Method and system for mitigating interference in communication system

• US 20060210001A1
• Filed: 03/18/2005
• Published: 09/21/2006
• Est. Priority Date: 03/18/2005
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Navini Networks, Inc. (Cisco Systems, Inc.)
• Inventors: Li, Hang, Xu, Guanghan
• Granted Patent: US 7,349,504 B2
• Time in Patent Office: Days
• US Class Current: 375/346
• CPC Class Codes: H04B 17/336 Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04W 52/243 taking into account interferences

Abstract

A method and system for mitigating interference in a communication system, comprising at least one base station and at least one terminal, are disclosed. The base stations and terminals communicate through a channel existing between them, and the channels include at least a first signal channel and a second signal channel. The method includes determination of channel, noise and self-interference characteristic, computation of a rate limit of the channels, computation of the rate assignment of the channels, and assignment of the computed rate assignments to the channels. In another aspect of the present invention, the method includes determination of channel characteristics; computation of a power control margin, self-interference characteristics, power control command; and assignment of the computed power control command to each communicating terminal and base station. The above power and rate control methods may operate jointly to mitigate both intra-cell and inter-cell interference in wireless communication systems.

Claims

1. A method for mitigating interference in a communication system comprising at least one base station and at least one terminal, a channel existing between each base station and each terminal, the channels comprising at least a first signal channel and a second signal channel, a first signal being communicated through the first signal channel, a second signal being communicated through the second signal channel, transmission and reception of signal in the communication system being done through the channels, each signal received through the channels comprising the first signal, the second signal and noise, the method comprising the steps of:

a. determining channel characteristics at each receiving end, the determination of the channel characteristics being based on at least the first signal, total signal quality being based on at least the second signal, and noise characteristics, wherein the receiving end being at least one of a terminal and base station;

b. computing a rate limit of the channels at each receiving end, the computation of the rate limit of the channels being based on at least the channel characteristics, the total signal quality, and the noise characteristics;

c. computing a rate assignment of the channels at the base station, the computation of the rate assignment of the channels being based on control information containing at least the rate limit; and

d. assigning the computed rate assignments to the channels for mitigating interference in the communication system.

2. The method of claim 1, wherein the first signal is a training signal, the training signal comprising known symbols.

3. The method of claim 1, wherein the second signal is a traffic signal comprising information bearing symbols.

4. The method of claim 1 wherein the noise comprises an inter-cell interference and thermal noise.

5. The method of claim 1, wherein the channels belong to uplink.

6. The method of claim 1, wherein the channels belong to downlink.

7. The method of claim 1, wherein the total signal quality is a Signal-to-all-lnterference-plus-thermal-Noise Ratio (SINR).

8. The method of claim 7, wherein the SINR is being computed for each of the terminals by using estimated symbols at each of the terminals, wherein symbol estimation is carried out by using one of a linear joint detection and a non-linear joint detection with group successive interference cancellation.

9. The method of claim 1, wherein control information containing a downlink rate limit is being sent from the terminal to the base station through an uplink control channel.

10. The method of claim 1, wherein the channel characteristics comprises channel impulse responses for receive antennas of each of the receiving ends.

11. The method of claim 1, wherein the rate limit is at least a combination of at least a number of code channels and modulation scheme.

12. The method of claim 1, wherein the rate limit is being computed as the number of code channels for each predetermined modulation scheme, the computation of rate limit comprises the steps of:

a. estimating self-interference power using the following equation;

P_SI=P_s·

(1SINR−

SNR), 

 

(1)

 

wherein P_SI is the self-interference power, P_S is signal power, SINR is the Signal-to-all-lnterference-plus-thermal-Noise Ratio, SNR is Signal-to-inter-cell-interference-plus-thermal Noise Ratio; and

b. computing the limit on the number of channels based on the self-interference power, total available transmission power, threshold for each modulation scheme, signal power, and noise power by using the following equation;

$\begin{array}{cc}\mathrm{NL}=\frac{P_s<br><br>P_m}{\mathrm{threshold}·<br><br>\left(P_n+P_{\mathrm{SI}}<br><br>P_m\right)},& \left(2\right)\end{array}$

 

wherein NL is the channel limit, P_S is the signal power, P_SP_m is the total available power, P_n is the noise power, P_SI is the self-interference power, threshold is an SINR requirement for a combination of modulation and coding scheme, rate limit is given by a triplet of the NL, the modulation scheme and the coding scheme with NL being determined by equation (2).

13. The method of claim 1, wherein the rate assignment is being determined by a combination of the number of code channels, at least one of a modulation scheme and code scheme, such that an effective data rate is not greater than the rate limit.

14. The method of claim 4, wherein the noise is being obtained by subtracting an estimated intra-cell signal from one of the first and the second signal.

15. The method of claim 4, wherein the noise is being obtained from at least one inactive slot in the channel, each inactive slot being configured by a base station in such a way that no communication involving the base station occurs in the slot while communication involving other base stations are present in the slot, each inactive slot being a continuous area in the time-frequency domain of the frame structure.

16. The method of claim 4, wherein the inter-cell interference along with the thermal noise characteristic is the power computed after one of a beam forming and nulling operation is being applied.

