Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-06-05
2001-10-09
Kizou, Hassan (Department: 2662)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S345000, C455S101000, C375S267000
Reexamination Certificate
active
06301236
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a transmission means with a transmission signal source and a transmission antenna for the radiation of radio signals of a determined transmission frequency according to a predetermined time protocol.
In radio systems, such as e.g. the GSM mobile radiotelephone system, transmission means are used for the radiation of radio signals as electromagnetic waves that are recorded and evaluated by receiving means. There are thus no line-bound connections between the transmission means and the receiving means. In the transmission means, the transmission signals are produced in a transmission signal source; these transmission signals are thereby at radio frequency. Via cable connections and various further means such as preamplifiers, etc., the transmission signals are supplied to a transmission antenna, which finally radiates the radio signals.
A transmission antenna thereby comprises a particular radiation characteristic. Under real conditions of use for radio systems, the radio signals are exposed to a wide variety of disturbances, and reach the receiver means via very different propagation paths. Besides a direct propagation path, the radio signals can also be reflected or bent at obstacles such as mountains, trees, buildings, etc. In the receiver means, the radio signals from the various propagation paths are superposed. This leads to extinguishing effects, which sometimes have a strong adverse effect on the reception of the radio signals; on this, see J. D. Parsons, “The Mobile Radio Propagation Channel,” Pentech Press Publishers, London, 1992, pp. 108-113.
In order to circumvent these extinguishing effects, also called fading effects, various methods are known. With several receiving antennas in the direction of reception, it is for example possible to reduce the extinguishing effect by means of antenna diversity. In addition, from the GSM mobile radiotelephone system it is known to effect an improvement of the reception conditions via frequency hopping, i.e. to change the transmission frequency for the transmission signals (M. Mouly, M. B. Pautet, “The GSM System for Mobile Communications,” 1992, i.a. pp. 218-223). However, the latter method has the disadvantage that it requires an expensive implementation. Also, it cannot be used if only one carrier frequency is available in the GSM mobile radiotelephone system, as is the case above all in simple and economical base stations.
From Prior art references EP-A-0 479 744, WO-A-95/32558, and GB-A-2 221 820, communication systems are known in which switching takes place between different antennas during a connection. These antennas can also comprise a different polarizations. In addition, in International reference WO-A-95/32558, the changeover is synchronized with a time protocol of the transmission.
In addition, the problem of strong fluctuations in signal level at the receiver can be compensated by increasing the transmission power. However, this has the disadvantage that increased disturbances must be reckoned with on adjacent radio paths.
SUMMARY OF THE INVENTION
The invention is thus based on the object of effecting a reduction of the extinction effect in radio paths between transmission means and receiver means in radio systems even if only one transmission frequency is available.
The basic idea of the invention is the use of a further dimension of the modification of the radiation diagram of the transmission means. On the transmission side of the radio path, by means of a time-controlled changeover switch the radiation characteristic of the transmission means is switched in such a way that for a sequence of information to be transmitted, at least two different decorrelated radio signals containing different items of information, with different radiation characteristics, arise successively, e.g. in successive time slots of a traffic relation, corresponding to a time protocol of the message transmission of the transmission means. The transmission frequency is thereby not modified.
Besides a further possible decorrelation of the channel condition by means of frequency modification, according to the invention an additional decorrelation of the channel condition can be achieved by means of the different radiation characteristic. If the transmission means does not have the possibility of carrying out a frequency modification, then for the first time the possibility of the decorrelation of radio signals on the transmission side is achieved.
If the communication system in whose context the transmission means is used is a communication system operated in time-slot multiplexing, the changeover switch is advantageously controlled by a timing element that changes over the radiation characteristic in accordance with the time slots, according to a predeterminable sequence. Examples of such communication systems operated in time-slot multiplexing include the GSM mobile radiotelephone system and the DECT wireless telephone system.
In order to influence the radiation characteristic of the transmission means without changing the frequency, it is possible to provide further transmission antennas, to realize radiation in different polarization planes, or also to modify the direction of radiation of the transmission antenna. These three measures can of course also be combined with one another.
If at least one further transmission antenna is provided, the changeover switch switches the transmission signals between the transmission antennas. If the one transmission antenna enables radiation in different polarization planes, then the changeover switch switches to the transmission antenna in such a way that a changeover takes place between the polarization planes. For the modification of the direction of radiation, the transmission antenna is advantageously marked as a phase-controlled group antenna, so that the changeover switch carries out the phase controlling of the group antenna in such a way that a changeover takes place between at least two different radiation characteristics.
Corresponding to a further embodiment of the invention, the transmission means is constructed as a mobile station or as a base station inside a GSM mobile radiotelephone network. The time protocol in the transmission means thus decides between time slots inside a frame, whereby frames can in turn be combined to form macroframes. The changeover switch thus switches over the radiation characteristic of the transmission means with each time slot, each frame or macroframe, in a manner conforming to the time slots. There are thus no disturbances in the message transmission.
The changeover, for example between different transmission antennas, takes place according to a freely determinable sequence, i.e., all existing transmission antennas can be driven successively, or can be driven according to another advantageous pattern. Different methods can thereby be used to achieve a statistical decorrelation of the radio signals. Advantageously, the transmission means for the case of several transmission antennas is constructed in such a way that the transmission antennas are positioned with respect to one another in such a way that in predetermined regions of the radio range of the transmission means, the radio signals with the different radiation characteristics comprise a least decorrelation. Particular problem regions in the radio range, e.g. tunnel interiors or the like, can thereby be taken specifically into account in the positioning of the transmission antennas. The effectiveness of the inventive transmission means can be concentrated on these problem areas, with respect to the equalization of the fluctuations of the transmission level at the receiver means.
REFERENCES:
patent: Re. 36591 (1999-01-01), Hayashi
patent: 3945013 (1976-03-01), Brunner
patent: 5339086 (1994-08-01), DeLuca
patent: 5689439 (1997-11-01), Weerackody
patent: 5710977 (1998-01-01), Nakazawa
patent: 6006075 (1999-12-01), Smith
Färber Michael
Schreib Franz
Kizou Hassan
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
Stevens Roberta
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