Arrangement for canceling interference in transmission systems
First Claim
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1. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, the method for removing a prescribed interference component in a signal received at a terminal comprising the steps of:
- storing a sequence of successive digital symbols 1, 2, . . . , N applied to the bidirectional transmission path in successive symbol time periods,generating a replica signal representative of the prescribed interference component in the received signal subsequent to the symbol time periods of the stored sequence of successive digital symbols; and
combining the replica signal with the received signal to cancel the prescribed interference component in the received signal subsequent to the time periods of the sequence of successive digital symbols;
the step of generating the prescribed interference component replica signal includingselecting the Nth stored symbol in the sequence in each symbol period of the received signal,forming an adaptive gain signal corresponding to the correlation of the replica signal and the signal representative of the received signal with the prescribed interference component removed in each symbol time period,modifying the Nth stored symbol by the adaptive gain signal, and recursively altering the modified Nth symbol with an expontentially decreasing infinite impulse response corresponding to the characteristics of the bidirectional transmission path subsequent to the time period of the Nth digital symbol of the sequence of successive digital symbols.
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Abstract
In an arrangement for simultaneously exchanging digital symbols between terminals over a bidirectional transmission path, near term interference in the signal received from the transmission path is canceled by storing the sequence of successive digital symbols 1, 2, . . . , N applied to the transmission path, forming a replica of the interference from the stored digital symbols and subtracting the replica from the received signal. A signal representative of a replica of the interference occurring subsequent to the Nth digital symbol of the successive digital symbols 1, 2, . . . , N is then generated and combined with the signal having the interference corresponding to the stored symbol sequence removed to cancel the subsequent interference in the received signal. The signal representing the interference subsequent to the Nth digital symbol is generated by modifying the Nth stored symbol by an adaptive gain signal corresponding to the correlation of the subsequent interference replica signal with the signal having the interference removed, and recursively altering the modified Nth stored digital symbol with a prescribed impulse response representative of the characteristics of the bidirectional transmission path subsequent to the time periods of the sequence of successive digital symbols 1, 2, . . . , N.
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Citations
20 Claims
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1. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, the method for removing a prescribed interference component in a signal received at a terminal comprising the steps of:
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storing a sequence of successive digital symbols 1, 2, . . . , N applied to the bidirectional transmission path in successive symbol time periods, generating a replica signal representative of the prescribed interference component in the received signal subsequent to the symbol time periods of the stored sequence of successive digital symbols; and combining the replica signal with the received signal to cancel the prescribed interference component in the received signal subsequent to the time periods of the sequence of successive digital symbols; the step of generating the prescribed interference component replica signal including selecting the Nth stored symbol in the sequence in each symbol period of the received signal, forming an adaptive gain signal corresponding to the correlation of the replica signal and the signal representative of the received signal with the prescribed interference component removed in each symbol time period, modifying the Nth stored symbol by the adaptive gain signal, and recursively altering the modified Nth symbol with an expontentially decreasing infinite impulse response corresponding to the characteristics of the bidirectional transmission path subsequent to the time period of the Nth digital symbol of the sequence of successive digital symbols. - View Dependent Claims (2)
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3. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, the method for removing the far end intersymbol interference component in a signal received at a terminal comprising the steps of:
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storing a sequence of successive digital symbols 1, 2, . . . , N applied to the bidirectional transmission path in successive symbol time periods, the digital symbols representing the N digital symbols applied to the bidirectional transmission path from the terminal at the other end of the bidirectional transmission path, generating a replica signal representative of the far end intersymbol interference component in the received signal subsequent to the symbol time periods of the stored sequence of successive digital symbols; and combining the replica signal with the received signal to cancel the far end intersymbol interference component in the received signal subsequent to the time periods of the sequence of successive digital symbols; the step of generating the far end intersymbol interference component replica signal including selecting the Nth stored symbol in the sequence in each symbol period of the received signal, forming an adaptive gain signal corresponding to the correlation of the replica signal and the signal representative of the received signal with the far end intersymbol interference component removed in each symbol time period, modifying the Nth stored symbol by the adaptive gain signal, and recursively altering the modified Nth stored symbol with an exponentially decreasing impulse response corresponding to the characteristics of the bidirectional transmission path subsequent to the time periods of the sequence of N successive digital symbols.
