Method and Arrangement for Transmitting and Receiving RF Signals Through Various Radio Interfaces of Communication Systems

Abstract

A method and arrangement for transmitting and receiving RF signals, associated with different radio interfaces of communication systems, employ a direct conversion based transceiver which substantially comprises one receive signal branch and one transmit signal branch. Mixing frequencies of the different systems are generated by a single common by use of an output frequency divider in combination with the synthesizer, and by use of filtering corresponding to a system channel bandwidth by means of a controllable low-pass filter operating at baseband frequency.

Claims

1. A direct-conversion transceiver configured for a plurality of radio interfaces, comprising: a low-noise amplifier of the direct conversion transceiver configured to amplify the filtered received signal according to a first gain control signal that controls an amount of gain, wherein the low-noise amplifier has a signal path common to the plurality of radio interfaces; a first programmable synthesizer of the direct conversion transceiver configured to generate a first mixing signal according to a first mixing control signal corresponding to the selected one of the plurality of radio interfaces, wherein the first programmable synthesizer has a signal path common to the plurality of radio interfaces; a first frequency divider of the direct conversion transceiver coupled to the first programmable synthesizer and configured to divide a frequency of the first mixing signal by at least two to provide a first divided frequency signal according to a first divider control signal corresponding to the selected one of the plurality of radio interfaces; a first mixer of the direct conversion transceiver coupled to the low-noise amplifier and configured to mix the amplified and filtered received signal with the first divided mixing signal to produce a first baseband quadrature signal, wherein the first mixer has a signal path common to the plurality of radio interfaces and wherein the first mixer produces the first baseband quadrature signal on a basis of two 90-degree phase-shifted components produced from the first frequency divider; a first low-pass filter of the direct conversion transceiver coupled to the first mixer and configured to low-pass filter the first baseband quadrature signal according to a first filter control signal corresponding to the selected one of the plurality of radio interfaces, wherein the first low-pass filter has a signal path common to the plurality of radio interfaces; a first gain-controlled amplifier of the direct conversion transceiver coupled to the first low-pass filter and configured to provide gain-controlled amplification of the first low-pass filtered baseband quadrature signal, wherein the first gain-controlled amplifier has a signal path common to the plurality of radio interfaces; an analog-to-digital converter of the direct conversion transceiver coupled to the first gain-controlled amplifier and configured to convert to digital form an output of the first gain-controlled amplifier; a digital signal processor of the direct conversion transceiver configured to receive digital output from the analog-to-digital converter and to further process said digital output; a digital-to-analog converter of the direct conversion transceiver coupled to the digital signal processor and configured to receive a second baseband quadrature signal therefrom and to provide analog output signals; a second low-pass filter of the direct conversion transceiver coupled to the digital-to-analog converter and configured to low-pass filter the analog output signals from the digital-to-analog converter according to a second filter control signal corresponding to the selected one of the plurality of radio interfaces, wherein the second low-pass filter has a signal path common to the plurality of radio interfaces; a second programmable synthesizer of the direct conversion transceiver configured to generate a second mixing signal according to a second mixing control signal corresponding to the selected one of the plurality of radio interfaces, wherein the second programmable synthesizer has a signal path common to the plurality of radio interfaces; a second frequency divider of the direct conversion transceiver coupled to the second programmable synthesizer and configured to divide a frequency of the second mixing signal by at least two to provide a second divided frequency signal according to a second divider control signal corresponding to the selected one of the plurality of radio interfaces; a second mixer of the direct conversion transceiver coupled to the second low-pass filter and configured to mix signals from the second low-pass filter and the second frequency divider to produce a carrier-frequency transmission signal, wherein the second mixer has a signal path common to the plurality of radio interfaces and wherein the second mixer produces the carrier-frequency transmission signal on the basis of two 90-degree phase-shifted components produced from the second frequency divider; a second gain-controlled amplifier of the direct conversion transceiver coupled to the second mixer and configured to control gain according to a second gain control signal corresponding to the selected one of the plurality of radio interfaces, wherein the second gain-controlled amplifier has a signal path common to the plurality of radio interfaces; a power amplifier of the direct conversion transceiver coupled to the second gain-controlled amplifier and configured to produce an amplified output and to respond to a control signal corresponding to the selected one of the plurality of radio interfaces, wherein the power amplifier has a signal path common to the plurality of radio interfaces; and a microprocessor of the direct conversion transceiver configured to generate one or more control signals to cause selection of the selected one of the plurality of radio interfaces, wherein at least one of the plurality of radio interfaces comprises a modulation, a channel spacing, and a channel bit rate that at least one other of the plurality of radio interfaces does not have.

2. The direct conversion transceiver of claim 1 wherein a bandpass filter is common to the plurality of radio interfaces.

Description

[0055] The invention will now be described in more detail with reference to the accompanying drawing wherein

[0056] FIG. 1 shows a block diagram of a dual-band direct-conversion transceiver according to the prior art,

[0057] FIG. 2 shows in the form of block diagram a solution according to the invention for a direct-conversion transceiver operating in multiple systems.

