# US 7,411,924 B2 · Method for allocating subchannels in an OFDMA mobile communication system

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- Number: US 7,411,924 B2
- Document ID: US7411924B2
- Status: Granted
- Kind: B2
- Application number: 10/996,699
- Filed: 2004-11-24
- Published: 2005-08-18
- Granted: 2008-08-12
- Earliest claimed: 2003-11-25
- Assignees: Samsung Electronics Co., Ltd.; Korea Advanced Institute of Science and Technology
- Inventors: Yoon-Ok Cho; Yong-Hoon Lee; Young-Ho Jung; Eung-Sun Kim; Jong-Hyeuk Lee; Jae-Hak Chung; Chang-Soo Hwang; Seung-Hoon Nam
- Web page: https://patentgrep.com/patent/US7411924B2

## CPC

- H04L 5/023: {Multiplexing of multicarrier modulation signals, e.g. multi-user orthogonal frequency division multiple access [OFDMA] (multicarrier modulation H04L27/2601)}
- H04L 1/0003: {by switching between different modulation schemes}
- H04L 1/0015: {characterised by the adaptation strategy}
- H04L 5/0044: {Allocation of payload; Allocation of data channels, e.g. PDSCH or PUSCH}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

An adaptive modulation scheme relating to an RA problem for maximizing the transmission rates of all users for maximum transmission rates in an OFDMA system including some users requiring to use services at fixed data rates. The scheme proposes introduction of an adaptive modulation using linear programming into an existing scheme for a system including a single kind of users, thereby enabling simultaneous execution of the adaptive modulation for all users in a system including two kinds of users. Further, the invention proposes another scheme of sequentially allocating subchannels to the users when the fixed transmission rate has a sufficiently small value, in order to reduce the complexity.

## Claims

### Claim 1

A method for allocating subchannels and bits to users in a mobile communication system including users requiring services of fixed transmission rates and users requiring services of variable transmission rates, for adaptive modulation, the method comprising the steps of:
determining a real number {z, ck} using a Lagrange Multiplier Method, the real number {z, ck} maximizing an objective equation in order to reconstruct a variable rate adaptive problem into a delivery problem;
solving the delivery problem through linear programming and allocating subchannels to the users; and
allocating bits to the subchannels allocated to the users using a Greedy Algorithm,
wherein the Lagrange Multiplier Method is based on
max
z
,
c
k
⁢
(
z
,
c
k
,
λ
,
μ
)
=
z
-
λ
⁡
(
∑
k
∈
U
Fixed
⁢
⁢
f
k
⁡
(
c
k
)
·
R
M
/
α
k
2
⁢
c
k
+
∑
k
∈
U
RA
⁢
⁢
f
k
⁡
(
c
k
)
·
z
/
α
k
2
⁢
c
k
-
P
T
)
-
μ
⁡
(
∑
k
∈
U
Fixed
⁢
⁢
R
M
/
c
k
+
∑
k
∈
U
RA
⁢
⁢
z
/
c
k
-
N
)
wherein ck denotes a number of bits to be allocated to a k-th user, Rk denotes a k-th user's data rate, PT denotes total allocated power, UFixed denotes a number of users requiring services of fixed transmission rates, URA denotes a number of users requiring services of variable transmission rates, ƒk(ck) denotes the K-th user's transmission power required for transmission satisfying a desired BER at a reception-side when a channel gain is 1, N denotes a number of the total subchannels, αk denotes a k-th user's channel gain, and λ and μ are parameters.

### Claim 2 (depends on 1)

The method as claimed in claim 1, wherein same bits are allocated to the subchannels allocated to the users.

### Claim 3 (depends on 1)

The method as claimed in claim 1, wherein the bits are first allocated to the users requiring the services of the fixed transmission rates and next to the users requiring the services of the variable transmission rates.

### Claim 4

A method for allocating subchannels and bits in a mobile communication system including users that are using two different kinds of services for adaptive modulation, first users requiring services of fixed transmission rates and second users requiring services of variable transmission rates, the method comprising the steps of:
(1) allocating subchannels and bits to the second users;
(2) determining an initial number NMA of subchannels to be allocated to the first users;
(3) consequently releasing the determined initial number NMA of subchannels from among the subchannels previously allocated to the second users;
(4) reallocating the released subchannels to the first users;
(5) allocating bits for the first users to reallocated subchannels; and
(6) repeating steps 3 through 5 a predetermined number of times for generating a number of non-initial released subchannels.

### Claim 5 (depends on 4)

The method as claimed in claim 4, wherein, in step 3, the initial number of subchannels are released according to a sequence in which a subchannel having a lowest channel quality precedes other channels.

