Abstract:
The invention is directed to a receiver arrangement, for example, in a mobile radio, which allows the use of slowly locking phase locked loops for a point-to-point connection between two transceivers, even in the case of a heterodyne receiver structure. The need to change channels between a transmission slot and a reception slot is avoided by virtue of a changeover device being provided for the purpose of interchanging the in-phase and quadrature components at the input side on a down-conversion frequency mixer. This advantageously allows either the upper sideband or the lower sideband of a useful signal to be down-converted without the need to change channel.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of PCT/DE03/02137, which was not published in English, which claims the benefit of the priority date of German Patent Application No. DE 102 28 757.0, filed on Jun. 27, 2002, the contents of which both are herein incorporated by reference in their entireties.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a receiver arrangement, particularly for mobile radio.  
       BACKGROUND OF THE INVENTION  
       [0003]     Normally, modern digital mobile radio systems are exclusively full-duplex systems. Full-duplex systems are distinguished in that it is possible to send and receive data simultaneously. Reference is also made to full-duplex systems in this context when sending and receiving are not performed simultaneously but changeover between the transmission directions takes place without being noticed by the subscriber.  
         [0004]     In principle, a distinction is drawn between two duplex methods. In the case of “frequency division duplex” (FDD), sending and receiving are performed in different, dedicated frequency bands. In the case of time division duplex (TDD), on the other hand, the transmission directions are divided into different times or time slots.  
         [0005]     In the widely used mobile radio standard GSM (Global System for Mobile Communication), TDD and FDD methods are used in combination in order to be able to provide transceivers which can be manufactured as inexpensively as possible and can be integrated as well as possible.  
         [0006]     Particularly in the reception part of modern mobile radio systems, the “low-IF receiver architecture” is increasingly being used instead of the homodyne receiver architecture (direct conversion) on account of the offset problems that arise therein. In the case of the low-IF-receiver architecture, the radio-frequency signal received is first of all down-converted to a relatively low intermediate frequency (IF) and in a second step to baseband.  
         [0007]     In transceivers designed in this manner between which there is a point-to-point connection, the problem regularly arises that the intermediate frequency differing from zero means that it is always necessary to change channels between the send and receive time slots. That is to say that the phase locked loop in the transceiver always needs to lock onto a new frequency between send and receive time slots, even when the nominal channel does not actually need to be changed. However, this disadvantageously results in the net data transmission rate achieved using the transmission channel being greatly reduced from the gross data rate.  
         [0008]     The document DE 100 46 586 specifies systems for data transmission that solve this problem by setting the reception sideband of the low-IF-receiver, “sideband selection”. In this case, for a point-to-point connection, one of the two receivers down-converts a received radio-frequency signal to a complex-value intermediate-frequency signal with a positive intermediate frequency and the other receiver down-converts it to an IQ signal with a negative intermediate frequency. This practice means that the phase locked loop does not need to lock onto a new carrier frequency between every send and receive time slot and that a phase locked loop (PLL) with a slow locking time can therefore advantageously be used.  
         [0009]     As an alternative to the use of positive or negative intermediate-frequency levels, a receiver structure with an image-frequency suppressing mixer may also be used in both radio parts of the point-to-point connection.  
         [0010]     However, it remains a drawback of such receiver structures that the receivers need to be designed, in terms of the second down-conversion mixing stage, which down-converts from intermediate frequency to baseband, both for a situation in which the channel frequency is below the local oscillator frequency of the second mixing stage and for a situation in which the channel frequency is above the local oscillator frequency of the second mixing stage.  
         [0011]     An at least theoretical possibility for solving this problem involves the corresponding analog and digital components being of duplicate design for the two regularly occurring cases described. This naturally means increased additional complexity.  
       SUMMARY OF THE INVENTION  
       [0012]     The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present one or more concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. The present invention relates to a two-point modulator arrangement that is suitable for controlled oscillators having only one control input and has good noise properties.  
         [0013]     The present invention is directed to a receiver arrangement, for example for a mobile radio or station, which is suitable for mobile radio methods with a time division duplex component, that allows the use of phase locked loops with a slow locking time and at the same time can be produced with little complexity.  
