TDMA single antenna co-channel interference cancellation

• US 6,249,518 B1
• Filed: 08/07/1998
• Issued: 06/19/2001
• Est. Priority Date: 08/07/1998
• Status: Expired due to Term

• Current Assignee: Hanger Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Cui, Jian
• Primary Examiner(s): Hsu, Alpus H.
• Assistant Examiner(s): Nguyen, Brian
• Application Number:
  US09/130,312
• Time in Patent Office: 1,047 Days
• Field of Search: 370/347, 370/337, 370/201, 370/203, 370/204, 370/205, 370/206, 370/208, 370/252, 370/268, 370/269, 370/503, 370/512, 370/514, 370/292, 375/142, 375/346, 375/340, 375/329, 375/332, 375/324, 375/254, 375/285, 455/501, 455/63
• US Class Current: 370/347
• CPC Class Codes: H04B 7/005 Control of transmission; Equalising
• CPC Class Codes: H04L 25/03006 Arrangements for removing intersymbol interference

Abstract

A demodulator, within a receiver attached to a single antenna, that cancels co-channel interference within a time division multiple access (TDMA) communication system is disclosed. The demodulator takes as input a series of received signals comprising an information signal and a co-channel interference signal, both using the π/4-differential quadrature phase shift keying (DQPSK) modulation protocol. During a training period, in which the information signals corresponds to a known SYNC word, the demodulator estimates the fading coefficients corresponding to the information and interference signals. After the completion of the training period, the demodulator uses these estimates to generate accurate estimations for future information and interference signals corresponding to future data received signals. Therefore, the information signal has been essentially separated from the co-channel interference signal and can be demodulated with a lower bit error rate (BER) than previous demodulation techniques under these circumstances.

Claims

1. In a demodulator that takes as input a series of received signals from a single antenna receiver system within a time division multiple access (TDMA) time slot, each received signal comprising an information component and an interference component, both components comprising a signal and a fading coefficient, the TDMA time slot comprising a training period when the information signals are known at the processor and a data period when the information signals are not known, a method of reducing interference during demodulation comprising the steps of:

inputting to the processor, during the training period, a plurality of training received signals and a plurality of known information signals that correspond to the training received signals;

estimating an information fading coefficient by processing the training received signals and the known information signals and deriving estimates of a plurality of information components corresponding to the training received signals;

estimating a plurality of interference components corresponding to the training received signals by processing the training received signals and the estimates of the information components;

inputting to the processor, during the data period, a first received signal;

correlating the first received signal with the estimates of the information and interference components to generate an estimate of a first information signal corresponding to the first received signal;

wherein each information signal and interference signal within the series of received signals is modulated according to a given information modulation scheme and a given interference modulation scheme respectively;

wherein the generation of the estimate for the first information signal comprises;

correlating the estimate of one of the plurality of information components and all possible information reference signals, each information reference signal being one of the closed set of all possible information signals recognized by the given information digital modulation scheme, to generate a plurality of information correlations;

correlating the estimate of one of the plurality of interference components and all possible interference reference signals, each interference reference signal being one of the closed set of all possible interference signals recognized by the given interference digital modulation scheme, to generate a plurality of interference correlations;

correlating the plurality of information correlations, the plurality of interference correlations, and the first received signal to generate a plurality of decision variables; and

comparing the plurality of decision variables to generate an estimate of the second information signal.

2. A method according to claim 1, wherein the generation of the plurality of decision variables is done by subtracting each combination of the plurality of information correlations and the plurality of interference correlations from the first received signal.

3. A method according to claim 1, wherein the generation of the estimate for the first information signal is done by choosing the information signal corresponding to the smallest squared decision variable.

