018/083114, the teachings of which are incorporated herein by reference, to feed back the whole matrix

or part of using a bit mask. The feedback

overhead in the first case is in the second case the

feedback overhead is where should increase with the

increase of the number of paths N X B.

As can be seen, the feedback overhead increases linearly with the product of the number of receive antennas and number of antenna ports. In NR, one UE can have up to eight receive antennas, which, in such a case of a time domain compression feedback scheme, can lead to a huge feedback overhead which cannot be supported. The present invention seeks to reduce CSI feedback overhead, but is not limited to this purpose.

SUMMARY

In a first aspect of the present invention, a method comprises receiving channel state information reference signals from a base station for computing channel state information feedback; constructing a time domain channel matrix from the channel state information reference signals; measuring a level of correlation among the received signals having a common polarization; determining, depending on the measured level of correlation, whether to use a feedback reduction scheme or no feedback reduction scheme; and informing the base station that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

In a second aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: receive channel state information reference signals from a base station for computing channel state information feedback; construct a time domain channel matrix from the channel state information reference signals; measure a level of correlation among the received signals having a common polarization; determine, depending on the measured level of correlation, whether to use a feedback reduction scheme or no feedback reduction scheme; and inform the base station that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

In a third aspect of the present invention, an apparatus comprises means for receiving channel state information reference signals from a base station for computing channel state information feedback; means for constructing a time domain channel matrix from the channel state information reference signals; means for measuring a level of correlation among the received signals having a common polarization; means for determining, depending on the measured level of correlation, whether to use a feedback reduction scheme or no feedback reduction scheme; and means for informing the base station that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used. In a fourth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: receiving channel state information reference signals from a base station for computing channel state information feedback; constructing a time domain channel matrix from the channel state information reference signals; measuring a level of correlation among the received signals having a common polarization; determining, depending on the measured level of correlation, whether to use a feedback reduction scheme or no feedback reduction scheme; and informing the base station that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

In a fifth aspect of the present invention, a method comprises transmitting channel state information reference signals to a user equipment for computing channel state information feedback; and receiving information from the user equipment that the user equipment is to use a feedback reduction scheme or that the user equipment is to use no feedback reduction scheme.

In a sixth aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: transmit channel state information reference signals to a user equipment for computing channel state information feedback; and receive information from the user equipment that the user equipment is to use a feedback reduction scheme or that the user equipment is to use no feedback reduction scheme.

In a seventh aspect of the present invention, an apparatus comprises means for transmitting channel state information reference signals to a user equipment for computing channel state information feedback; and means for receiving information from the user equipment that the user equipment is to use a feedback reduction scheme or that the user equipment is to use no feedback reduction scheme.

In an eighth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: transmitting channel state information reference signals to a user equipment for computing channel state information feedback; and receiving information from the user equipment that the user equipment is to use a feedback reduction scheme or that the user equipment is to use no feedback reduction scheme.

In a ninth aspect of the present invention, a method comprises receiving channel state information reference signals from a base station for computing channel state information feedback; constructing a time domain channel matrix from the channel state information reference signals; measuring a level of correlation among the received signals having a common polarization; transmitting the level of correlation to the base station; receiving information from the base station whether to use a feedback reduction scheme or no feedback reduction scheme; and using the feedback reduction scheme or no feedback reduction scheme as instructed by the base station.

In a tenth aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: receive channel state information reference signals from a base station for computing channel state information feedback; construct a time domain channel matrix from the channel state information reference signals; measure a level of correlation among the received signals having a common polarization; transmit the level of correlation to the base station; receive information from the base station whether to use a feedback reduction scheme or no feedback reduction scheme; and use the feedback reduction scheme or no feedback reduction scheme as instructed by the base station.

In an eleventh aspect of the present invention, an apparatus comprises means for receiving channel state information reference signals from a base station for computing channel state information feedback; means for constructing a time domain channel matrix from the channel state information reference signals; means for measuring a level of correlation among the received signals having a common polarization; means for transmitting the level of correlation to the base station; means for receiving information from the base station user equipment whether to use a feedback reduction scheme based on one of receiver antenna subsampling, differential quantization, and a reduced overhead bit mask; or to use no feedback reduction scheme; and means for using the feedback reduction scheme or no feedback reduction scheme as instructed by the base station.

In a twelfth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: receiving channel state information reference signals from a base station for computing channel state information feedback; constructing a time domain channel matrix from the channel state information reference signals; measuring a level of correlation among the received signals having a common polarization; transmitting the level of correlation to the base station; receiving information from the base station user equipment whether to use a feedback reduction scheme based on one of receiver antenna subsampling, differential quantization, and a reduced overhead bit mask; or to use no feedback reduction scheme; and using the feedback reduction scheme or no feedback reduction scheme as instructed by the base station.

In a thirteenth aspect of the present invention, a method comprises transmitting channel state information reference signals to a user equipment for computing channel state information feedback; receiving a measured level of correlation among the signals having common polarization from the user equipment; determining, depending on the measured level of correlation, whether the user equipment is to use a feedback reduction scheme or no feedback reduction scheme; and informing the user equipment that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

In a fourteenth aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: transmit channel state information reference signals to a user equipment for computing channel state information feedback; receive a measured level of correlation among the signals having common polarization from the user equipment; determine, depending on the measured level of correlation, whether the user equipment is to use a feedback reduction scheme or no feedback reduction scheme; and inform the user equipment that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

In a fifteenth aspect of the present invention, an apparatus comprises means for transmitting channel state information reference signals to a user equipment for computing channel state information feedback; means for receiving a measured level of correlation among the signals having common polarization from the user equipment; means for determining, depending on the measured level of correlation, whether the user equipment is to use a feedback reduction scheme or no feedback reduction scheme; and means for informing the user equipment that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

In a sixteenth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: transmitting channel state information reference signals to a user equipment for computing channel state information feedback; receiving a measured level of correlation among the signals having common polarization from the user equipment; determining, depending on the measured level of correlation, whether the user equipment is to use a feedback reduction scheme or no feedback reduction scheme; and informing the user equipment that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

In a seventeenth aspect of the present invention, a method comprises constructing a time domain channel matrix from reference signals received from a base station; constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; finding a strongest path in the amplitude subset matrix; constructing a phase subset matrix containing phase information for the elements in the subset matrix; constructing a row subset matrix for the strongest path in the amplitude subset matrix; constructing a quantization for the row subset matrix; constructing a quantization for the phase subset matrix; and sending the quantization for the row subset matrix and the quantization for the phase subset matrix to the base station.

In an eighteenth aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: construct a time domain channel matrix from reference signals received from a base station; construct a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; construct an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; find a strongest path in the amplitude subset matrix; construct a phase subset matrix containing phase information for the elements in the subset matrix; construct a row subset matrix for the strongest path in the amplitude subset matrix; construct a quantization for the row subset matrix; construct a quantization for the phase subset matrix; and send the quantization for the row subset matrix and the quantization for the phase subset matrix to the base station.

In a nineteenth aspect of the present invention, an apparatus comprises means for constructing a time domain channel matrix from reference signals received from a base station; means for constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; means for constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; means for finding a strongest path in the amplitude subset matrix; means for constructing a phase subset matrix containing phase information for the elements in the s subset matrix; means for constructing a row subset matrix for the strongest path in the amplitude subset matrix; means for constructing a quantization for the row subset matrix; means for constructing a quantization for the phase subset matrix; and means for sending the quantization for the row subset matrix and the quantization for the phase subset matrix to the base station.

In a twentieth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: constructing a time domain channel matrix from reference signals received from a base station; constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; finding a strongest path in the amplitude subset matrix; constructing a phase subset matrix containing phase information for the elements in the subset matrix; constructing a row subset matrix for the strongest path in the amplitude subset matrix; constructing a quantization for the row subset matrix; constructing a quantization for the phase subset matrix; and sending the quantization for the row subset matrix and the quantization for the phase subset matrix to the base station.

