# US 8,787,504 B2 · Enhancing channel estimates made in digital communications receivers

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- Number: US 8,787,504 B2
- Document ID: US8787504B2
- Status: Granted
- Kind: B2
- Application number: 13/679,942
- Filed: 2012-11-16
- Published: 2013-07-11
- Granted: 2014-07-22
- Earliest claimed: 2011-11-18
- Assignees: Cambridge Silicon Radio Limited
- Applicants: Cambridge Silicon Radio Limited
- Inventors: Andrei Barbu Popescu
- Web page: https://patentgrep.com/patent/US8787504B2

## CPC

- H04L 25/0202: {Channel estimation}
- H04L 25/022: {of frequency response}
- H04L 25/0228: {with direct estimation from sounding signals}
- H04L 27/2647: {Arrangements specific to the receiver only (equalisation H04L27/01)}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

Schemes for combining channel-estimates from different OFDM frames after compensating for changes in receiver-transmitter characteristics.

## Claims

### Claim 1

A method of refining a channel estimate for an OFDM sub-carrier, the method comprising:
calculating a first channel estimate for an OFDM sub-carrier for a first OFDM frame received at a receiver from a transmitter;
calculating a second channel estimate for the OFDM sub-carrier for a second OFDM frame received at the receiver from the transmitter at a time later than the first OFDM frame is received;
adjusting the first channel estimate to ameliorate a difference between the first and second channel estimates that arises from a shift in an operating state of the transmitter and the receiver between the times of reception of the first and second OFDM frames;
measuring a discrepancy between the second channel estimate and the adjusted first channel estimate;
modifying the second channel estimate by averaging the second channel estimate with the adjusted first channel estimate if the discrepancy is smaller than a predetermined amount; and
demodulating data from the second OFDM frame using the modified second channel estimate.

### Claim 2 (depends on 1)

A method according to claim 1, wherein the shift in the operating state comprises a change in a difference between an RF carrier angle of the receiver and an RF carrier angle of the transmitter.

### Claim 3 (depends on 2)

A method according to claim 2, wherein said adjusting step comprises estimating said change by:
a) for each of a plurality of OFDM sub-carriers:
i) providing a first channel estimate of that sub-carrier for the first OFDM frame;
ii) providing a second channel estimate of that sub-carrier for the second OFDM frame; and
iii) calculating the ratio of the first and second channel estimates for that sub-carrier; and
b) deducing an estimate of said change from an averaging-based calculation on the ratios deduced for said plurality of OFDM sub-carriers.

### Claim 4 (depends on 1)

A method according to claim 1, wherein the shift in the operating state comprises a change in the difference between the sampling instants of the transmitter and receiver.

### Claim 5 (depends on 4)

A method according to claim 4, wherein said adjusting step comprises estimating said change by:
a) for each of a plurality of OFDM sub-carriers:
i) providing a first channel estimate of that sub-carrier for the first OFDM frame;
ii) providing a second channel estimate of that sub-carrier for the second OFDM frame; and
iii) calculating the ratio of the first and second channel estimates for that sub-carrier; and
b) deducing an estimate of said change from an averaging-based calculation on the ratios deduced for said plurality of OFDM sub-carriers.

### Claim 6 (depends on 1)

A method according to claim 1, wherein the shift in the operating state comprises a change in an amplification gain imposed by at least one of the transmitter and the receiver.

### Claim 7 (depends on 6)

A method according to claim 6, wherein said adjusting step comprises estimating said change by:
a) for each of a plurality of OFDM sub-carriers:
i) providing a first channel estimate of that sub-carrier for the first OFDM frame;
ii) providing a second channel estimate of that sub-carrier for the second OFDM frame; and
iii) calculating the ratio of the first and second channel estimates for that sub-carrier; and
b) deducing an estimate of said change from an averaging-based calculation on the ratios deduced for said plurality of OFDM sub-carriers.