Abstract:
In mobile radio receivers, the transmission power must be raised before the start of the transmission process, and must be reduced again after the end of the transmission process. Until now, the transmission power has been controlled exclusively by varying the gain of the power amplifier. The inventive concept is based on using a scaling unit to additionally scale the amplitudes of the baseband signals in order to assist the switching-on and switching-off processes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of copending International Application No. PCT/DE02/01016, filed Mar. 20, 2002, which designated the United States and was not published in English. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a device for regulating the output power of radios, in particular mobile radios. The invention furthermore relates to a method for raising and reducing the transmission power of radios, in particular mobile radios. 
     One problem that arises when transmitting pulsed mobile radio transmission signals is that the transmission power must be raised within a specific time interval to its nominal value at the start of the transmission process before the data burst to be sent can be transmitted. Once the data burst has been transmitted, the transmission power must once again be reduced approximately to zero. In the process, the transmission power must not be switched on and off abruptly, because this would lead to an interference spectrum which, in particular, would cause major problems with the transmission quality on the adjacent channels. To this extent, the conventional mobile radio standards provide that the adjacent channel interference must not exceed a specified maximum level. 
     For this reason, the transmission power must be switched on and off continuously over a specific time interval in the form of a power ramp. This necessitates reliable control of the output power over a wide dynamic range. The required output power dynamic range is, for example, up to 48 dB. Furthermore, both a switching-on and a switching-off process are required for each data burst to be transmitted. 
     In the case of the GSM (global system for mobile communications) mobile radio system, which operates using the GMSK (Gaussian Minimum Shift Keying) modulation method, the described problem has been solved using complex circuitry for the power amplifier and for controlling the power amplifier. This meant that it was possible to comply with the required dynamic range with the required accuracy. However, with the EDGE extension to the GSM mobile radio system, the problem of reliably monitoring the output power has been raised in a more serious form since, in this case, both the phase and the amplitude information must be transmitted linearly by the output stage. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a device and a method for monitoring the output power of radios, which overcome the above-mentioned disadvantages of the prior art apparatus and methods of this general type. 
     In particular, it is an object of the invention to provide a device and a method for monitoring the output power of radios, by which the switching-on and switching-off process for the transmission power of the radio can be monitored reliably over a wide dynamic range with little complexity. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a device for monitoring the output power of radios, in particular of mobile radios that includes at least one radio-frequency module which converts baseband transmission signals to the radio-frequency band, and amplifies them. The radio-frequency module itself includes a power amplifier with a controllable gain. In order to monitor the output power, the device additionally has a scaling unit for varying the signal amplitudes of the baseband transmission signals. Further, the device includes a controller, which, on raising or reducing the output power, before or after the transmission of a data burst, synchronizes the variation of the signal amplitudes of the baseband transmission signals by the scaling unit with the variation of the gain of the power amplifier. 
     Until now, the transmission power has been controlled exclusively by varying the gain factor of the power amplifier, however, the inventive concept includes introducing a second control capability for influencing the transmission power. A controller synchronizes the second control capability with the first control capability. Even before the baseband transmission signals are passed to the power amplifier that is arranged in the radio-frequency module, their signal amplitude can be influenced using the inventive scaling unit. The majority of the power control is also still carried out by varying the gain of the power amplifier. However, since a second control mechanism is also provided, which influences the amplitudes of the input signals, this reduces the dynamic range that needs to be coped with by each individual control mechanism. The attenuation of the signal amplitudes of the baseband transmission signals means that the power amplifier need itself provide control only over a narrower dynamic range. This reduces the circuit complexity for controlling the gain of the power amplifier. 
     The invention can also be used to increase the dynamic range that is available for the output power. This dynamic range is increased by the amount of the additional attenuation caused by the scaling unit. This makes it possible to effectively prevent crosstalk from the input signal to the output signal during the switching-on and switching-off process. Before the start of transmission of the data burst, the input signal is sufficiently well isolated from the output that no interference noise is transmitted. The same applies to the time interval after completion of the transmission process. 
