Abstract:
A device  20  includes a receiver  21  for receiving and processing signals at least in a first frequency band and an antenna  216  which is connected to the receiver  21 . In order to improve the performance of such a receiver, the device  20  in addition includes a tuning component  217  for shifting a frequency response of the antenna  216  from the first frequency band to a second frequency band. Further, the device  20  includes a controlling portion  221  causing the tuning component  217  to shift the frequency response of the antenna  216  from the first frequency band to the second frequency band, in case a wideband noise is expected in the first frequency band. A corresponding method is shown as well.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is the U.S. National Stage of International Application Number PCT/IB2003/002174 filed 10 Jun. 2003 and published in English 15 Dec. 2004 under International Publication Number WO 2004/109942 A1 with International Search Report. 
   FIELD OF THE INVENTION 
   The invention relates to a device comprising a receiver for receiving and processing signals and an antenna which is connected to the receiver. The invention relates equally to a method for improving the performance of such a receiver. 
   BACKGROUND OF THE INVENTION 
   Receivers for receiving and processing signals are well known in the art, for example in the form of a GPS (Global Positioning System) receiver of a GPS system. 
   The performance of a receiver may be degraded during time intervals in which wideband noise in the frequency band used for the signals which are to be received by the receiver is present in the environment of the device, since this wideband noise may reduce the signal-to-noise ratio (SNR) of the received signals significantly. 
   The wideband noise can be generated in particular by a communication system transmitter integrated in the same device as the receiver, or by a nearby communication system transmitter external to this device. Such an internal or external communication system transmitter can be for instance part of a GSM (Global System for Mobile communications) transceiver, of a CDMA (Code Division Multiple Access) transceiver, of a US-TDMA transceiver or of a WCDMA (Wideband CDMA) transceiver. 
   In a GPS system, for example, several GPS satellites that orbit the earth transmit signals which are received and evaluated by GPS receivers. All GPS satellites use the same two carrier frequencies L 1  and L 2  of 1575.42 MHz and 1227.60 MHz, respectively. GPS signaling is based on a CDMA principle, i.e. the satellites and their signals are separated by the codes used to modulate the two carrier signals. The employed carrier modulation is a BPSK (bi-phase shift key) modulation, in which the carrier frequency phase is shifted by 180 degrees every time a chip changes from zero to one or vice versa. 
   The modulation of the carrier frequencies L 1  and L 2  is illustrated in  FIG. 1 . After a phase shift of 90 degrees, the sinusoidal L 1  carrier signal is BPSK modulated by each satellite with a different C/A (Coarse Acquisition) code known at the receivers. Thus, different channels are obtained for the transmission by the different satellites. The C/A code, which is spreading the spectrum over a 1.023 MHz bandwidth, is a pseudorandom noise sequence which is repeated every 1023 chips, the epoch of the code being 1 ms. The term chips is used to distinguish the bits of a modulation code from data bits. 
   In parallel, the L 1  carrier signal is BPSK modulated after an attenuation by 3 dB with a P-code (Precision code), and the L 2  carrier signal is BPSK modulated with the same P-code before an attenuation by 6 dB. Before transmission, the two differently modulated parts of the L 1  carrier signal are summed again. The L 2  carrier signal carries currently only the P-code. The P-code is much longer than the C/A code. Its chip rate is 10.23 MHz and it repeats every 7 days. In addition, the P-code is currently encrypted, and for that reason it is often referred to as P(Y)-code. Decrypting keys needed for using the P(Y)-code are classified and civil users cannot access them. Therefore, only the L 1  carrier C/A code is usable in civil GPS receivers. 
   Before the C/A code and P(Y)-code are modulated onto the L 1  signal and the L 2  signal, navigation data bits are added to the C/A and P(Y)-codes by using a modulo- 2  addition with a bit rate of 50 bits/s. The navigation information, which constitutes a data sequence, can be evaluated for example for determining the position of the respective receiver. The navigation information comprises e.g. precise satellite orbital parameters and clock correction parameters. When a receiver is able to despread a received signal based on the correct modulation code, it can extract and evaluate the navigation data. A GPS signal which is received at a GPS receiver is further modulated due to the Doppler effect and possibly due other higher order dynamic stresses. 
   The reception bandwidth of a GPS receiver receiving the modulated satellite signals is related to the reception code. For example, if GPS is based on the L 1  carrier C/A code, then the signal requires a frequency band of 1575.42 MHz +/−5 MHz. If a P-code capable receiver is used, then the reception band of the GPS receiver is much wider, it is likely to be 1575.42 MHz +/−24 MHz. The actual used GPS reception bandwidth is further related to the actual implementation, and thus the previously mentioned bandwidths are presented for demonstration purposes. The mentioned GPS bandwidth will thus be used in the following only by way of example. 
   The GPS standard is currently under modernization. One of the main components of the modernization consists in two new navigation signals that will be available for civil use in addition to the existing civilian service broadcast of the L 1 -C/A code at 1575.42 MHz. 