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4. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, the method for cancelling echoes in the signal received from the bidirectional transmission path comprising the steps of:
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storing a sequence of N successive digital symbols 1, 2, . . . , N applied to the bidirectional transmission path from the terminal in successive symbol periods n, forming a replica of the echo corresponding to the sequence of N successive digital symbols from the terminal responsive to the stored sequence, combining the echo replica corresponding to the sequence of N successive digital symbols with the current value of the signal received from the bidirectional transmission path to form a signal representative of the current value of the received signal with the echo replica corresponding to the stored sequence of N successive digital symbols removed therefrom, generating signal representative of a replica of the echo in the received signal subsequent to the stored sequence of N successive digital symbols; and combining the signal representative of the replica of the echo in the received signal subsequent to the stored sequence of N successive symbols with the signal representative of difference between the received signal and the echo replica corresponding to the stored sequence of N successive digital symbols to cancel the echo in the received signal subsequent to the symbol time periods of the stored sequence of N successive digital symbols; the step of generating the signal representative of the replica of the echo in the received signal subsequent to the stored sequence of N successive digital symbols comprising forming an adaptive gain signal corresponding to the correlation of the signal representative of the replica of the echo in the received signal subsequent to the symbol time periods of the sequence of stored N successive symbols and the received signal having the echo canceled therefrom, modifying the Nth stored successive symbol with the adaptive gain signal, and recursively altering the modified Nth stored successive sample with an exponentially decreasing infinite impulse response corresponding to the characteristics of the bidirectional transmission path subsequent to the sequence of N successive digital symbols.
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5. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, a method for cancelling the intersymbol interference component in the signal received from the bidirectional transmission path comprising the steps of:
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storing a sequence of successive digital symbols 1, 2, . . . , M received from the bidirectional transmission path in successive symbol periods n, forming a replica of the intersymbol interference component corresponding to the sequence of M successive digital symbols responsive to the stored sequence, combining the intersymbol interference component replica corresponding to the sequence of M successive digital symbols with the current value of the signal received from the bidirectional transmission path to form a signal representative of the current value of the received signal with the intersymbol interference component replica corresponding to the stored sequence of M successive digital symbols removed therefrom, generating a signal representative of a replica of the intersymbol interference component in the received signal subsequent to the stored sequence of M successive digital symbols; and combining the signal representative of the replica of the intersymbol interference component in the received signal subsequent to the stored sequence of M successive symbols with the signal representative of difference between the received signal and the intersymbol interference component replica corresponding to the stored sequence of M successive digital symbols to cancel the intersymbol interference component in the received signal subsequent to the time periods of the sequence of M successive digital symbols; the step of generating the signal representative of the replica of the intersymbol interference component in the received signal subsequent to the stored sequence of M successive digital symbols comprising forming an adaptive gain signal corresponding to the correlation of the signal representative of the replica of the intersymbol interference component in the received signal subsequent to the stored sequence of M successive symbols with the received signal having the intersymbol interference removed therefrom, modifying the Mth stored successive symbol by the adaptive gain signal, and recursively altering the modified Mth stored successive digital symbol with a prescribed impulse response corresponding to the characteristics of the bidirectional transmission path subsequent to the time periods of the M successive digital symbols to form the signal. - View Dependent Claims (6, 7, 8)
- 8. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, the method for cancelling intersymbol interference component in the signal received from the bidirectional transmission path according to claim 7 wherein
the adaptive gain signal gi (n) is updated on the occurrence of each successive symbol in accordance with the relationship - space="preserve" listing-type="equation">g.sub.i (n+1)=g.sub.i (n)+α
r.sub.i (n)sgn[p.sub.i (n)]sgn[g.sub.i (n)]
where n is the time period of the current symbol, n-1 is the time period of the immediately preceding symbol, α
is a constant,
space="preserve" listing-type="equation">r.sub.i (n)=q.sub.i (n)-p.sub.i (n-1),qi (n) is the signal representative of the difference between the received signal and the intersymbol interference component replica corresponding to the stored sequence of M symbols in the symbol period n, sgn[pi (n)] is the sign of the signal representative of the intersymbol interference component replica in the symbol period n, and sgn[gi (n)] is the sign of the adaptive gain signal in the symbol period n. - space="preserve" listing-type="equation">g.sub.i (n+1)=g.sub.i (n)+α
