Patent Application
20060030281
The present disclosure relates to a method for transmission power adjustments for a mobile communications terminal that is equipped with a power amplifier, whose output signal amplitude depends on the frequency of an input signal to the power amplifier, an RF connector, an internal antenna and a connection for an external antenna, and which is designed for operation in at least one standard mobile radio frequency band. The disclosure also relates to a communications terminal by means of which the method for transmission power adjustment can be carried out.
In order to set up a communication link by means of mobile radio terminals, such as mobile communications terminals, it is necessary for the electromagnetic waves to be transmitted via antennas to the communications terminals. The electromagnetic fields that are involved for the transmission of electromagnetic waves also penetrate into human tissue, for example in the situation when a user of a communications terminal is holding the terminal against his ear. This leads to a thermal load on the human tissue, which must be kept within permissible limits. One measure for assessment of the thermal load is the so-called “SAR value”, with the abbreviation “SAR” standing for specific absorption rate. Background information on limit values are specified in standards, such as EN 50361, IEEE Std 1528-200X.
Since the dimensions of mobile communications terminals are becoming ever smaller, power emission is concentrated over an ever narrower band. Accordingly, this can also result in an increased thermal load on the user in particular when the communications terminal is used for this purpose.
Furthermore, this also results in areas of maximum thermal load (hot spots), which determine the SAR value.
Conventional ways for reducing the SAR value has been to insert radiation-absorbent components, such as an absorber sheet, in the communications terminals. Alternatively, the dimensions of the mobile communications terminals can also be enlarged, although this influences the design of the terminals.
By way of example, the GSM specification stipulates what minimum RF output power must be available at an RF connector of a mobile communications terminal which not only has an internal antenna but is also designed for connection via the RF connector to an external antenna. In this context, it is important that the output signal amplitude of a power amplifier for a mobile communications terminal depends on the frequency of the input signal to the power amplifier. Accordingly, the antenna output power from the mobile communications terminal is frequency-dependent and channel-dependent. In order to satisfy the requirements from the GSM specification which has been mentioned here by way of example, adjustments have been made to the channel with the lowest power, so that it is possible to assume that all the channels satisfy the minimum GSM-specific power. This procedure leads to the SAR value being particularly high, for example for the channels located in the center of the frequency spectrum, assuming a typical profile for the frequency dependence of the emitted power.
For example, U.S. Pat. No. 5,995,813 Titled “Radio Telephone and Independently Controlled Booster”, which is a method for transmission power adjustment for a mobile communication terminal, that is equipped with a power amplifier. The output signal amplitude of this configuration depends on the frequency of an input signal to the power amplifier, an RF connector, an internal antenna and a connection for an external antenna, and for operation in at least one standard mobile radio frequency band, wherein the at least one standard mobile radio frequency band is subdivided into two or more frequency intervals, and power adjustment is carried out for each of at least some of the frequency intervals. Under the method described above, frequency intervals are referred to as individual radio channels.
In contrast, it has not yet been possible until now to consider the possibility of power adjustment deliberately in order to optimize the SAR value.
Against this background, the present disclosure is based on specifying a method for power adjustment for a mobile communications terminal, in which the SAR value can be effectively optimized. A further aim is to provide a communications terminal for carrying out the method.
The power adjustment is achieved by an exemplary method for transmission power adjustments for a mobile communications terminal, which is equipped with a power amplifier whose output signal amplitude depends on the frequency of an input signal to the power amplifier, an RF connector, an internal antenna and a connection for an external antenna, and which is designed for operation in at least one standard mobile radio frequency band, in which case the at least one standard mobile radio frequency band is subdivided into two or more frequency intervals, and one power adjustment operation is carried out in each case for at least some of the frequency intervals.
Accordingly, in contrast to situations where power adjustment can be carried out only for the entire frequency band, power adjustment is additionally carried out on a frequency-interval specific basis. The frequency intervals may have the same constant width, or a varying width.
This makes it possible to adjust the power, particularly for the central frequency intervals, which further makes it possible to reduce the SAR value of the central frequency intervals, and thus to optimize it.
The power adjustment can be carried out either for all the frequency intervals into which the standard mobile radio frequency band is subdivided, or only for a number of frequency intervals, for which the emitted power from the antenna is particularly high, due to the frequency dependency of the antenna. This makes it possible to simultaneously satisfy not only any specifications for a mobile radio standard but also the requirements for an SAR value that is as low as possible.
