PASSBAND REFLECTOMETER

• US 20120251125A1
• Filed: 03/31/2011
• Published: 10/04/2012
• Est. Priority Date: 03/31/2011
• Status: Active Grant

• Current Assignee: RPX Corporation
• Original Assignee: Alcatel-Lucent USA, Inc. (Nokia Corporation)
• Inventors: Harman, Dale D.
• Granted Patent: US 8,559,813 B2
• Time in Patent Office: Days
• US Class Current: 398/135
• CPC Class Codes: G01M 11/3145 Details of the optoelectronics or data analysis
• CPC Class Codes: G10L 25/48 specially adapted for particular use
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems

Abstract

A time-domain (TD) reflectometer that is designed to operate based on probe and response signals that are substantially fully spectrally confined to a designated frequency passband. In one embodiment, the TD reflectometer uses a passband transmitter to generate the probe signal based on a pseudo-random bit sequence and a passband receiver to demodulate the response signal. The TD reflectometer determines the impulse response of a channel under test based on cross-correlation of the transmitter and receiver baseband signals. In various embodiments, the TD reflectometer can be designed to operate in an acoustic-frequency range, a radio-frequency range, or an optical-frequency range. Due to its passband configuration, the TD reflectometer is advantageously capable of determining impulse responses without disrupting the operation and/or interfering with normal functions of the tested channel.

Claims

1. An apparatus comprising:

a passband transmitter configured to generate a drive signal (e.g., signal 122) based on a bit sequence (e.g., signal 110);

an interface (e.g., interface 108) configured to convert the drive signal into a probe signal (e.g., signal 132), apply the probe signal to a channel under test, and receive a response signal (e.g., signal 138) corresponding to the probe signal back from said channel; and

a passband receiver configured to receive, from the interface, an input signal (e.g., signal 152) corresponding to the response signal and to convert said input signal into a receiver-baseband signal (e.g., signal 162), wherein;

the probe signal is spectrally limited to a spectral band located at frequencies higher than a first specified nonzero threshold frequency; and

the apparatus is configured to characterize an impulse response of the channel under test based on the bit sequence and the receiver-baseband signal.

2. The apparatus of claim 1, wherein the bit sequence is a maximum-length sequence.

3. The apparatus of claim 1, wherein the passband transmitter comprises:

a coder module configured to convert the bit sequence into a corresponding sequence of constellation symbols; and

a transmit filter configured to convert the sequence of constellation symbols into a transmitter-baseband signal, wherein;

the passband transmitter is configured to generate the drive signal based on the transmitter-baseband signal; and

the apparatus is configured to determine the impulse response based on a correlation between the receiver-baseband signal and the transmitter-baseband signal.

4. The apparatus of claim 3, wherein the coder module is configured to convert the bit sequence into the sequence of constellation symbols using a constellation selected from a set consisting of a binary phase-shift keying (BPSK) constellation, a quadrature phase-shift keying (QPSK) constellation, an amplitude-shift keying (ASK) constellation, and a quadrature amplitude modulation (QAM) constellation.

5. The apparatus of claim 3, wherein the passband transmitter further comprises:

a frequency up-converter (e.g., up-converter 230) configured to inject a carrier frequency into the transmitter-baseband signal to generate a transmitter-passband signal; and

a drive circuit configured to generate the drive signal based on the transmitter-passband signal.

6. The apparatus of claim 5, wherein:

the interface comprises an ultrasonic transducer configured to convert the drive signal into the probe signal; and

the carrier frequency is selected from an ultrasonic frequency range.

7. The apparatus of claim 5, wherein:

the interface comprises an antenna or a radio-frequency coupler configured to convert the drive signal into the probe signal; and

the carrier frequency is selected from a radio-frequency range.

8. The apparatus of claim 3, wherein:

the interface comprises an optical modulator coupled to a laser and configured to generate the probe signal based on the drive signal and a carrier-frequency signal provided by the laser; and

the carrier frequency is in an optical-frequency range.

9. The apparatus of claim 3, further comprising a correlation module configured to:

generate a Fourier transform of the receiver-baseband signal;

generate a correlation function by multiplying the Fourier transform of the receiver-baseband signal and a Fourier transform of the transmitter-baseband signal;

generate an inverse Fourier transform of the correlation function; and

determine the impulse response based on the inverse Fourier transform.

10. The apparatus of claim 1, wherein the passband receiver comprises:

a receive filter configured to correct the input signal for filtering effects of the interface; and

a demodulator configured to down-convert the corrected input signal to generate the receiver-baseband signal.

11. The apparatus of claim 1, wherein:

the interface is designed to be coupled to a human vocal tract; and

the apparatus is an acoustic reflectometer.

12. The apparatus of claim 1, further comprising a high-pass filter coupled between the interface and the pas sband receiver, wherein the high-pass filter has a cut-off frequency that is lower than or about the same as the first threshold frequency.

13. The apparatus of claim 1, wherein the impulse response is a reflected impulse response.

14. A method of characterizing an impulse response, the method comprising:

generating a drive signal based on a bit sequence using a passband transmitter;

converting the drive signal into a probe signal, wherein the probe signal is spectrally limited to a spectral band located at frequencies higher than a first specified nonzero threshold frequency;

applying the probe signal to a channel under test;

receiving a response signal corresponding to the probe signal back from said channel;

generating a receiver-baseband signal based on the response signal using a passband receiver; and

characterizing an impulse response of the channel based on the bit sequence and the receiver-baseband signal.

15. The method of claim 14, wherein the bit sequence is a maximum-length sequence.

16. The method of claim 14, wherein the step of generating the drive signal comprises:

converting the bit sequence into a corresponding sequence of constellation symbols; and

converting the sequence of constellation symbols into a transmitter-baseband signal, wherein;

the drive signal is generated based on the transmitter-baseband signal; and

the impulse response is determined based on a correlation between the receiver-baseband signal and the transmitter-baseband signal.

17. The method of claim 16, wherein the bit sequence is converted into the sequence of constellation symbols using a constellation selected from a set consisting of a binary phase-shift keying (BPSK) constellation, a quadrature phase-shift keying (QPSK) constellation, an amplitude-shift keying (ASK) constellation, and a quadrature amplitude modulation (QAM) constellation.

18. The method of claim 16, wherein the step of generating the drive signal further comprises:

frequency up-converting the transmitter-baseband signal by injecting a carrier frequency into the transmitter-baseband signal to generate a transmitter-passband signal; and

generating the drive signal based on the transmitter-passband signal.

19. The method of claim 16, further comprising generating a carrier-frequency signal using a laser, wherein:

the probe signal is generated using an optical modulator configured to modulate the carrier-frequency signal based on the drive signal; and

the carrier frequency is in an optical-frequency range.

20. The method of claim 16, further comprising:

generating a Fourier transform of the receiver-baseband signal;

generating a correlation function by multiplying the Fourier transform of the receiver-baseband signal and a Fourier transform of the transmitter-baseband signal;

generating an inverse Fourier transform of the correlation function; and

determining the impulse response based on the inverse Fourier transform.