# US 12,003,350 B1 · Configurable orthogonal frequency division multiplexing (OFDM) signal and transmitter and receiver for user terminal to satellite uplink communications

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- Number: US 12,003,350 B1
- Document ID: US12003350B1
- Status: Granted
- Kind: B1
- Application number: 17/186,657
- Filed: 2021-02-26
- Granted: 2024-06-04
- Earliest claimed: 2020-02-29
- Assignees: Space Exploration Technologies Corp.
- Applicants: Space Exploration Technologies Corp.
- Inventors: Martin S. McCormick; Torbjorn Larsson; Alazar Tamrat; Jeffrey C. Strait; Chen Chen; Philip J. Treigherman; Stephan O. Roche; Ronald Gottula
- Web page: https://patentgrep.com/patent/US12003350B1

## CPC

- H04L 25/0202: {Channel estimation}
- H04B 7/1851: {Systems using a satellite or space-based relay (H04B7/18508, H04B7/18521 take precedence; providing specific services H04B7/18523 - H04B7/18576)}
- H04B 7/18513: {Transmission in a satellite or space-based system}
- H04B 7/18517: {Transmission equipment in earth stations}
- H04L 5/001: {the frequencies being arranged in component carriers}
- H04L 5/0048: {Allocation of pilot signals, i.e. of signals known to the receiver (allocation of control signalling H04L5/0053; use of control signalling H04L5/0091)}
- H04L 27/0014: {Carrier regulation (of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657)}
- 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]}
- H04W 56/002: {Mutual synchronization}
- H04W 56/0035: {detecting errors in frequency or phase}
- H04W 72/044: based on the type of the allocated resource
- H04W 72/0453: Resources in frequency domain, e.g. a carrier in FDMA
- H04L 2027/0026: {Correction of carrier offset}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H04B: TRANSMISSION
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)

## Abstract

A modem is configurable on a satellite, user terminal or gateway generates a radio frequency (RF) signal using an orthogonal frequency division multiplexing (OFDM) protocol including a radio frame including one or more bursts. A burst of the one or more bursts includes a first portion including burst detection data, a second portion including channel characteristic estimation data, a third portion including payload data, and fourth and fifth portions including pilot data. The first portion in a time domain is included in the burst prior to the second, third, fourth, and fifth portions. The first portion can include a pseudo-random noise sequence inserted in the time domain. The same physical modem can be configured to transmit signals on an uplink or downlink between a user terminal and a satellite or on the uplink or downlink between the satellite and the gateway.

## Claims

### Claim 1

A modem configured to transmit a waveform from a user terminal (UT) to a satellite (SAT), the modem comprising:
a transmitter, on the UT, configured to generate a transmission waveform directed to the SAT, the transmission waveform comprising:
a unique word configured in a first time period of a burst in a radio frame;
a channel estimation symbol configured in a second time period of the burst of the radio frame;
a first pilot subcarrier at a first frequency in a third time period of the burst in the radio frame;
a second pilot subcarrier at a second frequency in the third time period of the burst in the radio frame; and
a first pilot sub-band offset configured in the third time period and at a third frequency and a second pilot sub-band offset configured in the third time period and at a fourth frequency, wherein the third frequency of the first pilot sub-band offset is at a high frequency edge of a frequency band of the radio frame and the fourth frequency of the second pilot sub-band offset is at a low frequency edge of the frequency band of the radio frame;
a resource block comprising user data configured in the third time period and utilizing a set of frequency resources between the first pilot subcarrier and the second pilot subcarrier; and
a DC null configured in the third time period.

### Claim 2 (depends on 1)

The modem of claim 1, wherein the transmission waveform is configured to have a sampling rate of 62.5 MHz or 2×62.5 MHz.

### Claim 3 (depends on 1)

The modem of claim 1, wherein the modem further performs pre-compensation on the transmission waveform, the pre-compensation related to one or more of carrier frequency offset (CFO) and sampling frequency offset (SFO).

### Claim 4 (depends on 3)

The modem of claim 3, wherein the CFO is due to satellite movement and the SFO is due to local or remote reference crystal oscillator differences.

### Claim 5 (depends on 1)

The modem of claim 1, wherein the modem further comprises:
a crest factor reduction block that performs crest factor reduction on the transmission waveform.

### Claim 6 (depends on 1)

The modem of claim 1, wherein the modem further comprises:
a digital pre-distortion block that adjusts one or more of a power amplifier linearity, efficiency or power consumption for a given signal quality.

### Claim 7 (depends on 1)

The modem of claim 1, wherein the transmission waveform comprises an orthogonal frequency division multiplexed (OFDM) symbol, wherein the OFDM symbol comprises:
the first pilot subcarrier, the second pilot subcarrier and the resource block.

### Claim 8 (depends on 7)

The modem of claim 7, wherein the channel estimation symbol being associated with a channel and covering a channel estimation symbol set of frequency resources and wherein the OFDM symbol further comprises one or more of the channel estimation symbol, the first pilot subcarrier and the second pilot subcarrier.