     The invention allows the power amplifier isolation requirements with regard to the crosstalk from the input signal to the output signal to be reduced, to be precise by exactly the same amount as the attenuation of the baseband transmission signals using the scaling unit. 
     A further advantage of the inventive solution is that the control signal for controlling the gain of the power amplifier now covers only a narrower value range than in the past, since the power amplifier now need be controlled only over a narrower dynamic range than in the past. Interference which acts on the control signal thus becomes less important; and the robustness of the control is improved. 
     A further advantage is that the scaling unit can be implemented with little physical additional complexity. From the cost point of view as well, the solution is considerably more advantageous than any attempt to further widen the controllable dynamic range of the power amplifier by using complex circuitry. 
     It is advantageous for the scaling unit to have a multiplier for each baseband transmission signal. Each multiplier can scale the signal amplitude of the respective baseband signal. This means that it is possible to obtain any desired attenuation by multiplying the respective signal amplitude by the appropriate factor. This allows any required attenuation and any required attenuation profile to be provided in a flexible manner. A further advantage is that the scaling can be changed within very short time intervals using a multiplier. 
     It is particularly advantageous for the multipliers to be digital multipliers which are arranged upstream of the digital/analog converters in the signal path. In this embodiment of the invention, the scaling of the signal amplitude is not carried out in the power area of the circuit arrangement, but in the area in which the baseband signal is still in the form of a digital signal. In this area of the circuit, the signal amplitudes of the respective baseband signals can be influenced in a simple and cost-effective manner by the digital multipliers. Digital multipliers offer sufficient accuracy and speed for scaling the baseband signals while maintaining their phase. 
     It is advantageous for the device to have at least one baseband module which produces the baseband signals, and for the scaling unit to be arranged on the baseband module. Digital signal processing of the baseband signals is carried out on the baseband module. The baseband signal is then converted from digital to analog form, and is supplied to the radio-frequency module or modules. It is therefore possible to design the scaling unit using digital technology, and to integrate it on the baseband module. This also has the advantage that complex rising and decreasing amplitude profiles can be stored in digital form. 
     According to one advantageous embodiment of the invention, the baseband transmission signals include an in-phase and a quadrature signal. Signals are normally represented in the complex plane for mobile radio purposes. This means that a complex baseband transmission signal is represented by the real-value in-phase signal and a real-value quadrature signal. 
     The gain of the power amplifier is advantageously controllable by a power control device. Controllable power amplifiers such as these are known from the prior art and can advantageously be combined with the scaling unit. Two control mechanisms, which operate independently of one another, are therefore available in order to influence the output power. First, the output power can be influenced as before via the power control device for the power amplifier. In addition, the output power of the radio can be influenced by the scaling unit, which to this extent represents a second control mechanism. Since the two control mechanisms operate independently of one another, the dynamic range can be increased by combining the inventive amplitude scaling with the power control that is carried out in the power amplifier. 
     In this case, it is advantageous for the gain of the power amplifier to be readjusted by the power control device such that the actual transmission power in each case corresponds to a nominal value of the transmission power which is supplied to the power control device. The nominal value therefore does not predetermine the gain factor, but the desired actual transmission power, which can be represented as the product of the input signal amplitude and the gain factor of the power amplifier. 
     The actual power control device is implemented by a control loop in which the nominal value of the transmission power that is supplied is compared with the actually measured transmission power. The gain factor is then varied by the power control device depending on the error between the actual value and the nominal value, such that the actual transmission power is made to approach the nominal value. This automatically results in the signal amplitude of the input signal being taken into account: the gain factor is set such that the input signal level is raised to the output power determined by means of the nominal value. Since the desired output transmission power is predetermined as the nominal value, this allows the decreasing and raising of the output transmission power to be controlled in a very simple manner. 