         [0014]     The invention comprises a receiver arrangement, comprising a down-conversion frequency mixer, designed for multiplying complex-value signals. The mixer includes a first input comprising an in-phase connection and a quadrature connection, with a second input comprising an in-phase connection and a quadrature connection (or first and second phase connections, respectively), and an output comprising an in-phase connection and a quadrature connection. The receiver further comprises a switching device configured to switch the in-phase and quadrature connections on the basis of a control signal, wherein the device is connected to the first or second input of the down-conversion frequency mixer. The device includes an in-phase input and a quadrature input, and also an in-phase output and a quadrature output, with a first switching state, in which the in-phase input is connected to the in-phase output and the quadrature input is connected to the quadrature output, and a second switching state, in which the in-phase input is connected to the quadrature output and the quadrature input is connected to the in-phase output.  
         [0015]     The present invention provides for complex-value signal processing of the received useful signal. Depending on whether the useful signal is in the upper or lower reception sideband, the present invention selectively interchanges the in-phase and quadrature components of the complex-value signal. In this case, the interchange can be effected either for the complex-value useful signal itself or for the local oscillator signal which is likewise to be supplied to the mixer.  
         [0016]     This option of interchanging the in-phase and quadrature components of the complex-value signal at the mixer input allows the signal to be processed further regardless of whether the upper or the lower sideband was modulated. In line with the present invention, the local oscillator frequency may advantageously remain unchanged between sending and receiving, with it nevertheless being possible to down-convert the channel which is above the local oscillator frequency or the channel which is below the local oscillator frequency, depending on the modulated sideband.  
         [0017]     The principle described can also be implemented with little complexity, since only two or four multiplexers need to be additionally provided. The present invention requires no additional components for inverting the subsequent demodulation or for phase-shifting the signals. In addition, the down-conversion frequency mixer does not need to change its direction of rotation.  
         [0018]     Depending on whether the local oscillator signal or the useful signal itself is changed over or interchanged in terms of the I and Q signal components, the generated output signal from the down-conversion frequency mixer may also have a phase shift of 90° from the signal which is actually desired and/or an inverse arithmetic sign for the generated signal. This has no disadvantageous effects on the further signal processing in the receiver, however.  
         [0019]     In line with one embodiment of the invention, the device for interchanging the in-phase and quadrature connections comprises a first multiplexer and a second multiplexer. The outputs of the two multiplexers are connected to the in-phase and quadrature connections of the first or second inputs of the down-conversion frequency mixer.  
         [0020]     Accordingly, the device for interchanging the in-phase and quadrature connections with the two multiplexers interchanges the in-phase and quadrature components either of the useful signal or of the local oscillator signal at the input of the down-conversion frequency mixer.  
         [0021]     The two multiplexers, in one example, each have a first and a second input which are connected to one another such that the outputs of the multiplexers provide the complex-value signal split into in-phase and quadrature components either in unchanged form or in a form with interchanged components, depending on a control signal. In this case, the control inputs are preferably connected to one another in order to supply the changeover control signal. The control signal is provided on the basis of whether the down-conversion frequency mixer&#39;s useful signal at the input is modulated in terms of its upper or in terms of its lower sideband.  
         [0022]     The receiver arrangement, in one example, comprises a heterodyne structure, for example a low-IF receiver structure. In this arrangement, besides the aforementioned down-conversion frequency mixer, which down-converts an intermediate-frequency signal to baseband in this case, a further down-conversion frequency mixer, which converts a radio-frequency signal to a complex-value intermediate-frequency signal, is connected upstream on the input side. The two down-conversion frequency mixers are preferably each supplied with a suitable local oscillator signal that may be generated by a respective phase locked loop, for example. In the case of a heterodyne receiver structure of this type, the device for changing over the in-phase and quadrature connections is accordingly connected either in the complex-value useful-signal path between the two down-conversion frequency mixers or between the frequency generator which generates the local oscillator signal and that down-conversion frequency mixer which brings about the conversion from intermediate-frequency level to baseband.  
