GB2545450A - Method and system for wireless communications wherein the transmitted signal has an adapatable power - Google Patents

Abstract

The invention relates to the field of wireless communications, and in particular a transmitter configured to perform wireless communication with a receiver configured to receive a signal from the transmitter. The transmitter comprises an oscillator configured to supply a first emitted power for the emission of a signal as a function of a control signal; a communication interface to receive data concerning the reception of a previously-transmitted signal emitted with the first emitted power; a computing module configured to determine a control signal such that a signal-to-noise ratio (SNR) computed from the received signal exceeds a pre-determined signal-to-noise ratio threshold; and means for adapting the control signal as a function of the received data such that the oscillator can supply at least a second emitted power for the emission of a signal. The transmitter is thus able to adapt the power of the emitted signal by the oscillator as needed to exceed the predetermined signal-to-noise ratio threshold.

Description

METHOD AND SYSTEM FOR WIRELESS COMMUNICATIONS WHEREIN THE TRANSMITTED SIGNAL HAS AN ADAPTABLE POWER

FIELD OF THE INVENTION

The invention relates to the field of wireless communication systems, in particular to a system wherein the transmitted signal whose power may be adapted, and a method of adapting the power of the transmitted signal.

BACKGROUND OF THE INVENTION

Wireless communications, the transfer of data between a transmitter and a receiver not connected by wires, may be performed at different frequencies of the electromagnetic spectrum.

Figure 1 represents a conventional transmitter circuit 100 comprising a modulator 110, a local oscillator 120, a mixer 130, a lowpass filter 140, a variable gain power amplifier 150, a power amplifier control module 160, and an antenna 170. The modulator 110 receives on input a source signal comprising data DT to transmit, and transforms it to supply on output a modulated signal. The local oscillator 120 supplies a radio frequency signal on input, along with the modulated signal, to the mixer 130, which mixes them. The lowpass filter 140 receives on input the mixed signal from the mixer 130 and supplies on output a filtered signal from which the high frequency band resulting from the mixing has been removed. The power amplifier 150 receives the filtered signal on input and supplies an amplified signal amplified according to a control signal supplied by the power amplifier control module 160. The amplified signal is then supplied to the antenna 170 for transmission as a transmitted signal TS comprising the data.

Figure 2 represents a conventional receiver circuit 200 comprising an antenna 210, a filter 220 (for example a lowpass or a band pass filter), a Low Noise Amplifier LNA 230, a frequency transposition module 240, a demodulator 250, and a power measurement module 260. The antenna 210 receives the transmitted signal TS as a received signal RS, which is then filtered by the filter 220 before being supplied on input to the amplifier 230. The amplifier 230 supplies on output an amplified signal to the frequency transposition module 240, which supplies a transposed signal. The demodulator 250 demodulates the transposed signal and supplies the data DT on output. The power measurement module 260 also receives the transposed signal, and supplies a signal that controls the amount of amplification (gain) of the amplifier 230.

The distance between the transmitter 100 and the receiver 200 can vary greatly, affecting the power of the received signal RS by several orders of magnitude. The aim of the amplifier 230 is to maintain the signal in an acceptable range in order to improve the performances of the receiver 200.

Current transmitter/receiver communication systems use integrated circuits with transistors to perform amplification, which is a linear operation. Consequently, amplifiers must work within their linear domains of operation, yet a transistor can amplify only in the frequency domain below its defined transition frequency Ft. Stable amplifiers 230 require negative feedback, thus the frequency of operation must be in a decade lower than the transition frequency Ft.

Though experimental transistors can reach transition frequencies of 1 terahertz THz, current mass-produced devices using CMOS (Complementary Metal Oxide Semiconductor) transistors are only able to reach transition frequencies Ft of several hundred gigahertz GHz. Thus, current CMOS transistors cannot be used to produce a receiver with a Low Noise Amplifier 230 operating at THz frequencies, i.e. from 300 GHz to 3 THz.

