WO1990013188A1 - Receiver threshold extension - Google Patents

Receiver threshold extension Download PDF

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Publication number
WO1990013188A1
WO1990013188A1 PCT/US1990/001830 US9001830W WO9013188A1 WO 1990013188 A1 WO1990013188 A1 WO 1990013188A1 US 9001830 W US9001830 W US 9001830W WO 9013188 A1 WO9013188 A1 WO 9013188A1
Authority
WO
WIPO (PCT)
Prior art keywords
signal
receiver
unmodulated
further
received
Prior art date
Application number
PCT/US1990/001830
Other languages
French (fr)
Inventor
Robert E. Stengel
Paul David Marko
Original Assignee
Motorola, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US34332089A priority Critical
Priority to US343,320 priority
Application filed by Motorola, Inc. filed Critical Motorola, Inc.
Publication of WO1990013188A1 publication Critical patent/WO1990013188A1/en

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B1/00Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06Receivers
    • H04B1/10Means associated with receiver for limiting or suppressing noise or interference induced by transmission

Abstract

A receiver (10) is provided where an information signal (11) is received (12) and examined to determine (20) its signal strength. When the signal strength is at least equal to a threshold, an unmodulated signal (40) is added to the received signal to improve the sensitivity of the receiver.

Description

RECEIVER THRESHOLD EXTENSION

Technics F iς.

This invention relates generally to radio frequency receivers and more particularly to receivers with sensitivity improvement.

Ba ground Art

One measure of a receiver's performance is its ability to reject noise while providing a clear desired signal. Typically, this performance is rated by a signal-to-noise ratio. The higher the signal-to-noise ratio, the better the sensitivity (and performance) of the receiver.

Others skilled in the art have used complicated detector and compensation arrangements that attempt to improve the receiver's sensitivity. However, existing receiver sensitivity improvement techniques (such as "click swallowing") do not function well when the desired information signal has a received amplitude that is near the noise level. This noise barrier resides approximately below a 3dB signal-to-noise ratio, which is often called the noise range. Therefore, a need exists for a simple method to improve the receiver's sensitivity below the noise range. Summary of the Invention

Accordingly, it is an object of the present invention to improve sensitivity to a receiver when the information signal is near the noise level.

Briefly, according to the invention an information signal is received and examined to determine its signal strength. When the signal strength is at least equal to a threshold, an unmodulated signal is added to the received signal to improve 0 the sensitivity of the receiver.

Brief Description of the Drawings

Figure 1 is a block diagram of a receiver in accordance with the present invention. 5

Detailed Description of the Preferred Embodiment

Referring to Figure 1, a receiver 10 is shown having an information signal 11 being received by an antenna 12. The received information signal (and received noise) is filtered 0 (bandlimited) via a preselector 14 before being mixed (mixer 16) with an injection signal from an oscillator 18. The oscillator 18 is programmed (34) to provide a suitable injection signal by a controller 32 so that a desired information signal can be received. The mixer 16 provides an intermediate frequency (IF) signal to an 5 IF amplifier 20 to be amplified prior to being filtered by an IF filter 22. The filtered signal is processed by a detector 24 to provide a recovered signal. It will be appreciated that an additional intermediate frequency stage can be added before the mixer 16 along with additional bandpass filters. The detected or recovered fj signal is amplified in an optional audio amplifier 26 before being presented via a speaker 28.

According to the present invention, the signal strength of the desired received IF signal (processed at the IF frequency) is determined and compared to a threshold. Preferably, signal strength detection is accomplished in the IF amplifier 20, which has a receiver signal strength indicator (RSSI) output. Preferably, the IF amplifier 20 comprises an MC 3362 manufactured by Motorola Inc. or its functional equivalent.

The present invention adds an unmodulated signal to the received IF signal when the received IF signal is below a predetermined threshold (which may be set at the 3dB signal-to- noise ratio). If the RSSI output (30) indicates that the received IF signal is at or below the threshold (set near the noise level), the controller 32 programs (42) the frequency of another oscillator 40 to produce the unmodulated signal. Having its frequency set at the same frequency of the received IF signal, the unmodulated signal is amplified in an amplifier 38 controlled by the controller 32 (via line 36) before being added (summed 39) to the received IF signal at the input to the filter 22. The gain of the amplifier 38 is set (36) such that the amplitude of the unmodulated carrier signal is preferably at least 8dB above the threshold (which is set near the noise level). It will be appreciated that the summing node 39 may occur before or after the filter 22.

