US 9,425,870 B2 · Method for performing multiple access in wireless OFDM cellular systems over multipath wireless channels considering both space and frequency domains, base station and computer programs thereof

A method for performing multiple access in wireless OFDM cellular systems over multipath wireless channels considering both space and frequency domains, wherein at least one base station equipped with a large number of antennas according to a two-dimensional rectangular array has complete knowledge of the channel characteristics between it and each one of a number M′ of cell users, said rectangular array comprising N1 antenna elements along one axis with a regular spacing dx and N2 antenna elements along a perpendicular axis with a regular spacing dy, and each one of said users being characterized by angles (θ,φ) in a spherical coordinate system discretized through a grid spacing (Δu,Δv) in the (u, v) domain to achieve orthogonality by letting u=sin(θ)cos(φ), v=sin(θ)sin(φ), dx=λ/(N1Δu), dy=λ/(N2Δv), uk=k·Δu and vl=l·Δv, for k=0,1, . . . , N1−1, 1=0, 1, . . . , N2−1,

the method characterized in that the at least one base station comprises performing following steps:
obtaining, from known training or pilot signals transmitted by each one of the users, signals in the (u, v) domain by means of:
S
R
⁡
[
k
,
⁢
l
,
⁢
f
]
=
⁢
1
N
c
⁢
N
1
⁢
N
2
⁢
⁢
∑
r
=
0
N
c
-
1
⁢
∑
n
=
0
N
1
-
1
⁢
∑
m
=
0
N
2
-
1
⁢
A
R
[
⁢
n
,
m
,
t
]
⁢
⁢
exp
(
-
j
⁢
2
⁢
π
N
c
⁢
ft
)
⁢
exp
(
j
⁢
2
⁢
π
N
1
⁢
nk
)
⁢
exp
(
j
⁢
2
⁢
π
N
2
⁢
ml
)
where AR[n,m,t] denotes the time-domain signal received by antenna element (n, m), Nc denotes the number of subcarriers in the frequency domain, and SR[k,l,f] denotes the frequency components of the received beam in (k, l) direction;
estimating angular channel coefficients corresponding to each one of the users by means of using the following equation:
SR[k,l,f]=Hi[k,l,f]·Piloti[f]+N,
where Piloti[f] denotes the a-priori known pilot/training signals transmitted by user i, Hi[k,l,f] is the channel frequency response associated with user i in the direction (k, l), and N is a complex additive noise component;
estimating an angular profile φi characterizing each on of the users, said angular profile φi comprising a set of directions, or beams, (k, l) in the (u, v) domain for which the estimated angular channel coefficients Ĥi[k,l,f] are not zero:
φi={(kj,lj), ∀j=0, . . . , N1N2−1 such that Ĥi[k,l,f]≠0};
discarding, from said estimated angular profiles φi, those beams belonging to two or more different angular profiles as they would cause inter-user interference, thereby leading to new angular profiles {tilde over (φ)}i given by:
{tilde over (φ)}i={(kj,lj)∈φi:(kj,lj)∉φi′∀i′≠i},i=0, . . . , M″−1,
where M″ denotes the number of different angular profiles after excluding beams causing inter-user interference, which coincides with a number of simultaneously addressable users;
allocating powers to each of the beams contained in said angular profiles {tilde over (φ)}i, in such a way that the sun of powers of the beams in an angular profile of the angular profiles {tilde over (φ)}i does not exceed a power allocated to the corresponding user;
and
calculating excitation coefficients for each one of said large number of antennas by means of:
A
T
⁡
[
n
,
m
,
f
]
=
1
N
1
⁢
N
2
⁢
⁢
∑
(
k
,
l
)
∈
Φ
~
⁢
P
T
⁡
[
k
,
l
]
·
(
∑
(
k
′
,
l
′
)
∈
Φ
~
⁢
U
⁡
[
k
,
l
,
k
′
,
l
′
,
f
]
⁢
S
T
⁡
[
k
′
,
l
′
,
f
]
)
⨯
exp
⁡
(
-
j
⁢
2
⁢
π
N
1
⁢
nk
)
⁢
exp
(
-
j
⁢
2
⁢
π
N
2
⁢
ml
)
where AT[n,m,f] is the excitation coefficient of antenna (n, m) in the frequency domain,
U[k,l,k′,l′,f] are the elements of a precoding matrix in the frequency domain of a direction (k,l) and a multipath direction (k′,l′), PT[k,l] is the transmit power allocated to the beam in the direction (k,l) in the frequency domain, and {tilde over (φ)} denotes a superposition of the angular profiles of all the users with a number of elements or beams, given by
M
≥
M
″
:
Φ
~
≡
⋃
i
=
0
M
″
-
1
⁢
Φ
~
i
.