   The first one of these new signals will be a C/A code located at 1227.60 MHz, i.e. modulated onto the L 2  carrier frequency, and will be available for general use in non-safety critical applications. The new civilian signal at L 2 , referred to as “L 2 CS”, will generally be characterized by a 1.023 Mcps (mega chips per second) effective ranging code having a Time Division Multiplex of two ½ rate codes. The L 2 CS signal will be BPSK modulated onto the L 2  carrier, along with the P(Y)-code. This C/A code will be available beginning with the initial GPS Block IIF satellite scheduled for launch in 2003. 
   The second one of the new signals will be using a third carrier frequency L 5  located at 1176.45 MHz. The L 5  carrier frequency will be modulated with C/A codes, more specifically with a CL code of 767,250 chips and a CM code of 10,230 chips. The L 5  signal will provide a 10.23 Mcps ranging code, wherein it is expected that improved cross correlation properties will be realized. The L 5  signal will be message based. It will include an I (In-phase) channel carrying 10-symbol Neumann/Hoffman encoding and a Q (Quadrature) channel carrying 20-symbol Neumann/Hoffman encoding. The I and Q channels will be orthogonally modulated onto the L 5  carrier. The L 5  signal falls into a frequency band which is protected worldwide for aeronautical radionavigation, and therefore it will be protected for safety-of-life applications. Additionally, it will not cause any interference to existing systems. Thus, with no modification of existing systems, the addition of the L 5  signal will make GPS a more robust radionavigation service for many aviation applications, as well as for all ground-based users, like maritime, railways, surface, shipping, etc. The L 5  signal will provide significant benefits above and beyond the capabilities of the current GPS constellation, even after the planned second activity frequency L 2  becomes available. Benefits include precision approach navigation worldwide, increased availability of precision navigation operations in certain areas of the world, and interference mitigation. The new L 5  signal will be available on GPS Block IIF satellites scheduled for launch beginning in 2005. 
   At the current GPS satellite replenishment rate, all three civil signals, i.e. L 1 -C/A, L 2 -C/A and L 5 , will be available for initial operational capability by 2010, and for full operational capability approximately by 2013. 
   In particular communication systems operating in the 1900 band, like GSM1900, which are widely referred to as PCS (Personal Communication System), and communication systems operating in the 1800 band, like GSM1800, which are widely referred to as DCS (Digital Communication System), will generate wideband noise in this GPS L 1  band of 1575.42 MHz +/−5 MHz, when C/A code supported GPS is used. When new L 2  and L 5  frequency GPS signals are used, then lower frequency GSM signals, i.e. GSM900 and GSM800, will generate the same wide band noise problem as GSM1800 to the L 1  GPS signal. 
   Measurements show that if no measures are taken, the SNR of a GPS signal received by a GPS receiver degrades by about 2 dB in case a GSM transmitter implemented in the same device uses for transmissions a single slot TX (transmission) mode, and by about 3 dB in case the GSM transceiver implemented in the same device uses for transmissions a dual slot TX mode. 
   The GPS receiver, however, requires a sufficient SNR of received satellite signals for being able to correctly acquire and track the signal based on its C/A-code and thus to make use of its content. It is better for the performance of the GPS receiver to receive signals with a particularly low SNR than not to receive any signal at all during short time intervals. 
   Typically in spread spectrum systems, the AGC (Automatic Gain Control) tunes the received information signal level for A/D (analog to digital) conversion based on the noise level. In normal operating conditions, the noise is coming from background noise, which has a constant power level. The problem arises when the noise level rises rapidly and the AGC tries to adjust an incoming signal to a certain appropriate level for an A/D conversion. A quickly varying high noise level can cause saturation in the A/D converter and the amplitude of the signal is clipped. Of the signal is clipped in conversion, some information signal is lost and thus the receiver performance is degraded. 
   Also external interferences can block a GPS receiver operation completely, in case multiple communication system transmitters are transmitting in the same area at the same time. 
   The same problem may further occur when a Galileo receiver is used instead of a GPS receiver. Galileo is a European satellite positioning system, for which the beginning of commercial operations is scheduled for 2008. Galileo comprises 30 satellites, which are distributed to three circular orbits to cover the entire surface of the Earth. The satellites will further be supported by a worldwide network of ground stations. It is planned that Galileo will provide ten navigation signals in Right Hand Circular Polarization (RHCP) in the frequency ranges 1164-1215 MHz, using carrier signals E 5   a  and E 5   b,  1215-1300 MHz, using a carrier signal E 6 , and 1559-1592 MHz, using a carrier signal E 2 -L 1 -E 1 . Similarly as with GPS, the carrier frequencies E 5   a , E 5   b , E 6  and E 2 -L 1 -E 1  will be modulated by each satellite with several PRN codes spreading the spectrum and with data. Thus, GSM transmitters may equally generate wideband interferences in frequency bands employed by Galileo. 
