Progressive parallel interference canceller and method and receiver thereof
A progressive parallel interference canceller (PPIC) and a method and a receiver thereof are illustrated. The PPIC reconstructs each subchannel interference reconstruction signal through several iterations and subtracts the corresponding subchannel interference reconstruction signal from each subchannel frequency-domain reception signal to obtain a subchannel frequency-domain signal. Thereby, according to the present disclosure, inter-channel interference can be cancelled without re-performing channel coding or estimating the signal to noise ratio (SNR) or frequency offset.
1. A progressive parallel interference canceller (PPIC), adaptable to a receiver in a multiple input multiple output (MIMO) communication system based on an orthogonal frequency-division multiplexing (OFDM) modulation technique, wherein the receiver performs a plurality of iterations, the PPIC comprising:
a plurality of subchannel interference reconstruction units, wherein the k th subchannel interference reconstruction unit corresponding to a r th receiving antenna generates a k th subchannel interference reconstruction signal S ICI,r,k (i) corresponding to the r th receiving antenna during the i th iteration according to (2×i−2) subchannel frequency-domain estimation signals Ŝ t,((k−i+1)) N (1) , Ŝ t,((k−i+2)) N (2) , . . . , Ŝ t,((k−2)) N (i−2) , Ŝ t,((k−1)) N (i−1) , Ŝ t,((k+1)) N (i−1) , Ŝ t,((k+2)) N (i−2) , . . . , Ŝ t,((k+i−2)) N (2) , Ŝ t,((k+i−1)) N (1) , wherein i is an integer greater than 1, the subchannel frequency-domain estimation signal Ŝ t,q (x) represents a q th subchannel frequency-domain estimation signal corresponding to a t th transmitting antenna generated during the x th iteration, and ((•)) N represents a calculation of dividing by N to obtain a remainder, N is a number of subchannels in the MIMO communication system, k is an integer between 0 and (N−1), x is an integer between 1 and (i−1), and q=k−i+x or q=k+i−x; and
a plurality of subchannel interference cancellation units, wherein the k th subchannel interference cancellation unit corresponding to the r th receiving antenna is coupled to the k th subchannel interference reconstruction unit corresponding to the r th receiving antenna, and the k th subchannel interference cancellation unit obtains a k th subchannel frequency-domain signal Y′ r,k (i) corresponding to the r th receiving antenna according to a k th subchannel frequency-domain reception signal Y r,k and the k th subchannel interference reconstruction signal S ICI,r,k (i) corresponding to the r th receiving antenna during the i th iteration.
2. The PPIC according to claim 1 , wherein during the 1 st iteration, the k th subchannel interference reconstruction unit corresponding to the r th receiving antenna presets a k th subchannel interference reconstruction signal S ICI,r,k (1) corresponding to the r th receiving antenna to 0, and the k th subchannel interference cancellation unit corresponding to the r th receiving antenna obtains a k th subchannel frequency-domain signal Y′ r,k (1) corresponding to the r th r,k receiving antenna according to the k th subchannel frequency-domain reception signal Y r,k corresponding to the r th receiving antenna.
3. The PPIC according to claim 2 further comprising:
a MIMO detector, coupled to the subchannel interference reconstruction units and the subchannel interference cancellation units, for determining a plurality of bits b 0 , b 1 , . . . , and b MT−1 corresponding to k th subchannels of the transmitting antennas according to the k th subchannel frequency-domain signals Y′ 1,k (i) , Y′ 2,k (i) , . . . , and Y′ R,k (i) of the receiving antennas when the PPIC performs the i th iteration, wherein M is a bit modulation order, R is a number of the receiving antennas, T is a number of the transmitting antennas, and the bits b M(t−1) , b M(t−1)+1 , . . . , and b Mt−1 corresponding to the k th subchannel of the t th transmitting antenna are used for determining the subchannel frequency-domain estimation signal Ŝ t,k (i) .
4. The PPIC according to claim 3 , wherein the MIMO detector is a MIMO detector using a message passing algorithm (MPA).
5. The PPIC according to claim 3 , wherein the MIMO detector performs a plurality of sub iterations during the i th iteration, and during each of the sub iterations, the MIMO detector generates a probability message for the bit b n according to the subchannel frequency-domain signal Y′ r,k (i) and generates a probability message for the subchannel frequency-domain signal Y′ p,k (i) according to the bit b a , and during the last sub iteration, the MIMO detector generates probabilities of the bits b 0 , b 1 , . . . , and b MT−1 according to the probability messages, wherein p is an integer between 1 and T, and a and n are integers between 0 and (MT−1).
