Apparatus and method for controlling adaptive modulation and coding in an orthogonal frequency division multiplexing communication system

• US 20050157639A1
• Filed: 11/18/2004
• Published: 07/21/2005
• Est. Priority Date: 11/19/2003
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lee, Dong-Jun, Song, Kee-Bong
• Granted Patent: US 7,492,701 B2
• Time in Patent Office: Days
• US Class Current: 370/208
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0046 Determination of how many bits are transmitted on different sub-channels
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/006 Quality of the received signal, e.g. BER, SNR, water filling
• CPC Class Codes: H04W 52/262 taking into account adaptive modulation and coding [AMC] scheme AMC per se H04L1/0001

Abstract

A method and apparatus for controlling AMC in an OFDM communication system in which an entire frequency band is divided into a plurality of sub-carrier bands. In the AMC controlling method, power and a number of transmission bits are calculated for each of the sub-carriers in a predetermined method for each of coding methods available in the OFDM communication system. A data rate for each of the coding methods is calculated based on the number of transmission bits and the power for each sub-carrier. A coding method having a highest of the calculated data rates is selected and a modulation method is determined according to a number of transmission bits in the determined coding method.

Claims

1. A method of controlling adaptive modulation and coding (AMC) in an orthogonal frequency division multiplexing (OFDM) communication system in which an entire frequency band is divided into a plurality of sub-carrier bands, comprising the steps of:

(1) calculating a power and a number of transmission bits for each of the sub-carriers in a predetermined method for each coding method available in the OFDM communication system;

(2) calculating a data rate for each of coding method based on the number of transmission bits and the power for each sub-carrier;

(3) determining a coding method having a highest of the calculated data rates for the OFDM communication system; and

(4) determining a modulation method for the OFDM communication system according to a number of transmission bits in the determined coding method.

2. The method of claim 1, further comprising the steps of:

(5) applying a scaling factor to the calculated power for the determined coding method; and

(6) determining a resulting power as the power for each sub-carrier.

3. The method of claim 2, wherein the scaling factor is determined according to a number of bits included most in the transmission bits for each sub-carrier.

4. The method of claim 1, wherein the step of calculating the number of transmission bits and the power for each sub-carrier for each of the coding methods is performed by

$\underset{\underset{}{i\in }}{\max }$

{ 1 , ⋯

⁢

 

, V } m 1 , ⁢

 

⁢

⋯

⁢

 

⁢

m N P ~ 1 , ⋯

⁢

 

, P ~ N ⁢

 

⁢

R = r ⁡

( C i ) ⁢

 

⁢

∑

n = 1 N ⁢

m n

where i is an index of a coding method available in the OFDM communication system, r(C_i) is a coding rate of an ith coding method C_i, and m_n is a number of transmission bits for an nth sub-carrier.

5. The method of claim 4, wherein the number of transmission bits and the power for each sub-carrier calculated by

$\underset{\underset{}{i\in }}{\max }$

{ 1 , ⋯

⁢

 

, V } m 1 , ⁢

 

⁢

⋯

⁢

 

⁢

m N P ~ 1 , ⋯

⁢

 

, P ~ N ⁢

 

⁢

R = r ⁡

( C i ) ⁢

 

⁢

∑

n = 1 N ⁢

m n

are limited by

$m_n\le <br><br>\min <br><br>\left\{{\log }_2\left(1+\frac{d_H<br><br>\left(C_i\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>{<br><br>H_n<br><br>}^2<br><br>{\tilde{P}}_n}{\mathrm{\Gamma <br><br>}}\right),m_{\max }\right\}$

where d_H(C_i) is a minimum Hamming distance of bits coded in an ith coding method C_i, H_n is a fading coefficient of an nth sub-carrier, P_n is transmit power of bits transmitted on the nth sub-carrier, m_max is a maximum number of bits transmittable for each of the sub-carriers, and Γ

is a constant determined by a packet error rate,

$\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>{\tilde{P}}_n\le <br><br>P_T$

where P_T is a maximum transmit power available in the OFDM communication system.

6. The method of claim 1, wherein the modulation method is Gray mapping.

7. The method of claim 1, wherein the predetermined method is a Levin-Campello algorithm.

9. The apparatus of claim 7, further comprising a transmitter for performing an inverse fast Fourier transform (IFFT) on a modulated signal received from the modulator and RF (Radio Frequency)-processing the IFFT signal.

10. The apparatus of claim 9, wherein the AMC controller applies a scaling factor to the calculated power for the determined coding method and determines a resulting power as the power for each sub-carrier.

11. The apparatus of claim 10, wherein the AMC controller determines the scaling factor according to a number of bits included most in the transmission bits for each sub-carrier.

8. An apparatus for controlling adaptive modulation and coding (AMC) in an orthogonal frequency division multiplexing (OFDM) communication system in which an entire frequency band is divided into a plurality of sub-carrier bands, comprising:

an AMC controller for calculating a power and a number of transmission bits for each of the sub-carriers in a predetermined method for each coding method available in the OFDM communication system, calculating a data rate for each coding method based on the number of transmission bits and the power for each sub-carrier, determining a coding method having a highest of the calculated data rates for the OFDM communication system, and determining a modulation method for the OFDM communication system according to a number of transmission bits in the determined coding method;

an encoder for encoding input information data bits in the determined coding method; and

a modulator for modulating coded bits received from the encoder in the determined modulation method.

