Device and method for transmitting data

Abstract

A method for transmitting data, wherein along a transmission path: (i) a modulated carrier signal is generated based on the data to be transmitted, the carrier signal having a carrier frequency within a given transmission channel, which is comprised of a number of frequencies, and (ii) the modulated carrier signal is amplified to a transmission signal, wherein along a compensation path: (i) the modulated carrier signal is filtered, whereby the frequency components within the transmission channel are removed, and at least one of a phase, an amplitude, and/or a delay of the filtered signal is modified thereby generating a compensation signal, and wherein the compensation signal is subtracted from the transmission signal thereby generating a compensated transmission signal, and wherein the compensated transmission signal is transmitted. Also a respective data transmission device is disclosed.

Claims

1. A method for transmitting data, comprising: generating, along a transmission path based on the data to be transmitted, a modulated carrier signal with a constant envelope waveform, the carrier signal having a carrier frequency within a given transmission channel, which is comprised of a number of frequencies; amplifying the modulated carrier signal to a transmission signal; filtering, along a compensation path, the modulated carrier signal, wherein frequency components within the transmission channel are removed, and at least one of a phase, an amplitude, or a delay of the filtered signal is modified thereby generating a compensation signal; subtracting the compensation signal from the transmission signal, thereby generating a compensated transmission signal, wherein the compensated transmission signal is transmitted; and comparing, along a feedback path, the compensated transmission signal with the compensation signal or with the filtered signal, and at least one of the phase, the amplitude, or the delay of the compensation signal is adapted based on the comparison result.

2. The method according to claim 1, wherein the modulated carrier signal is generated according based on frequency modulation, frequency shift keying modulation, phase modulation, phase shift keying modulation, or continuous phase modulation.

3. The method according to claim 1, wherein the modulated carrier signal is amplified in the transmission path with a non-linear power amplifier.

4. The method according to claim 1, wherein the modulated carrier signal along the transmission path and the compensation signal along the compensation path are each frequency up-converted to a RF signal.

5. The method according to claim 4, wherein the modulated carrier signal is generated with a carrier frequency within an intermediate frequency band, and wherein both the modulated carrier signal and the compensation signal are frequency up-converted to a RF signal.

6. The method according to claim 4, wherein the modulated carrier signal is generated with an in-phase component and with a quadrature component, and wherein both the modulated carrier signal and the compensation signal with a quadrature-mixer are frequency up-converted to a RF signal.

7. The method according to claim 1, wherein the modulated carrier signal is generated as a digital signal, the digital signal being discrete in time and value.

8. The method according to claim 7, wherein the digital signal of the modulated carrier signal is digitally filtered and modified in at least one of a phase, an amplitude, or a delay.

9. The method according to claim 8, wherein a cross-correlation of the compensated transmission signal and the compensation signal or a cross-correlation of the compensated transmission signal and the filtered signal is regarded for comparison.

10. The method according to claim 8, wherein the compensated transmission signal is digitized, and wherein the digitized compensated transmission signal is compared with a digital signal of the compensation signal.

11. The method according to claim 1, wherein the compensated transmission signal is transmitted with an antenna by wireless transmission.

12. The method according to claim 11, wherein reflection signals from the antenna back into the transmission path are suppressed.

13. The method according to claim 12, wherein, along the transmission path, a back travelling of the compensation signal to the non-linear amplifier is suppressed.

14. A data transmission device comprising: along a transmission path: a modulator for generating a modulated carrier signal with a constant envelope; an amplifier; and a transmitter arranged downstream of the amplifier along the transmission path, and along a compensation path: a filter; and an adapter for modifying at least one of a phase, an amplitude, or a delay of a signal travelling along the compensation path, wherein, along the compensation path and the transmission path, a coupler is coupled in and located upstream of the transmitter, the coupler being designed for subtracting an output signal of the compensation path from an output signal of the transmission path, and wherein, along a feedback path, a comparator is connected with the transmission path upstream of the transmitter and downstream of the amplifier, the compensation path being downstream of the adapter, wherein the comparator with the adapter are configured to modify at least one of a phase, an amplitude, or a delay of the signal travelling along the compensation path, and wherein the coupler is located downstream of the amplifier along the transmission path.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 shows a block diagram explaining the basic concept for the compensation of undesired frequency components,

(3) FIG. 2 shows a block diagram explaining the compensation of undesired frequency components, where the modulated carrier signal is generated in an intermediate frequency channel,

(4) FIG. 3 shows a block diagram explaining the compensation of undesired frequency components, where the modulated carrier signal is generated as an IQ-signal,

(5) FIGS. 4-8 show power density spectra of signals to explain the concept of eliminating undesired frequency components by the use a compensation signal.

DETAILED DESCRIPTION

(6) FIG. 1 shows a data transmission device 1 for the transmission of data. Along a transmission path 2 data a.sub.k of an alphabet A, for example a binary alphabet A{1, +1}, are received at a modulator 4. The modulator 4 on the basis of the received data a.sub.k generates, for example according to a continuous phase modulation method (CPM), a modulated carrier signal s(t). The modulated carrier signal s(t) along the transmission path 2 after a specific delay time .sub.H is amplified in a power amplifier 5 with factor , thereby receiving a change in phase .sub.P and another delay time .sub.P. Accordingly, the output signal of the power amplifier 5 or transmission signal p(t) respectively, is given as:
p(t)=.Math.e.sup.j.sup.P.Math.s(t.sub.H.sub.P)

(7) A transmitter 6, for example an antenna 7, is implemented for transmitting the transmission signal p(t). The transmission signal p(t) comprises frequency components within the used transmission channel and also undesired frequency components outside the used channel, which interfere with transmission signals in adjoined transmission channels with the allocated frequency band.

(8) For compensation, along a compensation path 3 the modulated carrier signal s(t) is fed to a filter 9 having a response function H(f). The response function H(f) of the filter 9 is designed to eliminate in the modulated carrier signal s(t) the frequency components within the used transmission channel. Accordingly, the output signal s.sub.H(t) of the filter 9 is essentially comprised of the undesired frequency components outside the used channel. Along the compensation path 3 the signal s.sub.H(t) is further adapted in its amplitude by an amplification with the factor , in its phase and in its delay time .sub.0 thereby generating an optimized compensation signal c(t), which is given as:
c(t)=.Math.s.sub.H(t.sub.0).Math.e.sup.j

(9) The amplification factor , the phase and the delay time .sub.0 are adapted to reach an effective compensation of the undesired frequency components contained in the amplified transmission signal p(t) by subtraction of the compensation signal c(t) in the coupler 10. After subtraction of the compensation signal c(t) from the amplified transmission signal p(t) the compensated transmission signal v(t) to be transmitted over antenna 7 becomes:
v(t)=p(t)c(t)=.Math.s(t.sub.H.sub.P).Math.e.sup.j.sup.P.Math.s.sub.H(t.sub.0).Math.e.sup.j

(10) A simple solution of this equation is given by adapting the parameters =, .sub.0=.sub.H+.sub.P and =.sub.p in case of a rectangular highpass filter H(f)=1rect(f/2B). In the compensated transmission signal v(t) all frequency components outside the bandwidth B are completely eliminated.

(11) In real systems the parameters , .sub.H, .sub.P and in particular .sub.P are not constant over time and temperature. There is a need for an adaptive modification of these parameters. This can be achieved, for example, by regarding the cross-correlation between the compensation signal c(t) and the compensated transmission signal v(t). The cross-correlation can be determined in the regarded system as:

(12) $l_{\mathrm{cv}}\left(\right)=\underset{T.fwdarw.+}{\lim }\frac{1}{T}{}_{-T/2}^{+T/2}{c}^{*}\left(t\right).Math.v\left(t+\right)\mathrm{dt}$

(13) If the signals c(t) and v(t) are defined in a specific time period of T/2t<T/2 with c.sub.T(t) and v.sub.T(t), the spectra C.sub.T(f)=F{c.sub.T(t)} and V.sub.T(f)=F{v.sub.T(t)} can be calculated by using the Fourier transform function F{ . . . }. The cross-correlation function then can be written as:

(14) $l_{\mathrm{cv}}\left(\right)=\underset{T.fwdarw.+}{\lim }\frac{1}{T}{}_{-}^{+}{C}_T^{*}\left(f\right).Math.V_T\left(f\right).Math.e^{j2f}\mathrm{df}$

(15) One possible approach to calculate the parameters , and .sub.0 is, to analyze the cross-correlation function at =0. The cross-correlation function then is:

(16) $l_{\mathrm{cv}}\left(0\right)=\underset{T.fwdarw.+}{\lim }\frac{1}{T}{}_{-}^{+}{S}_T^{*}\left(f\right)H^{*}\left(f\right)e^{-j}{e}^{j2f{}_0}.Math.\left[S_T\left(f\right)e^{-j2f\left({}_H+{}_P\right)}{e}^{j{}_P}-S_{}\left(f\right)H\left(f\right)a{e}^j{e}^{-j2f{}_0}\right]\mathrm{df}$

(17) Having a linear phase |H(f)|.Math.e.sup.j2f.sup.H filter with H(f)=then it results:

(18) $l_{\mathrm{cv}}\left(0\right)=\underset{T.fwdarw.+}{\lim }\frac{1}{T}{}_{-}^{+}{.Math.S_T\left(f\right).Math.}^2\left[.Math.H\left(f\right).Math.e^{j2f{}_H}{e}^{j\left({}_P-\right)}{e}^{-j2f\left({}_H+{}_P-{}_0\right)}-{.Math.H\left(f\right).Math.}^2{}^2\right]\mathrm{df}$

(19) This can be simplified to:

(20) $l_{\mathrm{cv}}\left(0\right)=\underset{T.fwdarw.+}{\lim }\frac{1}{T}{}_{-}^{+}{.Math.S_T\left(f\right).Math.}^2.Math..Math.H\left(f\right).Math.\left[e^{j\left({}_P-\right)}{e}^{-j2f\left({}_P-{}_0\right)}-.Math.H\left(f\right).Math.{}^2\right]\mathrm{df}$

(21) For the calculation of the single parameters one can analyze parts of the cross-correlation function at =0. With regard to the phase , for example, the imaginary part with even |H(f)| and |S.sub.T(f)| can be analyzed:

(22) ${}_{}=\mathrm{Imag}\left\{l_{\mathrm{cv}}\left(0\right)\right\}=\underset{T.fwdarw.+}{\lim }\frac{2}{T}{}_{-}^{+}{.Math.S_T\left(f\right).Math.}^2.Math..Math.H\left(f\right).Math.\sin \left({}_P-\right)\cos \left(2f\left({}_P-{}_0\right)\right)\mathrm{df}$

(23) In case of =.sub.P the imaginary part becomes zero. In case of values other than zero the sign can be used as an indication for decreasing or increasing the phase respectively. A closed-loop control can be implemented for the adaption.

(24) The parameter .sub.0 can be determined when the components of the cross-correlation function are determined at positive and negative frequencies:

(25) ${}_{{}_0}=\mathrm{Imag}\left\{\underset{T.fwdarw.+}{\lim }\frac{1}{T}\left[{}_{-}^0{.Math.S_T\left(f\right).Math.}^2.Math..Math.H\left(f\right).Math.e^{j\left({}_P-\right)}{e}^{j2f\left({}_P-{}_0\right)}\mathrm{df}-{}_0^{+}{.Math.S_T\left(f\right).Math.}^2.Math..Math.H\left(f\right).Math.e^{j\left({}_P-\right)}{e}^{j2f\left({}_P-{}_0\right)}\mathrm{df}\right]\right\}$

(26) Accordingly, it results:

(27) ${}_{{}_0}\underset{T.fwdarw.+}{\lim }\frac{2}{T}{}_0^{+}{.Math.S_T\left(f\right).Math.}^2.Math..Math.H\left(f\right).Math.\cos \left({}_P-\right)\sin \left(2f\left({}_P-{}_0\right)\right)\mathrm{df}$

(28) In case of .sub.0==.sub.P the equation becomes zero. Values other than zero indicate with its sign a decrease or an increase for .sub.0. Again, a closed-loop control can be implemented for the adaption.

(29) For the adaption of the parameter a the real part of the cross-correlation function can be analyzed:

(30) $\begin{array}{c}{}_{}=\mathrm{Real}\left\{l_{\mathrm{cv}}\left(0\right)\right\}\\ =\underset{T.fwdarw.+}{\lim }\frac{2}{T}{}_0^{+}{.Math.S_T\left(f\right).Math.}^2.Math..Math.H\left(f\right).Math.\\ \left[\cos \left({}_P-\right)\cos \left(2f\left({}_P-{}_0\right)\right)-.Math.H\left(f\right).Math.{}^2\right]\mathrm{df}\end{array}$

(31) For an ideal rectangle highpass filter H(f) with parameters .sub.0=.sub.P and =.sub.P the real part of the cross-correlation function becomes zero in case =. Values other than zero indicate with its sign again a needed decrease or increase of the amplification factor .

(32) Accordingly, it has been shown that the phase, the amplitude and the delay of the compensation signal can be adaptively controlled to become an effective compensation of undesired frequency components outside the used channel in the transmission signal. However, the use of the cross-correlation function is a possible example to do so.

(33) In the data transmission device 1 according to FIG. 1 the adapter 12 is placed in a feedback path 11. The adapter 12 further comprises an implemented comparator 14, which compare, for example with the aid of a cross-correlation function, the compensated transmission signal v(t) with the compensation signal c(t).

(34) The data transmission device 25 according to FIG. 2 comprises a modulator 4, which generates a digital modulated carrier signal with a carrier frequency within an intermediate frequency band. A digital to analog converter DAC converts the digital modulated carrier signal, which is discrete in time and value, into an analog signal, which is continuous in time. Along the transmission path 2 frequency components in the continuous modulated carrier signal are removed subsequently with a respective filter, which for example is realized with a bandpass filter. Downstream of the filter the signal is frequency up-converted to a RF signal by frequency-mixing. In a radio frequency synthesizer 15 a radio frequency local oscillator signal LO3 is generated, which is mixed in the frequency-mixer 18 with the modulated carrier signal. In another subsequent bandpass filter undesired mixing products are eliminated. The radio frequency signal is then amplified in the power amplifier 5 to an intensity level needed for radio transmission. Undesired harmonics of the carrier frequency are removed in another filter. The output signal of the filter than in similar known devices will be used for radio transmission via the antenna 7.

(35) The shown data transmission device 25 additionally comprises a compensation path 3. For a compensation signal the digital output signal of the modulator 4 is also fed into a filter 9, which removes the frequency components of the digital modulated carrier signal within the used transmission channel. In the digital adapter 12, the filtered signal is adapted with regard to its amplitude, to its phase and/or to its delay time. In a subsequent digital to analog converter DAC a continuous compensation signal is generated. Undesired frequency components are eliminated with a filter. In a frequency mixer 18 the signal is frequency-up converted to a radio frequency compensation signal. For the up-conversion another radio frequency local oscillator signal LO1 of the synthesizer 15 is used. In a downstream filter undesired mixing products are eliminated. An amplifier 19 amplifies the compensation signal to the needed power level. In the coupler 10, the amplified compensation signal is subtracted from the amplified transmission signal. The undesired frequency components outside the own transmission channel are eliminated. The compensated transmission signal then is transmitted with antenna 7.

(36) The amplitude, the phase and/or the delay time of the compensation signal are adaptively controlled. With the coupler 17 the compensated transmission signal along a feedback path 11 is fed to an amplifier 20 and then frequency down-converted in a frequency mixer 18 to an intermediate carrier frequency. Another local oszillator signal LO2 of the synthesizer 15 is used for the down-conversion. In a subsequent filter undesired mixing components are removed. With an analog to digital converter ADC the compensated transmission signal, used as a reference signal, is converted to a digital signal discrete in time and value. In a comparator 14 the digital reference signal is compared with the already adapted digital compensation signal. Based on that comparison the phase, the amplitude and/or the delay time of the compensation signal are modified with a respective adapter 12.

(37) Along the transmission path 5, an isolator 21 is placed upstream of the antenna 7. Reflection signals travelling back from the antenna 7 into the transmission path 2 are removed. The coupling elements 17, which allow measuring of the compensated transmission signal in the transmission path 2 are placed downstream of the coupler 0. This avoids an undesired backtravelling of the compensation signal to the power amplifier 5.

(38) In FIG. 3 another data transmission device 30 is shown. In contrast to the data transmission device 20 according to FIG. 2 a digital modulated carrier signal in the modulator 4 is generated as an IQ-signal, comprising an in-phase component and a quadrature-component. With separate digital-to-analog converters both components are converted to continuous signals. In quadrature-mixers 24 the in-phase component and the quadrature-component both are mixed to a radio frequency signal. Similar to the device 20 shown in FIG. 2 mixers 24 are placed in the transmission path 2, the compensation path 3 and in the feedback path 11 respectively. Local oscillator signals LO1, LO2 and LO3 of a synthesizer 15 are used for frequency up-conversion and for frequency down-conversion respectively. Preferably, they are derived from the same reference oscillator in order to maintain a fixed phase relationship. In the easiest case these signals are just buffered versions of the same source.

(39) FIGS. 4 to 8 show power density spectra of CPM modulated carrier signals at different stages in a data transmission device 1 similar to FIG. 1. FIG. 4 shows the power spectral density of the modulated carrier signal s(t) generated in the modulator 4. The power density spectrum after having passed the filter 9 with a rectangle highpass characteristic is shown in FIG. 5. The cutting frequency is choosen at 0.625 f.sub.s. The frequency components within the used transmission channel are removed.

(40) FIG. 6 shows the amplified modulated carrier signal p(t) which has passed the power amplifier 5. The power density spectrum has not been changed due to the fact that a modulated signal with a constant envelope wave form is used.

(41) FIG. 7 displays the power density spectrum of the compensated transmission signal v(t). The undesired frequency components outside the used transmission channel are all removed.

(42) Retransmission of the compensated transmission signal v(t) to the power amplifier 5 will result in a reestablishment of the removed frequency components. This is shown in FIG. 8, which displays the power density spectrum of a re-amplified signal s.sub.K(t)=s(t)s.sub.H(t), which is similar to the compensated signal v(t). The power density spectrum according to FIG. 8 again shows significant spectral components outside the bandwidth of the used frequency channel.

(43) Accordingly, as shown in FIGS. 2 and 3 isolators like circulators should be placed downstream of the power amplifier 5.

(44) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.