# US 2021/0344389 A1 · Methods and apparatuses for cell-free massive mimo communication

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- Number: US 2021/0344389 A1
- Document ID: US20210344389A1
- Status: Published application
- Kind: A1
- Application number: 17/283,582
- Filed: 2018-11-06
- Published: 2021-11-04
- Earliest claimed: 2018-10-12
- Assignees: Telefonaktiebolaget LM Ericsson (publ)
- Applicants: Telefonaktiebolaget LM Ericsson (publ)
- Inventors: Pål FRENGER; Erik G. LARSSON; Giovanni INTERDONATO
- Web page: https://patentgrep.com/patent/US20210344389A1

## CPC

- H04B 7/0452: Multi-user MIMO systems
- H04W 52/146: {Uplink power control}
- 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 25/021: {Estimation of channel covariance}
- H04L 25/0228: {with direct estimation from sounding signals}
- H04W 52/34: TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
- H04W 52/42: in systems with time, space, frequency or polarisation diversity
- H04W 52/346: {distributing total power among users or channels}
- H04W 88/08: Access point devices
- H04B: TRANSMISSION
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

The present disclosure relates in general to telecommunications. In one of its aspects, the technology presented herein concerns a method, implemented in an Access Point (AP), for transmitting data intended for a terminal in a cell-free massive Multiple-Input and Multiple-Output (MIMO) communications system. The AP is grouped into a cluster together with other APs and the cluster operates autonomously. The cluster is connected to, and managed by, one Central Processing Unit (CPU). A message that the AP is selected to serve the terminal and data intended for said terminal are received from the CPU. Power control is independently conducted, exclusively considering the terminals that are served by the AP itself. Thereafter, said intended data is transmitted to the terminal.

## Claims

### Claim 1

A method implemented in an Access Point, AP, for transmitting data intended for a terminal in a cell-free massive Multiple-Input and Multiple-Output, MIMO, communications system, the AP being grouped into a cluster together with other APs and the cluster operates autonomously, and the cluster being connected to, and managed by, one Central Processing Unit, CPU, the method comprising:
receiving, from the CPU, a message that the AP is selected to serve the terminal and data intended for said terminal;
independently conducting power control, exclusively considering the terminals that are served by the AP itself; and
transmitting said intended data to the terminal.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the method further comprises:
receiving an uplink pilot from the terminal; and
estimating uplink channel condition from said uplink pilot.

### Claim 3 (depends on 1)

The method according to claim 1, wherein the method further comprises:
determining, based on a metric related to a relation between the AP and the terminal, that the AP can serve the terminal; and
transmitting a message to the CPU that the AP can serve the terminal.

### Claim 4 (depends on 3)

The method according to claim 3, wherein the metric is channel condition and wherein determining that the AP can serve the terminal is based on the channel condition estimated by the AP from uplink pilots received from the terminal.

### Claim 5 (depends on 1)

The method according to claim 1, wherein conducting power control comprises:
calculating a power control coefficient (η) for use with the terminal, wherein the power control coefficient (η) is calculated by a normalized function ƒ(⋅) of at least one parameter of the communications system, wherein the function ƒ(⋅) is normalized to ensure that a power constraint of the AP is fulfilled.

### Claim 6 (depends on 5)

The method according to claim 5, wherein the normalized function ƒ(⋅) is a function ƒ(⋅) of one or more local parameters of the communications system.

### Claim 7 (depends on 5)

The method according to claim 5, wherein the function ƒ(⋅) is a function ƒ(⋅) of variance of an estimated channel (γ) between the AP and the terminal.

### Claim 8 (depends on 5)

The method according to claim 5, wherein the function ƒ(⋅) is a function ƒ(⋅) of variances of estimated channels (γ) between the AP and at least a subset of terminals served by the AP.

