Radio station for transmitting and receiving digital information in a mobile communications system

The invention relates to a radio station for transmitting and receiving digital information in a mobile communication system according to the preamble of claim 1.

Radio stations are used to transmit information using electromagnetic waves. The frequency spectrum of the electromagnetic waves in question ranges from a few kHz to several hundred GHz, with the frequency spectrum in the lower gigahertz range in particular having become more important due to the development of mobile radio technology. Radio stations are used for mobile radio technology at approx. 0.9 and 1.8 GHz. A mobile communication system is, for example, the GSM mobile radio network (Global System for Mobile Communications), but also known wireless communication networks, for example according to the DECT standard, implement such a mobile communication system.

If these radio stations are intended to both transmit and receive information, they comprise at least one receiving unit and at least one transmitting unit. In the transmission unit, the information to be transmitted is modulated onto a carrier frequency and the generated transmission signals are amplified. The receiving unit is used to evaluate the information of the received signals and their separation from the carrier and noise disturbances.

Such a radio station is known, for example, as a base station from German patent application 195 472 88.8. This radio station further comprises an antenna for sending and receiving. This means that both the transmit signals and the receive signals are received via this antenna. However, this radio station has the disadvantage that diversity reception is not possible with it.

From the publication <img file="EP0805566A2_D0001.tif" />Telegraph and data transmission via shortwave ", L. Wiesner, Siemens Aktiengesellschaft, third edition, 1980, pages 94 to 104, various possibilities of implementing diversity reception are known. Among other things, the possibility of polarization diversity is presented, in which two antennas are used for diversity reception , of which one is polarized, for example, vertically and the other horizontally. Such an antenna system is also known from German patent DE 2 032 002 B2. These writings present implementations of diversity reception, which, however, are based on spatially separated antennas and, moreover, do not take into account the problems associated with transmission.

Conventional mobile communication systems, see Siemens Function Specification, A30862-X1001-A314-03-7659, MOBNET, dated August 25, 1995, p. 5-2, implement a radio station with diversity operation in that separate antennas for transmission and for each individual Diversity branch available. However, the two antennas for diversity reception must have a certain spatial separation in order to ensure decorrelation of the received signals. Another possible implementation provides the duplex of transmission signals on the antennas for diversity reception. However, there must also be a spatial separation of the antennas for diversity reception.

With current mobile communication systems, however, there is considerable pressure on network operators to make do with a few antenna locations. The provision of two separate antennas for diversity reception is a considerable disadvantage.

The invention is therefore based on the object of specifying a radio station for transmitting and receiving digital information in a mobile communication system, which has a small space requirement for the antenna location for transmitting and for receiving diversity. This object is achieved in each case by the radio station according to the invention of claims 1 and 4, starting from the features of the preamble, by the features of the characterizing part. Advantageous further developments can be found in the subclaims.

According to the invention, the antenna consists of a first and second excitation system with different polarization. To share the antenna for transmission and reception, a first duplexer connects at least a first transmission unit and a first reception unit to a common first antenna line. The first excitation system is connected to the first duplexer via the first antenna line. The second excitation system has a connection to at least the first receiving unit via a second antenna line. This ensures diversity reception at least via the first receiving unit and both excitation systems. Furthermore, the transmission of digital information is implemented at least via the first excitation system.

Alternatively, at least three excitation systems, two for receiving and one for transmitting, are provided in the antenna, the excitation systems differing in their polarization planes. With this solution, the duplexer can be saved, but there is an increased effort in realizing the antenna.

The radio station according to the invention advantageously simultaneously fulfills the requirement for a reduction in the number of antennas and the requirements of a mobile communication system with diversity reception. This enables network operators to meet strict requirements, particularly in conurbations, for example regarding the optical and aesthetic effects of the antenna system.

According to advantageous developments, the first and the second excitation system have a common geometric center. Such an arrangement of the excitation systems can further reduce the space requirement of the antenna. For a high antenna gain, element groups are advantageously used for the excitation systems. By arranging the elements of the excitation systems appropriately, it is possible to produce radiation diagrams of different polarization without great additional effort.