   Obviously, the performance of a receiver due to transmissions by a communication system transmitter may equally be degraded in a similar situation in case of a type of a communication system transmitter other than a GSM transmitter and/or a type of a receiver other than a GPS receiver or a Galileo receiver. 
   In U.S. Pat. No. 6,107,960, a method is proposed for reducing cross-interferences in a combined satellite positioning system receiver and communication system transceiver device. A control signal is transmitted from the communication system transceiver to the satellite positioning system receiver, when the communication transceiver transmits data at a high power level over a communication link. The control signal causes the satellite positioning system signals from satellites to be blocked from the receiving circuits of the satellite positioning system receiver, or to be disregarded by the processing circuits of the satellite positioning system receiver. 
   For a communication system transmitter which is combined in a single device with the satellite positioning system receiver, it has further been proposed to improve the SNR of received satellite signals by adding an external notch-filter to the transmission path of the communication system transmitter. The notch filter, which is arranged after a power amplifier in the transmission path, has a passband frequency range for passing on the frequencies required for the communication system, and a stop band frequency range for attenuating the frequencies required for the satellite positioning system. 
   For PCS and DCS, the passband frequency range of the notch filter has to be 1710 MHz to 1910 MHz, and in case GPS is used as a satellite positioning system, the stop band frequency range has to be 1558.42 MHz to 1580.43 MHz. In order to improve the SNR of received GPS signals to a useful level, a very high attenuation is required for the stop band. Applying a high attenuation, however, increases also the insertion loss of the notch filter at the pass band of the filter. Due to this additional loss after the power amplifier, more output power has to be taken from the power amplifier, which increases the current consumption. 
   Measurements show that an antenna isolation of about 10 dB is required for single slot GSM, if the GPS SNR is to be improved to a desired level of 0.5 dB degradation. To a GSM1800 transmission path, a 30 dB external GPS band attenuator has to be added for achieving the same desired level of 0.5 dB degradation. For dual slot GSM, the required attenuation is even higher. 
   The insertion loss of a GPS notch-filter with a 30 dB GPS band attenuation will lie between 0.7 dB and 1.0 dB. An insertion loss between 0.7 dB and 1.0 dB increases the current consumption of the power amplifier by about 20%, compared to a current consumption without insertion loss. 
   It is thus a disadvantage of the approach using a notch-filter that an extra component is needed in the communication system transmitter and that the power amplifier current consumption increases about 20%, which also results in an increased heating of the device. On the whole, the costs for improving the GPS SNR by only about 1.5 dB are high. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide an alternative to existing solutions for improving the performance of a receiver in interfering conditions. 
   On the one hand, a device is proposed, which comprises a receiver for receiving and processing signals at least in a first frequency band, and at least a first antenna which is connected to the receiver. The proposed device further comprises a tuning component for shifting a frequency response of the first antenna from the first frequency band to a second frequency band. The tuning component may include for instance a capacitance diode, but equally or any other suitable components. Moreover, the proposed device comprises a controlling portion causing the tuning component to shift the frequency response of the antenna from the first frequency band to the second frequency band, in case a wideband noise is expected in the first frequency band. 
   On the other hand, am method for improving the performance of a receiver is proposed. The receiver is able to receive and process signals at least in a first frequency band, and it is connected to at least a first antenna. The proposed method comprises as a first step determining whether a wideband noise is expected in the first frequency band. The proposed method comprises as a second step shifting a frequency response of the first antenna from the first frequency band to a second frequency band, in case a wideband noise is determined to be expected in the first frequency band. 
   The invention proceeds form the consideration that some receivers, like GPS receivers, have severe problems in coping with high noise levels, it is therefore proposed that when wideband noise is generated in the frequency band employed for the signals which are to be received by the receiver, the antenna is detuned out of the regular center frequency. As a result, the wideband noise cannot be received any more via the antenna and does thus not disturb the receiver. 
   It is an advantage of the invention that it provides an alternative to existing solutions. 
   When detuning the antenna, also the received signal is attenuated. If the received signal is weak, the attenuation causes as a result that the signal cannot be detected. However, if the signal is strong, it may be possible to detect the signal in spite of the attenuation. This constitutes an advantage compared to the solution proposed in the above cited document U.S. Pat. No. 6,107,960, as here, the blocking or disregarding of satellite signals affects satellite signals of any strength. 
   It is further an advantage of the invention that it requires no additional components in a communication system transmitter of the device. 
   Preferred embodiments of the invention become apparent from the detailed description that follows below. 
   The invention can be employed in any device comprising a receiver. The receiver can be for example a satellite positioning system receiver like a GPS receiver or a Galileo receiver, but equally any other type of receiver. 
   The invention can be employed in particular, though not exclusively, in any device comprising a receiver and in addition a communication system transmitter. The communication system transmitter can be for example part of a GSM transceiver, of a US-TDMA transceiver, of a WCDMA-GSM transceiver or of a CDMA-transceiver. 
