U.S. patent application number 10/143251 was filed with the patent office on 2002-10-31 for method for wireless information transfer.
This patent application is currently assigned to Nanotron Gesellschaft Fur Mikrotechnik Mbh. Invention is credited to Ianelli, Zbigniew, Koslar, Manfred.
Application Number | 20020159538 10/143251 |
Document ID | / |
Family ID | 7811445 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020159538 |
Kind Code |
A1 |
Koslar, Manfred ; et
al. |
October 31, 2002 |
Method for wireless information transfer
Abstract
Method for wireless information transfer, in particular for
mobile communications, in which an input signal (s.sub.1, g.sub.4)
is subjected to a modulation in a transmitter (2 to 8) and reaches
a receiver (11 to 15) through a transmission channel, whereby angle
modulated pulses, carrying information and possessing a frequency
spectrum, are generated in the transmitter in such a way that they
can be time compressed in a receiver by means of a filter (13) with
frequency dependent, differential delay time, also known as group
delay, in such a way, that pulses arise with shortened duration and
increased amplitude compared to the emitted pulses, and at least a
portion of the information is imprinted onto the pulses using an
additional modulation, independent of the angle modulation, and/or
is used for controlling a parameter of the angle modulation that
can then be registered in the receiver.
Inventors: |
Koslar, Manfred; (Berlin,
DE) ; Ianelli, Zbigniew; (Berlin, DE) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
Nanotron Gesellschaft Fur
Mikrotechnik Mbh
Berlin
DE
|
Family ID: |
7811445 |
Appl. No.: |
10/143251 |
Filed: |
May 9, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10143251 |
May 9, 2002 |
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09297182 |
Apr 26, 1999 |
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09297182 |
Apr 26, 1999 |
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PCT/DE97/02606 |
Nov 3, 1997 |
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Current U.S.
Class: |
375/271 ;
375/139; 375/E1.001 |
Current CPC
Class: |
H04B 2001/6912 20130101;
H04B 1/69 20130101; H03K 7/04 20130101; H03K 7/06 20130101 |
Class at
Publication: |
375/271 ;
375/139 |
International
Class: |
H03K 007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 1, 1996 |
DE |
196 46 747.0 |
Claims
1. Method for wireless transfer of information, in particular for
mobile communications, wherein an input signal is subjected to an
angle modulation in a transmitter (2 to 8; 16 to 26) and reaches a
receiver (11 to 15; 29 to 57) through a transmission channel,
whereby angle modulated pulses, possessing a frequency spectrum and
carrying information, are generated in the transmitter in such a
way, that they can be time compressed in the receiver using a
filter (13, 32, 33) with frequency dependent, differential delay
time, also referred to as group delay, in such a way that pulses
are created with shortened duration and increased amplitude,
compared to the emitted pulses, and at least a portion of the
information in the transmitter is imprinted onto the pulses using
an additional modulation, independent of the angle modulation,
and/or is used for controlling a parameter of the angle modulation
that can be measured in the receiver, whereby at first a sequence
of quasi-Dirac pulses is generated in the transmitter and fed to a
low-pass filter, the filter characteristic of which possesses a
peak shortly before the critical frequency, and which thus
transforms the delta-pulse sequence into a series of Sinc-pulses,
the shape of which is described by the Sinc-function
Sinc(x)=sin(x)/x, which is subsequently carried to an amplitude
modulator that imprints the Sinc-shaped envelope onto each pulse of
a carrier oscillation, and the signal generated in this manner is
fed to a dispersive filter, at the output of which arrives a
frequency modulated pulse sequence.
2. Method of claim 1, whereby the angle modulation and the
additional modulation method are modulation types that are at least
approximately orthogonal.
3. Method of claim 1 or 2 whereby the pulses are filtered according
to a default filter characteristic, whereby the angle modulation on
the transmitter side and the group delay response of the dispersion
filter (13, 32, 33) on the receiver side are matched in such a way
that the signal components of the angle modulated pulses (s.sub.6)
of the output signal (s.sub.9, g.sub.14) arrive at the output of
the dispersion filter, due to the filter's frequency dependent
variable signal delay time, essentially coincident and, due to the
superposition, with increased amplitude compared to the input.
4. Method of one of the previous claims whereby the input signal
(g.sub.4) possesses a carrier frequency, which is subjected pulse
by pulse to an angle modulation in the transmitter (16 to 26).
5. Method of claim 4 whereby the modulation characteristic of the
angle modulation determines the time variation of the phase angle
during the duration of each pulse, the amplitude of the angle
modulated pulses in particular is used for the imprinting of the
information contained in the input signal (s.sub.1), depending on
the input signal (s.sub.1), the group delay response of the
dispersion filter (13) in the receiver (11 to 15) is complementary
to the frequency-time characteristic of the transmission pulse, and
the amplitude of the pulse arriving compressed from the dispersion
filter (13) is evaluated for recovery of the information contained
in the input signal (s.sub.1) using a detector (14, 15), in
particular an amplitude demodulator.
6. Method of one of the previous claims whereby the additional
modulation method that imprints the information is, in particular,
a pulse position modulation (PPM), or optionally a pulse code
modulation (PCM), or a differential pulse code modulation (DPCM),
or a pulse delta modulation (PDM), or a modification of one or
several of these modulation methods.
7. Method of one of claims 3 to 6 whereby the pulse sequence, angle
modulated in the transmitter, is fed to a pair of dispersion
filters (32, 33) in the receiver (29 to 37), whereby the pair of
dispersion filters (32, 33) possess different group delay responses
which are matched in pairs to the modulation characteristic in such
a way, that the signal components of the pulses arrive with
increased amplitude at the output of only one of the dispersion
filters (32, 33), while such an increase in amplitude does not take
place for the other dispersion filter (33, 32), and the amplitudes
are evaluated comparatively at the output of the dispersion filters
(13, 32, 33) using a detector (14, 15, 34, 35).