The power of the transmitter should also be controlled to achieve a signal to noise ratio SNR that meets an expected Bit Error Rate (BER), regardless of the distance between the transmitter and the receiver. Nevertheless, current transmitters are unable to provide terahertz modulation with a variable gain amplification, such that the power of the transmitted signal cannot be properly controlled for use in a terahertz communication system.

Thus, the conventional transmitter and receiver architectures are unable to meet the requirements for a terahertz communication system.

SUMMARY OF THE INVENTION

The present invention has been devised to address at least one of the foregoing concerns, in particular to control the power of a transmitted signal for wireless communications, in particular terahertz communications.

Embodiments of the invention relate to a transmitter configured to perform wireless communication with a receiver configured to receive a signal from the transmitter, the transmitter comprising: an oscillator configured to supply a first emitted power for the emission of a signal as a function of a control signal; a communication interface to receive data concerning the reception of a previously-transmitted signal emitted with the first emitted power; a computing module configured to determine a control signal such that a signal-to-noise ratio computed from the received signal exceeds a pre-determined signal-to-noise ratio threshold; and means for adapting the control signal as a function of the received data such that the oscillator can supply at least a second emitted power for the emission of a signal.

The transmitter is thus able to adapt the power of the signal emitted by the oscillator based on feedback from the receiver, such that the signal-to-noise ratio computed from the received signal exceeds a signal-to-noise ratio threshold.

According to one embodiment, the computing module determines the control signal based on a relation between the signal-to-noise ratio computed from the received signal with respect to the emitted power of the oscillator.

According to one embodiment, the oscillator is a resonant-tunneling-diode.

The resonant-tunneling-diode allows terahertz communications.

According to one embodiment, the transmitter further comprises a control voltage source coupled to the oscillator and configured to adapt at least part of the control signal such that it comprises at least two control voltages, according to the received data.

The voltage source allows the power of the unmodulated carrier signal to be modified.

According to one embodiment, the transmitter further comprises a modulator configured to supply an alternating signal that modulates the transmitted signal.

According to one embodiment, the modulator is configured to receive a control signal that modifies the alternating signal supplied by the modulator.

The modulator is thus able to supply an alternating signal that is adapted in order to meet a new emitted power.

According to one embodiment, the received data is an acknowledgement signal, and the transmitter is further configured to: upon receipt of the acknowledgement signal, transmit further signals according to the first emitted power, and in the absence of the acknowledgement signal, adapt the power of the signal emitted by the oscillator, and transmit further signals with the adapted power.

The non-reception of an acknowledgement signal allows the transmitter to compute a new (second) emitted power allowing communication with a simple receiver.

According to one embodiment, the received data contains information relating to the power of the received signal.

The information relating to the power of the received signal simplifies the computing, by the transmitter, of the new emitted power.

According to one embodiment, the transmitter is further configured to stop the transmission of signals if the power of the transmitted signal exceeds a predetermined maximum power.

In this case, the transmitter determines it is not worthwhile to continue the transmission of signals.

According to one embodiment, the transmitter is further coupled to a memory for storing data relating to the control signals and the signal-to-noise ratios.

According to one embodiment, the transmitter is configured to transmit a signal of at least 100 gigahertz.

Embodiments of the invention also relate to a receiver configured to perform wireless communication with a transmitter according to an embodiment of the invention, the receiver comprising: an antenna to receive a signal from the transmitter, means for determining the power of the received signal, and a communication interface to send data relating to the determined power of the received signal to the transmitter.

The receiver is thus able to indicate to the transmitter the correct reception or not of the transmitted signal.

According to one embodiment, the sent data is an acknowledgement signal that the transmitted signal has been correctly received.

According to one embodiment, the communication interface is a radio communication module configured to perform wireless communication in accordance with near field communication standards.

According to one embodiment, the receiver further comprises a detector configured to receive on input the received signal from the antenna and to supply on output a detected signal, and wherein the power of the received signal is used to compute the signal-to-noise ratio of the detected signal.

According to one embodiment, the detector is a plasma wave field effect transistor. A plasma wave field effect transistor has the advantages of being an integrated low-cost solution, eliminating the need to use heterodyne detection circuitry.

According to one embodiment, the detector is a quadratic detector.