It is also possible to integrate further excitation systems into this antenna, whereby according to advantageous developments of the radio station according to the invention, these additional excitation systems are used either for diversity reception or for transmission.

If the transmission of the transmission signals should not only take place via an excitation system, a further advantageous embodiment of the radio station according to the invention provides for the connection of the second excitation system to the first receiving unit via a second duplexer, the second duplexer having a second transmitting unit and the first receiving unit having the common one second antenna line connects. According to various implementation options, the transmission energy of a transmission unit can thus be distributed over two excitation systems or different transmission units are each connected to one excitation system.

If several receiving units are used in the radio station, then it is advantageous to connect them to a first and a second isolating amplifier (in the case of two excitation systems) and to distribute the power of the received signals received by the two excitation systems accordingly between the receiving units. By using isolation amplifiers, a larger number of receiving units can be used.

According to further advantageous embodiments of the radio station according to the invention and in particular the antenna, the excitation systems are arranged in such a way that the cross-polarization decoupling of the excitation systems is at least 30 dB. This decoupling corresponds to the decoupling of two antennas at a distance of one meter at 900 MHz. This measure is intended to ensure that the interactions between the sending and receiving excitation systems are low. A high cross-polarization coupling is achieved, for example, by the polarization plane of the first and second excitation systems being inclined by approximately 90 degrees to one another. The inclination of the polarization planes of both excitation systems compared to the horizontal can be determined in different ways. It is particularly advantageous to approximate both polarization planes approx. 45 Tilt to the horizontal, so that after various reflections on the radio link or also due to the direct propagation path, they are on an equal footing with the receiving radio station. A further advantageous implementation variant provides that the polarization plane of an excitation system emitting the transmission signals is approximately perpendicular to the horizontal. This inclination corresponds to the arrangements of transmitting antennas that have been customary to date.

Power combiners are advantageously used to connect a large number of transmitter units, each of which connects a plurality of transmitter units with a duplexer or directly with an excitation system. If several transmission units are to be used and the losses in the transmission of the transmission energy of the transmission signals to the excitation systems are to be kept low, then, according to an advantageous development of the invention, power combiners are dispensed with by adding an additional antenna, the excitation systems of which for transmission or also to improve the diversity Reception can be used.

The radio station according to the invention is to be explained in more detail below with the aid of drawings.

It shows<dl id="dl0001"><dt>FIG 1</dt><dd>a radio station with two excitation systems, each inclined at 45 degrees to the horizontal, and four transmitting and receiving units,</dd><dt>FIG 2</dt><dd>a radio station with two excitation systems inclined at 90 degrees to each other and a vertical polarization plane for the emitted transmission signals,</dd><dt>FIG 3</dt><dd>a radio station with an antenna having four excitation systems, and</dd><dt>FIG 4</dt><dd>a radio station with two antennas and four excitation systems each connected to a transmitter unit.</dd></dl>

The radio station FS according to FIG. 1 consists of an antenna A, four receiving units RX1..4 and four transmitting units TX1..4. The transmission signals tx of the first and second transmission units TX1, TX2 are combined by a first power combiner H1 and fed to a first duplexer DX1. Correspondingly, the transmission signals tx of the third and fourth transmission units TX3, TX4 are combined by a second power combiner H2 and fed to a second duplexer DX2. The power combiners H1, H2 implement the adapted transmission of the transmission energy to the duplexers DX1, DX2.

Each of these duplexers DX1, DX2 has a connection to a first isolation amplifier FRX1 or a second isolation amplifier FRX2. These isolating amplifiers FRX1, FRX2 are each connected to four receiving units RX1..4 on the output side. Broadband filtering in accordance with the system bandwidth takes place in the isolating amplifier FRX1, FRX2 and amplification takes place before the energy of the received signals rx is evenly distributed to all receiving units RX1..4. In the receiving units RX1..4, the received signals RX are evaluated using a diversity method. For well-known diversity reception methods, for example, on JGProakis,<img file="EP0805566A2_D0001.tif" />Digital Communications ", McGraw Hill, 1989.