8. Method of claim 7 whereby the angle--the frequency or the
phase--of the carrier frequency changes, during the pulse duration
of the pulse modulated signals, linearly with time, monotonically
from a lower frequency or phase position to an upper frequency or
phase position, or in reverse direction, and the dispersion filter
in the receiver possesses a complementary linear or monotonic
response.
9. Method of one of the previous claims whereby the modulation
characteristics for the individual pulses of a series of pulses are
selected differently in such a way that the differences contain
part of the information.
10. Method of one of the previous claims whereby, for matching of
transmitter (2 to 8, 16 to 26) and receiver (11 to 15, 29 to 37), a
default digital reference signal is transmitted as input signal
(s.sub.1, g.sub.4) as alignment during the matching process, during
the matching process the amplitude or the pulse duration of the
output signal (s.sub.7, g.sub.10, g.sub.11) of the dispersion
filter (13, 32, 33) on the receiver side is measured, and the
modulation characteristic used on the transmitter side, or the
group delay response of the dispersion filter (13, 32, 33) on the
receiver side, is varied, until the pulse duration reaches a
minimum value, or the amplitude reaches a maximum value.
11. Method of one of claims 7 to 10 whereby the signal flow in the
receiver is split into two parallel branches, each with two
dispersion filters (39, 44, 40, 43) with group delay
characteristics that are inverse with respect, to each other, the
signal flow in the two branches is connected through or interrupted
for a predetermined time interval during each pulse, whereby the
interruption or connection occurs synchronous with the transmission
timing rate, and the two branches are joined on the output side by
a subtracter (45).
12. Transmitter and receiver arrangement for implementing the
method of one of the previous claims, comprising a transmitter (2
to 8, 16 to 26) for pick-up and transmission ,of an input signal
(s.sub.1, g.sub.4), containing a first modulator (2 to 6, 16 to 24)
for angle modulation of the input signal (s.sub.1, g.sub.4), as
well as a receiver (11 to 15, 29 to 37), containing a demodulator
(14, 15, 31 to 37) for recovery of the input signal (s.sub.1,
g.sub.4), whereby the transmitter contains means for generating a
quasi-Dirac pulse sequence and, connected to it on the input side,
a low-pass filter, the filter characteristic of which possesses a
peak shortly before the critical frequency, and thus transforms the
delta-pulse sequence into a series of Sinc-pulses, the shape of
which is described by the Sinc-function Sinc(x)=sin(x)/x, and
contains further, connected to the output of the low-pass filter,
an amplitude modulator, which imprints the Sinc-shaped envelope
onto a carrier oscillation, and a dispersion filter connected to
the output of the amplitude modulator, the first modulator (2 to 6,
16 to 24) generates angle modulated pulses according to a
modulation characteristic that determines the time variation of the
angle or phase position during the duration of each pulse, the
first modulator (2 to 6, 16 to 24) contains a control input for the
pick-up of the input signal (s.sub.1, g.sub.4) and for the setting
of the modulation characteristic depending on the input signal
s.sub.1, g.sub.4, and/or the transmitter (2 to 8, 16 to 26)
contains a second modulator (4) for an additional modulation of the
angle modulated pulses depending on the input signal (s.sub.1,
g.sub.4), the receiver (11 to 15, 29 to 37) contains a dispersion
filter (13, 32, 33), in particular a surface acoustic wave filter,
with a default group delay response for filtering the pulses, angle
modulated on the transmitter side, according to the default
modulation characteristic, and the group delay response of the
dispersion filter (13, 32, 33) is matched, for an increase in
amplitude of the output signal (s.sub.1, g.sub.14), to the
modulation characteristic used on the transmitter side in such a
way that the signal components of the pulses, angle modulated
according to this modulation characteristic, arrive time compressed
and with an amplitude enhancement at the output of the dispersion
filter, due to the filter's frequency dependent, variable signal
delay time.
13. Arrangement of claim 12 whereby the first modulator (16 to 24)
generates a series of angle modulated pulses, whereby the angle
modulation is carried out depending on the input signal (g.sub.4)
at the control input, either according to a default first
modulation characteristic or according to a second default
modulation characteristic, the receiver (29 to 37) contains two
dispersion filters (32, 33) connected in parallel, whereby the
variable group delay response of the two dispersion filters and the
first and second modulation characteristics are matched in such a
way that the signal components of the angle modulated pulse
sequence arrive time compressed and with increased amplitude at the
output of exactly one of the two dispersion filters.
14. Arrangement of claim 12 or 13 whereby the first modulator (16
to 24) on the transmitter side contains one dispersion filter (22,
23) each for generating the angle modulation pulses according to
the two modulation characteristics, the dispersion filters (22, 23)
arranged in the first modulator (16 to 24) are connected on the
input side by a controllable switching element (21) to a signal
source (16 to 20), which generates a high frequency signal
(g.sub.3) with essentially Sinc-shaped envelope, the switching
element (21), for triggering by the input signal (g.sub.4), is
connected to the control input of the modulator (16 to 24).
15. Arrangement of claim 12 or 13 whereby the first modulator (2 to
6) generates angle modulated pulses, whereby the angle modulation
occurs independent of the input signal (s.sub.1) according to a
default modulation characteristic, which determines the time
variation of the frequency during the duration of each pulse, the
second modulator (4) on the transmitter side, for imprinting the
information contained in the input signal (s.sub.1), is an
amplitude modulator (4), which determines the amplitude of the
angle modulated pulses depending on the input signal (s.sub.1), the
receiver (11 to 15) for filtering of the pulses, angle modulated on
the transmitter side according to the default modulation
characteristic, contains exactly one dispersion filter (13) with a
default group delay response that is matched to the modulation
characteristic used on the transmitter side in such a way that the
signal components of each angle modulated pulse arrive time
compressed and with increase in amplitude at the output of the
dispersion filter (13), and a detector (14, 15) is connected after
the dispersion filter (13) for recovery of the information
contained in the input signal (s.sub.1).
