# US 11,121,902 B2 · Signal generation for OFDM-based systems

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- Number: US 11,121,902 B2
- Document ID: US11121902B2
- Status: Granted
- Kind: B2
- Application number: 16/372,378
- Filed: 2019-04-01
- Published: 2019-10-10
- Granted: 2021-09-14
- Earliest claimed: 2018-04-05
- Assignees: QUALCOMM Incorporated
- Applicants: QUALCOMM Incorporated
- Inventors: Ayan Sengupta; Alberto Rico Alvarino
- Web page: https://patentgrep.com/patent/US11121902B2

## CPC

- H04L 27/2692: {with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver}
- H04L 27/2602: {Signal structure}
- H04L 27/2613: {Structure of the reference signals}
- H04L 27/26265: {Arrangements for sidelobes suppression specially adapted to multicarrier systems, e.g. spectral precoding}
- H04L 27/2636: {with FFT or DFT modulators, e.g. standard single-carrier frequency-division multiple access [SC-FDMA] transmitter or DFT spread orthogonal frequency division multiplexing [DFT-SOFDM]}
- H04L 27/2637: {with direct modulation of individual subcarriers}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

Methods, systems, and devices for wireless communications are described. A transmitting device may identify a first signal in a time domain, the first signal including multiple sequences spanning a bandwidth for multiple symbol periods. The transmitting device may segment the first signal into signal segments, where each signal segment corresponds to a respective symbol period of the multiple symbol periods. The transmitting device may apply a first transform operation to each signal segment of the signal segments and apply a bandwidth restriction in the frequency domain to the transformed signal segments. Then, the transmitting device may apply a second transform operation to each transformed signal segment to return the bandwidth-restricted segments to the time domain. The transmitting device may generate a second signal in the time domain based on the bandwidth-restricted segments. The transmitting device may then transmit the second signal to a receiving device.

## Claims

### Claim 1

A method for wireless communications, comprising:
identifying, at a first wireless device, a first signal in a time domain, the first signal comprising a plurality of sequences spanning a bandwidth for a plurality of symbol periods;
segmenting the first signal into a plurality of signal segments, wherein each signal segment corresponds to a respective symbol period of the plurality of symbol periods;
applying a first transform operation to each signal segment of the plurality of signal segments to obtain a plurality of transformed signal segments;
restricting frequency components of the plurality of transformed signal segments to the bandwidth;
applying a second transform operation different from the first transform operation to each transformed signal segment to obtain a plurality of output signal segments;
generating a second signal in the time domain based at least in part on obtaining the plurality of the output signal segments; and
transmitting the second signal to a second wireless device.

### Claim 2 (depends on 1)

The method of claim 1, further comprising:
determining frequency components for a transformed signal segment of the plurality of transformed signal segments; and
setting a value for the frequency components outside of the bandwidth to a predetermined value, wherein applying the second transform operation is based at least in part on setting the value for the frequency components.

### Claim 3 (depends on 1)

The method of claim 1, wherein applying the first transform operation comprises:
applying a fast Fourier transform (FFT) operation to at least one signal segment of the plurality of segments based at least in part on a length of the respective symbol period corresponding to the at least one signal segment.

### Claim 4 (depends on 1)

The method of claim 1, further comprising:
determining minimum mean square error (MMSE) estimate coefficients of at least one signal segment of the plurality of signal segments in the bandwidth, wherein applying the first transform operation is based at least in part on determining the MMSE estimate coefficients of the at least one signal segment; and
determining frequency components for at least one transformed signal segment in the bandwidth based at least in part on the MMSE estimate coefficients of the at least one signal segment, wherein applying the second transform operation is based at least in part on determining the frequency components for at least one transformed signal segment.

### Claim 5 (depends on 4)

The method of claim 4, further comprising:
adding at least one placeholder value to the MMSE estimate coefficients based at least in part on a length of the respective symbol period corresponding to the signal segment, wherein applying the second transform operation is based at least in part on adding the at least one placeholder value.

### Claim 6 (depends on 4)

The method of claim 4, wherein determining the MMSE estimate coefficients further comprises:
deriving a plurality of frequency components corresponding to the bandwidth using a preconfigured matrix that is based at least in part on the bandwidth and a length of the symbol period.