According to one embodiment, the receiver further comprises a demodulator configured to demodulate the received signal.

According to an embodiment, the receiver further comprises means for providing information calculated from the measured power, so that the communication interface may send the information to the transmitter for determining the control signal.

Embodiments of the invention also relate to a system comprising a transmitter according to an embodiment of the invention and a receiver according to one embodiment of the invention, the transmitter and the receiver being configured to perform wireless communication with each other.

Embodiments of the invention also relate to a method of determining a power of transmitted signal by a transmitter according to an embodiment of the invention to a receiver according to an embodiment of the invention, configured to receive the transmitted signal, the method comprising the steps of: supplying, by the transmitter, a first emitted power as a function of a first control signal; receiving, by a communication interface of the transmitter, data concerning the reception of a previously-transmitted signal emitted with the first emitted power; determining, by means of the received data, whether the signal was correctly received; and if the signal was not correctly received, then: - determining, by means of a computing module of the transmitter, a control signal such that a signal-to-noise ratio computed from the received signal exceeds a pre-determined signal-to-noise ratio threshold; and - adapting, by the transmitter, the control signal as a function of the received data such that the oscillator can supply at least a second emitted power for the emission of a signal.

The method thus provides a process for the transmitter to determine an optimum power for the transmitted signal, ensuring that signals are correctly received by a receiver and meeting a predetermined signal-to-noise ratio.

According to one embodiment, the method further comprises a step of transmitting further signals to the receiver according to the previous control signal if the previous signal was correctly received.

Once the correct parameters for the transmission have been established, they may be kept as long as necessary.

According to one embodiment, the step of adapting the control signal implies incrementing or decrementing a bias voltage supplied to the oscillator.

The method thus allows the optimum bias voltage to be converged upon.

According to one embodiment, the method further comprises the steps of: determining whether a maximum or minimum emitted power has been reached, and if the maximum or minimum emitted power has been reached, then stopping the procedure.

Once the maximum or minimum emitted power has been reached, it is not worthwhile to continue the transmission process, since the predetermined signal-to-noise ratio threshold will not be met.

Embodiments of the invention also relate to a computer program comprising instructions for implementing the method according to one embodiment of the invention.

Embodiments of the invention also relate to a non-transitory computer-readable medium comprising instructions stored thereon for implementing the method according to one embodiment of the invention.

Embodiments of the invention also relate to a method for determining the power of a transmitted signal substantially as hereinbefore described with reference to, and as shown in Figures 6, 7A, 7B and 8.

Embodiments of the invention also relate to a transmitter for transmitting a signal substantially as hereinbefore described with reference to, and as shown in Figure 3.

BRIEF DESCRIPTION OF THE DRAWINGS

Other particularities and advantages of the invention will also emerge from the following description, illustrated by the accompanying drawings, in which: - Figure 1, previously described, presents a conventional transmitter structure, - Figure 2, previously described, presents a conventional receiver structure, - Figure 3 presents a system comprising a transmitter and a receiver according to one embodiment of the invention, - Figures 4A, 4B are graphs of normalized output power of a transmitted signal according to embodiments of the invention, - Figure 5 is a graph of the signal-to-noise ratio of a detected signal with respect to the normalized power of the transmitted signal, - Figure 6 shows a process of adapting the bias voltage of the transmitter based on the power of the received signal according to one embodiment of the invention, - Figures 7A, 7B are graphs of normalized output power of a transmitted signal before and after the adaptation process of Figure 6, and - Figure 8 is a flow chart of a process of adapting the bias voltage.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In general, the aim of embodiments of the invention is to evaluate the SNR of a detected signal from a received signal with respect to the power of a transmitted unmodulated carrier signal, such that the transmitter may adapt the power of the transmitted signal, in particular to ensure that a minimum signal-to-noise ratio is met.

Figure 3 represents a system 300 comprising a transmitter 400 and a receiver 500 according to embodiments of the invention.

The transmitter 400 comprises an oscillator 410, a direct current DC voltage source 420, a modulator 430, an adder 440, a computing module 450, and a communication interface 460 (for example a radio communication module, such as a Near Field Communication or NFC module).