16. Arrangement of one of claims 12 to 15 whereby, to allow
alternating transmitting and receiving operation, the transmitter
(2 to 8, 16 to 26) and the receiver (11 to 15, 29 to 37) contain
corresponding, essentially identical component modules for
modulation or demodulation, each containing at least one dispersion
filter (6, 13, 22, 23, 32, 33).
17. Arrangement of one of claims 12 to 16 whereby the receiver (11
to 15, 29 to 37) contains a meter on the output side for measuring
the amplitude and/or the pulse duration of the output signal
(s.sub.9, g.sub.14), and an adjusting element is provided in the
receiver (11 to 15, 29 to 37) for setting the group delay response
of the dispersion filter (13, 32, 33), which is controlled by a
control unit connected with the meter, in such a way that the
amplitude of the output signal assumes a maximum value or the pulse
duration of the output signal assumes a minimum value.
18. Arrangement of one of claims 12 to 17 whereby the receiver
contains a noise suppression circuit (38, 47), essentially
consisting of two parallel branches, which are connected on the
output side to the inputs of a subtracter (45, 54), and in each of
which two dispersion filters (39, 44, 40, 43, 48, 52, 49, 53) with
group delay characteristics, inverse with respect to each other,
are series connected, whereby in each of the two branches, between
the two dispersion filters (39, 44, 40, 43, 48, 52, 49., 53), a
control element for controlling the signal flow is placed, which is
connected to a synchronizing circuit (46, 55 to 57) for
synchronization of the signal flow control with the transmission
timing rate.
19. Arrangement of claim 18 whereby the control element is a
multiplier (50, 51) that, on the input side, is connected to the
dispersion filter (48, 49), connected before, and, for tined
interruption or disconnection of the signal flow, with the
synchronizing circuit (55 to 57).
Description
DESCRIPTION
[0001] The invention relates to a method as in claim 1, as well as
to a transmitter and receiver arrangement for implementation of the
method as in claim 12.
[0002] In wireless information transfer methods, that are well
known to the expert from standard reference works, the information
signal to be transmitted is modulated upon a high frequency carrier
signal in the transmitter and transferred over a transmission path
to the receiver, which contains a corresponding demodulator for the
recovery of the information signal. A well known modulation method
in telecommunications is the angle modulation (as generic term for
frequency and phase modulation).
[0003] If the information signal to be transmitted is present in
digital form as a bit sequence, as is the case in modern mobile
radio networks, then the modulation is carried out by variation of
the frequency, or phase, or amplitude of the carrier signal,
depending on the bit sequence to be transmitted. Various digital
modulation methods are known, for example from COUCH, L. W.:
Digital and Analog Communication Systems, 4.sup.th Edition,
Macmillan Publishing Company (1993), among them amplitude-shift
keying (ASK: Amplitude Shift Keying), two phase-shift keying
(2-PSK: Phase Shift Keying) or two frequency-shift keying (2-FSK:
Frequency Shift Keying). Here too a demodulation is carried out in
the receiver according to the modulation method employed on the
transmitter side, thus effecting a recovery of the digital
information signal as a bit sequence in form of consecutive
pulses.
[0004] The use of several different modulation methods for
different messages, or message components, as part of a continuous
transmission process is known to the expert, for example from
analogue television engineering, where the vestigial side-band
amplitude modulation is used for the luminance signal, the
frequency modulation for the audio signal, and the IQ modulation
for the chrominance signal. Here too, the variation of the carrier
parameters serves only in the imprinting of the information and has
no effect on noise of the transmission path.
[0005] A method for expansion of emitted tracking pulses on the
transmitter side and compression on the receiver side is known from
radar technology ("Chirp"-technique); compare E. Philippow
(Publisher.): Taschenbuch der Elektrotechnik, Vol. 4, Systeme der
Informationstechnik, Berlin 1985, p. 340,341. Hereby an analogue
frequency modulation or a digital phase modulation is applied in
the compression., but no imprinting of information takes place.
This method serves in the reduction of the expended transmission
power, and thus a potential opponent's ability to detect the
signals, while simultaneously maintaining range and accuracy of
coverage.
[0006] A basic physical problem exists in all communication
methods: the quality of the information signal that is recovered on
the receiver side decreases with the amount of interference on the
transmission path (always present in reality), and thus with the
distance between transmitter and receiver. To obtain a desired
working distance at a predetermined noise immunity in a
communication over a noisy transmission path, a certain
transmission power is necessary, which, for example for mobile
communications, is in the range of Watts.
[0007] On one hand, the required transmitting power has the
disadvantage that the energy consumption during the transmitting
operation is correspondingly high, which in particular for battery
or accumulator battery operated devices, such as mobile telephones,
is a problem, due to the rapid depletion of the energy store. On
the other hand, the rising number of communication transmitters
caused by the explosive distribution of mobile telephones, the
increasing number of providers of radio broadcasts and television
programs etc, increases the total impact of electromagnetic
radiation on humans (so called "human exposure"). Harm to the human
body can not be ruled out, in particular for mobile telephones at
the presently customary transmitter power, due to the very low
distance of the transmitter to the user's head.
[0008] This invention has the objective to develop a method of the
type mentioned at the beginning, and an arrangement for the
implementation thereof, which allows a reduction in transmission
power and/or and increase in range while maintaining at least equal
transmission quality.
[0009] This objective is met, starting with a method according to
claim 1, by this method's characterizing features, and--regarding
the arrangement for implementing the method--by the features of
claim 12.
[0010] The invention includes the principal thought to use two
independent modulation methods to imprint the information onto a
carrier (information signal modulation) and to achieve extensive
suppression of noise on the transmission path, in particular of the
thermal or "white" noise (carrier signal modulation).
[0011] The pulses that have been modulated, or are to be modulated,
with the information according to a well known method of
telecommunications, in the transmitter are subjected to an angle
modulation (which here is to be understood as generic term for
phase and frequency modulation) with a special characteristic. The
angle modulated pulses, showing a predetermined frequency spectrum,
are time compressed in the receiver by introducing a frequency
dependent delay. Thus an amplitude enhancement results at the
receiver output, compared to the amplitude of the transmitted
signal, and thus to the noise level. In particular, this pulse
compression/amplitude enhancement can be carried out using a
dispersive filter. The information signal is recovered from the
carrier processed in this manner by demodulation, whereby the
demodulation of the information signal occurs with a signal/noise
ratio improved by the amplitude enhancement.
[0012] The improvement of the signal/noise ratio is dependent on
the bandwidth-time-product of the bandwidth used in the angle
modulation and the pulse duration, and is especially prominent in
poor transmission conditions.
[0013] The actual information can be imprinted onto the carrier by
pulse modulation techniques, or by carrying out the carrier
compression so that it can be evaluated in different ways for
different states of the information signal, so that the information
is contained in this variation of the angle modulation. Hereby it
is important that the modulation of the information has no, or only
secondary, influence on the signal delay time.
[0014] After the demodulation the available signal is of a quality,
which in the state of technology could only be achieved by
increased transmitting power or by costly methods for the
improvement of reception (such as diversity reception or redundant
transmission). A further advantage of this invention's method lies
in the essentially lower potential for interference compared to
other transmission paths, because a predetermined signal/noise
ratio can be achieved after the pulse compression in the receiver
using lower transmitting power. In addition, the lower demands on
the transmitting power lead to a reduced human exposure. The
disadvantage of this method, a higher required bandwidth, and thus
a reduced channel capacity or transfer rate (bit rate) can be
accepted for many areas of application, and can be partially
eliminated through the selection of a matching pulse modulation
method for the modulation of the information (see below).
[0015] A special angle modulation time characteristic is used in
the variable angle modulation, which corresponds to a "modulation
characteristic curve". Hereby, the modulation characteristic
curve--here referred to as modulation characteristic--determines
the time behavior of the frequency during the duration of each
pulse. When a linearly falling modulation characteristic is used,
the frequency of the transmitted signal decreases linearly, during
the duration of each pulse, from a value above the carrier
frequency to one lying below the carrier frequency. Analogously, a
linearly rising characteristic can be used. The filter on the
receiver side is matched to the employed modulation characteristic
by a corresponding differential, frequency dependent delay time
response (group delay response) in such a way that the signal
components of different phase position, generated on the
transmitter side are superimposed to a signal nearly coincident in
time (approximate .delta.-pulse).
[0016] In an advantageous embodiment of the invention the
imprinting of the information of the input signal occurs by
selecting or varying the modulation characteristic depending on the
input signal. If the input signal contains a high-level, then, for
example, a modulation characteristic decreasing (most simply
linearly) with the signal is used, which leads to a frequency
modulated pulse with a frequency decreasing during the pulse
duration ("Down-Chirp"). In contrast, a (linearly) rising
modulation characteristic is used for a low-level of the input
signal, which correspondingly yields a pulse with a frequency that
rises during the pulse duration ("Up-Chirp").
[0017] The filter means on the receiver side are matched by an
inverse or complementary characteristic. If the angle modulation on
the transmitter side is carried out according to a decreasing
modulation characteristic, then the frequency of the pulse
decreases during the pulse duration, which has as a result that the
signal components of higher frequency arrive on the receiver side
before the signal components of lower frequency. Thus, the delay
time response of the dispersion filter oil the receiver side has to
compensate for the "lead" of the high frequency signal components,
so that the spectral signal components of the frequency modulated
pulse superpose to form a pulse with increased amplitude at the
output of the dispersion filter.
[0018] To transmit a higher information content with each pulse, it
is possible to use more than two modulation characteristics for the
input signal. If, for example, four modulation characteristics are
available, then accordingly four different pulses can be
transmitted, which corresponds to an information content of 2 bit
for each transmitted pulse. By increasing the number of different
modulation characteristics, the data transfer rate can be
advantageously increased, whereby it must be noted that the
technical expense increases at the same time, and the different
pulses with a very large number of different modulation
characteristics become more difficult to distinguish, which
increases the transmission's susceptibility to errors.
[0019] In the previously described variation of the invention, the
modulation of pulses is carried out actively for a high-level as
well as for a low-level of the digital input signal. This means
that frequency modulated pulses are generated for a high-level as
well as for a low-level of the input signal, which can be
distinguished by the type of frequency variation during the pulse
duration. Hereby, the imprinting of the information contained in
the input signal occurs through selection or variation of a
modulation characteristic, depending on the input signal.
[0020] Alternatively, the transmission of the input signal can be
carried out actively for only one of two defined levels, while no
pulse is generated for the other level. For example, a linearly
rising frequency modulated pulse is generated for a high-level of
the input signal, while a pause of the pulse's length is inserted
for a low-level. This variation of the invention allows
implementing the method using a single modulation characteristic,
with low technical expense. In particular, only one dispersion
filter is required on the receiver side.
[0021] The imprinting of the information contained in the input
signal onto the transmitted signal occurs according to a known
digital modulation method, preferably using pulse position
modulation (PPM), in which the position of the individual frequency
modulated pulses is varied relative to a reference pulse, depending
on the input signal. Application of the pulse phase--or pulse width
modulations is in principle suitable, but potentially requires
higher technical expense, or does not match all the advantages of
the PPM.
[0022] Using the combination of "chirp" modulation, for carrier
noise suppression, and PPM, for imprinting the information, lends
itself in a particularly advantageous manner for utilizing the
increase in time resolution on the receiver side, that arises in
the pulse compression of pulses with very short rise time, for
increasing the transmission rate (with respect to the increased
band width), by utilizing the superposition principle in the
reception of pulses overlapping in time. Seen in its entirety, this
allows for extensive compensation of the original loss of
transmission rate. A (small) portion of the transmitting power
saved due to the compression is employed for the emitting of the
reference pulses needed for the PPM, and potentially for additional
encoding pulses in the same channel.
[0023] The recovery of the information that is contained in the
input signal is effected by a detector, connected after the
dispersion filter, that is matched to the modulation method that is
employed for imprinting the information, contained in the input
signal, on the transmitter side.
[0024] If one of several modulation characteristics is selected on
the transmitter side, depending on the amplitude of the input
signal, preferably a linearly falling modulation characteristic for
a high-level and a linearly rising modulation characteristic for a
low-level of the input signal, then two options exist for the
interpretation in the receiver.
[0025] One option consists of providing only one dispersion filter
on the receiver side, the differential phase delay, or group delay
response, of which is matched to one of the modulation
characteristics used on the transmitter side in such a way, that
the signal components of the pulse, frequency modulated according
to this modulation characteristic, arrive superposed at the output
of the dispersion filter, which leads to a pulse compression and
increase in amplitude. For a pulse of one of the other modulation
characteristics, that is not optimally matched to the delay time
response of the dispersion filter on the receiver side, the
spectral signal components arrive spread over time at the output of
the dispersion filter, and thus, due to the lower pulse
compression, with lower amplitude. Thus, in this embodiment the
amplitude of the pulse arriving at the output of the dispersion
filter depends on the modulation characteristic employed on the
transmitter side, and thus on the amplitude of the input signal
that was used in the selection of the modulation characteristic. To
recover the digital input signal from the output signal of the
dispersion filter, an amplitude sensitive detector, potentially
executed as amplitude demodulator, is connected after the
dispersion filter.
[0026] In the other option the frequency modulated pulse is fed to
several dispersion filters, connected in parallel, on the receiver
side. The frequency depending delay time response of the dispersion
filter on the receiver side and the modulation characteristics used
on the transmitter side are matched in pairs, in such a way that
the signal components of the frequency modulated pulse arrive
compressed at the output of exactly one of the dispersion filters,
thus leading to an increase in amplitude, while no increase occurs
in the output signals of the other dispersion filters, due to the
different characteristic. Thus the input signal can be
discriminated according to the particular dispersion filter at
which an increase in amplitude is present.
[0027] Advantageously, the dispersion filters are executed as
surface acoustic wave filters ("SAW filter"), which can be
manufactured with high accuracy and stability. In addition, SAW
filters offer the advantage that amplitude response and phase
response can be dimensioned independently of each other, which
offers the possibility to execute the narrow banded band-pass
filter required in each receiver and the dispersion filter as one
component.
[0028] The generation of the frequency modulated signal in the
transmitter can occur in different ways, some of which will be
briefly described as examples in the following.
[0029] In an advantageous variation of the invention, at first an
approximate (quasi-) Dirac pulse is generated and fed to a low-pass
filter, the filter characteristic of which possesses a peak shortly
before the critical frequency, and thus transforms the delta-pulses
into Sinc-pulses, the shape of which is described by the well known
Sinc-function, Sinc(x)=sin(x)/x. Subsequently, the Sinc-shaped
output signal of the low-pass filter is led to an amplitude
modulator that imprints the Sinc-shaped envelope onto a carrier
oscillation. If the signal generated in this mainer is fed to a
dispersive filter, then a frequency modulated pulse appears at the
output. Thus in this variation of the invention, at first a
dispersion filter on the transmitter side expands the relatively
sharp Sinc-pulse into a frequency modulated pulse, which is
broadened compared to the Sinc-pulse and has a correspondingly
lower amplitude. A compression of the pulse, with a corresponding
increase in amplitude, subsequently occurs on the receiver side,
also using a dispersion filter. Since one dispersion filter each is
used for the expansion of the pulses on the transmitter side, and
for the compression on the receiver side, this variation of the
invention is advantageously suited for a transceiver operation with
alternating transmitting and receiving operation. For this purpose,
the transmitter and receiver can contain corresponding identical
component modules with one dispersion filter each, that in
transmitting operation serve in the generation of the frequency
modulated pulse, and in receiving operation help in the compression
of the received frequency modulated pulses.
[0030] In another variation of the invention, the generation of the
frequency modulated pulses is effected using a PLL (PLL: Phase
Locked Loop) and a voltage controlled oscillator (VCO: Voltage
Controlled Oscillator). The individual pulses of the input signal,
that is present in digital form, hereby are at first converted to
saw-tooth shaped pulses in an integrator, whereby the rise
direction of the individual pulses depends on the amplitude of the
input signal. The signal generated in this manner is then used for
triggering the VCO, so that the frequency of the output pulse
linearly increases or decreases during the pulse duration,
depending on the level of the input signal.
[0031] In a further variation of the invention, a digital
signal-processing unit generates the frequency modulated pulse in
the transmitter, which advantageously allows the implementation of
any desired modulation characteristics.
[0032] In a variation of the invention, matched
transmitter-receiver pairs are produced to implement the
complementary transmitter-receiver characteristics, so that no
further tuning work is required when the system is put in
operation.
[0033] In another variation of the invention the receiver is
matched to the transmitter before or during the operation, by
varying the delay time response of the dispersion filter used on
the receiver side. Hereby, the transmitter, as part of a matching
process, generates a reference signal, which preferably corresponds
to a series of high-levels of the input signal, whereby the
modulation characteristic of the frequency modulation carried out
on the transmitter side, or the frequency dependent delay time
response of the dispersion filter on the receiver side, are varied
until an optimum pulse compression or increase in amplitude occurs
on the receiver side. This variation is especially advantageous
when using a digital signal processor for filtering and processing
in the receiver, since such a signal processor allows in simple
manner a variation of the frequency dependent delay time response
and a corresponding optimization, whereby the optimization
procedure can be executed automatically, by computer control.
[0034] In a further advantageous embodiment of this variation, the
data transfer occurs block by block, whereby the above mentioned
matching process is carried out renewed for each block, to be able
to dynamically compensate for fluctuations of the dispersion
characteristics on the transmission path.
[0035] Advantageous further developments of the invention are
identified in the secondary claims, or will be described, together
with the invention's preferred embodiment, in more detail in the
following.
[0036] FIGS. 1a, 1b show in a block diagram, as the invention's
preferred embodiment example, a transmitter and receiver of a
message transfer system.
[0037] FIGS. 2a to 2e show the digital input signal of the
transmitter, as well as several intermediary stages of the signal
processing in the transmitter up to the transmission signal.
[0038] FIGS. 3a to 3d show the received signal, as well as several
intermediary stages of the signal processing in the receiver, tip
to the demodulated signal.
[0039] FIGS. 4a, 4b show in a block diagram the transmitter and
receiver of a message transfer system with active transmission of
high and low levels.
[0040] FIGS. 5a to 5k show the digital input signal of the
transmitter of FIG. 4a, as well as several intermediary stages of
the signal processing in the transmitter.
[0041] FIGS. 6a to 6e show the signal picked up on the receiver
side, as well as several intermediary stages of the signal
processing in the receiver.
[0042] FIGS. 7, 8 each show a modified form of the receiver shown
in FIG. 4b with a noise suppression circuit.
[0043] FIGS. 9a and 9b show graphical illustrations of the
improvement in the signal/noise ratio obtainable with this
invention's method.
[0044] A transmitter, illustrated in FIG. 1a, serves in the
transmission of a signal s.sub.1, generated by signal source 1 and
present in a form that can be digitized, across a noisy
transmission path to the receiver, illustrated in FIG. 1b, whereby,
for predetermined requirements on range and noise immunity, the
transmission can advantageously be made with relatively low
transmitting power, which on one hand increases the battery life
for battery operated transmitters, and on the other hand reduces
the environmental impact by electromagnetic radiation--also known
as Electro-smog. In addition, compared to other communications
systems, the error potential of the transmitter is reduced due to
the relatively low transmission power.
[0045] In the transmitter, a digital input signal s.sub.1, the time
behavior of which is shown in detail in FIG. 2a, is at first fed to
a pulse shaper 2, which transforms the relatively wide square
pulses of input signal s.sub.1 to short needle pulses, that are
meant to emulate (quasi-) Dirac pulses. It can be seen in the
illustration of the needle pulse sequence s.sub.2 in FIG. 2b that
the generation of the individual needle pulses is triggered every
time by the rising edge of the square pulses of input signal
s.sub.1.
[0046] A needle pulse sequence s.sub.2 generated in this manner is
subsequently fed to a low-pass filter 3, the delay time response of
which possesses a peak shortly before the critical frequency, so
that the individual needle pulses--as can be seen in FIG. 2c--are
transformed to Sinc-pulses, the shape of which conforms to the well
known Sinc-function Sinc(x)=sin(x)/x.
[0047] Subsequently the Sinc-pulse series s.sub.3 is carried to an
amplitude modulator 4, which modulates this signal onto a carrier
oscillation of frequency f.sub.T, which is generated by oscillator
5, so that carrier frequency pulses with a Sinc-shaped envelope are
generated at the output of the amplitude modulator 4, as
illustrated in FIG. 2d. (For illustrative purposes the pulses are
shown broadened in the drawing, in reality, when shown to scale,
they are narrower).
[0048] A dispersion filter 6 is connected after the amplitude
modulator 4, which filters the modulated carrier frequency signal
s.sub.4 according to its frequency dependent, differential delay
time characteristics. At the output of the dispersion filter 6
arrive--as can be seen in FIG. 2e--linearly frequency modulated
pulses with constant amplitude, the frequency of which decreases
during the pulse duration from a value f.sub.T+.DELTA.f/2 above the
carrier frequency f.sub.T to a value f.sub.T-.DELTA.f/2 below the
carrier frequency.
[0049] Thus in the transmitter shown here, the transmission of the
input signal s.sub.1 is made unipolar, i.e. a transmission pulse is
only generated for a high level of the input signal s.sub.1, while
a low level can be recognized from a pause in the transmission
signal s.sub.5. For this reason transmitter and receiver can be
constructed reasonably simply, each only containing one dispersion
filter 6,13.
[0050] The pulse sequence s.sub.5 generated in this manner is
subsequently fed to a band-pass filter 7, the center frequency of
which is equal to the carrier frequency f.sub.T of the frequency
modulated pulses, so that signals outside the transmission band are
filtered out.
[0051] Finally, the band-pass limited signal is supplied to antenna
9 by a transmitter amplifier 8 and emitted.
[0052] The receiver shown in FIG. 1b allows the reception of the
linearly frequency modulated signal, emitted by the transmitter
described above, as well as the demodulation and recovery of the
digital input signal s.sub.3 or s.sub.1.
[0053] For this, the signal received by the receiver's antenna
10--for example in diversity operation--is fed to a pre-amplifier
11 and subsequently a band-pass filter 12, the center frequency of
which is equal to the carrier frequency f.sub.T of the band-pass
limited transmission signal, so that noise signals from other
frequency ranges can be filtered out of the receiver signal.
(Instead of a conventional band-pass filter a surface acoustic wave
filter can be used here.) The time behavior of the signal s.sub.6
prepared in this manner is shown in detail in FIG. 3a, whereby for
simplification a noise free transmission path is assumed.
[0054] The received signal s.sub.6 consists of a series of linearly
frequency modulated pulses, whereby the frequency decreases during
the pulse durations according to the modulation characteristic used
on the transmitter side, from a value f.sub.T+.DELTA.f/2 above the
carrier frequency f.sub.T to a value f.sub.T-.DELTA.f/2 below the
carrier frequency.
[0055] Subsequently the signal s.sub.6 is fed to a dispersion
filter 13, which time compresses the individual pulses of the input
signal s.sub.6, which leads to a corresponding increase in
amplitude, and thus an improved signal/noise ratio.
[0056] Hereby the pulse compression utilizes the fact that the
signal components of higher frequency arrive at the output of the
dispersion filter 13 before the lower frequency signal components,
due to the linear frequency modulation carried out on the
transmitter side. The dispersion filter 13 compensates for the
"lead" of the higher frequency signal components by delaying these
more than the lower frequency signal components.
[0057] Hereby the frequency dependent, differential delay time
response of dispersion filter 13 is matched to the modulation
characteristic of the frequency modulation carried out on the
transmitter side, in such a manner, that the spectral signal
components of the received signal arrive essentially coincident at
the output of dispersion filter 13. As seen in FIG. 3b, the
spectral components superpose to form a signal s.sub.7 with
Sinc-shaped envelope for each pulse, whereby the amplitude of the
individual pulses is significantly increased compared to the
received linear frequency modulated signal s.sub.6. (It should be
noted at this point that for improved clarity a distortion was
introduced in the schematic signal representations shown in the
figures. In reality the frequency-modulated pulses are closer
together and the compressed signals are much narrower.)
[0058] Subsequently the output signal of the dispersion filter 13
is fed to a demodulator 14, which separates signal s.sub.7 from the
high frequency carrier oscillation and--as seen in FIG.
3c--generates a discrete output signal s.sub.8 with needle shaped
pulses.
[0059] Subsequently, the original digital signal s.sub.9, the time
behavior of which is shown in detail in FIG. 3d, is recovered from
the needle shaped pulses using a pulse shaper 15.
[0060] FIGS. 4a and 4b show a further message transfer system
according to this invention, which differs from the simpler
embodiment example, described above and illustrated in FIGS. 1a and
1b, most importantly by the fact that both the high level as well
as the low level of the digital information signal are transmitted
actively, which contributes to a higher noise immunity.
[0061] The transmitter shown in FIG. 4a contains a pulse shaper 17,
which is triggered by a timing generator 16, using timing pulses
opposite in phase, shown in FIGS. 5a, 5b. At its output the pulse
shaper emits--as shown in FIG. 5c--a sequence g.sub.1 of needle
shaped pulses that form a (quasi-) Dirac delta sequence. The pulse
sequence g.sub.1 generated in this manner is subsequently fed to a
low-pass filter 18, the filter characteristic of which possesses a
peak just before the critical frequency, and that transforms the
needle shaped pulses to Sinc-shaped pulses, which are shown in
detail in FIG. 5d. Subsequently, this pulse sequence g.sub.2 is
modulated onto a carrier oscillation with carrier frequency
f.sub.T, generated by the oscillator 19, using an amplitude
modulator 20. Thus, at the output of amplitude modulator 20 arrives
a sequence g.sub.3 of equidistant carrier frequency pulses with
Sinc-shaped envelopes. It is important in this context, that the
pulse sequence g.sub.3 arriving at the output of the amplitude
modulator 20 is independent of the digital input signal g.sub.4,
and thus does not contain any information.
[0062] Subsequently, the imprinting of the information of input
signal g4 is effected by means of an analogue switch 21, which is
controlled by input signal g.sub.4, and, depending on the amplitude
of the input signal g.sub.4, directs the pulse sequence g.sub.3,
generated by amplitude modulator 20, either to a dispersion filter
22 with a frequency dependent linearly decreasing delay time, or to
a dispersion filter 23 with a frequency dependent linearly rising
delay time. At their outputs, the dispersion filters 22, 23, are
connected to a further analogue switch 24 or a mixer stage, which,
depending on the amplitude of input signal g.sub.4, selects the
output signal g.sub.7, g.sub.8 of one of the two dispersion filters
22, 23 and passes it on.
[0063] Thus, at the output of the analogue switch 24 arrives--as
shown in FIG. 5k--a sequence g.sub.9 of carrier frequency pulses,
linearly frequency modulated pulse by pulse, whereby for a high
level of the input signal g.sub.4 the individual pulses show a
linearly increasing frequency during the pulse duration, whereas
for a low level of input signal g.sub.4 the frequency during the
pulse decreases linearly.
[0064] The signal arriving at the output of analogue switch 24 is
subsequently filtered by a band-pass filter to suppress
interference signals located outside of the transmission band. The
signal obtained in this manner is then amplified by a transmitter
amplifier 26 and is emitted by the transmitter antenna 27.
[0065] FIG. 4b shows the associated receiver that receives the
signal, emitted by the transmitter shown in FIG. 4a, using an
antenna 28. The receiver amplifies the signal in a pre-amplifier
29, and in a band-pass filter 30 removes any interference signals,
the frequency of which lies outside the transmission band.
[0066] Subsequently, the received signal is carried to two
dispersion filters 32, 33 by a switching element 31. Hereby the
frequency dependent delay time response of the two dispersion
filters 32, 33 on the receiver side is matched in pairs to the
frequency dependent delay time response of the two dispersion
filters 22, 23 on the transmitter side, in such a way that the
spectral signal components of the received signal add to a pulse
with increased amplitude at the output of one of the two dispersion
filters, 32 or 33, while only a time expanded pulse arrives at the
output of the other dispersion filter, 33 or 32.
[0067] As seen in FIGS. 6a and 6b, the output signals g.sub.10 or
g.sub.11 of dispersion filters 32, 33 consist of a sequence of
carrier frequency pulses with Sinc-shaped envelopes.
[0068] The signals g.sub.10 or g.sub.11, appearing at the output of
the two dispersion filters 32, 33, are subsequently fed to a
demodulator 34, 35, which separates the signals g.sub.10 or
g.sub.11 from the carrier oscillation and generates needle shaped
pulses, as seen in FIG. 6c or 6d.
[0069] While each of the needle impulses at the output of
demodulator 34 corresponds to one high level of the input signal
g.sub.4, the needle impulses arriving at the output of the other
demodulator 35 indicate low levels of input signal g4
[0070] To recover the original input signal g.sub.4 from the two
signals g.sub.12, g.sub.13, the two signals g.sub.12, g.sub.13 are
fed to a timing generator 36 for triggering, which generates a
timing signal that reproduces the timing rate of the original input
signal g.sub.4. This timing signal, together with the output
signals g.sub.12, g.sub.13 of the two demodulators 34, 35 is fed to
the decoder 37, which recovers the original output signals,
g.sub.4, g.sub.14, as can bee seen in FIG. 6e.
[0071] FIG. 7 shows a modified form of the receiver shown in FIG.
4b, with a noise suppression circuit 38, which can be combined with
other receivers for such Chirp signals. Due to the very close
similarity of this receiver with the one shown in FIG. 4b,
functionally equivalent components are labeled by the same
reference signs in the two figures.
[0072] As in the previously described receiver, the signal chirped
on the transmitter side is received through an antenna 28 and at
first fed to an input amplifier 15 and a band-pass filter 30, which
is tuned to the carrier frequency and thus filters out noise
signals lying outside the transmission band. Subsequently, the
signal is carried to the noise suppression circuit 38 and split
into two parallel branches, in each of which two dispersion filters
39, 44 or 40, 43, inverse with respect to each other, are connected
in series. During an active transmission of a logic LOW level as
well as of a logic HIGH level, one of the two dispersion filters,
39 or 40, arranged on the input side, is tuned in such a way that a
time compressed signal arrives at the output of this dispersion
filter, 39 or 40. At the output of the other dispersion filter, 39
or 40, arrives a pulse that is time expanded to twice its original
length. The two analogue switches 41, 42 interrupt the signal flow
in the two branches symmetrically around the center of the
compressed pulse, so that the time compressed pulse is suppressed
and only the time expanded pulse in the other branch remains.
Hereby the analogue switches 41, 42 are controlled through the
synchronizing circuit 46, that is triggered by the timing generator
36, and thus reproduces the timing of the output signal, and thus
the transmission timing. The following dispersion filters 43, 44
generate the original pulse, with original width and
correspondingly also with original amplitude, from the time
expanded pulse. These pulses are then fed to the subtracter 45, at
the output of which appears essentially the original pulse.
[0073] The matter is different for the noise that is caused by the
noisy transmission path, and is received by the receiver together
with the useful signal. This noise is at first shifted into
different directions by the dispersion filters 39, 40. But the
dispersion filter 43, 44, connected after, reverse this shift, so
that the input noise is reconstructed in the two branches, except
the very short portion cut out by the analogue switches 41, 42.
Thus the subtraction by the subtracter 45 leads to extensive
suppression of the noise picked up on the receiver side.
[0074] The further processing of the signal that was prepared in
this manner then occurs as described in the description to FIG.
4b.
[0075] The receiver shown in FIG. 8 differs from the one described
above and illustrated in FIG. 7 essentially by the design and the
controlling of the noise suppression circuit 47. Due to the
extensive similarity of the two circuits, functionally equivalent
components or component modules are labeled by identical reference
signs in FIGS. 7 and 8.
[0076] As with the receiver shown in FIG. 7, the chirped pulses are
received by the antenna 28 and at first fed to an input amplifier
29 and a band-pass filter 30, which is tuned to the carrier
frequency and thus filters out noise signals lying outside the
transmission band.
[0077] Subsequently the signal is carried to the noise suppression
circuit 47, which splits the signal into two parallel branches,
that each contain two dispersion filters 48, 52 and 49, 53, inverse
with respect to each other, connected in series. At the output of
the noise suppression circuit 47 the two branches are joined by the
subtracter 54, whereby the noise in the received signal is
completely suppressed by the subtraction.
[0078] In contrast, the chirped signal is not cancelled by the
subtraction in the subtracter 54, so that the signal/noise ratio is
significantly increased. Hereby the dispersion filters 48, 49 on
the input side are matched to the chirped signals, generated on the
transmitter side, in such a way that a time compressed pulse with
correspondingly increased amplitude appears at the output of one of
the dispersion filters 48, 49, whereas a time expanded pulse with
correspondingly reduced amplitude appears at the output of the
other dispersion filter 49, 48. Upon arrival of the compressed
pulses, the signal flow in the two branches is suppressed
synchronously by the multipliers 50, 51,--as will be described in
detail--so that the compressed pulse is suppressed and there
remains only the time compressed pulse excluding the negligible
short cut-out. The original pulse is then generated from the time
expanded pulse by the dispersion filters 52, 53 connected after, so
that essentially the originally received signal, with a
significantly improved signal to noise ratio, arrives at the output
of the subtracter 54.
[0079] The triggering of the multipliers 50, 51 occurs in fixed
synchronization with the transmission timing rate, so that the
signal in the two branches of the noise suppression circuit 47 can
be suppressed exactly at the arrival of the time compressed pulse.
For this, the receiver contains a synchronizing circuit 57, which
on the input side is connected to the timing generator 36 for
synchronization. Subsequently, Sinc-pulses with amplitude 1, lying
inverted with the peak towards to zero, are generated by a pulse
shaper 56 and a low-pass filter 55, and are then fed to the
multipliers 50, 51. The multipliers 50, 51 multiply the signals in
the two branches of the noise suppression circuit 47, either by
zero or by unity, which accordingly either suppresses the signal or
leaves the signal to pass essentially unchanged. Thus the
multipliers 50, 51 here have the same effect as the switching
elements 41, 42 in the variation of the noise suppression circuit
38 described before.
[0080] The scope of the invention is not limited to the previously
listed preferred embodiments. A multitude of variations is possible
that make use of the presented solution even in fundamentally
different implementations. The embodiment examples shown here
should only be seen as basic types of a wide spectrum of
solutions.
[0081] FIGS. 9a and 9b illustrate the improvement of the
signal/noise ratio that can be achieved by this invention for
different expansion factors .iota.=T.sub.T/.delta., with T.sub.T as
mean duration of a transmission pulse processed using the "Chirp"
technique, and .delta. as the mean duration of the pulse compressed
in the receiver. FIG. 9a shows the signal to noise ratio (S+N)/N at
the receiver output as a function of S/N at the receiver input, and
FIG. 9b shows the dependence of the relation (S+N)/N=f(S/N)
normalized to .iota.=1--i.e. the degree of improvement as a
function of the original signal/noise ratio. Hereby, values in the
range from 1 to 160 are selected as parameter for .iota..
[0082] The figures illustrate that the improvement that can be
achieved becomes larger with increasing pulse
"expansion"/compression, and is especially distinct for small
original signal/noise ratios. This clearly documents that the
method can be utilized advantageously in particular in strongly
interfering surroundings, and/or for long transmission ranges,
and/or for low transmitting power.
* * * * *