# US 11,115,085 B1 · MIMO-OFDM system for increasing reliability

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- Number: US 11,115,085 B1
- Document ID: US11115085B1
- Status: Granted
- Kind: B1
- Application number: 17/084,606
- Filed: 2020-10-29
- Granted: 2021-09-07
- Earliest claimed: 2020-07-24
- Assignees: Industry-Academia Cooperation Group of Sejong University
- Applicants: Industry-Academia Cooperation Group of Sejong University
- Inventors: Hyoung-Kyu Song; Yu-Jin Na; Min-Jae Paek
- Web page: https://patentgrep.com/patent/US11115085B1

## CPC

- H04B 7/026: Co-operative diversity, e.g. using fixed or mobile stations as relays
- H04B 7/0413: MIMO systems
- H04B 7/046: {taking physical layer constraints into account}
- H04B 7/15507: {Relay station based processing for cell extension or control of coverage area, (network planning with network coordinated processing with regard to cell extension H04W16/26; network topologies using dedicated repeater stations H04W84/047; terminal devices adapted for relaying to or from an other terminal H04W88/04)}
- H04L 5/0007: {the frequencies being orthogonal, e.g. OFDM(A) or DMT}
- H04L 25/0204: {of multiple channels}
- H04L 25/0224: {using sounding signals}
- H04L 25/0248: {Eigen-space methods}
- H04L 25/0258: {Channel estimation using zero-forcing criteria}
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A MIMO-OFDM system for increasing reliability includes a transmission terminal that includes Nt transmission antennas and transmits a MIMO signal through relay terminals, and a reception terminal that receives the MIMO signal from the relay terminal through Nr reception antennas, and the transmission terminal extracts a composite channel coefficient from a composite channel generated by matching a channel between the transmission terminal and the reception terminal with a channel between each of a plurality of the relay terminals and the reception terminal, selects the relay terminal corresponding to the composite channel coefficient having a maximized channel capacity from among the plurality of relay terminals by using the extracted composite channel coefficient, and transmits a MIMO signal to the reception terminal through the selected relay terminal.

## Claims

### Claim 1

A MIMO-OFDM system for increasing reliability comprising:
a transmission terminal that includes Nt transmission antennas and transmits a MIMO signal through relay terminals; and
a reception terminal that receives the MIMO signal from the relay terminal through Nr reception antennas,
wherein the transmission terminal extracts a composite channel coefficient from a composite channel generated by matching a channel between the transmission terminal and the reception terminal with a channel between each of a plurality of the relay terminals and the reception terminal, selects the relay terminal corresponding to the composite channel coefficient having a maximized channel capacity from among the plurality of relay terminals by using the extracted composite channel coefficient, and transmits a MIMO signal to the reception terminal through the selected relay terminal,
wherein the transmission terminal includes:
a communication unit that estimates the composite channel by respectively transmitting pilot signals to the plurality of relay terminals;
a singular value extraction unit that acquires information on a channel matrix by using the estimated composite channel and extracts a singular value by applying a singular value decomposition (SVD) method to the channel matrix;
a composite channel coefficient calculation unit that calculates the composite channel coefficient by using the extracted singular value; and
a relay terminal selection unit that calculates a channel capacity by using the calculated composite channel coefficient and selects a relay terminal having a maximum value among the calculated channel capacities from among the plurality of relay terminals.

### Claim 2 (depends on 1)

The MIMO-OFDM system of claim 1, wherein the singular value extraction unit extracts a matrix for the singular value by using a following equation:
HK=UKΣKVKH
where HK denotes a composite channel matrix generated by using a K-th relay terminal, ΣK is a Nr×Nt matrix having a singular value σN2 of the composite channel matrix Hk as a diagonal component, UK is a Nr×Nr matrix consisting of a singular vector on the left side of a singular value HK, and VKH is a Nt×Nt matrix consisting of a singular vector on the right side of the singular value.

### Claim 3 (depends on 2)

The MIMO-OFDM system of claim 2, wherein the composite channel coefficient calculation unit calculates the composite channel coefficient by inserting the calculated singular value into a following equation:
ΛK=ΠNt(1+σN2)
where Λk denotes a product of the composite channel coefficients of the relay terminals, and σN2 denotes the singular value.

### Claim 4 (depends on 3)

The MIMO-OFDM system of claim 3, wherein the relay terminal selection unit calculates a channel capacity C for each of the plurality of relay terminals by using a following equation:
C=log2 ΠNt(1+ρσN2)
where ρ denotes
P
i
N
0
⁢
N
,
Pt is a power of a transmission signal, Nt denotes the number of transmission antennas, and NO denotes a noise power, and ΠN(1+σN2) is converted into a product ΛK of the composite channel coefficients of the relay terminals.

### Claim 5 (depends on 1)

The MIMO-OFDM system of claim 1, wherein the reception terminal includes:
a reception unit that receives the MIMO signal through the transmission terminal and the selected relay terminal;
a detection unit that detects an estimation signal {circumflex over (X)}sd transmitted through the channel between the transmission terminal and the reception terminal by applying a zero-forcing detection technique to the received MIMO signal and an estimation signal {circumflex over (X)}rd transmitted through the channel between the relay terminal and the reception terminal; and
a signal estimation unit that estimates a final signal by assigning a weighted value to each of the detected estimation signals.

### Claim 6 (depends on 5)

The MIMO-OFDM system of claim 5, wherein the received MIMO signal is represented by a following equation:
YDK=YSD+YRKD
HSDX+nSD+HRKDX+nRKD
where YSD denotes a reception signal transmitted through the channel between the transmission terminal and the reception terminal without passing through the relay terminal, and YRKD denotes a reception signal transmitted through a K-th relay terminal.

### Claim 7 (depends on 5)

The MIMO-OFDM system of claim 5, wherein the signal estimation unit estimates the final signal {circumflex over (X)}⋅ of a following equation by combining a weighted value consisting of channel coefficients σN2 with each of the detected estimation signals:
X
^
=
σ
s
⁢
d
σ
s
⁢
d
+
σ
rd
⁢
X
^
sd
+
σ
rd
σ
s
⁢
d
+
σ
rd
⁢
X
^
rd
where σsd denotes a channel coefficient between the transmission terminal and the reception terminal, and σrd denotes a channel coefficient between the selected relay terminal and the reception terminal.