Apparatus and method for cancelling in-band interferences
The present document discloses an apparatus and method for cancelling in-band interference in a cellular telecommunication system which using multiple-input multiple-output technique. The method includes: receiving a transmitted signal and obtaining an interfering data stream; calculating a value of a credit; deciding whether the credit is above a predefined threshold; regenerating an interference signal by using the interfering data stream if the credit is above the predefined threshold; subtracting the regenerated interference signal from the received transmitted signal to obtain a target signal; and demodulating and decoding the target signal. By using the apparatus and method, the concerned signal can be regenerated even when there is only small number of error bits while all the other bits are correctly decoded. Also, the target stream would be able to know whether the interfering stream can be regenerated or not, before the decoding.
1. An apparatus for cancelling in-band interference in a cellular telecommunication system which using multiple-input multiple-output technique, comprising:
a receiver for receiving a transmitted signal and obtaining an interfering data stream;
a credit assessment block for calculating a value of a credit;
a judgment block for deciding whether the credit is above a predefined threshold;
a regeneration block for regenerating an interference signal by using the interfering data stream;
a subtractor for subtracting the regenerated interference signal from the received transmitted signal to obtain a target signal; and
a demodulating and decoding block for demodulating and decoding the target signal;
wherein the credit assessment block is configured to calculate the value of the credit by using soft bits of the interfering data stream; and
wherein the credit assessment block comprises:
an extractor for extracting amplitudes of the soft bits, x i ;
a first calculator for calculating an average of the soft bits x i , A 1 ;
a second calculator for calculating an average of square of the soft bits x i , A 2 ;
a third calculator for calculating an average of power of three of the soft bits x i , A 3 ;
a forth calculator for calculating a decision variable
Z
=
A
3
-
A
1
·
A
2
A
3
-
A
1
·
A
2
+
A
1
3
;
a fifth calculator for calculating ρ value as the credit by using the calculated decision variable Z and an equation:
Z
(
ρ
)
=
2
ρ
+
2
π
ⅇ
-
ρ
2
2
(
2
ⅇ
-
π
2
·
ρ
-
1
)
2
ρ
+
2
π
ⅇ
-
ρ
2
2
(
2
ⅇ
-
π
2
·
ρ
-
1
)
+
[
ρ
+
2
π
ⅇ
-
π
2
·
ρ
ⅇ
-
ρ
2
2
]
3
.
2. The apparatus of claim 1 , wherein the soft bits is obtained after demodulation of the interfering data stream or Hybrid Automatic Repeat reQuest combining of the interfering data stream.
3. The apparatus of claim 1 , wherein the credit assessment block comprises:
a calculator for calculating a signal-to-noise-ratio of the soft bits as the credit.
4. The apparatus of claim 1 , wherein the predefined threshold is between −10 dB˜20 dB.
5. The apparatus of claim 1 , wherein the regeneration block is configured to regenerate the interference signal by using the soft bits before the interfering data stream is decoded.
6. The apparatus of claim 5 , wherein the regeneration block further comprises:
a modulator for modulating the soft bits.
7. The apparatus of claim 1 , wherein the regeneration block is configured to regenerate the interference signal after the interfering data stream is decoded.
8. The apparatus of claim 7 , wherein the regeneration block is further configured to regenerate the interference signal by using Log Likelihood Ratio values.
9. A method for cancelling in-band interference in a cellular telecommunication system which using multiple-input multiple-output technique, comprising:
receiving a transmitted signal and obtaining an interfering data stream;
calculating a value of a credit;
deciding whether the credit is above a predefined threshold;
regenerating an interference signal by using the interfering data stream if the credit is above the predefined threshold;
subtracting the regenerated interference signal from the received transmitted signal to obtain a target signal; and
demodulating and decoding the target signal;
wherein the step of calculating a value of a credit comprises:
calculating the value of the credit by using soft bits of the interfering data stream;
extracting amplitudes of the soft bits, x i ;
calculating an average of the soft bits x i , A 1 ;
calculating an average of square of the soft bits X i , A 2 ;
calculating an average of power of three of the soft bits x i , A 3 ;
calculating a decision variable
Z
=
A
3
-
A
1
·
A
2
A
3
-
A
1
·
A
2
+
A
1
3
;
calculating p value as the credit by using the calculated decision variable Z and an equation:
Z
(
ρ
)
=
2
ρ
+
2
π
ⅇ
-
ρ
2
2
(
2
ⅇ
-
π
2
·
ρ
-
1
)
2
ρ
+
2
π
ⅇ
-
ρ
2
2
(
2
ⅇ
-
π
2
·
ρ
-
1
)
+
[
ρ
+
2
π
ⅇ
-
π
2
·
ρ
ⅇ
-
ρ
2
2
]
3
.
10. The method of claim 9 , wherein the soft bits is obtained after demodulation of the interfering data stream or Hybrid Automatic Repeat reQuest combining of the interfering data stream.
11. The method of claim 9 , wherein the step of calculating a value of a credit further comprises:
calculating a signal-to-noise-ratio of the soft bits as the credit.
12. The method of claim 9 , wherein the predefined threshold is between −10 dB˜20 dB.
13. The method of claim 9 , wherein the step of regenerating an interference signal by using the interfering data stream comprises:
regenerating the interference signal by using the soft bits before the interfering data stream is decoded.
14. The method of claim 13 , wherein the step of regenerating an interference signal by using the interfering data stream further comprises:
modulating the soft bits.
15. The method of claim 9 , wherein the step of regenerating an interference signal by using the interfering data stream comprises:
regenerating the interference signal after the interfering data stream is decoded.
16. The method of claim 15 , wherein the step of regenerating an interference signal by using the interfering data stream further comprises:
regenerating the interference signal by using Log Likelihood Ratio values.