In a twenty-first aspect of the present invention, a method comprises receiving channel state information feedback from a user equipment in the form of a quantization for a row subset matrix for a strongest path in an amplitude subset matrix and a quantization for a phase subset matrix; reconstructing the phase subset matrix from the quantization of the phase subset matrix; reconstructing the amplitude subset matrix from the quantization of the row subset matrix; reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a twenty-second aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: receive channel state information feedback from a user equipment in the form of a quantization for a row subset matrix for a strongest path in an amplitude subset matrix and a quantization for a phase subset matrix; reconstruct the phase subset matrix from the quantization of the phase subset matrix; reconstruct the amplitude subset matrix from the quantization of the row subset matrix; reconstruct a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstruct a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a twenty-third aspect of the present invention, an apparatus comprises means for receiving channel state information feedback from a user equipment in the form of a quantization for a row subset matrix for a strongest path in an amplitude subset matrix and a quantization for a phase subset matrix; means for reconstructing the phase subset matrix from the quantization of the phase subset matrix; means for reconstructing the amplitude subset matrix from the quantization of the row subset matrix; means for reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and means for reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a twenty-fourth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: receiving channel state information feedback from a user equipment in the form of a quantization for a row subset matrix for a strongest path in an amplitude subset matrix and a quantization for a phase subset matrix; reconstructing the phase subset matrix from the quantization of the phase subset matrix; reconstructing the amplitude subset matrix from the quantization of the row subset matrix; reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment. In a twenty-fifth aspect of the present invention, a method comprises constructing a time domain channel matrix from reference signals received from a base station; constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; finding a strongest path in the amplitude subset matrix; constructing a phase subset matrix containing phase information for the elements in the subset matrix; constructing a row subset matrix for the strongest path in the amplitude subset matrix; constructing a quantization for the row subset matrix; constructing a quantization for the phase subset matrix; constructing a differential subset matrix using the amplitude subset matrix and the quantization of the row subset matrix; constructing a quantization of the differential subset matrix; and sending the quantization for the row subset matrix, the quantization for the phase subset matrix, the quantization for the differential subset matrix, and the strongest path in the amplitude subset matrix to the base station.

In a twenty-sixth aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: construct a time domain channel matrix from reference signals received from a base station; construct a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; construct an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; find a strongest path in the amplitude subset matrix; construct a phase subset matrix containing phase information for the elements in the subset matrix; construct a row subset matrix for the strongest path in the amplitude subset matrix; construct a quantization for the row subset matrix; construct a quantization for the phase subset matrix; construct a differential subset matrix using the amplitude subset matrix and the quantization of the row subset matrix; construct a quantization of the differential subset matrix; and send the quantization for the row subset matrix, the quantization for the phase subset matrix, the quantization for the differential subset matrix, and the strongest path in the amplitude subset matrix to the base station.

In a twenty-seventh aspect of the present invention, an apparatus comprises means for constructing a time domain channel matrix from reference signals received from a base station; means for constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; means for constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; means for finding a strongest path in the amplitude subset matrix; means for constructing a phase subset matrix containing phase information for the elements in the subset matrix; means for constructing a row subset matrix for the strongest path in the amplitude subset matrix; means for constructing a quantization for the row subset matrix; means for constructing a quantization for the phase subset matrix; means for constructing a differential subset matrix using the amplitude subset matrix and the quantization of the row subset matrix; means for constructing a quantization of the differential subset matrix; and means for sending the quantization for the row subset matrix, the quantization for the phase subset matrix, the quantization for the differential subset matrix, and the strongest path in the amplitude subset matrix to the base station.

In a twenty-eighth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: constructing a time domain channel matrix from reference signals received from a base station; constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; finding a strongest path in the amplitude subset matrix; constructing a phase subset matrix containing phase information for the elements in the subset matrix; constructing a row subset matrix for the strongest path in the amplitude subset matrix; constructing a quantization for the row subset matrix; constructing a quantization for the phase subset matrix; constructing a differential subset matrix using the amplitude subset matrix and the quantization of the row subset matrix; constructing a quantization of the differential subset matrix; and sending the quantization for the row subset matrix, the quantization for the phase subset matrix, the quantization for the differential subset matrix, and the strongest path in the amplitude subset matrix to the base station.

In a twenty-ninth aspect of the present invention, a method comprises receiving channel state information feedback from a user equipment in the form of a quantization for a row subset matrix for a strongest path in an amplitude subset matrix, a quantization for a phase subset matrix, a quantization for a differential subset matrix, and a strongest path in the amplitude subset matrix from a user equipment; reconstructing a row of the amplitude subset matrix having a strongest path with elements of the quantization of the row subset matrix; reconstructing remaining rows of the amplitude subset matrix with the quantization of the differential subset matrix; reconstructing the phase subset matrix from the quantization of the phase subset matrix; reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a thirtieth aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: receive channel state information feedback from a user equipment in the form of a quantization for a row subset matrix for a strongest path in an amplitude subset matrix, a quantization for a phase subset matrix, a quantization for a differential subset matrix, and a strongest path in the amplitude subset matrix from a user equipment; reconstruct a row of the amplitude subset matrix having a strongest path with elements of the quantization of the row subset matrix; reconstruct remaining rows of the amplitude subset matrix with the quantization of the differential subset matrix; reconstruct the phase subset matrix from the quantization of the phase subset matrix; reconstruct a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstruct a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a thirty-first aspect of the present invention, an apparatus comprises means for receiving channel state information feedback from a user equipment in the form of a quantization for a row subset matrix for a strongest path in an amplitude subset matrix, a quantization for a phase subset matrix, a quantization for a differential subset matrix, and a strongest path in the amplitude subset matrix from a user equipment; means for reconstructing a row of the amplitude subset matrix having a strongest path with elements of the quantization of the row subset matrix; means for reconstructing remaining rows of the amplitude subset matrix with the quantization of the differential subset matrix; means for reconstructing the phase subset matrix from the quantization of the phase subset matrix; means for reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and means for reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a thirty-second aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: receiving channel state information feedback from a user equipment in the form of a quantization for a row subset matrix for a strongest path in an amplitude subset matrix, a quantization for a phase subset matrix, a quantization for a differential subset matrix, and a strongest path in the amplitude subset matrix from a user equipment; reconstructing a row of the amplitude subset matrix having a strongest path with elements of the quantization of the row subset matrix; reconstructing remaining rows of the amplitude subset matrix with the quantization of the differential subset matrix; reconstructing the phase subset matrix from the quantization of the phase subset matrix; reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a thirty-third aspect of the present invention, a method comprises constructing a time domain channel matrix from reference signals received from a base station; constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; finding a strongest path in the amplitude subset matrix; constructing a phase subset matrix containing phase information for the elements in the subset matrix; constructing a row subset matrix for the strongest path in the amplitude subset matrix; storing the strongest path in the amplitude subset matrix into a part of a new amplitude subset matrix; storing the phase subset matrix into a part of a new phase subset matrix; storing the strongest path location in the amplitude subset matrix into an element of a strongest path indices vector; constructing a bit mask subset matrix based on the new amplitude subset matrix, wherein elements of said bit mask subset matrix are“1”, when a corresponding tap is significant, and“0”, when the corresponding tap is not significant; constructing a bit mask by repetition of the bit mask subset matrix; constructing a quantization for the new phase subset matrix for locations in the bit mask equal to“1”; constructing a quantization for the new amplitude subset matrix for locations in the bit mask subset matrix equal to“1”; and sending the bit mask subset matrix, the quantization for the new phase subset matrix, and the quantization for the new amplitude subset matrix to the base station.

In a thirty- fourth aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: construct a time domain channel matrix from reference signals received from a base station; construct a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; construct an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; find a strongest path in the amplitude subset matrix; construct a phase subset matrix containing phase information for the elements in the subset matrix; construct a row subset matrix for the strongest path in the amplitude subset matrix; store the strongest path in the amplitude subset matrix into a part of a new amplitude subset matrix; store the phase subset matrix into a part of a new phase subset matrix; store the strongest path location in the amplitude subset matrix into an element of a strongest path indices vector; construct a bit mask subset matrix based on the new amplitude subset matrix, wherein elements of said bit mask subset matrix are“1”, when a corresponding tap is significant, and“0”, when the corresponding tap is not significant; construct a bit mask by repetition of the bit mask subset matrix; construct a quantization for the new phase subset matrix for locations in the bit mask equal to“1”; construct a quantization for the new amplitude subset matrix for locations in the bit mask subset matrix equal to“1”; and send the bit mask subset matrix, the quantization for the new phase subset matrix, and the quantization for the new amplitude subset matrix to the base station.

In a thirty-fifth aspect of the present invention, an apparatus comprises means for constructing a time domain channel matrix from reference signals received from a base station; means for constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; means for constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; means for finding a strongest path in the amplitude subset matrix; means for constructing a phase subset matrix containing phase information for the elements in the subset matrix; means for constructing a row subset matrix for the strongest path in the amplitude subset matrix; means for storing the strongest path in the amplitude subset matrix into a part of a new amplitude subset matrix; means for storing the phase subset matrix into a part of a new phase subset matrix; means for storing the strongest path location in the amplitude subset matrix into an element of a strongest path indices vector; means for constructing a bit mask subset matrix based on the new amplitude subset matrix, wherein elements of said bit mask subset matrix are“1”, when a corresponding tap is significant, and“0”, when the corresponding tap is not significant; means for constructing a bit mask by repetition of the bit mask subset matrix; means for constructing a quantization for the new phase subset matrix for locations in the bit mask equal to“1”; means for constructing a quantization for the new amplitude subset matrix for locations in the bit mask subset matrix equal to“1”; and means for sending the bit mask subset matrix, the quantization for the new phase subset matrix, and the quantization for the new amplitude subset matrix to the base station.

