US4907087A
Expired / Lapsed
US
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Transmission of signals through analog channels using adaptive frequency modulation
Assignee: Massachusetts Institute of Technology
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Filing: 1987-06-10
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Granted: 1990-03-06
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Expires: 2007-06-10
Abstract
Abstract Improved effifiency of frequency-modulated (FM) transmission of signals through analog channels, i.e., achievement of a higher bandwidth and/or signal-to-noise ratio (SNR) in the received signal for a given channel bandwidth and channel carrier-to-noise ratio (CNR), is accomplished by adaptive adjustment of the modulation index in such a manner that the spectrum of the channel signal more nearly occupies the entire channel more of the time than it would otherwise. Data is transmitted, along with the signal, to enable the receiver to calculate the modulation index at each instant so that the signal can be properly demodulated. The invention has application to FM transmission of signals representing visual image or other information, such as sound, for which human perception of noise is greatest in areas of low amplitude and/or frequency and reduced in and immediately adjacent to areas of high amplitude and/or frequency.
Inventors
- 👤 William F. Schreiber
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 10:34
CPC Classifications
H; H04; H04N; H04N7/00; H04N7/08; H04N7/083; H04N11/00; H04N11/04; H04N11/042; H04N11/048; H04N7/04; H04N7/045; H04N19/00; H04N19/30
Claims Analysis
Total Claims: 62
Claim 1
Independent Claim
87 words
A system for processing a signal representative of information, such as sound or the high frequency content of a visual image, for which human perception of noise is greater in areas of low amplitude and/or frequency and reduced in and immediately adjacent to areas of high amplitude and/or frequency, comprising: modulation means for frequency modulating a carrier with said signal using a variable modulation index, adaptation means for varying said variable modulation index to widen the spectrum of the modulated carrier for selected segments of said signal.
Claim 2
Independent Claim
87 words
A system for processing a signal representative of information, such as sound or the high frequency content of a visual image, for which human perception of noise is greater in areas of low amplitude and/or frequency and reduced in and immediately adjacent to areas of high amplitude and/or frequency, comprising: modulation means for frequency modulating a carrier with said signal using a variable modulation index, adaptation means for varying said variable modulation index to widen the spectrum of the modulated carrier for selected segments of said signal.
Claim 3
Dependent Claim
59 words
The system of claim 1 wherein said signal is the high-frequency component of said visual image and further comprising spectrum-dividing means for spatially and/or temporally filtering said signal to produce a low-frequency component representative of luminance variations in a low-frequency band and a high-frequency component representative of luminance variations in a high-frequency band located spectrally above said low-frequency band.
Claim 4
Dependent Claim
31 words
The system of claim 2 wherein said adaptation means includes means for assigning a different valve of said variable modulation index to each of a plurality of blocks within said image.
Claim 5
Dependent Claim
12 words
The system of claim 3 wherein said blocks are equal in size.
Claim 6
Dependent Claim
15 words
The system of claim 4 wherein said size ranges from 4 to 512 picture elements.
Claim 7
Dependent Claim
53 words
The system of claim 2 wherein said adaptation means includes means for assigning said different values of said variable modulation index to specific locations within said image and spatial and/or temporal interpolation means for choosing a value of said variable modulation index at points between said specific locations by spatial and/or temporal interpolation.
Claim 8
Dependent Claim
46 words
The system of claim 3 wherein said adaption means includes means for assigning said different values of said variable modulation index to the centers of said blocks and interpolation means for choosing a value of said variable modulation index at locations between said centers by interpolation.
Claim 9
Dependent Claim
37 words
The system of claim 2 wherein said adaptation means includes means for making said variable modulation index a function of an image characteristic that is correlated with the width of the short-term spectrum of the modulated carrier.
Claim 10
Dependent Claim
16 words
The system of claim 8 wherein said image characteristic is the magnitude of said high-frequency component.
Claim 11
Dependent Claim
18 words
The system of claim 8 wherein said image characteristic is the rate of change of said high-frequency component.
Claim 12
Dependent Claim
52 words
The system of claim 8 wherein said adaptation means includes means for assigning a different valve of said variable modulation index to each of a plurality of blocks within said image and making said modulation index within each block a function of the highest value of said image characteristic within that block.
Claim 13
Dependent Claim
10 words
The system of claim 8 wherein said function is nonlinear.
Claim 14
Dependent Claim
50 words
The system of claim 8 wherein said adaptation means includes means for determining said short-term spectrum in real time for different areas of said image and increasing said variable modulation index, and thereby said short term spectrum, in those areas where less than the available bandwidth would otherwise be used.
Claim 15
Dependent Claim
36 words
The system of claim 2 wherein said adaptation means includes means for measuring transmission error owing to the short-term spectrum exceeding the available bandwidth and increasing said variable modulation index until a predetermined small error results.
