Abstract:
To support a plurality of different mobile radio standards in mobile radio terminal devices using a single system oscillator, a sampling rate converter converts the sampling rates from an input rate to an output rate and additionally outputs control information which is suitable for operating signal processing components. The components receiving the control information are arranged in the signal flow upstream of the sampling rate converter, on average exactly at a virtual sampling frequency. The virtual sampling pattern is mapped onto the frame of the physical operating clock by simply gating out edges of the physical operating clock. Using the control signal, a clock control device generates a masked clock that has, on average, an edge repetition rate which corresponds to the virtual sampling frequency of the samples or to an integer multiple thereof.

Description:
RELATED APPLICATION 
     This application is a national stage application of International Application No. PCT/DE03/00309, filed Feb. 4, 2003, which is entitled “CLOCK CONTROL IN TRANSMISSION-SIGNAL PROCESSING DEVICES IN MOBILE RADIO TERMINAL DEVICES”, which was not published in English, and claims priority to German Patent Application Serial No. 102 05 305.7, which was filed on Feb. 8, 2002, which is hereby incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of mobile communication and to the generation of mobile communication transmission signals for different mobile radio standards. In particular, the invention relates in this context to an apparatus and to a method for clock control in transmission-signal processing devices in mobile radio terminal devices such as mobile stations. 
     BACKGROUND OF THE INVENTION 
     The GSM standard currently used in mobile communication involves the use of “GSMK” (Gaussian Minimum Shift Keying) Modulation, which uses a signal space having signal points which have a phase difference of 180°. To this end, the packet service GPRS (General Packet Radio Service) has been developed, which allows operation at higher data rates. Another standard currently used is the TIA/EIA-136 (IS 136) standard, which involves the use of a π/4-DQPSK (D-quaternary-PSK) modulation method for generating the transmission signals. To a certain extent as a transitional standard between GSM and GPRS, on the one hand, and UMTS, on the other, the EDGE standard and also the associated EGPRS (enhanced GPRS) packet service have been defined. Although EDGE is a TDMA (Time Division Multiple Access) method, there is already a transition from GMSK modulation to 8-PSK modulation. 8-PSK modulation involves the use of a signal space having 8 signal points, the phase difference between the individual signal points being 45°. By contrast, UMTS uses the CDMA (Code Division Multiple Access) method (also in combination with TDMA and/or FDMA), which involves the signals in any radio link being encrypted using a respective proprietary code, the “spread code”. 
     One general aim is to develop mobile communication appliances which are designed for operation with a plurality of different mobile radio standards and which may accordingly be used in the various mobile radio systems. One problem in this context, however, is the fact that the modulation methods described above are based on different symbol clock frequencies which cannot be converted into one another by integer factors or simple rational ratios. Consequently, at least two different system clocks are normally required which are usually derived from separate crystal oscillators. 
     Previous transmission apparatuses for combined UMTS and GSM/EDGE applications thus have exclusively a plurality of crystals or PLL (Phase Locked Loop) circuits which supply system clock frequencies precisely co-ordinated with the respective standard which are usually an integer multiple of the inverse symbol period in the transmission method. The architecture of the signal processing lines is rigidly linked to these frequencies. Both the physical operating clock and the physical sampling clock are thus not independent of the standard-specific digital signal processing, particularly the standard-specific symbol period, in these transmission apparatuses. 
     German patent application DE 100 45 547.6 “Verfahren zur systemunabhangigen digitalen Erzeugung von Mobilkommunikations-Sendesignalen verschiedener Mobilfunkstandards” [Method for system-independent digital generation of mobile communication transmission signals in various mobile radio standards], which is prior art in line with §3(2) of the German Patent Act, describes a related method which, by way of example, is not designed for the specific requirements of the UMTS standard, however, and, in particular, has the property that it not only uses a single crystal oscillator but also makes joint use of the same digital/analog converter (DAC) and other circuit components for a plurality of standards, and also operates the DAC at the same sampling frequency for all of the standards, which is not advantageous for a system which supports the UMTS and GSM/EDGE standards, for example. 
