Duplex decision feedback equalization system

• US 6,031,866 A
• Filed: 05/30/1997
• Issued: 02/29/2000
• Est. Priority Date: 05/29/1997
• Status: Expired due to Fees

• Current Assignee: Telecommunications Research Laboratories
• Original Assignee: Telecommunications Research Laboratories
• Inventors: Sesay, Abu B., Oler, Kevin S., Petersen, Brent R.
• Primary Examiner(s): Bocure, Tesfaldet
• Application Number:
  US08/866,906
• Time in Patent Office: 1,005 Days
• Field of Search: 375/229, 375/230, 375/231, 375/232, 375/219, 375/220, 375/346, 375/350, 375/285, 375/296, 455/507, 455/524, 364/724.19, 364/724.2
• US Class Current: 375/219
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H
• CPC Class Codes: H04L 2025/03375 Passband transmission
• CPC Class Codes: H04L 2025/0349 as a feedback filter
• CPC Class Codes: H04L 2025/03789 Codes therefore
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end

Abstract

A system for equalization of two-way digital communications between a base and portable unit is described. Equalization is implemented in a manner so as to reduce the complexity of the portable unit. The reverse link (portable to base transmission) is equalized by a decision feedback equalizer (DFE). The forward link (base to portable) is equalized by an asymmetric decision feedback equalizer (ADFE), which consists of a forward filter located at the transmitter, and a decision feedback filter at the receiver.

Claims

1. A duplex radio transceiver, having a transmitter section and a receiver section, the radio transceiver comprising:

a first forward filter in the transmitter section, the first forward filter being defined by first filter coefficients selected to reduce precursor intersymbol interference in data symbols transmitted by the radio transceiver and received by a remote transceiver;

a decision feedback equalizer in the receiver section, the decision feedback equalizer being defined by feedback coefficients selected to reduce the probability of an error in receiving and detecting data symbols in the receiver section;

a second forward filter in the receiver section, the second forward filter being defined by second filter coefficients selected to reduce precursor intersymbol interference in data symbols received by the radio transceiver; and

a source of filter coefficients and feedback coefficients operably connected to each of the first forward filter, the second forward filter and the decision feedback equalizer.

2. The radio transceiver of claim 1 in which the first and second filter coefficients are the same.

3. The radio transceiver of claim 1 further comprising a source of a forward link training sequence in the transmitter section.

4. The radio transceiver of claim 3 in which the forward link training sequence is characterized by having a diagonal autocorrelation matrix.

5. The radio transceiver of claim 1 in which the decision feedback equalizer comprises:

a plurality of adders, each adder having an output and first and second operands, each adder except an initial adder having a feedback coefficient as the first operand and output from a preceding adder as the second operand, the initial adder having a feedback coefficient as the first operand and zero as the second operand; and

a feedback line connected to supply binary data symbols received by the receiver section to the adders as control signals to select the sign of the feedback coefficients whereby no multiplications are required to implement the decision feedback equalizer.

6. The radio transceiver of claim 1 in which the first forward filter comprises, for each of an in phase channel and a quadrature channel:

a plurality of adders, each adder having an output and first and second operands, each adder except an initial adder having a first filter coefficient as the first operand and output from a preceding adder as the second operand, the initial adder having a first filter coefficient as the first operand and zero as the second operand; and

an input line connected to supply binary data symbols to the adders as control signals to select the sign of the first filter coefficients whereby no multiplications are required to implement the first forward filter.

7. A remote radio transceiver having a transmitter section and a receiver section, the radio transceiver comprising:

a decision feedback equalizer in the receiver section, the decision feedback equalizer having a feedback filter defined by feedback coefficients selected to reduce postcursor intersymbol interference in data symbols received by the radio transceiver,

a source of feedback coefficients operably connected to the decision feedback equalizer, and

a source of a forward link training sequence operably connected to the source of feedback coefficients, the forward link training sequence being characterized by having a diagonal autocorrelation matrix.

8. The remote radio transceiver of claim 7 in which the decision feedback equalizer comprises:

a plurality of adders, each adder having an output and first and second operands, each adder except an initial adder having a feedback coefficient as the first operand and output from a preceding adder as the second operand, the initial adder having a feedback coefficient as the first operand and zero as the second operand; and

a feedback line connected to supply binary data symbols received by the receiver section to the adders as control signals to select the sign of the feedback coefficients whereby no multiplications are required to implement the decision feedback equalizer.

9. The remote radio transceiver of claim 8 in which the source of feedback coefficients is a channel estimator.

10. The remote radio transceiver of claim 9 in which the channel estimator comprises:

a received signal input line;

a plurality of adders, each adder having first and second inputs and an output, the first input being connected to the received signal input line;

a delay element on the output;

a feedback line connected between the output and the second input; and

a control port for selectively negating one of the first and second inputs, the control port being connected to the source of the forward link training sequence.

11. System for two way duplex data communications between (A) a base station transceiver having a base station transmitter section and a base station receiver section and (B) a remote radio transceiver having a remote transmitter section and a remote receiver section, the system comprising:

a first forward filter in the base station transmitter section, the first forward filter being defined by first filter coefficients selected to reduce precursor intersymbol interference in data symbols transmitted by the radio transceiver and received by a remote transceiver;

a base station decision feedback equalizer in the base station receiver section, the base station decision feedback equalizer being defined by first feedback coefficients selected to reduce the probability of an error in receiving and detecting data symbols in the base station receiver section;

a source of first filter coefficients and first feedback coefficients operably connected to each of the first forwards filter and the base station decision feedback equalizer;

a remote decision feedback equalizer in the remote receiver section, the remote decision feedback equalizer being defined by second feedback coefficients selected to reduce the probability of an error in receiving and detecting data symbols in the remote receiver section; and

a source of second feedback coefficients operably connected to the remote decision feedback equalizer.

12. The system of claim 11 in which the first and second feedback coefficients are the same.

13. The system of claim 11 further comprising:

a source of a forward link training sequence operably connected to the source of second feedback coefficients, in which the forward link training sequence in characterized by having a diagonal autocorrelation matrix.

14. The system of claim 13 further comprising a second forward filter in the base station receiver section, the second forward filter being defined by second filter coefficients selected to reduce precursor intersymbol interference in data symbols received by the base station radio transceiver.

15. The system of claim 14 in which the first and second filter coefficients are the same.

16. The system of claim 11 further comprising a first source of a forward link training sequence operably connected to the source of second feedback coefficients.

17. The system of claim 16 further comprising a second source of the forward link training sequence in the base station transmitter section.

18. The system of claim 16 in which at least one of the forward link training sequence is characterized by having a diagonal autocorrelation matrix.

19. The system of claim 11 in which the first decision feedback equalizer comprises:

a plurality of adders, each adder having an output and first and second operands, each adder except an initial adder having a first feedback coefficient as the first operand and output from a preceding adder as the second operand, the initial adder having a first feedback coefficient as the first operand and zero as the second operand; and

a feedback line connected to supply binary data symbols received by the base station receiver section to the adders as control signals to select the sign of the first feedback coefficients whereby no multiplications are required to implement the base station decision feedback equalizer.

20. The system of claim 11 in which the first forward filter comprises, for each of an in phase channel and a quadrature channel:

a plurality of adders, each adder having an output and first and second operands, each adder except an initial adder having a first filter coefficient as the first operand and output from a preceding adder as the second operand, the initial adder having a first filter coefficient as the first operand and zero as the second operand; and

an input line connected to supply binary data symbols to the adders as control signals to select the sign of the filter coefficients whereby no multiplications are required to implement the first forward filter.