   In case the invention is employed in a device comprising in addition a communication system transmitter, it can be used in particular for attenuating wideband noise generated by this communication system transmitter in the first frequency band. Wideband noise in the first frequency band can then be expected by the controlling portion at least whenever the communication system transmitter is known to be transmitting signals. The controlling portion may either be part of the communication system transmitter or receive a corresponding information about transmissions from the communication system transmitter. It has to be noted, however, that the invention can equally be employed for attenuating wideband noise generated by a unit external to the device. 
   In an advantageous embodiment, the receiver comprises at least a first receiving chain for receiving and processing radio frequency signals in the first frequency band and a second receiving chain for receiving and processing radio frequency signals in the second frequency band. In this embodiment, the first antenna is connected to the first receiving chain and in addition via a switching component to the second receiving chain. The controlling portion can then cause the switching component to connect the first antenna in addition to the second receiving chain, whenever a wideband noise is expected in the first frequency band. Thereby, the performance of the receiver can be improved, as signals may be available for evaluation at the second frequency band while the signals at the first frequency band are being disturbed by wideband noise. 
   In case the receiver comprises two receiving chains, the device according to the invention comprises advantageously in addition a second antenna, which has a frequency response at the second frequency band and which is equally connected via the switching component to the second receiving chain. The second antenna can be used for a diversity reception improvement in the receiver. The controlling portion may then cause the switching component to disconnect the second antenna from the second receiving chain, whenever the first antenna is connected via the switching component to the second receiving chain since a wideband noise is expected in the first frequency band. 
   In such a device, the controlling portion advantageously further causes the switching component to connect the first antenna to the second receiving chain and to disconnect the second antenna from the second receiving chain, in case a wideband noise is expected in the second frequency band. 
   The noise in the second frequency band can be generated for example by a second communication system transmitter of the device, which transmits signals via a radio interface in a different frequency band than the first communication system transmitter of the device. In this case, wideband noise in the second frequency band can be expected by the controlling portion at least whenever the second communication system transmitter is known to be transmitting signals. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawing. 
       FIG. 1  illustrates the modulation of GPS carrier frequencies; 
       FIG. 2  is a schematic block diagram of a mobile phone, in which a first embodiment of the invention is implemented; 
       FIG. 3  is a diagram illustrating the operation of the first embodiment of the invention; 
       FIG. 4  is a schematic block diagram of a mobile phone, in which a second embodiment of the invention is implemented; 
       FIG. 5  is a diagram illustrating the operation of the second embodiment of the invention; 
       FIGS. 6   a  and  6   b  are further diagrams illustrating the operation of the second embodiment of the invention; 
       FIG. 7  is a schematic block diagram of a mobile phone, in which a third embodiment of the invention is implemented; and 
       FIGS. 8   a ,  8   b  and  8   c  are diagrams illustrating the operation of the third embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2  is a schematic block diagram of a mobile phone  20 , in which a first embodiment of the invention is implemented. Only selected components of the mobile phone  20  are depicted. 
   The mobile phone supports a GPS positioning and a mobile communication via a GSM network. 
   For supporting the GPS positioning, the mobile phone  20  comprises a GPS receiver  21 . The GPS receiver  21  includes, connected to each other in series, a low noise amplifier LNA  211 , a mixer  212 , a variable gain attenuator  213  and a converters and DSP (digital signal processor) processor block  214 . A local oscillator  215  is connected in addition to the mixer  212 . The local oscillator  215  provides a signal having a frequency required for downconverting an L 1  signal. The mobile phone  20  further comprises a GPS antenna  216  which is connected via a tuning component  217  to the low noise amplifier  211  of the GPS receiver  21 . The tuning component  217  comprises a detuning circuitry, e.g. a capacitance diode, for tuning the frequency band which can be received via the GPS antenna  216 . 
   For supporting the mobile communication, the mobile phone  20  comprises a GSM1800 transmitter  22 , which is part of a GSM1800 transceiver. The transmitter  22  comprises, connected to each other in series, a converters and DSP processor block  221 , a first variable power amplifier  222 , a mixer  223  and a second variable power amplifier  224 . The transmitter  22  further comprises a local oscillator  225 , which is connected to the mixer  223 . The mobile phone  20  moreover comprises a GSM antenna  226 , which is connected to the second variable amplifier  224 . The converters and DSP processor block  221  of the transmitter  22  has a controlling access to the tuning component  217 . 