The power adjustment for the frequency intervals can be carried out by accessing a reference table, in which an adjustment factor is associated with each frequency interval. These adjustment factors reflect the frequency profile on the power amplifier and, if appropriate the antenna characteristics. Under an exemplary embodiment, the entries in the reference table may correspond to the reciprocal of a normalized frequency profile of the power amplifier. This makes it possible to reduce the SAR value for the given frequency interval at that time.
The power adjustment for the RF connector is preferably carried out as a function of whether the mobile communications terminal is operated with its own internal antenna or with an external antenna. In the latter case, a reference table can be provided which ensures that an input signal whose amplitude is independent of frequency is produced at an input to the RF connector. As such, the appropriate specifications are taken into account.
It is also preferable to use an antenna detector to determine whether the mobile communications terminal is operating with its own internal antenna or with an external antenna, with the antenna detector responding, for example, when the internal antenna is being used, thus resulting in a situation in which the SAR value is of particular importance.
In one preferred embodiment, the power adjustment, when using the internal antenna, can be carried out such that the emitted power level from the mobile communications terminal is essentially independent of the frequency of the input signal to the power amplifier. This means that the output power from a transmission antenna for the mobile communications terminal is independent of frequency. This has the advantage that, for example, weak channels at the edge of the standard mobile radio frequency band have their power increased, to produce an improved communication link for an uplink connection to a base station.
The power is adjusted in a particularly advantageous manner by giving priority to the optimization of the SAR value over the at least one standard mobile radio frequency band.
It should be noted that the system and method in the present disclosure may, also be carried out for transmission power adjustment for a mobile communications terminal that can operate in two or more standard mobile radio frequency bands. In this case, two or more reference tables, for example, are provided, and are used in the manner described above.
The aforementioned power adjustment is achieved in a communications terminal by a mobile communications terminal having a power amplifier whose output signal amplitude depends on the frequency of the input signal to the power amplifier, and having a device for adjusting power for the output of the communications terminal in at least one standard mobile radio frequency band. In this case, the device for power adjustment is preferably designed to adjust the output power for two or more frequency intervals in the at least one standard mobile radio frequency band.
One feature of the communications terminal is that the required means for respective power adjustment are provided for individual frequency intervals in a standard mobile radio frequency band. These means may be the reference table, disclosed above. The use of an antenna detector allows different reference tables to be used for power adjustment for different operating conditions of the mobile communications terminal, with the operating conditions being distinguished on the basis of whether the antenna is external or internal.
It is noted that the software-implemented solution utilizing a reference table will be the more cost-effective, and is thus preferred overall.
The various objects, advantages and novel features of the present disclosure will be more readily apprehended from the following Detailed Description when read in conjunction with the enclosed drawings, in which
As can be seen from
The frequency profile, which results after the power adjustment, for the amplitude of the output signal from the power amplifier PA is also illustrated in
The separate power adjustment for all six frequency intervals furthermore means that the power that is emitted from an antenna A, and is based on the amplitude of the output signal from the power amplifier PA is reduced for particularly strong channels, such as the channels or frequency intervals 3 and 4 in
For the weak frequency intervals 1 and 6, the power can be increased until the associated SAR value is slightly below a predetermined maximum SAR value, with a value range (which is predetermined by the relevant mobile radio specification) for the channel power being taken into account as a boundary condition. Overall, this results in a more uniform power capability for the mobile communications terminal over the mobile radio frequency spectrum on which it is being used at that time.
An output signal from power amplifier PA is passed to RF connector K, whose output signal is supplied to internal antenna AI. In the embodiment shown in
Reference table V2 is accessed when antenna detector D detects that internal antenna AI for the mobile communications terminal is being used, whose radiated power is relied upon for obtaining a SAR value. The reference table V1 contains adjustment values for the power amplifier PA which, in the end, lead to the emitted power from the communications terminal being substantially constant over the standard mobile radio spectrum that is being used at that time.
If antenna detector D finds that external antenna AE, connected to RF connector via a suitable connection, as shown in
The adjustment factors in reference table V2 are chosen such that the SAR value is slightly below the predetermined maximum SAR value for all of the frequency intervals. The adjustment factors that are required for this purpose may be determined empirically.
The above described description and drawings are only to be considered illustrative of exemplary embodiments, which achieve the features and advantages of the invention. Modifications and substitutions to specific process conditions and structures can be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be considered as being limited by the foregoing description and drawings, but is only limited by the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102 51 465.8 | Nov 2002 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE03/03425 | 10/15/2003 | WO | 5/5/2005 |
