FR2990321A1 - Device for transmitting and/or receiving radio frequency for cognitive radio system, has set of mixing stages mixing filtered signal from band pass filter with local oscillator frequency signal and delivering output frequency signal - Google Patents

Abstract

The invention relates to a device for transmitting and / or receiving radiofrequency signals comprising three local oscillators (20, 24, 28) for digitally controlling the filtering and frequency transposition of the device. This transmitting and / or receiving device is particularly suitable for cognitive radio systems.

Description

Technical Field The present invention is in the field of cognitive radio. The invention more particularly relates to a device for receiving and / or transmitting radio frequency signals in accordance with different communication standards operating more particularly, although not exclusively, in the frequency band corresponding to the zones of the unlicensed digital dividend.

STATE OF THE ART The ever-increasing demand for new wireless applications accentuates the problem of the availability of frequencies for the implementation of these applications. The recent shift from analog to digital television has freed frequency ranges, called the digital dividend, for these applications. Some frequency areas of this digital dividend have been reallocated and licensed for specific applications. The remaining areas, commonly referred to as "white space" in English, mainly located in the UHF band, have been left unrestricted for other applications as long as they do not generate interference in the licensed frequency bands. It is envisaged to use these "white space" areas for applications in the field of wireless communications and mobile networks, for example for WiFi, Wimax or LTE applications (for Long Term Evolution in English). However, this requires having a very agile "universal" cognitive radio terminal capable of dynamically addressing any standard according to customer needs. In particular, this terminal must be capable of receiving or transmitting radio frequency signals in any transmission channel meeting these standards, each transmission channel being defined by its central frequency and its bandwidth. The terminal must therefore be able to stall, in transmission and / or reception, on any transmission channel in the frequency band corresponding to the "white space".

SUMMARY OF THE INVENTION An object of the invention is to propose a universal transmission or reception device able to transmit or receive dynamically the radio frequency signals coming from different standards, such as for example WiFi, Wimax or LTE. The invention proposes a transmission device and a radiofrequency signal receiving device based on a simple architecture employing three local oscillators digitally controlled by a control circuit.

More particularly, the invention relates to a receiving device adapted to selectively receive signals according to different communication standards comprising a front circuit for receiving a radio frequency signal in accordance with a communication standard among a plurality of communication standards, said radio frequency signal being present in a transmission channel having a center frequency Fc and a channel width Bc, and a radio frequency circuit for filtering said transmission channel and transposing the radio frequency signal contained in said transmission channel at a foot output frequency less than said center frequency . It further comprises a control circuit for digitally controlling the radio frequency circuit and in that the radio frequency circuit comprises: - a first mixer stage for mixing the radio frequency signal with a local oscillator signal of frequency LO1 and delivering a first intermediate signal, said frequency LO1 being selected by the control circuit, a first band-pass filter of central frequency Fo and of bandwidth Bo for filtering the first intermediate signal, a second stage mixer for mixing the signal from the first pass filter. band with a local oscillator signal of frequency L02 and delivering a second intermediate signal, said frequency L02 being selected by the control circuit, - a second bandpass filter substantially identical to the first bandpass filter for filtering the second intermediate signal , and - a third mixer stage for mixing the signal from u second band-pass filter with a local oscillator signal of frequency L03 and output the frequency output signal Fout, said frequency L03 being selected by the control circuit. The two bandpass filters and the second mixer stage constitute an active bandpass filter whose bandwidth and center frequency can be adjusted numerically by acting on the frequency L02. This gives a simple reception architecture that can be controlled numerically. The filtering and the frequency translation of the radio frequency signal are performed numerically by appropriately controlling the frequencies L01, L02 and L03 delivered by local oscillators.