17. The method as claimed in claim 1 wherein the method is carried out by a computer program product.

18. A method for mitigating interference in a communication system comprising at least one base station and at least one terminal, a channel existing between each base station and each terminal, the channels comprising at least a first signal channel and a second signal channel, a first signal being communicated through the first signal channel, a second signal being communicated through the second signal channel, transmission and reception of signal in the communication system being done through the channels, each signal received through the channels comprising the first. signal, the second signal and noise, the method comprising the steps of:

a. determining channel characteristics at each receiving end, the determination of channel characteristics being based on at least the first signal, total signal quality based on at least the second signal, and noise characteristics, wherein the receiving end being at least one of a terminal and base station;

b. computing a power control margin at each receiving end by using at least an estimated and a received signal quality characteristic of a current frame and previous frames;

c. computing self-interference characteristics at each receiving end by using at least the first and the second signal;

d. computing a power control command at each receiving end, the computation of power control command being based on at least the power control margin, noise characteristics, and the self-interference characteristics; and

e. assigning the computed power control command to each communicating terminal and base station for mitigating interference in the communication system.

19. The method of claim 18, wherein the total signal quality is a Signal-to-all-Interference-plus-thermal-Noise Ratio (SINR).

20. The method of claim 18, wherein the total signal quality is a Signal-to-inter-cell-interference-plus-Noise Ratio (SNR).

21. The method of claim 19, wherein the computation of power control margin comprises the steps of:

a. determining SINR_p as a value from the set {SINR(t−

i), i=0, i₁, . . . , i<sub>T−

1</sub>}, such that the following conditions are met;

i. ┌

pT┐

values in the set are greater than SINR_p; and

 

 

(3)
ii. T−

┌

pT┐

values are smaller than SINR_p, 

 

(4)

 

wherein the SINR values at the t^th frame are defined as;

SINR(t−

i), i=0, i₁, . . . , i<sub>T−

1</sub>, 

 

(5)

 

‘

p’

is outage probability, ‘

T’

is history length in frame, SINR_p is the SINR at outage probability ‘

p’

; and

b. updating the power control margin (PCM) based on a threshold and the SINR_p.

22. The method of claim 18, wherein the self-interference characteristic is the self-interference-to-noise ratio.

23. The method of claim 20, wherein the computation of power control margin comprises the steps of:

a. determining SNR_p as a value from the set {SNR(t−

i), i=0, i₁, . . . , i<sub>T−

1</sub>}, such that the following conditions are met;

i. ┌

pT┐

values in the set are greater than SNR_p; and

 

 

(3)
ii. T−

┌

pT┐

values are smaller than SNR_p, 

 

(4)

 

wherein the SNR values at the t^th frame are defined as;

SNR(t−

i), i=0, i₁, . . . , i<sub>T−

1</sub>, 

 

(5)

 

‘

p’

is outage probability, ‘

T’

is history length in frame, SNR_p is the SNR at outage probability ‘

p’

; and

b. updating the power control margin (PCM) based on a threshold and the SNR_p.

24. The method of claim 21, wherein updating the PCM is done by the following equation:

PCM (k+1)=PCM(k)*Threshold/SINR_p,

wherein k is the frame index, and Threshold is the required SINR for the current modulation and coding scheme.

25. The method of claim 18, wherein the computing of power control command generates a transmission power increment value, the computation of the transmission power increment value depending on at least a combination SNR, SINR, PCM, and a signal quality power threshold for a selected combination of channel coding and modulation scheme.

26. The method as claimed in claim 18 wherein the method is carried out by a computer program product.

27. A method for mitigating interference in a communication system comprising at least one base station and at least one terminal, a channel existing between each base station and each terminal, the channels comprising at least a first signal channel and a second signal channel, a first signal being communicated through the first signal channel, a second signal being communicated through the second signal channel, transmission and reception of data in the communication system being done through the channels, each signal received through the channels comprising the first signal, the second signal and noise, the method comprising the steps of:

a. determining channel characteristics at each receiving end, the determination of channel characteristics based on at least the first signal, total signal quality based on at least the second signal, and noise characteristics, wherein the receiving end is at least one of a terminal and base station;

b. computing a rate limit of the channels between the base station and the terminal at each receiving end, the computing of rate limit being based on at least the channel characteristics, the total signal quality, and the noise characteristics;

c. computing a power control margin at each receiving end by using current and past values of at least the received total signal quality;

d. computing self-interference characteristic at each receiving end by using at least the first and the second signal;

e. computing power control command at each receiving end, the computation of the power control command being based on at least the power control margin, the noise characteristics, and the self-interference characteristic;

f. computing rate assignment of the channels at the base station, the computation of the rate assignment being based on at least the rate limit; and

g. assigning the rate assignment and the power control command to each communicating terminal and base station for mitigating interference in the communication system.

28. The method as claimed in claim 27 wherein the method is carried out by a computer program product.

29. An apparatus for mitigating interference in a communication system comprising at least one base station and at least one terminal, a channel existing between each base station and each terminal, the channels comprising at least a first signal channel and a second signal channel, a first signal being communicated through the first signal channel, a second signal being communicated through the second signal channel, transmission and reception of signal in the communication system being done through the channels, each signal received through the channels comprising the first signal, the second signal and noise, the apparatus comprising:

a. means for determining channel characteristics at each receiving end, the determination of the channel characteristics being based on at least the first signal, total signal quality based on at least the second signal, and noise characteristics, wherein the receiving end is at least one of a terminal and base station;

b. means for computing a rate limit of the channels at each receiving end, the computation of the rate limit of the channels being based on at least the channel characteristics, the total signal quality, and the noise characteristics;

c. means for computing a power control margin at each receiving end, the computation of the power control margin being done by using current and past values of at least received total signal quality;

d. means for computing self-interference characteristics at each receiving end, the computation of the interference characteristics done by using at least the first and the second signal;

e. means for computing power control command at each receiving end, the computation of the power control command based on at least the power control margin, the noise characteristics, and the interference characteristics;

f. means for computing rate assignment of the channels at the base station, the computation of the rate assignment of the channels being based on at least the rate limit; and

g. means for assigning the rate assignment and the power control command for mitigating interference in the communication system.