   A radio frequency signal reaching the mobile phone  20  is received by the GPS antenna  216 , in case the signal lies within the frequency band of the frequency response of the GPS antenna  216 . The tuning component  217  is able to switch the frequency response of the GPS antenna  216  between two different frequency bands, one of which is the GPS L 1  frequency band. A radio frequency signal received via the GPS antenna  216  is processed by the GPS receiver  21 . More specifically, the received signal is amplified by the LNA  211  and mixed by the mixer  212  with a signal provided by the local oscillator  215 . In case the received signal is an L 1  signal, the mixing results in a down-conversion to the base band. The downconverted signal is then attenuated or amplified by the variable gain attenuator  213  with a gain currently set by an AGC (automatic gain control), and finally processed in a conventional way in the converters and DSP processor block  214 . The processing in the converters and DSP processor block  214  may comprise for instance determining and tracking a C/A-code in the signal, decoding a navigation information comprised in the tracked signal and performing positioning calculations for determining the current position of the mobile phone  20 . 
   A signal, which is to be transmitted by the GSM transmitter  22  in the scope of a mobile communication to a base station, is processed for transmission in a conventional way by the GSM transmitter  22 . The signal is provided by the converters and DSP processor block  221  to the first variable power amplifier  222 , which amplifies the signal with a currently set amplification factor. The amplified signal is then mixed by the mixer  223  with a signal provided by the local oscillator  225  for an up-conversion to a radio frequency signal. The radio frequency signal is further amplified by the second variable power amplifier  224  with a currently set amplification factor. The amplification factors are set by an AGC according to a request by the base station of a communication network to which the mobile phone  20  is currently connected. The signal output by the second variable power amplifier  224  is then transmitted via the GSM antenna  226 . 
   The detuning of the GPS antenna  216  to another frequency band by the tuning component  217  will be explained in more detail in the following with reference to  FIG. 3 .  FIG. 3  is a diagram which depicts on a frequency line the GSM1800 TX band of 1710-1785 MHz, the GPS L 1  band of 1570.30-1580.53 MHz, the GPS L 2  band around 1227 MHz, the GPS L 5  band around 1176.45 MHz and the GSM900 TX band of 880-925 MHz. 
   In a first state, the GSM transmitter  22  does not transmit any signals. In this first, basic state, the GPS antenna  216  is tuned by the tuning component  217  to receive satellite signals in the GPS L 1  frequency band of 1570.30 MHz to 1580.53 MHz. The corresponding original GPS antenna frequency response is shown as a first curve in  FIG. 3 . 
   In a second state, the GSM transmitter  22  transmits signals having a carrier frequency in the range of 1710-1785 MHz, causing wideband noise in the GPS L 1  frequency band of 1575.42 MHz +/−5 MHz. The distribution of the power level of transmitted GSM1800 signals over the frequency is depicted as second curve in  FIG. 3 . The generated wideband noise is superimposed on any satellite signal reaching the GSP antenna  216 . The wideband noise degrades the performance of the GPS receiver  21 , in case it reduces the SNR of received GSP L 1  satellite signals below an acceptable value. 
   When the GSM transmitter  22  transmits signals with a power level exceeding a predetermined low power level, the converters and DSP processor block  221  of the GSM transmitter  22  therefore provides a control signal to the tuning component  217 . Thereupon, the tuning component  217  detunes the GSP antenna  216  to somewhat lower or higher frequencies. The resulting shifted GPS antenna frequency response is depicted as third curve in  FIG. 3  in the case the frequency is tuned to a lower frequency. 
   With the shifted GPS antenna frequency response, the antenna isolation between the GSM antenna  226  and the GPS antenna  216  is improved, as indicated by a double headed arrow in  FIG. 3 . When a GPS signal reaching the mobile phone  20  is strong, and has thus a rather high SNR in spite of the superimposed wideband noise, the signal received via the GSP antenna  216  may be strong enough for a detection even though the GPS antenna  216  is detuned. When a GPS signal reaching the mobile phone  20  is weak, however, and has thus a rather low SNR due to the superimposed generated wideband noise, the signal received via the GPS antenna  216  is not strong enough for a detection, and thus errors in the evaluation in the converters and DSP processor block  214  are prevented. Therefore, the increased isolation between the GSM antenna  226  and the GSP antenna  216  that is achieved by the control signal from the GSM transmitter  22  to the tuning component  217  eases the performance degradation of the GSP receiver  21 . 
   It is also possible to relate the amount of detuning to the extent of the respective amplification applied by GSM transmitter  22  to signals which are to be transmitted. 
   A second and a third embodiment of the invention, which will be presented further below, take into account planned future development of GPS. 
   The second embodiment of the invention is based on the assumption that in addition to the C/A-code of the L 1  signal, also the P-code of the L 1  signal and the L 2  signal including a C/A code and a P-code are taken into civil usage. 
     FIG. 4  is a schematic block diagram of a mobile phone  40 , in which the second embodiment of the invention is implemented. As in  FIG. 2 , only selected components of the mobile phone  40  are depicted. 
   The mobile phone  40  of  FIG. 4  supports again a GPS positioning and a mobile communication via a GSM network. 
