# US 11,121,760 B2 · Multiple-input multiple output communication system with virtual trajectory reception for doubly selective channels

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- Number: US 11,121,760 B2
- Document ID: US11121760B2
- Status: Granted
- Kind: B2
- Application number: 16/603,172
- Filed: 2017-04-06
- Published: 2020-01-30
- Granted: 2021-09-14
- Earliest claimed: 2017-04-05
- Assignees: Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional
- Applicants: Centro de Investigación y de Estudios Avanzados ..
- Inventors: Fernando Peña Campos; Ramón Parra Michel; Valeri Kontorovich Mazover
- Web page: https://patentgrep.com/patent/US11121760B2

## CPC

- H04B 7/086: {using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming}
- H04L 25/03891: {Spatial equalizers (MIMO diversity systems H04B7/0413)}
- G01S 13/505: {using Doppler effect for determining closest range to a target or corresponding time, e.g. miss-distance indicator}
- H04B 7/0857: {using maximum ratio combining techniques, e.g. signal-to- interference ratio [SIR], received signal strenght indication [RSS]}
- H04B 7/088: {using beam selection}
- H04W 24/02: Arrangements for optimising operational condition
- H04W 72/0453: Resources in frequency domain, e.g. a carrier in FDMA
- H04B 7/0413: MIMO systems
- H04B 7/068: {using space frequency diversity (space-frequency coding H04L1/0606)}
- H04L 5/001: {the frequencies being arranged in component carriers}
- H04L 25/0244: {with inversion}
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)

## Abstract

The invention described herein presents a system and method to overcome the distortions and affectations introduced by the highly variant channels of one or several antennas both in the transmitter and in the receiver. Unlike any existing invention that operates under the same conditions, this device uses a completely new reception technique based on the concept of virtual trajectories in which iterative calculations or solution of linear systems in operating time are not required, thus saving a considerable amount of operations. The receiver of this device manages to convert the fast variations of the channel into virtual antennas, thus achieving a considerable increase in the signal to noise-interference ratio. The resulting performance in terms of noise immunity is much better than any technique found so far and also requires a much smaller amount of calculations in the receiver.

