Method and device for generating broadcast beams in massive MIMO systems

Patent metadata

Field	Value
Publication number	US-11038562-B2
Application number	US-202017032708-A
Country	US
Kind code	B2
Filing date	Sep 25, 2020
Priority date	Sep 26, 2019
Publication date	Jun 15, 2021
Grant date	Jun 15, 2021

Abstract

A method and transmitter for generating broadcast beam patterns in massive MIMO systems, the transmitter comprising a rectangular antenna array with a number N 1 of antenna elements in the horizontal direction and a number N 2 of antenna elements in the vertical direction. The MIMO transmitter generates broadcast beam patterns with determined beam widths in horizontal and vertical dimensions to cover a sector area of a cell by the rectangular antenna array radiating N 1 ×N 2 radiofrequency signals at a carrier frequency, the sector area being where a user equipment requests from the MIMO transmitter access to the cell. The beam widths in horizontal and vertical directions are determined by using an optimum set of complex excitation coefficients calculated from a discretized continuous-space array factor ψ(θ,φ), which is based on a discretization over the elevation angle θ and the azimuth angle φ of the antenna elements.

First claim

The invention claimed is:

1. A method for generating broadcast beam patterns in massive MIMO systems comprising:
defining a sector area of a cell covered by a MIMO transmitter, the sector area being where at least one user equipment requests from the MIMO transmitter access to the cell;
generating broadcast beam patterns with determined beam widths in horizontal and vertical dimensions to cover the sector area by a rectangular antenna array of the MIMO transmitter, the rectangular antenna array formed by a number N 1 of antenna elements in the horizontal direction and a number N 2 of antenna elements in the vertical direction radiating N 1 ×N 2 radiofrequency signals at a carrier frequency, with inter-antenna spacing in the horizontal and vertical directions given by d x and d y respectively, the beam widths in horizontal and vertical directions being determined by using an optimum set of excitation coefficients;
wherein the excitation coefficients are calculated by means of the following steps:
discretizing a continuous-space array factor ψ(θ, φ) to obtain a discretized array factor ψ(u k , v l )≡ψ kl ∈ , formed by a discrete set of complex values ψ kl ∈ , k=0, . . . , N 1 −1, l=0, . . . , N 2 −1, where the indices k, l, obey to a discretization over the elevation angle θ and the azimuth angle φ of the antenna elements; and
obtaining the optimum set of excitation coefficients {a nm }, in which a nm ∈ are complex excitation coefficients that minimize the following expression:
A vec =argmin{ −H ( A vec ) −H (Ψ vec )},

where
A vec ={a nm ,n= 0, . . . , N 1 −1, m= 0, . . . , N 2 −1} N 1 N 2 ×1 ,

Ψ vec ={ψ kl ,k= 0 , . . . ,N 1 −1 ,l= 0, . . . , N 2 −1} N 1 N 2 ×1

and H denotes the Shannon entropy for a sequence of N complex numbers {X n } which is defined as:

H
⁡

(
X
)

=

-

∑

n
=
0

N
-
1

|

X
n

⁢

|
2

⁢
ln
|

X
n

⁢

|
2

.

2. The method according to claim 1 , wherein the discretization of the continuous-space array factor ψ(θ, φ) comprises:
introducing the directional cosines u, v as functions of the elevation angle θ and azimuth angle φ, by means of the expressions:
u =sin θ cos φ,

v =sin θ sin φ;

and
discretizing said directional cosines by introducing sampling periods Δu, Δv that obey the Nyquist criterion, according to the following expressions:

Δ
⁢
u

=

2

N
1

,

Δ
⁢

⁢
v

=

2

N
2

,

⁢

u
k

=

k
·
Δ

⁢

⁢
u

,

k
=

-

N
1

⁢

2

,
…
⁢

,

N
1

2

-
1

,

⁢

v
l

=

l
·
Δ

⁢

⁢
v

,

l
=

-

N
2

2

,
…
⁢

,

N
2

2

-

1
.

3. The method according to claim 1 , wherein the discretized array factor ψ(u k ,v l )≡ψ kl ∈ is obtained, for the set of complex excitation coefficients a nm , in the form:

ψ

k
⁢
l

=

1

N
1

⁢

N
2

⁢

∑

n
=
0

N

Assignees

• Telefonica Sa

Inventors

• Lorca Hernando Javier
• Serna Santiago Elena
• Marti Molina Monica

Classifications

• H04B7/0456

  Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting · CPC title

• H04B7/0452 Primary

  Multi-user MIMO systems · CPC title

• H04B7/043 Primary

  using best eigenmode, e.g. beam forming or beam steering · CPC title

• H04B7/0617

  for beam forming · CPC title

• H01Q21/28

  Combinations of substantially independent non-interacting antenna units or systems {(multiple beam H01Q25/00)} · CPC title