# US 7,609,616 B2 · Sparse channel estimation for orthogonal frequency division multiplexed signals

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- Number: US 7,609,616 B2
- Document ID: US7609616B2
- Status: Granted
- Kind: B2
- Application number: 11/750,039
- Filed: 2007-05-17
- Published: 2007-09-27
- Granted: 2009-10-27
- Earliest claimed: 2001-05-10
- Assignees: Intel Corporation
- Inventors: Eric A. Jacobsen
- Web page: https://patentgrep.com/patent/US7609616B2

## CPC

- H04L 25/0234: {by non-linear interpolation}
- 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

A computationally efficient channel estimation technique for use within an orthogonal frequency division multiplexing (OFDM) communication system determines coefficients of a channel transfer function by calculating the dot products of a pilot vector and a plurality of interpolation vectors. One dot product is preferably calculated for each subcarrier of interest within the system. The pilot vector is extracted from an OFDM symbol received from a communication channel. In a preferred approach, a number of interpolation vectors are precalculated and stored within a communication device for subsequent use during channel estimation and equalization operations. The technique is highly flexible and can be implemented using, for example, a variable user block size or a variable pilot vector size.

## Claims

### Claim 1

A method comprising:
receiving an OFDM symbol using a communication device, wherein the OFDM symbol includes a plurality of data subcarriers and a plurality of pilot symbols;
assigning a subset of the data subcarriers to a user terminal on a dynamic basis, wherein those data subcarriers assigned to user terminals are subcarriers of interest;
extracting a pilot vector from the OFDM symbol using a subset of the pilot symbols;
identifying subcarriers of interest in the OFDM symbol;
retrieving a stored interpolation vector for each subcarrier of interest;
generating an equalization coefficient for each subcarrier of interest by calculating a dot product between the pilot vector and each of the retrieved interpolation vectors; and
modifying the subcarriers of interest within the received OFDM symbol using the equalization coefficients.

### Claim 2 (depends on 1)

The method of claim 1, further comprising dynamically varying the number of data subcarriers assigned to the user terminal during operation of the communication device.

### Claim 3 (depends on 2)

The method of claim 2, also further comprising dynamically varying the number of subcarriers in each of a plurality of OFDM symbols,
wherein receiving an OFDM symbol includes receiving the plurality of OFDM symbols, and
wherein identifying subcarriers of interest in the OFDM symbols includes identifying a varying number of data subcarriers assigned to the user terminal.

### Claim 4 (depends on 1)

The method of claim 1, also further comprising dynamically varying the number of pilot symbols in each OFDM symbol.

### Claim 5 (depends on 1)

The method of claim 1, wherein retrieving a stored interpolation vector for each subcarrier of interest also includes:
predetermining an interpolation vector for each subcarrier of interest; and
storing the interpolation vector in a memory of the communication device.

### Claim 6 (depends on 5)

The method of claim 5, wherein predetermining the interpolation vector includes calculating the interpolation vector In according to
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,
where M is the length of the interpolation vector, N is the number of subcarriers in the OFDM symbol.

### Claim 7

A communication device, for use in a communication system implementing orthogonal frequency division multiplexing (OFDM), comprising:
a receiver subsystem configured to receive an OFDM symbol from a communication channel, wherein the OFDM symbol includes a plurality of data subcarriers, and
an equalization subsystem including:
a pilot vector unit configured to extract a pilot vector from the OFDM symbol;
a subcarrier tracking unit configured to track subcarriers of interest, wherein subcarriers of interest are those data subcarriers assigned to user terminals on a dynamic basis;
an interpolation vector retrieval unit configured to retrieve an interpolation vector stored in a memory for each subcarrier of interest; and
a computation unit configured to generate an equalization coefficient for each subcarrier of interest by calculating a dot product between the pilot vector and each retrieved interpolation vector and to modify the subcarriers of interest within the received OFDM symbol using the equalization coefficients.

### Claim 8 (depends on 7)

The communication device of claim 7, wherein the computation unit is configured to equalize a subcarrier of interest using an equalization coefficient to determine a channel estimate.

### Claim 9 (depends on 7)

The communication device of claim 7, wherein the computation unit is configured to divide a subcarrier of interest by an equalization coefficient to remove undesired channel effects from the OFDM symbol.

### Claim 10 (depends on 7)

The communication device of claim 7, wherein the computation unit includes a soft-PHY architecture processor to calculate the dot product of the pilot vector and an interpolation vector.

### Claim 11 (depends on 7)

The communication device of claim 7, wherein the subcarrier tracking unit is configured to track a varying number of data subcarriers assigned to a user terminal.

### Claim 12 (depends on 7)

The communication device of claim 7, wherein the pilot vector unit is configured to extract pilot vectors from a plurality of OFDM symbols having a varying number of pilot symbols.

### Claim 13 (depends on 7)

The communication device of claim 7, wherein the subcarrier tracking unit is configured to track a varying number of subcarriers of interest in each of a plurality OFDM symbols.

### Claim 14 (depends on 7)

The communication device of claim 7, also including a memory to store a predetermined interpolation vector for each subcarrier of interest.

### Claim 15

A radio frequency (RF) transceiver comprising:
a receiver subsystem configured to receive an orthogonal frequency division multiplexing (OFDM) symbol from a communication channel, wherein the OFDM symbol includes a plurality of data subcarriers; and
an equalization subsystem including:
a pilot vector unit configured to extract a pilot vector from the OFDM symbol;
a subcarrier tracking unit configured to track subcarriers of interest, wherein a subset of the plurality of data subcarriers are dynamically assigned to a user terminal, and wherein the subcarriers of interest are those data subcarriers assigned to user terminals;
a flash memory to store a predetermined interpolation vector for each subcarrier of interest;
an interpolation vector retrieval unit configured to retrieve a interpolation vector for each subcarrier of interest from the flash memory; and
a computation unit configured to generate an equalization coefficient for each subcarrier of interest by calculating a dot product between the pilot vector and each of the retrieved interpolation vectors and modify the subcarriers of interest within the received OFDM symbol using the equalization coefficients.

### Claim 16 (depends on 15)

The radio frequency (RF) transceiver of claim 15, wherein the subcarrier tracking unit is configured to track a varying number of data subcarriers assigned to a user terminal, wherein the data subcarriers assigned to a user are non-adjacent to one another in the OFDM symbol.

### Claim 17 (depends on 16)

The radio frequency (RF) transceiver of claim 16, wherein the computation unit is configured to equalize the non-adjacent data subcarriers assigned to the user terminal using the equalization coefficients.