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9. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, the circuit for removing a prescribed interference component in a signal received at a terminal comprising
means for storing a sequence of successive digital symbols 1, 2, . . . , N applied to the bidirectional transmission path in successive symbol periods n, means responsive to the stored sequence of N successive digital symbols for generating a replica signal representative of the prescribed interference component in the received signal subsequent to the stored sequence of successive digital symbols; - and
means for combining the replica signal p(n) with the received signal to cancel the prescribed interference component in the received signal subsequent to the time periods of the sequence of N successive digital symbols; the means for generating the replica signal includes means for selecting the Nth stored symbol in the sequence in each symbol period of the received signal, means responsive to the replica signal and the signal representative of the received signal with the prescribed interference component removed for forming an adaptive gain signal corresponding to the correlation of the replica signal and the signal representative of the received signal with the prescribed interference component removed, means for modifying the Nth stored symbol by the adaptive gain signal, and means for recursively altering the modified Nth symbol with an exponentially decreasing infinite impulse response corresponding to the characteristics of the bidirectional transmission path subsequent to the sequence of N successive digital symbols. - View Dependent Claims (10)
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11. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, a circuit for removing the far end intersymbol interference component in a signal received at a terminal comprising
means for storing a sequence of successive digital symbols 1, 2, . . . , N representative of the N digital symbols applied to the bidirectional transmission path from the terminal at the other end of the bidirectional transmission path in successive symbol periods n, means responsive to the stored sequence of N successive digital symbols for generating a replica signal representative of the far end intersymbol interference component in the received signal subsequent to the stored sequence of successive digital symbols; - and
means for combining the replica signal with the received signal to cancel the far end intersymbol interference component in the received signal subsequent to the time periods of the sequence of N successive digital symbols; the means for generating the replica signal includes means for selecting the Nth stored symbol in the sequence in each symbol period of the received signal, means responsive to the replica signal and the signal representative of the received signal with the far end intersymbol interference component removed for forming an adaptive gain signal corresponding to the correlation of the replica signal and the signal representative of the received signal with the far end intersymbol interference component removed, means for modifying the Nth stored symbol by the adaptive gain signal, and means for recursively altering the modified Nth symbol with a prescribed impulse response corresponding to the characteristics of the bidirectional transmission path subsequent to the time periods of the sequence of N successive digital symbols to form the replica signal.
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12. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, the circuit for cancelling echoes in the signal received from the bidirectional transmission path comprising:
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means for storing a sequence of N successive digital symbols from the terminal in successive symbol periods n, means responsive to the stored sequence of N successive digital symbols for forming a replica of the echo corresponding to the sequence of N successive digital symbols from the terminal responsive to the stored sequence, means for combining the echo replica corresponding to the sequence of N successive digital symbols with the current value of the signal received from the bidirectional transmission path to form a signal representative of the current value of the received signal with the echo replica corresponding to the stored sequence of N successive digital symbols removed therefrom, means for generating signal representative of a replica of the echo in the received signal subsequent to the stored sequence of N successive digital symbols; and means for combining the signal representative of the replica of the echo in the received signal subsequent to the stored sequence of N successive symbols with the signal representative of difference between the received signal and the echo replica corresponding to the stored sequence of N successive digital symbols to cancel the echo in the received signal subsequent to the symbol periods of the stored sequence of N successive digital symbols; the means for generating the signal representative of the replica of the echo in the received signal subsequent to the stored sequence of N successive digital symbols comprising means for forming an adaptive gain signal corresponding to the correlation of the signal representative of the replica of the echo in the received signal subsequent to the stored sequence of N successive samples and the received signal having the echo canceled therefrom, means responsive to the adaptive gain signal for modifying the Nth stored successive symbol, and means for recursively altering the modified Nth stored successive sample with an exponentially decreasing infinite impulse response corresponding to the characteristics of the bidirectional transmission path subsequent to the sequence of N successive digital symbols.