To compensate for the suppression of the desired signal due to the injection of the unmodulated signal, additional amplification is provided by the audio amplifier 26 by adjusting (44) its gain. The injection of the unmodulated signal suppresses the noise more than the desired signal when the received signal's amplitude resides at a level below the noise threshold. As a result, the recovered signal has a much greater signal-to-noise ratio. Therefore, sensitivity of the receiver increases. What is claimed is:

Claims

Claims
1. A method of receiving an information signal, comprising the steps of:
(a) receiving said information signal to provide a received signal;
(b) determining when said received signal has a signal strength at least equal to a threshold; and
(c) adding an unmodulated signal to said received signal when said signal strength is at least equal to said threshold.
2. The method of claim 1 , further comprising the step of controlling a gain of an amplifier stage in response to said step
(b).
3. The method of claim 1 , further comprising the step of detecting said received signal and said unmodulated signal to provide an output signal.
4. The method of claim 3, further comprising the step of amplifying said output signal.
5. The method of claim 1 , further comprising the step of synthesizing a frequency of said unmodulated signal.
6. The method of claim 5, wherein said unmodulated signal has a frequency substantially the same as said information signal's frequency.
7. The method of claim 1 , further comprising the step of adapting an amplitude of said unmodulated signal.
8. The method of claim 7, wherein said amplitude of said unmodulated signal is approximately 8dB above a noise level.
9. A receiver for receiving an information signal, comprising:
means for receiving said information signal to provide a received signal;
means for determining when said received signal has a signal strength at least equal to a threshold; and
means for adding an unmodulated signal to said received signal when said signal strength is at least equal to said threshold.
10. The receiver of claim 9, further comprising means for controlling a gain of an amplifier portion of said receiver as a function of response to said signal strength.
11. The receiver of claim 9, further comprising means for detecting said received signal and said unmodulated signal to provide an output signal.
12. The receiver of claim 11 , further comprising means for amplifying said output signal.
13. The receiver of claim 9, further comprising means for programming a frequency source to provide said unmodulated signal.
14. The receiver of claim 13, wherein said unmodulated signal has a frequency substantially the same as said information signal's frequency.
15. The receiver of claim 9, further comprising means for adapting an amplitude of said unmodulated signal.
16. The receiver of claim 15, wherein said amplitude of said unmodulated signal is approximately 8dB above a noise level.
PCT/US1990/001830 1989-04-26 1990-04-09 Receiver threshold extension WO1990013188A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US34332089A true 1989-04-26 1989-04-26
US343,320 1989-04-26

Publications (1)

Publication Number Publication Date
WO1990013188A1 true WO1990013188A1 (en) 1990-11-01

Family

ID=23345613

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1990/001830 WO1990013188A1 (en) 1989-04-26 1990-04-09 Receiver threshold extension

Country Status (3)

Country Link
EP (1) EP0470089A4 (en)
JP (1) JPH04504935A (en)
WO (1) WO1990013188A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001089100A1 (en) * 2000-05-17 2001-11-22 Infineon Technologies Ag Method and device for avoiding a parasitic state

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3588705A (en) * 1969-11-12 1971-06-28 Nasa Frequency-modulation demodulator threshold extension device
US3983488A (en) * 1974-06-17 1976-09-28 California Microwave, Inc. Frequency-modulation demodulator threshold extension device
US4270222A (en) * 1979-03-20 1981-05-26 Thomson-Csf Radio-frequency head having a self-adaptive dynamic range
US4380824A (en) * 1980-04-18 1983-04-19 Hitachi, Ltd. Receiving reproducing system
US4672632A (en) * 1984-02-03 1987-06-09 Motorola, Inc. Optimized communications system and method employing channel synthesis and phase lock detection

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS645121A (en) * 1987-06-27 1989-01-10 Tokyo Gas Co Ltd Noise suppression device for fm transmitter-receiver

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3588705A (en) * 1969-11-12 1971-06-28 Nasa Frequency-modulation demodulator threshold extension device
US3983488A (en) * 1974-06-17 1976-09-28 California Microwave, Inc. Frequency-modulation demodulator threshold extension device
US4270222A (en) * 1979-03-20 1981-05-26 Thomson-Csf Radio-frequency head having a self-adaptive dynamic range
US4380824A (en) * 1980-04-18 1983-04-19 Hitachi, Ltd. Receiving reproducing system
US4672632A (en) * 1984-02-03 1987-06-09 Motorola, Inc. Optimized communications system and method employing channel synthesis and phase lock detection

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP0470089A4 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001089100A1 (en) * 2000-05-17 2001-11-22 Infineon Technologies Ag Method and device for avoiding a parasitic state
US6765970B2 (en) 2000-05-17 2004-07-20 Infienon Technologies Ag Method and apparatus for preventing interference

Also Published As

Publication number Publication date
EP0470089A4 (en) 1992-09-16
JPH04504935A (en) 1992-08-27
EP0470089A1 (en) 1992-02-12

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