Method and apparatus for estimating PSK modulated signals

• US 5,590,158 A
• Filed: 10/11/1995
• Issued: 12/31/1996
• Est. Priority Date: 01/28/1993
• Status: Expired due to Term

• Current Assignee: Advantest Corporation
• Original Assignee: Advantest Corporation
• Inventors: Nakada, Juichi, Tajiri, Shinsuke, Yamaguchi, Takahioro
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US08/538,943
• Time in Patent Office: 447 Days
• Field of Search: 375/281, 375/283, 375/329-332, 375/344-345, 329/304, 329/345
• US Class Current: 375/331
• CPC Class Codes: G01R 25/00 Arrangements for measuring phase angle between a voltage and a current or between voltages or currents
• CPC Class Codes: G01R 29/06 Measuring depth of modulation
• CPC Class Codes: H04L 1/206 for modulated signals
• CPC Class Codes: H04L 2027/0028 at passband only
• CPC Class Codes: H04L 2027/0057 quadrature phase
• CPC Class Codes: H04L 27/2332 using a non-coherent carrier

Abstract

An in-phase component and a quadrature component of a digitized input DQPSK modulated signal are provided from interpolation filters, respectively. An instantaneous amplitude and an instantaneous phase of the input signal for each symbol clock are detected from the in-phase and quadrature components and are fed to adders. At the same time, that one of symbols "0, 0," "0, 1," "1, 0" and "1, 1" which corresponds to the instantaneous phase is detected by a symbol detector. An ideal reference signal generating part generates an ideal amplitude component and an ideal phase component corresponding to the detected symbol and provides them to a parameter calculating part. In an I-Q origin offset detecting part, an I-Q origin offset is calculated on the basis of the relationship between a triangle formed by the current detected vector corresponding to an ideal symbol and a vector detected one symbol clock before and a triangle formed by the said two vectors. An amplitude and a phase corresponding to the calculated I-Q origin offset are provided to the adders, respectively, and are corrected with respect to the detected instantaneous amplitude and phase, thereafter being fed to the parameter calculating part 22. In the parameter calculating part, a transmitter gain, and an amplitude variation, offset frequency and phase error per symbol clock are calculated.

Claims

1. A Phase-Shift Keying(PSK) modulated signal estimating apparatus comprising:

analog-digital (A/D) converting means for converting an input PSK modulated signal to a converted digital signal;

orthogonal transformation means, receiving the converted digital signal from said A/D converting means as an in-phase component thereof, for providing a quadrature component of said converted digital signal;

amplitude and phase detecting means for detecting an instantaneous amplitude and an instantaneous phase of the input PSK modulated signal from said in-phase component and said quadrature component of the input PSK modulated signal;

symbol generating means for determining an ideal modulation symbol using the detected instantaneous phase;

ideal signal generating means, supplied with said ideal modulation symbol, for generating an ideal reference signal corresponding to the determined ideal modulation symbol;

I-Q origin offset detecting means for obtaining an I-Q origin offset from said in-phase and quadrature components of said input PSK modulated signal and said ideal reference signal;

subtracting means for subtracting the amplitude and phase of said I-Q origin offset from said detected instantaneous amplitude and said detected instantaneous phase of the input PSK modulated signal, respectively; and

parameter calculating means, receiving said ideal reference signal and the subtracted instantaneous amplitude and phase of the input PSK modulated signal, for deriving an amplitude, an offset frequency and a phase error of the input PSK modulated signal therefrom.

2. The apparatus of claim 1, wherein said I-Q origin offset detecting means comprises:

first accumulating means for accumulating an in-phase component and a quadrature component of said ideal reference signal, respectively;

second accumulating means for accumulating said in-phase component and said quadrature component of said input PSK modulated signal, respectively;

counting means for counting the number of accumulations of said first accumulating means and said second accumulating means;

means for effecting operations of said first accumulating means, said second accumulating means and said counting means in synchronization with one another;

means for obtaining a difference between individual corresponding accumulated values of said first accumulating means and said second accumulating means; and

dividing means for dividing said difference by the number of accumulations counted by said counting means to obtain said I-Q origin offset.

3. The apparatus of claim 1, wherein said input PSK modulated signal is a Differential Quadrature Phase-Shift Keying (DQPSK) modulated signal.

4. A Phase-Shift Keying (PSK) modulated signal estimation method comprising the steps of:

converting an input PSK modulated signal to a digital signal;

obtaining a quadrature component of said digital signal with respect to an in-phase component of the digital signal;

obtaining an I-Q origin offset from said in-phase and quadrature components of said input PSK modulated signal and an in-phase component and a quadrature component of an ideal reference signal;

detecting an instantaneous amplitude and an instantaneous phase of the input PSK modulated signal from said in-phase and quadrature components of the input PSK modulated signal;

subtracting the amplitude and phase of said I-Q origin offset from the detected instantaneous amplitude and instantaneous phase of the input PSK modulated signal, respectively;

determining an ideal modulation symbol from the detected instantaneous phase;

generating said ideal reference signal corresponding to the determined ideal modulation symbol;

calculating an amplitude, an offset frequency and a phase error of the input PSK modulated signal using said ideal reference signal and the subtracted instantaneous amplitude and phase of the input PSK modulated signal; and

using the subtracted instantaneous amplitude and phase of the input PSK modulated signal to calculate said amplitude, said offset frequency and said phase error of the input PSK modulated signal.

5. The method of claim 4, wherein said I-Q origin offset obtaining step comprises the steps of:

accumulating said in-phase component and said quadrature component of said ideal reference signal, respectively;

accumulating said in-phase component and said quadrature component of said input PSK modulated signal, respectively;

counting the numbers of accumulations of both of said accumulating steps;

obtaining a difference between the accumulated values of the in-phase components, and a difference between the accumulated values of the quadrature components, of both of said accumulating steps, respectively; and

dividing each of said differences by the counted number of accumulations to obtain said I-Q origin offset.

6. The method of claim 4, wherein said input PSK modulated signal is a Differential Quadrature Phase-Shift Keying (DQPSK) modulated signal.