12. The apparatus of claim 8, wherein the AMC controller calculates the number of transmission bits and the power for each sub-carrier for each of the coding methods by

$\underset{\underset{}{i\in }}{\max }$

{ 1 , ⋯

⁢

 

, V } m 1 , ⁢

⋯

⁢

 

⁢

m N ⁢

 

P ~ 1 , ⋯

⁢

 

, P ~ N ⁢

 

⁢

R = r ⁡

( C i ) ⁢

 

⁢

∑

n = 1 N ⁢

m n

where i is an index of a coding method available in the OFDM communication system, r(C_i) is a coding rate of an ith coding method C_i, and m_n is a number of transmission bits for an nth sub-carrier.

13. The apparatus of claim 12, wherein the AMC controller limits the number of transmission bits and the power for each sub-carrier calculated by

$\begin{array}{c}\underset{\underset{}{i\in }}{\max }\end{array}$

{ 1 , ⋯

⁢

 

, V } m 1 , ⁢

⋯

⁢

 

⁢

m N ⁢

 

P ~ 1 , ⋯

⁢

 

, P ~ N ⁢

 

⁢

R = r ⁡

( C i ) ⁢

 

⁢

∑

n = 1 N ⁢

m n using m n ≤

min ⁢

{ log 2 ( 1 + d H ⁡

( C i ) ⁢



H n 

2 ⁢

P ~ n Γ

) , m max }

where d_H(C_i) is a minimum Hamming distance of bits coded in an ith coding method C_i, H_n is a fading coefficient of an nth sub-carrier, P_n is transmit power of bits transmitted on the nth sub-carrier, m_max is a maximum number of bits transmittable for each of the sub-carriers, and Γ

is a constant determined by a packet error rate,

$\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>{\tilde{P}}_n\le <br><br>P_T$

where P_T is a maximum transmit power available in the OFDM communication system.

14. The apparatus of claim 8, wherein the modulation method is Gray mapping.

15. The apparatus of claim 8, wherein the predetermined method is a Levin-Campello algorithm.

16. A method of receiving a signal transmitted in an adaptive modulation and coding (AMC) scheme from a transmitter in an orthogonal frequency division multiplexing (OFDM) communication system in which an entire frequency band is divided into a plurality of sub-carrier bands, comprising the steps of:

RF (Radio Frequency)-processing a received signal;

performing a fast Fourier transform (FFT) on the RF-processed signal;

demodulating the FFT signal in correspondence with a modulation method used in the transmitter; and

decoding the demodulated signal in correspondence with a coding method used in the transmitter and outputting information data bits.

17. The method of claim 16, wherein the decoding step comprises the steps of:

calculating a power and a number of transmission bits for each sub-carrier in a predetermined method for each coding method available to the transmitter in the OFDM communication system;

calculating a data rate for each coding method based on the number of transmission bits and the power for each sub-carrier; and

determining a coding method having a highest of the calculated data rates as the coding method.

18. The method of claim 17, wherein the demodulation step comprises the step of determining a modulation method according to the number of transmission bits in the determined coding method.

19. The method of claim 16, wherein the demodulation step comprises the step of calculating a bit-by-bit soft metric by

${\lambda }^{}$

′

⁡

( y n ⁡

( l ) , n , b ) = - min x ∈

χ

b ( i , n ) ⁢



y n ⁡

( l ) - H n ⁢

x 

2 σ

2

where 1 is an index of an OFDM symbol, n is an index of a sub-carrier, H_n is a fading coefficient of an nth sub-carrier, y_n(1) is a received complex signal on the nth sub-carrier in an lth OFDM symbol, σ

² is a noise variance under Gaussian distribution, and Ω

_b^(i,n) is a set of complex signals with an ith bit being b on the nth sub-carrier.

20. The method of claim 19, wherein the decoding step comprises the step of outputting a code sequence that maximizes the bit-by-bit soft metric as the information data bits.

21. The method of claim 16, wherein the modulation method is Gray mapping.

22. The method of claim 17, wherein the predetermined method is a Levin-Campello algorithm.

23. An apparatus for receiving a signal transmitted in an adaptive modulation and coding (AMC) scheme from a transmitter in an orthogonal frequency division multiplexing (OFDM) communication system in which an entire frequency band is divided into a plurality of sub-carrier bands, comprising:

a receiver for RF (Radio Frequency)-processing a received signal; and

performing a fast Fourier transform (FFT) on the RF-processed signal;

a demodulator for demodulating the FFT signal in correspondence with a modulation method used in the transmitter; and

a decoder for decoding the demodulated signal in correspondence with a coding method used in the transmitter and outputting information data bits.

24. The apparatus of claim 23, wherein the coding method is determined by calculating a power and a number of transmission bits for each sub-carrier in a predetermined method for each coding method available to the transmitter in the OFDM communication system, calculating a data rate for each coding method based on the number of transmission bits and the power for each sub-carrier, and selecting a coding method having a highest of the calculated data rates.

25. The apparatus of claim 24, wherein the modulation method is determined according to the number of transmission bits in the determined coding method.

26. The apparatus of claim 23, wherein the demodulator calculates a bit-by-bit soft metric by

${\lambda }^{}$

′

⁡

( y n ⁡

( l ) , n , b ) = - min x ∈

χ

b ( i , n ) ⁢



y n ⁡

( l ) - H n ⁢

x 

2 σ

2

where 1 is an index of an OFDM symbol, n is an index of a sub-carrier, H_n is a fading coefficient of an nth sub-carrier, y_n(1) is a received complex signal on the nth sub-carrier in an lth OFDM symbol, σ

² is a noise variance under Gaussian distribution, and Ω

_b^(i,n) is a set of complex signals with an ith bit being b on the nth sub-carrier.

27. The apparatus of claim 26, wherein the decoder outputs a code sequence that maximizes the bit-by-bit soft metric as the information data bits.

28. The apparatus of claim 23, wherein the modulation method is Gray mapping.

29. The apparatus of claim 24, wherein the predetermined method is a Levin-Campello algorithm.