Receiving device and channel estimator for use in a CDMA communication system

• US 6,661,835 B1
• Filed: 08/30/1999
• Issued: 12/09/2003
• Est. Priority Date: 08/31/1998
• Status: Expired due to Term

• Current Assignee: National University of Singapore, Wipro Limited
• Original Assignee: National University of Singapore, OKI Techno Centre Pte Limited
• Inventors: Sugimoto, Hiroki, Lim, Teng Joon, Rasmussen, Lars, Cheah, Kok Leong, Sun, Sumei, Matsumoto, Yoshihiro, Oyama, Takashi
• Primary Examiner(s): Ghayour, Mohammad H.
• Application Number:
  US09/385,359
• Time in Patent Office: 1,562 Days
• Field of Search: 375/148, 375/149, 375/150, 375/144, 375/145, 375/346, 375/347, 375/348, 370/335, 370/342, 370/441
• US Class Current: 375/148
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
• CPC Class Codes: H04B 1/7183 Synchronisation

Abstract

At a base station 2, a CDMA received signal coming in through an antenna 4 is fed to a radio frequency unit (RFU) or high frequency unit 6. The RFU 6 demodulates a baseband signal BB from a signal RF and delivers the signal BB to an analog-to-digital converter (A/D) 8. The resulting digital signal output from the A/D 8 is input to a hybrid interference canceller (HIC) 12 as a received signal Rx Data 10. The HIC 12 divides users into two groups and assigns one combination of a parallel interference canceller and a serial interference canceller to each group. The HIC 12 cancels interference contained in the received signal Rx Data 10 for thereby estimating symbols particular to a plurality of users.

Claims

1. A receiving device for CDMA (Code Division Multiple Access) communication, comprising:

receiving means for receiving signals for CDMA sent from a plurality of transmitting stations to thereby output received signals;

a first group of interference cancellation stage for estimating signals sent from the transmitting stations from the received signals by using despreading codes corresponding to spreading codes respectively assigned to the transmitting stations, wherein said first group of interference cancellation stage includes N (integer greater than 2 inclusive) interference cancelling units (ICUs) each for estimating an interstation interference ascribable to interference between the despreading codes, and estimates interstation interferences in parallel, cancels the interstation interferences and estimates the signals sent from said N transmitting stations in parallel; and

a second group of interference cancellation stage for estimating, from signals from which the interstation interferences have been cancelled by said first group of interference cancellation stage, interstation interferences in parallel with M (integer greater than 2 inclusive) ICUs, cancelling the interstation interferences and estimates signals sent from said M transmitting stations in parallel, and outputting signals free from the interstation interferences;

wherein a plurality of interference cancellation stages each comprising said first group of interference cancellation stage and said second group of interference cancellation stage are serially connected to construct a hybrid interference cancelling unit, and wherein each of said plurality of interference cancellation stages estimates interstation interferences while the ICLJs of a last one of said plurality of interference cancellation stages output the signals sent from the individual transmitting stations,

wherein each of said ICUs includes

finger circuits for performing Rake receipt, processing of estimated received symbols output from a previous one of said plurality of interference cancellation stages, and channel estimation,

a signal correction and decision circuit for executing correction and decision with signals output from said finger circuits, and

a respreading circuit for restoring signals output from said signal correction and decision circuit to same conditions as on a channel;

wherein for the channel estimation, use is made of a known pilot symbol portion and a data portion included in each of the signals received from the transmitting stations;

wherein each of said finger circuits estimates a channel by eliminating a phase of a correlation detection output by decision feedback based on a result of hard decision output from said signal correction and decision circuit, uses a moving average of several symbols of said correlation detection output as channel estimation information, and multiplies said correlation detection output by a complex conjugate of said channel estimation information to thereby produce a finger output; and

wherein each of said finger circuits first estimates a channel by using only the pilot symbol portion and restores a phase rotation of a data symbol next to said pilot symbol portion to thereby demodulate a finger input, inputs the pilot symbol portion to a moving average filter, returns a result of hard decision executed with a result of demodulation of data to a channel estimator to thereby eliminate a data phase of a next correlation detection output, inputs a result of data phase elimination to said moving average filter, produces a mean of said pilot symbol portion and one symbol of data in said moving average filter and uses said mean as a result of channel estimation for demodulating a second data symbol as counted from said pilot symbol section, returns a result of hard decision executed with a result of demodulation of said second data symbol also to said channel estimator to thereby restore a phase of a third data symbol, and inputs said phase of said third data symbol to said moving average filter.