     SUMMARY OF THE INVENTION 
     It is thus an object of the present invention to specify a method and an apparatus for clock control in transmission-signal processing devices in mobile radio terminal devices such as mobile stations or base stations which are designed for the demands of as many mobile radio standards as possible and, in particular, are suitable for a system which supports the UMTS and GSM/EDGE standards. 
     A fundamental concept of the invention is the use of a sampling rate converter which, besides the actual signal conversion, additionally outputs control information which is suitable for operating signal processing components, which are arranged in the signal flow upstream of the sampling rate converter, on average exactly at the virtual sampling frequency, even though the virtual sampling frequency is not necessarily available as the physical operating clock in the apparatus. The sampling rate converter converts the samples provided in the virtual time frame into samples of the physical sampling pattern in the digital/analog converter and outputs a control signal which a clock controller uses to generate a signal which, on average, has an edge repetition rate which corresponds exactly to the virtual sampling frequency, particularly to an integer multiple of the virtual sampling frequency. 
     In the text below, the terms have the following meanings: 
     “Sampling frequency” is the clock frequency at which the digital/analog converter (DAC) or an analog/digital converter (ADC) is operated or would need to be operated in order to convert a signal from the digital domain into the analog domain (or vice versa),
 
“Sampling rate” is the number of samples of a discrete-time signal per unit time, averaged over a defined period,
 
“Sampling pattern” is the periodic structure containing samples of a discrete-time signal at a defined interval in relation to a freely selectable reference variable (length, time, etc).
 
     The invention permits the advantages below—possibly in connection with developments which are specified in the subclaims. 
     The transmission apparatus is operated just with a single crystal oscillator or just one system clock which is used for processing signals in all of the supported standards. This system clock or a clock which is derived therefrom by a phase locked loop (PLL) is used as the DAC&#39;s physical sampling clock in the transmission path (physical sampling clock). The same clock or another clock derived from the system clock by a phase locked loop or a clock splitter is used as the physical operating clock for the digital circuit components in the transmission path (physical operating clock). 
     The only demand on the frequency of the physical operating clock in this connection is merely to ensure that, taking into account the available circuit resources, it is fast enough to achieve the necessary computation power for real-time processing. The most important demand on the frequency of the physical sampling clock is merely to ensure that it is high enough to observe the sampling theorem or to achieve a desired oversampling factor. 
     The clocks derived from the crystal oscillator by any PLLs used are achieved by comparatively simple PLL division factors which permit the PLL to be designed beneficially, but which are not necessarily suited to the additional standard which is to be supported. 
     The standard-specific digital signal processing (e.g. operations at chip level in the case of UMTS signals) may be based on sampling patterns which are independent of the time frame of the system clock and/or independent of the time frame of the physical operating clock in the digital circuit components and/or independent of the time frame of the physical sampling clock. 
     The sampling rates or sampling frequencies associated with the sampling patterns, which (sampling rates or sampling frequencies) are crucial to the standard-specific signal processing and depend specifically on the parameters of the mobile radio standard, e.g. chip period duration, symbol period duration etc., do not need to arise physically in the arrangement. They are thus virtual sampling frequencies. 
     The transmission apparatus contains at least one sampling rate converter, particularly a fractional sampling rate converter (SRC), which converts the virtual sampling pattern into the physical sampling pattern. The sampling rate converter supplies control information which can be used to map the virtual sampling pattern onto the physical operating clock&#39;s frame, which is prescribed by the system clock. This flow of control information is in the opposite direction to the signal flow. 
     The virtual sampling pattern is mapped onto the physical operating clock&#39;s frame simply by gating out edges of the physical operating clock (“clock gating”). The rate of the remaining edges of this clock corresponds, on average, precisely to the virtual sampling rate (or to an integer multiple of the virtual sampling rate). 