### Claim 9

An Access Point, AP, configured to transmit data intended for a terminal in a cell-free massive Multiple-Input and Multiple-Output, MIMO, communications system, the AP being grouped into a cluster together with other APs and the cluster operates autonomously and the cluster being connected to, and managed by, one Central Processing Unit, CPU, the AP comprises:
a processing circuitry; and
a memory circuitry storing computer program code which, when run in the processing circuitry, causes the AP to:
receive, from the CPU, a message that the AP is selected to serve the terminal and data intended for said terminal;
independently conduct power control, exclusively considering the terminals that are served by the AP itself; and
transmit said intended data to the terminal.

### Claim 10 (depends on 9)

The AP according to claim 9, wherein the memory circuitry storing computer program code which, when run in the processing circuitry, further causes the AP to:
receive an uplink pilot from the terminal; and
estimate uplink channel condition from said uplink pilot.

### Claim 11 (depends on 9)

The AP according to claim 9, wherein the memory circuitry storing computer program code which, when run in the processing circuitry, causes the AP to:
determine, based on a metric related to a relation between the AP and the terminal, that the AP can serve the terminal; and
transmit a message to the CPU that the AP can serve the terminal.

### Claim 12 (depends on 11)

The AP according to claim 11, wherein the metric is channel condition and the memory circuitry storing computer program code which, when run in the processing circuitry, causes the AP to determine that the AP can serve the terminal based on the channel condition estimated by the AP from uplink pilots received from the terminal.

### Claim 13 (depends on 9)

The AP according to claim 9, wherein the memory circuitry storing computer program code which, when run in the processing circuitry, causes the AP to conduct power control by:
calculate a power control coefficient (η) for use with the terminal, wherein the power control coefficient (η) is calculated by a normalized function ƒ(⋅) of at least one parameter of the communications system, wherein the function ƒ(⋅) is normalized to ensure that a power constraint of the AP is fulfilled.

### Claim 14 (depends on 13)

The AP according to claim 13, wherein the normalized function ƒ(⋅) is a function ƒ(⋅) of one or more local parameters of the communications system.

### Claim 15 (depends on 13)

The AP according to claim 13, wherein the function ƒ(⋅) is a function ƒ(⋅) of variance of an estimated channel (γ) between the AP and the terminal.

### Claim 16 (depends on 13)

The AP according to claim 13, wherein the function ƒ(⋅) is a function ƒ(⋅) of variances of estimated channels (γ) between the AP and at least a subset of terminals served by the AP.

### Claim 17

A method, implemented in a Central Processing Unit, CPU, for transmitting data intended for a terminal in a cell-free massive Multiple-Input and Multiple-Output, MIMO, communications system, wherein the CPU is being connected to, and managing, a cluster of Access Points, APs, and the cluster operates autonomously, the method comprising:
transmitting, to all APs in the cluster, a message that the receiving APs are selected to serve the terminal and said data intended for the terminal.

### Claim 18 (depends on 17)

The method according to claim 17, wherein the method further comprises:
receiving, from an AP within the cluster, a message that said AP can serve the terminal; and
identifying all APs in the cluster that the CPU manages.

### Claim 19

A Central Processing Unit, CPU, configured to transmit data intended for a terminal in a cell-free massive Multiple-Input and Multiple-Output, MIMO, communications system, the CPU is being connected to, and managing, a cluster of Access Points, APs, and the cluster operates autonomously, the CPU comprising:
a processing circuitry; and
a memory circuitry storing computer program code which, when run in the processing circuitry, causes the CPU to:
transmit, to all APs in the cluster, a message that the receiving APs are selected to serve the terminal and said data intended for the terminal.

### Claim 20 (depends on 19)

The CPU according to claim 19, wherein the memory circuitry storing computer program code which, when run in the processing circuitry, further causes the CPU to:
receive, from an AP within the cluster, a message that said AP can serve the terminal; and
identify all APs in the cluster that the CPU manages.

### Claim at position 21

-23. (canceled)