         [0023]     When the device for interchanging the in-phase and quadrature connections is connected between the two down-conversion frequency mixers, a further device for interchanging the in-phase and quadrature paths is advantageously connected to the output of the down-conversion frequency mixer that converts from intermediate frequency to baseband. This has the advantage that there is again compensation for an arithmetic sign caused as a result of interchanging the components of the useful signal.  
         [0024]     Connected to the output side of the down-conversion frequency mixer provided in the general form of the invention is preferably a demodulator which demodulates the signal down-converted from intermediate-frequency level to baseband. This demodulator is preferably in the form of a quadricorrelator or in the form of a delay demodulator, depending on whether the rest of the signal processing takes place in analog or digital form.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The invention is explained in more detail below using a plurality of exemplary embodiments with reference to the figures, in which:  
         [0026]      FIG. 1  shows a first exemplary embodiment of the invention using a simplified block diagram, and  
         [0027]      FIG. 2  shows a further exemplary embodiment of the present invention using a simplified block diagram. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]      FIG. 1  shows a receiver arrangement with a down-conversion frequency mixer  1  which is designed to down-convert a useful signal, which is available as a complex-value signal, from an intermediate-frequency level to baseband. In this case, the complex-value signal is a signal that is split into an in-phase component and a quadrature component that is orthogonal thereto. Such frequency mixers  1  designed for complex-value signal processing are also called IQ mixers. The present down-conversion frequency mixer  1  comprises four mixer cells  2  to  5  which each have two inputs and one output, and which each provides a multiplied signal. The first input of the first mixer cell  2  is connected to the in-phase input  6  of the frequency mixer  1 , as is the first input of the second mixer cell  3 . The first inputs of the third and fourth mixer cells  4 ,  5  are connected to the quadrature input  7  of the down-conversion frequency mixer  1 .  
         [0029]     The second inputs of the mixer cells  2  to  5  are supplied with a local oscillator signal at the carrier frequency of the useful signal I, Q applied to the inputs  6 ,  7 . In this case, however, there is a device for interchanging the in-phase and quadrature components of the local oscillator signal  8 ,  9  (e.g., first and second phases of the local oscillator signal), said device being connected between a frequency generator  17  and the second inputs of the mixer  1 . This device  8 ,  9  comprises a first multiplexer  8  and a second multiplexer  9 . The multiplexers  8 ,  9  each have two inputs and one output and also a control input  10  for supplying a changeover command. The output of the multiplexer  8  is connected to the second inputs of the mixer cells  3 ,  4 . The output of the second multiplexer  9  is connected to the second inputs of the first and fourth mixer cells  2 ,  5 . The first and second inputs of the two multiplexers  8 ,  9  are respectively connected to one another in order to form a local oscillator input for supplying a local oscillator signal containing signal components which are at 90° to one another (e.g., the first and second phases of the local oscillator signal).  
         [0030]     Connected to the 0°/90° local oscillator input formed in this manner is a frequency generator  17 , designed as a phase locked loop with signal conditioning. The down-conversion frequency mixer  1  comprises not only the mixer cells  2  to  5  but also two summing nodes  11 ,  12  which each have two inputs and one output. The inputs of the summing node  11  are connected to the outputs of the mixer cells  2  and  4 , the output of the mixer cell  4  being connected in a non-inverting fashion. The outputs of the mixer cells  3 ,  5  are connected to the inputs of the summing node  12 , with the output of the mixer cell  3  being connected thereto in an inverting fashion. The outputs of the summing nodes  11 ,  12  form the IQ outputs of the down-conversion frequency mixer  1  and are connected to a further signal processing stage  13 , whose output in turn has a demodulator  14  connected to it. Up to the demodulator  14 , the signal to be demodulated is supplied as a complex-value signal.  
         [0031]     The IQ input  6 ,  7  has a further down-conversion frequency mixer stage  18  connected to it that converts a radio-frequency signal received by an antenna to an intermediate-frequency level. On the intermediate-frequency level, further signal conditioning means, such as amplifiers and filters, are also provided between the mixing stage  18  and the mixing stage  1 , but these are not shown in the present case since they are not required in order to understand the present invention.  
         [0032]     Depending on which sideband of the useful signal has been modulated, the present invention allows the local oscillator frequency to be left unchanged by interchanging the in-phase and quadrature components of the local oscillator signal, and still allows down-conversion of the channel which is above the local oscillator frequency, on the one hand, and of the channel which is below the local oscillator frequency, on the other. This will be explained below with reference to a mathematical, exemplary description using a complex-value signal s(t)=I(t)+jQ(t): 
 