   For supporting a GPS positioning, the mobile phone  40  of  FIG. 4  comprises a GPS receiver  41 . The GPS receiver  41  includes a first receiving chain  43  for receiving and processing L 1  signals and a second receiving chain  44  for receiving and processing L 2  signals. The L 1  receiving chain  43  comprises, connected to each other in series, a first low noise amplifier LNA  431 , a first mixer  435  and a first variable gain attenuator  434 . The L 1  receiving chain  43  further comprises a first local oscillator  432 , which is connected to the first mixer  435 . The first local oscillator  432  provides a signal having a frequency which is required for downconverting an L 1  signal. The L 2  receiving chain  44  comprises, connected to each other in series, a second low noise amplifier LNA  441 , a second mixer  442  and a second variable gain attenuator  443 . The L 2  receiving chain  44  further comprises a second local oscillator  445 , which is connected to the second mixer  442 . The second local oscillator  445  provides a signal having a frequency which is required for downconverting an L 2  signal. The GPS receiver  41  comprises in addition a converters and DSP processor block  414 . The first variable gain attenuator  434  of the L 1  receiving chain  43  and the second variable gain attenuator  443  of the L 2  receiving chain  44  are both connected to this converters and DSP processor block  414 . 
   For supporting a GPS positioning, the mobile phone  40  moreover comprises a GSP antenna  416 . The GPS antenna  416  is connected by means of an enhanced diplexer  417  on the one hand to the first low noise amplifier  431  of the L 1  receiving chain  43  and on the other hand via a switch  418  to the second low noise amplifier  441  of the L 2  receiving chain  44 . Typically, a diplexer combines two input path signals having different frequencies to one output path signal. The enhanced diplexer  417  comprises detuning circuitry and diplexer functionalities. The detuning function can be done with a capacitance diode or any other suitable component. The detuning circuitry tunes the frequency band, which can be received via the GPS antenna  416 . 
   For supporting a mobile communication, the mobile phone  40  comprises a GSM1800 transmitter  42 , which is part of a GSM1800 transceiver. The transmitter  42  comprises a converters and DSP processor block  415 , a first variable power amplifier  414 , a mixer  413  and a second variable power amplifier  411 . The transmitter  42  further comprises a local oscillator  412  which is connected to the mixer  413 . The mobile phone  40  further comprises a GSM antenna  426 , which is connected to the second variable amplifier  411 . The converters and DSP processor block  415  has in addition a controlling access to the diplexer  417  and the switch  418 . 
   For supporting a mobile communication, the mobile phone  40  may comprise in addition a GSM900 transmitter (not shown), which is part of a GSM900 transceiver and designed similarly as the GSM1800 transmitter. 
   Transmissions via the GSM1800 transmitter and a GSM900 transmitter take place as described above with reference to  FIG. 2  for the GSM1800 transmitter. 
   While the GSM1800 transmitter  42  is not transmitting any signals, the GSP antenna  416  is connected via the diplexer  417  only to the L 1  (“first”) receiver chain  43 . The GSP antenna  416  is in resonance at the center frequency of the L 1  frequency band, and received L 1  signals are forwarded to the L 1  receiver chain  43  and processed as described above with reference to  FIG. 2 . 
   When the GSM1800 transmitter  42  is transmitting signals, wideband noise is generated in the L 1  frequency band. The converters and DSP processor block  415  therefore provides a control signal to the switch  418 , which causes the switch  418  to be closed. As a result, signals received by the GSP antenna  416  are provided to both the L 1  and the L 2  (“second”) receiving chain  43 ,  44 ,. At the same time, the converters and DSP processor block  415  provides a control signal to the diplexer  417 , which causes the detuning circuitry in the diplexer  417  to detune the GPS antenna  416  to be in resonance at the center frequency of the L 2  frequency band. 
   The shift of the GPS antenna frequency response is illustrated in  FIG. 5 .  FIG. 5  is a diagram which corresponds to the diagram of  FIG. 3 , except that here, the GPS antenna frequency response was shifted exactly to the L 2  frequency band. The resulting improvement of the isolation between the GSP antenna  416  and the GSM antenna  426  is advantageously rather high, as indicated by a double-headed arrow in  FIG. 5 . 
   Due to the specific detuning in the second embodiment of the invention, a good reception of the L 2  frequency band by the GPS antenna  416  and thus a good reception of the L 2  band C/A and P-code in the L 2  receiving chain  44  is achieved. From the L 1  band, the C/A-code and the P-code can still be received in some conditions via the L 1  receiving chain  43 , that is, if the L 1  signal reaching the mobile phone is particularly strong. In case of a strong L 1  carrier signal, also the SNR of the L 1  signal will be sufficiently strong for an evaluation in spite of the wideband noise. 