     It is advantageous for the device to have a power measurement unit for determining the actual transmission power, which outputs and evaluates a fraction of the transmission power. A portion of the output transmission power is extracted directly at the antenna, is advantageously rectified, and represents a measurement of the actual output transmission power. The signal obtained in this way is used as the actual value for the power control loop described above. Since the power is detected directly at the antenna and not at some upstream point in the signal path, the actual value of the output transmission power can be determined appropriately. This improves the control accuracy. 
     The device advantageously has a power ramp generator for producing switching-on and switching-off ramps which have a continuous profile for the nominal value of the transmission power. Using a switching-on ramp with a continuous profile ensures that the output transmission power is raised continuously before the start of the transmission process, and is raised continuously from zero to the desired transmission power level. The switching-off ramp is used in a corresponding manner to decrease the transmission power continuously once again after completing the transmission process to approximately zero, thus avoiding abrupt changes in the output signal power. The extent of adjacent channel interference can thus be kept below the permissible limit value. 
     According to one advantageous embodiment of the invention, the power ramp generator is arranged on the module which contains the scaling unit. In this case, it is particularly advantageous to design both the scaling device and the power ramp generator using digital technology, and to integrate them on the baseband module. The power ramp generator in this embodiment of the invention produces a rising or falling digital signal that is converted by a digital/analog converter to an analog nominal value of the transmission power. This analog nominal value of the transmission power can then be supplied to the power control device for the power amplifier. 
     As an alternative to this, it would be possible to design both the power ramp generator and the scaling device using analog technology and to arrange them on the radio-frequency module. This would have the advantage that the digital/analog conversion of the digital nominal value signal could be avoided. 
     One advantageous embodiment of the invention provides for the scaling unit to have a memory for a sequence of rising or falling scaling values, by which means, a rising or falling profile of the amplitudes of the baseband transmission signals can be produced. These scaling values may, for example, be supplied successively as factors to the multipliers in the scaling unit. The baseband transmission signals which are applied to the multipliers can then be successively multiplied by the various successive scaling values, so that a rising or falling profile of the amplitudes of the baseband transmission signals can be produced. Instead of having to change the scaling abruptly, this allows an approximately continuous variation in the scaled signal amplitudes. 
     It is advantageous for the rising or falling profile for the baseband transmission signals to be initiated by trigger signals which are supplied to the scaling unit. For example, a first trigger signal can be provided which produces a rising profile of the amplitudes of the baseband transmission signals. In a corresponding way, a second trigger signal can be provided which initiates a falling profile of the amplitudes. There is therefore no need to transmit the entire sequence of rising or falling scaling values to the scaling unit. Instead of this, it is sufficient to transmit the corresponding trigger signal to the scaling unit, in response to which, the scaling unit can automatically produce the entire rising or falling amplitude profile. This simplifies the control of the scaling unit. 
     It is particularly advantageous for a trigger signal to be in each case transmitted to the scaling unit at a defined time in the switching-on and switching-off ramps, in which case, in particular, the time interval between the start of the switching-on or switching-off ramp and the trigger signal can be chosen freely. The nominal value of the transmission power is transmitted in the form of a switching-on or switching-off ramp to the power control device for the power amplifier. Let us consider the switching-on ramp first of all. The continuously increasing nominal value results in the gain factor of the power amplifier being increased more and more. A trigger signal is now transmitted at a defined time to the scaling unit, causing the scaling unit to continuously raise the amplitudes of the baseband transmission signals corresponding to the stored profile. The signal amplitude at the input of the power amplifier thus increases continuously, and the rise in the output power which is predetermined by the switching-on ramp can therefore be achieved without any significant further increase in the gain. The trigger signal thus activates the mechanism for scaling the signal amplitudes, with the time synchronization between the control of the gain factor on the one hand and the amplitude scale on the other hand being predetermined by the time interval between the start of the signal ramp and the trigger signal. Suitable time matching between the nominal value profile for the power control and the amplitude scaling makes it possible to choose an optimum relationship between the profile of the signal amplitude and the profile of the gain control. 