According to one embodiment, the control circuit selects the frequencies L01, L02 and L03 of one of the following frequency groups: LO2 = 2 x Fo + (B-Bo) - LO1 = Fo + L02 / 2 LO3 = 1L01 - L021 + Fo + Fout LO2 = 2 x Fo + (B - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo - Fout ILO2 = 2x Fo - (Bu - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo + Fout LO2 = 2x Fo - (Bu - Bo) - LO1 = Fo + L02 / 2. L03 = 1L01- L021 + Fo - Fout The different groups of frequencies are advantageously pre-calculated and stored in one or more tables to consult ("look up tables" or LUTs in the English terminology).

The receiving device further comprising a demodulator for demodulating the output signal, the control circuit advantageously selects one of the frequency groups based on information from the demodulator.

According to a preferred embodiment, the control circuit selects one of the frequency groups as a function of the quantity of disturbing signals generated, in the bandwidth of the radiofrequency signal transmission channel, by the mixing operations performed by the circuit. radio frequency.

According to a particular embodiment, the bandpass filters are surface acoustic wave filters. The invention also relates to a transmission device capable of selectively transmitting signals conforming to different communication standards comprising a radio frequency circuit capable of generating from a baseband signal a radiofrequency signal conforming to a communication standard, said radiofrequency signal being transmitted in a transmission channel having a center frequency Fc and a channel width Bc, and a front circuit for transmitting said radio frequency signal in said transmission channel. The device further comprises a control circuit for digitally controlling the radio frequency circuit and the radio frequency circuit comprises: - a first mixer stage for mixing the baseband signal with the local oscillator signal of frequency L03 and delivering a first intermediate signal , said frequency L03 being selected by the control circuit, - a first band-pass filter of central frequency Fo and of bandwidth Bo for filtering the first intermediate signal, - a second stage mixer for mixing the signal from the first pass filter -band with a local oscillator signal of frequency L02 and deliver a second intermediate signal, said frequency L02 being selected by the control circuit, - a second bandpass filter substantially identical to the first bandpass filter for filtering the second signal intermediate, and - a third mixer stage for mixing the signal from of the second bandpass filter with a local oscillator signal of frequency LO1 and outputting the radiofrequency signal, said frequency LO1 being selected by the control circuit. According to one embodiment, the control circuit selects the frequencies L01, L02 and L03 of one of the following frequency groups: LO2 = 2 x Fo + (B-Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo + Fout LO2 = 2x Fo + (B - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo - Fout ILO2 = 2x Fo - (Bu - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01-L021 + Fo + Fout ILO2 = 2x Fo - (Bu-Bo) advantageously pre- - LO1 = Fo + L02 / 2 also has a L03 = 1L01-L021 + Fo - Fout The different frequency groups are calculated and stored in one or more LUTs.

According to one embodiment, the modulator device generating the baseband signal and the control circuit selects one of the frequency groups based on information from the modulator. According to a preferred embodiment, the control circuit selects one of the frequency groups as a function of the quantity of disturbing signals generated, in the bandwidth of the radiofrequency signal transmission channel, by the mixing operations performed by the circuit. radio frequency.

Furthermore, the bandpass filters are advantageously surface acoustic wave filters. Finally, the invention also relates to a cognitive radio terminal capable of transmitting and receiving radiofrequency signals conforming to a plurality of communication standards, comprising a device for receiving said radio frequency signals and a device for transmitting said radio frequency signals as defined above. . BRIEF DESCRIPTION OF THE FIGURES Other advantages may still be apparent to those skilled in the art on reading the examples below, illustrated by the appended figures, given by way of illustration: FIG. 1 represents a schematic diagram of a terminal of cognitive radio according to the invention; FIG. 2 represents diagrams illustrating the transformation of WiFi, Wimax and LTE radiofrequency signals into baseband signals; FIG. 3 is a diagram illustrating the operating characteristics of the active bandpass filter of the terminal of FIG. 1, and FIG. 4 is a flowchart detailing a process for selecting the frequencies of the local oscillators of the terminal of FIG. it operates in receive mode. DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT FIG. 1 illustrates a cognitive radio terminal capable of receiving and transmitting radio frequency signals in transmission channels having a channel width Bc and a center frequency Fc that can be dynamically and numerically adjusted by a circuit in a given frequency band, in particular the "white space".