4. In a demodulator that takes as input a series of received signals from a single antenna receiver system within a time division multiple access (TDMA) time slot, each received signal comprising an information component and an interference component, both components comprising a signal and a fading coefficient, the TDMA time slot comprising a training period when the information signals are known at the processor and a data period when the information signals are not known, a method of reducing interference during demodulation comprising the steps of:

inputting to the processor, during the training period, a plurality of training received signals and a plurality of known information signals that correspond to the training received signals;

estimating an information fading coefficient by processing the training received signals and the known information signals and deriving estimates of a plurality of information components corresponding to the training received signals;

estimating a plurality of interference components corresponding to the training received signals by processing the training received signals and the estimates of the information components;

inputting to the processor, during the data period, a first received signal;

correlating the first received signal with the estimates of the information and interference components to generate an estimate of a first information signal corresponding to the first received signal;

wherein the generation of the estimate for the first information signal further generates an estimate for a first interference signal corresponding to the first received signal, the method further comprising the steps of;

estimating a second information fading coefficient by processing a plurality of previously received signals and a plurality of previously estimated information signals that correspond to the previously received signals and deriving estimates of a second plurality of information components that correspond to the previously received signals;

estimating a second plurality of interference components corresponding to the previously received signals by processing the previously received signals, the estimates of the second information components, and a plurality of previously estimated interference signals that correspond to the previously received signals;

inputting to the processor a second received signal; and

correlating the second received signal with the estimates of the second information and interference components, to generate an estimate of a second information signal and a second interference signal corresponding to the second received signal.

5. A method according to claim 4, wherein the estimation of the second information fading coefficient and the second interference components occurs subsequent to estimating a plurality of information signals during the data period.

6. A method according to claim 4, wherein the estimation of the second information fading coefficient and the second interference components occurs directly after estimating the first information signal;

wherein the plurality of previously received signals comprises the first received signal and at least one of the plurality of training received signals.

7. A method according to claim 4, wherein the estimation of the second interference components comprises estimating a second interference fading coefficient corresponding to the previously received signals by processing the previously received signals with the estimates of the second information components removed and the previously estimated interference signals.

8. In a demodulator that takes as input a series of received signals from a single antenna receiver system within a time division multiple access (TDMA) time slot, each received signal comprising an information component and an interference component, both components comprising a signal and a fading coefficient, the TDMA time slot comprising a training period when the information signals are known at the processor and a data period when the information signals are not known, a method of reducing interference during demodulation comprising the steps of:

inputting to the processor, during the training period, a plurality of training received signals and a plurality of known information signals that correspond to the training received signals;

estimating an information fading coefficient by processing the training received signals and the known information signals and deriving estimates of a plurality of information components corresponding to the training received signals;

estimating a plurality of interference components corresponding to the training received signals by processing the training received signals and the estimates of the information components;

inputting to the processor, during the data period, a first received signal;

correlating the first received signal with the estimates of the information and interference components to generate an estimate of a first information signal corresponding to the first received signal;

wherein the TDMA time slot further comprises a second training period, further comprising the steps of;

inputting to the processor, prior to the second training period, a third received signal;

inputting to the processor, during the second training period, a second plurality of training received signals and a second plurality of known information signals that correspond to the second training received signals;

estimating a third information fading coefficient by processing the second training received signals and the second known information signals and deriving estimates of a third plurality of information components that correspond to the second training received signals;

estimating a third plurality of interference components corresponding to the second training received signals by processing the second training received signals and the estimates of the third information components; and

correlating the third received signal with the estimates of the third information and interference components to generate an estimate of a third information signal corresponding to the third received signal.

9. A method according to claim 8, wherein the second known information signals contain information used by a receiver containing the processor for at least one of frame synchronization, timing recovery, and information type recovery.

10. In a demodulator that takes as input a series of received signals from a single antenna receiver system within a time division multiple access (TDMA) time slot, each received signal comprising an information component and an interference component, both components comprising a signal and a fading coefficient, the TDMA time slot comprising a training period when the information signals are known at the processor and a data period when the information signals are not known, a method of reducing interference during demodulation comprising the steps of:

inputting to the processor, during the training period, a plurality of training received signals and a plurality of known information signals that correspond to the training received signals;

estimating an information fading coefficient by processing the training received signals and the known information signals and deriving estimates of a plurality of information components corresponding to the training received signals;