Claim 16
Independent Claim
39 words
The system of 2 wherein said adaptation means includes means for varying said variable modulation index sufficiently gradually across said image as to make the modulation of said modulation means more linear than that provided by static nonlinear companding.
Claim 17
Independent Claim
39 words
The system of 2 wherein said adaptation means includes means for varying said variable modulation index sufficiently gradually across said image as to make the modulation of said modulation means more linear than that provided by static nonlinear companding.
Claim 18
Dependent Claim
22 words
The system of claim 2 wherein said spectrum-dividing means includes means for filtering said signal in one dimension (x, y, or t).
Claim 19
Dependent Claim
21 words
The system of claim 2 wherein said spectrum-dividing means includes means for filtering said signal in two dimensions (x and y).
Claim 20
Dependent Claim
22 words
The system of claim 2 wherein said spectrum-dividing means includes means for filtering said signal in three dimensions (x, y, and t).
Claim 21
Dependent Claim
14 words
The system of claim 2 further comprising means for statically companding said high-frequency component.
Claim 22
Dependent Claim
16 words
The system of claim 19 wherein said static componding attenuates high amplitudes less than low amplitudes.
Claim 23
Dependent Claim
17 words
The system of claim 2 wherein said signal representing said visual image is an analog television signal.
Claim 24
Dependent Claim
43 words
The system of claim 2 wherein said signal representing said visual image is a component color television signal and said spectrum-dividing means includes means for processing said signal to separate it into a mixed high-frequency component and separate low-frequency components for each color.
Claim 25
Dependent Claim
15 words
The system of claim 2 wherein said modulating means includes means for narrow-index frequency modulation.
Claim 26
Dependent Claim
33 words
The system of claim 2 further comprising means for transmitting said high-frequency component through a first channel, said low-frequency component through a second channel, and said variable modulation index through a third channel.
Claim 27
Dependent Claim
13 words
The system of claim 24 wherein said second and third channels are digital.
Claim 28
Dependent Claim
13 words
The system of claim 24 wherein said second and third channels are analog.
Claim 29
Dependent Claim
29 words
The system of claim 24 further comprising subsampling means for subsampling said low-frequency component before transmission at a spatial sampling rate lower than that associated with said high-frequency component.
Claim 30
Dependent Claim
19 words
The system of claim 24 further comprising means for demodulating said frequency modulated carrier using said transmitted modulation index.
Claim 31
Dependent Claim
79 words
The system of claim 2 wherein said adaptation means includes means for selecting the valve of said variable modulation index so that the valve of said index for a given point in the image depends on the image activity in the neighborhood of the point rather than only on the activity at the particular point, thereby taking advantage of the fact that high activity at one point in an image suppresses noise visibility in an area around that point.
Claim 32
Dependent Claim
25 words
The system of claim 2 wherein the variation in the variable modulation index from one area of the image to another is greater than ten-to-one.
Claim 33
Dependent Claim
12 words
The system of claim 30 wherein said variation is greater than 32-to-1.
Claim 34
Dependent Claim
40 words
The system of claim 3 wherein said adaptation means includes means for determining said variable modulation index using a single-pass procedure in which the index is computed for each block based on a characteristic of the image within that block.
Claim 35
Dependent Claim
101 words
The system of claim 3 wherein said adaptation means includes means for determining said variable modulation index by following a recursive procedure in which (1) the index (or equivalently the adaptation factor) is varied for a particular said block, said variation resulting in distortion in a demodulated signal generated by demodulating the modulated carrier signal (2) the effect of the variation on the distortion in the demodulated signal is determined by examining a measure or predictor of that distortion, and (3) a decision is made as to whether to further increase the variable modulation index based on the degree of distortion.
Claim 36
Dependent Claim
25 words
The system of claim 33 wherein said adaptation means includes means for varying said variable modulation index until the distortion exceeds a predetermined small level.
Claim 37
Dependent Claim
21 words
The system of claim 33 wherein said adaptation means includes means for varying said variable modulation index using a logarithmic search.
Claim 38
Dependent Claim
41 words
The system of claim 3 wherein said adaptation means includes means for starting a search for the value of the variable modulation index for a block with the valve of the index used for the same block in the previous frame.
Claim 39
Dependent Claim
34 words
The system of claim 33 wherein said adaptation means includes means for starting said recursive procedure for a block with the valve of the index used for the same block in the previous frame.
Claim 40
Dependent Claim
40 words
The system of claim 33 wherein the distortion in the demodulated signal is calculated for each picture element (as opposed to each block) of the image prior to transmission, and the variable modulation index revised if undesirably high distortion results.
Claim 41
Dependent Claim
14 words
The system of claim 2 wherein said adaptation means is implemented with digital circuitry.