The oscillator 410 is configured to emit an oscillating signal, the power of which depends on a bias voltage BV. In some embodiments, the oscillator may be a resonant-tunneling-diode or RTD capable of oscillating in the terahertz THz range. For the sake of simplicity only, in the following reference will be made to an RTD.

The direct current voltage source 420 receives on input a control signal CS1 from the computing module 450 and supplies on output a voltage VA, relating to the power of a carrier signal to be transmitted, and causing the RTD to oscillate even when no modulation is present. The modulator 430 receives on input the input data DT and a control signal CS2 from the computing module 450. The modulator 430 supplies on output a modulation voltage ± VB (with respect to the control signal CS2) relating to the data, for example + VB for logic value T and - VB for logic value O’, according to convention. The determination of the control signals CS1, CS2 will be described in further detail with respect to equation 4 (described in further detail below), by the computing module 450 applying equation 4 and using tables equivalent to the curve shown in Figure 4A, look-up tables comprising VA and VB values pre-computed for all possibilities, or hardware computing. The control signals CS1, CS2 are determined based on information received from the communication interface 460.

The voltages VA, VB are combined by the adder 440 to generate the bias voltage BV supplied to the RTD, which oscillates and generates a radio frequency signal for transmission by means of an antenna (not shown), the power of the transmitted signal TS depending on the bias voltage BV. The antenna may be directly coupled to the oscillator 410 in the case of an RTD or by electromagnetic coupling in other cases. The transmitted signal TS itself cannot be amplified, thus the power of the transmitted signal depends on the outputs of the DC source 420 and the modulator 430.

The transmitter 400 may further comprise a filter comprising a resistor and an inductor in series and in parallel with the RTD, configured to supress parasitic oscillations of the RTD.

The transmitted signal TS is defined as follows: TS = (C+M(t)) * cos(oop*t) [equation 1] wherein C is the amplitude [Volts] of the carrier signal, M(t) is the amplitude modulation [Volts] with an unsuppressed carrier signal, ωρ is the wavelength expressed as 2*ττ*ίρ, fp being the frequency of the carrier signal.

The receiver 500 comprises a detector 510, a communication interface 520, a demodulator 530, and an optional power measurement module 540 (shown in dashed lines), depending on whether or not the receiver 500 is configured to determine the power of the received signal.

The detector 510 processes the received signal RS as described below and outputs a baseband signal BBS which is then demodulated by the demodulator 530. The demodulator 530 supplies on output the data DT for the purposes of the receiver.

The detector 510 used in the receiver 500 works as a quadratic detector, and also supplies a detected signal DS: DS = n*(Sc(t)+Sm(t))A2 [equation 2] = n*(C+M(t))A2 * (cos (ωρ*ί))Λ2 [equation 2a] = n*(CA2+M(t)A2+2C*M(t))*((1+cos(2oop*t))/2) [equation 2b] = (1/2) * (n*(CA2+M(t)A2+2C*M(t))+(CA2+M(t)A2+2C*M(t))*((cos(2ujp*t))/2)) [equation 2c] wherein n is the sensitivity [Volt/Watt] of the receiver.

The second component (CA2+M(t)A2+2C*M(t)) of the equation 2c modulates a very high frequency signal since it is twice the carrier frequency. This second component is not necessary for the detection of the data, and is generally removed by means of a filter (not shown), such that only frequencies below the carrier frequency are retained, and only the first component (1/2 n*(CA2+M(t)A2+2C*M(t))) of equation 2c remains.

The detected signal, after filtering, becomes: DS = (n*CA2)/2 + n*(M(t)A2)/2 + n*C*M(t) [equation 3]

The first term (n*CA2)/2 is a DC signal, and the second term n* (M(t)A2)/2 is a signal whose frequency depends on the type of modulation signal M(t). When the modulation is of the 2-ASK type, the second term becomes a DC signal, such that if M(t) = +/- B, then the squared term M(t)A2 = BA2.