## Claims

### Claim 1

A communication system of Multiple Inputs and Multiple Outputs (“MIMO”) for doubly selective channels with reception of virtual trajectories comprising:
a. a variant that implements pilot transmission and consistent reception through:
(i) a transmitter structure where the data is entered into a space frequency encoder with space frequency block coding “(SFBC”) coding by annexing pilot subcarriers so that the receiver can perform coherent data detection, to achieve the above, wherein:
(1) an assignment of the symbols to the carriers of each virtual antenna is carried out,
(2) each branch is modulated in a conventional orthogonal frequency multiplexing (OFDM) scheme,
(3) next transmission modes are converted to antennas,
(3) Doppler virtual trajectories are estimated to obtain diagonalized models free of interference so that the virtual path coefficients are obtained using equations:
ϑ
^
b
=
⁢
Ψ
†
⁢
Y
b
=
∑
a
=
0
M
T
-
1
⁢
⁢
Ψ
†
⁢
ΨΩ
a
,
b
⁢
β
a
+
Ψ
†
⁢
w
b
≈
∑
a
=
0
M
T
-
1
⁢
⁢
Ω
a
,
b
⁢
β
a
+
b
Ψ
†
=
⁢
(
Ψ
H
⁢
Ψ
)
-
1
⁢
Ψ
.
⁢
⁢
where
(4) an estimation of virtual trajectories is made using a matrix that is inverted out of execution, said estimation process is carried out at a design stage and an inverse matrix is saved in a receiver, so that said receiver only requires execution of a matrix-vector product to obtain estimates of virtual coefficients of interference-free data, and
(5) for consistent estimation of low complexity data, a suboptimal detector is used, so that the observation equation for the b-th reception mode and the q-th Doppler trajectory is found as
ϑ
^
b
,
q
=
∑
a
=
0
M
T
-
1
⁢
D
⁡
(
Γα
a
,
b
,
q
)
⁢
β
a
+
b
,
q
(6) wherein in said previous step a diagonalized data observation model is obtained, which is equivalent to a conventional MIMO-OFDM system in the presence of non-time-varying channels, and therefore Doppler diversity is manipulated as if were additional receiving antennas, thus obtaining an equivalent MIMO model with MD×MR virtual antennas receivers, and
ii A receiver structure, where after the stages of analog/digital coupling to the propagation medium, a signal received on each antenna of said receiver is projected in reception modes for conversion of physical antennas into virtual antennas, wherein said step requires each output signals of said receiver to be treated independently by each reception mode in each of virtual trajectory separators that operate based on the equations:
Ψ†FHFYb=Λub iii.
where
Λ
≡
Ψ
†
⁢
F
H
u
b
≡
FY
b
⁢
⁢
y
⁢
[
F
]
n
,
n
′
=
1
R
⁢
e
(
-
j
⁢
⁢
2
⁢
π
⁢
⁢
n
′
⁢
n
/
N
)
,
n
,
n
′
=
[
0
,
…
⁢
,
N
-
1
]
and (1) the case of a system with coherent detection, the result of said virtual trajectory estimator is used by a channel estimation algorithm that operates based on the equation:
a,b,q=Θ†{circumflex over (ν)}b,qP=(ΘHΘ)−1ΘH{circumflex over (ν)}b,qP
which in turn passes virtual trajectory coefficients along with estimated channel parameters to a SFBC decoder, and wherein temporary space decoder (SFBC for the coherent case) delivers estimated data, and
b. a variant that uses differential coding and incoherent reception by:
i. a transmitter structure where data is introduced to a space frequency encoder by means of differential DSFBC encoding so that a receiver uses incoherent detection of the data, and to achieve the above the following steps are implemented
(1) an assignment of symbols to carriers of each virtual antenna is carried out,
(2) each branch is modulated in a conventional orthogonal frequency multiplexing (OFDM) scheme and subsequently, the transmission modes are converted to antennas,
(3) Doppler virtual paths are estimated to obtain diagonalized models free of interference so that virtual trajectory coefficients are obtained as:
ϑ
^
b
=
⁢
Ψ
†
⁢
Y
b
=
∑
a
=
0
M
T
-
1
⁢
⁢
Ψ
†
⁢
ΨΩ
a
,
b
⁢
β
a
+
Ψ
†
⁢
w
b
≈
∑
a
=
0
M
T
-
1
⁢
⁢
Ω
a
,
b
⁢
β
a
+
b
Ψ
†
=
⁢
(
Ψ
H
⁢
Ψ
)
-
1
⁢
Ψ
.
⁢
⁢
where
(4) virtual paths are estimated using a matrix that is inverted out of execution, wherein a receiver only requires execution of a matrix-vector product to obtain estimates of virtual coefficients of the interference-free data, and
(5) using the model
ϑ
^
b
,
q
=
∑
a
=
0
M
T
-
1
⁢
D
⁡
(
β
a
)
⁢
Γα
a
,
b
,
q
+
b
,
q
and assuming that from the total amount of subcarriers {βa,i|i∈0, . . . , NI−1, a∈0, . . . , MT−1}, a un subset {βa,iP|p∈P} have pilots, provides an input/output ratio in a MIMO system is equivalent to a MIMO-OFDM system in invariant systems with the additional advantage of incorporating temporal variability in the form of virtual receiving antennas, wherein, inconsistent reception techniques based on differential space-frequency coding (DSFBC) can be transparently incorporated into this system, and a receiver structure where after stages of analog/digital coupling to propagation medium, the signal received on each antenna is projected in reception modes for conversion of physical antennas into virtual antennas, according to the following steps:
each output signals of this module is treated independently by each reception mode in each of the virtual trajectory separators that operate based on the equations
Ψ†FHFYb=Λub
where
Λ
≡
Ψ
†
⁢
F
H
u
b
≡
FY
b
⁢
⁢
y
⁢
[
F
]
n
,
n
′
=
1
R
⁢
e
(
-
j
⁢
⁢
2
⁢
π
⁢
⁢
n
′
⁢
n
/
N
)
,
n
,
n
′
=
[
0
,
…
⁢
,
N
-
1
]
and,
wherein there is a variant with incoherent reception, virtual path coefficients are transferred directly to the DSFBC differential decoder and wherein temporary space decoder (DSFBC for incoherent cases) delivers estimated data.