With reference to FIG. 1, the terminal comprises a front circuit 1 for transmitting and / or receiving a radiofrequency signal in accordance with a given communication standard, for example for WiFi, Wimax or LTE (or 3GPP), a radio frequency circuit 2 for filtering and frequency transposing the signals received or to be transmitted by the front circuit and a signal processing block 3 comprising in particular a control circuit 30. In these communication standards, the RF signals are transmitted in transmission channels having different channel widths and center frequencies. The channel width is for example 20 or 40 MHz in the case of WiFi, 1.25, 2.5, 5, 10, 15 or 20 MHz in the case of LTE and 3.5, 5, 7 or 10 MHz in the case of Wimax The function of the terminal of the invention is to be able, in reception, to receive selectively and dynamically the RF signals of the transmission channels of these standards, to filter them and to transpose them at a frequency of lower output and emission to do the opposite as shown in fig.2. This figure illustrates the baseband transposition of radio frequency signals according to WiFi 20M, 3GPP, WiMax and WiFi 40M standards. We will first describe the terminal as a radiofrequency signal receiving device and then as a radiofrequency signal transmitting device Receiving radio frequency signals In reception, the terminal has the function of receiving radiofrequency signals present in a transmission channel given, filtering and transposing them to baseband or to a non-zero intermediate frequency. For the sake of simplicity, only the case of a baseband transposition of the signals received by the terminal will be dealt with here. The present description can be transposed by analogy to the case where the received signals are transposed at an intermediate frequency. For reception, the front circuit 1 comprises a low noise amplifier 10 whose input is connected to an antenna for both transmission and reception.

The radio frequency circuit 2 comprises a first local oscillator 20 delivering a frequency signal LO1 to a mixer 21a. A first input of the mixer 21a is connected to the output of the low noise amplifier 10 via a frequency-adjustable low pass filter 22a and a second input of the mixer 21a is connected to the output of the local oscillator 20. The mixer 21a delivers at its output the result of mixing between the radiofrequency signal delivered by the filter 22a and the frequency signal LO1 delivered by the local oscillator 20. The local oscillator 20 is frequency-controlled by a control signal CmdLaw issued by the control circuit 30 of the processing block 3. The output of the mixer 21a is connected via a switch Si to an active bandpass filter F. The switch Si has two positions, namely a reception position and a transmission position. The output of the mixer 21a is connected to the active bandpass filter F when the switch Si is in the receiving position. The active bandpass filter F comprises a bandpass filter 23 of central frequency Fo and of bandwidth Bo for filtering the intermediate signal delivered by the mixer 21a, a local oscillator 24 adjustable in frequency delivering a local oscillator signal of frequency L02, a mixer 25 for mixing the signal from the bandpass filter 23 with the local oscillator signal of frequency L02 and a bandpass filter 26 substantially identical to the bandpass filter 23 for filtering the signal delivered by the mixer 25.

The input of the bandpass filter 23 is connected via the switch S1 to the output of the mixer 21a. The output of the bandpass filter 23 is connected to a first input of the mixer 25. The output of the local oscillator 24 is connected to a second input of the mixer 25. Finally, the output of the mixer is connected to the input of the filter The frequency L02 is selected by the control circuit 30 via a control signal CmcIL02. The operation of the active bandpass filter is described below with reference to FIG. The center frequency and the resulting bandwidth of the active bandpass filter are controlled by the frequency L02 of the signal delivered by the local oscillator 24. This frequency is controlled by the control signal CmcIL02 delivered by the control circuit 30.