     FIGS. 6   a  and  6   b  illustrate the detuning in another type of representation. In  FIG. 6   a , the insertion loss S 11  in dB of the GPS antenna  416  is depicted over the frequency for the case that there is no GSM1800 transmission. It can be seen that the insertion loss S 11  is in general at a basically constant, high value, but decreases to a minimum value at a center frequency of 1575 MHz with a transition range on both sides of this center frequency. This enables a good reception of the L 1  band C/A-code and the L 1  band P-code in the L 1  receiver chain  43 . The L 2  receiver chain  44  is not in use. The GSM1800 transceiver may receive signals at the same time, and if the mobile phone  40  comprises in addition a GSM900 transceiver, the GSM900 transceiver may receive or transmit signals at the same time, as such operations do not generate any wideband noise in the L 1  frequency band. 
   In  FIG. 6   b , the insertion loss S 11  in dB of the GPS antenna  416  is depicted over the frequency for the case that there is an ongoing GSM1800 transmission. It can be seen that the insertion loss S 11  is in general at a basically constant, high value, but decreases to a minimum value at a shifted center frequency of 1227 MHz with a transition range on both sides of this center frequency. This enable a good reception of the L 2  band P-code in the L 2  receiver chain  44 . At the same time, the wideband noise generated by the GSM1800 transmission is attenuated. 
   The same result as for the European bands GSM1800 and GSM900 depicted in  FIGS. 6   a  and  6   b  can be achieved for the U.S. bands GSM1900 and GSM850. 
   The third embodiment of the invention is based on the assumption that in addition to the C/A-code of the L 1  signal, also the P-code of the L 1  signal and of the L 2  signal and a newly introduced C/A-code of the L 2  signal are taken into civil usage. 
     FIG. 7  is a schematic block diagram of a mobile phone  70 , in which the third embodiment of the invention is implemented. As in  FIGS. 2 and 4 , only selected components of the mobile phone  70  are depicted. 
   The mobile phone  70  of  FIG. 7  supports again a GPS positioning and a mobile communication via a GSM network. The C/A-code and the P-code of the L 2  band are made use of in the GPS positioning for a diversity reception improvement. 
   The design of the mobile phone  70  of  FIG. 7  is very similar to the design of the mobile phone of  FIG. 4 . 
   For supporting a GPS positioning, the mobile phone  70  of  FIG. 7  thus comprises a GPS receiver  71 . The GPS receiver  71  includes a first receiving chain  63  for receiving and processing L 1  signals and a second receiving china  74  for receiving and processing L 2  signals. The L 1  receiving chain  63  comprises, connected to each other in series, a first low noise amplifier LNA  631 , a first mixer  635  and a first variable gain attenuator  634 . The L 1  receiving chain  63  further comprises a first local oscillator  632 , which is connected to the first mixer  635 . The first local oscillator provides a signal having a frequency which is required for downconverting an L 1  signal. The L 2  receiving chain  74  comprises, connected to each other in series, a second low noise amplifier LNA  741 , a second mixer  742  and a second variable gain attenuator  743 . The L 2  receiving chain  74  further comprises a second local oscillator  745 , which is connected to the second mixer  742 . The second local oscillator  745  provides a signal having a frequency which is required for downconverting an L 2  signal. The GSP receiver  71  comprises in addition a converters and DSP processor block  714 . The first variable gain attenuator  634  of the L 1  receiving chain  63  and the second variable gain attenuator  743  of the L 2  receiving chain  74  are both connected to this converters and DSP processor block  714 . 
   For supporting GPS positioning, the mobile phone  70  moreover comprises a first GPS antenna  716  and a second GPS antenna  719 . The first GPS antenna  716  is connected by means of an enhanced diplexer  717  on the one hand to the first low noise amplifier  631  of the L 1  receiving chain  63  and on the other hand via a switch  718  to the second low noise amplifier  741  of the L 2  receiving china  74 . The enhanced diplexer  717  comprises a detuning circuitry for tuning the frequency band which can be received via the first GSP antenna  716  from the L 1  frequency band to the L 2  frequency band. The second GPS antenna  719  is connected equally via the switch  718  to the second low noise amplifier  741  of the L 2  receiving chain  74 . The second GPS antenna  719  is tuned in a fixed manner to the L 2  frequency band. The switch  716  allows to connect either the first GPS antenna  716  or the second GPS antenna  719  to the second GPS receiving chain  74 . 
   For supporting a mobile ocmmunicaiton, the mobile phone  70  comprises a GSM1900 transmitter  72 , which is part of a GSM1900 transceiver. The transmitter  72  comprises a converters and DSP processor block  715 , a first variable power amplifier  714 , a mixer  713  and a second variable power amplifier  711 . The transmitter  72  further comprises a local oscillator  712  which is connected to the mixer  713 . The mobile phone  70  further comprises a GSM antenna  726 , which is connected to the second variable amplifier  711 . The converters and DSP processor block  715  has in addition a controlling access to the diplexer  717  and the switch  718 . 
   For supporting a mobile communication, the mobile phone  70  comprises in addition a GSM850 transmitter (not shown), which is part of a GSM850 transceiver and designed similarly as the GSM1900 transmitter. 