### Claim 2 (depends on 1)

The Multiple Inputs and Multiple Outputs (“MIMO”) communications system for doubly selective channels with virtual trajectories reception according to claim 1 wherein said system is compatible with MIMO OFDM systems wherein said transmitter requires changes only in a carrier assignment stage, and said receiver it is required to incorporate the estimation stage of virtual paths.

### Claim 3

A method for calculating parameters and matrices in a transmitter and receiver system for a Multiple Inputs and Multiple Outputs communication system for doubly selective channels with virtual trajectory reception comprising:
a first step of calculating of parameters and matrices in said transmitter and receiver system offline at a predetermined time
wherein said calculation step is not performed when said system is trasmitting or receiving signals, and said calculation comprises;
(1) calculation of system parameters,
(2) calculation of channel expansion functions that are necessary according to the equation:
h
⁡
[
v
,
ρ
;
n
,
l
]
=
∑
a
=
0
M
T
⁢
⁢
∑
b
=
0
M
R
⁢
⁢
∑
r
=
0
M
τ
-
1
⁢
⁢
∑
q
=
0
M
D
-
1
⁢
⁢
α
a
,
b
,
r
,
q
⁢
ϕ
a
IV
⁡
[
v
]
⁢
ϕ
b
III
⁡
[
ρ
]
⁢
ϕ
r
II
⁡
[
l
]
⁢
ϕ
q
I
⁡
[
n
]
+
ɛ
⁡
[
v
,
ρ
,
n
,
l
]
,
where
ϕaIV[v], ϕbIII[ρ], ϕrII[l], ϕqI[n] and αa,b,r,q
are functions that expand the domain of receiving antennas, receiving antennas, the delay time and the time respectively, each with the coefficient αa,b,r,q, and wherein
(III) information of parameters of maximum dispersion in time and frequency, correlation of the channel or in its absence maximum dispersions of arrival angles, as well as block size and bandwidth of the system are used, in said second calculation step, and
(i) expansion functions are used to calculate the quantity and distribution of carriers that the transmitter using the equation:
ki=iMD−N/2
, and
(ii) results of the previous said calculations are used to further calculate a virtual trajectory separation matrix A in a transmission modes using a truncated version of the matrix defined in the equation:
Ψ†FHFYb=Λub
where
Λ
≡
Ψ
†
⁢
F
H
u
b
≡
FY
b
⁢
⁢
and
⁢
[
F
]
n
,
n
′
=
1
R
⁢
e
(
-
j
⁢
⁢
2
⁢
π
⁢
⁢
n
′
⁢
n
/
N
)
,
n
,
n
′
=
[
0
,
…
⁢
,
N
-
1
]
it is verified if the system has coherent detection, if it is not, a calculation of parameters is completed since the calculation of additional system parameters is not required, and
for coherent detection a calculation of a channel estimation matrix is performed Θ†, by using information on the position of the pilot carriers as well as their respective values in the equations
b,q=Φ†{circumflex over (ν)}b,qP=(ΦHΦ)−1ΦH{circumflex over (ν)}b,qP
{circumflex over (ν)}b,qP=D(βaP)ΓPαa,b,q+b,qP=Θαa,b,q+b,qP
where Θ□D(βaP)ΓP,
parameters of base expansion of the channel is then calculated separately for each of the transmission modes, using the least squares criterion.