2. A receiving device in accordance with claim 1, wherein a number of symbols in said moving average filter is sequentially increased up to a number of taps of said moving average filter, wherein said moving average filter performs usual moving average processing when the number of symbols reaches the number of taps, wherein a window representative of a section of the moving average has a size sequentially slid in a slot up to a next pilot symbol portion, wherein information existing in said moving average filter is cleared when a last data symbol of said slot preceding said next pilot symbol is fully demodulated, and then channel estimation is repeated only with said next pilot symbol portion.

3. A receiving device for CDMA (Code Division Multiple Access) communication, comprising:

receiving means for receiving signals for CDMA sent from a plurality of transmitting stations to thereby output received signals;

a first group of interference cancellation stage for estimating signals sent from the transmitting stations from the received signals by using despreading codes corresponding to spreading codes respectively assigned to the transmitting stations, wherein said first group of interference cancellation stage includes N (integer greater than 2 inclusive) interference cancelling units (ICUs) each for estimating an interstation interference ascribable to interference between the despreading codes, and estimates interstation interferences in parallel, cancels the interstation interferences and estimates the signals sent from said N transmitting stations in parallel; and

a second group of interference cancellation stage for estimating, from signals from which the interstation interferences have been cancelled by said first group of interference cancellation stage, interstation interferences in parallel with M (integer greater than 2 inclusive) ICUs, cancelling the interstation interferences and estimates signals sent from said M transmitting stations in parallel, and outputting signals free from the interstation interferences;

wherein a plurality of interference cancellation stages each comprising said first group of interference cancellation stage and said second group of interference cancellation stage are serially connected to construct a hybrid interference cancelling unit, and wherein each of said plurality of interference cancellation stages estimates interstation interferences while the ICLJs of a last one of said plurality of interference cancellation stages output the signals sent from the individual transmitting stations,

wherein each of said ICUs includes

finger circuits for performing Rake receipt, processing of estimated received symbols output from a previous one of said plurality of interference cancellation stages, and channel estimation,

a signal correction and decision circuit for executing correction and decision with signals output from said finger circuits, wherein said signal correction and decision circuit normalizes output signals of said finger circuits, multiplies said output signals normalized by a coefficient corresponding to a slope, and limits a result of multiplication with a threshold corresponding to a maximum value, and

a respreading circuit for restoring signals output from said signal correction and decision circuit to same conditions as on a channel.

4. A receiving device in accordance with claim 3, wherein said signal correction and decision circuit executes normalization with total power of channel estimates of multipaths.

5. A receiving device in accordance with claim 3, wherein said signal correction and decision circuit executes normalization with a moving mean of power.

6. A receiving device for CDMA (Code Division Multiple Access) communication, comprising:

receiving means for receiving signals for CDMA sent from a plurality of transmitting stations to thereby output received signals;

a first group of interference cancellation stage for estimating signals sent from the transmitting stations from the received signals by using despreading codes corresponding to spreading codes respectively assigned to the transmitting stations, wherein said first group of interference cancellation stage includes N (integer greater than 2 inclusive) interference cancelling units (ICUs) each for estimating an interstation interference ascribable to interference between the despreading codes, and estimates interstation interferences in parallel, cancels the interstation interferences and estimates the signals sent from said N transmitting stations in parallel; and

a second group of interference cancellation stage for estimating, from signals from which the interstation interferences have been cancelled by said first group of interference cancellation stage, interstation interferences in parallel with M (integer greater than 2 inclusive) ICUs, cancelling the interstation interferences and estimates signals sent from said M transmitting stations in parallel, and outputting signals free from the interstation interferences;