     Since the digital circuit components operate using a proprietary physical operating clock which may possibly be chosen to be identical for the two standards, the circuit may have a “synchronous design”. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail below with reference to exemplary embodiments in conjunction with the figures of the drawing, in which: 
         FIG. 1  shows a first embodiment of a transmission apparatus based on the invention; 
         FIG. 2  shows a second embodiment of a transmission apparatus based on the invention; 
         FIG. 3  shows a timing diagram to illustrate the various signal profiles; 
         FIG. 4  shows an embodiment of a clock control device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  schematically shows a general embodiment of an apparatus based on the invention. This apparatus has a system clock source  100  with a single crystal which is used for processing signals in a plurality of standards. The system clock source  100  supplies at least one physical operating clock  103 , which in the simplest case is identical to the physical sampling clock  104 , which is likewise supplied by the system clock source  100 . 
     In addition, the first embodiment of an apparatus based on the invention as shown in  FIG. 1  has a sampling rate converter  203 , which accepts samples  213 , which are in a virtual sampling pattern, and converts them into samples  215 , based on the physical sampling pattern of the digital/analog converter (DAC)  205 . The DAC  205  is operated using the physical sampling clock  104  and outputs the analog signal  216  at the output. 
     In addition, the sampling rate converter  203  operated using the physical operating clock  103  supplies a control signal  106 , which is supplied to the input of a clock controller  105  which likewise has the physical operating clock  103  supplied to it. Using the control signal  106 , the clock controller  105  generates a masked clock  107 , specifically such that the clock  107  has, on average, an edge repetition rate which corresponds exactly to the virtual sampling frequency of the samples  213  or to an integer multiple thereof. 
     The masked clock  107  is supplied to the modulator  202 , the modulator  202  taking input data  211  from the upstream memory  201  in correspondence with the virtual sampling clock using the address and/or control information  212 . 
     On the basis of the flow of control information  106  or  212  in the opposite direction to the signal flow, the SRC  203  uses the control information  106  which it itself has generated to control the number of operating clock cycles per unit time in the preceding signal processing stages  202  and thus ultimately also determines the speed at which the modulation data  211  are read from the memory  201 . The memory  201  or a control unit associated therewith can request further data from the preceding data source before the memory  201  becomes empty. This backwardly directed chain-like flow of control means that the data throughput of the transmission path is determined exclusively by the physical sampling clock  104  of the DAC and the conversion ratio of the SRC  203 , but not by the physical operating clock  103  in the signal processing stages. 
     The flexibility of the inventive arrangement with regard to the choice of system clock allows the crystal oscillator and/or the PLL to be chosen to suit the properties and demands of the first standard in order to simplify matters, with it merely being necessary to ensure that a computation power which is adequate for the second standard can thus also be attained. No consideration needs to be given to the standard-specific symbol period from the second standard, however, which is a very significant advantage when producing a clock design for circuit implementation. In this case, the block for supporting the first standard normally does not require a sampling rate converter. 
     The arrangement shown in  FIG. 1  additionally has the following special features:
     a) The physical operating clock  103  and the physical sampling clock  104  may differ from one another; by way of example, the clock frequency of the operating clock  103  can be chosen as an integer multiple of that of the sampling clock  104  in order to achieve better utilization of the circuit components of the modulator  202  and/or of the sampling rate converter  203  through time division multiplexing.   b) It is frequently desirable to operate the DAC  205  at a much higher sampling frequency than the signal bandwidth so as to have to use just one comparatively simple reconstruction low pass filter for obtaining the analog signal  216  as a result of this high oversampling ratio. To keep down the computation complexity and hence also the circuit complexity in the modulator  202  and, in particular, in the sampling rate converter  203 , however, i.e. to use a sampling pattern therein for the signals  213  and  215  which is aligned with the signal bandwidth, it is advantageous in this case to use an interpolator  204  with a fixed integer conversion ratio upstream of the DAC  205 , as shown in  FIG. 2 .   c) One particular advantage is that cases a) and b) can be combined if, in case b), the high oversampling ratio means that the high-frequency sampling clock  104  is also used as a physical operating clock  103  and, at the same time, use is made of the advantage from case a) to subject circuit components (adders, multipliers, . . . ) to time division multiplexing.   