   Transmissions via the GSM1900 transmitter  72  or the GSM850 transmitter are carried out as described above with reference to  FIG. 2  for the GSM1800 transmitter  22 , only in other frequency bands. 
   While neither the GSM1900 transmitter  72  nor the GSM850 transmitter is transmitting signals, the first GPS antenna  716  is connected via the diplexer  717  only to the first GPS receiver chain  63 . At the same time, the second GPS antenna  719  is connected via the switch  718  to the second GPS receiver chain  74 . The first GPS antenna  716  is in resonance at the L 1  frequency band, and received L 1  signals are forwarded to the first GPS receiver chain  63  and processed analogously as described above with reference to  FIG. 2 . The second GPS antenna  719  is in resonance at the L 2  frequency band, and received L 2  signals are forwarded to the second GPS receiver  74  chain and processed analogously as described above with reference to  FIG. 2 . The GSM1800 transceiver and the GSM900 transceiver may be receiving signals at the same time. 
   This first situation is illustrated in  FIG. 8   a , in which the insertion loss S 11  in dB of both GPS antennas  716 ,  719  is depicted over the frequency for the case that there is no GSM transmission. At the first GPS antenna  716 , the insertion loss S 11  is in general at a basically constant, high value, but decreases to a minimum value at a center frequency of 1575 MHz with a transition range on both sides of this center frequency. This enables a good reception of the L 1  band C/A-code and P-code via the first GPS antenna  716  in the first GSP receiving chain  63 . At the second GSP antenna  719 , the insertion loss S 11  is in general at a basically constant, high value, but decreases to a minimum value at a center frequency of 1227 MHz with a transition range on both sides of this center frequency. This enables a good reception of the L 2  band C/A-code and P-code via the second GPS antenna  719  in the second GPS receiving chain  74 . 
   When the GSM1900 transmitter  72  is transmitting signals, wideband noise is generated in the L 1  frequency band. The converters and DSP processor block  715  therefore provides a control signal to the switch  718 , which causes the switch  718  to connect the diplexer  717  instead of the second GPS antenna  719  to the second GSP receiving chain  74 . Thereby, signals received by the first GPS antenna  716  are provided to both, the first and the second GPS receiving chain  63 ,  74 . The second GPS antenna  719  is now disconnected. At the same time, the converters and DSP processor block  715  causes the first GPS antenna  716  to be detuned to be in resonance at the L 2  frequency band. 
   This second situation is illustrated in  FIG. 8   b , in which the insertion loss of the first GPS antenna  716  is depicted over the frequency for the case that there is a GSM1900 transmission. At the first GPS antenna  716 , the insertion loss S 11  is in general at a basically constant, high value, but decreases to a minimum value at a shifted center frequency of 1227 MHz with a transition range on both sides of this center frequency. This enables a good reception of the L 2  band C/A-code and P-code via the first GPS antenna  716  in the second GPS receiving chain  74 . The wideband noise generated by the GSM1900 transmission is thus attenuated. From the L 1  band, the C/A-code and the P-code can be received in some conditions via the first GPS antenna  716  in the first GPS receiving chain  63 , that is, if the L 1  satellite signal reaching the mobile phone  70  is particularly strong. The disconnected second GPS antenna  719  does not forward any signals. 
   When the GSM850 transmitter is transmitting signals, wideband noise is generated in the L 2  frequency band. The converters and DSP processor block (not shown) of the GSM850 transmitter therefore provides a control signal to the switch  718 , which causes the switch  718  to connect the diplexer  717  instead of the second GPS antenna  719  to the second GPS receiving chain  74 . Thereby, signals received by the first GPS antenna  716  are provided to both, the first and the second GPS receiving chain  63 ,  74 . The second GPS antenna  719  is now disconnected. The first antenna is kept to be tuned to be in resonance at the L 1  frequency band. 
   This third situation is illustrated in  FIG. 8   c , in which the insertion loss S 11  of the first GPS antenna  716  is depicted over the frequency for the case that there is a GSM850 transmission. At the first GPS antenna  716 , the insertion loss S 11  is in general at a basically constant, high value, but decreases to a minimum value at a center frequency of 1575 MHz with a transition range on both sides of this center frequency. This enables a good reception of the L 1  band C/A-code and P-code via the first GPS antenna  716  in the second GPS receiving chain  74 . The disconnected second GPS antenna  719  does not forward any signals. The wideband noise generated by the GSM850 transmission is thus attenuated. From the L 2  band, the C/A-code and the P-code can be received in some conditions via the first GPS antenna  716  in the second GPS receiving chain  74 , that is, if the L 2  satellite signal reaching the mobile phone  70  is particularly strong. 
   It is to be understood that in the second and third embodiment, one of the GPS receiver chains or an additional GPS receiver chain could also be a receiver chain for receiving GPS signals at the L 5  band, if suitable signals are transmitted at this band. 
   It is further to be noted that the described embodiments constitute only three of a variety of possible embodiments of the invention.