In a thirty-sixth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: constructing a time domain channel matrix from reference signals received from a base station; constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; finding a strongest path in the amplitude subset matrix; constructing a phase subset matrix containing phase information for the elements in the subset matrix; constructing a row subset matrix for the strongest path in the amplitude subset matrix; storing the strongest path in the amplitude subset matrix into a part of a new amplitude subset matrix; storing the phase subset matrix into a part of a new phase subset matrix; storing the strongest path location in the amplitude subset matrix into an element of a strongest path indices vector; constructing a bit mask subset matrix based on the new amplitude subset matrix, wherein elements of said bit mask subset matrix are “1”, when a corresponding tap is significant, and“0”, when the corresponding tap is not significant; constructing a bit mask by repetition of the bit mask subset matrix; constructing a quantization for the new phase subset matrix for locations in the bit mask equal to“1”; constructing a quantization for the new amplitude subset matrix for locations in the bit mask subset matrix equal to“1”; and sending the bit mask subset matrix, the quantization for the new phase subset matrix, and the quantization for the new amplitude subset matrix to the base station. In a thirty-seventh aspect of the present invention, a method comprises receiving channel state information feedback from a user equipment in the form of a bit mask subset matrix, a quantization for a new phase subset matrix, and a quantization for a new amplitude subset matrix; constructing a bit mask vector from a corresponding row of the bit mask subset matrix; constructing a new bit mask subset matrix by repetition of the bit mask vector; constructing an amplitude subset matrix from the quantization of the new amplitude subset matrix using the new bit mask subset matrix; constructing a phase subset matrix from the quantization of the new phase subset matrix; reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a thirty-eighth aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: receive channel state information feedback from a user equipment in the form of a bit mask subset matrix, a quantization for a new phase subset matrix, and a quantization for a new amplitude subset matrix; construct a bit mask vector from a corresponding row of the bit mask subset matrix; construct a new bit mask subset matrix by repetition of the bit mask vector; construct an amplitude subset matrix from the quantization of the new amplitude subset matrix using the new bit mask subset matrix; construct a phase subset matrix from the quantization of the new phase subset matrix; reconstruct a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstruct a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a thirty-ninth aspect of the present invention, an apparatus comprises means for receiving channel state information feedback from a user equipment in the form of a bit mask subset matrix, a quantization for a new phase subset matrix, and a quantization for a new amplitude subset matrix; means for constructing a bit mask vector from a corresponding row of the bit mask subset matrix; means for constructing a new bit mask subset matrix by repetition of the bit mask vector; means for constructing an amplitude subset matrix from the quantization of the new amplitude subset matrix using the new bit mask subset matrix; means for constructing a phase subset matrix from the quantization of the new phase subset matrix; means for reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and means for reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a fortieth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: receiving channel state information feedback from a user equipment in the form of a bit mask subset matrix, a quantization for a new phase subset matrix, and a quantization for a new amplitude subset matrix; constructing a bit mask vector from a corresponding row of the bit mask subset matrix; constructing a new bit mask subset matrix by repetition of the bit mask vector; constructing an amplitude subset matrix from the quantization of the new amplitude subset matrix using the new bit mask subset matrix; constructing a phase subset matrix from the quantization of the new phase subset matrix; reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a forty-first aspect of the present invention, a method comprises constructing a time domain channel matrix from reference signals received from a base station; constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; finding a strongest path in the amplitude subset matrix; constructing a phase subset matrix containing phase information for the elements in the subset matrix; constructing a row subset matrix for the strongest path in the amplitude subset matrix; constructing a quantization for the row subset matrix; constructing a differential subset matrix using the amplitude subset matrix and the quantization of the row subset matrix; storing the strongest path in the amplitude subset matrix into a part of a new amplitude subset matrix; storing the phase subset matrix into a part of a new phase subset matrix; storing the strongest path location in the amplitude subset matrix into an element of a strongest path indices vector; storing the differential subset matrix into a part of a new differential subset matrix; constructing a bit mask subset matrix based on the new amplitude subset matrix, wherein elements of said bit mask subset matrix are“1”, when a corresponding tap is significant, and“0”, when the corresponding tap is not significant; constructing a bit mask by repetition of the bit mask subset matrix; constructing a quantization for the new phase subset matrix for locations in the bit mask equal to“1”; constructing a quantization for the new amplitude subset matrix for locations in the bit mask subset matrix equal to“1”; constructing a quantization for the new differential subset matrix for locations in the bit mask equal to“1”; and sending the bit mask subset matrix, the quantization for the new phase subset matrix, the quantization for the new amplitude subset matrix, and the quantization for the new differential subset matrix to the base station.

In a forty-second aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: construct a time domain channel matrix from reference signals received from a base station; construct a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; construct an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; find a strongest path in the amplitude subset matrix; construct a phase subset matrix containing phase information for the elements in the subset matrix; construct a row subset matrix for the strongest path in the amplitude subset matrix; construct a quantization for the row subset matrix; construct a differential subset matrix using the amplitude subset matrix and the quantization of the row subset matrix; store the strongest path in the amplitude subset matrix into a part of a new amplitude subset matrix; store the phase subset matrix into a part of a new phase subset matrix; store the strongest path location in the amplitude subset matrix into an element of a strongest path indices vector; store the differential subset matrix into a part of a new differential subset matrix; construct a bit mask subset matrix based on the new amplitude subset matrix, wherein elements of said bit mask subset matrix are “1”, when a corresponding tap is significant, and“0”, when the corresponding tap is not significant; construct a bit mask by repetition of the bit mask subset matrix; construct a quantization for the new phase subset matrix for locations in the bit mask equal to“1”; construct a quantization for the new amplitude subset matrix for locations in the bit mask subset matrix equal to“1”; construct a quantization for the new differential subset matrix for locations in the bit mask equal to“1”; and send the bit mask subset matrix, the quantization for the new phase subset matrix, the quantization for the new amplitude subset matrix, and the quantization for the new differential subset matrix to the base station. In a forty-third aspect of the present invention, an apparatus comprises means for constructing a time domain channel matrix from reference signals received from a base station; means for constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; means for constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; means for finding a strongest path in the amplitude subset matrix; means for constructing a phase subset matrix containing phase information for the elements in the subset matrix; means for constructing a row subset matrix for the strongest path in the amplitude subset matrix; means for constructing a quantization for the row subset matrix; means for constructing a differential subset matrix using the amplitude subset matrix and the quantization of the row subset matrix; means for storing the strongest path in the amplitude subset matrix into a part of a new amplitude subset matrix; means for storing the phase subset matrix into a part of a new phase subset matrix; means for storing the strongest path location in the amplitude subset matrix into an element of a strongest path indices vector; means for storing the differential subset matrix into a part of a new differential subset matrix; means for constructing a bit mask subset matrix based on the new amplitude subset matrix, wherein elements of said bit mask subset matrix are“1”, when a corresponding tap is significant, and“0”, when the corresponding tap is not significant; means for constructing a bit mask by repetition of the bit mask subset matrix; means for constructing a quantization for the new phase subset matrix for locations in the bit mask equal to“1”; means for constructing a quantization for the new amplitude subset matrix for locations in the bit mask subset matrix equal to “1”; means for constructing a quantization for the new differential subset matrix for locations in the bit mask equal to“1”; and means for sending the bit mask subset matrix, the quantization for the new phase subset matrix, the quantization for the new amplitude subset matrix, and the quantization for the new differential subset matrix to the base station.

In a forty-fourth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: constructing a time domain channel matrix from reference signals received from a base station; constructing a subset matrix from the time domain channel matrix, said subset matrix containing channel coefficients corresponding to a common polarization; constructing an amplitude subset matrix containing the magnitudes of the elements in the subset matrix; finding a strongest path in the amplitude subset matrix; constructing a phase subset matrix containing phase information for the elements in the subset matrix; constructing a row subset matrix for the strongest path in the amplitude subset matrix; constructing a quantization for the row subset matrix; constructing a differential subset matrix using the amplitude subset matrix and the quantization of the row subset matrix; storing the strongest path in the amplitude subset matrix into a part of a new amplitude subset matrix; storing the phase subset matrix into a part of a new phase subset matrix; storing the strongest path location in the amplitude subset matrix into an element of a strongest path indices vector; storing the differential subset matrix into a part of a new differential subset matrix; constructing a bit mask subset matrix based on the new amplitude subset matrix, wherein elements of said bit mask subset matrix are“1”, when a corresponding tap is significant, and“0”, when the corresponding tap is not significant; constructing a bit mask by repetition of the bit mask subset matrix; constructing a quantization for the new phase subset matrix for locations in the bit mask equal to“1”; constructing a quantization for the new amplitude subset matrix for locations in the bit mask subset matrix equal to“1”; constructing a quantization for the new differential subset matrix for locations in the bit mask equal to“1”; and sending the bit mask subset matrix, the quantization for the new phase subset matrix, the quantization for the new amplitude subset matrix, and the quantization for the new differential subset matrix to the base station.

