Interference cancellation apparatus capable of adaptive equalization and interference cancellation at a high speed on fading diversity channels

• US 5,524,125 A
• Filed: 06/27/1994
• Issued: 06/04/1996
• Est. Priority Date: 06/25/1993
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Tsujimoto, Ichiro
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): ESPOSO, HUONG L
• Application Number:
  US08/265,754
• Time in Patent Office: 708 Days
• Field of Search: 375/347, 375/346, 375/232, 375/233, 455/273, 455/275, 455/276.1, 455/278.1
• US Class Current: 375/347
• CPC Class Codes: H04B 7/0845 per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch rake receivers as such H04B1/7115
• CPC Class Codes: H04B 7/0851 using training sequences or error signal minimizing error signal H04B7/0854
• CPC Class Codes: H04B 7/0854 using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
• CPC Class Codes: H04B 7/0857 using maximum ratio combining techniques, e.g. signal-to- interference ratio [SIR], received signal strenght indication [RSS]
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence

Abstract

In an interference cancellation apparatus for use in combination with a diversity receiving system, the apparatus includes first and second transversal filters, first and second tap gain controllers, third transversal filter, third tap gain controller, decision unit, first error producing subtractor, and second subtractor which are operable as a first MMSE control loop for controlling first and second controllable tap gains and third controllable tap gains with reference to a first error signal. The apparatus further includes diversity combiner which is operable as a second MMSE control loop for controlling a combined signal with reference to a difference between the combined signal and a decision signal. An adaptive equalization and an interference cancellation are processed in parallel by the first and the second MMSE control loops, so that the control of the adaptive equalization and the interference cancellation can be converged at a high speed.

Claims

1. An interference cancellation apparatus for use in combination with a diversity receiving system which has first and second diversity routes, said apparatus being supplied with first and second diversity reception signals corresponding to said first and said second diversity routes and being operable as a decision feedback equalizer to produce an equalized signal, said apparatus comprising:

first transversal filter means which has a plurality of first taps and second transversal filter means which has a plurality of second taps, said first and said second transversal filter means filtering said first and said second diversity reception signals into first and second transversal filtered signals in accordance with first and second controllable tap gains, respectively;

first control means for controlling said first controllable tap gains with reference to a first error signal and a first distributed signal distributed in each one of said first taps in accordance with a predetermined adaptive algorithm;

second control means for controlling said second controllable tap gains with reference to a first error signal and a second distributed signal distributed in each one of said second taps in accordance with said predetermined adaptive algorithm;

third transversal filter means which has a plurality of third taps and which filters a decision signal into a third transversal filtered signal in accordance with third controllable tap gains;

third control means for controlling said third controllable tap gains with reference to said first error signal and a third distributed signal distributed in each of said third taps in accordance with said predetermined adaptive algorithm;

decision means for detecting a level of said equalized signal to decide a decision level for said equalized signal and to produce a decision signal representative of said decision level to supply said decision signal to said third transversal filter means;

first error producing means for producing said first error signal indicative of a difference between said equalized signal and said decision signal, said first error signal being supplied to said first, said second and said third control means;

a subtractor means for subtracting said third transversal filtered signal from a combined signal to supply a subtracted signal to said decision means and said first error producing means as said equalized signal; and

diversity combining means for combining said first and said second transversal filtered signals to produce said combined signal;

said diversity combining means comprising;

adder means for calculating a total sum of a first complex multiplied signal and a second complex multiplied signal to produce a total sum signal as said combined signal representative of said total sum;

first and second complex multiplier means for complexly multiplying said first and said second transversal filtered signals by first and second correlated values α and

β

to produce said first and said second complex multiplied signals, respectively;

first and second correlation means for correlating said first and said second transversal filtered signals with a second error signal in each of said first and said second diversity routes to produce first and second correlation signals indicative of said first and said second correlated values α and

β

, respectively; and

second error producing means for producing said second error signal indicative of a difference between said total sum signal and said decision signal, and second error signal being supplied to said first and said second correlation means, respectively.