The first and second duplexers DX1, DX2 connect the transmitter units DX1..4 and receiver units RX1..4 to a first and second antenna line Ltg1, Ltg2. These antenna lines Ltg1, Ltg2 lead to antenna A. This antenna A consists of two excitation systems AE1, AE2. The first excitation system AE1 is connected to the first antenna line Ltg1 and the second excitation system AE2 is connected to the second antenna line Ltg2. Both excitation systems AE1, AE2 are approx. 45 Degrees to the horizontal of the earth and inclined to each other by approx. 90 degrees. The polarization planes of their radiation directions are also inclined accordingly. The excitation systems are group antennas, for example, each consisting of several individual elements.

The radio station FS according to FIG. 2 again consists of an antenna A, four transmitter units TX1..4 and four receiver units RX..4. However, in contrast to the radio station FS according to FIG. 1, the combination of the transmission energies of the transmission signals tx of the four transmission units TX1..4 takes place in a different way. After the combination of the transmission signals tx of the first and second transmission units TX1, TX2 in a first power combiner H1 and the combination of the transmission signals tx of the third and fourth transmission units TX3, TX4 in a second power combiner H2, these transmission signals tx are combined once again in a third power combiner H3 and only fed to the first duplexer DX1. The second duplexer DX2 is terminated on the transmitter unit side. The reception units RX1..4 are connected in accordance with the arrangement of the reception units RX1..4 according to FIG. 1.

The connection of the first and second excitation systems AE1, AE2 of antenna A is in turn carried out via first and second antenna lines Ltg1, Ltg2 to the first and second duplexers DX1, DX2. The first excitation system AE1 is arranged perpendicular to the horizontal and inclined approximately 90 degrees to the second excitation system AE2. The radiation diagram of the transmission signals tx thus has vertical polarization. As in FIG. 1, the received signals rx are received in both polarization planes. This arrangement of the excitation systems AE1, AE2, just as for the radio station FS according to FIG. 1, implements a polarization diversity reception.

The radio station FS according to FIG. 3 shows a further implementation possibility, the antenna A consisting of four excitation systems AE..4. These are, for example, each inclined at 45 degrees to one another, but it could be used on a different number of excitation systems with a different inclination. A first excitation system AE1 is connected to a first isolation amplifier FRX1 and a second excitation system AE2 is connected to a second isolation amplifier FRX2. Both isolating amplifiers FRX1, FRX2 are each connected to a first and second receiving unit RX1, RX2 and both feed the received signals rx received by the first and second excitation systems AE1, AE2. A first and a second transmitter unit TX1, TX2 are connected directly to a third and fourth excitation system AE3, AE4. With this configuration, duplexers and power combiners can be dispensed with. However, it would also be possible to combine the powers of the first and second transmitter units TX1, TX2 and to only feed them to a single excitation system AE3 and to dispense with the fourth excitation system AE4.

The radio station FS according to FIG. 4, however, ensures a significant reduction in the attenuation of the transmission signals tx when there is an increased space requirement. The use of two separate antennas A, each with two, for example, cross-polarized excitation systems AE1, AE2, saves the power combiners and thus enables a higher power radiation from the radio station FS with the same output power from the transmitter units TX1..4. The excitation systems of the additional antenna A are used for diversity reception, so that a triple diversity is also possible and for transmitting the transmission signals tx from two transmission units TX1, TX2. The distribution of the use of the excitation systems AE1, AE2 of the two antennas A can, however, also take place in a different way, according to the invention different variants are possible according to the specific requirements of the space requirement and the transmission power.

For the radio stations FS according to FIGS. 1 to 4, the antenna lines Ltg1, Ltg2 can also be reduced to a single one or to a number that is less than that of the excitation systems AE1..4 by duplexes.