CDMA demodulating apparatus

• US 6,137,788 A
• Filed: 02/12/1997
• Issued: 10/24/2000
• Est. Priority Date: 06/13/1995
• Status: Expired due to Term

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: NTT Mobile Communications Network Inc. (Nippon Telegraph and Telephone Corporation)
• Inventors: Andou, Hidehiro, Higuchi, Kenichi, Sawahashi, Mamoru, Miki, Yoshinori
• Primary Examiner(s): OLMS, DOUGLAS W
• Assistant Examiner(s): Ho, Tuan Q.
• Application Number:
  US08/793,051
• Time in Patent Office: 1,350 Days
• Field of Search: 370/332, 370/320, 370/333, 370/280, 370/335, 370/337, 370/342, 370/344, 370/347, 370/441, 370/442, 370/468, 370/321, 370/326, 370/479, 375/367, 375/358, 375/242, 375/200, 455/501
• US Class Current: 370/342
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 2001/71077 Partial interference cancellation
• CPC Class Codes: H04W 52/12 Outer and inner loops

Abstract

A CDMA demodulating apparatus with an improved interference canceling effect when there are a large number of communicators. A reception signal having a frame configuration in which a pilot signal of a known pattern is inserted between information signals is received from a plurality of communicators. Transmission data of each communicator is demodulated, an interference canceler for estimating is provided in a plurality of stages, in each channel of each stage, a variation of transmission path is estimated in each path to achieve data demodulation and estimation of interference replica. The later the stage, the more error of interference signal replica can be reduced, thereby improving the interference canceling effect. An even better effect can be obtained when interference canceling is performed after detecting a reception level of each channel by summation of reception power of each path of each channel, and channel ranking is determined in the order of higher reception level.

Claims

1. A CDMA (Code Division Multiple Access) demodulating apparatus for use in a CDMA communication system that performs spreading information data by a spreading code faster than an information rate to a wideband signal and the wideband signal is transmitted to achieve multiple access transmission, wherein a pilot symbol of know pattern is received to estimate channel variation, individual reception signals received through a plurality of channels are compensated by the estimated channel variation, and the compensated reception signal is demodulated to reproduce the information data, comprising:

a correlation detector using a spreading code as a spreading code replica synchronized with a reception timing of each path of each of the channel for correlation detection of the spreading code replica with the reception signal of each path;

a received level detector for determining a sum of a reception power of a corresponding path of said correlation detector and detecting a desired wave reception signal level;

a channel ranking unit for controlling order of demodulation of the user according to the reception signal level of each user detected by said received level detector; and

an interference canceler of a plurality of stages for making interference canceling according to a control signal outputted from said channel ranking unit, in each of the plurality of stages, making estimation of channel variation using the pilot symbol on each channel, compensating the reception signal of the channel by the estimated channel variation, and respreading the compensated reception signal to produce an interference signal replica.

2. The CDMA demodulating apparatus as claimed in claim 1, wherein said interference canceler of an i'"'"'th (i being an integer of 2 or more) stage of the plurality of stages uses the interference signal replica of each user estimated by the interference canceler of the (i-1)th stage as an input to supply the interference signal replica of each user estimated by the interference canceler of the i'"'"'th stage to said interference canceler of a (i+1)'"'"'th stage.

3. The CDMA demodulating apparatus as claimed in claim 2, wherein each of said interference canceler of each stage comprises a sub-interference canceler for each user for producing the interference signal replica, said sub-interference canceler of a k'"'"'th (k=any of 1, 2, . . . , M) user of said interference canceler of the i'"'"'th stage comprising:

an interference subtractor for subtracting interference signal replicas in said interference canceler of the i'"'"'th stage as interference signal replicas of first, second . . . and (k-1)th users from the reception signal, subtracting interference signal replicas in said interference canceler of an (i-1)'"'"'th stage as interference replicas of (k+1)'"'"'th, . . . (M-1)'"'"'th and M'"'"'th users from the reception signal;

a channel variation estimator for estimating a channel variation of the pilot symbol in the output signal of said interference subtractor for each path, and estimating the channel variation by interpolating the channel variation of the estimated pilot symbol into a position of each symbol of the information data in the output signal of said interference subtractor;

a channel variation compensator for compensating the reception signal for the channel variation estimated for each path by said channel variation estimator;

a RAKE combiner for synthesizing the reception signal of each path outputted from said channel variation compensator;

a data decision block for deciding the output signal of said RAKE combiner;

a channel variation adder for adding a channel variation obtained as an output of said channel variation estimator to the decision data outputted from said data decision block;

a respreader for spreading a signal of each path outputted from said channel variation adder by a spreading code synchronized with reception timing of each path; and

an adder for adding the output of said respreader to produce an interference signal replica of the k'"'"'th user.