     When switching off the transmission power, a decreasing profile is predetermined for the nominal value of the transmission power using the switching-off ramp. The gain of the power amplifier is reduced continuously in a corresponding manner. A trigger signal is transmitted to the scaling unit at a defined time in the switching-off ramp, in response to which the scaling unit continuously reduces the amplitudes of the baseband transmission signals. In consequence, the transmission power is reduced further continuously, without any need for a significant further reduction in the gain for this purpose. 
     The invention is particularly suitable for use in mobile radio stations, since it can be implemented with little hardware complexity using digital technology. In particular, the invention is suitable for use in mobile radio stations in which the data is transmitted in accordance with one of the Standards GSM, EDGE, TIA-/EIA-136, UMTS or in accordance with partial combinations of these Standards. One common feature of the cited mobile radio standards is that the data is transmitted in the form of data bursts. To this extent, it is necessary for the cited standards for the transmission power to be raised before the start of the transmission of a data burst, and to be decreased again after completion of the transmission. For this reason, mobile radio stations which support one of the cited standards or partial combinations of these standards are suitable for using the inventive scaling of the baseband transmission signals. 
     With the foregoing and other objects in view there is also provided, in accordance with the invention, a method that is suitable for raising the transmission power of radios, in particular mobile radios that have at least one radio-frequency module converting baseband transmission signals to the radio-frequency band and amplifying them. The radio-frequency module includes a power amplifier with a controllable gain. Raising the transmission power is performed prior to the transmission of a data burst. While carrying out the method for raising the transmission power, a switching-on ramp is, in a first step, applied to a power control device for the transmission power such that the gain of the power amplifier raises. After a defined time on the switching-on ramp, the amplitudes on the baseband transmission signals are then increased continuously from a minimum value to a maximum value simultaneously with the profile of the switching-on ramp. 
     The method for raising the transmission power allows two different control mechanisms to be combined and to be synchronized such that an increase in the controllable dynamic range can be achieved overall. This also applies to the largely analogous method for decreasing the transmission power of mobile radios. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a device and method for regulating the output power of mobile radio stations, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an inventive circuit configuration; 
         FIG. 2A  is a graph showing the time profile of the switching-on and switching-off ramp for the transmission power; 
         FIG. 2B  is a graph showing the amplitude profile of the baseband transmission signals during the switching-on and switching-off processes; and 
         FIG. 2C  is a graph showing the time profile of the control signal for the power amplifier while raising and decreasing the transmission power. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a block diagram of a circuit arrangement. The functional units on the baseband side  2 , that is to say to the left of the module boundary  1 , are arranged on one or more baseband modules. The functional units on the radio-frequency side  3 , that is to say to the right of the module boundary  1 , are responsible for the radio-frequency signal processing; these functional units are integrated on one or more radio-frequency modules. 
     The baseband modulator  4  produces digital baseband signals, specifically a digital in-phase signal  5  and a digital quadrature signal  6 , and transmits these to the IQ scaling unit  7 . A multiplier  8  for the in-phase signal path, as well as a multiplier  9  for the quadrature signal path, are arranged in the IQ scaling unit  7 . These multipliers are in the form of digital multipliers, with the scaling values  10  by which the in-phase signal  5  and the quadrature signal  6  are multiplied being provided by the IQ scaling table  11 . The IQ scaling table  11  includes a digital memory for storage of at least one sequence of digital scaling values. The scaled digital in-phase signal  12  can be tapped off at the output of the multiplier  8 , and is supplied to the digital/analog converter  14  where it is converted to the analog in-phase signal  16 . In a corresponding manner, the scaled digital quadrature signal  13  is supplied to the digital/analog converter  15  and is converted to the analog quadrature signal  17 . Both the analog in-phase signal  16  and the analog quadrature signal  17  are passed from the baseband side  2  to the radio-frequency side  3 , where they are up-mixed by the radio-frequency modulator  18  to the radio-frequency band. The analog radio-frequency signal which is produced by the radio-frequency modulator  18  is used as an input signal  19  for the power amplifier  20 . The gain factor of the power amplifier  20  is predetermined by the analog control signal  21  from the power control device  22 . The amplified radio-frequency signal  23  which is produced at the output of the power amplifier  20  is supplied to the antenna  24 , and is transmitted. 