2. An interference cancellation apparatus as claimed in claim 1, said equalized signal being a binary signal specified by a binary level, wherein said decision means detects whether or not the binary level of said equalized signal exceeds a predetermined threshold level to decide a detected binary level for said equalized signal and to produce a decision signal representative of said detected binary level.

3. An interference cancellation apparatus as claimed in claim 1, said equalized signal being a multilevel signal having a plurality of levels greater than two, wherein said decision means detects which one of said levels said multilevel signal has as a decision level to produce a decision signal representative of said decision level.

4. An interference cancellation apparatus for use in combination with a diversity receiving system, said apparatus being supplied with first and second diversity reception signals and being operable as a decision feedback equalizer to produce an equalized signal, said apparatus comprising:

first and second transversal filter means for filtering said first and said second diversity reception signals into first and second transversal filtered signals in accordance with first and second controllable tap gains, respectively;

first and second control means for controlling said first and said second controllable tap gains with reference to a first error signal in accordance with a predetermined adaptive algorithm;

third transversal filter means for filtering a decision signal into a third transversal filtered signal in accordance with third controllable tap gains;

third control means for controlling said third controllable tap gains with reference to said first error signal in accordance with said predetermined adaptive algorithm;

decision means for detecting a level of said equalized signal to decide a decision level for said equalized signal and to produce a decision signal representative of said decision level to supply said decision signal to said third transversal filter means;

first error producing means for producing said first error signal indicative of a difference between said equalized signal and said decision signal, said first error signal being supplied to said first, said second, and said third control means;

subtractor means for subtracting said third transversal filtered signal from a combined signal to supply a subtracted signal to said decision means and said first error producing means as said equalized signal;

diversity combining means for combining said first and said second transversal filtered signals to produce said combined signal;

said first and said second transversal filter means, first and second control means, third transversal filter means, third control means, decision means, first error producing means, and subtractor means being operable as a first control loop for controlling said first and said second controllable tap gains and said third controllable tap gains with reference to said first error signal; and

said diversity combining means comprising a second control loop for controlling said combined signal with reference to a difference between said combined signal and said decision signal.

5. An interference cancellation apparatus as claimed in claim 4, said predetermined adaptive algorithm being minimum mean square error algorithm, wherein said second control loop is operated in accordance with an additional predetermined adaptive algorithm of the minimum mean square error algorithm.

6. An interference cancellation apparatus for use in combination with a diversity receiving system, said apparatus being supplied with first and second diversity reception signals and being operable as a decision feedback equalizer to produced an equalized signal, said apparatus comprising:

first and second transversal filter means for filtering said first and said second diversity reception signals into first and second transversal filtered signals in accordance with first and second controllable tap gains, respectively;

first and second control means for controlling said first and said second controllable tap gains with reference to a first error signal in accordance with a predetermined adaptive algorithm;

third transversal filter means for filtering a decision signal into a third transversal filtered signal in accordance with third controllable tap gains;

third control means for controlling said third controllable tap gains with reference to said first error signal in accordance with said predetermined adaptive algorithm;

decision means for detecting a level of said equalized signal to decide a decision level for said equalized signal and to produce a decision signal representative of said decision level to supply said decision signal to said third transversal filter means;

first error producing means for producing said first error signal indicative of a difference between said equalized signal and said decision signal, said first error signal being supplied to said first, said second, and said third control means;

subtractor means for subtracting said third transversal filtered signal from a combined signal to supply a subtracted signal to said decision means and said first error producing means as said equalized signal;

diversity combining means for combining said first and said second transversal filtered signals to produce said combined signal;

said first and said second transversal filter means, first and second control means, third transversal filter means, third control means, decision means, first error producing means, and subtractor means being operable as a first control loop for controlling said first and said second controllable tap gains and said third controllable tap gains with reference to said first error signal; and

said diversity combining means functions to control said combined signal with reference to a difference between said combined signal and said decision signal.