Adaptive feedback method for cellular communication

• US 20060256805A1
• Filed: 04/20/2006
• Published: 11/16/2006
• Est. Priority Date: 04/20/2005
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd., Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Cho, Sung-Hyun, Yun, Sang-Boh, Tang, Taiwen, Heath, Robert W.
• Granted Patent: US 7,693,100 B2
• Time in Patent Office: Days
• US Class Current: 370/431
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0645 Variable feedback
• CPC Class Codes: H04W 24/10 Scheduling measurement reports ; Arrangements for measurement reports
• CPC Class Codes: H04W 72/1268 of uplink data flows

Abstract

In an adaptive feedback method for a cellular communication system having plural terminals feeding back channel information to an access point, the system selects one of an opportunistic mode and a polling mode as a feedback mode between an access point and the terminals on the basis of system and traffic parameters, sets up the access point and the terminals for the selected feedback mode, and feeds back the channel information from the terminals to the access point in the selected feedback mode. The adaptive feedback method changes the feedback mechanism adaptively to the system and traffic environment, making it possible to increase the system throughput as well as to decrease the MAC overhead regardless of the variation of the number of MSs.

Claims

1. An adaptive feedback method for a cellular communication system having plural terminals feeding back channel information to an access point, comprising:

selecting one of at least two feedback modes on the basis of system parameters;

optimizing control parameters associated with the selected feedback mode; and

feeding back the channel information from the terminals to the access point using the optimized control parameter in the selected feedback mode.

2. The method of claim 1, wherein the feedback modes include a dedicated channel mode, an opportunistic mode, a random backoff with carrier sensing mode, a polling mode, and a coordinated mode.

3. The method of claim 1, wherein the step of selecting a feedback mode includes:

analyzing the system parameters;

computing a mode selection parameter from the system parameters;

comparing the mode selection parameter with at least one predetermined threshold; and

selecting a feedback mode based on the comparison result.

4. The method of claim 3, wherein the system parameters include a number of terminals ‘

N’ and

a number of mini-slots ‘

K’

carrying the channel information.

5. The method of claim 4, wherein the mode selection parameter is calculated according to Q=N−

α

K, where α

is a tradeoff parameter for determining a switching point between the feedback modes.

6. The method of claim 2, wherein the control parameters include a channel power threshold η

and a random feedback probability p.

7. The method of claim 6, wherein the step of optimizing the control parameters for the opportunistic mode includes:

calculating a mean sum rate of all the terminals;

determining the channel power threshold η and

the random feedback probability p to maximize the mean sum rate.

8. The method of claim 7, wherein the mean sum rate is calculated according to

$C$

( p , η

) = ∑

j = 1 N ⁢

 

⁢

E ( χ

j , S j , T ) ⁡

[ log 2 ⁡

( 1 + ρ

⁢

 

⁢

χ

j ) ⁢

I ⁢

{ S j = 1 } ]

where χ

_j is the channel power of a j^th terminal, denoted by χ

_j=|h_j|², S_j is an event that the j^th terminal is selected at the access point, T is the number of terminals whose channel powers are above the channel power threshold η

, ρ

is the average signal-to-noise ratio (SNR), and I{·

} is an indicator function.

9. The method of claim 8, wherein the channel power threshold η

and the random feedback probability p are determined according to;

max_p,η

C(p,η

)
s.t. 0≦

p≦

1, η

≧

0·

10. The method of claim 9, wherein the step of feeding back the channel information includes:

determining, at each terminal, whether a channel gain of the terminal is greater than the channel power threshold η

; and

feeding back the channel information with the random feedback probability p when the channel gain of the terminal is greater than the channel power threshold η

.

11. An adaptive feedback method for a cellular communication system having plural terminals feeding back channel information to an access point, comprising:

selecting one of an opportunistic mode and a polling mode as a feedback mode between the access point and the terminals on the basis of system and traffic parameters;

setting the access point and the terminals for the selected feedback mode;

feeding back the channel information from the terminals to the access point in the selected feedback mode.