       FIG. 3  shows the relationship between the physical operating clock  103  or the physical sampling clock  104  and the masked operating clock  107  and also the relationship between the virtual sampling pattern and the sampling pattern at the output of the sampling rate converter  203  and the physical sampling pattern of the DAC  205 . 
     In line with the refinement according to section c) above, the frequency of the sampling clock  104  or of the operating clock  103  in the present exemplary embodiment is four times the output rate of the sampling rate converter  203 , specifically 65 MHz or 62.4 MHz, in particular. The interpolator  204  accordingly has the interpolation factor 4. The two frequencies can be derived from rational multiples of the GSM/EDGE-typical system frequency of 13 MHz (factor 5 or 192/40), which corresponds to 48 times the inverse symbol period of a GSM/EDGE symbol. In this case, the sampling rate converter  203  has a conversion ratio from the input to the output of 64/65 or 1.536/1.625. In both variants, this results in a virtual sampling frequency for the signal  213  of 15.36 MHz, which corresponds exactly to four times the UMTS-typical inverse symbol period (3.84 MHz) and corresponds to the output rate from the modulator  202 , which is normally designed for an oversampling factor of 4. 
     As  FIG. 3  shows, the sampling rate converter outputs a sample  215  upon every fourth clock edge of the operating clock  103  (index n). To calculate each output value, there are thus four operating clock cycles available which can be used for subjecting circuit resources to time division multiplexing. Similarly,  FIG. 3  shows the samples of the input signal  213 , from which the sampling rate converter  203  calculates the samples of the output signal  215 , in the virtual sampling pattern (index m). The samples  213  on the input side are transferred to the sampling rate converter  203  at the times of the rising edges of the marked pulses of the masked clock  107 . 
     In this case too, it can be seen that a value needs to be generated by the modulator  202  only upon every fourth operating clock cycle at first, i.e. the modulator  202  can also be operated using a multiplex factor of 4. 
     Since the virtual sampling pattern  301  has somewhat longer periods than the output-side sampling pattern  302  of the converter  203 , situations ( 303 ) arise in which a further output value  215  needs to be calculated without a new input value  213  being provided. This is taken into account by the sampling rate converter  203  by virtue of it deactivating the control signal  106  for the period of four successive operating clock cycles. If the physical operating clock  103  is subjected to logic ANDing with the control signal  106  in the clock control device  105  as shown in  FIG. 4 , then what is obtained is precisely the masked operating clock  107  which stops the modulator  202  at exactly the times at which no new sample is required at the input of the sampling rate converter  203 . Hence, the modulator  202  is automatically stopped just often enough for it to output the samples exactly at the virtual sampling rate on average. 
     On account of its being actuated using the masked clock  107 , the modulator  202  may advantageously be implemented in terms of signal processing parameters, such as filter coefficients etc., as though it were supplying exactly at the virtual sampling frequency. If the virtual and output-side sampling frequencies in the sampling rate converter  203  differ only slightly, as is the case in the present exemplary embodiment (15.36 MHz and 15.6 MHz), then the situation ( 303 ) occurs only relatively rarely, i.e. the modulator  202  is stopped only comparatively rarely and the computation power available in terms of circuitry is used almost completely. 
     The modulator  202  itself likewise operates using the oversampling factor 4, which means that, considering the multiplex factor 4, it takes a value  211  from the memory  201 , under the control of the signal  212 , upon every 16th rising edge of the masked operating clock  107 . The modulator  202  and hence ultimately the sampling rate converter  203  thus determine the average read speed in the memory  201 . If the memory  201  is being monitored by a filling level regulator, then the memory  201  can be filled with new modulation data promptly. This propagates the flow of control information, which ultimately regulates the data rate for transmission.