246 more elements

A method for performing multiple access in wireless OFDM cellular systems over multipath wireless channels considering both space and frequency domains, wherein at least one base station equipped with a large number of antennas according to a two-dimensional rectangular array has no information on the channel characteristics between it and each one of a number M′ of cell users, said rectangular array comprising N1 antenna elements along one axis with a regular spacing dx and N2 antenna elements along a perpendicular axis with a regular spacing dy, and each one of said users being characterized by angles (θ,φ) in a spherical coordinate system discretized through a grid sparing (Δu,Δv) in the (u, v) domain to achieve orthogonality by letting u=sin(θ)cos(φ), v=sin(θ)sin(φ), dx=λ/(N1Δu), dy=λ/(N2Δv), uk=k·Δu and vl=l·Δv, for k=0,1, . . . , N1−1, l=0,1, . . . , N2−1,

the method being characterized in that the at least one base station comprises performing following steps:
obtaining, from known training or pilot signals transmitted by each one of the users, signals in the (u, v) domain by means of:
S
R
⁡
[
k
,
l
,
f
]
=
1
N
c
⁢
N
1
⁢
N
2
⁢
⁢
∑
r
=
0
N
c
-
1
⁢
∑
n
=
0
N
1
-
1
⁢
∑
m
=
0
N
2
-
1
⁢
A
R
[
⁢
n
,
m
,
t
]
⁢
exp
(
-
j
⁢
2
⁢
π
N
c
⁢
ft
)
⁢
exp
(
j
⁢
2
⁢
π
N
1
⁢
nk
)
⁢
⁢
exp
(
j
⁢
2
⁢
π
N
2
⁢
ml
)
,
where AR[n,m,t] denotes the time-domain signal received by antenna element (n, m), Nc denotes the number of subcarriers in the frequency domain, and SR[k,l,f] denotes the frequency components of the received beam in (k, l) direction;
estimating an angular profile φi characterizing each one of the users, said angular profile φi comprising a set of directions, or beams, (k, l) in the (u, v) domain for which received powers from each one of the users are not zero:
φi={(kj,lj), ∀j=0, . . . , N1N2−1 such that non-null signal is received by user i};
discarding, from said estimated angular profiles φi, those beams belonging to two or more different angular profiles as they would cause inter-user interference, thereby leading to new angular profiles {tilde over (φ)}i given by:
{tilde over (φ)}i={(kj, lj)∈φi:(kj,lj)∉φi′∀i′≠i},i=0, . . . , M″−1,
where M″ denotes the number of different angular profiles after excluding beams causing inter-user interference, which coincides with a number of simultaneously addressable users;
allocating powers to each of the beams in an angular profile of the angular profiles {tilde over (φ)}i, in such a way that the sum of powers of the beams in an angular profile of the angular profiles {tilde over (φ)}i does not exceed a power allocated to the corresponding user;
and
calculating excitation coefficients for each one of said large number of antennas by means of:
A
T
⁡
[
n
,
m
,
f
]
=
1
N
1
⁢
N
2
⁢
∑
(
k
,
l
)
∈
Φ
~
⁢
P
T
⁡
[
k
,
l
]
·
S
T
⁡
[
k
,
l
,
f
]
⁢
exp
⁡
(
-
j
⁢
2
⁢

N
1
⁢
nk
)
⁢
exp
⁡
(
-
j
⁢
2
⁢
π
N
2
⁢
ml
)
where AT[n,m,f] is the excitation coefficient of antenna (n, m) in the frequency domain, PT[k,l] is the transmit power allocated to the beam in the direction (k, l), ST[k,l,f] is the data corresponding to the direction (k,l) in the frequency domain, and {tilde over (φ)}i denotes a superposition of the angular profiles of all the users with a number of elements or beams, given by
M
≥
M
″
:
Φ
~
≡
⋃
i
=
0
M
″
-
1
⁢
Φ
~
i
.

208 more elements

A base station, comprising a large number of antennas according to a two-dimensional rectangular array and said base station being configured for performing multiple access in a wireless OFDM cellular system over a multipath wireless channel considering both space and frequency domains to a number M′ of cell users, said two-dimensional rectangular array comprising N1 antenna elements along one axis with a regular spacing dx and N2 antenna elements along a perpendicular axis with a regular spacing dy, and