12. The method of claim 11, wherein the step of selecting the feedback mode includes:

collecting the system and traffic parameters;

computing a mode selection parameter from the system and traffic parameters;

comparing the mode selection parameter with a predetermined threshold; and

selecting the opportunistic mode if the mode selection parameter is greater than or equal to the threshold; and

selecting the polling mode, if the mode selection parameter, is less than the threshold.

13. The method of claim 12, wherein the traffic parameters include a number of terminals ‘

N’ and

the system parameters include a number of mini-slots ‘

K’

carrying the channel information.

14. The method of claim 13, wherein the mode selecting parameter is obtained by Q=N−

α

K, α

is a tradeoff parameter for determining a switching point between the feedback modes.

15. The method of claim 14, wherein the threshold is ‘

0.’

16. The method of claim 11, wherein the step of setting the access point and the terminals includes:

optimizing control parameters associated with the selected feedback mode.

17. The method of claim 16, wherein the control parameters includes a channel power threshold η

and a random feedback probability p.

18. The method of claim 17, wherein the step of optimizing the control parameters for the opportunistic mode includes:

calculating a mean sum rate of all the terminals; and

determining the channel power threshold η and

the random feedback probability p to maximize the mean sum rate.

19. The method of claim 18, wherein the mean sum rate is calculated according to:

$C<br><br>\left(p,\mathrm{\eta <br><br>}\right)=\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>E_{\left({\mathrm{\chi <br><br>}}_j,S_j,T\right)}<br><br>\left[{\log }_2<br><br>\left(1+\mathrm{\rho <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\chi <br><br>}}_j\right)<br><br>I<br><br>\left\{S_j=1\right\}\right]$

where χ

_j is the channel power of a j^th terminal, denoted by, χ

_j=|h_j|² S_j is an event that the j^th terminal is selected at the access point, T is the number of terminals whose channel powers are above the channel power threshold η

, ρ

is the average signal-to-noise ratio (SNR), and I{·

} is an indicator function.

20. The method of claim 19, wherein the channel power threshold η

and the feedback probability η

are determined according to;

max_p,η

C(p,η

)
s.t. 0≦

p≦

1, η

≧

0·

21. The method of claim 17, wherein the step of feeding back the channel information includes:

determining, at each terminal, whether a channel gain of the terminal is greater than the channel power threshold η

; and

feeding back the channel information with the feedback probability p when the channel gain of the terminal is greater than the channel power threshold η

.

22. An adaptive feedback system for cellular communication comprising:

an access point which selects one of at least two feedback modes on the basis of a mode selection parameter; and

a plurality of mobile stations, each feeding back channel information based on the selected feedback mode.

23. The system of claim 22, wherein the access point includes:

a scheduler which schedules services to the mobile stations and determines service rates based on the channel information and traffic information associated with the services; and

a central feedback controller which generates a feedback control signal for controlling the selected feedback mode.

24. The system of claim 23, wherein the central feedback controller includes:

a mode selector which compares the mode selection parameter with a threshold value and selects the feedback mode on the basis of a comparison result; and

an optimizer which dynamically optimizes control parameters associated with the feedback mode selected by the mode selector.

25. The system of claim 24, wherein the mode selection parameter is derived from a number of terminals ‘

N’ and

a number of mini-slots ‘

K’

carrying the channel information.

26. The system of claim 25, wherein the mode selection parameter is calculated according to Q=N−

α

K, where α

is a tradeoff parameter for determining a switching point between the feedback modes.

27. The system of claim 26, wherein the control parameters includes a channel power threshold η

and a random feedback probability p.

28. The system of claim 27, wherein the optimizer optimizes the control parameters so as to maximize a system throughput.

29. The system of claim 28, wherein the system throughput is indicated by a mean sum rate of all mobile stations.

30. The system of claim 29, wherein the optimizer selects the channel power threshold η

and the random feedback probability p which maximize the mean sum rate, as optimal control parameters.