### Claim 7 (depends on 1)

The method of claim 1, wherein applying the second transform operation comprises:
applying an inverse fast Fourier transform (IFFT) operation to at least one transformed signal segment based at least in part on a length of the symbol period corresponding to the at least one transformed signal segment.

### Claim 8 (depends on 1)

The method of claim 1, further comprising:
appending at least a portion of at least one cyclic prefix to at least one output signal segment of the plurality of output signal segments.

### Claim 9 (depends on 8)

The method of claim 8, wherein a first length of a first cyclic prefix for a first output signal segment is different than a second length of a second cyclic prefix for a second output signal segment, and wherein appending the at least a portion of the at least one cyclic prefix to the at least one output signal segment of the plurality of output signal segments comprises:
appending a portion of the first cyclic prefix having the first length to the first output signal segment of the plurality of output signal segments and a portion of the second cyclic prefix having the second length to the second output signal segment of the plurality of output signal segments.

### Claim 10 (depends on 1)

The method of claim 1, wherein generating the second signal in the time domain further comprises:
combining the plurality of output signal segments using a sequential ordering of the plurality of output signal segments that approximates the first signal using the plurality of output signal segments.

### Claim 11 (depends on 1)

The method of claim 1, further comprising:
determining a set of samples for each signal segment based at least in part on a subcarrier spacing and a base sampling frequency, wherein applying the first transform operation and the second transform operation are based at least in part on the set of samples.

### Claim 12 (depends on 1)

The method of claim 1, wherein a symbol period of the plurality of symbol periods comprises an information period and a cyclic prefix period.

### Claim 13 (depends on 12)

The method of claim 12, wherein a length of the information period is based at least in part on a subcarrier spacing and a base sampling frequency.

### Claim 14 (depends on 1)

The method of claim 1, wherein the first signal comprises a set of zero values at a start of the first signal, wherein the set of zero values is based at least in part on a number of sequences in the plurality of sequences and a length of the plurality of sequences.

### Claim 15 (depends on 1)

The method of claim 1, wherein the plurality of transformed signal segments corresponds to a frequency domain, and the plurality of output signal segments corresponds to the time domain.

### Claim 16 (depends on 1)

The method of claim 1, wherein the first transform operation is based at least in part on:
a first matrix comprising an inverse discrete Fourier transform (DFT) kernel, wherein an order of the first matrix corresponds to a length of the respective symbol period;
a second matrix, wherein the second matrix is the first matrix with only a set of columns corresponding to the bandwidth; and
an identity matrix, wherein an order of the identity matrix corresponds to a length of a cyclic prefix of the respective symbol period.

### Claim 17 (depends on 1)

The method of claim 1, wherein a sequence of the plurality of sequences is a pseudorandom noise sequence or a Zadoff-Chu sequence.

### Claim 18

An apparatus for wireless communications, comprising:
a processor,
memory in electronic communication with the processor; and
instructions stored in the memory and executable by the processor to cause the apparatus to:
identify, at a first wireless device, a first signal in a time domain, the first signal comprising a plurality of sequences spanning a bandwidth for a plurality of symbol periods;
segment the first signal into a plurality of signal segments, wherein each signal segment corresponds to a respective symbol period of the plurality of symbol periods;
apply a first transform operation to each signal segment of the plurality of signal segments to obtain a plurality of transformed signal segments;
restrict frequency components of the plurality of transformed signal segments to the bandwidth;
apply a second transform operation different from the first transform operation to each transformed signal segment to obtain a plurality of output signal segments;
generate a second signal in the time domain based at least in part on obtaining the plurality of the output signal segments; and
transmit the second signal to a second wireless device.

### Claim 19 (depends on 18)

The apparatus of claim 18, wherein the instructions are further executable by the processor to cause the apparatus to:
determine frequency components for a transformed signal segment of the plurality of transformed signal segments; and
set a value for the frequency components outside of the bandwidth to a predetermined value, wherein applying the second transform operation is based at least in part on setting the value for the frequency components.

### Claim 20 (depends on 18)

The apparatus of claim 18, wherein the instructions to apply the first transform operation are executable by the processor to cause the apparatus to:
apply a fast Fourier transform (FFT) operation to at least one signal segment of the plurality of segments based at least in part on a length of the respective symbol period corresponding to the at least one signal segment.