 s   LO =exp(− jω   IF   t ), 
 
 s   +IF =exp( j[ω   IF   t+φ ( t )]), 
 
 s   −IF =exp( j[−ω   IF   t+φ ( t )]), 
 
 s   +IF   * s   LO =exp( jω   IF   t+φ ( t )−ω IF   t ])=exp( jφ ( t )), 
 
 s   −IF   *s   LO,I&lt;−&gt;Q   =j* exp( j[−ω   IF   t+φ ( t )]+ jω   IF   t ])= j* exp( jφ ( t )). 
 
 where s LO  is the local oscillator signal, s LO,I&lt;−&gt;Q  is the local oscillator signal with interchanged quadrature components, s +IF  and s −IF  are the IF signals with modulated upper and lower sidebands, and ω IF  is the angular frequency of the intermediate-frequency signal. 
 
         [0033]     It is thus advantageously possible to dispense with a duplicate design for analog and digital components for the cases where the upper or lower sideband has been modulated. As a further advantage, it is possible to use a phase locked loop as a frequency generator  17 , wherein the phase locked loop does not need to change its frequency between send and receive time slots if the nominal channel remains the same.  
         [0034]     As already mentioned, the multiplexing which brings about interchange of in-phase and quadrature components may alternatively also be provided in the useful signal instead of the LO signal. An exemplary embodiment of this type is shown in  FIG. 2 .  
         [0035]      FIG. 2  shows a block diagram of an alternative embodiment of the invention using an exemplary block diagram whose components used, advantageous interconnection and manner of operation largely correspond to those in  FIG. 1 . In this respect, the description is not repeated at this juncture. The only difference is that the arrangement of the multiplexers  8 ,  9  in the illustration shown in  FIG. 2  is not provided in the supply of the local oscillator signal and accordingly upstream of the second inputs of the mixer cells  2  to  5 , but rather at the first inputs of the mixer cells  2  to  5  and accordingly in the useful-signal path. In addition, to compensate for any negative arithmetic sign occurring in the useful signal, a further device for interchanging the in-phase and quadrature connections is provided which has the reference symbols  15 ,  16  and is connected in the I and Q paths between the processing unit  16  and the demodulator  14 .  
         [0036]     Specifically, the in-phase input  6  of the down-conversion mixing stage is connected to the first input of the first multiplexer  8  and to the second input of the second multiplexer  9 . The quadrature input  7  is connected to the second input of the first multiplexer  8  and to the first input of the second multiplexer  9 . The control inputs of the two multiplexers  8 ,  9  are in turn connected to one another and to a changeover input  10  for the purpose of changing over between a first and a second switching state for the changeover device  8 ,  9 . The output of the multiplexer  8  is connected to the first inputs of the first and second mixer cells  2 ,  3 , while the output of the second multiplexer  9  is connected to the first inputs of the third and fourth mixer cells  4 ,  5 .  
         [0037]     A component of the local oscillator signal is supplied to the second inputs of the first and fourth mixer cells  2 ,  5 , while the other component, which is orthogonal thereto, of the complex-value local oscillator signal is supplied to the second and third mixer cells  3 ,  4 . For this purpose, the second inputs of the mixer cells  2  to  5  are connected to the 0-degree/90-degree output of the frequency generator  17 . The design of the down-conversion frequency mixer  1  is unchanged from the diagram shown in  FIG. 1 . The rest of the device for interchanging the in-phase and quadrature connections comprises two multiplexers  15 ,  16 , each with two inputs and one output. Like the multiplexers  8 ,  9  in  FIG. 2 , these are connected such that, depending on the control signal, the in-phase and quadrature components at the output of the intermediate-processing stage  13  are supplied to the demodulator  14  either unchanged or interchanged.  
         [0038]     This allows the modulation signal to be processed with the correct arithmetic sign by interchanging the I and Q paths again.  
         [0039]     The way in which the circuit shown in  FIG. 2  works is likewise explained using a mathematical description in a similar manner to the example from  FIG. 1 : 
 
 s   −IF,I&lt;−&gt;Q   *s   LO   =j* exp(− j[−ω   IF   t+φ ( t )]− jω   IF   t )= j* exp(− jφ ( t )), 
 
 where s −IF,I&lt;−&gt;Q  represents the useful signal with interchanged quadrature components. 
 
         [0040]     It will be seen that, as in the case of  FIG. 1 , the signals that can be tapped off at the output of the circuit have a phase shift of 90° with respect to the wanted signal, but this has no disadvantageous influence on the rest of the signal processing.  
         [0041]     The advantages of the circuit in  FIG. 2  correspond to those of the exemplary embodiment in  FIG. 1  and are therefore not presented again at this juncture.  
         [0042]     It is naturally within the scope of the invention for other circuit means to be used as well in order to achieve the inventive principle&#39;s underlying interchange of the in-phase and quadrature components on the basis of a control signal.  
         [0043]     While the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.