### Claim 6 (depends on 4)

The method as claimed in claim 4, wherein, in step 2, the initial number NMA is determined by
N
MA
=
∑
k
∈
U
Fixed
⁢
⁢
n
k
=
∑
k
∈
U
Fixed
⁢
⁢
R
M
/
c
k
*
wherein ck denotes a number of bits to be allocated to a k-th user, Rk denotes a k-th user's data rate, and UFixed denotes a number of the first users requiring services of fixed transmission rates.

### Claim 7 (depends on 4)

The method as claimed in claim 4, wherein ck is obtained by applying parameters (λ, μ) to
max
c
k
,
z
⁢
(
z
,
c
k
,
λ
,
μ
)
⁢
=
z
-
λ
⁡
(
∑
k
=
1
K
1
⁢
⁢
f
k
⁡
(
c
k
)
·
R
M
/
α
k
2
⁢
c
k
+
∑
k
=
1
K
2
⁢
⁢
f
k
⁡
(
c
k
)
·
z
/
α
k
2
⁢
c
k
-
P
T
)
-
⁢
μ
⁡
(
∑
k
=
1
K
1
⁢
⁢
R
M
/
c
k
+
∑
k
=
1
K
2
⁢
⁢
z
/
c
k
-
N
)
⁢
≈
z
1
-
λ
1
⁡
(
∑
k
=
1
K
2
⁢
⁢
f
k
⁡
(
c
k
)
·
z
1
/
α
k
2
⁢
c
k
-
P
T
)
-
μ
1
⁡
(
∑
k
=
1
K
2
⁢
⁢
z
1
/
c
k
-
N
)
,
wherein PT denotes a total allocated power, K1 denotes a number of the first users requiring services of fixed transmission rates, K2 denotes a number of the second users requiring services of variable transmission rates, ƒk(ck) denotes the K-th user's transmission power required for transmission satisfying a desired BER at a reception-side when a channel gain is 1, N denotes a number of the total subchannels, and αk denotes a k-th user's channel gain.

### Claim 8

An apparatus for transmitting data to users through adaptive modulation in a mobile communication system including users requiring services of fixed transmission rates and users requiring services of variable transmission rates, the apparatus comprising:
a subchannel allocation and bit loading algorithm unit for determining a real number {z, ck} that maximizes an objective equation using a Lagrange Multiplier Method in order to reconstruct a variable rate adaptive problem into a delivery problem, solving the delivery problem through linear programming and allocating subchannels to each of the users, and allocating bits to the subchannels allocated to the users by using a Greedy Algorithm;
an adaptive modulator for adaptively modulating user data by means of the subchannels and bits allocated to the users and separately outputting the data for the allocated subchannels; and
an Inverse Fast Fourier Transform (IFFT) unit for converting the separated user data into a time domain signal and outputting the time domain signal as a signal sequence,
wherein the Lagrange Multiplier Method is based on
max
z
,
c
k
⁢
(
z
,
c
k
,
λ
,
μ
)
=
z
-
λ
⁡
(
∑
k
∈
U
Fixed
⁢
⁢
f
k
⁡
(
c
k
)
·
R
M
/
α
k
2
⁢
c
k
+
∑
k
∈
U
RA
⁢
⁢
f
k
⁡
(
c
k
)
·
z
/
α
k
2
⁢
c
k
-
P
T
)
-
μ
⁡
(
∑
k
∈
U
Fixed
⁢
⁢
R
M
/
c
k
+
∑
k
∈
U
RA
⁢
⁢
z
/
c
k
-
N
)
wherein ck denotes a number of bits to be allocated to a k-th user, Rk denotes a k-th user's data rate, PT denotes a total allocated power, UFixed denotes a number of users requiring services of fixed transmission rates, URA denotes a number of users requiring services of variable transmission rates, ƒk(ck) denotes the K-th user's transmission power required for transmission satisfying a desired BER at a reception-side when a channel gain is 1, N denotes a number of the total subchannels, αk denotes a k-th user's channel gain, and λ and μ are parameters.

### Claim 9 (depends on 8)

The apparatus as claimed in claim 8, wherein the subchannel allocation and bit loading algorithm unit allocates same bits to the subchannels allocated to the users.

### Claim 10 (depends on 8)

The apparatus as claimed in claim 8, wherein the subchannel allocation and bit loading algorithm unit first allocates the bits to the users requiring the services of the fixed transmission rates and next to the users requiring the services of the variable transmission rates.