In a forty-fifth aspect of the present invention, a method comprises receiving channel state information feedback from a user equipment in the form of a bit mask subset matrix, a quantization for a new phase subset matrix, a quantization for a new amplitude subset matrix, and a quantization for a new differential subset matrix from a user equipment; constructing a bit mask vector from a corresponding row of the bit mask subset matrix; constructing a new bit mask subset matrix by repetition of the bit mask vector; constructing a row of an amplitude subset matrix corresponding to the strongest path in the new amplitude subset matrix from the quantization of the new amplitude subset matrix using the new bit mask subset matrix and a location of a strongest path; reconstructing remaining rows of the amplitude subset matrix using the new differential subset matrix; reconstructing the phase subset matrix from the quantization of the new phase subset matrix; reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a forty-sixth aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: receive channel state information feedback from a user equipment in the form of a bit mask subset matrix, a quantization for a new phase subset matrix, a quantization for a new amplitude subset matrix, and a quantization for a new differential subset matrix from a user equipment; construct a bit mask vector from a corresponding row of the bit mask subset matrix; construct a new bit mask subset matrix by repetition of the bit mask vector; construct a row of an amplitude subset matrix corresponding to the strongest path in the new amplitude subset matrix from the quantization of the new amplitude subset matrix using the new bit mask subset matrix and a location of a strongest path; reconstruct remaining rows of the amplitude subset matrix using the new differential subset matrix; reconstruct the phase subset matrix from the quantization of the new phase subset matrix; reconstruct a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstruct a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a forty-seventh aspect of the present invention an apparatus comprises means for receiving channel state information feedback from a user equipment in the form of a bit mask subset matrix, a quantization for a new phase subset matrix, a quantization for a new amplitude subset matrix, and a quantization for a new differential subset matrix from a user equipment; means for constructing a bit mask vector from a corresponding row of the bit mask subset matrix; means for constructing a new bit mask subset matrix by repetition of the bit mask vector; means for constructing a row of an amplitude subset matrix corresponding to the strongest path in the new amplitude subset matrix from the quantization of the new amplitude subset matrix using the new bit mask subset matrix and a location of a strongest path; means for reconstructing remaining rows of the amplitude subset matrix using the new differential subset matrix; means for reconstructing the phase subset matrix from the quantization of the new phase subset matrix; means for reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and means for reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

In a forty-eighth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: receiving channel state information feedback from a user equipment in the form of a bit mask subset matrix, a quantization for a new phase subset matrix, a quantization for a new amplitude subset matrix, and a quantization for a new differential subset matrix from a user equipment; constructing a bit mask vector from a corresponding row of the bit mask subset matrix; constructing a new bit mask subset matrix by repetition of the bit mask vector; constructing a row of an amplitude subset matrix corresponding to the strongest path in the new amplitude subset matrix from the quantization of the new amplitude subset matrix using the new bit mask subset matrix and a location of a strongest path; reconstructing remaining rows of the amplitude subset matrix using the new differential subset matrix; reconstructing the phase subset matrix from the quantization of the new phase subset matrix; reconstructing a subset matrix by multiplying the amplitude subset matrix by the phase subset matrix; and reconstructing a time domain channel matrix from the subset matrix to determine reference signals received by the user equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of these teachings are made more evident in the following detailed description, when read in conjunction with the attached drawing figures.

Figure 1 illustrates the explicit feedback of channel state information in frequency-division duplex.

Figure 2 illustrates an array of antennas.

Figure 3 illustrates channel amplitude versus channel support for the same polarization for beam 1 and 6.

Figure 4 illustrates the procedure carried out by a user equipment in a first embodiment of the present invention.

Figure 5 illustrates the procedure carried out by a base station in the first embodiment. Figure 6 illustrates the procedure carried out by the user equipment in a second embodiment of the present invention.

Figure 7 illustrates the procedure carried out by the base station in the second embodiment.

Figures 8 and 9 illustrate the procedure carried out by the user equipment in a first variant of a third embodiment of the present invention.

Figures 10 and 11 illustrate the procedure carried out by the base station in the first variant of the third embodiment.

Figures 12 and 13 illustrate the procedure carried out by the user equipment in a second variant of the third embodiment of the present invention.

Figures 14 and 15 illustrate the procedure carried out by the base station in the second variant of the third embodiment.

Figure 16 illustrates the procedures carried out by the user equipment and the base station in a first option of a fourth embodiment of the present invention.

Figure 17 illustrates the procedures carried out by the user equipment and the base station in a second option of the fourth embodiment.

Figure 18 illustrates the geometric mean of user throughput.

Figure 19 illustrates user edge spectral efficiency versus spectral efficiency.

Figure 20 shows a simplified block diagram of certain apparatus according to various exemplary embodiments of the present invention.

Figure 21 shows part of another exemplary radio network.

DETAILED DESCRIPTION

The idea of the present invention is to exploit the correlation between the channels observed with receiver antennas having the same polarization.

With reference to Figure 2, which illustrates an array of antennas 200, for one dominant path at one time instant t, let the signal received by the first element m=0 be:

where is the carrier frequency, b is some random phase, is the

amplitude of the signal, and

is the information carrying component.

The signal received at m=l is:

Therefore, if the angular spread at the UE side is not very high, there will be a strong correlation on the amplitude of the received signals on receive antennas which have the same polarization. In the frequency domain, this will lead to a correlation between the received signals on receive antennas which have the same polarization.

Referring to equation 7.3-22 in the 3GPP channel model description (see 3GPP TS 38.211, VI.0.0 (2017-09), Technical Specification Group Radio Access Network; NR; Physical channels and modulation (Release 15)), copied here for convenience:

if the UE has omnidirectional antennas, the field patterns

equal to 1. This means that the only part dependent on the receive antenna index is the exponential term describing the array manifold.

For a LOS (line of sight) user, the channel coefficient can be computed as equation 7.3-27 in 3GPP TR 36.873, V12.4.0 (2017-03), 3^rd Generation Partnership Project; Technical Specification Group Radio Access Network; Study on 3D channel model for LTE (Release 12):

where it is clear now that for high values of K_R there is one dominant path, because the LOS component will be higher inside LL_A„(t). Two receive antennas sharing the same polarization will therefore see very close amplitude for that path and at the same time instant t. Although we expect this strong correlation in LOS users, we also see some degree of amplitude correlation for NLOS (non-line-of-sight) users.

Furthermore, after a first stage of GoB precoding, we expect the effective channel to have a more dominant path.

In the discussion to follow, frequent reference will be made to the variables identified in the table below:

Assuming

where P is the number of polarizations, in this case and is the number of receive antennas with the same polarization, the

correlation on the same polarization receive antennas can be exploited in accordance with the following four embodiments:

1. Embodiment 1 : Receiver Antenna Subsampling

(1) In summary, instead of feeding back all the amplitude values on all receive antennas, for antennas receiving the same polarization, the UE feeds back only the amplitude values of the strongest path.

(2) For every polarization p=0...P-l and for every path to every Xpol (cross- polarized) antenna b=0...B-l :

Collect the channel coefficients for the paths which have a common polarization, therefore build out of (time domain channel matrix) as

(3) The whole phase information in is fed back, but only the amplitudes of

the strongest row are fed back. The ratio between the newly required feedback overhead using the proposed approach and the baseline is:

Figure 3 depicts channel tap amplitude vs channel support for same polarization for beam 1 and 6; we can see there is a high degree of correlation between the amplitudes meaning that this subsampling procedure should provide a reasonable approximation.

In greater detail, the procedure of Embodiment 1 may be summarized as follows:

Quantization algorithm:

The total feedback overhead is then At the

gNB, the approximation to the matrix

is reconstructed for each p and b, using constant amplitudes (the quantized for each row.

The procedure of Embodiment 1 is summarized in Figures 4 and 5. Figure 4 sets forth the procedure carried out by the UE, and Figure 5 sets forth the procedure carried out by the gNB. It should be understood that both the UE and the gNB are aware that the receiver antenna subsampling (Embodiment 1) feedback reduction scheme is being used, and that the time domain channel matrix is available at the UE.

Referring first to Figure 4, at the UE, a time domain channel matrix is constructed from a channel state information message according to Equation 1.1 in block 400. Then, a subset matrix is constructed from the time domain channel matrix according to Equation 1.2 in block 402. The subset matrix contains channel coefficients corresponding to a common polarization. An amplitude subset matrix containing the magnitudes of the elements in the subset matrix is also constructed according to Equation 1.3 in block 402. The strongest path in the amplitude subset matrix is then found using Equation 1.4 in block 404. A phase subset matrix containing phase information for the elements in the subset matrix is constructed using Equation 1.5, as is a row subset matrix for the strongest path in the amplitude subset matrix using Equation 1.6, in block 406. From them, quantizations for the row subset matrix and the phase subset matrix are constructed in block 408. Subsequently, the quantizations for the row subset matrix and the phase subset matrix are sent to the gNB as channel state information feedback in block 410.