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13. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, a circuit for cancelling the intersymbol interference component in the signal received from the bidirectional transmission path comprising:
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means for storing a sequence of successive digital symbols 1, 2, . . . , M received from the bidirectional transmission path in successive symbol periods n, means responsive to the received sequence of M successive digital symbols for forming a replica of the intersymbol interference component corresponding to the sequence of M successive digital symbols, means for combining the intersymbol interference component replica corresponding to the sequence of M successive digital symbols with the current value of the signal received from the bidirectional transmission path to form a signal representative of the current value of the received signal with the intersymbol interference component replica corresponding to the stored sequence of M successive digital symbols removed therefrom, means for generating a signal representative of a replica of the intersymbol interference component in the received signal subsequent to the symbol periods of the stored sequence of M successive digital symbols; and means for combining the signal representative of the replica of the intersymbol interference component in the received signal subsequent to the symbol periods of the stored sequence of M successive symbols with the signal representative of difference between the received signal and the intersymbol interference component replica corresponding to the stored sequence of M successive digital symbols to cancel the intersymbol interference component in the received signal subsequent to the symbol periods of the stored sequence of M successive digital symbols; the means for generating the signal representative of the replica of the intersymbol interference component in the received signal subsequent to the symbol periods of the stored sequence of M successive digital symbols comprising means responsive to the replica signal for forming an adaptive gain signal corresponding to the correlation of the signal representative of the replica of the intersymbol interference component in the received signal subsequent to the symbol periods of the stored sequence of M successive digital symbols and the received signal having the intersymbol interference removed therefrom, means for modifying the Mth stored successive symbol with the adaptive gain signal, and means for recursively altering the modified Mth stored successive digital symbol with a prescribed impulse response corresponding to the characteristics of the bidirectional transmission path subsequent to the symbol periods of the sequence of M successive digital symbols to form the signal. - View Dependent Claims (14)
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15. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, the method for removing a prescribed interference component in a signal received at a terminal comprising the steps of:
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storing a sequence of successive digital symbols 1, 2, . . . , N applied to the bidirectional transmission path in successive symbol time periods, generating a replica signal representative of the prescribed interference component in the received signal subsequent to the symbol time periods of the stored sequence of successive digital symbols; and combining the replica signal with the received signal to cancel the prescribed interference component in the received signal subsequent to the time periods of the sequence of successive digital symbols; the step of generating the prescribed interference component replica signal including selecting the Nth stored symbol in the sequence in each symbol period of the received signal, forming an adaptive gain signal corresponding to the correlation of the replica signal and the signal representative of the received signal with the prescribed interference component removed in each symbol time period, modifying the Nth stored symbol by the adaptive gain signal, and recursively altering the modified Nth stored symbol with an exponentially decreasing impulse response characterized by a single pole and performed in accordance with the relationship
space="preserve" listing-type="equation">p(n)=β
[p(n-1)+g(n)×
(n)]where p(n) is the value of the replica signal representative of the prescribed interference component in the received signal subsequent to the symbol time periods of the stored sequence of successive digital symbols in the symbol period n, β
is a constant determinative of the single pole of the impulse responsep(n-1) is the value of the signal representative of the prescribed interference component subsequent to the stored sequence of digital symbols in the symbol period n-1, g(n) is the value of the adaptive gain signal in the symbol period n, and x(n) is the value of the stored Nth symbol in the symbol period n. - View Dependent Claims (16)
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17. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, the method for cancelling echoes in the signal received from the bidirectional transmission path comprising the steps of:
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storing a sequence of successive digital symbols 1, 2, . . . , N applied to the bidirectional transmission path from the terminal in successive symbol periods n, forming a replica of the echo corresponding to the sequence of N successive digital symbols from the terminal responsive to the stored sequence, combining the echo replica corresponding to the sequence of N successive digital symbols with the current value of the signal received from the bidirectional transmission path to form a signal representative of the current value of the received signal with the echo replica corresponding to the stored sequence of N successive digital symbols removed therefrom, generating a signal representative of a replica of the echo in the received signal subsequent to the stored sequence of N successive digital symbols; and combining the signal representative of the replica of the echo in the received signal subsequent to the stored sequence of N successive symbols with the signal representative of the difference between the received signal and the echo replica corresponding to the stored sequence of N succesive digital symbols to cancel the echo in the received signal subsequent to the symbol time periods of the stored sequence of N successive digital symbols; the step of generating the signal representative of the replica of the echo in the received signal subsequent to the stored sequence of N successive digital symbols comprising forming an adaptive gain signal corresponding to the correlation of the signal representative of the replica of the echo in the received signal subsequent to the symbol time periods of the sequence of stored N successive symbols and the received signal having the echo canceled therefrom, modifying the Nth stored successive symbol with the adaptive gain signal, and recursively altering the modified Nth stored successive digital symbol with an exponentially decreasing impulse response corresponding to the characteristics of the bidirectional transmission path subsequent to the sequence of N successive digital symbols to form the signal representative of the replica of the echo in the received signal in accordance with the relationship
space="preserve" listing-type="equation">p.sub.e (n)=β
[p.sub.e (n-1)+g.sub.e (n)×
(n)]where pe (n) is the value of the signal representative of a replica of the echo in the received signal subsequent to the stored sequence of N symbols in the symbol period n, β
is a constant determinative of the pole of the impulse response,pe (n-1) is the value of the signal representative of the echo replica subsequent to the stored sequence of N symbols in the symbol period n-1, ge (n) is the value of the adaptive gain signal in the symbol period n, and x(n) is the value of the stored Nth symbol in the symbol period n. - View Dependent Claims (18)
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19. In a communication system for exchanging digital symbols between terminals over a bidirectional transmission path, a circuit for removing a prescribed interference component in a signal received at a terminal comprising
means for storing a sequence of successive digital symbols 1, 2, . . . , N applied to the bidirectional transmission path in successive symbol periods n, means responsive to the stored sequence of N successive digital symbols for generating a replica signal representative of the prescribed interference component in the received signal subsequent to the stored sequence of successive digital symbols; - and
means for combining the replica signal with the received signal to cancel the prescribed interference component in the received signal subsequent to the time periods of the sequence of N successive digital symbols; the means for generating the replica signal includes means for selecting the Nth stored symbol in the sequence in each symbol period of the received signal, means responsive to the replica signal and the signal representative of the received signal with the prescribed interference component removed for forming an adaptive gain signal corresponding to the correlation of the replica signal and the signal representative of the received signal with the prescribed interference component removed, means for modifying the Nth stored symbol by the adaptive gain signal, and means for recursively altering the modified Nth stored successive symbol with an impulse response characterized by a single pole comprising means for forming a signal in accordance with the relationship
space="preserve" listing-type="equation">p(n)=β
[p(n-1)+g(n)×
(n)]where p(n) is a value of the replica signal representative of the prescribed interference component in the received signal subsequent to the stored sequence of N successive digital symbols in the symbol period n, β
is a constant determinative of the single pole of the impulse responsep(n-1) is the value of the signal representative of the prescribed interference replica subsequent to the sequence of N symbols in the symbol period n-1, g(n) is the value of the adaptive gain signal in the symbol period n, and x(n) is the value of the stored selected symbol in the symbol period n. - View Dependent Claims (20)
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Current AssigneeAmerican Telephone & Telegraph Company (AT&T, Inc.), Bell Telephone Laboratories, Inc. (Nokia Corporation)
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Original AssigneeAT&T, Inc.
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InventorsAgazzi, Oscar E., Koh, Taiho
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Primary Examiner(s)Ng, Jin F.
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Assistant Examiner(s)Augustus, Jhancy
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Application NumberUS07/291,817Time in Patent Office733 DaysField of Search379/410, 379/411, 370/32.1, 370/32, 375/103, 375/101, 375/14, 333/18, 333/28US Class Current379/406.08CPC Class CodesG06F 9/3869 Implementation aspects, e.g...G06F 9/3877 using a slave processor, e....