6. The PPIC according to claim 5 , wherein if the i th iteration is the last iteration, the MIMO detector makes a hard decision according to the probabilities of the bits b 0 , b 1 , . . . , and b MT−1 to determine the bits b 0 , b 1 , . . . , and b MT−1 , and if the i th iteration is not the last iteration, the MIMO detector makes a soft decision according to the probabilities of the bits b 0 , b 1 , . . . , and b MT−1 to determine the bits b 0 , b 1 , . . . , and b MT−1 .
7. The PPIC according to claim 3 further comprising a channel decoder coupled to the MIMO detector, wherein the channel decoder determines the subchannel frequency-domain estimation signal Ŝ t,k (i) according to the bits b m(t−1) , b M(t−1)+1 , . . . , and b Mt−1 of the k th subchannel of the t th transmitting antenna.
8. The PPIC according to claim 3 , wherein the MIMO detector determines the subchannel frequency-domain estimation signal Ŝ t,k (i) according to the bits b M(t−1) , b M(t−1)+1 , . . . , and b Mt−1 of the k th subchannel of the t th transmitting antenna.
9. The PPIC according to claim 1 , wherein a k th subchannel frequency-domain signal Y′ r,k (i) corresponding to the r th receiving antenna is equivalent to a k th subchannel frequency-domain reception signal Y r,k corresponding to the r th receiving antenna minus the k th subchannel interference reconstruction signal S ICI,r,k (i) .
10. The PPIC according to claim 1 , wherein the k th subchannel interference reconstruction unit corresponding to the r th receiving antenna has a memory, and the k th subchannel interference reconstruction unit of the r th receiving antenna stores the subchannel frequency-domain estimation signals Ŝ t,((k+i−1)) N (1) , Ŝ t,((k−i+2)) N (2) , . . . , Ŝ t,((k−2)) N (i−2) , Ŝ t,((k−1)) N (i−1) , Ŝ t,((k+1)) N (i−1) , Ŝ t,((k+2)) N (i−2) , . . . , Ŝ t,((k+i−2)) N (2) , Ŝ t,((k+i−1)) N (1) into the memory, transmits the subchannel frequency-domain estimation signals Ŝ t,((k−i+2)) N (1) , Ŝ t,((k−i+3)) N (2) , . . . , Ŝ t,((k−1)) N (i−2) , Ŝ t,((k)) N (i−1) to the (k+1) th subchannel interference reconstruction unit corresponding to the r th receiving antenna, and transmits the subchannel frequency-domain estimation signals Ŝ t,((k+i−2)) N (1) , Ŝ t,((k+i−3)) N (2) , . . . , Ŝ t,((k+1)) N (i−2) , Ŝ t,((k)) N (i−1) to the (k−1) th subchannel interference reconstruction unit corresponding to the r th receiving antenna.
11. The PPIC according to claim 1 further comprising a channel estimator, wherein the channel estimator estimates a plurality of channel impulse responses of a wireless channel and calculates a plurality of coefficients according to the channel impulse responses, wherein the k th subchannel interference reconstruction unit corresponding to the r th receiving antenna generates a k th subchannel interference reconstruction signal S ICI,r,k (i) corresponding to the r th receiving antenna according to the (2×i−2) subchannel frequency-domain estimation signals Ŝ t,((k−i+1)) N (1) , Ŝ t,((k−i+2)) N (2) , . . . , Ŝ t,((k−2)) N (i−2) , Ŝ t,((k+2)) N (i−2) , Ŝ t,((k−1)) N (i−1) , Ŝ t,((k+1)) N (i−1) , . . . , Ŝ t,((k+i−2)) N (2) , Ŝ t,((k+i−1)) N (1) and the coefficients during the i th iteration.