4. The CDMA demodulating apparatus as claimed in claim 1, wherein said correlation detector comprises a plurality of matched filters.

5. The CDMA demodulating apparatus as claimed in claim 1, wherein said correlation detector comprises a plurality of sliding correlators.

6. The CDMA demodulating apparatus as claimed in claim 3, wherein the pilot symbol is inserted periodically between the information data.

7. The CDMA demodulating apparatus as claimed in claim 3, wherein said interference canceler of each stage comprises one unit of said sub-interference canceler, and memories for storing interference replicas of individual users of individual stages, using said sub-interference canceler in the mode of time division.

8. The CDMA demodulating apparatus as claimed in claim 6, wherein said interference canceler uses a block as a processing unit of a block of constant time including at least two adjacent pilot signal sections, and said sub-interference canceler further comprises an extrapolating unit for an information symbol outside the pilot signal section for extrapolating the pilot symbol closest to the information symbol to determine channel variation of the information symbol.

9. The CDMA demodulating apparatus as claimed in claim 3, wherein a subtractor for subtracting an interference signal replica other than of a j'"'"'th path of the k'"'"'th communicator in an (i-1)'"'"'th stage from the output signal of said interference subtractor is provided at the input side of said correlation detector of the j'"'"'th (j being 1 to a path number Lk of RAKE combining) of the k'"'"'th user of the i'"'"'th (i being an integer of 2 or more) stage interference canceler.

10. The CDMA demodulating apparatus as claimed in claim 3, wherein said sub-interference canceler further comprising:

a reception signal power detector for detecting a power of the reception signal of each path after despreading outputted from said correlation detector;

an adder for adding the reception signal powers of the individual paths;

an amplitude converter for detecting amplitudes of in-phase component and quadrature component from the output of said adder;

an averaging unit for averaging the output signal of said amplitude converter; and

a multiplier for multiplying the decision data by an output of said averaging unit.

11. The CDMA demodulating apparatus as claimed in claim 1, wherein said interference canceler of the first stage comprises a decorrelation filter for using a signal of each path of K'"'"'th (K being an integer of 2 to spreading factor PG) user from the higher reception signal level to obtain a despread output vector which is interference removed from each other;

and a coherent detector/interference generator for estimating transmission data of K users outputted from said decorrelation filter and generating an estimated interference amount of each user, wherein

said interference canceler uses the interference signal replica outputted from said coherent detector/interference generator as interference signal replicas of the K users to produce individual interference signals replicas of the remaining (M-K) users.

12. The CDMA demodulating apparatus as claimed in claim 11, wherein said interference canceler of i'"'"'th (i being an integer of 2 or more) stage of the plurality of stages uses the interference signal replica of each user estimated by said interference canceler of the (i-1)'"'"'th stage as an input and supplies said interference canceler of (i+1)'"'"'th stage with an estimated interference amount of each user estimated by said interference canceler of the i'"'"'th stage.

13. The CDMA demodulating apparatus as claimed in claim 12, wherein said first stage interference canceler comprises a sub-interference canceler for producing the estimated interference amount for each user after (K+1)'"'"'th user, and said sub-interference canceler of k'"'"'th (k=(K+1), (K+2), . . . , or M) user comprises:

an interference subtractor for subtracting interference signal replicas in said interference canceler of the i'"'"'th stage as interference signal replicas as estimated interference amounts of first, second . . . and K'"'"'th users from the reception signal, and subtracting interference signal replicas in said interference canceler of the first stage as interference replicas of (K+1), . . . (k-1)'"'"'th users from the reception signal;

a channel variation estimator for estimating a channel variation of the pilot symbol in the output signal of said interference subtractor for each path, and estimating the channel variation of each information symbol by interpolating the channel variation of the estimated pilot symbol into a position of each symbol of the information data in the output signal of said interference subtractor;