FIG. 3 illustrates the central frequency and the resulting bandwidth of the filter F as a function of the frequency L02 of the local oscillator 24. In this figure, it is considered that the filters 23 and 26 have a central frequency Fo equal to 500 MHz and a 40 MHz bandwidth. As can be seen in this figure, the resulting bandwidth of the filter F is maximum (40 Mhz) when the frequency L02 is equal to 2 times the central frequency Fo. When the frequency L02 is lower or higher than this value, the resulting bandwidth of the filter F decreases. It may be noted that, to obtain a given bandwidth for the bandpass filter, two L02 frequency values are possible. As will be explained later, the L02 frequency value generating the least possible interference signal will advantageously be selected. Referring again to FIG. 1, the radio frequency circuit 2 also comprises a frequency-adjustable local oscillator 28 delivering a local oscillator signal of frequency L03 and a mixer 27a for mixing the signal coming from the band-pass filter 26 with the local oscillator signal of frequency L03 and deliver the component I (in phase) of the baseband signal. Another mixer 27a 'and a phase shifter circuit 29 are also provided to generate the Q component (in quadrature phase) of the baseband signal. The phase-shifting circuit 29 has the function of phase-shifting the signal delivered by the local oscillator 28 by 90 ° and the mixer 27a mixes the signal coming from the filter 26 and the phase-shifted signal delivered by the phase-shifting circuit 29. The frequency L03 is selected by the control circuit 30 via a control signal CmdLo3. The I and Q components of the baseband signal are then processed by a demodulator 31a. As mentioned above, the radio frequency circuit 2 does not necessarily deliver a baseband signal. It can output an output signal at a non-zero foot output frequency. The radio frequency circuit 2 then has neither mixer 27a 'nor phase shifter 29.

With this device, the filtering and the frequency transposition of the radiofrequency signal are performed numerically through the local oscillators. The bandpass filters 23 and 26 are preferably high rejection filters, for example external filters such as surface acoustic wave filters or Surface Acoustic Wave (SAW) filters. The frequencies L01, L02 and L03 are digitally controlled by the control circuit. Frequency L02 is set first to obtain the desired bandwidth for the active bandpass filter. The frequency LO1 and the frequency L03 are then adjusted as a function of the frequency of the input signal to be received and of the output signal to be delivered. For a desired resulting bandwidth Bc, there are two possible L02 frequencies: L02_1 = 2 x Fo-E (Bc-Bo) and L02_2 = 2 x Fo- (13c-Bo) For each value of L02, there is a possible frequency value LO1, ie L01_1 = Fc-FLO2_1 / 2 and L01_2 = Fc-EL02_2 / 2 And, for each value of L02, there is a value of two possible L03 frequencies: - L03_1 = 11_01_1- L02_11 + Fo + Fout - L03_2 = 11_01_1 - L02_11 + Fo - Fout - L03_3 = 1L01_2- L02_21 + Fo + Fout - L03_4 = 1L01_2- L02_21 + Fo - Fout This amounts to selecting one of the following 4 frequency groups: LO2 = 2 x Fo + (B - Bo) - LO1 = Fo + L02 / 2 LO3 = 1L01- L021 + Fo + Fout LO2 = 2 x Fo + (B - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo - Fout iL02 = 2x Fo - (Bu - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo + Fout LO2 = 2x Fo - (Bu - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo - Fout The circuit 30 selects one of the frequency groups based on information from the demodulator, in particular depending on the quantity spurious signals (or spurious signais in the English terminology) generated in the bandwidth of the radiofrequency signal transmission channel by the mixing operations performed by the radio frequency circuit or disturbances generated by the channels adjacent to the selected channel.