12. A receiver, adaptable to a MIMO communication system based on an OFDM modulation technique, wherein the receiver performs a plurality of iterations and comprises:
a plurality of receiving antennas;
a plurality of OFDM demodulators, wherein each of the OFDM demodulators is coupled to one of the receiving antennas;
a PPIC, coupled to the OFDM demodulators, the PPIC comprising:
a plurality of subchannel interference reconstruction units, wherein the k th subchannel interference reconstruction unit corresponding to the r th receiving antenna generates a k th subchannel interference reconstruction signal S ICI,r,k (i) corresponding to the r th receiving antenna according to (2×i−2) subchannel frequency-domain estimation signals Ŝ t,((k−i+1)) N (1) , Ŝ t,((k−i+2)) N (2) , . . . , Ŝ t,((k−2)) N (i−2) , Ŝ t,((k+1)) N (i−1) , Ŝ t,((k+2)) N (i−2) , Ŝ t,((k−1)) N (i−1) , . . . , Ŝ t,((k+i−2)) N (2) , Ŝ t,((k+i−1)) N (1) during the i th iteration, wherein i is an integer greater than 1, the subchannel frequency-domain estimation signal represents the q th subchannel frequency-domain estimation signal corresponding to a t th transmitting antenna generated during the x th iteration, ((•)) N represents a calculation of dividing by N to obtain a remainder, N is a number of subchannels in the MIMO communication system, k is an integer between 0 and (N−1), x is an integer between 1 and (i−1), and q=k−i+x or q=k+i−x; and
a plurality of subchannel interference cancellation units, wherein the k th subchannel interference cancellation unit corresponding to the r th receiving antenna is coupled to the k th subchannel interference reconstruction unit corresponding to the r th receiving antenna, and the k th subchannel interference cancellation unit obtains a k th subchannel frequency-domain signal Y r,k (i) corresponding to the r th receiving antenna according to a k th subchannel frequency-domain reception signal Y r,k and the k th subchannel interference reconstruction signal S ICI,r,k (i) corresponding to the r th receiving antenna during the i th iteration; and
a MIMO detector, coupled to the subchannel interference reconstruction units and the subchannel interference cancellation units, for determining a plurality of bits b 0 , b 1 , . . . , and b MT−1 corresponding to k th subchannels of the transmitting antennas according to the k th subchannel frequency-domain signals Y′ 1,k (i) , Y′ 2,k (i) , . . . , and Y′ R,k (i) of the receiving antennas when the PPIC performs the i th iteration, wherein M is a bit modulation order, R is a number of the receiving antennas, T is a number of the transmitting antennas, and the bits b M(t−1) , b M(t−1)+1 , . . . , and b Mt−1 corresponding to the k th subchannel of the t th transmitting antenna are used for determining the subchannel frequency-domain estimation signal Ŝ t,k (i) .
13. The receiver according to claim 12 , wherein when the PPIC performs the 1 st iteration, the k th subchannel interference reconstruction unit corresponding to the r th receiving antenna presets a k th subchannel interference reconstruction signal S ICI,r,k (1) corresponding to the r th receiving antenna to 0, and the k th subchannel interference cancellation unit corresponding to the r th receiving antenna obtains a k th subchannel frequency-domain signal Y′ r,k (1) corresponding to the r th receiving antenna according to the k th subchannel frequency-domain reception signal Y r,k corresponding to the r th receiving antenna.
14. The receiver according to claim 12 , wherein a k th subchannel frequency-domain signal Y′ r,k (i) corresponding to the r th receiving antenna is equivalent to a k th subchannel frequency-domain reception signal Y r,k corresponding to the r th receiving antenna minus the k th subchannel interference reconstruction signal S ICI,r,k (i) .
15. The receiver according to claim 12 , wherein the k th subchannel interference reconstruction unit corresponding to the r th receiving antenna has a memory, and the k th subchannel interference reconstruction unit corresponding to the r th receiving antenna stores the subchannel frequency-domain estimation signals Ŝ t,((k−i+1)) N (1) , Ŝ t,((k−i+2)) N (2) , . . . , Ŝ t,((k−2)) N (i−2) , Ŝ t,((k−1)) N (i−1) , Ŝ t,((k)) N (i−1) , Ŝ t,((k+1)) N (i−1) , . . . , Ŝ t,((k+2)) N (i−2) , . . . , Ŝ t,((k+i−2)) N (2) , Ŝ t,((k+i−1)) N (1) into the memory, transmits the subchannel frequency-domain estimation signals Ŝ t((k−i+2)) N (1) , Ŝ t((k−i+3)) N (2) , . . . , Ŝ t,((k−1)) N (i−2) , Ŝ((k)) N (i−1) to the (k+1) th subchannel interference reconstruction unit corresponding to the r th receiving antenna, and transmits the subchannel frequency-domain estimation signals Ŝ t((k+i−2)) N (1) , Ŝ t((k+i−3)) N (2) , . . . , Ŝ t,((k+1)) N (i−2) , Ŝ((k)) N (i−1) to the (k−1) th subchannel interference reconstruction unit corresponding to the r th receiving antenna.