The third term (n*C*M(t)) is the modulation signal M(t) multiplied by a factor (n*C) that varies with the amplitude of the carrier signal and the sensitivity of the receiver.

If the transmitter uses a modulation signal M(t) such that M(t)A2 is constant (thus of the BPSK or 2ASK type), and the receiver has another filter removing the DC component, only the last component remains, such that: BBS = n*C*M(t). [equation 3.1]

If the receiver 500 is configured to determine the power of the received signal RS, the power measurement module 540 also receives the signal RS (dashed arrow) and computes the power of the signal when there is no modulation of the carrier signal. The power measurement module 540 then supplies on output to the communication interface 520 either simply a value relating to the power of the received signal (if it is unable to apply equation 4 below), or else the values A, VA, VB by application of equation 4. The communication interface 520 then sends information concerning the received signal RSI (“received signal information”), which may include the power of the received signal RS or the values A, VA, VB (the parameters of the transmitter 400), to the transmitter 400 by means of the communication link LNK.

If the receiver 500 is not configured to determine the power of the received signal, then simply the correct reception of the signal, such as an acknowledgement message ACK, is communicated to the transmitter 400 by means of the communication link LNK.

As a first example, the acknowledgement ACK may be generated once a signal has been generated by the demodulator.

As a second example, the acknowledgement ACK may be generated once a signal has been generated by the detector as illustrated in Figure 3.

The communication link LNK may be for example communication interfaces of the NFC (Near Field Communication) type, WiFi or any other wireless type.

For BPSK (Binary phase-shift keying), the relationship between the bit error ratio (BER) and the signal-to-noise ratio SNR is theoretically defined. The measure of the SNR of a signal once detected provides the theoretical BER achievable, and when a specific BER value is desired, it defines the required minimum value of the SNR.

In practice, the SNR of the detected signal is estimated from the received signal, for example by the power measurement module 540 or by the computing module 450.

Figure 4A is a plot of the power P of the transmitted signal TS normalized from 0 to 1 on the y-axis, versus the bias voltage BV on the x-axis for the oscillator 410 at an oscillation at 350 GHz. It may be seen that the output power OP with respect to the bias voltage BV forms a bell-like curve. The value VA corresponds to the DC voltage supplied by the DC source 420, and the values -VB, +VB correspond to the modulation by the modulator 430 around the voltage VA, providing a voltage range AV between VA-VB, VA, and VA+VB, corresponding respectively to a lower power value A-B, a median power value A, and an upper power value A+B.

The maximum power Pmax corresponds to a normalized value of 1, and in reality depends on the design and fabrication of the RTD, such that it cannot be varied. It should be noted here that the difference between for example A+B and A is not necessarily equal to the difference between VA+VB and VA, though the same terms {A} and {B} are used. These terms are merely used for convenience, to illustrate the relationship between the range of bias voltages and the range of power. As the curve OP is not strictly linear, the difference between A+B and A is not equal to the difference between A and A-B.

The power of the received signal P(RS) depends on the bias voltage parameters as a proportion of the maximum power, that is to say P(RS) = A (+0, +B, or -B) * Pmax. Consequently, the power of the transmitted signal TS and consequently of the received signal RS depends on the selection of the values VA, VB with respect to the maximum power Pmax. A value of 0.4 on the y-axis corresponds to a bias voltage BV of approximately VA = 1.46 V. To obtain a null transmitted power (zero on the y-axis), a value of VB = 0.06 V is necessary with respect to the graph shown, providing a voltage range AV of approximately 1.40 V to 1.52 V, and a corresponding power range of 0 (A- B) to 0.9 (A+B).

Figure 4B is a variation of the plot of Figure 4A showing two possibilities for the median power values A. In order to limit the error during the demodulation process, the range AV provided by the bias voltages should be maximized. Two possibilities are available: 1) If A is less than or equal to 0.5, then B should be set equal to A, and 2) If A is greater than 0.5, then B should be set to (1 - A).