Referring to Figure 5, at the gNB, the amplitude subset matrix is reconstructed from the quantization of the row subset matrix in block 500. The phase subset matrix is reconstructed from the quantization of the phase subset matrix in block 502. Then, the subset matrix is reconstructed by multiplying the amplitude subset matrix by the phase subset matrix in block 504. Finally, a time domain channel matrix is reconstructed from the subset matrix according to Equations 1.1 and 1.2 to determine a channel state information message received by the user equipment in block 506.

2) Embodiment 2: Differential Quantization

(1) In summary, instead of feeding back all the amplitude values on all receive antennas, for antennas receiving the same polarization, UE feeds back the amplitude values of the strongest path plus the differential amplitude values from the rest of the paths of the same receive polarization.

Collect the channel coefficients for the paths which have a common polarization, therefore build out of as

(3) The whole phase information in ί is fed back plus the amplitudes of the

strongest row plus an index referring to the index of the strongest row in

(4) The rest of the rows are sent differentially with respect to the strongest row, using N_diff bits. Two ways to encode this information are:

(a) Ratio function: divide each element in every column by the element in the strongest row

(b) Subtraction function: subtract each element in every column by the element in the strongest row

(5) The ratio between the newly required feedback overhead using the proposed approach and the baseline is:

In greater detail, the procedure of Embodiment 2 may be summarized as follows:

Quantization algorithm:

end end

Total feedback overhead is

The procedure of Embodiment 2 is summarized in Figures 6 and 7. Figure 6 sets forth the procedure carried out by the UE, and Figure 7 sets forth the procedure carried out by the gNB. It should be understood that both the UE and the gNB are aware that the differential quantization (Embodiment 2) feedback reduction scheme is being used, and that the time domain channel matrix is available at the UE.

Referring first to Figure 6, at the UE, a time domain channel matrix is constructed from a channel state information message according to Equation 2.1 in block 600. Then, a subset matrix is constructed from the time domain channel matrix according to Equation 2.2 in block 602. The subset matrix contains channel coefficients corresponding to a common polarization. An amplitude subset matrix containing the magnitudes of the elements in the subset matrix is also constructed according to Equation 2.3 in block 602. The strongest path in the amplitude subset matrix is then identified using Equation 2.4 in block 604. A phase subset matrix containing phase information for the elements in the subset matrix is constructed using Equation 2.5, as is a row subset matrix for the strongest path in the amplitude subset matrix using Equation 2.6, in block 606. From them, quantizations for the row subset matrix and the phase subset matrix are constructed in block 608. Then, a differential subset matrix is constructed using the amplitude subset matrix and the quantization of the row subset matrix according to Equation 2.7 in block 610. Next, a quantization of the differential subset matrix is constructed in block 612. Subsequently, the quantizations for the row subset matrix, the phase subset matrix, the differential subset matrix, and the strongest path in the amplitude subset matrix are sent to the gNB as channel state information feedback in block 700 of Figure 7.

Referring to Figure 7, the gNB receives the channel state information feedback in block 702. The row of the amplitude subset matrix having the strongest path is reconstructed from the quantization of the row subset matrix in block 704. The remaining rows of the amplitude subset matrix are reconstructed using the quantization of the differential subset matrix in block 706. The phase subset matrix is reconstructed from the quantization of the phase subset matrix in block 708. Then, the subset matrix is reconstructed by multiplying the amplitude subset matrix by the phase subset matrix in block 710. Finally, a time domain channel matrix is reconstructed from the subset matrix according to Equations 2.1 and 2.2 to determine a channel state information message received by the user equipment in block 712.

3) Embodiment 3: Reduced Overhead Bit Mask

The location of the significant taps can be fed back by means of a combination of the channel support vector 5 and a bit mask The bit mask M_{VSs ¾} is a matrix of

size

where every element is a binary variable“1” or“0”, indicating whether the corresponding tap is significant or not, respectively.

and a subset matrix constructed from the bit mask is:

where each row corresponds to a single ( b,p ) combination.

Embodiment 3 is really two separate cases, one dependent on Embodiment 1, and the other on Embodiment 2. For the Embodiment 3 extension of Embodiment 1, start with h (time domain channel matrix) and then generate

as before in Embodiment 1. Using fi, generate the row of

corresponding to the current values of b and p by determining the significant taps for this

Next, quantize only the columns of it indicated by the significant taps (that is, the l’s in this row of

using the quantization approach in Embodiment 1. The additional step over Embodiment 1 is to determine the significant taps which define the row This step occurs after

constructing the row subset matrix for the strongest path (but could conceivably be earlier). The quantization steps then only quantize the elements of It corresponding to the significant taps. For the Embodiment 3 extension of Embodiment 2, this is the same idea as above where the significant taps are determined after constructing the row subset matrix for the strongest path.

Note that the total feedback is now correctly indicated by the equations:

nt 1;

the

extension of Embodiment 2 where N_$,k is the number of‘ 1’ bits in row k of the bit mask.

More specifically now, the Embodiment 3 extension of Embodiment 1 is summarized in Figures 8 to 11. Figures 8 and 9 set forth the procedure carried out by the UE, and Figures 10 and 11 set forth the procedure carried out by the gNB. It should be understood that both the UE and the gNB are aware that the receiver antenna subsampling (Embodiment 1) and reduced overhead bit mask (Embodiment 3) feedback reduction schemes are being used, and that the time domain channel matrix is available at the UE.

Referring first to Figures 8 and 9, at the UE, a time domain channel matrix is constructed from a channel state information message according to Equation 1.1 in block 800. As in Embodiment 1, the steps to follow are repeated for all values of p and b, as indicated in Figures 8 and 9. Then, a subset matrix is constructed from the time domain channel matrix according to Equation 1.2 in block 802. The subset matrix contains channel coefficients corresponding to a common polarization. An amplitude subset matrix containing the magnitudes of the elements in the subset matrix is also constructed according to Equation 1.3 in block 802. The strongest path in the amplitude subset matrix is then found using Equation 1.4 in block 804. A phase subset matrix containing phase information for the elements in the subset matrix is constructed using Equation 1.5, as is a row subset matrix for the strongest path in the amplitude subset matrix using Equation 1.6, in block 806. In block 808, the procedure departs from that shown in Figure 4 for Embodiment 1; in block 808, the strongest path in the amplitude subset matrix is stored into a part of a new amplitude subset matrix; the phase subset matrix is stored into a part of a new phase subset matrix; and the strongest path location in the amplitude subset matrix is stored into an element of a strongest path indices vector.

The UE procedure then continues onto Figure 9. In block 900, a bit mask subset matrix is constructed based on the new amplitude subset matrix. Next, a bit mask is constructed in block 902 by repetition of the bit mask subset matrix. Quantizations for the new phase subset matrix for locations in the bit mask which are equal to“1” and for the new amplitude subset matrix for locations in the bit mask subset matrix which are equal to“1” (X == 1 means locations in X where X = 1) are constructed in block 904. Finally, the bit mask subset matrix and these two quantizations are sent to the gNB as channel state information feedback in block 906.

Referring now to Figure 10, at the gNB, where, as in Embodiment 1, the steps to follow are repeated for all values of p and b, as indicated in Figures 10 and 11, a bit mask vector is constructed from the corresponding row of the bit mask subset matrix in block 1000. Then, a new bit mask subset matrix is constructed in block 1002 by repetition of the bit mask vector. Subsequently, in block 1004, using the new bit mask subset matrix, an amplitude subset matrix is constructed from the quantization of the new amplitude subset matrix; and, in block 1006, a phase subset matrix is constructed from the quantization of the new phase subset matrix. Then, the subset matrix is reconstructed by multiplying the amplitude subset matrix by the phase subset matrix in block 1008. Finally, a time domain channel matrix is reconstructed from the subset matrix to determine a channel state information message received by the user equipment according to Equations 1.1 and 1.2 in block 1010, as was done in Embodiment 1 discussed above.

The gNB procedure then continues onto Figure 11. A common channel support vector, as discussed in International Application No. PCT/CN2018/083114, and the reconstructed time domain channel matrix (channel state information feedback) are used in block 1102 to construct a channel frequency response HNB _X NFFT, which is used for DF precoding and scheduling at the gNB in block 1104.