16. The receiver according to claim 12 further comprising a channel estimator, wherein the channel estimator estimates a plurality of channel impulse responses of a wireless channel and calculates a plurality of coefficients according to the channel impulse responses, wherein the k th subchannel interference reconstruction unit corresponding to the r th receiving antenna generates a k th subchannel interference reconstruction signal S ICI,r,k (i) corresponding to the r th receiving antenna according to (2×i−2) subchannel frequency-domain estimation signals Ŝ t,((k−i+1)) N (1) , Ŝ t,((k−i+2)) N (2) , . . . , Ŝ t,((k−2)) N (i−2) , Ŝ t,((k−1)) N (i−1) , Ŝ t,((k+1)) N (i−1) , Ŝ t,((k+2)) N (i−2) , . . . , Ŝ t,((k+i−2)) N (2) , Ŝ t,((k+i−1)) N (1) , and the coefficients during the i th iteration.
17. The receiver according to claim 12 , wherein the MIMO detector is a MIMO detector using a MPA.
18. The receiver according to claim 12 , wherein the MIMO detector performs a plurality of sub iterations during the i th iteration, and during each of the sub iterations, the MIMO detector generates a probability message for the bit b n according to the subchannel frequency-domain signal Y′ r,k (i) and then generates a probability message for the subchannel frequency-domain signal Y′ p,k (i) according to the bit b a , and during the last sub iteration, the MIMO detector generates probabilities of the bits b 0 , b 1 , . . . , and b MT−1 according to the probability messages, wherein p is an integer between 1 and T, and a and n are integers between 0 and (MT−1).
19. The receiver according to claim 18 , wherein if the i th iteration is the last iteration, the MIMO detector makes a hard decision according to the probabilities of the bits b 0 , b 1 , . . . , and b MT−1 to determine the bits b 0 , b 1 , . . . , and b MT−1 , and if the i th iteration is not the last iteration, the MIMO detector makes a soft decision according to the probabilities of the bits b 0 , b 1 , . . . , and b MT−1 to determine the bits b 0 , b 1 , . . . , and b MT−1 .
20. The receiver according to claim 12 further comprising a channel decoder coupled to the MIMO detector, wherein the channel decoder determines the subchannel frequency-domain estimation signal Ŝ t,k (i) according to the bits b M(t−1) , b M(t−1)+1 , . . . , and b Mt−1 of the k th subchannel of the t th transmitting antenna.
21. The receiver according to claim 12 , wherein the MIMO detector determines the subchannel frequency-domain estimation signal Ŝ t,k (i) according to the bits b M(t−1) , b M(t−1)+1 , . . . , and b Mt−1 of the k th subchannel of the t th transmitting antenna.
22. A progressive parallel interference cancellation method, adaptable to a receiver in a MIMO communication system based on an OFDM modulation technique, wherein the receiver performs a plurality of iterations, the progressive parallel interference cancellation method comprising:
generating a k th subchannel interference reconstruction signal S ICI,r,k (i) corresponding to the r th receiving antenna according to (2×i−1) subchannel frequency-domain estimation signals Ŝ t,((k−i+1)) N (1) , Ŝ t,((k−i+2)) N (2) , . . . , Ŝ t,((k−2)) N (i−2) , Ŝ t,((k−1)) N (i−1) , Ŝ t,((k+2)) N (i−2) , Ŝ t,((k+1)) N (i−1) , . . . , Ŝ t,((k+i−2)) N (2) , Ŝ t,((k+i−1)) N (1) , during the i th iteration, wherein i is an integer greater than 1, the subchannel frequency-domain estimation signal Ŝ 1, q (x) represents the q th subchannel frequency-domain estimation signal corresponding to a t th transmitting antenna generated during the x th iteration, ((•)) N represents a calculation of dividing by N to obtain a remainder, N is a number of subchannels in the MIMO communication system, k is an integer between 0 and (N−1), x is an integer between 1 and (i−1), q=k−i+x or q=k+i−x; and
obtaining a k th sub channel frequency-domain signal Y′ r,k (i) corresponding to the r th receiving antenna according to a k th subchannel frequency-domain reception signal Y r,k and the k th subchannel interference reconstruction signal S ICI,r,k (i) corresponding to the r th receiving antenna during the i th iteration.