To clarify, these two cases are respectively shown in Figure 4B, the first wherein A1 is set to 0.30, and the second wherein A2 is set to 0.60. In the first case, B1 can only be a maximum of 0.30 (= A1), since a value greater than A1 would lead to (A - B) being less than 0. In the second case, B2 should be no more than 0.40 (= 1 - 0.60), since a greater value would lead to (A+B) passing to the right half of the curve, where the transmitted power begins to decrease again.

Now, the SNR at the output of the detector is equal to the power P(DS) of the detected signal DS divided by the noise power. More particularly, it may be defined as follows: SNR = P(BBS)/Pnoise = (A*B*(Pmax/PL)A2)/(NEPA2*BW) [equation 4] wherein A is the power of the carrier signal (normalized), B is the power of the modulated signal (normalized), Pmax is maximum transmitted power of the transmitter [-10 dBm], PL is the path loss (which varies according to system parameters and transmission conditions), NEP is the Noise Equivalent Power of the detector [W/sqrt(Hz)], and BW is the bandwidth [20 GHz],

For the two cases 1) and 2) above, equation 4 may be expressed as follows: for A < 0.5, such that B = A being substituted for B in equation 4, then: SNR1 = ((AA2 * (Pmax/PL)A2) / (NEPA2 * BW) [equation 4.1] otherwise, for A > 0.5, such that B = 1 - A being substituted for B in equation 4, then: SNR2 = ((A * (1-A) * (Pmax/PL)A2) / (NEPA2 * BW) [equation 4.2]

If the transmitted power and the received power are known, the path loss PL can be deduced from the measurement of the received power without modulation. The values of A and B can then be determined, and thus the values VA, VB. The control signals CS1, CS2 are adapted accordingly.

Figure 5 shows a graph of the SNR (y-axis) of the detected signal by the receiver versus the normalized power P of the transmitted signal TS, by implementation of the above equations 4.1, 4.2, to obtain a curve SNR = f(A). An SNR threshold value SNRth is defined, based on the well-known relationship between the BER and the SNR, such that for an expected BER, a required minimum SNR may be determined.

This graph has been determined according to an embodiment of the invention, based on the equation 4.

In general, the power of the transmitted signal may be increased to maximize the SNR of the detected signal, but it may be noted here that the SNR of the detected signal does not increase with the power of the transmitted signal over the entire range of the power. Instead, the SNR peaks at a certain power, here termed Apeak. The intersection of the threshold value SNRth and the curve provides a working zone WZ with a lower value Amin and an upper value Amax. The working zone thus provides the values of A (between Amin and Amax) available to guarantee that the SNR is greater than the threshold SNRth.

In practice, A is chosen to be between Amin and Apeak. The selection of A close to the value Apeak will provide the maximum SNR available for the chosen BER value, but with the drawback of increased power consumption by the transmitter and an emitted power that may disturb other communication systems. Likewise, a value between Apeak and Amax would provide no benefit due to increased power consumption.

Thus, if A is chosen to be Amin or slightly greater than Amin, the SNR value is greater than the threshold SNRth and thus meets the system requirements, but with a power consumption as low as possible while still meeting the system requirements. In the illustrated case, A may be chosen to be equal to 0.4.

Figure 6 shows a process of adapting the bias voltage of a transmitter based on the power of the transmitted signal, according to one embodiment. More particularly, the VA and VB values are adapted depending on the transmission conditions between the transmitter 400 and the receiver 500 of Figure 3.

At time to the transmitter 400 begins transmitting an unmodulated carrier signal. At time t1, the receiver 500 sends information to the transmitter 400 concerning the power of the received signal RS by means of the link LNK. The path loss PL may be calculated therefrom and since the other parameters (NEP, bandwidth BW, maximum power Pmax, threshold SNRth) are known, the bias voltages VA and VB may be determined as described above.

As shown in Figure 7A, the transmitter 400 is initially set with VA = 1.48 Volts, and VB = ± 0.3 Volts, providing a transmitted signal TS with a normalized power varying between approximately 0.25 and 0.85. At time t2, the transmitter 400 begins transmitting a modulated carrier signal comprising data, modulated between +0.50 and +1.50.