The Embodiment 3 extension of Embodiment 2 is summarized in Figures 12 to 15. Figures 12 and 13 set forth the procedure carried out by the UE, and Figures 14 and 15 set forth the procedure carried out by the gNB. It should be understood, as previously, that both the UE and the gNB are aware that the differential quantization (Embodiment 2) and reduced overhead bit mask (Embodiment 3) feedback reduction schemes are being used, and that the time domain channel matrix is available at the UE. Referring first to Figure 12, at the UE, a time domain channel matrix is constructed from a channel state information message according to Equation 2.1 in block 1200. As in Embodiment 2, the steps to follow are repeated for all values of p and b, as indicated in Figures 12 and 13. Then, a subset matrix is constructed from the time domain channel matrix according to Equation 2.2 in block 1202. The subset matrix contains channel coefficients corresponding to a common polarization. An amplitude subset matrix containing the magnitudes of the elements in the subset matrix is also constructed according to Equation 2.3 in block 1202. The strongest path in the amplitude subset matrix is then found using Equation 2.4 in block 1204. A phase subset matrix containing phase information for the elements in the subset matrix is constructed using Equation 2.5, as is a row subset matrix for the strongest path in the amplitude subset matrix using Equation 2.6, in block 1206. Then, a differential subset matrix is constructed using the amplitude subset matrix and the quantization of the row subset matrix according to Equation 2.7 in block 1208. In block 1210, the procedure departs from that shown in Figure 6 for Embodiment 2; in block 1210, the strongest path in the amplitude subset matrix is stored into a part of a new amplitude subset matrix; the phase subset matrix is stored into a part of a new phase subset matrix; the strongest path location in the amplitude subset matrix is stored into an element of a strongest path indices vector; and the differential subset matrix is stored into a part of a new differential subset matrix.

The UE procedure then continues onto Figure 13. In block 1300, a bit mask subset matrix is constructed based on the new amplitude subset matrix. Next, a bit mask is constructed in block 1302 by repetition of the bit mask subset matrix. A new bit mask is constructed in block 1304 by repetition of the bit mask subset matrix. Quantizations for the new phase subset matrix for locations in the bit mask which are equal to“1”; for the new amplitude subset matrix for locations in the bit mask subset matrix which are equal to“1” (X == 1 means locations in X where X = 1); and for the new differential subset matrix for locations in the bit mask which are equal to“1” are constructed in block 1306. Finally, the bit mask subset matrix and these three quantizations are sent to the gNB as channel state information feedback in block 1308.

Referring now to Figure 14, at the gNB, where, as in Embodiment 2, the steps to follow are repeated for all values of p and b, as indicated in Figures 14 and 15, a bit mask vector is constructed from the corresponding row of the bit mask subset matrix in block 1400. Then, a new bit mask subset matrix is constructed in block 1402 by repetition of the bit mask vector. Subsequently, in block 1404, using the new bit mask subset matrix as well as the location of the strongest path, a row corresponding to the strongest path, that is, the row of the new amplitude subset row matrix, of an amplitude subset matrix is constructed from the quantization of the new amplitude subset matrix; and, in block 1406, the remaining rows of the amplitude subset matrix are constructed using the new differential subset matrix. In block 1408, a phase subset matrix is constructed from the quantization of the new phase subset matrix. Then, the subset matrix is reconstructed by multiplying the amplitude subset matrix by the phase subset matrix in block 1410. Finally, a time domain channel matrix is reconstructed from the subset matrix to determine a channel state information message received by the user equipment according to Equations 2.1 and 2.2 in block 1412, as was done in Embodiment 2 discussed above.

The gNB procedure then continues onto Figure 15. A common channel support vector, as discussed in International Application No. PCT/CN2018/083114, and the reconstructed time domain channel matrix (channel state information feedback) are used in block 1502 to construct a channel frequency response HNB _X NFFT, which is used for DL precoding and scheduling at the gNB in block 1504.

4) Embodiment 4: UE Signaling of UE Antennas Correlation Level

After measuring CSI from DL CSI-RS and after obtaining the time domain channel matrix h_NEyN^ the UE can measure the level of correlation among the signals received by the UE receive antennas of the same polarization. The UE has several options:

1. Option A: Depending on the level of correlation, the UE can signal to the gNB whether it will use a reduced feedback overhead scheme, for example, as explained in connection with Embodiments 1 to 3, or that it will not use any reduced feedback overhead scheme.

At low levels of correlation, the UE can decide not to use any reduced feedback overhead scheme, because it will lead to an inaccurate estimation of the CSI at the gNB. For medium levels of correlation, the UE can opt to use differential quantization, as explained in Embodiment 2. For high levels of correlation, the UE can opt to use receiver antenna subsampling, explained in Embodiment 1. For medium and high correlation, bit mask overhead reduction, explained in Embodiment 3, can also be combined with the selected method for feedback reduction.

The procedure of Embodiment 4, Option A is summarized in Figure 16, which sets forth the procedures carried out by the UE and the gNB.

Referring more specifically to Figure 16, the gNB transmits channel information reference signals to a user equipment for computing channel state information feedback in block 1600. The user equipment receives the channel state information reference signals from the base station for computing channel state information feedback, and constructs a time domain channel matrix from the channel state information reference signals in block 1602. The user equipment then measures the level of correlation among the received signals having a common polarization in block 1604. Then, the user equipment determines whether to use one of the feedback reduction schemes described herein, or no feedback reduction scheme at all, in block 1606. The user equipment informs the base station of its decision in block 1608, making the gNB aware of the feedback scheme to be used, if any, in block 1610.

2. Option B: The UE can signal an indicator of the level of UE antenna correlation and leave it to the gNB to decide which reduction mode to use, if any.

The procedure of Embodiment 4, Option B is summarized in Figure 17, which sets forth the procedures carried out by the UE and the gNB.

Referring more specifically to Figure 17, the gNB transmits channel information reference signals to a user equipment for computing channel state information feedback in block 1700. The user equipment receives the channel state information reference signals from the base station for computing channel state information feedback, and constructs a time domain channel matrix from the channel state information reference signals in block 1702. The user equipment then measures the level of correlation among the received signals having a common polarization in block 1704. Then, the user equipment transmits the level of correlation to the base station in block 1706. The base station determines whether to use one of the feedback reduction schemes described herein, or no feedback reduction scheme at all, in block 1708, and informs the user equipment of its decision in block 1710. Subsequently, the user equipment is aware of the feedback scheme to be used, if any, in block 1712. 3. Option C: Another option in Embodiment 4 is for the UE vendors to decide ahead of time which UE antennas are expected to be correlated. Then, that information could be signaled to the gNB in the UE capability information. For example, if the UE has cross-pol elements, then the UE capability information could indicate that the left-45 ° antennas are all expected to be correlated with each other, and then the right-45 ° antennas are all expected to be correlated with each other. This option might be a lower-complexity (and lower-performing) alternative to the idea of the UE measuring the correlation and signaling that information on a dynamic/recurring basis.

Example:

Simulation results on a system with M = 16 antenna ports, UMi channel (see 3GPP TS 38.211, VI.0.0 (2017-09), Technical Specification Group Radio Access Network; NR; Physical channels and modulation (Release 15)), each UE has ¾ = 2 Xpol Antennas (i.e. N = 4). We assumed a bandwidth of lOMHz with 50 physical resource blocks (PRBs), at a carrier frequency of 2GHz. We also assumed a channel frequency oversampling factor of 12, that is, assuming one pilot subcarrier per PRB. MU-MIMO scheme is carried out, where all UEs are spatially multiplexed on the same time- frequency resources. Up to 2 layers can be transmitted per UE. We assumed a feedback periodicity of 10ms and SLNR precoding.

As we can see, very small loss of -2.8% and -1% relative to a baseline (bar 1802) is observed by applying subsampling (bar 1804) and differential quantization (bar 1806), respectively, while saving 22% (point 1904) and 12% ( point 1906) of the required feedback overhead relative to the baseline (point 1902), as shown in Figures 18 and 19.

Reference is now made to Figure 20 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing an exemplary embodiment of the present invention. In Figure 20, a wireless network 2001 is adapted for communication over a wireless link 2011 with an apparatus, such as a mobile communication device, which is referred to as a UE 2010, via a wireless network access node, such as a base station or relay station or remote radio head, and more specifically shown as a gNodeB (gNB) 2012. The network 2001 may include a network element 2014, which serves as a gateway to a broader network, such as a public switched telephone/data network and/or the Internet.

The UE 2010 includes a controller, such as a computer or a data processor (DP) 2010A, a computer-readable memory medium embodied as a memory (MEM) 2010B, which stores a program of computer instructions (PROG) 2010C, and a suitable radio frequency (RF) transmitter and receiver 2010D for bi-directional wireless communications with the gNodeB (gNB) 2012 via one or more antennas. The gNodeB 2012 also includes a controller, such as a computer or a data processor (DP) 2012 A, a computer-readable memory medium embodied as a memory (MEM) 2012B that stores a program of computer instructions (PROG) 2012C, and a suitable RF transmitter and receiver 2012D for communication with the UE 2010 via one or more antennas. The gNodeB 2012 is coupled via a data/control path 2013 to the network element 2014. The path 2013 may be implemented as an Sl interface when the network 2001 is an LTE network. The gNodeB 2012 may also be coupled to another gNodeB or to an eNodeB via data/control path 2015, which may be implemented as an X2 interface when the network 2001 is an LTE network.