23. The progressive parallel interference cancellation method according to claim 22 further comprising:
during the first iteration, presetting a k th subchannel interference reconstruction signal S ICI,r,k (1) corresponding to the r th receiving antenna to 0, and obtaining a k th subchannel frequency-domain signal Y′ r,k (1) corresponding to the r th receiving antenna according to the k th subchannel frequency-domain reception signal Y r,k corresponding to the r th receiving antenna.
24. The progressive parallel interference cancellation method according to claim 22 , wherein a k th subchannel frequency-domain signal Y′ r,k (i) corresponding to the r th receiving antenna is equivalent to a k th subchannel frequency-domain reception signal Y r,k corresponding to the r th receiving antenna minus the k th subchannel interference reconstruction signal S ICI,r,k (i) .
25. The progressive parallel interference cancellation method according to claim 22 further comprising:
estimating a plurality of channel impulse responses of a wireless channel, and calculating a plurality of coefficient according to the channel impulse responses,
wherein a k th subchannel interference reconstruction signal S ICI,r,k (i) corresponding to the r th receiving antenna is generated according to (2×i−2) subchannel frequency-domain estimation signals Ŝ t,((k−i+1)) N (1) , Ŝ t,((k−i+2)) N (2) , . . . , Ŝ t,((k−2)) N (i−2) , Ŝ t,((k−1)) N (i−1) , Ŝ t,((k+2)) N (i−2) , Ŝ t,((k+1)) N (i−1) , . . . , Ŝ t,((k+i−2)) N (2) , Ŝ t,((k+i−1)) N (1) and the coefficients during the i th iteration.
26. The progressive parallel interference cancellation method according to claim 22 further comprising:
determining a plurality of bits b 0 , b 1 , . . . , and b MT−1 corresponding to the k th subchannels of the transmitting antennas according to the k th subchannel frequency-domain signals Y′ 1,k (i) , Y′ 2,k (i) , . . . , and Y′ R,k (i) of the receiving antennas during the i th iteration, wherein M is a bit modulation order, R is a number of the receiving antennas, T is a number of the transmitting antennas, and the bits b M(t−1) , b M(t−1)+1 , . . . , and b Mt−1 corresponding to the k th subchannel of the t th transmitting antenna are used for determining the subchannel frequency-domain estimation signal Ŝ t,k (i) .
27. The progressive parallel interference cancellation method according to claim 26 , wherein a plurality of sub iterations is performed during the i th iteration, and during each of the sub iteration, a probability message is generated for the bit b n according to the subchannel frequency-domain signal Y′ r,k (i) , and a probability message is then generated according to the bit b a for the subchannel frequency-domain signal Y′ p,k (i) , and during the last sub iteration, probabilities of the bits b 0 , b 1 , . . . , and b MT−1 are generated according to the probability messages, wherein p is an integer between 1 and T, and a and n are integers between 0 and (MT−1).
28. The progressive parallel interference cancellation method according to claim 27 , wherein if the i th iteration is the last iteration, a hard decision is made according to the probabilities of the bits b 0 , b 1 , . . . , and b MT−1 to determine the bits b 0 , b 1 , . . . , and b MT−1 , and if the i th iteration is not the last sub iteration, a soft decision is made according to the bits b 0 , b 1 , . . . , and b MT−1 to determine the bits b 0 , b 1 , . . . , and b MT−1 .
29. The progressive parallel interference cancellation method according to claim 26 further comprising:
determining the subchannel frequency-domain estimation signal Ŝ t,k (i) according to the bits b M(t−1) , b M(t−1)+1 , . . . , and b Mt−1 of the k th subchannel of the t th transmitting antenna.