Generating a channel state information (“CSI”) report
Apparatuses, methods, and systems are disclosed for generating a CSI report. One apparatus includes a transceiver that receives a set of reference signals transmitted from a base station and a processor that transforms the set of reference signals to obtain per-layer vectors of amplitude and phase coefficients of a DFT-compressed codebook. Here, the first element of the amplitude coefficient vector corresponding to one particular beam is unity and the first element of the phase coefficient vector corresponding to the particular beam is zero. The apparatus transmits CSI feedback that includes an indication of one or more elements of the vectors of amplitude coefficient vectors and phase coefficient vectors corresponding to at least one identified beam, and does not include the first element of the amplitude coefficient vector and the first element of the phase coefficient vector corresponding to the particular beam.
1. A method in a user equipment for generating a channel state information (“CSI”) report, the method comprising:
receiving a set of reference signals transmitted from a base station;
identifying a set of beams based on the set of reference signals;
transforming the set of reference signals to obtain per-layer vectors of amplitude and phase coefficients of a Discrete Fourier Transform (DFT)-compressed codebook, each amplitude coefficient vector and phase coefficient vector corresponding to a tap in at least one identified beam,
wherein transforming the set of reference signals includes performing a Fourier-based transformation comprising at least one of: a DFT and an inverse DFT,
wherein transforming the set of reference signals to obtain vectors of amplitude and phase coefficients of a DFT-compressed codebook comprises performing a phase offset operation on the set of beams prior to the Fourier-based transformation, the phase offset operation based on a phase of a particular beam,
wherein a first element of the amplitude coefficient vector corresponding to the particular beam is unity, and
wherein the first element of the phase coefficient vector corresponding to the particular beam is zero; and
calculating no more than half of the taps for the at least one identified beam, wherein an i-th tap of the at least one identified beam is a complex conjugate of a tap for a number of subbands minus i, wherein each tap is an inverse Fourier transform of rows of time-domain coefficient vectors;
transmitting CSI feedback comprising the calculated taps to the base station, wherein the CSI feedback comprises an indication of one or more elements of the vectors of amplitude coefficient vectors and phase coefficient vectors corresponding to the at least one identified beam, wherein the CSI feedback does not include the first element of the amplitude coefficient vector and the first element of the phase coefficient vector corresponding to the particular beam.
2. The method of claim 1 , wherein the first element of the amplitude coefficient vector corresponding to the particular beam is greater than or equal to each of the elements of the amplitude coefficient vectors corresponding to all identified beams.
3. The method of claim 1 , further comprising reporting an index corresponding to the particular beam.
4. The method of claim 3 , wherein the reported index is identified based on a summation of the magnitude values of elements of input vectors, wherein the input vectors are input to the Fourier-based transformation, and wherein each input vector corresponds to an identified beam.
5. The method of claim 1 , wherein the particular beam is identified based on a summation of the magnitude values of elements of input vectors, wherein the input vectors are input to the Fourier-based transformation, and wherein each input vector corresponds to an identified beam.
6. The method of claim 1 , wherein transforming the set of reference signals includes normalizing amplitude coefficient vectors of the identified set of beams based on the first element of the amplitude coefficient vector of the particular beam.
7. The method of claim 1 , wherein transforming the set of reference signals includes subtracting the first element of the phase coefficient vector of the particular beam from the phases of the identified set of beams.
8. The method of claim 1 , wherein transforming the set of reference signals includes quantizing the amplitude and phase coefficients of the identified set of beams.
9. A user equipment (“UE”) apparatus for generating a channel state information (“CSI”) report, the apparatus comprising:
a transceiver that receives a set of reference signals transmitted from a base station; and
a processor that:
identifies a set of beams based on the set of reference signals;
transforms the set of reference signals to obtain per-layer vectors of amplitude and phase coefficients of a Discrete Fourier Transform (DFT)-compressed codebook, each amplitude coefficient vector and phase coefficient vector corresponding to a tap in at least one identified beam,
wherein transforming the set of reference signals includes performing a Fourier-based transformation comprising at least one of: a DFT and an inverse DFT,
wherein transforming the set of reference signals to obtain vectors of amplitude and phase coefficients of a DFT-compressed codebook comprises performing a phase offset operation on the set of beams prior to the Fourier-based transformation, the phase offset operation based on a phase of a particular beam,
wherein a first element of the amplitude coefficient vector corresponding to the particular beam is unity, and
wherein the first element of the phase coefficient vector corresponding to the particular beam is zero; and
calculates no more than half of the taps for the at least one identified beam, wherein an i-th tap of the at least one identified beam is a complex conjugate of a tap for a number of subbands minus i, wherein each tap is an inverse Fourier transform of rows of time-domain coefficient vectors;
transmits CSI feedback comprising the calculated taps to the base station, wherein the CSI feedback comprises an indication of one or more elements of the vectors of amplitude coefficient vectors and phase coefficient vectors corresponding to the at least one identified beam, wherein the CSI feedback does not include the first element of the amplitude coefficient vector and the first element of the phase coefficient vector corresponding to the particular beam.
10. The apparatus of claim 9 , wherein the first element of the amplitude coefficient vector corresponding to the particular beam is the greater than or equal to each of the elements of the amplitude coefficient vectors corresponding to all identified beams.
11. The apparatus of claim 9 , wherein the processor reports an index corresponding to the particular beam.
12. The apparatus of claim 11 , wherein the reported index is identified based on a summation of the magnitude values of elements of input vectors, wherein the input vectors are input to the Fourier-based transformation, and wherein each input vector corresponds to an identified beam.
13. The apparatus of claim 9 , wherein the particular beam is identified based on a summation of the magnitude values of elements of input vectors, wherein the input vectors are input to the Fourier-based transformation, and wherein each input vector corresponds to an identified beam.
14. The apparatus of claim 9 , wherein transforming the set of reference signals includes normalizing amplitude coefficient vectors of the identified set of beams based on the first element of the amplitude coefficient vector of the particular beam.
15. The apparatus of claim 9 , wherein transforming the set of reference signals includes subtracting the first element of the phase coefficient vector of the particular beam from the phases of the identified set of beams.
16. The apparatus of claim 9 , wherein transforming the set of reference signals includes quantizing the amplitude and phase coefficients of the identified set of beams.