wherein a plurality of interference cancellation stages each comprising said first group of interference cancellation stage and said second group of interference cancellation stage are serially connected to construct a hybrid interference cancelling unit, and wherein each of said plurality of interference cancellation stages estimates interstation interferences while the ICUs of a last one of said plurality of interference cancellation stages output the signals sent from the individual transmitting stations, wherein signals representative of interferences of the individual transmitting stations belonging to said first group of said last stage are added to an interference-free signal output from said first group of said last stage, resulting sums are respectively fed to searchers respectively assigned to said transmitting stations of said first group for acquiring synchronization, signals representative of interferences of the individual transmitting stations belonging to said second group of said last stage are added to an interference-free signal output from said second group of said last stage, and resulting sums are respectively fed to searchers respectively assigned to said transmitting stations of said second group for acquiring synchronization.

12. A receiving device in accordance with claim 6, further comprising tracking means for executing synchronous tracking on the basis of signals acquired by said searchers to thereby execute tracking control over chip clocks each being used by a particular one of said ICUs.

17. A receiving device in accordance with claim 6, further comprising tracking means for executing synchronous tracking with the received signals or the signals input to the ICUs of the transmitting stations on the basis of the signals acquired by said searchers to thereby effect tracking control over chip clocks each being used by a particular one of said ICUs.

7. A receiving device for CDMA (Code Division Multiple Access) communication, comprising:

receiving means for receiving signals for CDMA sent from a plurality of transmitting stations to thereby output received signals;

a first group of interference cancellation stage for estimating signals sent from the transmitting stations from the received signals by using despreading codes corresponding to spreading codes respectively assigned to the transmitting stations, wherein said first group of interference cancellation stage includes N (integer greater than 2 inclusive) interference cancelling units (ICUs) each for estimating an interstation interference ascribable to interference between the despreading codes, and estimates interstation interferences in parallel, cancels the interstation interferences and estimates the signals sent from said N transmitting stations in parallel; and

a second group of interference cancellation stage for estimating, from signals from which the interstation interferences have been cancelled by said first group of interference cancellation stage, interstation interferences in parallel with M (integer greater than 2 inclusive) ICUs, cancelling the interstation interferences and estimates signals sent from said M transmitting stations in parallel, and outputting signals free from the interstation interferences;

wherein a plurality of interference cancellation stages each comprising said first group of interference cancellation stage and said second group of interference cancellation stage are serially connected to construct a hybrid interference cancelling unit, and wherein each of said plurality of interference cancellation stages estimates interstation interferences while the ICLJs of a last one of said plurality of interference cancellation stages output the signals sent from the individual transmitting stations;

wherein each of said ICUs includes

finger circuits for performing Rake receipt, processing of estimated received symbols output from a previous one of said plurality of interference cancellation stages, and channel estimation,

a signal correction and decision circuit for executing correction and decision with signals output from said finger circuits, and

a respreading circuit for restoring signals output from said signal correction and decision circuit to same conditions as on a channel; and

wherein ratios B/A estimates B output from said ICUs of said last stage to differences A between symbol estimates output from said signal correction and decision circuits of said ICUs of said last stage and symbol estimates output from said ICUs of a previous stage are determined, interference estimate signals respectively output from respreading circuits of said ICUs of said last stage are respectively multiplied by said ratios B/A, resulting products are respectively added to interference-free signals output from said last group of said last stage, and resulting sums are respectively applied to searchers respectively assigned to the transmitting stations for acquiring synchronism.

13. A receiving device in accordance with claim 7, further comprising tracking means for executing synchronous tracking on the basis of signals acquired by said searchers to thereby execute tracking control over chip clocks each being used by a particular one of said ICUs.

18. A receiving device in accordance with claim 7, further comprising tracking means for executing synchronous tracking with the received signals or the signals input to the ICUs of the transmitting stations on the basis of the signals acquired by said searchers to thereby effect tracking control over chip clocks each being used by a particular one of said ICUs.