Fig.4 illustrates a process of selecting frequencies L01, L02 and L03. According to a step El, the transmission channel to be received is determined. According to a step E2, a first frequency L02 is selected, among the frequencies L02_1 and L02_2. Then, at a step E3, the frequency LO1 associated with the selected frequency L02 is determined, the frequency L01_1 if the frequency L02_1 has been previously selected, or else the frequency L01_2. According to a step E4, one of the two L03 frequencies associated with the selected frequency L02 is selected. A transposition and filtering step E5 is performed with the device of the invention. At a step E6, the signal obtained with the demodulator 31a is demodulated. At a step E7, the level of disturbers in the demodulated signal is tested. If the level of interference is less than or equal to a predetermined threshold T, the selected frequency values L01, L02 and L03 are retained. Otherwise, it is then tested at a step E8 if it is the first frequency L03 tested among the two possible values. If the level of interference is greater than the threshold T and if the value of L03 is the first value tested among the possible values, the second value of L03 is selected from the two possible values in a step E11. Then steps E5 to E7 are repeated with this new value of the frequency L03. If the level of interference is less than or equal to a predetermined threshold T, the selected frequency values L01, L02 and L03 are retained. Otherwise, it is tested in a step E10 if the selected frequency L02 is the first value tested among the two possible values. If so, the second frequency value L02 is selected at a step El1, the steps E3 to E10 are repeated. If the level of disturbing signals is always greater than the threshold T, the frequencies L01, L02 and L03 generating the least possible disturbing signals are preferably selected. For this, for each of the 4 groups of frequencies, the level of disturbers is stored after determination of the latter and, after having tested the 4 groups, the group generating the least possible disturbers is selected. The operation of the receiving device according to the invention can be illustrated by an example. In this example, it is sought to receive the radio frequency signal present in a transmission channel having a central frequency Fo = 200 MHz and a channel width Bo = 2 MHz. The frequency of the output signal Fout is equal to 0 (baseband). The bandpass filters 23 and 26 have a center frequency Fo = 500 MHz and a bandwidth Bo = 40 MHz. The frequencies of one of the following groups are then selected as a function of the level of the disturbing signals: LO2 = 962 MHz LO2 = 1038 MHz LO1 = 681 MHz LO1 = 719 MHz LO3 = 481 MHz LO3 = 519 MHz Indeed, since the frequency Fout is zero, only two possible groups remain. Transmission of radio frequency signals In transmission, the terminal has the function of transforming signals into baseband for transmitting them in a given transmission channel. The same elements of the radio frequency circuit can be reused to generate the radiofrequency signal. In FIG. 1, only certain elements are used for both transmission and reception, namely the local oscillators 20 and 28, the active bandpass filter F and the phase-shifter 29.

A baseband signal is generated by a modulator 31b. The component I of the baseband signal is mixed by a mixer 27b with a frequency signal L03 supplied by the local oscillator 28. The component Q of the baseband signal is mixed by a mixer 27b 'with a frequency signal The two signals are then filtered by the active band-pass filter F. The filtered signal is then mixed by a mixer 21b with a frequency signal LO1 supplied by the local oscillator 21. signal delivered by the mixer 21b is then filtered by a low-pass filter 22b and amplified by a power amplifier 11 before being supplied to the terminal antenna. During transmission, the switches S1 and S2 are in the transmit position. For the transmission, the frequencies L01, L02 and L03 are selected as for the reception For the sake of simplicity, only the case of a baseband transposition of the radiofrequency signals received by the terminal has been dealt with here. But of course, the present description can be transposed by analogy to the case where the received signals are transposed at an intermediate frequency.

Claims (11)

