Apparatuses for DMRS design or processing for guard interval or zero tail DFT spread OFDM systems

1. An apparatus for a communication device, comprising:

control circuitry configured to:

generate an appended constant amplitude zero-autocorrelation waveform (CAZAC) sequence including a CAZAC sequence with zeros appended thereto, wherein a length N SEQ of the CAZAC sequence used in the appended CAZAC sequence is determined by selecting a largest prime number such that:

N

×

N

SEQ

M

≤

N

-

N

GI

,

where N is a number of samples in orthogonal frequency-division multiplexing OFDM) symbols, M is a length of the appended CAZAC sequence, and N GI is a length of a guard interval of the OFDM symbols;

determine a discrete Fourier transform (DFT) of the appended CAZAC sequence to obtain a frequency domain interpolated CAZAC sequence;

determine an inverse discrete Fourier transform (IDFT) of the frequency domain interpolated CAZAC sequence to generate a demodulation reference signal (DMRS) for coherent demodulation of OFDM symbols; and

cause communication elements of the communication device to transmit the DMRS through a cellular data network to a far-end communication device.

2. The apparatus of claim 1 , wherein the control circuitry is configured to add a guard interval (GI) sequence to the DMRS before causing the communication elements to transmit the DMRS through the cellular data network.

3. The apparatus of claim 1 , wherein the control circuitry is also configured to map the frequency domain interpolated CAZAC sequence into a plurality of subcarriers.

4. The apparatus of claim 1 , wherein the CAZAC sequence is a Zadoff-Chu sequence.

5. The apparatus of claim 1 , wherein the control circuitry is configured to determine the length of the guard interval of the OFDM symbols based, at least in part, on an expected delay spread of a communication channel between the one or more communication elements and the far-end communication device.

6. The apparatus of claim 5 , wherein the control circuitry is configured to dynamically modify the length of the guard interval as the expected delay spread of the communication channel changes.

7. The apparatus of claim 1 , wherein the control circuitry comprises control circuitry of a user equipment (UE) and the far-end communication device comprises a base station.

8. The apparatus of claim 7 , wherein the CAZAC sequence is a cyclically shifted version of CAZAC sequences assigned to other UEs communicating with the base station.

9. The apparatus of claim 1 , wherein the control circuitry comprises control circuitry of a cellular base station, and the far-end communication device comprises a user equipment (UE).

10. The apparatus of claim 9 , wherein:

the cellular base station has base sequences corresponding to different possible DMRS lengths assigned thereto, the base sequences different from base sequences assigned to other base stations; and

the CAZAC sequence is one of the base sequences assigned to the cellular base station.

11. The apparatus of claim 1 , wherein the control circuitry is configured to engage in time division duplex (TDD) communications with the far-end communication device.

12. An apparatus for a communication device, comprising:

control circuitry configured to operably couple to one or more communication elements, the control circuitry configured to:

process a demodulation reference signal (DMRS) received from a far-end communication device through one or more communication elements of the communication device;

perform a Fourier transform on the received DMRS to obtain a resulting signal;

use the resulting signal as a reference to demodulate orthogonal frequency-division multiplexing (OFDM) symbols received from the far-end communication device; and

perform a minimum mean squares estimation (MMSE) channel estimation on the resulting signal to estimate a communication channel between the communication device and the far-end communication device, wherein the MMSE channel estimation takes into account that the DMRS was generated from an appended constant amplitude zero-autocorrelation (CAZAC) sequence including zeros appended to a CAZAC sequence, wherein a length N SEQ of the CAZAC sequence used in the appended CAZAC sequence comprises a largest prime number such that:

N

×

N

S

⁢

⁢

E

⁢

⁢

Q

M

≤

N

-

N

G

⁢

⁢

I

,

where N is a number of samples in the OFDM symbols, M is a length of the appended CAZAC sequence, and N GI is a length of a guard interval of the OFDM symbols.

13. The apparatus of claim 12 , wherein the control circuitry includes a non-equal weight filter configured to process the OFDM symbols received from the far-end communication device as at least part of the MMSE channel estimation.

14. The apparatus of claim 12 , wherein the control circuitry is configured to, after channel equalization, remove guard interval (GI) interference resulting from GIs of the OFDM signals.

15. The apparatus of claim 14 , wherein the control circuitry is configured to remove the GI interference with an iterative channel estimation algorithm using previously determined channel estimates.

16. The apparatus of claim 12 , wherein the control circuitry is configured to de-map subcarriers of the resulting signal.

17. The apparatus of claim 12 , wherein the resulting signal is a frequency domain interpolated Zadoff-Chu sequence.

18. The apparatus of claim 12 , wherein the control circuitry is control circuitry for a user equipment (UE), and the far-end communication device includes a cellular base station.

19. The apparatus of claim 12 , wherein the control circuitry is control circuitry for a cellular base station, and the far-end communication device includes a user equipment (UE).

20. An apparatus for a user equipment (UE), comprising:

control circuitry configured to:

generate an appended Zadoff-Chu (ZC) sequence including a ZC sequence with zeros appended thereto, wherein a length N SEQ of the ZC sequence used in the appended ZC sequence is determined by selecting a largest prime number such that:

N

×

N

S

⁢

⁢

E

⁢

⁢

Q

M

≤

N

-

N

G

⁢

⁢

I

,

where N is a number of samples in orthogonal frequency-division multiplexing (OFDM) symbols, M is a length of the appended NZ sequence, and N GI is a length of a guard interval of the OFDM symbols;

spread the appended ZC sequence to obtain a frequency domain interpolated ZC sequence;

determine an inverse discrete Fourier transform (IDFT) of the frequency domain interpolated ZC sequence to generate a demodulation reference signal (DMRS) for coherent demodulation of orthogonal frequency-division multiplexing (OFDM) symbols transmitted by the UE to a cellular base station; and

cause the DMRS to be transmitted through a cellular data network to the cellular base station.

21. The apparatus of claim 20 , wherein the DMRS is a guard interval (GI) DMRS.

22. The apparatus of claim 20 , wherein the DMRS is a zero-tail DMRS.

23. The apparatus of claim 20 , wherein the control circuitry is configured to spread the appended ZC sequence by determining a discrete Fourier transform (DFT) of the ZC sequence.