[0058] FIG. 1 was already discussed in conjunction with the description of the prior art. Next, a transceiver according to the invention will be described, referring to FIG. 2.

[0059] FIG. 2 shows in the form of block diagram a transceiver according to the invention. A RF signal received through an antenna is conducted via matching circuits 1 to controllable bandpass filters 2. The matching circuits 1 may advantageously be controllable (AX) with respect to the operating frequency band. A controllable bandpass filter 2 may be advantageously realized using a plurality of bandpass filters so that the RF signal is conducted via switch elements controlled by a control signal FX1 from the matching circuit 1 to the bandpass filter that corresponds to the selected operating frequency band. The bandpass filter may also be realized so as to be adjustable and tuneable by means of programming. The bandpass filtered carrier-frequency signal is further conducted to a low-noise amplifier 4, the gain of which is advantageously controllable. The control signal is marked GX1 in the drawing. In addition to amplifier 4, it is also possible to have integrated amplifiers in connection with the bandpass filters.

[0060] The signal is then conducted to a mixer 5 in which the carrier-frequency signal is mixed with an RX mixing signal at the receive frequency to produce a baseband quadrature signal. The RX mixing signal is advantageously generated by a synthesizer 10 the output signal frequency of which is divided by a divider 11 so as to correspond to the selected receive frequency. The synthesizer 10 operates in a similar manner as the synthesizers depicted in FIG. 1. Thus it comprises a voltage-controlled oscillator VCO which produces an output signal. The frequency of the VCO output signal is divided by S1 in a divider in the phase-locked loop PLL. The resulting signal is conducted to a first input of a phase comparator in the phase-locked loop. Similarly, the frequency of a signal generated by a reference oscillator in the phase-locked loop PLL is divided by an integer and conducted to a second input of the phase comparator. The phase comparator produces a signal which is proportional to the phase difference of the two input signals and conducted to a low-pass filter, and the filtered signal then controls the voltage-controlled oscillator VCO. The output frequency is controlled by varying the divisor S1.

[0061] The synthesizer output signal is divided in divider 11 by N1 so that the RX mixing signal corresponds to the selected receive frequency band. The output frequency of the synthesizer may be e.g. in the 4-GHz band, so that with 2-GHz systems the synthesizer output frequency is divided by two, and with 1-GHz systems it is divided by four (N1). This way, systems operating in the 1-GHz and 2-GHz bands can be covered with a synthesizer the operating frequency band of which is narrow with respect to the operating frequency.

[0062] To produce a quadrature baseband signal the mixer needs two mixing signals with a phase shift of 90 degrees. Phase-shifted components may be produced by a phase shifter in connection with the mixer or they may be produced as quotients generated already in the frequency divider 11, thus achieving an accurate phase difference. Therefore, it is advantageous to use a synthesizer operating frequency which is a multiple of the highest system frequency.

[0063] The in-phase component 1 and quadrature component Q from the mixer 5 are further conducted to low-pass filters 6. The higher cut-off frequency of the low-pass filters is advantageously controllable with control signal FX3. Thus the filtering can be performed at a bandwidth corresponding to the selected radio interface, and since the filtering is performed at baseband, it is easy to get the filtering function steep. Also, no strict demands are set on the bandpass filtering (2) of the RF signal.

[0064] The baseband signal is further conducted to a gain control block 7 which possibly includes an offset voltage correction block. On the other hand, considering the broad bandwidth of the CDMA system, the offset voltage can easily be removed by high-pass filtering. The amplifier advantageously realizes automatic gain control (AGC). Finally, the signal is convened digital in an analog-to-digital converter 8, and the digital baseband signal is further processed in a digital signal processor (DSP) 9. Channel filtering may also be performed digitally in the DSP, whereby the low-pass filtering of the baseband signal may be performed using a fixed cut-off frequency. Then, however, the dynamics of the analog-to-digital converter must be considerably better.

[0065] In the transmitter part, a quadrature baseband signal is first digitally generated in block 9 on the basis of the information signal to be sent. The components of the digital signal are converted analog by digital-to-analog converters 14, whereafter the analog signals are low-pass filtered by low-pass filters 15. Advantageously, the cutoff frequency of the low-pass filters can be controlled with control signal FX4 so as to correspond to the specifications of the selected radio interface.

[0066] A TX mixing signal at the carrier frequency is generated by a synthesizer 13 and divider 12. The synthesizer 13 operates in a similar manner as the synthesizer 10 in the receiver pan. Moreover, the synthesizers may share a reference oscillator. The frequency of the synthesizer output signal is controlled with control signal S2 within the synthesizer's operating frequency range. The frequency of the output signal from synthesizer 13 is divided in divider 12 so as to correspond to the selected transmission frequency band. Components phase-shifted by 90 degrees are generated from the TX mixing signal in order to perform complex mixing in mixer 16. The phase-shifted components may be generated in the same way as in the receiver part.