estimating a plurality of interference components corresponding to the training received signals by processing the training received signals and the estimates of the information components;

inputting to the processor, during the data period, a first received signal;

correlating the first received signal with the estimates of the information and interference components to generate an estimate of a first information signal corresponding to the first received signal;

wherein each received signal further comprises another information component comprising another information signal and another information fading coefficient, the other information signal being known during the training period and not being known during the data period, the method further comprising the steps of;

inputting to the processor, during the training period, a plurality of known other information signals that correspond to the training received signals; and

estimating another information fading coefficient by processing the training received signals and the known other information signals and deriving estimates of a plurality of other information components corresponding to the training received signals;

wherein the estimating a plurality of interference components further processes the estimates of the other information components; and

wherein the correlating the first received signal with the estimates of the information and interference components further correlates the first received signal with the other information components and further generates an estimate of a first other information signal corresponding to the first received signal.

11. A demodulator that takes as input a series of received signals from a single antenna receiver system within a time division multiple access (TDMA) time slot, each received signal comprising an information component and an interference component, both components comprising a signal and a fading coefficient, the TDMA time slot comprising a training period when the information signals are known at the processor and a data period when the information signals are not known, the demodulator comprising:

an estimation stage for generating an estimation of an information fading coefficient upon receipt of a plurality of training received signals and a corresponding plurality of known information signals during the training period;

an interference demodulation stage for generating estimations of a plurality of interference components corresponding to the training received signals upon receipt of the training received signals and estimations of a plurality of corresponding information components comprising the estimation of the information fading coefficient and the known information signals;

a correlation stage for generating an estimation of a first information signal corresponding to a first received signal by correlating the first received signal with the estimations of the information and interference components;

wherein the interference demodulation stage comprises;

an interference component isolator for generating estimations of a plurality of interference components by estimating the training received signals with the corresponding information components removed;

an interference demodulator for generating estimations of a plurality of interference signals corresponding to the training received signals upon receipt of the estimations of the interference components;

a second fading coefficient estimator for generating an estimation of an interference fading coefficient upon receipt of the estimations of the interference components and the estimations of the interference signals;

wherein the estimation stage comprises a first fading coefficient estimator; and

wherein the first and second fading coefficient estimators are of the same apparatus.

12. A receiver coupled to a single antenna comprising:

a gain controller coupled to the antenna, that amplifies the signals input from the antenna;

an analog to digital converter coupled to the gain controller that converts the output from the gain controller into digital format;

a receiver filter coupled to the analog to digital converter that generates a series of received signals within a time division multiple access (TDMA) time slot, each received signal comprising an information component and an interference component, both components comprising a signal and a fading coefficient, the TDMA time slot comprising a training period when the information signals are known at the processor and a data period when the information signals are not known;

a first demodulator that takes as input the series of received signals comprising;

an estimation stage for generating an estimation of an information fading coefficient upon receipt of a plurality of training received signals and a corresponding plurality of known information signals during the training period;

an interference demodulation stage for generating estimations of a plurality of interference components corresponding to the training received signals upon receipt of the training received signals and estimations of a plurality of corresponding information components comprising the estimation of the information fading coefficient and the known information signals;

a correlation stage for generating an estimation of a first information signal corresponding to a first received signal by correlating the first received signal with the estimations of the information and interference components;

a second demodulator that takes as input the series of received signals,

a detector that determines a critical performance factor corresponding to the series of received signals; and

a switching means for disabling one of the first and second demodulators and enabling the other one of the first and second demodulators if the critical performance factor is within a predetermined threshold range, and enabling the one of the first and second demodulators and disabling the other one of the first and second demodulators if the critical performance factor is not within the predetermined threshold range.

13. A receiver according to claim 12, wherein the critical performance factor is a signal to interference plus noise ratio (SINR).

14. A receiver according to claim 13, wherein the second demodulator is a conventional demodulator;

and

the switching means disables the first demodulator and enables the second demodulator if the SINR is above 6 dB, and enables the first demodulator and disables the second demodulator if the SINR is below 6 dB.