     A controller  25  is provided on the baseband side  2  in order to control the switching-on and switching-off processes, and produces on the one hand the control signals  26  for the power ramp generator  27  and, on the other hand, the trigger signals  28  for the IQ scaling unit  7 . The IQ scaling unit  7  and the power ramp generator  27  can be activated, deactivated and configured by the controller  25 . The control signals  26  cause the power ramp generator  27  to produce a switching-on or a switching-off ramp for the transmission power. The digital power ramp signal  29  is converted by the digital/analog converter  30  to the analog power ramp signal  31 , which is transmitted from the baseband side  2  to the radio-frequency side  3 . 
     The analog power ramp signal  31  is supplied to the power control device  22 , and is used to predetermine the nominal value for the output transmission power of the mobile station. The actual value of the output transmission power is detected in the power measurement unit  32  by extracting a fraction of the radio-frequency transmission signal and, in particular, rectifying it. The power measurement signal  33  which is emitted from the power measurement unit  32  represents a measure of the output transmission power which actually occurs at the antenna  24 , that is to say the actual value of the transmission power, and is supplied to the power control device  22 . 
     The power control device  22  is in the form of a control loop. In order to produce the control signal  21  for the power amplifier  20 , a comparison is carried out continuously between the analog power ramp signal  31  that is used as the nominal value, and the power measurement signal  33  which represents the actual value. When the nominal value which is predetermined by the power ramp signal  31  is higher than the actual value, then the control signal  21  is readjusted such that the gain of the power amplifier  20  is increased. Conversely, when the actual value of the transmission power as indicated by the power measurement signal  33  is greater than the nominal value represented by the analog power ramp signal  31 , then the output transmission power is reduced. This is done by decreasing the gain factor of the power amplifier  20 . 
     The use of this power control loop ensures that the output transmission power always follows the profile predetermined by the power ramp signal. The described control loop means that this can always be ensured irrespective of the signal amplitude of the input signal  19 . 
     In order to produce a switching-on ramp, a trigger signal  28  is transmitted to the IQ scaling unit  7  at a specific time interval from the control signal  26  which causes the power ramp generator  27  to produce the switching-on ramp, and this trigger signal  28  assists the switching-on process by producing a rising profile of the scaling values  10  for the baseband transmission signals. The rising sequence of scaling values  10  is stored in the IQ scaling table  11 . The scaling values are read successively and are transmitted to the multipliers  8  and  9  in order that the digital in-phase signal  5  and the digital quadrature signal  6  can be multiplied by these factors. This results in the scaled digital signals  12  and  13  having a rising profile, thus assisting the switching-on process. The scaling of the IQ signals should have a continuous profile, which can be differentiated, over the entire profile and in particular at the start and end of the IQ ramp, in order to prevent the power amplifier control from having to smooth out abrupt discontinuities. 
     When, on the other hand, a control signal  26  which causes the production of a switching-off ramp is transmitted to the power ramp generator  27 , then a trigger signal  28  which triggers a falling profile of the scaling for the baseband transmission signals is transmitted to the IQ scaling unit  7  at a specific time interval from this control signal  26 . This is done by reading a falling sequence of scaling values from the IQ scaling table  11 , and transmitting these to the multipliers  8  and  9 . The decreasing sequence of scaling values can be stored as a separate sequence of scaling data. However, the decreasing sequence of scaling values can also be produced by reading the rising sequence of scaling values that are used in conjunction with the switching-on ramp in the opposite sequence. 
