# US 2018/0324003 A1 · Channel estimation in communications

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- Number: US 2018/0324003 A1
- Document ID: US20180324003A1
- Status: Published application
- Kind: A1
- Application number: 15/778,381
- Filed: 2015-11-26
- Published: 2018-11-08
- Earliest claimed: 2015-11-26
- Assignees: Nokia Solutions and Networks Oy
- Applicants: Nokia Solutions and Networks Oy
- Inventors: Wolfgang Zirwas; Berthold Panzner; Rakash Sivasiva Ganesan; Markus Jaeger; Gerhard Kramer
- Web page: https://patentgrep.com/patent/US20180324003A1

## CPC

- H04L 25/0204: {of multiple channels}
- H01Q 21/22: Antenna units of the array energised non-uniformly in amplitude or phase, e.g. tapered array or binomial array
- H04B 7/0417: Feedback systems
- H04B 7/0626: {Channel coefficients, e.g. channel state information [CSI]}
- H04B 7/066: {Combined feedback for a number of channels, e.g. over several subcarriers like in orthogonal frequency division multiplexing [OFDM]}
- H04B 7/265: {for channel frequency control}
- H04L 1/0026: {Transmission of channel quality indication}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H01Q: ANTENNAS, i.e. RADIO AERIALS (radiators or antennas for microwave heating H05B6/72)
- H04B: TRANSMISSION

## Abstract

A method is provided for channel estimation of an antenna array comprising multiple antenna elements. The method comprises obtaining channel state information for antenna elements with a high-end radio frequency chain, wherein the antenna elements with the high-end radio frequency chain are placed in the antenna array intermittently with antenna elements with a low-cost radio frequency chain. Channel state information is estimated for the antenna elements with the low-cost radio frequency chain, by interpolating the channel state information obtained for the antenna elements with the high-end radio frequency chain.

## Claims

### Claim 1

A method for channel estimation of an antenna array, the antenna array comprising multiple antenna elements, the method comprising performing the steps of:
obtaining channel state information for antenna elements with a high-end radio frequency chain, wherein the antenna elements with the high-end radio frequency chain are placed in the antenna array intermittently with antenna elements with a low-cost radio frequency chain;
estimating channel state information for the antenna elements with the low-cost radio frequency chain, by interpolating the channel state information obtained for the antenna elements with the high-end radio frequency chain.

### Claim 2 (depends on 1)

A method according to claim 1, wherein the channel state information estimation is based on a relative placement of the antenna elements in the antenna array.

### Claim 3 (depends on 1)

A method according to claim 1, wherein
the antenna elements with the low-cost radio frequency chain comprise antenna elements with a low-cost analog-to-digital converter; and/or
the antenna elements with the low-cost radio frequency chain comprise antenna elements with a low-cost digital-to-analog converter.

### Claim 4 (depends on 1)

A method according to claim 1, wherein the method comprises performing the steps of:
estimating the phase of an Rx signal in case the Rx signal is a single sinus signal, a rectangular signal, or a signal of some other suitable signal type;
using the Rx signal phase estimate to estimate the phase of a wideband radio channel by sequentially transmitting single-frequency reference signals;
changing frequency per reference signal subcarrier from one transmission to another until a full bandwidth has been sampled,
wherein, for time division duplex transmission, each antenna element with the low-cost radio frequency chain is able to estimate its phase from a single user equipment Tx signal;
combining the Rx signal phase estimate with an interpolated channel transfer function to correct phase estimation errors in the interpolated channel transfer function.

### Claim 5 (depends on 4)

A method according to claim 4, wherein the method comprises performing the step of:
utilizing the Rx signal phase estimate or channel state information estimate for calibrating low-cost frontend Tx and Rx radio frequency chains.

### Claim 6 (depends on 1)

A method according to claim 1, wherein the method comprises performing the steps of:
utilizing a few-bit digital-to-analog converter for downlink transmission; and
utilizing a high-end analog-to-digital converter in an uplink Rx radio frequency chain.

### Claim 7 (depends on 1)

A method according to claim 1, wherein the method comprises performing the steps of:
storing received signals as analogue samples in sample and hold devices included in the antenna elements with the low-cost radio frequency chain;
reading the stored analogue samples out in a time-multiplexed manner by using one or more available high-end analog-to-digital converters from full radio frequency frontends.

### Claim 8 (depends on 1)

A method according to claim 1, wherein the antenna array comprises a uniform linear antenna array, a rectangular antenna array, or an antenna array of some other shape.

### Claim 9 (depends on 1)

A method according to claim 1, wherein the method comprises:
switching full radio frequency frontends to a different subset of antenna elements, wherein the switching is carried out semi-statically or at the beginning of data transmission.

### Claim 10 (depends on 1)

A method according to claim 1, wherein the method comprises:
combining the interpolated channel state information with amplitude estimation, and after that using test signals and varying Rx thresholds for the analog-to-digital converters for achieving more accurate channel state information.

### Claim 11 (depends on 1)

A method according to claim 1, wherein the antenna array comprises a massive multiple input multiple output antenna array, wherein a majority of the radio frequency chains in the antenna array comprise low-cost radio frequency chains, and a minority of the radio frequency chains in the antenna array comprise high-end radio frequency chains.

### Claim 12 (depends on 1)

A method according to claim 1, wherein the antenna elements with the high-end radio frequency chain are placed in the antenna array in a regular grid with the antenna elements with the low-cost radio frequency chain.

### Claim 13 (depends on 1)

A method according to claim 1, wherein the interpolating is performed over an azimuth direction of the antenna array, over an elevation direction of the antenna array, or over some other direction of the antenna array.

### Claim 14

An apparatus comprising
at least one processor; and
at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to
obtain channel state information for antenna elements with a high-end radio frequency chain, wherein the antenna elements with the high-end radio frequency chain are placed in an antenna array intermittently with antenna elements with a low-cost radio frequency chain;
estimate channel state information for the antenna elements with the low-cost radio frequency chain, by interpolating the channel state information obtained for the antenna elements with the high-end radio frequency chain.

### Claim 15

(canceled)

### Claim 16

(canceled)

### Claim 17 (depends on 1)

A computer program product embodied on a non-transitory distribution medium readable by a computer and comprising program instructions which, when loaded into the computer, execute a computer process comprising causing a network node to perform any of the method of claim 1.

### Claim at position 18

-20. (canceled)