Adaptive channel equalizer for use in digital communication system utilizing OFDM method

• US 5,963,592 A
• Filed: 12/01/1997
• Issued: 10/05/1999
• Est. Priority Date: 12/28/1996
• Status: Expired due to Term

• Current Assignee: Dongbu Daewoo Electronics Corporation
• Original Assignee: Daewoo Electronics (Government of South Korea)
• Inventors: Kim, Young-Sang
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): WEBSTER, BRYAN E
• Application Number:
  US08/982,222
• Time in Patent Office: 673 Days
• Field of Search: 375/229, 375/232, 375/233, 375/235, 375/236, 708/322, 708/323, 370/480, 370/210, 370/479, 370/203, 370/206
• US Class Current: 375/232
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

An adaptive channel equalizer for use in OFDM receiver is disclosed. The adaptive channel equalizer comprises a first complex multiplier for outputting a first in-phase complex multiplication signal and a first quadrature phase complex multiplication signal; a reference signal generator for generating a reference signal; an error calculator for outputting an in-phase error signal and a quadrature phase error signal; a delay unit for outputting an in-phase delay signal and a quadrature phase delay signal; a gain controller for outputting an in-phase gain control signal and a quadrature phase gain control signal; a second complex multiplier for outputting a second in-phase complex multiplication signal and a second quadrature phase complex multiplication signal; an adder for outputting updated in-phase and quadrature phase coefficients; an address generator for generating a write address signal and a read address signal; a storage unit for storing the updated in-phase and quadrature phase coefficients, and outputting the updated coefficients; an initial coefficients generator for generating an initial coefficients; a selecting signal generator for generating a selecting signal; and a multiplexing unit for selecting one of the initial coefficients and the updated coefficients according to the selecting signal.

Claims

1. An adaptive channel equalizer for use in a digital communication system utilizing OFDM method, comprising:

first complex multiplying means for outputting a first in-phase complex multiplication signal and a first quadrature phase complex multiplication signal by performing a complex multiplication for received in-phase and quadrature phase channel signals and the in-phase and quadrature phase coefficients;

reference signal generating means for generating a reference signal;

error calculating means for outputting an in-phase error signal and a quadrature phase error signal by calculating a phase error from the first in-phase and quadrature phase complex multiplication signals and the reference signal;

delaying means for outputting an in-phase delay signal and a quadrature phase delay signal by delaying the in-phase and quadrature phase channel signals;

gain controlling means for outputting an in-phase gain control signal and a quadrature phase gain control signal by controlling a gain of the in-phase and quadrature phase delay signals;

second complex multiplying means for outputting a second in-phase complex multiplication signal and a second quadrature phase complex multiplication signal by performing a complex multiplication for the in-phase and quadrature phase error signals, and the in-phase and quadrature phase gain control signals;

adding means for outputting updated in-phase and quadrature phase coefficients after adding respectively the second in-phase and quadrature phase complex multiplication signals and the in-phase and quadrature phase coefficients;

address generating means for generating a write address signal and a read address signal;

storing means for storing the updated in-phase and quadrature phase coefficients according to the write address signal, and outputting the updated coefficients stored according to the read address signal;

initial coefficients generating means for generating an initial coefficients;

selecting signal generating means for generating a selecting signal according to a symbol sync signal; and

multiplexing means for selecting one of the initial coefficients from said initial coefficients generating means and the updated coefficients from said storing means according to the selecting signal, to supply said first complex multiplying means as the in-phase and quadrature phase coefficients.

2. The adaptive channel equalizer of claim 1, wherein said first complex multiplying means comprises:

a first FIR filter for outputting a first filtering signal by filtering the in-phase channel signal as the in-phase coefficient;

a second FIR filter for outputting a second filtering signal by filtering the in-phase channel signal as the quadrature phase coefficient;

a third FIR filter for outputting a third filtering signal by filtering the quadrature phase channel signal as the quadrature phase coefficient;

a fourth FIR filter for outputting a fourth filtering signal by filtering the quadrature phase channel signal as the in-phase coefficient;

an adder for adding the first filtering signal to the third filtering signal; and

a subtracter for subtracting the second filtering signal from the fourth filtering signal.

3. The adaptive channel equalizer of claim 2, wherein each of said first to fourth FIR filters is implemented by 1 tap.

4. The adaptive channel equalizer of claim 1, wherein the reference signal generated from said reference signal generating means is a SPC signal.

5. The adaptive channel equalizer of claim 1, wherein said selecting signal generating means counts symbols according to the symbol sync signal, outputs the selecting signal for selecting the initial coefficients until fourth symbol, whereas outputs the selecting signal for selecting the updated coefficients beginning with fifth symbol.