At least one of the PROGs 2010C and 2012C is assumed to include program instructions that, when executed by the associated DP, enable the device to operate in accordance with the exemplary embodiments of this invention as was detailed above with respect to Figures 3 to 17. That is, the exemplary embodiments of this invention may be implemented at least in part by computer software executable by the DP 2010A of the UE 2010 and/or by the DP 2012A of the gNodeB 2012, or by hardware, or by a combination of software and hardware (and firmware).

In general, the various embodiments of the UE 2010 can include, but are not limited to, cellular telephones; personal digital assistants (PDAs) having wireless communication capabilities; portable computers having wireless communication capabilities; image capture devices, such as digital cameras, having wireless communication capabilities; gaming devices having wireless communication capabilities; music storage and playback appliances having wireless communication capabilities; and Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.

The computer-readable MEMs 2010B and 2012B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic-memory devices and systems, optical-memory devices and systems, fixed memory and removable memory. The DPs 2010A and 2012A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multicore processor architecture, as non-limiting examples.

It should be noted that the various DPs 2010 A, 2012A may be implemented as one or more processors/chips, either or both of the UE 2010 and the gNodeB 2012 may include more than one transmitter and/or receiver 2010D, 2012D, and particularly the gNodeB 2012 may have its antennas mounted remotely from the other components of the gNodeB 2012, such as for example tower-mounted antennas.

Reference is now made to Figure 21 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing another exemplary embodiment of the present invention. In the following, different exemplifying embodiments will be described using, as an example of an access architecture to which the embodiments may be applied, a radio access architecture based on long term evolution advanced (LTE Advanced, LTE-A) or new radio (NR, 5G), without restricting the embodiments to such an architecture, however. It is obvious for a person skilled in the art that the embodiments may also be applied to other kinds of communications networks having suitable means by adjusting parameters and procedures appropriately. Some examples of other options for suitable systems are the universal mobile telecommunications system (UMTS) radio access network (UTRAN or E- UTRAN), long term evolution (LTE, the same as E-UTRA), wireless local area network (WLAN or WiFi), worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS), ZigBee®, wideband code division multiple access (WCDMA), systems using ultra-wideband (UWB) technology, sensor networks, mobile ad-hoc networks (MANETs), and Internet Protocol multimedia subsystems (IMS) or any combination thereof.

Figure 21 depicts examples of simplified system architectures only showing some elements and functional entities, all being logical units, whose implementation may differ from what is shown. The connections shown in Figure 21 are logical connections; the actual physical connections may be different. It is apparent to a person skilled in the art that the system typically comprises also other functions and structures than those shown in Figure 21. The embodiments are not, however, restricted to the system given as an example, but a person skilled in the art may apply the solution to other communication systems provided with necessary properties.

The example of Figure 21 shows a part of an exemplifying radio access network.

Figure 21 shows user devices 2100 and 2102 configured to be in a wireless connection on one or more communication channels in a cell with an access node (such as (e/g)NodeB) 2104 providing the cell. The physical link from a user device to a/an (e/g)NodeB is called uplink or reverse link and the physical link from the (e/g)NodeB to the user device is called downlink or forward link. It should be appreciated that (e/g)NodeBs or their functionalities may be implemented by using any node, host, server, or access point, etc., entity suitable for such a usage.

A communications system typically comprises more than one (e/g)NodeB in which case the (e/g)NodeBs may also be configured to communicate with one another over links, wired or wireless, designed for the purpose. These links may be used for signaling purposes. The (e/g)NodeB is a computing device configured to control the radio resources of communication system to which it is coupled. The NodeB may also be referred to as a base station, an access point, or any other type of interfacing device including a relay station capable of operating in a wireless environment. The (e/g)NodeB includes or is coupled to transceivers. From the transceivers of the (e/g)NodeB, a connection is provided to an antenna unit that establishes bi-directional radio links to user devices. The antenna unit may comprise a plurality of antennas or antenna elements. The (e/g)NodeB is further connected to core network 2110 (CN or next generation core NGC). Depending on the system, the counterpart on the CN side can be a serving gateway (S- GW, routing and forwarding user data packets), packet data network gateway (P-GW), for providing connectivity of user devices (UEs) to external packet data networks, or mobile management entity (MME), etc.

The user device (also called UE, user equipment, user terminal, terminal device, etc.) illustrates one type of an apparatus to which resources on the air interface are allocated and assigned, and thus any feature described herein with a user device may be implemented with a corresponding apparatus, such as a relay node. An example of such a relay node is a layer 3 relay (self-backhauling relay) towards the base station.

The user device typically refers to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (mobile phone), smartphone, personal digital assistant (PDA), handset, device using a wireless modem (alarm or measurement device, etc.), laptop and/or touch screen computer, tablet, game console, notebook, and multimedia device. It should be appreciated that a user device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. A user device may also be a device having capability to operate in an Internet of Things (IoT) network which is a scenario in which objects are provided with the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction. The user device may also utilize cloud. In some applications, a user device may comprise a small portable device with radio parts (such as a watch, earphones or eyeglasses) and the computation is carried out in the cloud. The user device (or in some embodiments a layer 3 relay node) is configured to perform one or more of user equipment functionalities. The user device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal or user equipment (UE) just to mention but a few names or apparatuses.

Various techniques described herein may also be applied to a cyber physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the implementation and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors microcontrollers, etc.) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals.

It should be understood that, in Figure 21, user devices may include two antennas. The number of reception and/or transmission antennas may naturally vary according to a current implementation.

Additionally, although the apparatuses have been depicted as single entities, different units, processors and/or memory units (not all shown in Figure 21) may be implemented.

5G enables the use of multiple input-multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and employing a variety of radio technologies depending on service needs, use cases and/or spectrum available. 5G mobile communications supports a wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications (such as (massive) machine-type communications (mMTC)), including vehicular safety, different sensors and real-time control. 5G is expected to have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also being integrable with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and 5G radio interface access comes from small cells by aggregation to the LTE. In other words, 5G is planned to support both inter-RAT operability (such as LTE-5G) and inter-RI operability (inter-radio interface operability, such as below 6GHz - cmWave, below 6GHz - cmWave - mmWave). One of the concepts considered to be used in 5G networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

The current architecture in LTE networks is fully distributed in the radio and fully centralized in the core network. The low latency applications and services in 5G require to bring the content close to the radio which leads to local break out and multi access edge computing (MEC). 5G enables analytics and knowledge generation to occur at the source of the data. This approach requires leveraging resources that may not be continuously connected to a network such as laptops, smartphones, tablets and sensors. MEC provides a distributed computing environment for application and service hosting. It also has the ability to store and process content in close proximity to cellular subscribers for faster response time. Edge computing covers a wide range of technologies, such as wireless sensor networks, mobile data acquisition, mobile signature analysis, cooperative distributed peer-to-peer ad hoc networking and processing also classifiable as local cloud/fog computing and grid/mesh computing, dew computing, mobile edge computing, cloudlet, distributed data storage and retrieval, autonomic self- healing networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (massive connectivity and/or latency critical), critical communications (autonomous vehicles, traffic safety, real-time analytics, time-critical control, healthcare applications).

The communication system is also able to communicate with other networks, such as a public switched telephone network or the Internet 2112, or utilize services provided by them. The communication network may also be able to support the usage of cloud services, for example, at least part of core network operations may be carried out as a cloud service (this is depicted in Figure 21 by“cloud” 2114). The communication system may also comprise a central control entity, or the like, providing facilities for networks of different operators to cooperate, for example, in spectrum sharing.

Edge cloud may be brought into radio access network (RAN) by utilizing network function virtualization (NVF) and software defined networking (SDN). Using edge cloud may mean access node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head or base station comprising radio parts. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. Application of cloudRAN architecture enables RAN real time functions being carried out at the RAN side (in a distributed unit, DU 2104) and non-real time functions being carried out in a centralized manner (in a centralized unit, CU 2108).

It should also be understood that the distribution of labor between core network operations and base station operations may differ from that of the LTE or even be non-existent. Some other technology advancements probably to be used are Big Data and all-IP, which may change the way networks are being constructed and managed. 5G (or new radio, NR) networks are being designed to support multiple hierarchies, where MEC servers can be placed between the core and the base station or nodeB (gNB). It should be appreciated that MEC can be applied in 4G networks as well.

5G may also utilize satellite communication to enhance or complement the coverage of 5G service, for example, by providing backhauling. Possible use cases are providing service continuity for machine-to -machine (M2M) or Internet of Things (IoT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future railway/maritime/aeronautical communications. Satellite communication may utilize geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular mega-constellations (systems in which hundreds of (nano)satellites are deployed). Each satellite 2106 in the mega-constellation may cover several satellite-enabled network entities that create on-ground cells. The on ground cells may be created through an on-ground relay node 2104 or by a gNB located on-ground or in a satellite.