[0067] The signal at the carrier frequency is then amplified in an amplifier 17, the gain of which is advantageously controllable in order to set the transmission power and realize automatic gain control (AGC). The control signal is marked GX3 in FIG. 2. The signal is then conducted to a power amplifier 18. The operating frequency band of the power amplifier is advantageously selectable with control signal BX. This can be achieved e.g. such that the amplifier comprises partly separate signal lines for the different operating frequency bands.

[0068] The RF signal generated is filtered by a bandpass filter 3. The pass band of the bandpass filter is advantageously controllable with control signal FX2. This can be realized in the same way as in the receiver part. The receiver and transmitter part filters 2 and 3 are advantageously realized in duplex filter pairs for each transmit-receive frequency band associated with a given system. The filters may advantageously be surface acoustic wave (SAW) or bulk acoustic wave (BAW) filters so that several filters with their switches may be attached to one component.

[0069] The control signals in the mobile station transceiver according to FIG. 2 are preferably generated in a control block of the mobile station which advantageously comprises a processing unit such as a microprocessor. The control block generates the signal on the basis of a system switch instruction input from the keypad of the mobile station, for example. System selection may be e.g. menu-based so that the desired system is selected by choosing it from a displayed menu by pressing a certain key on the keypad. The control block then generates the control signals that correspond to the selected system. The system switch instruction may also come via the mobile communication system in such a manner that data received from the system may include a system switch instruction on the basis of which the control block performs the system switch. Advantageously, a control program is stored in a memory unit used by the control block, which control program monitors the received data and, as it detects a system switch instruction in the data, gives the control block an instruction to set the control signals into states according to the selection instruction.

[0070] The implementation of the blocks described above is not illustrated in more detail as the blocks can be realized on the basis of the information disclosed above, applying the usual know-how of a person skilled in the art.

[0071] Above it was described embodiments of the solution according to the invention. Naturally, the principle according to the invention may be modified within the scope of the invention as defined by the claims appended hereto, e.g. as regards implementation details and fields of application. It is especially noteworthy that the solution according to the invention may be well applied to communication systems other than the mobile communication systems mentioned above. Apart from the cellular radio interface proper, the solution may be used to realize e.g. a GPS receiver for the location of a mobile station or other apparatus. Furthermore, the operating frequencies mentioned are given by way of example only, and the implementation of the invention is in no way restricted to them.

[0072] It is also noteworthy that the solution according to the invention may be applied to all current coding techniques such as the narrow-band FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access), as well as the broadband CDMA (Code Division Multiple Access) technique. In addition, the solution according to the invention may be used to realize an FM (Frequency Modulation) receiver.

[0073] Below is a table listing some of the so-called second generation mobile communication systems to which the present invention may be applied. The table shows the most important radio interface related characteristics of the systems.

TABLE-US-00001 DECT PHS GSM Digital Personal Global System PDC European Handy IS-95 US for Mobile Personal Digital Cordless Phone CELLULAR SYSTEM AMPS IS-54/136 CDMA Communications DCS 1800 Cellular Telephone System RX FREQ. (MHz) 869-894 869-894 869-894 935-960 1805-1880 810-826, 1880-1900 1895-1918 1429-1453 TX FREQ. (MHz) 824-849 824-849 824-849 890-915 1710-1785 940-956 1880-1900 1895-1918 1477-1501 RF BANDWIDTH 25 MHz 25 MHz 25 MHz 25 MHz 75 MHz 16 MHz, 24 MHz 20 MHz 23 MHz MULTIPLE ACCESS FDMA TDMA/ CDMA/ TDMA/ TDMA/ TDMA/ TDMA/ TDMA/ METHOD FDMA FDMA FDMA FDMA FDMA FDMA FDMA DUPLEX METHOD FDD FDD FDD FDD FDD FDD TDD TDD NUMBER OF 832 832, 20, 124, 374, 1600, 10, 300, CHANNELS 3 users/ 798 users/ 8 users/ 8 users/ 3 users/ 12 users/ 4 users/ channel channel channel channel channel channel channel CHANNEL SPACING 30 kHz 30 kHz 1250 kHz 200 kHz 200 kHz 25 kHz 1.728 MHz 300 kHz MODULATION FM /4 DQPSK QPSK/ GMSK 0.3 GMSK 0.3 /4 DQPSK GFSK 0.3 /4 DQPSK OQPSK Gaussian filter Gaussian filter Gaussian filter

[0074] Below is another table listing some of the so-called third generation mobile communication systems to which the present invention may be applied. The table shows the most important radio interface related characteristics of the system.

TABLE-US-00002 CELLULAR SYSTEM WCDMA RX FREQ. (MHz) 2110-2170 1900-1920 TX FREQ. (MHz) 1920-1980 1900-1920 MULTIPLE ACCESS CDMA TDMA METHOD DUPLEX METHOD FDD TDD CHANNEL SPACING 5 MHz 5 MHz MODULATION QPSK CHANNEL BIT RATE 144 kb/s in rural outdoor, 500 kb/s in urban outdoor and up to 2 Mb/s in indoor