### Claim 11

An apparatus for transmitting data to users through adaptive modulation in a mobile communication system including first users requiring services of fixed transmission rates and second users requiring services of variable transmission rates, the apparatus comprising:
a subchannel allocation and bit loading algorithm unit for allocating subchannels and bits to the second users, determining an initial number of subchannels to be allocated to the first users, releasing the initial number of subchannels from among the subchannels allocated to the second users, reallocating the released subchannels to the first users, and allocating bits for the first users to reallocated subchannels;
an adaptive modulator for adaptively modulating user data by means of the subchannels and bits allocated to the users and separately outputting the data for each of the allocated subchannels; and
an Inverse Fast Fourier Transform (IFFT) unit for converting the separated user data into a time domain signal and outputting the time domain signal as a signal sequence,
wherein the subchannel allocation and bit loading algorithm unit repeats the process from the releasing of the initial number of subchannels to the allocation of the bits a predetermined number of times.

### Claim 12 (depends on 11)

The apparatus as claimed in claim 11, wherein the subchannel allocation and bit loading algorithm unit releases the initial number of subchannels according to a sequence in which a subchannel having a lowest channel quality precedes other channels.

### Claim 13 (depends on 11)

The apparatus as claimed in claim 11, wherein the subchannel allocation and bit loading algorithm unit determines the initial number NMA by
N
MA
=
∑
k
∈
U
Fixed
⁢
⁢
n
k
=
∑
k
∈
U
Fixed
⁢
⁢
R
M
/
c
k
*
,
wherein ck denotes a number of bits to be allocated to a k-th user, Rk denotes a k-th user's data rate, and UFixed denotes a number of the first users requiring services of fixed transmission rates.

### Claim 14 (depends on 13)

The apparatus as claimed in claim 13, wherein ck is obtained by applying parameters (λ, μ) to
max
c
k
,
z
⁢
(
z
,
c
k
,
λ
,
μ
)
⁢
=
z
-
λ
⁡
(
∑
k
=
1
K
1
⁢
⁢
f
k
⁡
(
c
k
)
·
R
M
/
α
k
2
⁢
c
k
+
∑
k
=
1
K
2
⁢
⁢
f
k
⁡
(
c
k
)
·
z
/
α
k
2
⁢
c
k
-
P
T
)
-
⁢
μ
⁡
(
∑
k
=
1
K
1
⁢
⁢
R
M
/
c
k
+
∑
k
=
1
K
2
⁢
⁢
z
/
c
k
-
N
)
⁢
≈
z
1
-
λ
1
⁡
(
∑
k
=
1
K
2
⁢
⁢
f
k
⁡
(
c
k
)
·
z
1
/
α
k
2
⁢
c
k
-
P
T
)
-
μ
1
⁡
(
∑
k
=
1
K
2
⁢
⁢
z
1
/
c
k
-
N
)
,
wherein PT denotes a total allocated power, K1 denotes a number of the first users requiring services of fixed transmission rates, K2 denotes a number of the second users requiring services of variable transmission rates, ƒk(ck) denotes the K-th user's transmission power required for transmission satisfying a desired BER at a reception-side when a channel gain is 1, N denotes a number of the total subchannels, and αk denotes a k-th user's channel gain.

### Claim 15

An apparatus for receiving user data transmitted through adaptive modulation in a mobile communication system including users requiring services of fixed transmission rates and users requiring services of variable transmission rates, the apparatus comprising:
a Fast Fourier Transform (FFT) unit for dividing the user data for each subchannel and converting divided user data streams into frequency domain signals;
a subchannel allocation and bit loading algorithm unit for determining a real number {z, ck} using a Lagrange Multiplier Method, which maximizes an objective equation in order to reconstruct a variable rate adaptive problem into a delivery problem, solving the delivery problem through linear programming and allocating subchannels to each of the users, and allocating bits to the subchannels allocated to the users using a Greedy Algorithm; and
an adaptive demodulator for adaptively demodulating the user data streams of the frequency domain by using the allocated subchannels and bits,
wherein the Lagrange Multiplier Method is based on
max
z
.
,
c
.
k
⁢
(
z
,
c
k
,
λ
,
μ
)
=
z
-
λ
⁡
(
∑
k
∈
U
Fixed
⁢
f
k
⁡
(
c
k
)
·
R
M
/
α
k
2
⁢
c
k
+
∑
k
∈
U
RA
⁢
f
k
⁡
(
c
k
)
·
z
/
α
k
2
⁢
c
k
-
P
T
)
-
μ
⁡
(
∑
k
∈
U
Fixed
⁢
R
M
/
c
k
+
∑
k
∈
U
RA
⁢
z
/
c
k
-
N
)
wherein ck denotes a number of bits to be allocated to a k-th user, Rk denotes a k-th user's data rate, PT denotes a total allocated power, UFixed denotes a number of users requiring services of fixed transmission rates, URA denotes a number of users requiring services of variable transmission rates, ƒk(ck) denotes the K-th user's transmission power required for transmission satisfying a desired BER at a reception-side when a channel gain is 1, N denotes a number of the total subchannels, αk denotes a k-th user's channel gain, and λ and μ are parameters.