It is obvious for a person skilled in the art that the depicted system is only an example of a part of a radio access system and in practice, the system may comprise a plurality of (e/g)NodeBs, the user device may have an access to a plurality of radio cells and the system may also comprise other apparatuses, such as physical layer relay nodes or other network elements, etc. At least one of the (e/g)NodeBs or may be a Home (e/g)nodeB. Additionally, in a geographical area of a radio communication system, a plurality of different kinds of radio cells as well as a plurality of radio cells may be provided. Radio cells may be macro cells (or umbrella cells) which are large cells, usually having a diameter of up to tens of kilometers, or smaller cells such as micro-, femto- or picocells. The (e/g)NodeBs of Figure 21 may provide any kind of these cells. A cellular radio system may be implemented as a multilayer network including several kinds of cells. Typically, in multilayer networks, one access node provides one kind of a cell or cells, and thus a plurality of (e/g)NodeBs are required to provide such a network structure.

For fulfilling the need for improving the deployment and performance of communication systems, the concept of “plug-and-play” (e/g)NodeBs has been introduced. Typically, a network which is able to use“plug-and-play” (e/g)Node Bs, includes, in addition to Home (e/g)NodeBs (H(e/g)nodeBs), a home node B gateway, or HNB-GW (not shown in Figure 21). An HNB Gateway (HNB-GW), which is typically installed within an operator’s network may aggregate traffic from a large number of HNBs back to a core network.

In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software, which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto.

While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

It should thus be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components, such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry, as well as possibly firmware, for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. For example, while the exemplary embodiments have been described above in the context of advancements to the 5G NR system, it should be appreciated that the exemplary embodiments of this invention are not limited for use with only this one particular type of wireless communication system. The exemplary embodiments of the invention presented herein are explanatory and not exhaustive or otherwise limiting of the scope of the invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms“a”,“an”, and“the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or“comprising”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

Various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications of the teachings of this disclosure will still fall within the scope of the non-limiting embodiments of this invention.

Although described in the context of particular embodiments, it will be apparent to those skilled in the art that a number of modifications and various changes to these teachings may occur. Thus, while the invention has been particularly shown and described with respect to one or more embodiments thereof, it will be understood by those skilled in the art that certain modifications or changes may be made therein without departing from the scope of the invention as set forth above, or from the scope of the claims to follow.

Claims

WHAT IS CLAIMED IS:

1. A method comprising:

receiving channel state information reference signals from a base station for computing channel state information feedback;

constructing a time domain channel matrix from the channel state information reference signals;

measuring a level of correlation among the received signals having a common polarization;

determining, depending on the measured level of correlation, whether to use a feedback reduction scheme or no feedback reduction scheme; and

informing the base station that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

2. The method as claimed in claim 1 wherein, when the level of correlation is low, no feedback reduction scheme is used.

3. The method as claimed in claim 1 wherein, when the level of correlation is medium, a feedback reduction scheme based on differential quantization is used.

4. The method as claimed in claim 3 wherein the feedback reduction scheme based on differential quantization is combined with bit mask overhead reduction.

5. The method as claimed in claim 1 wherein, when the level of correlation is high, a feedback reduction scheme based on receiver antenna subsampling is used.

6. The method as claimed in claim 5 wherein the feedback reduction scheme based on receiver antenna subsampling is combined with bit mask overhead reduction.

7. An apparatus comprising:

at least one processor; and

at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following: receive channel state information reference signals from a base station for computing channel state information feedback;

construct a time domain channel matrix from the channel state information reference signals;

measure a level of correlation among the received signals having a common polarization;

determine, depending on the measured level of correlation, whether to use a feedback reduction scheme or no feedback reduction scheme; and

inform the base station that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

8. An apparatus comprising:

means for receiving channel state information reference signals from a base station for computing channel state information feedback;

means for constructing a time domain channel matrix from the channel state information reference signals;

means for measuring a level of correlation among the received signals having a common polarization;

means for determining, depending on the measured level of correlation, whether to use a feedback reduction scheme or no feedback reduction scheme; and

means for informing the base station that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

9. A computer program product comprising a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing:

determining, depending on the measured level of correlation, whether to use a feedback reduction scheme or no feedback reduction scheme; and informing the base station that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

10. A method comprising :

transmitting channel state information reference signals to a user equipment for computing channel state information feedback; and

receiving information from the user equipment that the user equipment is to use a feedback reduction scheme or that the user equipment is to use no feedback reduction scheme.

11. The method as claimed in claim 10 wherein the feedback reduction scheme is based on differential quantization.

12. The method as claimed in claim 11 wherein the feedback reduction scheme based on differential quantization is combined with bit mask overhead reduction.

13. The method as claimed in claim 10 wherein the feedback reduction scheme is based on receiver antenna subsampling.

14. The method as claimed in claim 13 wherein the feedback reduction scheme based on receiver antenna subsampling is combined with bit mask overhead reduction.

15. An apparatus comprising :

at least one processor; and

at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the following:

transmit channel state information reference signals to a user equipment for computing channel state information feedback; and

receive information from the user equipment that the user equipment is to use a feedback reduction scheme or that the user equipment is to use no feedback reduction scheme.

16. An apparatus comprising: means for transmitting channel state information reference signals to a user equipment for computing channel state information feedback; and

means for receiving information from the user equipment that the user equipment is to use a feedback reduction scheme or that the user equipment is to use no feedback reduction scheme.

17. A computer program product comprising a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing:

18. A method comprising :

transmitting the level of correlation to the base station;

receiving information from the base station whether to use a feedback reduction scheme or no feedback reduction scheme; and

using the feedback reduction scheme or no feedback reduction scheme as instructed by the base station.

19. The method as claimed in claim 18 wherein, when the level of correlation is low, no feedback reduction scheme is used.

20. The method as claimed in claim 18 wherein, when the level of correlation is medium, a feedback reduction scheme based on differential quantization is used.

21. The method as claimed in claim 20 wherein the feedback reduction scheme based on differential quantization is combined with bit mask overhead reduction.

22. The method as claimed in claim 18 wherein, when the level of correlation is high, a feedback reduction scheme based on receiver antenna subsampling is used.

23. The method as claimed in claim 22 wherein the feedback reduction scheme based on receiver antenna subsampling is combined with bit mask overhead reduction.

24. An apparatus comprising:

at least one processor; and

receive channel state information reference signals from a base station for computing channel state information feedback;

transmit the level of correlation to the base station;

receive information from the base station whether to use a feedback reduction scheme or no feedback reduction scheme; and

use the feedback reduction scheme or no feedback reduction scheme as instructed by the base station.

25. An apparatus comprising:

means for transmitting the level of correlation to the base station; means for receiving information from the base station user equipment whether to use a feedback reduction scheme based on one of receiver antenna subsampling, differential quantization, and a reduced overhead bit mask; or to use no feedback reduction scheme; and

means for using the feedback reduction scheme or no feedback reduction scheme as instructed by the base station.

26. A computer program product comprising a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing:

transmitting the level of correlation to the base station;

receiving information from the base station user equipment whether to use a feedback reduction scheme based on one of receiver antenna subsampling, differential quantization, and a reduced overhead bit mask; or to use no feedback reduction scheme; and

27. A method comprising:

transmitting channel state information reference signals to a user equipment for computing channel state information feedback;

receiving a measured level of correlation among the signals having common polarization from the user equipment;

determining, depending on the measured level of correlation, whether the user equipment is to use a feedback reduction scheme or no feedback reduction scheme; and informing the user equipment that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

28. The method as claimed in claim 27 wherein, when the level of correlation is low, no feedback reduction scheme is used.

29. The method as claimed in claim 27 wherein, when the level of correlation is medium, a feedback reduction scheme based on differential quantization is used.

30. The method as claimed in claim 29 wherein the feedback reduction scheme based on differential quantization is combined with bit mask overhead reduction.

31. The method as claimed in claim 27 wherein, when the level of correlation is high, a feedback reduction scheme based on receiver antenna subsampling is used.

32. The method as claimed in claim 31 wherein the feedback reduction scheme based on receiver antenna subsampling is combined with bit mask overhead reduction.

33. An apparatus comprising :

at least one processor; and

transmit channel state information reference signals to a user equipment for computing channel state information feedback;

receive a measured level of correlation among the signals having common polarization from the user equipment;

determine, depending on the measured level of correlation, whether the user equipment is to use a feedback reduction scheme or no feedback reduction scheme; and inform the user equipment that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

34. An apparatus comprising:

means for transmitting channel state information reference signals to a user equipment for computing channel state information feedback;

means for receiving a measured level of correlation among the signals having common polarization from the user equipment; means for determining, depending on the measured level of correlation, whether the user equipment is to use a feedback reduction scheme or no feedback reduction scheme; and

means for informing the user equipment that the feedback reduction scheme is to be used or that no feedback reduction scheme is to be used.

35. A computer program product comprising a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: