APPARATUS FOR TRANSMITTING SIGNALS BASED ON REFLECTIONS AND RELATED METHOD

Abstract

It is described a transmitter of signals, comprising: an encoder (1) configured to generate a two-state modulation signal (x.sub.D(t)) from a first input signal (x(t)), means (2) configured to act on a second input signal (y(t)) as a function of the two-state modulation signal; the means are configured to reflect the second input signal from the transmitter in correspondence of only one state (ON) of two states (ON, OFF) of the two-state modulation signal.

Claims

1. Transmitter of signals, comprising: an encoder (1) configured to generate a two-state modulation signal (x.sub.D(t)) from a first input signal (x(t)), means (2) configured to act on a second input signal (y(t)) as a function of the two-state modulation signal, characterized in that said means are configured to reflect (z(t)) said second input signal in correspondence of only one state (ON) of the two states (ON, OFF) of the two-state modulation signal.

2. Transmitter according to claim 1, characterized in that said encoder (1) is a duty-cycle encoder and said means (2) are configured to reflect said second input signal (y(t)) for the duration of said one state (ON) of the two states (ON, OFF) of the two-state modulation signal.

3. Transmitter according to claim 2, characterized in that in the case wherein the first input signal is an analog signal (x(t)), the duty-cycle encoder (1) encodes the amplitude of said analog signal onto the two-state modulation signal (x.sub.D(t)).

4. Transmitter according to claim 3, characterized in that the transmitter has an input clock signal (ck(t)), said duty-cycle encoder (1) has at the input the input clock signal (ck(t)) and periodically sample and maps the instantaneous amplitude of the analog signal (x(t)) onto said two-state modulation signal (x.sub.D(t)) and wherein the duration of said one state (ON) of the two states (ON, OFF) of the two-state modulation signal is proportional to the value of the analog signal (x(t)).

5. Transmitter according to claim 4, characterized by comprising a sample and hold device (11) adapted to sample the analog signal x(t) at the sample times established by the clock signal (ck(t)) and to output a further signal (x.sub.SH(t)) with the same amplitude of the analog-signal x(t), a sawtooth generator (12) adapted to generate a periodic and symmetric triangular waveform (r(t)) that is synchronized with the sample and hold device (11), a comparator (15) configured to compare the further signal (x.sub.SH(t)) and the periodic and symmetric triangular waveform (r(t)) and to output said two-state modulation signal (x.sub.D(t)) wherein the duration of said one state (ON) of the two states (ON, OFF) of the two-state modulation signal depends on the amplitude of the further signal (x.sub.SH(t)).

6. Transmitter according to claim 1, characterized in that in the case wherein the first input signal is a digital signal (x_bit), the encoder (1) encodes the value of said digital signal onto the two-state modulation signal (x.sub.D(t)).

7. Transmitter according to claim 1, characterized in that said reflecting means comprise an optical mirror and the second input signal (y(t)) is an optical signal.

8. Transmitter according to claim 7, characterized in that said reflecting means (2) comprise an optical amplifier (52), said two-state modulation signal (x.sub.D(t)) controlling the gain of said optical amplifier (52) to allow the passage of the optical signal (y(t)) toward the optical mirror in said one state (ON) of the two states (ON, OFF) of the two-state modulation signal (x.sub.D(t)) and prevents the passage of the optical signal (y(t) toward the mirror in said other state (OFF) of the two states (ON, OFF) of the two-state modulation signal.

9. Transmission and reception apparatus of signals comprising a transmitter (100) as defined in claim 1 and a receiver (200) configured to generate the second input signal (y(t)) of the transmitter and receive the reflected signal (z(t)) at the output of the transmitter.

10. Apparatus according to claim 9, characterized in that said receiver comprises a generator (REF) of a synchronization signal (SYNC), said synchronization signal (SYNC) being sent to the transmitter superimposed to the second input signal (y(t)) for the formation of the clock signal.

11. Apparatus according to claim 9, characterized in that said receiver comprises a generator (REF) of a synchronization signal (SYNC), said synchronization signal (SYNC) being sent to the transmitter superimposed to the second input signal (y(t)) for the synchronization of the transmitter and the receiver.

12. Apparatus according to claim 10, characterized in that the receiver (200) comprises even a saturation device (66) configured to avoid the fluctuations induced by the synchronization signal (SYNC) superimposed to the second input signal (y(t)) for the sake of synchronizing the transmitter to the receiver timings.

13. Apparatus according to claim 9, characterized in that said transmitter (100) comprises further means (14) configured to decouple the reflected signal (z(t)) at the output from the transmitter and at the input of the receiver and the second input signal of the transmitter.

14. Method for transmitting signals, comprising: generating a two-state modulation signal (x.sub.D(t)) from a first input signal (x(t)), acting on a second input signal (y(t)) as a function of the two-state modulation signal, characterized by comprising reflecting said second input signal in correspondence of only one state (ON) of the two states (ON, OFF) of the two-state modulation signal.

15. Method according to claim 14, characterized in that said reflecting step comprises reflecting said second input signal (y(t)) for the duration of said one state (ON) of the two states (ON, OFF) of the two-state modulation signal.

16. Method according to claim 14, characterized in that the first input signal is an analog signal and by comprising periodically sampling and mapping the instantaneous amplitude of the analog signal (x(t)) onto said two-state modulation signal (x.sub.D(t)) and wherein the duration of said one state (ON) of the two states (ON, OFF) of the two-state modulation signal is proportional to the value of the analog signal (x(t)).

17. Method according to claim 16, characterized by comprising sampling the analog signal x(t) at the sample times established by an input clock signal (ck(t)), generating a further signal (x.sub.SH(t)) with the same amplitude of the analog-signal x(t), generating a periodic and symmetric triangular waveform (r(t)) that is synchronized with the sampling step, comparing the further signal (x.sub.SH(t)) and the periodic and symmetric triangular waveform (r(t)) and to output said two-state modulation signal (x.sub.D(t)) wherein the duration of said one state (ON) of the two states (ON, OFF) of the two-state modulation signal depends on the amplitude of the further signal (x.sub.SH(t)).

18. Method according to claim 14, characterized in that the first input signal is a digital signal (x_bit) and by comprising encoding the value of said digital signal onto the two-state modulation signal (x.sub.D(t)) and by comprising periodically mapping the value of said digital signal (x_bit) onto said two-state modulation signal (x.sub.D(t)) and wherein the duration of said one state (ON) of the two states (ON, OFF) of the two-state modulation signal is derived from the digital signal (x_bit).

19. Method according to claim 14, characterized in that the first input signal is a digital signal (x_bit) and by comprising encoding the value of said digital signal onto the two-state modulation signal (x.sub.D(t)).

Description

[0026] For a better understanding of the present invention, some embodiments thereof are now described, purely by way of non-limiting examples and with reference to the annexed drawings, wherein:

[0027] FIG. 1 is a schematic view of an apparatus for transmitting and receiving signals according to prior art;

[0028] FIG. 2 is a schematic view of a transmitter of signals based on reflections according to the present invention;

[0029] FIG. 3 is a schematic view of an apparatus for transmitting and receiving signals which comprises the transmitter in FIG. 1 according to a first embodiment of the present invention;

[0030] FIG. 4 is a more detailed view of the transmitter in FIG. 1;

[0031] FIG. 5 is a time diagram of some of the signal in play in the transmitter of FIG. 3;

[0032] FIG. 6 is a schematic view of an apparatus for transmitting and receiving signal which comprises the transmitter in FIG. 2 according to a second embodiment of the present invention;

[0033] FIG. 7 shows the influence of the synchronism signal on the backscattering signal of the receiver of a known transmission and reception apparatus;

[0034] FIG. 8 is a schematic view of a transmitter of signal according to a variant of the first embodiment of the present invention.

[0035] With reference to FIG. 2 a transmitter 100 of signals, that is electromagnetic or optical signals, based on reflections according to the present invention is described.

[0036] The transmitter 100 comprises an encoder 1, preferably a duty-cycle encoder, configured to generate a two-state modulation signal x.sub.D(t), particularly the two states ON and OFF, from a first input signal x(t).

[0037] The transmitter comprises means 2 configured to reflect a second input signal y(t) as a function of two-state modulation signal x.sub.D(t); particularly, the reflecting means 2 are configured to reflect the second input signal y(t) from the transmitter 100 at the correspondence of only one state ON of the two states ON, OFF of the two-state modulation signal x.sub.D(t) so as to output a reflected signal z(t) from the transmitter 100. The second input signal y(t) may be an analog signal, preferably a radiofrequency signal, or an optical signal; preferably, in the case of analog or optical input signal, the reflecting means 2 are configured to reflect the second input signal y(t) for the whole duration of the state ON of the two-state modulation signal x.sub.D(t).

[0038] During the state ON, the reflected signal z(t) has possibly the same frequency or wavelength of the signal y(t), and possibly with comparable amplitude or power except some minor absorption related to the technical capability of the device, or even larger amplitude than the amplitude of the signal y(t) if the reflecting means 2 have amplification capabilities. The absorption-state, that is the state OFF, is when the signal y(t) is not reflected, or when only a minor quantity is reflected, say smaller than 1/10 or even smaller than 1/100 of the power of the signal y(t) when in ON state.

[0039] The reflector 2 controlled by the two-state modulation signal x.sub.D(t) is specifically designed to make for z(t) a copy of the signal y(t) upon all the duration of the state ON, and to disable any reflections on the state OFF except minor leakage that can due to the imperfections of the isolation. Reflector 2 can include any processing that is instrumental to avoid self-interference and self-oscillation such as a predefined frequency translation between the output z(t) and the signal y(t), an amplification, a predefined change of polarization, or any combination of these.

[0040] An example of reflecting means for radiofrequency signals as further detailed in FIG. 3 contains a switch on the signal y(t) controlled by the two-state modulation signal x.sub.D(t) that, on the OFF state, disable any further connection, while on ON state the signal y(t) is electrically connected to a multiplier that translates the frequency of y(t) according to the reference periodic signal extracted from the timing block 50 connected to the synchronization signal SYNC.

[0041] Another example of reflecting means is an electrically controllable mirror or an optical device as a semiconductor optical amplifier (SOA) and a mirror. Another example of reflecting means is the backscattering of the impinging radiofrequency signal as for RFID.

[0042] The input signal x(t) may be an analog signal, a digital signal or an optical signal.

[0043] With reference to FIG. 3, an electromagnetic signal transmission and reception apparatus is described wherein the transmitter 100 is disclosed in FIG. 2 and the receiver is configured to receive the signal z(t). Preferably the input signal y(t) of the transmitter 100 is sent from the receiver 200; the signal y(t), which is a probing signal, is derived from a device REF of the receiver 200 which outputs reference signals.

[0044] The receiver 200 is equipped with a coupler 3 that has the capability to decouple the signal y(t) generated by the device REF from the reflected signal z(t) containing the modulated information from the transmitter 100 in term of reflect/no-reflect information with appropriate duty-cycle that maps onto the reflect/no-reflect durations. A duty-cycle decoder or DCD 4 resumes the original information that can be either digitally converted by means of an analog-to-digital converter or ADC 5, or used as it is after some filtering to recover the analog signal from the samples according to the duration of the states ON or of its duty-cycle.

[0045] An application of the electromagnetic signal transmission and reception apparatus according to the present invention is for radio access in mobile phone networks. The upstream and downstream connections between RU and BB are indicated as Up IQ-streaming from RU to BBU and as Down IQ-streaming from BBU to RU and are based on the exchange of the IQ digitized streams of the radiofrequency signals; the transmitter 100 belonging to the RU while the receiver 200 belonging to the BBU.

[0046] The transmitter 100 is described in more detail in FIG. 4 in the case of a radiofrequency wireless application. The analog signal x(t) at time t is input to the duty-cycle encoder or DCE 1 that encodes the amplitude of the analog signal onto the two-state signal x.sub.D(t) of states ON and OFF using a monotonic mapping function (x) of the input amplitude. Particularly, the DCE 1 has at the input a clock signal ck(t) preferably deriving from a clock generator 50 belonging to the transmitter 100 and having at the input the synchronization signal SYNC deriving from the receiver 200; the DCE 1, using the monotonic mapping function r (x), periodically sample and maps the instantaneous amplitude x(t) onto a two-state signal x.sub.D(t) with the states ON and OFF and wherein the duration of the state ON is proportional to the value x(t). The two-state signal x.sub.D(t) controls the reflecting means 2; particularly in the state ON of the two-state signal x.sub.D(t) the reflecting means 2 reflect the signal y(t) undistorted, preferably amplified by an amplifier 13 and preferably altered in some other characteristics such as polarization, frequency, wavelength just to exemplify, for the whole duration of the state ON while in the state OFF of the two-state signal x.sub.D(t) the reflecting means absorb the signal y(t). The reflecting means 2 have the capability to reflect the probing signal y(t) as a function of the state of the two-state signal)(x.sub.D(t); the reflecting means 2 act as a switch controlled by the DCE 1 signals for the signal y(t). The peculiarity is that the transmitter 100 has no capability to autonomously and locally generate the signal used for the transmission but only to reflect to some degree the probing signal y(t) depending on the two-state signal x.sub.D(t) that encodes the analog signal x(t) in term of duty-cycle.

[0047] Preferably the input signal y(t) of the transmitter is generated at the receiver 200 by means of the device REF, or any device different from the transmitter 100, for example as non-modulated signal with some periodic signal SYNC for synchronization of the transmitter 100.

[0048] Duty-cycle information is related to the accuracy of the rising (or positive) and falling (or negative) edges as any error in edges due to noise or timing is interpreted at receiver as a duty-cycle and thus as an amplitude of the analog signal. Jitter can be controlled centrally at the receiver 200 that sends the signal y(t) by adding a synchronization signal SYNC, superimposed to the signal y(t), that does not impairs the functionalities of the reflection-based modulation and which is reflected back from the reflecting means 2 during the state ON of the two-state signal x.sub.D(t). The signal SYNC derived from the device REF belonging to the receiver 200 has several additional practical benefits such as it is used to estimate the RU-BBU propagation delay, to enable multiple RUs to operate synchronously by aligning the time-offsets, or in general to estimate the distance between receiver 200 and transmitter 100. Furthermore, the superimposed synchronization signal SYNC enables the transmitter 100 to extract the reference timing for the transmitter synchronization of the transmitter 100 to the receiver 200 and for the clock generator 50 that extracts the signals of the DCE 1.

[0049] As shown in FIG. 4, the analog signal x(t) is sent to the DCE 1 including a sample and hold device 11 adapted to sample the signal x(t) at the sample times established by the clock signal ck(t) deriving from the clock generator 50 having at the input the synchronization signal SYNC; the sample and hold device 11 outputs an analog signal x.sub.SH(t) with the same amplitude of the instantaneous analog-signal x(t). The DCE 1 comprises also a sawtooth generator 12 that is configured to generate a periodic and symmetric triangular waveform r(t) (shown in FIG. 5) that is synchronized with the sample and hold device 11 and is controlled by the clock signal ck(t). The DCE 1 comprises a comparator 15 configured to compare the analog signal x.sub.SH(t) (at the non-inverting input terminal of the comparator) and the periodic and symmetric triangular waveform r(t) (at the inverting input terminal of the comparator); the duration of the state ON of the output signal, that is the two-state signal x.sub.D(t), depends on the amplitude of the analog signal x.sub.SH(t).

