Method of interference cancellation based on smart antenna

• US 20020109631A1
• Filed: 02/11/2002
• Published: 08/15/2002
• Est. Priority Date: 08/11/1999
• Status: Active Grant

• Current Assignee: China Academy of Telecom Technology (China Information Communication Technology Group Co. Ltd.)
• Original Assignee: China Academy of Telecom Technology (China Information Communication Technology Group Co. Ltd.)
• Inventors: Li, Feng, Li, Shihe
• Granted Patent: US 6,639,551 B2
• Time in Patent Office: Days
• US Class Current: 342/378
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling

Abstract

This invention discloses an interference cancellation method based on smart antenna, which can solve various interference in mobile communication systems such as multipath propagation, etc., while using smart antenna. The invention includes the steps of: with a beam forming matrix, beam forming the output signal of a receiver based on smart antenna, then getting a set of digital signals NR_k(m); canceling other users main path signal included in NR_k(m), then getting another set of digital signals NS_k(m), which only includes needed signals and all interference signals; searching in digital signal NS_k(m) and getting all multipath interference signals coming from other users; canceling other multipath interference signal in NS_k(m); and superposing the user main path and each multipath signal in phase coincidence, then getting a digital signal with interference canceled.

Claims

1. An interference cancellation method for a smart antenna comprising the steps of:

a) implementing beam formation for output digital signals of a receiver adopting a smart antenna using a beam forming matrix provided by a real time beam forming algorithm and obtaining a set of digital signals represented as NR_k(m) after beam forming, wherein k represents code channels and m represents sample points;

b) canceling the main path signal of other users included in the set of digital signals NR_k(m) to provide another set of digital signals represented as NS_k(m), which includes needed signals and all interference signals, wherein k represents code channels and m represents sample points;

c) searching digital signals NS_k(m) to provide all multipath signals distributed in the direction of the beam;

d) canceling multipath interference signals coming from other users in the digital signals NS_k(m); and

e) superposing main path and multiple path signals of working user terminals in phase coincidence to provide a digital signal with interference canceled.

2. The method according to claim 1, wherein the output digital signal of the receiver adopting the smart antenna in step a) is on a sample level.

3. The method according to claim 1, wherein step a) is performed in a base band signal processor and comprises the steps of:

synchronizing and eliminating over sampling of the output digital signal of the receiver adopting the smart antenna;

de-scrambling, de-spreading and dividing the output digital signal into each code channel signal;

forming a receiving beam for every link using a beam forming composite algorithm in a beam former, and

obtaining the composite results.

4. The method according to claim 3, wherein said beam forming composite algorithm is a maximum power composite algorithm.

5. The method according to claim 1, wherein step a) further comprises:

demodulating the smart antenna output signal which is outputted by a beam former and detecting a signal-to-noise ratio of a training sequence; and

outputting the receiving data directly and ending the procedure when the signal-to-noise ratio is greater than a threshold value, or executing steps b) to e) when the signal-to-noise ratio is less than a threshold value.

6. The method according to claim 3, wherein step a) further comprises:

demodulating the output signal of the smart antenna which is outputted by a beam former and detecting the signal-to-noise ratio of a training sequence; and

outputting the receiving data directly and ending the procedure when the signal-to-noise ratio is greater than a threshold value, or executing steps b) to e) when the signal-to-noise ratio is less than a threshold value.

7. The method according to claim 1, wherein step b) further comprises:

identifying the main path of signals coming from other terminal users in the formed beam of a working code channel;

spreading the spectrum for the main path signals, adding scrambling code to the main path signals and recovering the main path signals as a sample level digital signal; and

subtracting the main path of signals from other users having energy greater than a threshold value from the digital signals NR_k(m) to provide the signals NS_k(m).

8. The method according to claim 7, wherein the step of identifying the main path of signals coming from other terminal users in the formed beam of a working code channel comprises identifying the signal voltage level of other code channels in the working code channel beam.

9. The method according to claim 1, wherein step b) is executed on a sample level.

10. The method according to claim 1, wherein step c) further comprises:

moving the position of a sample point individually within one symbol and providing multiple sets of chip level signals;

correlating a scrambling code with the chip level signals to provide multiple sets of output with energy greater than a threshold value;

adding a known scrambling code to the output and recovering multipath interference of multiple sets with sample level;

subtracting multipath interference coming from other users from digital signals NS_k(m) from step b), superposing the main path and multipath signals of a k^th channel in phase coincidence and getting a k^th channel sample value after interference cancellation; and

de-scrambling, de-spreading and demodulating the sample value of the k^th channel and getting the k^th channel signal after interference cancellation, wherein k is any positive integer.

11. The method according to claim 1, wherein the step of searching in step c) is only taken within one symbol, and searching times equal the sample numbers within each chip times the spread spectrum coefficient minus 1.

12. The method according to claim 1, wherein step d) further comprises subtracting interference digital signals coming from other terminal users from digital signals NS_k(m) from step b) to cancel multipath interference signals coming from other terminal users.

13. The method according to claim 1, wherein step d) is taken on a sample level, and the signals are converted to sample level signals.

14. The method according to claim 1, wherein step e) further comprises:

calculating a chip value by canceling the sample value of the main path and the multipath interference signals coming from other users;

after de-scrambling and de-spreading with a k^th spread spectrum code, superposing the main path and multipath signals coming from working terminal users in phase coincidence to provide the outputting signal after interference cancellation; and

after demodulating, providing the result after interference cancellation.

15. The method according to claim 1, wherein steps a), b), c), d) and e) cancel interference for all channels having a signal-to-noise ratio less than a threshold value.

16. The method according to claim 1, wherein steps a), b), c), d) and e) are used for interference cancellation in a mobile communication base station.

17. The method according to claim 1, wherein steps b), c), d) and e) are used for interference cancellation in a user terminal.