a channel variation compensator for compensating the reception signal for the channel variation estimated for each path by said channel variation estimator;

a RAKE combiner for synthesizing the reception signal of each path outputted from said channel variation compensator;

a data decision block for deciding the output signal of said RAKE combiner;

a channel variation adder for adding a channel variation obtained as an output of the channel variation estimator to the decision data outputted from said data decision block;

a respreader for spreading a signal of each path outputted from said channel variation adder by a spreading code synchronized with reception timing of each path; and

an adder for adding the output of the respreader to produce an interference signal replica of the k'"'"'th user,

wherein each of said interference canceler of and after the second stage comprises a sub-interference canceler for each user for producing the interference signal replica, said sub-interference canceler of a k'"'"'th (k=any of 1, 2, . . . , M) user of said interference canceler of the i'"'"'th stage comprising;

an interference subtractor for subtracting interference signal replicas in said interference canceler of the i'"'"'th stage as interference signal replicas of first, second . . . and (k-1)th users from the reception signal, and subtracting interference signal replicas in said interference canceler of an (i-1)'"'"'th stage as interference replicas of (k+1)'"'"'th, . . . (M-1)'"'"'th and M'"'"'th users from the reception signal;

a channel variation estimator for estimating a channel variation of the pilot symbol in the output signal of said interference subtractor for each path, and estimating the channel variation of the information symbol by interpolating the channel variation of the estimated pilot symbol into a position of each symbol of the information data in the output signal of said interference subtractor;

a channel variation compensator for compensating the reception signal for the channel variation estimated for each path by said channel variation estimator;

a RAKE combiner for synthesizing the reception signal of each path outputted from said channel variation compensator;

a data decision block for deciding the output signal of said RAKE combiner;

a channel variation adder for adding a channel variation obtained as an output of said channel variation estimator to the decision data outputted from said data decision block;

a respreader for spreading a signal of each path outputted from said channel variation adder by a spreading code synchronized with reception timing of each path; and

an adder for adding the output of said respreader to produce an interference signal replica of the k'"'"'th user.

14. The CDMA demodulating apparatus as claimed in claim 11, wherein said correlation detector comprises a plurality of matched filters.

15. The CDMA demodulating apparatus as claimed in claim 11, wherein said correlation detector comprises a plurality of sliding correlators.

16. The CDMA demodulating apparatus as claimed in claim 13, wherein the pilot symbol is inserted periodically between the information data.

17. The CDMA demodulating apparatus as claimed in claim 13, wherein said interference canceler of each stage comprises one unit of said sub-interference canceler, and memories for storing interference replicas of individual users of individual stages, using said sub-interference canceler in the mode of time division.

18. The CDMA demodulating apparatus as claimed in claim 11, wherein said coherent detector/interference generator comprises:

a channel variation estimator for estimating a channel variation of the pilot symbol in the output signal of said interference subtractor for each path, and estimating the channel variation of each information symbol by interpolating the channel variation of the estimated pilot symbol into a position of each symbol of the information data in the output signal of said interference subtractor;

a channel variation compensator for compensating the reception signal for the channel variation estimated for each path by said channel variation estimator;

a RAKE combiner for synthesizing the reception signal of each path outputted from said channel variation compensator;

a data decision block for deciding the output signal of said RAKE combiner;

a channel variation adder for adding a channel variation obtained as an output of said channel variation estimator to the decision data outputted from said data decision block;

a respreader for spreading a signal of each path outputted from said channel variation adder by a spreading code synchronized with reception timing of each path; and

an adder for adding the output of the respreader to produce an interference signal replica of the k'"'"'th user.

19. The CDMA demodulating apparatus as claimed in claim 1 further comprising:

an SIR measuring unit for measuring an SIR of the output of said correlation detector;

a reception quality measuring unit for measuring a reception quality of the output signal of said interference canceler;

a target SIR setting unit for setting a target SIR according to the measured reception quality and a required reception quality; and

a transmission power control signal generator for comparing SIR outputted from said SIR measuring unit with the target SIR.

20. The CDMA demodulating apparatus as claimed in claim 19, wherein said SIR setting unit sets an initial value of the target SIR according to the number of simultaneous communicators.