Claim 42
Dependent Claim
44 words
The system of claim 8 wherein said adaptation means includes means for assigning a different valve of said variable modulation index to each of a plurality of blocks within said image, and said image characteristic is the largest pel-to-pel horizontal difference in a block.
Claim 43
Dependent Claim
61 words
The system of claim 3 wherein said adaptation means includes means for calculating the valve of said variable modulation index for a block from (1) the modulation index used for the same block in the previous frame and (2) either the spectrum or a distortion that resulted from using that valve of the index for that block in the previous frame.
Claim 44
Dependent Claim
23 words
The system of claim 40 wherein said image characteristic is a linear combination of the highest amplitude and the highest pel-to-pel horizontal difference.
Claim 45
Dependent Claim
32 words
The system of claim 1 wherein said adaptation means includes means for making said variable modulation index a function of a signal characteristic that is correlated with the width of said spectrum.
Claim 46
Dependent Claim
23 words
The system of claim 43 wherein said signal is representative of sound and said characteristic is the rate of change of sound amplitude.
Claim 47
Dependent Claim
48 words
The system of claim 1 wherein said adaptation means includes means for determining said spectrum in real time for different time blocks of said signal and increasing said variable modulation index, and thereby said spectrum, in those blocks where less than the available bandwidth would otherwise be used.
Claim 48
Dependent Claim
39 words
The system of claim 1 wherein said adaptation means includes means for measuring a transmission error across said channel (owing to said spectrum exceeding the available bandwidth) and increasing said variable modulation index until a predetermined small error results.
Claim 49
Independent Claim
41 words
The system of 1 wherein said adaptation means includes means for varying said variable modulation index sufficiently gradually across said image so as to make the modulation of said variable modulation index more linear than that provided by static nonlinear companding.
Claim 50
Independent Claim
41 words
The system of 1 wherein said adaptation means includes means for varying said variable modulation index sufficiently gradually across said image so as to make the modulation of said variable modulation index more linear than that provided by static nonlinear companding.
Claim 51
Dependent Claim
13 words
The system of claim 1 further comprising means for statically companding said signal.
Claim 52
Dependent Claim
19 words
The system of claim 48 wherein said static companding attenuates high amplitudes less than low amplitudes (opposite conventional companding).
Claim 53
Dependent Claim
102 words
The system of claim 1 wherein said adaptation means includes means for determining said variable modulation index by following a recursive procedure in which (1) the index (or equivalently the adaptation factor) is varied for a particular block of said signal, said variation resulting in distortion in a demodulated signal generated by demodulating the modulated carrier signal (2) the effect of the variation on distortion in the demodulated signal is determined by examining a measure or predictor of that distortion, and (3) a decision is made as to whether to further vary the variable modulation index based on the degree of distortion.
Claim 54
Dependent Claim
23 words
The system of claim 50 wherein said adaptation means includes means for varying said index until the distortion exceeds a predetermined small level.
Claim 55
Dependent Claim
21 words
The system of claim 50 wherein said adaptation means includes means for varying said variable modulation index using a logarithmic search.
Claim 56
Dependent Claim
39 words
The system of claim 50 wherein the distortion in the demodulated signal is calculated for each sample of said signal (as opposed to each block) prior to transmission, and the variable modulation index revised if undesirably high distortion results.
Claim 57
Dependent Claim
14 words
The system of claim 1 wherein said adaptation means is implemented with digital circuitry.
Claim 58
Dependent Claim
38 words
The system of claim 1 wherein said signal represents sound, and said adaptation means includes means for assigning a different valve of said variable modulation index to each of a plurality of blocks of time in said signal.
Claim 59
Dependent Claim
38 words
The system of claim 55 wherein said adaptation means includes means for making the variable modulation index for a particular sample is based on an asymmetrically located block, extending further before the sample in time than after it.
Claim 60
Dependent Claim
36 words
The system of claim 56 wherein said asymmetrically located block is on the order of 250 to 500 milliseconds long, and extends 50 to 100 milliseconds afterward of a sample and 200 to 400 milliseconds before.
Claim 61
Dependent Claim
43 words
The system of claim 2 wherein said signal representing a visual image is a composite color television signal and said spectrum dividing means includes means for dividing said composite signal into separate high and low-frequency components, the high-frequency component being a composite signal.
Claim 62
Dependent Claim
75 words
The system of claim 3 wherein said adaptation means includes means for determining said variable modulation index by following a frame-recursive procedure in which the valve of said index (or equivalently the adaptation factor) is calculated for a block in the current frame based, at least in part, on the valve of said used for the same block in the previous frame and on a measure of the distortion that resulted in the previous frame.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-03-05 | 1993-09-04 | 1994-03-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-03-05 | 1997-09-04 | 1998-03-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-03-05 | 2001-09-04 | 2002-03-06 | $7700.00 | Window Closed / Lapsed |