### Claim 9 (depends on 8)

The modem of claim 8, wherein the transmission waveform transmitted from the UT is configured to be combined over an air interface with a second transmission waveform from a second UT such that the burst comprises:
the unique word;
the channel estimation symbol covering the channel estimation symbol set of frequency resources that correspond do the resource block;
the first pilot subcarrier;
the second pilot subcarrier;
the DC null;
a second channel estimation symbol covering a second channel estimation symbol set of frequency resources that correspond to a second resource block having second user data from the second UT;
a third pilot subcarrier associated with the second resource block; and
a fourth pilot subcarrier associated with the second resource block.

### Claim 10 (depends on 9)

The modem of claim 9, wherein the radio frame comprises a plurality of bursts, and wherein each burst of the plurality of bursts comprises data from one to four different UTs.

### Claim 11 (depends on 1)

The modem of claim 1, wherein the transmission waveform is modulated using a modulation and coding scheme chosen based on data received from the SAT.

### Claim 12 (depends on 1)

The modem of claim 1, wherein a first group of pilot subcarriers adjacent to the first pilot sub-band offset and a second group of pilot subcarriers adjacent to the second pilot sub-band offset are used to perform phase linear interpolation across a frequency band of the radio frame to correct for delay.

### Claim 13 (depends on 12)

The modem of claim 12, wherein when the SAT performs a phase linear interpolation across the frequency band of the radio frame based on the first group of pilot subcarriers and the second group of pilot subcarriers, the modem assumes a line-of-sight channel.

### Claim 14 (depends on 12)

The modem of claim 12, wherein the first pilot sub-band offset comprises a first group of pilot sub-band symbols and the second pilot sub-band offset comprises a second group of pilot sub-band symbols.

### Claim 15 (depends on 12)

The modem of claim 12, wherein the channel estimation symbol is first used by the SAT to estimate a channel and wherein a first group of pilot subcarriers adjacent to the first pilot sub-band offset and a second group of pilot subcarriers adjacent to the second pilot sub-band offset are used to correct for any residual delays or offset in the channel.

### Claim 16

A method performed by a user terminal (UT) for generating a transmission waveform for transmission to a satellite (SAT), the method comprising:
inserting a unique word in a first time period of a burst in a radio frame;
inserting a channel estimation symbol configured in a second time period of the burst of the radio frame;
configuring a first pilot subcarrier at a first frequency in a third time period of the burst in the radio frame;
configuring a second pilot subcarrier at a second frequency in the third time period of the burst in the radio frame;
inserting a first pilot sub-band offset configured in the third time period and at a third frequency;
inserting a second pilot sub-band offset configured in the third time period and at a fourth frequency, wherein the third frequency of the first pilot sub-band offset is at a high frequency edge of a frequency band of the radio frame and the fourth frequency of the second pilot sub-band offset is at a low frequency edge of the frequency band of the radio frame;
configuring a resource block comprising user data in the third time period within the burst of the radio frame, the resource block comprising a resource block set of frequency resources between the first pilot subcarrier and the second pilot subcarrier, the resource block being associated with the user data; and
configuring a DC null configured in the third time period.

### Claim 17 (depends on 16)

The method of claim 16, wherein the transmission waveform is configured to have a sampling rate of 62.5 MHz or 2×62.5 MHz.

### Claim 18 (depends on 16)

The method of claim 16 wherein the method further comprises:
performing pre-compensation on the transmission waveform, the pre-compensation related to one or more of carrier frequency offset (CFO) and sampling frequency offset (SFO).

### Claim 19 (depends on 18)

The method of claim 18, wherein the CFO is due to satellite and/or UT movement and SFO is due to local and remote reference oscillator differences.

### Claim 20 (depends on 16)

The method of claim 16, wherein the method further comprises:
performing crest factor reduction on the transmission waveform prior to transmission from the UT.

### Claim 21 (depends on 16)

The method of claim 16, wherein the method further comprises:
performing digital pre-distortion on the transmission waveform that adjusts one or more of a power amplifier linearity, efficiency or power consumption for a given signal quality.

### Claim 22 (depends on 16)

The method of claim 16, wherein the transmission waveform comprises an orthogonal frequency division multiplexed (OFDM) symbol, wherein the OFDM symbol comprises:
the first pilot subcarrier, the second pilot subcarrier and the resource block.

### Claim 23 (depends on 22)

The method of claim 22, wherein the OFDM symbol further comprises one or more of the channel estimation symbol, the first pilot subcarrier or the second pilot subcarrier.

### Claim 24 (depends on 16)

The method of claim 16, wherein the transmission waveform transmitted from the UT is configured to be combined over an air interface with a second transmission waveform from a second UT such that the burst comprises:
the unique word;
the channel estimation symbol covering a channel estimation symbol set of frequency resources that correspond do the resource block;
the first pilot subcarrier;
the second pilot subcarrier;
the DC null;
a second channel estimation symbol covering a second channel estimation symbol set of frequency resources that correspond to a second resource block having second user data from the second UT;
a third pilot subcarrier associated with the second resource block; and
a fourth pilot subcarrier associated with the second resource block.