### Claim 21 (depends on 18)

The apparatus of claim 18, wherein the instructions are further executable by the processor to cause the apparatus to:
determine minimum mean square error (MMSE) estimate coefficients of at least one signal segment of the plurality of signal segments in the bandwidth, wherein applying the first transform operation is based at least in part on determining the MMSE estimate coefficients of the at least one signal segment; and
determine frequency components for at least one transformed signal segment in the bandwidth based at least in part on the MMSE estimate coefficients of the at least one signal segment, wherein applying the second transform operation is based at least in part on determining the frequency components for at least one transformed signal segment.

### Claim 22 (depends on 18)

The apparatus of claim 18, wherein the instructions to apply the second transform operation are executable by the processor to cause the apparatus to:
apply an inverse fast Fourier transform (IFFT) operation to at least one transformed signal segment based at least in part on a length of the symbol period corresponding to the at least one transformed signal segment.

### Claim 23 (depends on 18)

The apparatus of claim 18, wherein the instructions to generate the second signal in the time domain further are executable by the processor to cause the apparatus to:
combine the plurality of output signal segments using a sequential ordering of the plurality of output signal segments that approximates the first signal using the plurality of output signal segments.

### Claim 24 (depends on 18)

The apparatus of claim 18, wherein the instructions to apply the second transform operation are executable by the processor to cause the apparatus to:
apply an inverse fast Fourier transform (IFFT) operation to at least one transformed signal segment based at least in part on a length of the symbol period corresponding to the at least one transformed signal segment.

### Claim 25 (depends on 18)

The apparatus of claim 18, wherein the instructions are further executable by the processor to cause the apparatus to:
append at least a portion of at least one cyclic prefix to at least one output signal segment of the plurality of output signal segments.

### Claim 26 (depends on 25)

The apparatus of claim 25, wherein a first length of a first cyclic prefix for a first output signal segment is different than a second length of a second cyclic prefix for a second output signal segment, and wherein the instructions are further executable by the processor to cause the apparatus to:
append a portion of the first cyclic prefix having the first length to the first output signal segment of the plurality of output signal segments and a portion of the second cyclic prefix having the second length to the second output signal segment of the plurality of output signal segments.

### Claim 27 (depends on 18)

The apparatus of claim 18, wherein the instructions to generate the second signal in the time domain further are executable by the processor to cause the apparatus to:
combine the plurality of output signal segments using a sequential ordering of the plurality of output signal segments that approximates the first signal using the plurality of output signal segments.

### Claim 28 (depends on 18)

The apparatus of claim 18, wherein the instructions are further executable by the processor to cause the apparatus to:
determine a set of samples for each signal segment based at least in part on a subcarrier spacing and a base sampling frequency, wherein applying the first transform operation and the second transform operation are based at least in part on the set of samples.

### Claim 29

An apparatus for wireless communications, comprising:
means for identifying, at a first wireless device, a first signal in a time domain, the first signal comprising a plurality of sequences spanning a bandwidth for a plurality of symbol periods;
means for segmenting the first signal into a plurality of signal segments, wherein each signal segment corresponds to a respective symbol period of the plurality of symbol periods;
means for applying a first transform operation to each signal segment of the plurality of signal segments to obtain a plurality of transformed signal segments;
means for restricting frequency components of the plurality of transformed signal segments to the bandwidth;
means for applying a second transform operation different from the first transform operation to each transformed signal segment to obtain a plurality of output signal segments;
means for generating a second signal in the time domain based at least in part on obtaining the plurality of the output signal segments; and
means for transmitting the second signal to a second wireless device.

### Claim 30

A non-transitory computer-readable medium storing code for wireless communications, the code comprising instructions executable by a processor to:
identify, at a first wireless device, a first signal in a time domain, the first signal comprising a plurality of sequences spanning a bandwidth for a plurality of symbol periods;
segment the first signal into a plurality of signal segments, wherein each signal segment corresponds to a respective symbol period of the plurality of symbol periods;
apply a first transform operation to each signal segment of the plurality of signal segments to obtain a plurality of transformed signal segments;
restrict frequency components of the plurality of transformed signal segments to the bandwidth;
apply a second transform operation different from the first transform operation to each transformed signal segment to obtain a plurality of output signal segments;
generate a second signal in the time domain based at least in part on obtaining the plurality of the output signal segments; and
transmit the second signal to a second wireless device.