31. The system of claim 30, wherein the mean sum rate is calculated according to:

$C<br><br>\left(p,\mathrm{\eta <br><br>}\right)=\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>E_{\left({\mathrm{\chi <br><br>}}_j,S_j,T\right)}<br><br>\left[{\log }_2<br><br>\left(1+\mathrm{\rho <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\chi <br><br>}}_j\right)<br><br>I<br><br>\left\{S_j=1\right\}\right]$

where χ

_j is the channel power of a j^th terminal, denoted by χ

_j=|h_j|², S_j is an event that the j^th terminal is selected at the access point, T is the number of terminals whose channel powers are above the channel power threshold η

, ρ

is the average signal-to-noise ratio (SNR), and I{·

} is an indicator function.

32. The system of claim 31, wherein the optimal control parameters are determined according to:

max_p,η

C(p,η

)
s.t. 0≦

p≦

1, η

≧

0·

33. The system of claim 23, wherein the mobile stations include:

a receiving processor which measures channel status and generates channel information; and

a local feedback controller which adjusts a feedback setting based on the feedback control signal received from the access point and feeds back the channel information with the feedback settings.

34. The system of claim 33, wherein the local feedback controller includes:

a local mode selector which selects the feedback mode based on the feedback control signal from the access point; and

a parameter selector which selects parameters to be utilized for the selected feedback mode and feeds back the channel information with the selected parameter on the feedback settings.

35. An access node of a cellular communication system including plural access nodes operating with one of at least two feedback modes selected on the basis of a mode selection parameter and a plurality of mobile stations feeding back channel information according to the selected feedback mode, comprising:

a scheduler which schedules services for the mobile stations and decides a service rate on the basis of the channel information and the traffic information with the respect to the services;

a central feedback controller which generates feedback control signals for controlling the selected feedback mode.

36. The access node of claim 35, wherein the central feedback controller includes:

a mode selector which selects the feedback mode by comparing the mode selection parameter with a threshold; and

an optimizer for optimizing the feedback mode selected by the mode selector and the control parameters.

37. The access node of claim 36, wherein the mode selection parameter is selected on the basis of a number of mobile stations and a number of mini slots carrying the channel information.

38. The access node of claim 37, wherein the mode selection parameter is calculated according to Q=N−

α

K, where Q is the selection parameter, N is the number of mobile stations, K is the number of minislots, and α

is a tradeoff parameter for deciding a mode switching point.

39. The access node of claim 38, wherein the control parameter includes a channel power threshold η

and a random feedback probability p.

40. The access node of claim 39, wherein the optimizer optimizes the selected feedback mode for maximizing system throughput.

41. The access node of claim 40, wherein the system throughput is a mean sum rate of the mobile terminals.

42. The access node of claim 41, wherein the optimizer selects the channel power threshold and the random feedback probability maximizing the mean sum rate as the optimal control parameters.

43. The access node of claim 42, wherein the mean sum rate is calculated according to:

$C<br><br>\left(p,\mathrm{\eta <br><br>}\right)=\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>E_{\left({\mathrm{\chi <br><br>}}_j,S_j,T\right)}<br><br>\left[{\log }_2<br><br>\left(1+{\mathrm{\rho <br><br>\chi <br><br>}}_j\right)<br><br>I<br><br>\left\{S_j=1\right\}\right],$

where χ

_j is the channel power of a j^th terminal, denoted by χ

_j=|h_j|², S_j is an event that the j^th terminal is selected at the access point, T is the number of terminals whose channel powers are above the channel power threshold η

, ρ

is the average signal-to-noise ratio (SNR), and I{·

}is an indicator function.

44. The access node of claim 43, wherein the channel power threshold η

and the feedback probability p are determined according to;

max_p,η

C(p,η

)
s.t. 0≦

p≦

1, η

≧

0·

45. A mobile terminal of a cellular communication system including plural access nodes operating with one of at least two feedback modes selected on the basis of mode selection parameter and a plurality of mobile stations feeding back channel information according to the selected feedback mode, comprising:

a reception processor which generates channel information by measuring channel states; and

a feedback controller which adjusts a feedback configuration according to feedback control signals received from the access node and feeds back the channel information together with the feedback configuration.

46. The mobile terminal of claim 45, wherein the feedback controller includes:

a mode selector which selects a feedback mode on the basis of the feedback control signal; and

a parameter selector which selects parameters to be used for the selected feedback mode and feeds back the selected parameters as the channel information.