CLAIMS1) Receiving device adapted to selectively receive radio frequency signals in accordance with different communication standards comprising: - a front circuit (1) for receiving a radio frequency signal in accordance with a communication standard from among a plurality of communication standards, said radiofrequency signal being present in a transmission channel having a center frequency Fc and a channel width Bc; - a radio frequency circuit (2) for filtering said transmission channel and transposing the radiofrequency signal contained in said transmission channel at a lower output frequency Fout at said central frequency, characterized in that it further comprises a control circuit (30) for digitally controlling the radio frequency circuit and that the radio frequency circuit comprises: - a first mixer stage (21a, 20) for mixing the radio frequency signal with a local oscillator signal of fr equation LO1 and outputting a first intermediate signal, said frequency LO1 being selected by the control circuit, - a first bandpass filter (23) of central frequency Fo and of bandwidth Bo for filtering the first intermediate signal, - a second mixer stage (24, 25) for mixing the signal from the first bandpass filter with a local oscillator signal of frequency L02 and outputting a second intermediate signal, said frequency L02 being selected by the control circuit, - a second bandpass filter (26) substantially identical to the first bandpass filter for filtering the second intermediate signal; and - a third mixer stage (27a, 27a ', 28, 29) for mixing the signal from the second pass filter. band with a local oscillator signal of frequency L03 and output the frequency output signal Fout, said frequency L03 being selected by the control circuit. 2) Device according to claim 1, characterized in that the control circuit selects the frequencies L01, L02 and L03 of one of the following frequency groups: LO2 = 2 x Fo + (B -B0) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo + Fout LO2 = 2 x Fo + (B - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo - Fout ILO2 = 2 x Fo - (Bu - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo + Fout iL02 = 2 x Fo - (Bu - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01-L021 + Fo - Fout 3) Device according to claim 2, characterized in that it further comprises a demodulator (31a) of the output signal and in that the control circuit (30) selects one of the frequency groups according to information from the demodulator. 4) Device according to claim 3, wherein the control circuit (30) selects one of the frequency groups as a function of the amount of disturbing signals generated, in the bandwidth of the radiofrequency signal transmission channel, by the operations mixing done by the radio frequency circuit. 5) Device according to any one of claims 1 to 4, characterized in that said first and second bandpass filters (23,26) are surface acoustic wave filters. 6) Transmission device capable of selectively transmitting radio frequency signals in accordance with different communication standards comprising: a radio frequency circuit (2) capable of generating from a baseband signal a radiofrequency signal conforming to a communication standard, said signal radiofrequency being to be transmitted in a transmission channel having a central frequency Fc and a channel width Bc; - a front circuit (1) for transmitting said radio frequency signal in said transmission channel, characterized in that it further comprises a circuit control unit (30) for digitally controlling the radio frequency circuit and in that the radio frequency circuit comprises: - a first mixer stage (27b, 27b ', 28, 29) for mixing the baseband signal with a local oscillator signal of frequency L03 and deliver a first intermediate signal, said frequency L03 being selected by the control circuit; a first bandpass filter (26) of central frequency Fo and bandwidth Bo for filtering the first intermediate signal, - a second stage mixer (24, 25) for mixing the signal from the first bandpass filter with a signal local frequency oscillator L02 and deliver a second intermediate signal, said frequency L02 being selected by the control circuit, - a second bandpass filter (23) substantially identical to the first bandpass filter for filtering the second intermediate signal, and a third mixer stage (21b, 20) for mixing the signal from the second bandpass filter with a local oscillator signal of frequency LO1 and delivering the radio frequency signal, said frequency LO1 being selected by the control circuit. 7) Device according to claim 6, characterized in that the control circuit selects the frequencies L01, L02 and L03 of one of the following frequency groups: LO2 = 2 x Fo + (B-Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo + Fout ILO2 = 2 x Fo + (B - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01 - L021 + Fo - Fout ILO2 = 2 x Fo - (Bu - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01-L021 + Fo + Fout iL02 = 2 x Fo - (Bu - Bo) - LO1 = Fo + L02 / 2 L03 = 1L01-L021 + Fo - Fout 8) Device according to claim 7, characterized in that it further comprises a modulator generating the baseband signal and in that the control circuit selects one of the frequency groups according to information from the modulator . 9) Device according to claim 8, wherein the control circuit selects one of the frequency groups as a function of the amount of disturbing signals generated, in the bandwidth of the radiofrequency signal transmission channel, by the mixing operations carried out. by the radiofrequency circuit. 10) Device according to any one of claims 6 to 9, characterized in that said first and second bandpass filters are surface acoustic wave filters. 11) A cognitive radio terminal capable of transmitting and receiving radiofrequency signals in accordance with a plurality of communication standards, comprising a device for receiving said radio frequency signals and a device for transmitting said radio frequency signals, characterized in that the reception device is in conformity with in any one of claims 1 to 5 and in that the transmitting device is in accordance with any one of claims 6 to 10.5