After a certain period of time, upon prompting by the receiver, or before each transmission, it may be desirable or necessary to re-measure the power of the received signal and modify the settings of VA, VB if necessary in order to maintain the requested SNR and BER values, or if these values should change. Furthermore, the transmission conditions and/or system settings may change, changing the path loss PL. A new computation of equation 4, providing new VA and VB values, is then desirable.

At time tN, the transmitter again transmits an unmodulated carrier signal to the receiver. The transmitted signal now has a weaker power, so the A (and consequently VA) value must be increased. At time tN+1 the receiver provides power feedback to the transmitter, which then adapts values VA and VB accordingly to VA’ and VB’, as may be seen in Figure 7B, for example VA’ = 1.5 Volts, and VB = ± 0.2 Volts, for a transmitted signal with a normalized power varying between approximately 0.60 and 0.95.

At time tN+2, the transmitter applies the new bias values and transmits data to the receiver by means of the modulated carrier signal, modulated between +0.75 and +1.25 for example.

Figure 8 represents a flow chart of a procedure P1 performed by the transmitter for determining a value A to calibrate the transmitter/receiver system 300.

At a step S1, the value of A is set to an initial value Ai, such as Amin. At a step S2, the transmitter sends a modulated carrier signal comprising data and waits for an acknowledgement message ACK from the receiver, for example by means of the link LNK. At a step S3, the transmitter determines whether it has received an acknowledgement ACK. If the response at step S3 is no N, the receiver did not receive the data, and thus did not send the acknowledgement ACK. At a step S4, the transmitter determines whether A is equal to Apeak.

If the response at step S4 is no N, at step S5 the transmitter increases the A value. At a step S6, the transmitter sends another modulated carrier signal comprising data according to the new parameters and waits for an acknowledgement, returning to step S3. This sequence is repeated until an acknowledgement ACK is received.

If however the response at step S4 is yes Y, A is equal to the maximum value Amax, then the process goes to step S7 and stops, since the maximum A value has been reached without successful communication.

If the response at step S3 is yes Y, that is to say the receiver received the data and sent the acknowledgement ACK, then at a step S8 the present settings for A (then VA and VB) are retained. At a step S9, the transmitter transmits more data using the same values. This process may be repeated after a certain amount of time, before each new set of data, or as soon as the receiver stops sending acknowledgements.

The above-described process may be carried out in different manners. For example, instead of the initial value Ai being set to Amin, it may be set to 0 and gradually increased (though several cycles may pass before an acknowledgement is received), or set to a commonly acceptable value as determined from previous communications or a median value, for example 1.45, In this case, the transmitter can target the optimum value by gradual increases and decreases of A with respect to Amin, Apeak, and Amax.

At least parts of the methods according to the invention may be computer implemented. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.

In some embodiments, the detector of the receiver is a plasma wave field effect transistor detector, which has the advantages of being an integrated low-cost solution, eliminating the need to use heterodyne detection circuitry.

Since the present invention can be at least partly implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications which lie within the scope of the present invention will be apparent to a person skilled in the art. Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention as determined by the appended claims. In particular different features from different embodiments may be interchanged, where appropriate.

Claims (28)

1. A transmitter configured to perform wireless communication with a receiver configured to receive a signal from the transmitter, the transmitter comprising: an oscillator configured to supply a first emitted power for the emission of a signal as a function of a control signal; a communication interface to receive data concerning the reception of a previously-transmitted signal emitted with the first emitted power; a computing module configured to determine a control signal such that a signal-to-noise ratio computed from the received signal exceeds a pre-determined signal-to-noise ratio threshold; and means for adapting the control signal as a function of the received data such that the oscillator can supply at least a second emitted power for the emission of a signal.

2. A transmitter according to claim 1, wherein the computing module determines the control signal based on a relation between the signal-to-noise ratio computed from the received signal with respect to the emitted power of the oscillator.

3. The transmitter according to one of claims 1 or 2, wherein the oscillator is a resonant-tunneling-diode.

4. The transmitter according to one of claims 1 to 3, further comprising a control voltage source coupled to the oscillator and configured to adapt at least part of the control signal such that it comprises at least two control voltages, according to the received data.