8. A channel estimator comprising:

interference cancelling means for estimating signals sent from said plurality of transmitting stations from the received signals by use of despreading codes respectively corresponding to spreading codes respectively assigned to said plurality of transmitting stations, said interference cancelling means estimating interstation interferences ascribable to interference between said spreading codes and/or interference between said despreading codes, and cancelling said interstation interferences contained in the received signals to thereby output an interference-free signal;

demodulating means for demodulating the received signals to thereby output demodulated signals; and

tracking means for executing synchronous tracking on the basis of the demodulated signals to thereby execute tracking control over chip clocks to be used by said interference cancelling means.

9. A device for receiving a signal from a transmitting station and estimating a channel by using pilot symbols, which is a known signal, and a data portion included in the signal, said device comprising:

correlation detecting means for performing correlation detection with the signal received; and

channel estimating means for eliminating a phase of the data portion by decision feedback, producing a moving average of several symbols of an output of said correlation detecting means as channel estimate information, and multiplying said output of said correlation detecting means by a complex conjugate of said channel estimate information, wherein said channel estimating means first estimates a channel by using only a pilot symbol portion, uses the channel estimated for restoring a phase rotation of a data symbol next to said pilot symbol portion to thereby demodulate fingers, feeds a signal in said pilot symbol portion to a moving average filter, uses a hard decision value derived from a result of data demodulation to estimate a channel, eliminates a data phase of a next output of said correlation detecting means and inputs a resulting output thereof to said moving average filter, causes said moving average filter to output a mean of said pilot symbol portion and one data symbol, uses said means for demodulation of a second data symbol, as counted from said pilot symbol portion, by said fingers, uses a result of hard decision derived from said second data symbol for channel estimation, and restores a phase of a next data symbol and inputs said phases to said moving average filter.

10. A device in accordance with claim 9, wherein a number of symbols in said moving average filter is increased up to a number of taps of said moving average filter, wherein said moving average filter performs usual moving average processing when the number of symbols reaches the number of taps, wherein a size of a window representative of a moving average processing section is sequentially extended in a slot until said window reaches a next pilot symbol portion, wherein information existing in said moving average filter is cleared when a last data symbol of the slot preceding said next pilot symbol portion is demodulated, and wherein said channel estimating means repeats channel estimation only with said next pilot symbol portion.

11. A receiving device for CDMA (Code Division Multiple Access) communication, comprising:

receiving means for receiving signals for CDMA sent from a plurality of transmitting stations to thereby output received signals;

a first group of interference cancellation stage for estimating signals sent from the transmitting stations from the received signals by using despreading codes corresponding to spreading codes respectively assigned to the transmitting stations, wherein said first group of interference cancellation stage includes N (integer greater than 2 inclusive) interference cancelling units (ICUs) each for estimating an interstation interference ascribable to interference between the despreading codes, and estimates interstation interferences in parallel, cancels the interstation interferences and estimates the signals sent from said N transmitting stations in parallel; and

a second group of interference cancellation stage for estimating, from signals from which the interstation interferences have been cancelled by said first group of interference cancellation stage, interstation interferences in parallel with M (integer greater than 2 inclusive) ICUs, cancelling the interstation interferences and estimates signals sent from said M transmitting stations in parallel, and outputting signals free from the interstation interferences;

wherein a plurality of interference cancellation stages each comprising said first group of interference cancellation stage and said second group of interference cancellation stage are serially connected to construct a hybrid interference cancelling unit, and wherein each of said plurality of interference cancellation stages estimates interstation interferences while the ICLJs of a last one of said plurality of interference cancellation stages output the signals sent from the individual transmitting stations, further comprising

a plurality of searchers each being assigned to the received signal from a particular transmitting station for acquiring synchronization, said plurality of searchers respectively receiving sums of said interference-free signal output from said last group of said last stage and signals representative of station-by-station interferences, and

tracking means for executing synchronous tracking on the basis of signals acquired by said searchers to thereby execute tracking control over chip clocks each being used by a particular one of said ICUs.