       FIGS. 2A to 2C  show the time profiles of the various signals which are required to produce a switching-on ramp and a switching-off ramp.  FIG. 2A  shows the output power of the power amplifier as a function of time, showing the time profile of a switching-on ramp  34  followed by a switching-off ramp  35 . The profile of the switching-on and the switching-off ramp is predetermined by the analog power ramp signal  31 , whose time profile therefore in principle corresponds to the illustrated profile of the output power. 
     The time t 1  marks the start of the switching-on ramp  34 . This leads to a rise in the output power of the power amplifier from the minimum output power P MIN  to the maximum output power P MAX . The power ramp reaches its maximum after a fixed elapsed time at the time t 4 . 
     The switching-off ramp  35  starts at the time t 5 . This is then followed by a decrease in the output value from the value P MAX  (the maximum output power) to the value P MIN  (the minimum output power). The power ramp reaches the minimum after a fixed elapsed time at the time t 8 . 
       FIG. 2B  shows the associated time profile of the power for the complex baseband signal. The power for the complex baseband signal can be derived from the scaled analog in-phase signal  16  and from the scaled analog quadrature signal  17 . To this extent, the profile illustrated in  FIG. 2B  shows the scaling of the baseband transmission signals by the IQ scaling unit  7 . Initially, the output power is at its minimum value, and the power of the complex baseband signal is also scaled down to a minimum value. The illustrated value IQ MIN  indicates the minimum value of the power of the complex baseband signal relative to the maximum value. After the time t 1 , at which the switching-on ramp is activated, a time interval that can be defined as required starts to run in the controller  25 . Once this time interval has elapsed, at the time t 2 , a trigger signal  28  is transmitted to the IQ scaling unit  7 , which activates the IQ scaling rise  36  for the switching-on ramp. The IQ scaling reaches its maximum after a fixed elapsed time at the time t 3 . 
     In a corresponding way, the IQ scaling decrease  37  for the switching-off ramp is activated at the time t 6 , which occurs at a time interval which can be chosen freely after the time t 5 . This is once again done using a trigger signal  28 . The scaling of the baseband transmission signals once again reaches the minimum IQ MIN  after a fixed elapsed time at the time t 7 . 
       FIG. 2C  shows the time profile of the analog control signal  21  that is used to adjust the gain factor of the power amplifier  20 . The signal profile  38 , which is shown as a dashed line, relates to the situation where the amplitudes of the in-phase signal  16  and of the quadrature signal  17  are constant—this is the situation corresponding to the prior art. Without the inventive IQ scaling, the gain factor of the power amplifier  20  must be varied over a wide dynamic range, and the control signal  21  therefore also has to pass over a wide voltage range from the minimum voltage U MIN2  UP to the maximum voltage U MAX  and back to the minimum voltage U MIN2 . 
     The signal profile  39 , which is shown as a solid line, indicates the profile of the control signal  21  when using the IQ scaling. Since the analog in-phase signal  16  as well as the analog quadrature signal  17  are scaled in accordance with the profile shown in  FIG. 2B , the gain factor of the power amplifier  20  during the switching-on and switching-off processes need be varied to a lesser extent than was the case with the prior art. The control signal  21  for the power amplifier therefore also covers a narrower value range, which extends from the minimum voltage U MIN1  to the maximum voltage U MAX . 
     The use of the IQ scaling according to the invention therefore results in the gain factor of the power amplifier  20  needing to be changed to a considerably lesser extent than in the past in order to achieve a predetermined transmission power dynamic range. Conversely, the use of the scaling of the signal amplitudes of the in-phase and quadrature signals allows the dynamic range of the output transmission power to be widened in comparison to the prior art.