21. The CDMA demodulating apparatus as claimed in claim 19, wherein said reception quality measuring unit comprises an error ratio measuring unit for measuring a frame error ratio, and means for comparing the frame error ratio with a predetermined threshold value of frame error ratio to decide the reception quality.

22. The CDMA demodulating apparatus as claimed in claim 19, wherein said reception quality measuring unit comprises an error ratio measuring unit for measuring a bit error ratio of the pilot symbol, and means for comparing the bit error ratio with a predetermined threshold value of bit error ratio to decide the reception quality.

23. The CDMA demodulating apparatus as claimed in claim 19, wherein said correlation detector is a matched filter.

24. The CDMA demodulating apparatus as claimed in claim 23, wherein said interference canceler comprises a reception vector generator for generating a reception vector comprising despread signal of each path for each channel from the output signal of said matched filter, a cross-correlation inverse matrix generator for calculating cross-correlation of all spreading codes other than the spreading code of own channel and receiver input to produce an inverse matrix of a matrix comprising cross-correlation, and a matrix vector multiplier for compensating the reception vector by the inverse matrix to remove cross-correlation between individual reception vectors thereby removing interference.

25. A CDMA (Code Division Multiple Access) demodulating apparatus for use in a CDMA system that performs multiple access transmission by transmitting a spread signal, the spread signal being generated by spreading information data into a wideband signal with a spreading code whose rate is higher than an information rate, wherein a pilot symbol of a known pattern to estimate a channel variation, each reception signal received through a plurality of channels is compensated by the estimated channel variation, and the compensated reception signal is demodulated to reproduce the information data, the demodulating apparatus comprising:

a correlation detector, using a spreading code in phase with reception timing of each path of each channel, for detecting correlation of the spreading code with the reception signal of each path;

a received level detector for determining a sum of a reception power of a corresponding path of the correlation detector and detecting a desired wave reception signal level;

a channel ranking unit for controlling order of demodulation of the user according to the reception signal level of each user detected by said received level detector;

an interference canceler of a plurality of stages for despreading the reception signal for individual users according to an order determined by the control signal outputted from said channel ranking unit, respreading the despread signal, and subtracting an interference signal replica of other users obtained by respreading from the reception signal of the corresponding user; and

a pilot interpolation/coherent detector for estimating a channel variation using the pilot symbol in the signal after subtracting by an interference amount of other users in said interference canceler of the last stage in the plurality of stages, compensating the information data using the estimated channel variation to perform absolute synchronization detection of the compensated information data.

26. The CDMA demodulating apparatus as claimed in claim 25, wherein an i'"'"'th (i being an integer of 2 or more) stage interference canceler uses the interference signal replica of each user estimated in the (i-1)'"'"'th stage interference canceler as an input to supply the interference signal replica estimated in said i'"'"'th stage interference canceler to the (i+1)'"'"'th stage interference canceler.

27. The CDMA demodulating apparatus as claimed in claim 26, wherein each interference canceler of each of the stages comprises a sub-interference canceler for each user for producing the interference signal replica, said sub-interference canceler of a k'"'"'th (k=1, 2, . . . , or M) user of said i'"'"'th stage interference canceler comprising:

an interference subtractor for subtracting interference signal replicas in said interference canceler of the i'"'"'th stage as interference signal replicas of first, second . . . and (k-1)th users from the reception signal, subtracting interference signal replicas in said interference canceler of an (i-1)'"'"'th stage as interference replicas of (k+1)'"'"'th, . . . (M-1)'"'"'th and M'"'"'th users from the reception signal;

a matched filter for making correlation detection between the output signal of said interference subtractor and a spreading code replica in phase with reception timing of each path to obtain a despread signal of each path; and

a respreading/combiner unit for spreading the despread signal of each path with a spreading code in phase with the reception timing of each path, estimating an interference signal replica of the path of each user, and adding the estimated interference signal replica to produce an interference signal replica of each user.

28. The CDMA demodulating apparatus as claimed in claim 25, wherein the pilot symbol is inserted periodically between the information data.

29. The CDMA demodulating apparatus as claimed in claim 25, wherein said interference canceler of each stage comprises one unit of said sub-interference canceler, and memories for storing interference replicas of individual users of individual stages, using said sub-interference canceler in the mode of time division.