### Claim 25 (depends on 24)

The method of claim 24, wherein the radio frame comprises a plurality of bursts, and wherein each burst of the plurality of bursts comprises data from one to four different UTs.

### Claim 26 (depends on 16)

The method of claim 16, wherein the transmission waveform is modulated using a modulation and coding scheme chosen based on data received from the SAT.

### Claim 27 (depends on 16)

The method of claim 16, wherein a first group of pilot subcarriers adjacent to the first pilot sub-band offset and a second group of pilot subcarriers adjacent to the second pilot sub-band offset are used to perform phase linear interpolation across a frequency band of the radio frame to correct for delay.

### Claim 28 (depends on 16)

The method of claim 16, wherein when the SAT performs a phase linear interpolation across a frequency band of the radio frame based on a first group of pilot subcarriers adjacent to the first pilot sub-band offset and a second group of pilot subcarriers adjacent to the second pilot sub-band offset, the SAT assumes a line-of-sight channel.

### Claim 29 (depends on 16)

The method of claim 16, wherein the first pilot sub-band offset comprises a first group of pilot sub-band symbols and the second pilot sub-band offset comprises a second group of pilot sub-band symbols.

### Claim 30 (depends on 16)

The method of claim 16, wherein the channel estimation symbol is first used by the SAT to estimate a channel and wherein the first pilot sub-band offset and the second pilot sub-band offset are used to correct for any residual delays or offset in the channel.

### Claim 31

A modem configured on a satellite (SAT) to receive a waveform transmitted to the SAT from a user terminal (UT), the modem comprising:
a receiver configured to receive the waveform from the UT, the waveform comprising:
a unique word configured in a first time period of a burst in a radio frame;
a channel estimation symbol configured in a second time period of the burst of the radio frame, the second time period adjacent to the first time period, the channel estimation symbol being associated with a channel and covering a channel estimation symbol set of frequency resources;
a first pilot subcarrier at a first frequency in a third time period of the burst in the radio frame;
a second pilot subcarrier at a second frequency in the third time period of the burst in the radio frame;
a first pilot sub-band offset configured in the third time period and at a third frequency;
a second pilot sub-band offset configured in the third time period and at a fourth frequency, and wherein the third frequency of the first pilot sub-band offset is at a high frequency edge of a frequency band of the radio frame and the fourth frequency of the second pilot sub-band offset is at a low frequency edge of the frequency band of the radio frame;
a resource block comprising user data configured in the third time period and utilizing a set of frequency resources between the first pilot subcarrier and the second pilot subcarrier; and
a DC null configured in the third time period;
a channel estimation component in the receiver that estimates the channel by extracting the channel estimation symbol; and
a pilot symbol processing component that performs phase linear interpolation across a frequency band of the radio frame, wherein the pilot symbol processing component performs phase linear interpolation across a frequency band of the radio frame using a first group of subcarriers adjacent to the first pilot sub-band offset and a second group of subcarriers adjacent to the second pilot sub-band offset and to correct for delay.

### Claim 32 (depends on 31)

The modem of claim 31, wherein the receiver further corrects for a carrier frequency offset (CFO) and a sampling frequency offset (SFO), wherein the CFO is due to satellite movement and the SFO is due to local or remote reference crystal oscillator differences.

### Claim 33 (depends on 31)

The modem of claim 31, wherein the waveform comprises an orthogonal frequency division multiplexed (OFDM) symbol, wherein the OFDM symbol comprises the first pilot subcarrier, the second pilot subcarrier and the resource block.

### Claim 34 (depends on 31)

The modem of claim 31, wherein the waveform received from the UT is configured to be combined over an air interface with a second transmission waveform from a second UT such that the burst comprises:
the unique word;
the channel estimation symbol covering the channel estimation symbol set of frequency resources that correspond do the resource block;
the first pilot subcarrier;
the second pilot subcarrier;
the DC null;
a second channel estimation symbol covering a second channel estimation symbol set of frequency resources that correspond to a second resource block having second user data from the second UT;
a third pilot subcarrier associated with the second resource block; and
a fourth pilot subcarrier associated with the second resource block.

### Claim 35 (depends on 34)

The modem of claim 34, wherein the radio frame comprises a plurality of bursts, and wherein each burst of the plurality of bursts comprises data from one to four different UTs.

### Claim 36 (depends on 31)

The modem of claim 31, wherein when the SAT performs the phase linear interpolation across the frequency band of the radio frame based on the first pilot sub-band offset and the second pilot sub-band offset, the modem assumes a line-of-sight channel.

### Claim 37 (depends on 31)

The modem of claim 31, wherein the first group of subcarriers and the second group of subcarriers each comprise one or more subcarriers.

### Claim 38 (depends on 31)

The modem of claim 31, wherein the channel estimation symbol is first used by the SAT to estimate the channel and wherein the first group of subcarriers and the second group of subcarriers are used to correct for any residual delays or offset in the channel.