[0050] The reflecting means 2, controlled by the two-state signal x.sub.D(t), act as a switch that reflects or not the signal y(t) as function of the state of the two-state signal x.sub.D(t). Preferably, to compensate the attenuation from transmitter 100 to receiver 200, the signal y(t) can be amplified and/or frequency shifted by means of a device 13 before being retransmitted back. A decoupling device 14 such as a circulator, known in the state of the art, decouples the signal y(t) transmitted from the receiver to the transmitter from the signal z(t) generated at the transmitter 100 and transmitted back to the receiver.

[0051] According to a second embodiment of the present invention, FIG. 6 shows a transmission and reception apparatus of signals for optical fiber.

[0052] The transmitter 100 is similar to the transmitter 100 in FIG. 5 except for the reflecting means 2 that comprise an optical mirror 51 that is electrically controlled by the two-state signal x.sub.D(t) deriving from the DCE 1 by a comparator configured to compare the analog signal x.sub.SH(t) (at the non-inverting input terminal of the comparator) and the periodic and symmetric triangular waveform r(t) (at the inverting input terminal of the comparator). Preferably the two-state signal x.sub.D(t) controls the gain of an amplifier 52, preferably a semiconductor optical amplifier or SOA, and the optical mirror 51, preferably a Faraday rotator mirror; the SOA 52 allows the passage of the optical signal y(t) toward the mirror in the state ON of the two-state signal x.sub.D(t) and prevents the passage of the optical signal y(t) toward the mirror in the state OFF of the two-state signal x.sub.D(t).

[0053] The receiver 200 comprises a photodiode 61 configured to receive the optical signals reflected by the optical mirror 51. The device REF in this case comprises a master clock 62 configured to generate the signal SYNC and a phase shifter 63 controlling a duty-cycle decoder by means of the clock signal ck(t). Preferably the duty-cycle decoder comprises an integrate-and-dump block 64, controlled by the phase shifter 63, that integrates the received signal and a sample and hold 65, controlled by the phase shifter 63, that samples the integrated signal x.sub.RX(t) before being dumped.

[0054] Preferably the receiver 200 comprises even a saturation device 66 configured to avoid the fluctuations of the amplitude induced by the synchronization signal SYNC superimposed to the signal y(t) for the sake of synchronizing the transmitter to the receiver timings.

[0055] FIG. 7 illustrates the influences of the synchronization signal SYNC on the signal y(t). The presence of the synchronization signal leaves a residual fluctuation on the signal z(t) and also downstream the duty-cycle encoder 1 that causes errors in the amplitude/duty-cycle mapping in the DCD of the receiver; the saturation device 66 represents one method for removing the DCD artifacts illustrated in FIG. 7. Alternatively, the fluctuations can be compensated after mapping the amplitude to time by a preliminary calibration procedure by transmitting a set of known analog-values and creating a look-up table for the corrections at the receiver. The calibration procedure can be repeated periodically if artifacts might change in time.

[0056] The transmitter 100 can be configured to accept digital signal x_bit as shown in FIG. 8. The DCE 1 accepts the encoded bits x_bit that represent the information to be transmitted and in turn generates the states ON/OFF to control the reflecting means 2 for the reflection of the signal y(t) according to a predefined duty-cycle mapping that maps the encoded bits x_bit onto a state ON of appropriate duty-cycle of the two states ON/OFF. The mapping is embedded into the DCE 1 as a look-up table or any other duty-cycle mapping device that accept bits x_bit and outputs the two-state signal x.sub.D(t). To exemplify, the encoded bits x_bit can be stored in a local memory unit or buffer at transmitter 100 for transferring to the receiver. As an alternative solution the transmitter 100 can include an ADC stage 70 of the analog input signal x(t), as shown in FIG. 8 according to a variant of the first or the second embodiment of the present invention.

[0057] As a further alternative, the set of encoded bits of x_bit are each individually encoding the ON/OFF states to control the reflecting means 2 for the reflection of the signal y(t) without the duty-cycle mapping by the DCE, and the reflected signal z(t) has the same duration for every state ON.