Method and device for adaptive modulation and coding based on second order statistics of channel information

• US 20040264588A1
• Filed: 06/25/2004
• Published: 12/30/2004
• Est. Priority Date: 06/27/2003
• Status: Active Grant

• Current Assignee: Alcatel SA (Nokia Corporation)
• Original Assignee: Alcatel SA (Nokia Corporation)
• Inventors: Song, Pengpeng, Cai, Liyu, Wan, Yan
• Granted Patent: US 7,542,514 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• 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 1/0019 in which mode-switching is based on a statistical approach
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 5/0044 allocation of payload

Abstract

The present invention discloses a method and device for adaptive modulation and coding based on second order statistics of channel information in OFDM system, characterized in that, by means of variance of Signal-to-Noise ratio (SNR) an appropriate adaptation time window is selected dynamically to trace time-varying channel better; and in that a decision criterion of second order, namely selecting an appropriate modulation and coding schemes (MCS) according to average value of SNR and variance of SNR, is employed to obtain accurate mapping from SNR to MCS. The mapping enhances practicability of the adaptive modulation and coding, decreases probability of system outage, and thus results in better performance of bit error rate.

Claims

1. A method for adaptive modulation and coding based on second order statistics of channel information in orthogonal frequency divisional multiplexing (OFDM) systems, said method comprises following steps:

a) a mobile station determining the largest among a set of adaptation time windows T₁, T₂, . . . T_n as a current adaptation time window;

b) said mobile station receiving a set of pilot signals from a base station in the current adaptation time window, obtaining Signal-to-Noise ratio (SNR) samples based on the pilot signals, calculating variance of the SNRβ and

average value of the SNRγ

;

c) comparing said variance of SNRβ

in step b) with threshold values β

0, β

k, obtaining final current adaptation time window and current modulation and coding scheme according to the results from comparison and said average value of SNRγ

;

d) feeding the related information of the final current adaptation time window and the current modulation and coding scheme, which are obtained in step c), back to the base station as parameters for the base station to transmit data next time.

2. A method for adaptive modulation and coding as claimed in claim 1, characterized in that, said step c) comprises the steps of:

e) comparing β

with β

0, if β

>

β

0, then updating the current adaptation time window in step b) to a lower level and returning to step b), otherwise implementing step f);

f) obtaining a current modulation and coding scheme in accordance with the average value γ

of SNR obtained in step b);

g) comparing β

with β

k, if β

k<

β

<

β

0, then updating the current modulation and coding scheme to a lower level, otherwise keeping the current modulation and coding scheme unchanged.

3. A method for adaptive modulation and coding as claimed in claim 1, characterized in that, in step a) a set of adaptation time windows T₁, T₂, . . . T_n corresponding to various moving velocities v₁, v₂, . . . v_n of the mobile station respectively is obtained by pre-simulating and calculating channel coherence time, said channel coherence time meaning a period of time in which the correlation coefficient of two a received signals is larger than 0.9.

4. A method for adaptive modulation and coding as claimed in claim 1, characterized in that, in step c) the threshold values β

0 and β

k are obtained in combination with simulation test where a target bit error rate and target throughput are approached, β

0 being the threshold value for changing adaptation time window, β

_k being the threshold value for changing modulation and coding scheme, and β

0 >

β

k, and said target bit error rate and target throughout being determined by wireless communications service.

5. A method for adaptive modulation and coding as claimed in claim 1, characterized in that, in step b) the pilot signal is known data from the base station.

6. A device for adaptive modulation and coding based on second order statistics of channel information in orthogonal frequency divisional multiplexing (OFDM) systems, said device comprising calculation means and comparison-update means which are located in a mobile station, wherein:

a channel estimation means of a mobile station for obtaining a sample average of Signal-to-Noise Ratio (SNR) in accordance with pilot signals received from a base station by the mobile station as the largest among a set of adaptation time windows T₁, T₂, . . . T_n being the current adaptation time window;

the calculation means for calculating variance of the SNRβ and

average value of the SNRγ

in accordance with the SNR samples obtained by said channel estimation means; and

the comparison-update means for comparing the obtained variance of the SNR β

with the threshold values β

0, β

k, then obtaining final current adaptation time window and current modulation and coding scheme according to results from comparison and the average value of SNR γ

obtained from the calculation means, the related information of said final current adaptation time window and the current modulation and coding scheme is fed back to said base station as parameters for said base station to transmit data next time.

7. A device as claimed in claim 6, characterized in that,) a set of adaptation time windows T₁, T₂, . . . T_n corresponding to various moving velocities v₁, v₂, . . . v_n of the mobile station respectively is obtained by pre-simulating and calculating channel coherence time, said channel coherence time meaning a period of time in which the correlation coefficient of two a received signals is larger than 0.9.

8. A device as claimed in claim 6, characterized in that, said pilot signal is known data from the base station.

9. A device as claimed in claim 6, characterized in that, the threshold values β

0 and β

k are obtained in combination with simulation test where a target bit error rate and target throughput are approached, β

0 being the threshold value for changing adaptation time window, β

_k being the threshold value for changing modulation and coding scheme, and β

0>

β

k, and said target bit error rate and target throughout being determined by wireless communications service.

10. A device as claimed in claim 6, characterized in that, the comparison-update means comparing the obtained variance of SNRβ

with the threshold values β

0, β

k and then obtaining final current adaptation time window and current modulation and coding scheme according to results from comparison result and the average value of SNRγ

, the following steps are implemented;

comparing β

obtained by the calculation means with β

0, if β

>

β

0, then updating the current adaptation time window to a lower level;

the channel estimation means obtaining Signal-to-Noise Ratio (SNR) samples in accordance with the current adaptation time window;

the calculation means calculating variance of the SNR β and

average value of the SNRγ

in accordance with the SNR, which step being implemented repeatedly until β

<

=β

0, then obtaining final current adaptation time window;

otherwise obtaining current modulation and coding scheme in accordance with the current average value of the SNRγ

; and

comparing β

with β

k, if β

k<

β

<

β

0, then updating the current modulation and coding scheme to a lower level, otherwise keeping the current modulation and coding scheme unchanged.