5. The transmitter according to one of claims 1 to 4, further comprising a modulator configured to supply an alternating signal that modulates the transmitted signal.

6. The transmitter according to claim 5, wherein the modulator is configured to receive a control signal that modifies the alternating signal supplied by the modulator.

7. The transmitter according to claim 1, wherein: the received data is an acknowledgement signal, and the transmitter is further configured to: upon receipt of the acknowledgement signal, transmit further signals according to the first emitted power, and in the absence of the acknowledgement signal, adapt the power of the signal emitted by the oscillator, and transmit further signals with the adapted power.

8. The transmitter according to claim 1, wherein the received data contains information relating to the power of the received signal.

9. The transmitter according to one of claims 1 to 8, wherein the transmitter is further configured to stop the transmission of signals if the power of the transmitted signal exceeds a pre-determined maximum power.

10. The transmitter according to one of claims 1 to 9, further coupled to a memory for storing data relating to the control signals and the signal-to-noise ratios.

11. The transmitter according to one of claims 1 to 10, configured to transmit a signal of at least 100 gigahertz.

12. A receiver configured to perform wireless communication with a transmitter according to any claims 1 to 11, the receiver comprising: an antenna to receive a signal from the transmitter, means for determining the power of the received signal, and a communication interface to send data relating to the determined power of the received signal to the transmitter.

13. The receiver according to claim 12, wherein the sent data is an acknowledgement signal that the transmitted signal has been correctly received.

14. The receiver according to claim 12, wherein the communication interface is a radio communication module configured to perform wireless communication in accordance with near field communication standards.

15. The receiver according to any one of claims 12 to 14, further comprising a detector configured to receive on input the received signal from the antenna and to supply on output a detected signal, and wherein the power of the received signal is used to compute the signal-to-noise ratio of the detected signal.

16. The receiver according to claim 15, wherein the detector is a plasma wave field effect transistor.

17. The receiver according to claim 15, wherein the detector is a quadratic detector.

18. The receiver according to one of claims 15 to 17, further comprising a demodulator configured to demodulate the detected signal.

19. The receiver according to one of claims 12 to 18, further comprising means for providing information calculated from the measured power, so that the communication interface may send the information to the transmitter for determining the control signal.

20. A system comprising a transmitter according to one of claims 1 to 11 and a receiver according to one of claims 12 to 19, the transmitter and the receiver being configured to perform wireless communication with each other.

21. A method of determining a power of transmitted signal by a transmitter according to one of claims 1 to 11, to a receiver according to one of claims 12 to 19 configured to receive the transmitted signal, the method comprising the steps of: supplying, by the transmitter, a first emitted power as a function of a first control signal; receiving, by a communication interface of the transmitter, data concerning the reception of a previously-transmitted signal emitted with the first emitted power; determining, by means of the received data, whether the signal was correctly received; and if the signal was not correctly received, then: - determining, by means of a computing module of the transmitter, a control signal such that a signal-to-noise ratio computed from the received signal exceeds a pre-determined signal-to-noise ratio threshold; and - adapting, by the transmitter, the control signal as a function of the received data such that the oscillator can supply at least a second emitted power for the emission of a signal.

22. The method according to claim 21, further comprising a step of transmitting further signals to the receiver according to the previous control signal if the previous signal was correctly received.

23. The method according to claim 21, wherein the step of adapting the control signal implies incrementing or decrementing a bias voltage supplied to the oscillator.

24. The method according to claim 23, further comprising the steps of: determining whether a maximum or minimum emitted power has been reached, and if the maximum or minimum emitted power has been reached, then stopping the procedure.

25. A computer program comprising instructions for implementing the method according to one of claims 21 to 24.

26. A non-transitory computer-readable medium comprising instructions stored thereon for implementing the method according to one of claims 21 to 24.

27. A method for determining the power of a transmitted signal substantially as hereinbefore described with reference to, and as shown in Figures 6, 7A, 7B and 8.

28. A transmitter for transmitting a signal substantially as hereinbefore described with reference to, and as shown in Figure 3.