14. A receiving device for CDMA communication, comprising:

receiving means for receiving signals for CDMA sent from a plurality of transmitting stations to thereby output received signals; and

interference cancelling means for estimating signals sent from said plurality of transmitting stations from the received signals by use of despreading codes respectively corresponding to spreading codes respectively assigned to said plurality of transmitting stations, said interference cancelling means estimating interstation interferences ascribable to interference between said spreading codes and/or interference between said despreading codes, and cancelling said interstation interferences contained in the received signals to thereby output an interference-free signal;

wherein signals respectively reproduced from the interferences of said plurality of transmitting stations are individually added to said interference-free signal, and resulting sums are respectively fed to searchers each being assigned to one of said plurality of transmitting stations for acquiring synchronization,

further comprising first and second tracking means each for executing synchronous tracking based on signals output from said searchers corresponding to said first group or said second group to thereby execute tracking control over chip clocks to be used by either one of said first and second interference cancelling means associated with said first group or said second group.

15. A receiving device for CDMA communication comprising:

receiving means for receiving signals for CDMA sent from a plurality of transmitting stations to thereby output received signals; and

at least first interference cancelling means and second interference cancelling means for respectively cancelling interferences from signals received from at least a first group of transmitting stations and a second group of transmitting stations,wherein said first interference cancelling means estimates signals sent from said first group of transmitting stations from the received signals by use of despreading codes respectively corresponding to spreading codes respectively assigned to said first group of transmitting stations, estimates interstation interferences ascribable to interference between said spreading codes and/or interference between said despreading codes, and cancels said interstation interferences contained in the received signals to thereby output a first interference-free signal, and wherein said second interference cancelling means estimates signals sent from said second group of transmitting stations from the received signals by use of despreading codes respectively corresponding to spreading codes respectively assigned to said second group of transmitting stations,estimates interstation interferences ascribable to interference between said spreading codes and/or interference between said despreading codes, and cancels said interstation interferences contained in the received signals to thereby output a second interference-free signal;

wherein signals respectively reproduced the interferences of said first group of transmitting stations are individually added to said first interference-free signal, and resulting sums are respectively fed to searchers respectively assigned to said first group of transmitting stations in order to acquire synchronization, and wherein signals respectively reproduced the interferences of said second group of transmitting stations are individually added to said second interference-free signal, and resulting sums are respectively fed to searchers respectively assigned to said second group of transmitting stations in order to acquire synchronization, further comprising first and second tracking means each for executing synchronous tracking based on signals output from said searchers corresponding to said first group or said second group to thereby execute tracking control over chip clocks to be used by either one of said first and second interference cancelling means associated with said first group or said second group.

16. A receiving device for CDMA (Code Division Multiple Access) communication, comprising:

receiving means for receiving signals for CDMA sent from a plurality of transmitting stations to thereby output received signals;

a first group of interference cancellation stage for estimating signals sent from the transmitting stations from the received signals by using despreading codes corresponding to spreading codes respectively assigned to the transmitting stations, wherein said first group of interference cancellation stage includes N (integer greater than 2 inclusive) interference cancelling units (ICUs) each for estimating an interstation interference ascribable to interference between the despreading codes, and estimates interstation interferences in parallel, cancels the interstation interferences and estimates the signals sent from said N transmitting stations in parallel; and

a second group of interference cancellation stage for estimating, from signals from which the interstation interferences have been cancelled by said first group of interference cancellation stage, interstation interferences in parallel with M (integer greater than 2 inclusive) ICUs, cancelling the interstation interferences and estimates signals sent from said M transmitting stations in parallel, and outputting signals free from the interstation interferences;

wherein a plurality of interference cancellation stages each comprising said first group of interference cancellation stage and said second group of interference cancellation stage are serially connected to construct a hybrid interference cancelling unit, and wherein each of said plurality of interference cancellation stages estimates interstation interferences while the ICLJs of a last one of said plurality of interference cancellation stages output the signals sent from the individual transmitting stations, further comprising a plurality of searchers each being assigned to the received signal from a particular transmitting station for acquiring synchronization, said plurality of searchers respectively receiving sums of said interference-free signal output from said last group of said last stage and signals representative of station-by-station interferences,

further comprising tracking means for executing synchronous tracking with the received signals or the signals input to the ICUs of the transmitting stations on the basis of the signals acquired by said searchers to thereby effect tracking control over chip clocks each being used by a particular one of said ICUs.