each one (UE1, UE2, . . . , UEM′) of said users being characterized by angles (θ,φ) in a spherical coordinate system discretized through a grid spacing (Δu,Δv) in the (u, v) domain to achieve orthogonality by letting u=sin(θ)cos(φ), v=sin(θ)sin(φ), dx=λ/(N1Δu), dy=λ/(N2Δv), uk=k·Δu and vl=l·Δv, for k=0,1, . . . , N2−1, characterized in that the base station includes:
a scheduler configured for receiving, from each one (UE1, UE2, . . . , UEM′) of the users known training or pilot signals, and for obtaining the received known training or pilot signals in the (u, v) domain by means of:
S
R
⁡
[
k
,
l
,
f
]
=
1
N
c
⁢
N
1
⁢
N
2
⁢
⁢
∑
r
=
0
N
c
-
1
⁢
∑
n
=
0
N
1
-
1
⁢
∑
m
=
0
N
2
-
1
⁢
A
R
[
⁢
n
,
m
,
t
]
⁢
exp
(
-
j
⁢
2
⁢
π
N
c
⁢
ft
)
⁢
exp
(
j
⁢
2
⁢
π
N
1
⁢
nk
)
⁢
⁢
exp
(
j
⁢
2
⁢
π
N
2
⁢
ml
)
,
where AR[n,m,t] denotes the time-domain signal received by antenna element (n, m), Nc denotes the number of subcarriers in the frequency domain, and SR[k,l,f] denotes the frequency components of the received beam in (k, l) direction;
and
a processor configured for:
estimating an angular profile φi characterizing each one (UE1, UE2, . . . , UEM′) of the users,
wherein if the base station has complete knowledge of the characteristics of the multipath wireless channel between it and each one (UE1, UE2, . . . , UEM′) of said users, said angular profile φi comprises a set of directions, or beams, (k,l) in the (u,v) domain for which angular coefficients Ĥi[k,l,f] previously estimated by the base station are not zero:
φi={(kj,lj),∀j=0, . . . , N1N2−1 such that Ĥi[k,l,f]≠0};
or
wherein if the base station has no information of the characteristics of the multipath wireless channel between it and each one (UE1, UE2, . . . , UEM′) of said users, said angular profile φi comprises a set of directions or beams, (k,l) in the (u,v) domain for which received powers from each one of the users are not zero:
φi={(kj,lj), ∀j=0, . . . , N1N2−1 such that non-null signal is received by user i};
discarding from said estimated angular profiles φi those beams belonging to two or more different angular profiles as they would cause inter-user interference, thereby leading to new angular profiles {tilde over (φ)}i given by:
{tilde over (φ)}i={(kj, lj)∈φi:(kj,lj)∉φi′∀i′≠i},i=0, . . . , M″−1,
where M″ denotes the number of different angular profiles after excluding beams causing inter-user interference, which coincides with a number of simultaneously addressable users;
allocating powers to each of the beams contained in said angular profiles {tilde over (φ)}i, in such a way that the sum of powers of the beams in an angular profile of the angular profiles {tilde over (φ)}i does not exceed a power allocated to the corresponding user;
and
calculating excitation coefficients for each one of said large number of antennas, wherein if the base station has complete knowledge of the characteristics of the multipath wireless channel between it and each one (UE1, UE2, . . . , UEM′) of said users, by means of:
A
T
⁡
[
n
,
m
,
f
]
=
1
N
1
⁢
N
2
⁢
∑
(
k
,
l
)
∈
Φ
~
⁢
P
T
⁡
[
k
,
l
]
·
(
∑
(
k
,
l
)
∈
Φ
~
⁢
U
⁡
[
k
,
l
,
k
′
,
l
′
,
f
]
⁢
S
T
⁡
[
k
′
,
l
′
,
f
]
)
⨯
exp
⁡
(
-
j
⁢
2
⁢
π
N
1
⁢
nk
)
⁢
⁢
exp
(
-
j
⁢
2
⁢
π
N
2
⁢
ml
)
where AT[n,m,f] is the excitation coefficient of antenna (n, m) in the frequency domain,
U[k,l,k′,l′,f] are the elements of a precoding matrix in the frequency domain of a direction (k,l) and a multipath direction (k′,l′), PT[k,l] is the transmit power allocated to the beam in the direction (k,l), ST[k,l,f] is the data corresponding to the direction (k,l) in the frequency domain, and {tilde over (φ)} denotes a superposition of the angular profiles of all the users with a number of elements, or beams given by
M
≥
M
″
:
Φ
~
≡
⋃
i
=
0
M
″
-
1
⁢
Φ
~
i
;
or wherein if the base station has no information of the characteristics of the multipath wireless channel between it and each one (UE1, UE2, . . . , UEM′) of said users, the calculation of the excitation coefficients is by means of:
A
T
⁡
[
n
,
m
,
f
]
=
1
N
1
⁢
N
2
⁢
∑
(
k
,
l
)
∈
Φ
~
⁢
P
T
⁡
[
k
,
l
]
·
S
T
⁡
[
k
,
l
,
f
]
⁢
exp
⁡
(
-
j
⁢
2
⁢
π
N
1
⁢
nk
)
⁢
exp
(
-
j
⁢
2
⁢
π
N
2
⁢
ml
)
where AT[n,m,f] is the excitation coefficient of antenna (n, m) in the frequency domain, PT[k,l] is the transmit power allocated to the beam in the direction (k, l), ST[k,l,f] is the data corresponding to the direction (k, l) in the frequency domain, and {tilde over (φ)} denotes the superposition of the angular profiles of all the users with a number of elements, or beams, given by
M
≥
M
″
:
Φ
~
≡
⋃
i
=
0
M
″
-
1
⁢
Φ
~
i
.

344 more elements

Method for performing multiple access in wireless OFDM cellular systems over multipath wireless channels considering both space and frequency domains, base station and computer programs thereof

Life of this patent

Method for performing multiple access in wireless OFDM cellular systems over multipath wireless channels considering both space and frequency domains, base station and computer programs thereof

Life of this patent

Abstract

Claims14